View Full Version : Can a jet on a treadmil fly?
This is a well known mind bender and creates debates even among those who study the topic for a living, and it's a topic that far as i can tell put to bed, but I'm still looking for the conclusive source. Q goes like this and two basic versions:
The first goes like this (as depicted on the image above): “Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?”
Is that Q as written is not actually possible, it can't actually be answered as such; "The object will not stay motionless because we have unbalanced forces. So we can not design the conveyor belt to move at the same speed as wheels."
Hence, that Q is moot. The Q that makes more sense that most think of when they think of that Q, that is possible and does not ignore Newtonian physics is:
“An airplane cannot take off from a runway which is moving backward (like a treadmill) at a speed equal to its normal ground speed during takeoff“ - as shown in Mythbusters – is a different matter, and yes, the plane would fly.
Answers to both:
http://c-aviation.net/plane-conveyor-belt-explained-debunked/
How does it get lift being in the same spot??
Airspeed =\= groundspeed. Is anybody this silly?
I watched the video and it looked like the plane's forward motion was faster than the conveyor going backwards, which gave it enough air movement over its wings thus creating lift. Which is what I would have expected with any forward movement. What I thought they were going to do is keep the plane basically stationary as the belt went backwards, at which point no lift is created. Am I missing something?
Adrenaline_6
10-13-20, 17:48
It should be able to take off. The thrust from the engines is pushing it, not the wheels driving it like a car. The thrust will overcome the pull of the treadmill rolling backwards.
Now if you want to play devils advocate and put zero physical constraints on the treadmills capabilities, in theory I guess, the acceleration of the backward pulling treadmill could match the thrust of the engines, but that acceleration would have to be never ending. In reality that is impossible.
If the the thrust of the engines equals the speed of the belt, there is no air flow over the wings, thus no lift. The differential air flow over the wings does the lifting not the thrust of the engines.
Didn't think that one through sufficiently!
This is embarrassing.
Next up - https://www.montyhallproblem.com/
Oh I see my mistake now. I shouldn't give it away I suppose.
Air has to move over and under the wings to create lift.
Lift is about airspeed over the wings creating a low pressure region.
If the wing has zero airspeed, plane’s not going anywhere.
But the wings will have airspeed.
Finally read the article and it’s incredibly flawed.
Mentions nothing about airspeed; focuses on speed of the wheels which is dumb.
A plane that can takeoff without lift is called a rocket.
But the wings will have airspeed.
If the plane is stationary relative to its position in the air?
The only thing that’s moving are the wheels and it’s relative position to the ground (treadmill).
If the plane is stationary relative to its position in the air?
The only thing that’s moving are the wheels and it’s relative position to the ground (treadmill).
So when the jet engines spool up to full throttle, what does Newton's 3rd law say must happen?
So when the jet engines spool up to full throttle, what does Newton's 3rd law say must happen?
That's where I made my mistake, I must of been thinking of cars.
Tires/wheels spinning at 2X normal, otherwise no difference that I can tell in theory. Of course if the tires can't handle the RPM it could get kinda messy.
Tires/wheels spinning at 2X normal, otherwise no difference that I can tell in theory. Of course if the tires can't handle the RPM it could get kinda messy.
The treadmill is a red herring. It's the shiny object distracting us.
Tires/wheels spinning at 2X normal, otherwise no difference that I can tell in theory. Of course if the tires can't handle the RPM it could get kinda messy.
That's a good start, but a gigantic treadmill moving at that speed would drag a lot of air with it in the boundary layer. Would the airspeed under the wing be greater than that over the wing?
So when the jet engines spool up to full throttle, what does Newton's 3rd law say must happen?
Is it a rocket or an airplane?
Also the treadmill moves fast enough to keep the plane’s position relative to the earth constant?
That's a good start, but a gigantic treadmill moving at that speed would drag a lot of air with it in the boundary layer. Would the airspeed under the wing be greater than that over the wing?
It’s the airspeed over the wing that creates the low pressure area that lifts the wing.
The wheels on the plane rotate freely. If you crank up the treadmill the plane will stand still because the plane wheels rotate freely. The wheels only will rotate at the same speed of the treadmill. Now add thrust. Thrust is acting independent of the treadmill.
Diamondback
10-13-20, 20:31
The plane version of a "treadmill" is called an aircraft carrier--the wings do the flying and carry the rest of the plane along with them, and the carrier generates that extra lift by steaming at max power straight into the wind which is like a free 30 knots airspeed. This is also why you see B-52's pitch DOWN in climbout, the wing is set very high pitch-up (incidence) to maximize lift and once the rest of the plane catches up the wing settles down into normal flying attitude pitching the rest of the plane with it.
FromMyColdDeadHand
10-13-20, 20:35
That's a good start, but a gigantic treadmill moving at that speed would drag a lot of air with it in the boundary layer. Would the airspeed under the wing be greater than that over the wing?
That would be my guess too.
Let me put it this way, if you could launch jets with a conveyor belt don’t you think the Navy would have figured this out by now?
It’s the airspeed over the wing that creates the low pressure area that lifts the wing.
So couldn't air rushing by under the wing, dragged by the treadmill surface, disrupt that balance?
Diamondback
10-13-20, 20:44
So couldn't air rushing by under the wing, dragged by the treadmill surface, disrupt that balance?
You'd need a LOT of it in close proximity to the wing, and no treadmill is gonna get a boundary layer thick enough. Your viable "plane treadmill" is a catapult/ski jump/combo thereof aboard a ship with all engines ahead Flank at 30+ knots and a good strong headwind.
eightmillimeter
10-13-20, 20:57
The plane will take off. The engines do not move the plane across the ground. The engines move the plane through the air (even when on the ground). The driving forces are applied to the air, not torque through the wheels.
You'd need a LOT of it in close proximity to the wing, and no treadmill is gonna get a boundary layer thick enough.
Ever stood ten feet from a mile long freight train doing 60 mph? A treadmill "as wide and long as a runway" going 200 mph or whatever is going to have one hell of a draft. Not enough to disrupt the takeoff perhaps but it would have a significant effect.
The plane will take off. The engines do not move the plane across the ground. The engines move the plane through the air (even when on the ground). The driving forces are applied to the air, not torque through the wheels.
bingo!
How is this even a mind bender?
Air must pass over the wing to create lift. The speed the wheels are turning don’t matter here. This is why things with no wheels like float planes can fly.
A treadmill going a million miles an hour would not slow a plane down. It’s jets are pushing it forward, not it’s wheels. It’s wheels are not powered.
I can’t belive I even took the time to type this.
eightmillimeter
10-13-20, 21:10
bingo!
To go even farther...
Treadmill : Car = Wind Tunnel : Plane
So who is going to put on their bat suit & hover in the gym...I'm sure we can rig a unit to get the rpm's needed if it would work.
Without lift you are grounded...how does the belt speed under the tires put air speed under the wings??
How fast does a plane w/ wind speed stating she's going 100mph going against a 100mph head wind??
To go even farther...
Treadmill : Car = Wind Tunnel : Plane
If we put a plane in the wind tunnel then I'm game...making the wheels spin in place does nothing for wind speed / lift.
how does the belt speed under the tires put air speed under the wings??
Air "sticks" to the surface and is pulled along with it. Unlike a wind tunnel the air velocity would not be uniform but faster near the ground/treadmill. That could produce downforce.
How is this even a mind bender?
Air must pass over the wing to create lift. The speed the wheels are turning don’t matter here. This is why things with no wheels like float planes can fly.
A treadmill going a million miles an hour would not slow a plane down. It’s jets are pushing it forward, not it’s wheels. It’s wheels are not powered.
I can’t belive I even took the time to type this.
Again since the wheels are FREE spinning your million miles per hour is appropriate. The plane would just sit there going nowhere. The only thing turning are the wheels and the treadmill. Add thrust and the plane moves forward to takeoff.
If we put a plane in the wind tunnel then I'm game...making the wheels spin in place does nothing for wind speed / lift.
Thrust from the engines will move the plane forward.
The plane will take off. The engines do not move the plane across the ground. The engines move the plane through the air (even when on the ground). The driving forces are applied to the air, not torque through the wheels.
I think most of us have said this same thing in various ways.
LOL. I remember when they did this on TOS and it went for 18 pages or something.
Would a treadmill on a jet fly?
Coal Dragger
10-14-20, 03:04
No a plane can’t fly on a treadmill, planes fly in the air. I have yet to see a plane in the gym flying its ass off on a treadmill.
How very Barfcom.
Of course it flies. It gets total lift and thrust totally independent of the ground. Especially jets.
This post made me want to be a Make a Wish kid and have my wish be that I was dead.
The plane will take off. The engines do not move the plane across the ground. The engines move the plane through the air (even when on the ground). The driving forces are applied to the air, not torque through the wheels.
What hangs people up on that is the fact the plane is not moving forward, therefore no air contacting lift surfaces, therefore no lift. I get that, but via OP article and others I find, there's additional forces and factors at work that will see the plane lift:
https://jalopnik.com/here-s-the-actual-science-behind-that-plane-takeoff-mem-1797763299
LOL. I remember when they did this on TOS and it went for 18 pages or something.
It's a fascinating paradox. Even after what seems an authoritative source I posted, yes/no answers abound. I'm not a aerospace engineer and such so have to rely mostly on sources read. Most indicated plane flies:
https://jalopnik.com/here-s-the-actual-science-behind-that-plane-takeoff-mem-1797763299
And yet, an opinion left from somone claiming to have the creds says no:
"...as an aerospace engineer and private pilot. The airplane on the treadmill would not take off because the propeller does not provide airflow over the entire span of the wing, which you need to generate the lift to rise off the ground. It’s true that a plane moves relative the air around it and airspeed, not ground speed, determines if it can takeoff. This was illustrated in the video. But, if it were to move forward enough to generate the lift necessary for takeoff, then it would fall of the treadmill / conveyor belt. The Mythbusters example allows the plane to actually move forward. The meme example would does not because the conveyor belt is not much longer than the airplane.
However, if the propeller produced enough lift at the portion of the wings closest to the fuselage, it could lift off from the conveyor belt... Then it would crash because it would not have enough airflow over the ailerons to prevent itself from rolling to either side."
Hmmmm.
Oh I see my mistake now. I shouldn't give it away I suppose.
The trick in that Q, which frankly I missed, was the fact the treadmill is as long as the normal runway. In that case, the wheels would spin twice as fast, but that's the only impact it has, the plane would fly as forward motion to get lift via speed would happen due to thrust created independent of the ground. That's obvious. In my (thick head) I pictured a short treadmill perhaps the length of the plane matching at all times the speed of the plane attempting to move forward under thrust and obtain lift, and under that condition, does not fly. I was tricked by the trick Q myself. Doh!
Steve Shannon
10-14-20, 09:45
The plane will take off. The engines do not move the plane across the ground. The engines move the plane through the air (even when on the ground). The driving forces are applied to the air, not torque through the wheels.
Just one correction. The driving forces for a jet are not “applied to the air.” A jet operates by ejecting mass. The force necessary to push the exhaust out the nozzle of the jet engine also pushes the engine forward to satisfy Newton’s Third Law. Conservation of momentum results in motion. If a jet had its own source of combustion air it could propel itself in a vacuum like a rocket.
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It's a fun exercise & like this chap, my mind can't grasp a stationary plane getting lift regardless of thrust...there is a reason aircraft carriers go full speed into the wind when launching.
A plane reading 100 knots with a 50 knot tail wind is going 150...a plane reading 50 knots going with a 50 knot tail wind??
It's a fascinating paradox. Even after what seems an authoritative source I posted, yes/no answers abound. I'm not a aerospace engineer and such so have to rely mostly on sources read. Most indicated plane flies:
https://jalopnik.com/here-s-the-actual-science-behind-that-plane-takeoff-mem-1797763299
And yet, an opinion left from somone claiming to have the creds says no:
"...as an aerospace engineer and private pilot. The airplane on the treadmill would not take off because the propeller does not provide airflow over the entire span of the wing, which you need to generate the lift to rise off the ground. It’s true that a plane moves relative the air around it and airspeed, not ground speed, determines if it can takeoff. This was illustrated in the video. But, if it were to move forward enough to generate the lift necessary for takeoff, then it would fall of the treadmill / conveyor belt. The Mythbusters example allows the plane to actually move forward. The meme example would does not because the conveyor belt is not much longer than the airplane.
However, if the propeller produced enough lift at the portion of the wings closest to the fuselage, it could lift off from the conveyor belt... Then it would crash because it would not have enough airflow over the ailerons to prevent itself from rolling to either side."
Hmmmm.
It's a fun exercise & like this chap, my mind can't grasp a stationary plane getting lift regardless of thrust...there is a reason aircraft carriers go full speed into the wind when launching.
A plane reading 100 knots with a 50 knot tail wind is going 150...a plane reading 50 knots going with a 50 knot tail wind??
Per above, two different issues: The trick in that Q, which frankly I missed, was the fact the treadmill is as long as the normal runway. In that case, the wheels would spin twice as fast, but that's the only impact it has, the plane would fly as forward motion to get lift via speed would happen due to thrust created independent of the ground. That's obvious.
The chap above is actually answering a different Q, and one i was got stuck on myself. In my (thick head) I pictured a short treadmill perhaps the length of the plane matching at all times the speed of the plane attempting to move forward under thrust and obtain lift, and under that condition, does not fly. I was tricked by the trick Q myself. Doh!
Lol...I'm dense. I don't grasp why runway length makes any difference if stationary is stationary & the thrust doesn't put lift along the entire wingspan. When we talk treadmill, all I see is the belt moving in conjunction to how much thrust is applied & it just spins faster as the throttle is goosed. If the thrust over powers the belt speed to gain forward momentum then the treadmill sucks.
Thanks for posting...nice to have a teaser vs all the other stupidity we concern ourselves with.
...A plane reading 100 knots with a 50 knot tail wind is going 150...a plane reading 50 knots going with a 50 knot tail wind??
An aircraft traveling at 100 knots Indicated Airspeed (IAS) with a 50 knot tail wind has an airspeed of 100 knots and a ground speed of 150 knots (assuming the tail wind is coming directly at the tail).
The meat of it is relative speeds and thrust vectors. The speed of the belt relative to the airplane. The speed of the belt relative to the ground. The speed of the airplane relative to the ground. The speed of the of the airplane relative to the air. What creates lift and get the airplane flying is the speed of the airplane wing relative to the air. The speed of the belt relative to the airplane and ground is a red herring and have nothing to do with solving the problem. What generates airplane speed is thrust vectored forward.
As stated earlier, airplane wheels are nothing but rollers. They are nothing more than pneumatic roller skate wheels designed to support the weight of the aircraft while on the ground and provide as little as practical rolling resistance during taxiing and takeoff. They provide zero thrust. No thrust from any vector.
Airplanes develop thrust by creating a high pressure area behind the propulsion unit, which can be a jet engine or a propeller (or a bit of both). Nature abhors a vacuum. High pressure must push into low pressure. The high pressure area behind the propulsion unit must push (vector) into the low pressure area in front of it creating thrust. The treadmill belt provides no thrust from any vector (or at least not enough to matter.)
There is a small amount of thrust from the belt through rolling resistance. Enough that the belt can vector the airplane backward relative to the ground but not enough to impede take-off. All the pilot has to do to counteract this is increase forward vectored thrust a tiny amount. This gives the airplane a speed of 0 relative to the ground and the wind. To take-off, the pilot simply applies full thrust and accelerate to a speed relative to the air to gain lift. The result, assuming 0 airspeed relative to the ground, the aircraft accelerates to an airspeed of 80 knots and a ground speed of the same. As the treadmill is programmed to match wheel speed, belt speed relative to ground is 80 knots and 160 knots to the airplane.
What if, as suggested in an earlier post, we place the airplane inside a wind tunnel instead of on a treadmill? If the wind speed is increased to take-off speed, say 80 knots, the aircraft could take off with an IAS of 80 knots and a ground speed of 0 knots. Increase the wind sped to 100 knots and the airplane could fly at an IAS of 100 knots and a ground speed of 0.
Let's change the experiment again. Let's say we strap the airplane to the belt and move it forward relative to the air at 80 knots. There would be enough airspeed for take off. In fact, this is exactly what an aircraft carrier catapult does. Now, let's move the ground the treadmill is mounted forward relative to the air at 20 knots. The treadmill (catapult) would only have to move the airplane 60 knots for take-off speed.
Once the misleading parts of the question are cleared away, the answer is relatively easy.
Coal Dragger
10-14-20, 11:29
Lol...I'm dense. I don't grasp why runway length makes any difference if stationary is stationary & the thrust doesn't put lift along the entire wingspan. When we talk treadmill, all I see is the belt moving in conjunction to how much thrust is applied & it just spins faster as the throttle is goosed. If the thrust over powers the belt speed to gain forward momentum then the treadmill sucks.
Thanks for posting...nice to have a teaser vs all the other stupidity we concern ourselves with.
Dude Mythbusters did the experiment with an RC airplane. It took virtually no throttle at all to make the plane move forward just like it would normally and it took off just like it normally would. The propeller in that case is what is making thrust to move the object in question, an airplane, the method of propulsion is thrust applied to the atmosphere. The wheels on the landing gear do nothing but spin, the plane is still on earth. Just because the ground speed is going in one direction doesn’t mean the atmosphere is too, and even if it were the plane would still achieve lift over the wing due to relative difference in airflow. Remember in WWII US Army bombers flying to bomb Japan would get into the jet stream and have their relative ground speed be almost zero, they didn’t fall out of the sky. Same concept at 35K feet as 1 foot.
That said in real life the plane will get a wing into the treadmill control stand or the uprights on either side and crash. Treadmills makes shitty runways.
Lol...I'm dense. I don't grasp why runway length makes any difference if stationary is stationary & the thrust doesn't put lift along the entire wingspan. When we talk treadmill, all I see is the belt moving in conjunction to how much thrust is applied & it just spins faster as the throttle is goosed. If the thrust over powers the belt speed to gain forward momentum then the treadmill sucks.
Thanks for posting...nice to have a teaser vs all the other stupidity we concern ourselves with.
The length of the treadmil is the crux of the answer. The plane moves independent of the ground and thus will move forward and has the distance required to achieve lift off.
teufelhund1918
10-14-20, 12:16
Engines create propulsion which moves the plane forward. The "lift" to take the airplane skyward is created by the differential of airflow over the wings airfoil. The top of the air foil is longer than the bottom. If two particles of air start at the same point in front of the airfoil, they have to meet at the same time at the rear of the air foil. Therefore the top particle has to travel faster than the bottom one which creates a low pressure on top of the air foil which in turn creates lift.
Engines create propulsion which moves the plane forward. The "lift" to take the airplane skyward is created by the differential of airflow over the wings airfoil. The top of the air foil is longer than the bottom. If two particles of air start at the same point in front of the airfoil, they have to meet at the same time at the rear of the air foil. Therefore the top particle has to travel faster than the bottom one which creates a low pressure on top of the air foil which in turn creates lift.
All true of course, but how does that answer the quiz? I suspect most aware the basic concept of how the lift happens, via Bernoulli effect, but it does not answer the quiz per se.
The plane version of a "treadmill" is called an aircraft carrier--the wings do the flying and carry the rest of the plane along with them, and the carrier generates that extra lift by steaming at max power straight into the wind which is like a free 30 knots airspeed. This is also why you see B-52's pitch DOWN in climbout, the wing is set very high pitch-up (incidence) to maximize lift and once the rest of the plane catches up the wing settles down into normal flying attitude pitching the rest of the plane with it.
The B-52 lands with a nose down attitude because the B-52 was designed to fly efficiently at very high altitudes.
In order to minimize drag the fuselage is kept parallel to the airflow, but at high altitude where the air is thin, the wings must have a high angle of attack to generate sufficient lift, and have a lot of surface area. So, the wings of a B-52 are very large and set to the fuselage at a high angle in relation to the longitudinal axis of the fuselage. Down in the dense air near sea-level, the angle of attack of the wings required to generate sufficient lift keep the aircraft flying is less than the angle of incidence between the fuselage and the wing, hence the nose down attitude.
The length of the treadmil is the crux of the answer. The plane moves independent of the ground and thus will move forward and has the distance required to achieve lift off.
The length of the threadmill will have to be just as long as a stationary runway, maybe even longer.
The aircraft must accelerate relative to the air, and the distance required to accelerate to a speed high enough to generate sufficient lift to lift the weight of the aircraft is fixed by the aircraft weight, the aircraft shape (lift coefficient and drag coefficient), thrust available, and rolling resistance.
Since the treadmill is rolling opposite the direction of travel there will be more rolling resistance from the wheels trying to spin faster, but probably not enough to measure.
With a very small model airplane, the propeller can generate enough wind over the inner part of the wing to get sufficient lift for the airplane "take-off". That is the principle behind these guys, increase the air speed over the top of the wing and you generate lift at low airspeeds:
https://upload.wikimedia.org/wikipedia/commons/e/e2/Russian_Air_Force_-_Antonov_An-72.jpg
Lol...I'm dense. I don't grasp why runway length makes any difference.
It doesn’t. It also does not matter if plane has wheels (skids) or how fast they spin.
What matters is engine thrust invokes Newton’s 3rd law which gets plane moving in opposite direction. Enough thrust produces enough speed which creates enough lift for takeoff.
Adrenaline_6
10-14-20, 14:06
What hangs people up on that is the fact the plane is not moving forward, therefore no air contacting lift surfaces, therefore no lift. I get that, but via OP article and others I find, there's additional forces and factors at work that will see the plane lift:
https://jalopnik.com/here-s-the-actual-science-behind-that-plane-takeoff-mem-1797763299
Correct. The treadmill can do nothing to keep the plane from moving forward except acceleration of the wheels on the treadmill which in a real world environment would be temporary and small.
The length of the threadmill will have to be just as long as a stationary runway, maybe even longer.
The aircraft must accelerate relative to the air, and the distance required to accelerate to a speed high enough to generate sufficient lift to lift the weight of the aircraft is fixed by the aircraft weight, the aircraft shape (lift coefficient and drag coefficient), thrust available, and rolling resistance.
Since the treadmill is rolling opposite the direction of travel there will be more rolling resistance from the wheels trying to spin faster, but probably not enough to measure.
With a very small model airplane, the propeller can generate enough wind over the inner part of the wing to get sufficient lift for the airplane "take-off". That is the principle behind these guys, increase the air speed over the top of the wing and you generate lift at low airspeeds:
That's the aspect that is easy to overlook and get locked into the treadmill part (hence why it's a good trick question for us average IQ types) vs the fact nothing really changes of the treadmill is the length of runway and the wheels simply turning 2X normal take off speeds.
Adrenaline_6
10-14-20, 14:15
The length of the threadmill will have to be just as long as a stationary runway, maybe even longer.
The aircraft must accelerate relative to the air, and the distance required to accelerate to a speed high enough to generate sufficient lift to lift the weight of the aircraft is fixed by the aircraft weight, the aircraft shape (lift coefficient and drag coefficient), thrust available, and rolling resistance.
Since the treadmill is rolling opposite the direction of travel there will be more rolling resistance from the wheels trying to spin faster, but probably not enough to measure.
With a very small model airplane, the propeller can generate enough wind over the inner part of the wing to get sufficient lift for the airplane "take-off". That is the principle behind these guys, increase the air speed over the top of the wing and you generate lift at low airspeeds:
https://upload.wikimedia.org/wikipedia/commons/e/e2/Russian_Air_Force_-_Antonov_An-72.jpg
Yup. That is why the fanwing is so interesting but not used, probably due to complexity and maintenance.
http://www.fanwing.com/
It doesn’t. It also does not matter if plane has wheels (skids) or how fast they spin.
What matters is engine thrust invokes Newton’s 3rd law which gets plane moving in opposite direction. Enough thrust produces enough speed which creates enough lift for takeoff.
Which still requires a minimum distance which will be = the distance the plane requires to accelerate to a speed high sufficient for lift, so the runway/treadmill distance is essential there. May be different for different planes and all that, but unless it's a jumpjet something, it requires a minimum take off distance. So unclear why you'd say runway or treadmill in the Q does not matter. Or, maybe you're saying it's not length of runway per se, but whether the plane reaches it's minimum speed for lift and runway length a function of that? If so, we are saying the same thing.
What happens if someone yanks the kill switch?
Which still requires a minimum distance which will be = the distance the plane requires to accelerate to a speed high sufficient for lift, so the runway/treadmill distance is essential there.
Well I think it is kind of given the runway has to be long enough for a 747 to take off from....
And I NEVER said runway/treadmill length does not matter. I said wheels and wheel speed does not matter.
This problem has nothing to do with wheels.
Adrenaline_6
10-14-20, 14:30
What happens if someone yanks the kill switch?
The treadmill kill switch? Practically nothing. A little acceleration due to the wheel assembly losing some friction until the wheels slow to match speed. Other than that....nada.
Well I think it is kind of given the runway has to be long enough for a 747 to take off from....
But many people look at the Q, and say no, it will not fly. It's easy to overlook the aspect that the treadmill is the length of a runway long enough for the 747 to fly. Regardless, all planes other than a few specialized designs, require a minimum distance to take off, so runway length does matter right?
Well I think it is kind of given the runway has to be long enough for a 747 to take off from....
And I NEVER said runway/treadmill length does not matter. I said wheels and wheel speed does not matter.
This problem has nothing to do with wheels.
Artos said: " I don't grasp why runway length makes any difference."
You responded: "It doesn’t'
Maybe rephrase it?
Artos said: " I don't grasp why runway length makes any difference."
You responded: "It doesn’t'
Maybe rephrase it?
It doesnt assuming of course it is a runway a 747 can take off from. My bad I guess for not realizing some would use a 100 foot runway as an example
thanks...and I think this is where some folks only focus on the hypothetical question. It's pretty simple to see thrust overcoming a moving runway and if it can move forward you get lift. The question presents itself as a treadmill with the ability to work in the same way as a motorized vehicle say like top fuel / funny car type speed with wings. If the wheels can't go faster than the t-mill she stationary.
Can't believe I hadn't heard all this already.
It doesn’t. It also does not matter if plane has wheels (skids) or how fast they spin.
What matters is engine thrust invokes Newton’s 3rd law which gets plane moving in opposite direction. Enough thrust produces enough speed which creates enough lift for takeoff.
The treadmill and wheels were just a diversion, look over here so you can get distracted and confused. Worked on me for about 10 minutes, then I came to my senses.
militarymoron
10-14-20, 20:33
I think a simple free body diagram will explain why the plane takes off.
The only way the wheels/tires even come into play would be if they can't take the stress of spinning at 360mph(2x V1 speed) while holding up 800,000 lbs.
Of course then I am ruining the hypothetical question with what may seem logical points. However, they pale in comparison to the idea of building the treadmill in the first place. Wet blanket, that's me.
The only way the wheels/tires even come into play would be if they can't take the stress of spinning at 360mph(2x V1 speed) while holding up 800,000 lbs.
Wheels would spin at normal speed, just like your legs move at normal speed when running on a treadmill, not 2x. See post #66.
Wheels turning or not it doesn't matter. Set the parking brake while on the catapult on an aircraft carrier and the jet still goes flying just fine. The tires blow...but it goes flying fine.
Averageman
10-14-20, 21:21
I don't know about all of that, but I would sure like to see one land on a tread mill. Seems like we have the tech and it could shorten runways.
I don't know about all of that, but I would sure like to see one land on a tread mill. Seems like we have the tech and it could shorten runways.
Classic!
Wheels would spin at normal speed, just like your legs move at normal speed when running on a treadmill, not 2x. See post #66.
Only if the runner runs just fast enough to maintain their relative position. If the goal is to move fast enough to go forward, the runner has to run faster than the treadmill belt.
For an airplane to take off, it has to move forward with enough speed relative to the air. If the airplane needs 80 knots ground speed on a normal runway, the wheels turn at 80 knots. If taking off from a treadmill that matches wheel speed, the wheels turn at twice the ground speed.
You will want to reread post #47.
Only if the runner runs just fast enough to maintain their relative position. If the goal is to move fast enough to go forward, the runner has to run faster than the treadmill belt.
For an airplane to take off, it has to move forward with enough speed relative to the air. If the airplane needs 80 knots ground speed on a normal runway, the wheels turn at 80 knots. If taking off from a treadmill that matches wheel speed, the wheels turn at twice the ground speed.
You will want to reread post #47.
the runners leg are providing the thrust, not the same as the plane.
As someone said you could put the parking brake on, and with enough thrust it still takes off, without the wheels turning at all, because wheels are irrelevant.
Or just swap a 747 for a skid plane plane, no wheels at all, treadmill goes as fast as it wants under the skids still takes off.
the runners leg are providing the thrust, not the same as the plane.
As someone said you could put the parking brake on, and with enough thrust it still takes off, without the wheels turning at all, because wheels are irrelevant.
Or just swap a 747 for a skid plane plane, no wheels at all, treadmill goes as fast as it wants under the skids still takes off.
MistWolf not claiming the wheels provide thrust, only that they will indeed be turning at 2x the speed as the only physical impact the treadmill has one the plane. OP article covers that also:
"...With such a specific data we can even say with certainty that on take off the wheels will be turning at twice the normal speed. So if the takeoff speed for a passenger plane is 130 knots, the wheels of this plane will rotate like the plane was moving 260 knots.
The increased friction of the wheels turning at twice the usual speed will increase the takeoff distance, but apart from that – nothing will be significantly different."
"...The increased friction of the wheels turning at twice the usual speed will increase the takeoff distance, but apart from that – nothing will be significantly different."
The difference in friction between the wheel turning at 260 knots vs 130 knots isn't going to be enough to have much impact on take-off distance of a BBJ (Big Boeing Jet). The author only threw that in there because they don't know what they're talking about.
MistWolf not claiming the wheels provide thrust, only that they will indeed be turning at 2x the speed as the only physical impact the treadmill has one the plane. OP article covers that also:
"...With such a specific data we can even say with certainty that on take off the wheels will be turning at twice the normal speed. So if the takeoff speed for a passenger plane is 130 knots, the wheels of this plane will rotate like the plane was moving 260 knots.
The increased friction of the wheels turning at twice the usual speed will increase the takeoff distance, but apart from that – nothing will be significantly different."
The wheels don’t provide thrust.
The treadmill does not provide thrust.
The wheels can only spin as fast as they would rolling relative to airspeed.
The treadmill does not increase that speed on the wheels. There is no 2x overdrive.
The wheels don’t provide thrust.
The treadmill does not provide thrust.
The wheels can only spin as fast as they would rolling relative to airspeed.
The treadmill does not increase that speed on the wheels. There is no 2x overdrive.
And to repeat yet again, no claims the wheels add propulsion, and yes, the wheels will be rotating faster which was easily explained above. You're simply wrong about that.
Again, repeating again, not a factor to the plane taking off, no propulsion from the wheels, just a reality of the one point the treadmill has any effects on the plane: you have a treadmill going in one direction and a plane attempting to go in the opposite direction and so the wheels will turn at the combined speeds of the two.
Or, one can think of it as pulling a runway backwards under the plane at 2X normal speed. No effects on the plane, but the wheels are turning at 2X their usual speed. As long as the wheels don't explode and the treadmill the minimum length the plane requires to achieve lift, the plane takes off.
Newtonian physics still intact and all that.
The difference in friction between the wheel turning at 260 knots vs 130 knots isn't going to be enough to have much impact on take-off distance of a BBJ (Big Boeing Jet). The author only threw that in there because they don't know what they're talking about.
Author concludes "nothing will be significantly different." Hence he's quite clear that while there will be technically be some added resistance, it will not have any real world impact. I'd guess he threw that in because he knows that's one of the objections some bring up.
The wheels can only spin as fast as they would rolling relative to airspeed.
The wheels spin relative to the speed of the treadmill belt. If the aircraft were to maintain its position relative to the ground (0 ground speed) the tires spin at the same speed the belt travels. If the belt speed was 130 knots while the airplane maintains 0 knots relative to the ground, the wheels are turning at 130 knots. If the aircraft increases its ground speed (speed relative to the ground) to 130 knots and the belt continues at 130 knots, total wheel speed is 260 knots (ground speed of airplane + belt speed) assuming the belt runs opposite to the direction of takeoff.
Let's turn that around. Let's assume the belt runs in the direction of take-off at a speed relative to the ground of 130 knots. If the airplane holds a ground speed of 0 knots, the wheels turn at 130 knots but backwards. If the airplane increases its ground speed to 130 knots take off speed, the wheels are no longer turning. 130 knots - 130 knots = 0 knots.
The treadmill does not increase that speed on the wheels. There is no 2x overdrive.
Ah, but it does and there is. If the treadmill belt did not increase the speed of the wheels, the wheels wouldn't turn at all.
Take a toy car to the check-out at your favorite grocery store grocery store. Ignoring the incredulous look of the check-out girl, place the toy car on the conveyor belt. Assuming the belt is moving at 1 mph, the wheels of your toy car are now spinning at 1 mph. Move the car "upstream" against the direction of the moving belt at 1 mph. The speed of the wheels are now 2 mph. 1+1=2. Your 2x overdrive. (Remember, in this scenario, the only thrust the toy cars gets is from your hand, independent of the moving belt.)
While ignoring other shoppers behind you wanting to check out, move the car in the direction of the belt at 1 mph. The toy car is now moving at the same speed as the belt, but the wheels are stationary. They no longer spin. 1-1=0.
Because you're the curious type and the check-out girl is pretty, you continue the experiment further. You move the toy car in the direction the belt is traveling, but only at a half a mph. The wheels are now spinning at a half mile an hour, but backwards from the direction the car is moving. 1-.5=.5. Now, it's an underdrive.
Amazing! The laws of physics are still in play. More amazing is the discovery that instead of giving you her phone number, the pretty check-out girl has called for security and it's time to leave before they frog-march you out the door.
Adrenaline_6
10-15-20, 12:04
The wheels spin relative to the speed of the treadmill belt. If the aircraft were to maintain its position relative to the ground (0 ground speed) the tires spin at the same speed the belt travels. If the belt speed was 130 knots while the airplane maintains 0 knots relative to the ground, the wheels are turning at 130 knots. If the aircraft increases its ground speed (speed relative to the ground) to 130 knots and the belt continues at 130 knots, total wheel speed is 260 knots (ground speed of airplane + belt speed) assuming the belt runs opposite to the direction of takeoff.
Let's turn that around. Let's assume the belt runs in the direction of take-off at a speed relative to the ground of 130 knots. If the airplane holds a ground speed of 0 knots, the wheels turn at 130 knots but backwards. If the airplane increases its ground speed to 130 knots take off speed, the wheels are no longer turning. 130 knots - 130 knots = 0 knots.
Ah, but it does and there is. If the treadmill belt did not increase the speed of the wheels, the wheels wouldn't turn at all.
Take a toy car to the check-out at your favorite grocery store grocery store. Ignoring the incredulous look of the check-out girl, place the toy car on the conveyor belt. Assuming the belt is moving at 1 mph, the wheels of your toy car are now spinning at 1 mph. Move the car "upstream" against the direction of the moving belt at 1 mph. The speed of the wheels are now 2 mph. 1+1=2. Your 2x overdrive. (Remember, in this scenario, the only thrust the toy cars gets is from your hand, independent of the moving belt.)
While ignoring other shoppers behind you wanting to check out, move the car in the direction of the belt at 1 mph. The toy car is now moving at the same speed as the belt, but the wheels are stationary. They no longer spin. 1-1=0.
Because you're the curious type and the check-out girl is pretty, you continue the experiment further. You move the toy car in the direction the belt is traveling, but only at a half a mph. The wheels are now spinning at a half mile an hour, but backwards from the direction the car is moving. 1-.5=.5. Now, it's an underdrive.
Amazing! The laws of physics are still in play. More amazing is the discovery that instead of giving you her phone number, the pretty check-out girl has called for security and it's time to leave before they frog-march you out the door. As you make haste for the door, still confused, the gay bag boy winks and says "I like toy cars too!"
Fixed.
Amazing! The laws of physics are still in play. More amazing is the discovery that instead of giving you her phone number, the pretty check-out girl has called for security and it's time to leave before they frog-march you out the door.
Your explanation is way superior to my explanation(s).
Really, the question about whether or not the plane could take off is a brain teaser? It scares me that some people can't answer that question.
If the treadmill is going forward yes the plane will take off. All that is required for lift is wind over the airfoil at high enough speed. Same reasons catapults on carriers work.
Sent from my iPhone using Tapatalk
The treadmill does not increase that speed on the wheels. There is no 2x overdrive.
Ah, but it does and there is. If the treadmill belt did not increase the speed of the wheels, the wheels wouldn't turn at all.
Take a toy car to the check-out at your favorite grocery store grocery store. Ignoring the incredulous look of the check-out girl, place the toy car on the conveyor belt. Assuming the belt is moving at 1 mph, the wheels of your toy car are now spinning at 1 mph. Move the car "upstream" against the direction of the moving belt at 1 mph. The speed of the wheels are now 2 mph. 1+1=2. Your 2x overdrive.
I get what you are saying, but this creates an infinite sequence. If the wheels are now 2, the conveyor must now go 2, so now the wheels are at 4, now the conveyor must go 4, and the wheels are at 8, and so on ...
Hence I interpret the rules ("The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction") to mean the conveyor can match the speed, but cannot increase the speed of the wheels.
Really, the question about whether or not the plane could take off is a brain teaser? It scares me that some people can't answer that question.
I give very few LIKES but you earned one. Not just any LIKE but one from Wolf Hollow.
Congratulations!
fedupflyer
10-15-20, 18:01
I can’t beleiev this more than decade old question actually made it to this site.
The answer is simple.
No relative wind over the airfoil (wing) means no lift. Ie that plane ain’t taking off.
Side note.
If you can achieve a greater than 1:1 thrust to weight ratio then you can make anything “fly”.
Really, the question about whether or not the plane could take off is a brain teaser? It scares me that some people can't answer that question.
I guess brains are still being teased.
Adrenaline_6
10-15-20, 21:58
I can’t beleiev this more than decade old question actually made it to this site.
The answer is simple.
No relative wind over the airfoil (wing) means no lift. Ie that plane ain’t taking off.
Side note.
If you can achieve a greater than 1:1 thrust to weight ratio then you can make anything “fly”.
No dude., the plane is not gong straight up, it just needs the same thrust it usually does for acceleration. The wheel friction is almost irrelevant.
Let's put it into a more 1 to 1 example.
You attach a cable to the front of the aircraft that is designed to break if the amount of tension on the cable exceeds the thrust that the aircrafts engines produce. This is the thrust of the airplane that cannot be exceeded.
That cable is pulled at that constant tension down the treadmill runway. No more, no less. The treadmill starts matching the wheel speed. The friction/drag that the wheel assembly is taking away from the total thrust is minor and irrelevant to the amount of tension being put on the cable. Thus, the airplane will easily move down the treadmill, no matter how fast the wheels spin until it gets to rotation speed, in which it will takeoff.
Yeah, I dont see the force from bearing friction Overcoming the force from the engines.
Going to the 2 scenarios in the op: in either case the wheels will be spinning twice as fast as normal.
If you have a scale hooked to the front of the plane (stationary) and the belt moves 2x takeoff speed rearwards, how much force is that applying to the plane at steady state? What about at 1x takeoff speed? Is the difference enough force prevent the plane from taking off from a normal runway?
I doubt it.
fedupflyer
10-16-20, 10:14
No dude., the plane is not gong straight up, it just needs the same thrust it usually does for acceleration. The wheel friction is almost irrelevant.
Let's put it into a more 1 to 1 example.
You attach a cable to the front of the aircraft that is designed to break if the amount of tension on the cable exceeds the thrust that the aircrafts engines produce. This is the thrust of the airplane that cannot be exceeded.
That cable is pulled at that constant tension down the treadmill runway. No more, no less. The treadmill starts matching the wheel speed. The friction/drag that the wheel assembly is taking away from the total thrust is minor and irrelevant to the amount of tension being put on the cable. Thus, the airplane will easily move down the treadmill, no matter how fast the wheels spin until it gets to rotation speed, in which it will takeoff.
Your example is so dumb and misinformed I am not even sure how to respond to it.
Friction has zero to do with the question.
Basic aerodynamics dictate. No airflow over the wing = no lift = aircraft stays put regardless of what the wheel are doing.
(technically speaking its excess thrust that makes an aircraft climb)
If the treadmill is going forward yes the plane will take off. All that is required for lift is wind over the airfoil at high enough speed. Same reasons catapults on carriers work.
Sent from my iPhone using Tapatalk
It is in fact the opposite to how catapult functions. Catapults add thrust, the treadmill has no impact on the thrust and is moving the opposite direction to the plane where as the catapult goes in the same direction as the plane, so apples to blender comparison. As long as the treadmill is the length of a runway, the plane achieves needed speed to lift. Any shorter, and no, due to reasons you covered.
Your example is so dumb and misinformed I am not even sure how to respond to it.
Friction has zero to do with the question.
Basic aerodynamics dictate. No airflow over the wing = no lift = aircraft stays put regardless of what the wheel are doing.
(technically speaking its excess thrust that makes an aircraft climb)
Does anyone even read any more before they respond? He wrote:
"the friction/drag that the wheel assembly is taking away from the total thrust is minor and irrelevant."
Hence, not claiming friction/drag is a major factor. However, while friction is obviously not a factor to answering the Q, there would not be zero resistance however minor it would be.
My head is starting to hurt reading this so let’s make this simple. Whether a jet is on a treadmill, runway or whatever, flight is a function of airspeed not ground speed.
Does anyone even read any more before they respond? He wrote:
"the friction/drag that the wheel assembly is taking away from the total thrust is minor and irrelevant."
Hence, not claiming friction/drag is a major factor. However, while friction is obviously not a factor to answering the Q, there would not be zero resistance however minor it would be.
Anyone who is looking at this puzzle and is factoring in runway length, friction, drag, etc., has completely missed what this puzzle is about.
ChattanoogaPhil
10-16-20, 13:26
my mind can't grasp a stationary plane getting lift regardless of thrust...there is a reason aircraft carriers go full speed into the wind when launching.
Of course you can. Most of us learned this at a very young age flying a kite. It's about airspeed. On a windy day you can launch a kite without running. On a calm day you have to run like hell to create airspeed for the kite.
Anyone who is looking at this puzzle and is factoring in runway length, friction, drag, etc., has completely missed what this puzzle is about.
As I'd say the treadmill/runway length literally the crux of the answer as to whether the plane will fly or not, what do you feel the puzzle is about?
If the treadmill is the length of the runway the plane requires to fly it flies. If it's not, it does not. The quiz states the conveyor is the length of the runway the 747 needs to take off, so the answer is, it takes off.
...my mind can't grasp a stationary plane getting lift regardless of thrust...
An airplane stationary relative to airflow makes no lift.
An airplane can hover (remain stationary relative to the ground) if the headwind has enough speed. (Although the airplane is stationary relative to the ground, it its not stationary relative to the air.)
fedupflyer
10-16-20, 13:47
As I'd say the treadmill/runway length literally the crux of the answer as to whether the plane will fly or not, what do you feel the puzzle is about?
And you are very very wrong.
The original question, when posed about 15 yrs ago, dealt a hypothetical from a student.
It stated that a treadmill that could match the movement of the wheels of the aircraft. It does not matter how long the treadmill is as there would be zero relative movement from an observer standing next too it.
This boils down to basic aerodynamics.
Again, the wheels a free to move but just because the wheels are moving does not generate any airflow over the wing. No airflow over the wing means no lift.
So many have trouble separating the fact the wheels can move and that is seperate from airflow over the wing.
Or you can look at in the reverse.
Lock the wheels and put a really big fan in front of the aircraft. Once the fan has induced enough air flow (velocity) the aircraft will takeoff.
And you are very very wrong.
The original question, when posed about 15 yrs ago, dealt a hypothetical from a student.
It stated that a treadmill that could match the movement of the wheels of the aircraft. It does not matter how long the treadmill is as there would be zero relative movement from an observer standing next too it.
This boils down to basic aerodynamics.
Again, the wheels a free to move but just because the wheels are moving does not generate any airflow over the wing. No airflow over the wing means no lift.
So many have trouble separating the fact the wheels can move and that is seperate from airflow over the wing.
Or you can look at in the reverse.
Lock the wheels and put a really big fan in front of the aircraft. Once the fan has induced enough air flow (velocity) the aircraft will takeoff.
Are you factoring in the thrust from the jet/prop? I’d think that would overcome any input from the treadmill.
fedupflyer
10-16-20, 13:58
Are you factoring in the thrust from the jet/prop? I’d think that would overcome any input from the treadmill.
It doesn't matter what method of achieving thrust is used, whether it be jet, prop or rocket engine.
There is no input from the treadmill.
No airflow over the wing = no lift = no takeoff.
And you are very very wrong.
The original question, when posed about 15 yrs ago, dealt a hypothetical from a student.
It stated that a treadmill that could match the movement of the wheels of the aircraft. It does not matter how long the treadmill is as there would be zero relative movement from an observer standing next too it.
This boils down to basic aerodynamics.
Again, the wheels a free to move but just because the wheels are moving does not generate any airflow over the wing. No airflow over the wing means no lift.
So many have trouble separating the fact the wheels can move and that is seperate from airflow over the wing.
Or you can look at in the reverse.
Lock the wheels and put a really big fan in front of the aircraft. Once the fan has induced enough air flow (velocity) the aircraft will takeoff.
Not sure if we are saying the same thing or not here, but the Q stipulates the treadmill the length of a runway, the treadmill has no impact on the the thrust of the the plane which will move forward and will achieve speed require for flight.
If the treadmill could in fact keep the plane from gaining forward motion (which as covered by the OP linked article not possible as written), then obviously no lift. OP article on aviation site discusses both versions of the Q.
There's two versions of the quiz which I posted in the OP, and the version that has been tested and is actually hypothetically possible will see the plane fly and would require...wait for it...a treadmill the length of a runway to achieve speed to fly due to basic aerodynamics.
SMH...
The wheels are irrelevant. They're just hold the plane up and are free to spin at any speed.
The treadmill is irrelevant. The plane doesn't push against the ground to accelerate...It pushes against the air. Well, actually it forces a large quantity of air rearward at high speed, which produces forward thrust...Newton's laws and all that.
The thrust against the air will push the plane forward regardless of the speed of the wheels/treadmill. If the length of the treadmill is sufficient for the plane to achieve its minimum takeoff speed, it will take off. Simple as that. The treadmill turning backwards against the free-wheeling landing gear is irrelevant.
Will, clear out your excess PMs
What you have to get past is the thrust overcomes the treadmill...the way this hypo presents itself is the TM indeed keeps up with the thrust, the wheels are actually spinning faster to where the plane stays stationary / no lift which is logical if you keep it in that paradigm.
In reality, the argument is there is no physical way for a moving runway to overcome & defeat actual thrust so the TM cannot stop forward momentum...this is why debate gets stuck.
It doesn't matter what method of achieving thrust is used, whether it be jet, prop or rocket engine.
There is no input from the treadmill.
No airflow over the wing = no lift = no takeoff.
Exactly, but you're conclusion is wrong. Due to the treadmill having no input the plane will move forward. The wheels will be turning at 2X normal speed (see past pages discussing that one...) but the plane will move forward at usual speed and lift, if, the treadmill is the length of a runway needed for wind speed over lift surfaces of the plane.
As the treadmill has no input on the plane as you point out, whether the treadmill is doing 1mph or 500mph, it only effects the rate at which the wheels are turning and nothing else.
SMH...
The wheels are irrelevant. They're just hold the plane up and are free to spin at any speed.
The treadmill is irrelevant. The plane doesn't push against the ground to accelerate...It pushes against the air. Well, actually it forces a large quantity of air rearward at high speed, which produces forward thrust...Newton's laws and all that.
The thrust against the air will push the plane forward regardless of the speed of the wheels/treadmill. If the length of the treadmill is sufficient for the plane to achieve its minimum takeoff speed, it will take off. Simple as that. The treadmill turning backwards against the free-wheeling landing gear is irrelevant.
Not irrelevant, just not relevant in the way some seem to think it is. By what you wrote above, the length of the treadmill is relevant as if it's too short plane does not reach its minimum takeoff speed. What's relevant is the plane reaches minimum takeoff speed and that will require a treadmill long enough to achieve that.
Effects treadmill has on plane, not relevant to flying, but the length of the treadmill is very relevant to fly/no fly.
What you have to get past is the thrust overcomes the treadmill...the way this hypo presents itself is the TM indeed keeps up with the thrust, the wheels are actually spinning faster to where the plane stays stationary / no lift which is logical if you keep it in that paradigm.
In reality, the argument is there is no physical way for a moving runway to overcome & defeat actual thrust so the TM cannot stop forward momentum...this is why debate gets stuck.
E
X
A
C
T
L
Y
The plane flies if the treadmill is the length of a runway per the quiz...
Will, clear out your excess PMs
Roger that. Done.
fedupflyer
10-16-20, 14:26
Exactly, but you're conclusion is wrong. Due to the treadmill having no input the plane will move forward. The wheels will be turning at 2X normal speed (see past pages discussing that one...) but the plane will move forward at usual speed and lift, if, the treadmill is the length of a runway needed for wind speed over lift surfaces of the plane.
As the treadmill has no input on the plane as you point out, whether the treadmill is doing 1mph or 500mph, it only effects the rate at which the wheels are turning and nothing else.
I went back a read the original posting.
The first questioned you asked is the same question (for the most part) that started the entire debate on a flying web forum and made it to magazines and TV shows.
For the folks that think it will take-off lack a basic understanding of aerodynamics. There even some CFIs that don't understand it.
I don't car how long the treadmill is, the aircraft WILL NOT TAKEOFF.
I am not sure why the second question would even be posed as it is evident that the answer would be double.
I went back a read the original posting.
The first questioned you asked is the same question (for the most part) that started the entire debate on a flying web forum and made it to magazines and TV shows.
For the folks that think it will take-off lack a basic understanding of aerodynamics. There even some CFIs that don't understand it.
I am not sure why the second question would even be posed as it is evident that the answer would be double.
I think Artos #105 above summarized that issue well and my response in #108.
The plane will fly as long as the wheels don't explode. :neo:
fedupflyer
10-16-20, 14:37
I think Artos #105 above summarized that issue well and my response in #108.
You both lack an understanding of basic aerodynamics.
And the original question is poised as a hypothetical.
You both lack an understanding of basic aerodynamics.
And the original question is poised as a hypothetical.
And you apparently don't understand Basic aerodynamics is perfectly accounted for and still don't get what the issues are. Treadmill has no impact on the plane (other than the wheels having to turn faster) Plane reaches required speed to fly, if the treadmill the length of the runway needed for that to happen, and away plane goes. That is as basic aerodynamics as it gets. No discussions needed on principles of aerodynamics required to figure that out.
Plane does not reach required speed to lift, no fly.
Not sure how anyone could argue/say otherwise to that simple fact. So the actual debate becomes: does the plane move forward or not? That's the only aspect that matters, and per his comments in #105 as summary - which requires no understanding or discussion of aerodynamics - the plane moves forward under its own thrust.
The issue is actually not one of basic aerodynamics per se, but basic physics, ergo, Newton's third law.
Ergo, the treadmill will not prevent the plane from moving forward to reach lift speeds...
Adrenaline_6
10-16-20, 15:05
Your example is so dumb and misinformed I am not even sure how to respond to it.
Friction has zero to do with the question.
Basic aerodynamics dictate. No airflow over the wing = no lift = aircraft stays put regardless of what the wheel are doing.
(technically speaking its excess thrust that makes an aircraft climb)
You shouldn't respond, because your lack of the understanding of physics is unbelievable. What you seem to not understand is the aircraft WILL accelerate no matter how fast the stupid treadmill spins because the wheel assembly is not the driving force providing the forward motion. The thrust of the engines are. The wheel will just spin at 2x the speed the aircraft is actually moving down the runway (the actual speed of the aircraft + the treadmill matching that speed). It accelerates down the treadmill runway and takes off just like normal.
Your basic aerodynamics point is irrelevant because there is airflow over the wing.
You shouldn't respond, because your lack of the understanding of physics is unbelievable. What you seem to not understand is the aircraft WILL accelerate no matter how fast the stupid treadmill spins because the wheel assembly is not the driving force providing the forward motion. The thrust of the engines are. The wheel will just spin at 2x the speed the aircraft is actually moving down the runway (the actual speed of the aircraft + the treadmill matching that speed). It accelerates down the treadmill runway and takes off just like normal.
Your basic aerodynamics point is irrelevant because there is airflow over the wing.
The really odd part of it is, he understands the treadmill has no impact on the plane, yet can't seem to fathom that = the "plane accelerates down the treadmill runway and takes off just like normal"
Being condescending to people who "get it" while he apparently does not, makes it that much worse.
Being condescending and wrong is not a good combo.
As I'd say the treadmill/runway length literally the crux of the answer as to whether the plane will fly or not, what do you feel the puzzle is about?
The puzzle is about whether a plane can move forward or not when on a conveyor or treadmill.
Specifically, do you understand a plane moves via engine thrust and not wheel torque, that is what this is about. If you do, you say "yes", if you do not, you say "no", if you are "that guy", you argue endlessly about friction, runway lengths for a 747 given an unknown weight, treadmill friction and all kinds of other meaningless nonsense.
A similar puzzle that has made the rounds is you are on a train moving at 300 m/s. If you fire gun at 300 m/s does it leave the barrel. Even better is if you ask if it leaves barrel, is it at 300 m/s or 600 m/s? Of course there is always "that guy" who points out there are no trains that can move 300 m/s. Likewise, there are plenty of "that guy" in the plane/conveyor puzzle.
The original question, when posed about 15 yrs ago, dealt a hypothetical from a student.
I first heard about it in the 1980s on the USENIX newsgroup rec.aviation.
But yes, the wording has changed like a game of spaghetti over the years.
Lock the wheels and put a really big fan in front of the aircraft. Once the fan has induced enough air flow (velocity) the aircraft will takeoff.
Yep, plenty of Utube vids showing parked but strapped planes during winds storms.
https://cdn.boldmethod.com/images/blog/lists/2016/03/11-facts-about-the-harrier-jump-jet/2.jpg
Don’t mind me. I’m just bitterly disappointed people took this question seriously
The puzzle is about whether a plane can move forward or not when on a conveyor or treadmill.
Specifically, do you understand a plane moves via engine thrust and not wheel torque, that is what this is about. If you do, you say "yes", if you do not, you say "no", if you are "that guy", you argue endlessly about friction, runway lengths for a 747 given an unknown weight, treadmill friction and all kinds of other meaningless nonsense.
A similar puzzle that has made the rounds is you are on a train moving at 300 m/s. If you fire gun at 300 m/s does it leave the barrel. Even better is if you ask if it leaves barrel, is it at 300 m/s or 600 m/s? Of course there is always "that guy" who points out there are no trains that can move 300 m/s. Likewise, there are plenty of "that guy" in the plane/conveyor puzzle.
An essential aspect to be sure, but it still aint gonna fly if the treadmill is not the minimum length the plane - in this case a 747 - needs to take off. Hence, whether the plane will fly vs simply move forward, 100% reliant on the length of the treadmill. Summary:
We know the plane will indeed move forward
We know the treadmill will have no impact on whether the plane can reach minimum take off speed to get lift and take off
We know the plane will not take off unless the minimum distance it requires to take off exists, be it a standard run way or the treadmill.
Hence, the length of that treadmill/runway is in fact the crux of whether or not the plane flies and there's no physics, knowledge of aerodynamics, etc required to conclude that one.
The effect of the treadmill on the plane is not relevant (as it has none), but the length of the treadmill is.
The effect of the treadmill on the plane is not relevant (as it has none),
Wrong. The effect of the treadmill on the plane does matter given the verbage of your OP as I point out below.
but the length of the treadmill is.
Did you even read your OP? The treadmill (Conveyor belt) is defined as the length of the runway ("Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway.").
An essential aspect to be sure, but it still aint gonna fly if the treadmill is not the minimum length the plane - in this case a 747 - needs to take off. .
There are about a billion conditions needed for it to fly, and reasonable people take these as a given for the puzzle and do not need to start itemizing them.
We know the plane will indeed move forward
We know the treadmill will have no impact on whether the plane can reach minimum take off speed to get lift and take off
Wrong and wrong.
The plane defined in your example (“Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?") is a dichotomy as a result of the effect the treadmill has on the plane (wheels) creating an infinite sequence the instant it were to move. You have to change the assumptions as I already mentioned a few days ago to get it to move and take off.....
This language from the original rec.aviation post I mentioned is better:
If a 747 is on a treadmill as long as the runway, going the same speed that the aircraft is going. Will it still take off?
https://media1.giphy.com/media/Wn74RUT0vjnoU98Hnt/giphy.gif
Wrong. The effect of the treadmill on the plane does matter given the verbage of your OP as I point out below.
Are you asserting the moving belt of the tread mill will keep the 747 from taking off?
Are you asserting the moving belt of the tread mill will keep the 747 from taking off?
As written in the OP:
“Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"
Not only will the plane NOT take off, it will not move, as the condition of the "The conveyor belt is designed to exactly match the speed of the wheels" creates an infinite sequence which is impossible, as I pointed out earieir in the week.
Changing the wording to rec.aviation language:
"If a 747 is on a treadmill as long as the runway, going the same speed that the aircraft is going. Will it still take off?"
then yes it will take off.
fedupflyer
10-16-20, 20:22
As written in the OP:
“Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"
Not only will the plane NOT take off, it will not move, as the condition of the "The conveyor belt is designed to exactly match the speed of the wheels" creates an infinite sequence which is impossible, as I pointed out earieir in the week.
I understand this and you understand this but certain other (non-aviation) folks here don't seem to understand this.
As written in the OP:
“Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"
I see what you're driving at, but the problem is, once the airplane starts moving (which it will when take-off power is applied) the belt speed cannot be matched to the wheel speed because the wheel speed will always be faster than the belt speed (wheel speed=ground speed+belt speed). Once take-off power is applied, the belt cannot hold the plane stationary relative to the ground. Therefore, the treadmill belt cannot be designed to match the wheel speed once the airplane starts moving forward relative to the ground.
Instead, the experiment must be changed to match wheel of the belt. To accomplish this, the pilot must apply only enough thrust to hold the plane stationary relative to the ground (0 ground speed). If the pilot applies any more thrust than needed to hold the plane stationary, the wheel speed will exceed belt speed and speeding up the belt to match wheel speed will only speed up the wheels more. (Again wheel speed=belt speed+ground speed).
If the plane has any ground speed at all, positive or negative (forward or backward) wheel speed will not match belt speed.
As stated, the belt cannot be programmed to match wheel speed as the plane begins its take-off roll. Therefore, the answer isn't the plane can or cannot take off, the answer is the experiment is flawed and cannot work.
Turn it around so the wheels must match belt speed, the answer is the plane must be held to 0 ground speed and therefore cannot take off.
Therefore, the answer isn't the plane can or cannot take off, the answer is the experiment is flawed and cannot work.
Well let see what the question was:
“Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"
The correct answer is NO, the plane cannot take off.
I see what you're driving at, but the problem is, once the airplane starts moving (which it will when take-off power is applied) the belt speed cannot be matched to the wheel speed because the wheel speed will always be faster than the belt speed (wheel speed=ground speed+belt speed).
Uh, yeah that is what I told you yesterday (infinite sequence) in post #85, and repeated it for WillBrink in post #121 today.
Man, this is Awesome!! First time I've ever been correct on both sides of the argument...can we make this a sticky??
Well let see what the question was:
“Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"
The correct answer is NO, the plane cannot take off.
Negative. The experiment requires that the belt speed must change to match wheel speed. The belt cannot be programmed to match the wheel speed of the airplane as it moves. As stated in my post above, the real answer is the experiment is flawed. It would break the laws of physics.
To match wheel and belt speed, the thrust of the aircraft has to be changed so the aircraft remains stationary. The original premise does not allow or require maintaining aircraft position to match wheel speed to belt speed
Negative. The experiment requires that the belt speed must change to match wheel speed. The belt cannot be programmed to match the wheel speed of the airplane as it moves. As stated in my post above, the real answer is the experiment is flawed. It would break the laws of physics.
To match wheel and belt speed, the thrust of the aircraft has to be changed so the aircraft remains stationary. The original premise does not allow or require maintaining aircraft position to match wheel speed to belt speed
Q: Can the plane take off?
A: The plane can not take off.
It does not ask why it cant take off.....
But whatever you need to save face and not admit I was right all along and you were wrong ....
Man, this is Awesome!! First time I've ever been correct on both sides of the argument...can we make this a sticky??
In order for "Yes, the aircraft will take off" to be the correct answer, the requirement for the belt to match wheel speed must be dropped from the experiment.
In order for "No, it will not take off" the experiment requirements must be changed so that thrust is limited to matching wheel speed to belt speed.
The correct answer is "The experiment cannot be conducted without first resolving conflicting parameters."
Q: Can the plane take off?
A: The plane can not take off.
It does not ask why it cant take off.....
But whatever you need to save face and not admit I was right all along and you were wrong ....
I freely admit that I was wrong concluding that the airplane would take off was the right answer. The conclusion that the airplane cannot take off is not the right answer either. The right answer is the experiment has conflicting parameters.
The experiment requires you to match wheel speed to belt speed. That means belt speed must be adjusted in response to wheel speed. That is an impossible task because as stated earlier, wheel speed=belt speed+ground speed. Not being able to conduct the experiment due to conflicting parameters doesn't prove either conclusion. In this case answering "Can the plane take off?" is answering the wrong question. The right question is "Will the experiment definitively answer the question?" This experiment is somewhat like the story of the researcher cutting off a frog's limbs one at a time and ordering to jump to determine if frogs can hear without legs.
Now, if you stated belt speed relative to the ground and wheel speed relative to the belt must match before take-off (thus resolving the conflicting parameters) then the correct answer would be "The airplane cannot move, let alone take off."
You're right only if the experiment requires you to match wheel speed to belt speed.
How many more times does it have to be posted? It requires exactly that:
"Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"
However, the requirement is to match belt speed to wheel speed, an impossible task.
No it is not impossible. It just results in an infinite sequence. Long before infinity is reached, the tires/wheels will literally come off, slowing down to zero and preventing the plane from taking off. Go watch a video of a Top Fuel Dragster without the tires properly bead locked for an example.
You should just stop posting, as everything you post is wrong.
...No it is not impossible...
Matching belt speed to wheel speed only becomes possible if you include the requirement that the two must match before attempting take-off. Remember, during take-off, the pilot is going to push the throttles to full take-off power and the aircraft will move forward, adding to wheel speed.
Wheel speed=belt speed+airplane ground speed.
To not add to wheel speed, the airplane has to be held to 0 ground speed. That's not gonna happen under take-off power.
"Always Look For the Straight Line"
should just stop posting, as everything you post is wrong.
Thank you
Matching belt speed to wheel speed only becomes possible if you include the requirement that the two must match before attempting take-off.
Seriously, just stop.
"Imagine a 747 is sitting on a conveyor belt..."
Before thrust is applied, and plane is "sitting", wheels are at zero and so is the conveyor. Like a regular takeoff. No need to "require it".
It is in fact the opposite to how catapult functions. Catapults add thrust, the treadmill has no impact on the thrust and is moving the opposite direction to the plane where as the catapult goes in the same direction as the plane, so apples to blender comparison. As long as the treadmill is the length of a runway, the plane achieves needed speed to lift. Any shorter, and no, due to reasons you covered.
Catapults do not add thrust, they propel the aircraft to provide air flow over the airfoil. For the same reason carriers turn into the wind and have a certain speed they need to be going for the plane to not go into the drink. The only part of the equation that adds thrust is the prop or engine.
And you obviously did not read what I had said, I plainly said the treadmill would need to be going in the direction of the plane for enough air flow over the airfoil to create enough lift for the plane to rotate.
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Catapults do not add thrust, they propel the aircraft to provide air flow over the airfoil.
That is called thrust.
https://image.slidesharecdn.com/lesson2forcesofflight-130606142556-phpapp02/95/lesson-2-forces-of-flight-1-638.jpg
64049
I’m amazed that this thread has this many replies. I figured all the aviators would have chimed in by now to set this straight.
The people that think the plane will fly off the treadmill just because the wheels are spinning need to research the meaning of ‘relative wind’. As was mentioned before, an airfoil requires air moving over it to create lift - Bernoulli‘s principle, Newton’s 2nd law.
That said, if you put a giant-ass fan in front of the airplane on the treadmill and it produced enough airflow, the plane would fly. Think wind-tunnel.
The only other way the plane would depart the treadmill would be a Thrust & Vector component upward greater than the weight of the airplane. Think of the AV8 Harrier and you’ll get the idea.
It doesn't matter what method of achieving thrust is used, whether it be jet, prop or rocket engine.
There is no input from the treadmill.
No airflow over the wing = no lift = no takeoff.
Exactly.
Planes do not fly unless you have air flow over the airfoil. And you have to mantain x amount to mantain stable flight.
That is why headwind windshear lifts the plane and doesn’t make it descend faster on an aproach. And why the tailwind windshear forces the plane below glideslope.
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I think Artos #105 above summarized that issue well and my response in #108.
The plane will fly as long as the wheels don't explode. :neo:
What pilot ratings do you have? Lets start there.
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Seriously, just stop.
"Imagine a 747 is sitting on a conveyor belt..."
Before thrust is applied, and plane is "sitting", wheels are at zero and so is the conveyor. Like a regular takeoff. No need to "require it".
Ok, let's see what happens if we don't require the wheel speed and belt speed match before take off.
Pilot applies power. Plane starts rolling at 5 knots ground speed (air speed is 0 relative to ground so we'll combine the two for simplicity). Belt speeds up to 5 knots. However, this adds 5 knots to wheel speed. Wheel speed is now 10 knots (5+5+10). In response, belt kicks up to 10 knots.
In the meantime, the plane continues to accelerate to 50 knots. Wheel speed is now 60 knots (10+50=60). Belt reads wheel speed at 60 and increases its speed in response. Belt speed kicks up to 60. Let's say for some reason the pilot throttles back and holds the speed of the airplane to 50 knots. Wheel speed is now 110 and steadily increasing (50 ground speed+60 belt speed=110).
Pilot realizes things are not going so well. As long as the airplane has greater than 0 ground speed, the belt keeps kicking up it's speed in a vain attempt to match wheel speed. To keep the machinery from coming apart, the pilot must either abort the experiment, or figure out a way to match wheel speed to belt speed. The pilot has two options-
1) throttle back the engines until ground speed drops to 0, thus being unable to achieve take-of speed
2) apply the brakes until wheel speed matches belt speed. The result is wheels match belt speed but as the airplane still has ground speed, they are turning slow enough relative to the belt that the tires are skidding down the runway wearing away the rubber.
Pilot opts for 2 and applies full power, skidding all the way until take-off speed is achieved. Pilot rotates nose and begins climb out from a cloud of blue smoke from the skidding tires.
Ok, let's see what happens if we don't require the wheel speed and belt speed match before take off.
You do not need to require something that already exists.
That is called thrust.
https://image.slidesharecdn.com/lesson2forcesofflight-130606142556-phpapp02/95/lesson-2-forces-of-flight-1-638.jpg
64049
Yes, I somewhat mistated that, they are thrusting the plane forward to provide it with additional speed to get the air over the wing/under the wing.
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https://youtu.be/-JDogTLtels
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Yes, I somewhat mistated that, they are thrusting the plane forward to provide it with additional speed to get the air over the wing/under the wing.
Yeah we usually think of thrust as something provided by engines, which a cat does not do, but in the realm of the four forces, a catapult is effectively thrust.
https://youtu.be/-JDogTLtels
takeoffs are easy, landings are harder.
Catapults do not add thrust, they propel the aircraft to provide air flow over the airfoil. For the same reason carriers turn into the wind and have a certain speed they need to be going for the plane to not go into the drink. The only part of the equation that adds thrust is the prop or engine.
The catapult and the forward speed of the carrier add thrust. If they did not, they could not assist propelling the airplane for launch. Once the plane disconnects from the cat, it loses both sources of thrust (or propulsion) and must rely entirely on the thrust from its engines. During launch, the catapult accelerates the planes faster than the engines could on their own.
And you obviously did not read what I had said, I plainly said the treadmill would need to be going in the direction of the plane for enough air flow over the airfoil to create enough lift for the plane to rotate.
Only if the plane was relying on the belt for thrust. In this example, the plane is free to roll along the belt. To use the belt for thrust, it would have to be connected to it like a catapult
You do not need to require something that already exists.
Are we changing the parameters of the experiment by not requiring the belt speed to match wheel speed?
Or are you asserting that wheel speed does not equal belt speed+aircraft ground speed?
I really can't believe this is still going.
The belt and the tires will be matched as long as they are touching. They (the belt and the tires) also have nothing to do with the aircraft's ability to move forward and induce lift.
Think of it this way, if you set and airplane (or anything with free-spinning wheels) on the belt and hold it with the hand of God from the top, it will sit stationary (with tires spinning away). The belt and wheels can speed up, slow down, or stop. The wheels spin freely, so it does not matter.
Now take that hand (or even better the trust of the engines) and you can easily push the plane forward. The belt can speed up, slow down or stop. It will not change how fast you can push the plane forward.
I see what you're driving at, but the problem is, once the airplane starts moving (which it will when take-off power is applied) the belt speed cannot be matched to the wheel speed because the wheel speed will always be faster than the belt speed (wheel speed=ground speed+belt speed). Once take-off power is applied, the belt cannot hold the plane stationary relative to the ground. Therefore, the treadmill belt cannot be designed to match the wheel speed once the airplane starts moving forward relative to the ground.
Instead, the experiment must be changed to match wheel of the belt. To accomplish this, the pilot must apply only enough thrust to hold the plane stationary relative to the ground (0 ground speed). If the pilot applies any more thrust than needed to hold the plane stationary, the wheel speed will exceed belt speed and speeding up the belt to match wheel speed will only speed up the wheels more. (Again wheel speed=belt speed+ground speed).
If the plane has any ground speed at all, positive or negative (forward or backward) wheel speed will not match belt speed.
As stated, the belt cannot be programmed to match wheel speed as the plane begins its take-off roll. Therefore, the answer isn't the plane can or cannot take off, the answer is the experiment is flawed and cannot work.
Turn it around so the wheels must match belt speed, the answer is the plane must be held to 0 ground speed and therefore cannot take off.
That's been pointed out countless times now and covered in the OP linked article, so either he/they refuse to admit that, don't understand that, or just wanna play contrarian game.
" It is impossible right from the very beginning where the preassumption is that the speeds will always match. If we know (and we know!) the forces applied on the plane we know that during the takeoff there is a huge imbalance of forces. So quoting the Newtonian law:
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
The object will not stay motionless because we have unbalanced forces. So we can not design the conveyor belt to move at the same speed as wheels."
So, on this planet, putting a plane on a treadmill the length of a run way (Q # 2 in OP), running in the opposite direction regardless of speed, the plane flies cuz physics.
Catapults do not add thrust, they propel the aircraft to provide air flow over the airfoil. For the same reason carriers turn into the wind and have a certain speed they need to be going for the plane to not go into the drink. The only part of the equation that adds thrust is the prop or engine.
And you obviously did not read what I had said, I plainly said the treadmill would need to be going in the direction of the plane for enough air flow over the airfoil to create enough lift for the plane to rotate.
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You really don't understand what's wrong with that statement?
I’m amazed that this thread has this many replies. I figured all the aviators would have chimed in by now to set this straight.
The people that think the plane will fly off the treadmill just because the wheels are spinning need to research the meaning of ‘relative wind’. As was mentioned before, an airfoil requires air moving over it to create lift - Bernoulli‘s principle, Newton’s 2nd law.
That said, if you put a giant-ass fan in front of the airplane on the treadmill and it produced enough airflow, the plane would fly. Think wind-tunnel.
The only other way the plane would depart the treadmill would be a Thrust & Vector component upward greater than the weight of the airplane. Think of the AV8 Harrier and you’ll get the idea.
Exactly.
Planes do not fly unless you have air flow over the airfoil. And you have to mantain x amount to mantain stable flight.
That is why headwind windshear lifts the plane and doesn’t make it descend faster on an aproach. And why the tailwind windshear forces the plane below glideslope.
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And you're both missing the actual point and issue, will the plane move? That's what's being debated and what matters to if the plane achieves lift or it does not. No movement, no fly. If the plane achieves speed required for air flow over the airfoil for lift on a treadmill the length of a runways, it flies, and Newton's Third law what's applicable there. Article posted on OP via aviation source covers that in depth.
What pilot ratings do you have? Lets start there.
Says the person who does not think catapults add thrust... What you et al fail to understand is it's not an aerodynamics problem but a "will the plane stand still or move forward?" problem.
I have edited the OP to add additional clarity to that issue if that helps.
As written in the OP:
“Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"
Not only will the plane NOT take off, it will not move, as the condition of the "The conveyor belt is designed to exactly match the speed of the wheels" creates an infinite sequence which is impossible, as I pointed out earieir in the week.
Changing the wording to rec.aviation language:
"If a 747 is on a treadmill as long as the runway, going the same speed that the aircraft is going. Will it still take off?"
then yes it will take off.
By the belt matching the speed if the wheels, that means the wheels have to move. If the plane isnt moving there is no speed to match. If it stated the force on the plane from the treadmill matched the thrust from the engines, then it would be stationary, but it doesnt.
I have to assume some people here are just stirring the pot, but...
The wheels of an airplane are free-spinning (as long as the brakes are not applied). The wheels on an airplane are not involved with propulsion or thrust. On the belt, the plane's speed is completely independent of the speed of the wheels. The wheels are free spinning.
This part is very easy to model in scale. If you placed a toy car (or plane) with free spinning wheels on a tread mill, you can easily hold it in place with the treadmill running. You can also move the toy forward or back on the treadmill with ease. The wheels are free spinning. If you push on the back of the toy (thrust), the toy will move forward on the belt. The wheels are free spinning.
I have to assume some people here are just stirring the pot, but...
The wheels of an airplane are frees-pinning (as long as the brakes are not applied). The wheels on an airplane are not involved with propulsion or thrust. On the belt, the planes speed is completely independent of the speed of the wheels. The wheels are free spinning.
This part is very easy to model in scale. If you placed a toy car (or plane) with free spinning wheels on a tread mill, you can easily hold it in place with the treadmill running. You can also move the toy forward or back on the treadmill with ease. The wheels are free spinning. If you push on the back of the toy (thrust), the toy will move forward on the belt. The wheels are free spinning.
I'd hope so by some of the responses, but I don't think that's the case sadly.
I can't believe how this thread is going. It seems really simple, I mean I can see it being one of those head smack " How did I not see that, I wasn't really thinking" kind of riddles.
As I see it we are talking about an aircraft. Planes only really use a surface for steering and braking while taxiing and to support their weight until they have sufficient lift to fly. Rolling resistance and friction may create a marginal increase in drag in this hypothetical, but the plane would take off.
Let's look at four "speeds": speed in relation to air, speed in relation to the surrounding ground surface, speed in relation to belt, and the speed of the belt moving in the opposite direction expressed as a negative. The 747 starts out stationary on a stationary belt 0,0,0,-0. Pilot applies full power and plane begins to move and belt begins to travel in opposition to aircrafts motion. So as airspeed begins to climb let's just go through at 10kn intervals of airspeed (no wind for simplicity) 10kn,10kn, 20kn, -10kn; 20kn, 20kn, 40kn, -20kn; 30kn, 30kn, 60kn, -30kn; ... continuing to 160kn airspeed at takeoff 160kn airspeed, 160kn in relation to the surrounding surface, 320kn in relation to the belt, and the belt moving opposite the aircraft at -160kn.
Perfectly willing to hear where this example is wrong. Perhaps I misunderstood the wording and there is a trick in the phrasing of the question.
Adrenaline_6
10-17-20, 22:29
I do agree about the wording of the treadmill matching wheel speed. That's a flaw in the wording of the problem. Although I don't think the person putting forth this problem had the intention to do so and also did not have the wheel assembly speed limits as part of the equation eitherornthose specs would have been given. So calling these types of details to the problem is just being disengenuous about the whole thing.
The real question being asked is if the aircraft will move down the runway treadmill. It will. The end. To make it even simpler for people not able to grasp the concept of jet engine thrust, let's use a different example to try and make it clearer to understand.
Let's give the aircraft a takeoff rotation speed. Let's say 120 knots. Let's give the treadmill the advantage and have it spinning at 120 knots from the get go.
To counteract the aircraft from rolling backward and keeping its place on the treadmill the aircraft would have to apply a very small amount of thrust from the engines to just overcome the friction of the wheel assembly. Let's just give it a number like 5%.
What do you think will happen if the rest of the 95% of thrust is applied. Simple it will accelerate that aircraft down the treadmill, even if you let that treadmill accelerate another 120 knots.
Wow. Okay. Wow.
Airflow from the relative wind over the wing is what produces lift. Period. If the wing does not move relative to the wind (or vice-versa), the aircraft will not fly. The conveyer and wheels could be moving at .9x the speed of light and it wouldn't make one difference. If the wing (and plane, by extension, as the wings are attached) does not travel forward on a ground track (and therefore into the relative wind, as the wind is implied to be at rest), there is no lift.
To be clear, if you still don't understand: the aircraft WILL NOT fly.
Source: basic f'ing ground school. I'm an AGI and flight instructor, among other things.
Wow. Okay. Wow.
Airflow from the relative wind over the wing is what produces lift. Period. If the wing does not move relative to the wind (or vice-versa), the aircraft will not fly. The conveyer and wheels could be moving at .9x the speed of light and it wouldn't make one difference. If the wing (and plane, by extension, as the wings are attached) does not travel forward on a ground track (and therefore into the relative wind, as the wind is implied to be at rest), there is no lift.
To be clear, if you still don't understand: the aircraft WILL NOT fly.
Source: basic f'ing ground school. I'm an AGI and flight instructor, among other things.
#151 and or #158 above, OP, OP article linked on aviation site, and many other posts, plane will fly under the Q that's actually possible and really the spirit of the quiz. You may be a FI, but it's your physics that's failing you here. Hint, the plane does travel forward...
Wow. Okay. Wow.
Airflow from the relative wind over the wing is what produces lift. Period. If the wing does not move relative to the wind (or vice-versa), the aircraft will not fly. The conveyer and wheels could be moving at .9x the speed of light and it wouldn't make one difference. If the wing (and plane, by extension, as the wings are attached) does not travel forward on a ground track (and therefore into the relative wind, as the wind is implied to be at rest), there is no lift.
To be clear, if you still don't understand: the aircraft WILL NOT fly.
Source: basic f'ing ground school. I'm an AGI and flight instructor, among other things.
#151 above, OP, OP article, and many other posts, plane will fly under the Q that's actually possible and really the spirit of the quiz. You may be a FI, but it's your physics that's failing you here.
Adrenaline_6
10-18-20, 08:55
#151 above, OP, OP article linked on aviation site, and many other posts, plane will fly under the Q that's actually possible and really the spirit of the quiz. You may be a FI, but it's your physics that's failing you here. Hint, the plane does travel forward...
I don't understand how they don't get that the aircraft will move forward. My example shows simply how thrust will overcome the treadmill and how it will have no effect on acceleration down the treadmill. Unbelievable.
As far as his claim about ground school, being an FI, etc. I graduated from Embry Riddle Aeronautical University with an Aeronautical Science degree and some of the pilots that I conversed with, not all for fairness, were absolute dolts. My point is saying you are in the field of flying accounts for nothing.
#151 and or #158 above, OP, OP article linked on aviation site, and many other posts, plane will fly under the Q that's actually possible and really the spirit of the quiz. You may be a FI, but it's your physics that's failing you here. Hint, the plane does travel forward...
If you're using the excuse that they can't ever move at the same speed (wheels and conveyer belt), then that's a disingenuous question and, bluntly, silly, because the entire thought experiment is about the principles at play (this question is asked to every new student pilot to help them understand relative wind vs motion vs lift vs lift vector), not semantics of minutia. There's nothing new to science here.
The question, at its core, is this: does a aircraft producing thrust, but no forward movement into the relative wind, generate lift? That answer is a resounding "no." This is critically important because new pilots (and those unfamiliar with basic airmanship) mistake thrust and movement for lift. That is what the question is designed to tackle.
The plane does NOT travel forward relative to the relative wind. That is what most people miss. The plane can travel forward at the speed of sound; but, if the relative wind is not moving relative to the wings, it doesn't matter - the aircraft will generate zero lift. The air over the conveyer belt DOES NOT move. There is no airflow over the wings because of this. How then, can the wings produce lift? This is the actual problem; the conveyer belt is simply the mechanism that keeps the aircraft stationary. Again, if I'm wrong, then you'll have to explain how the aircraft is moving into the relative wind if it is stationary on a conveyer belt.
Want proof? Aircraft that are parked (but not tied down) can "fly" when a gust of wind hits them. How? Because the wind is moving over the wings; or, more accurately, the relative wind is traveling from the leading edge to the trailing edge of the wing with enough velocity to generate sufficient lift for flight. This is the only thing that will make aircraft fly. On your conveyer example, the wind AROUND the aircraft is not moving; ergo, the motion of the aircraft itself is irrelevant as it cannot move foward into the relative wind.
Also, the discussion here regarding the speed of the wheels being faster than the conveyer belt are flawed because it assumes a base speed vs acceleration. The aircraft must hit Vs0 to be able to generate lift. Just because a plane can move faster than the treadmill is no guarantee it can move fast enough to achieve enough relative airflow for lift. The experiments with mythbusters that seemingly proved this used a STOL aircraft which can take off in mere feet, as opposed to traditional utility aircraft which require hundreds of feet - the aircraft moved faster than the "treadmill."
That said, if all forces were balanced (which is what the actual thought experiment is based on), then it cannot and will not achieve lift.
You've made it much more complicated that necessary and even then, the introduced complications ignore the basic principles of flight, namely that the movement of air over the wing alone does not guarantee enough lift to make the aircraft fly.
Also, the post linked in the OP? The guy isn't even an actual pilot. He's a computer gamer with no actual aviation background. http://c-aviation.net/about-c-aviation-net/. Even his "try it at home example" shows PRECISELY what I stated above. You must BLOW on the tube to create lift. Blowing is a stand-in for the relative wind. This would not occur in an actual test scenario, as a stationary aircraft would have no airflow over the wings.
The question, at its core, is this: does a aircraft producing thrust, but no forward movement into the relative wind, generate lift? That answer is a resounding "no." This is critically important because new pilots (and those unfamiliar with basic airmanship) mistake thrust and movement for lift. That is what the question is designed to tackle.
You are correct that an aircraft with no air movement over the wings cannot fly, however that does not apply here.
The aircraft will absolutely move forward (thereby creating lift). The thrust of the engines pushes the aircraft right down the conveyor belt regardless of the belt speed. This is why the belt must be runway length.
I don't understand how they don't get that the aircraft will move forward. My example shows simply how thrust will overcome the treadmill and how it will have no effect on acceleration down the treadmill. Unbelievable.
As far as his claim about ground school, being an FI, etc. I graduated from Embry Riddle Aeronautical University with an Aeronautical Science degree and some of the pilots that I conversed with, not all for fairness, were absolute dolts. My point is saying you are in the field of flying accounts for nothing.
I'm really mystified by that one myself at this point. At a loss how to make that one any clearer or easier to understand, and others like yourself, etc all tried various approaches to explain that one.
You are correct that an aircraft with no air movement over the wings cannot fly, however that does not apply here.
The aircraft will absolutely move forward (thereby creating lift). The thrust of the engines pushes the aircraft right down the conveyor belt regardless of the belt speed. This is why the belt must be runway length.
There is NO AIR (relative wind) moving with a conveyer belt. The air around the aircraft remains stationary. On an actual runway, the air and runway are both stationary. The movement of the aircraft on the runway propels it through the surrounding air. This is what creates relative wind. On a conveyer belt, the air does not move because the aircraft is stationary relative to the wind. The aircraft is stationary to the wind because the conveyer belt moves it backwards at the same rate it tries to propel itself forwards. The air around the aircraft does not move over the wings, so there is no lift generated.
That is only true if the wheels provided propulsion, which they do not.
I'm really mystified by that one myself at this point. At a loss how to make that one any clearer or easier to understand, and others like yourself, etc all tried various approaches to explain that one.
Let me simplify it for you:
In the treadmill example, the treadmill (hypothetically) is moving at a rate that negates all forward movement of the aircraft. In other words, regardless of the throttle setting of the aircraft, the conveyer belt will adjust its speed accordingly so that the aircraft does not move forward to a fixed point on the ground next to it.
We both agree on that premise, correct?
Let's make this even simpler: simply tie the aircraft to an immovable object, let the aircraft pull the rope taught, and then apply max throttles. It will not fly.
Why is this? In both cases, the aircraft has the exact same movement into the relative wind. Once you understand that they are the same concept, you'll understand why it won't fly with a conveyer belt. And if you don't agree with the premise, then you'll understand where we're not stating the same thing.
That is only true if the wheels provided propulsion, which they do not.
Not true. Again, thrust does NOT equal lift because thrust does NOT create relative wind (or rather, it does not create any appreciable relative wind in a jet aircraft - conventional prop aircraft do have some airflow over the wings due to the placement and operation of a propeller). This is precisely why the thought experiment was created, to show that thrust is not relative wind and vice-versa.
Let me simplify it for you:
In the treadmill example, the treadmill (hypothetically) is moving at a rate that negates all forward movement of the aircraft. In other words, regardless of the throttle setting of the aircraft, the conveyer belt will adjust its speed accordingly so that the aircraft does not move forward to a fixed point on the ground next to it.
We both agree on that premise, correct?
This is exactly what we do not agree on. The aircraft will move forward because the wheels are free spinning. The movement of the conveyor belt cannot prevent this. An aircraft can continue to accelerate once the wheels leave the ground because the wheels have nothing to do with propulsion (aside from the brakes being able to inhibit it).
In the treadmill example, the treadmill (hypothetically) is moving at a rate that negates all forward movement of the aircraft.
Can a seaplane take off into a current, or does the moving water "negates all forward movement of the aircraft"?
I love this puzzle!
This is exactly what we do not agree on. The aircraft will move forward because the wheels are free spinning. The movement of the conveyor belt cannot prevent this. This is why an aircraft can continue to accelerate once the wheels leave the ground.
Then you've completely butchered and misunderstood the thought experiment. I teach both in the classroom and in the cockpit. The question is not "can the aircraft move forward if it's on a conveyer belt" - the question is about the relative motion of the aircraft that remains stationary because of a treadmill. The idea is that the treadmill will prevent any forward motion of the aircraft. This is the hypothetical - remove that and you've got an entirely different argument.
Again, this was thought up originally to teach the concept of thrust vs relative wind.
Explain to me how a conveyor belt can leave an aircraft stationary.
Can a seaplane take off into a current, or does the moving water "negates all forward movement of the aircraft"?
I love this puzzle!
Firstly, you're not supposed to land or operate in a current that would be moving at such a speed. But, if you happened to try to fly against the current - no, you could not (unless you overcame the current's speed and were able to add to it your own airspeed needed for rotation).
Explain to me how a conveyor belt can leave an aircraft stationary.
This is where you're missing the point (and I said it in my very first post): you're trying to apply minutia without understanding the context of a question.
The question isn't "can a conveyer belt really prevent an aircraft from taking off"; the question is "imagine that a conveyer belt could move in such a way that it negated an aircraft's forward speed at full thrust - would it fly?" Again, this is the topic discussed in EVERY flight school.
You're trying to make a simple question something that is uberly complicated. The question was designed to teach about relative wind and airflow over an airfoil, not Newton's 3rd law.
Firstly, you're not supposed to land or operate in a current that would be moving at such a speed. But, if you happened to try to fly against the current - no, you could not (unless you overcame the current's speed and were able to add to it your own airspeed needed for rotation).
The A/C is not under power and is drifting back due to small current. Thrust is applied, either the A/C moves forward despite the current, or it does not.
Can an airboat move forward into a current?
All variations of the same principle.
If you're using the excuse that they can't ever move at the same speed (wheels and conveyer belt), then that's a disingenuous question and, bluntly, silly, because the entire thought experiment is about the principles at play (this question is asked to every new student pilot to help them understand relative wind vs motion vs lift vs lift vector), not semantics of minutia. There's nothing new to science here.
Not "my excuse" but physics explained about 8,195,012 times here by various people,
Adrenaline_6, M wolf, etc.
The question, at its core, is this: does a aircraft producing thrust, but no forward movement into the relative wind, generate lift? That answer is a resounding "no." This is critically important because new pilots (and those unfamiliar with basic airmanship) mistake thrust and movement for lift. That is what the question is designed to tackle.
And you're wrong. On the Q that's based on reality, plane flies. On the Q that's poorly worded that can't in fact exist, where by the plane can't move forward, the plane does not lift.
The plane does NOT travel forward relative to the relative wind. That is what most people miss. The plane can travel forward at the speed of sound; but, if the relative wind is not moving relative to the wings, it doesn't matter - the aircraft will generate zero lift. The air over the conveyer belt DOES NOT move. There is no airflow over the wings because of this. How then, can the wings produce lift? This is the actual problem; the conveyer belt is simply the mechanism that keeps the aircraft stationary. Again, if I'm wrong, then you'll have to explain how the aircraft is moving into the relative wind if it is stationary on a conveyer belt.
Again, covered here by various and really not that complex to understand, plane is not, nor can be, stationary on the conveyor belt. Why you and some others can't/refuse, to grasp that aspect is unclear, but it's a physics issue, not an aerodynamics issue.
Want proof? Aircraft that are parked (but not tied down) can "fly" when a gust of wind hits them. How? Because the wind is moving over the wings; or, more accurately, the relative wind is traveling from the leading edge to the trailing edge of the wing with enough velocity to generate sufficient lift for flight. This is the only thing that will make aircraft fly. On your conveyer example, the wind AROUND the aircraft is not moving; ergo, the motion of the aircraft itself is irrelevant as it cannot move foward into the relative wind.
Also, the discussion here regarding the speed of the wheels being faster than the conveyer belt are flawed because it assumes a base speed vs acceleration. The aircraft must hit Vs0 to be able to generate lift. Just because a plane can move faster than the treadmill is no guarantee it can move fast enough to achieve enough relative airflow for lift. The experiments with mythbusters that seemingly proved this used a STOL aircraft which can take off in mere feet, as opposed to traditional utility aircraft which require hundreds of feet - the aircraft moved faster than the "treadmill."
The above truly exposes a lack of understanding of the topic. Covered at length int this thread and I'm not repeating it yet again.
That said, if all forces were balanced (which is what the actual thought experiment is based on), then it cannot and will not achieve lift.
The the forces can't be balanced, one thought experiment based on reality finds the plane will lift, the other does not. My focus has been on the Q that's based on reality and clearly what the spirit of the Q i based on, but you can stay focused on the first version of that Q if it makes you happy. Again, if in magic land forces were perfectly balanced and it prevented the plane from moving forward, yet again, to repeat yet again, NO, the plane does not lift.
You've made it much more complicated that necessary and even then, the introduced complications ignore the basic principles of flight, namely that the movement of air over the wing alone does not guarantee enough lift to make the aircraft fly.
I didn't "make" anything, I posted two common versions of the quiz that exist, and focused on the one that can actually exist and be tested and maffed out.
Also, the post linked in the OP? The guy isn't even an actual pilot. He's a computer gamer with no actual aviation background. http://c-aviation.net/about-c-aviation-net/. Even his "try it at home example" shows PRECISELY what I stated above. You must BLOW on the tube to create lift. Blowing is a stand-in for the relative wind. This would not occur in an actual test scenario, as a stationary aircraft would have no airflow over the wings.
It's not a pilot problem, it's a Newtonian physics problem, Adrenaline_6 with a degree in Aeronautical Science is telling you the same thing as have others, plane flies...
It's not a pilot problem, it's a Newtonian physics problem, Adrenaline_6 with a degree in Aeronautical Science is telling you the same thing as have others, plane flies...
Look at my post prior to yours. As I pointed out, the original post is made by a NON-PILOT whose only flight experience is VIDEO GAMES.
He butchers the question and then jumps to a completely unrelated conclusion because he doesn't understand the context and purpose of the question. The question was never "would it fly under Newtonian physics," the question is "does an aircraft at full thrust but no forward motion generate lift from relative wind." This is what happens when amateurs throw themselves into a topic without context and that's exactly what the blog poster did with his topic.
For the 5th time, the question was made not to describe or address Newtonian physics, but to help pilots understand that thrust and movement alone do not generate lift; all lift is always generated in relation to the relative wind. This topic requires an understanding of the context of the question. But hey, I only teach it, what would I know?
Let me simplify it for you:
In the treadmill example, the treadmill (hypothetically) is moving at a rate that negates all forward movement of the aircraft. In other words, regardless of the throttle setting of the aircraft, the conveyer belt will adjust its speed accordingly so that the aircraft does not move forward to a fixed point on the ground next to it.
We both agree on that premise, correct?
Let's make this even simpler: simply tie the aircraft to an immovable object, let the aircraft pull the rope taught, and then apply max throttles. It will not fly.
Why is this? In both cases, the aircraft has the exact same movement into the relative wind. Once you understand that they are the same concept, you'll understand why it won't fly with a conveyer belt. And if you don't agree with the premise, then you'll understand where we're not stating the same thing.
Let me simplify, that can't happen. The treadmil has no impact on the planes rate of forward motion no matter how fast it turns, and the thrust from the plane will easilty overcome any minor resistance the wheels experience and move forward happely down the treadmil, that's the lenghth of the runaway and acheice required speed for lift, and off it goes.
Again, I can't come up with any way to make that simpler.
Again, if you want to stick to the quiz that posits its magically able to prevent the plane from moving forward, then the plane does not fly.
Clear enough?
The A/C is not under power and is drifting back due to small current. Thrust is applied, either the A/C moves forward despite the current, or it does not.
Can an airboat move forward into a current?
All variations of the same principle.
Once again, if it drifts backward, then that drift must be subtracted from the vector of the relative wind.
This is why general aviation has so many accidents....
Look at my post prior to yours. As I pointed out, the original post is made by a NON-PILOT whose only flight experience is VIDEO GAMES.
He butchers the question and then jumps to a completely unrelated conclusion because he doesn't understand the context and purpose of the question.
Congratulations. You are the second person to actually read the OP/Link and see the questioned was butchered.
But we have moved past that butchering and are using a more general example:
This language from the original rec.aviation post I mentioned is better:
If a 747 is on a treadmill as long as the runway, going the same speed that the aircraft is going. Will it still take off?
Once again, if it drifts backward, then that drift must be subtracted from the vector of the relative wind.
This is why general aviation has so many accidents....
So the thrust of a seaplane cannot overcome a slight current.
And you claim to be a pilot.
It's not a pilot problem, it's a Newtonian physics problem, Adrenaline_6 with a degree in Aeronautical Science is telling you the same thing as have others, plane flies...
Heavy jet driver here with almost 30 years of flying under my belt... Given the treadmill is as long as the standard runway for control purposes...
As long as the jet is not tied down/back and the wheel brakes are off, it will accelerate forward under it's own power. The wheels will spin faster than normal though. Regardless how fast the treadmill spins, the plane will accelerate to a certain point until the wheels explode... The maximum tire speed on most large transport category aircraft is 195 knots. Assuming the plane gained enough "air speed" to generate lift before the tires blow up, she'll fly.
So the thrust of a seaplane cannot overcome a slight current.
And you claim to be a pilot.
---
The A/C is not under power and is drifting back due to small current. Thrust is applied, either the A/C moves forward despite the current, or it does not.
Overcoming the current of the water DOES NOT create relative wind. You're asserting (somehow) that a plane can lose forward velocity (due to drift) and then regain it as relative wind airflow. The air above the water is not moving with it (at least to any noticeable effect), therefore overcoming the drift does not add to lift. However much you drift backwards is lost in airflow and must be overcome. It's the same concept as landing with a tailwind, only in reverse.
Heavy jet driver here with almost 30 years of flying under my belt... Given the treadmill is as long as the standard runway for control purposes...
As long as the jet is not tied down/back and the wheel brakes are off, it will accelerate forward under it's own power. The wheels will spin faster than normal though. Regardless how fast the treadmill spins, the plane will accelerate to a certain point until the wheels explode... The maximum tire speed on most large transport category aircraft is 195 knots. Assuming the plane gained enough "air speed" to generate lift before the tires blow up, she'll fly.
THANK YOU! If you were not a dude I'd ask you to marry me at this point. Mind blowing how/why that's been so difficult for so many to fathom here, some claiming to be pilots. Ugh.
THANK YOU! If you were not a dude I'd ask you to marry me at this point. Mind blowing how/why that's been so difficult for so many to fathom here, some claiming to be pilots. Ugh.
I cant wait till you post this puzzle again!
I think the example of the toy was helpful.
Let's say we have a toy jet with functioning engines...if we hold it in place on the TM & add thrust of say 100 knots, the TM doesn't turn. So, let's now speed up the TM to match the the travel of 100 knots to the wheels & then let it go.
I think the example of the toy was helpful.
Let's say we have a toy jet with functioning engines...if we hold it in place on the TM & add thrust of say 100 knots, the TM doesn't turn. So, let's now speed up the TM to match the the travel of 100 knots to the wheels & then let it go.
First time using tappatalk and it's pita.ignore me
I cant wait till you post this puzzle again!Never posted before and will never post it again though I find it interesting until some get condensending and obtuse about it.
Sent from my GM1917 using Tapatalk
Sent from my GM1917 using Tapatalk
double tap
Sent from my GM1917 using Tapatalk
Sent from my GM1917 using Tapatalk
Yeah, like stated it was a fun exercise & got both sides...not sure why it's worth getting riled up.
Never posted before and will never post it again though I find it interesting until some get condensending and obtuse about it.
militarymoron
10-18-20, 22:44
One man shoots a .45 while standing on a treadmill while another shoots 9mm while standing on roller skates. The treadmill will move backward to match the velocity of the bullet. Which man is wearing the more effective camo pattern?
Discuss.
One man shoots a .45 while standing on a treadmill while another shoots 9mm while standing on roller skates. The treadmill will move backward to match the velocity of the bullet. Which man is wearing the more effective camo pattern?
Discuss.
At 850 fps rearward velocity, the 45 shooter will become a camo pattern.
Heavy jet driver here with almost 30 years of flying under my belt... Given the treadmill is as long as the standard runway for control purposes...
As long as the jet is not tied down/back and the wheel brakes are off, it will accelerate forward under it's own power. The wheels will spin faster than normal though. Regardless how fast the treadmill spins, the plane will accelerate to a certain point until the wheels explode... The maximum tire speed on most large transport category aircraft is 195 knots. Assuming the plane gained enough "air speed" to generate lift before the tires blow up, she'll fly.
This guy gets it. You sir, have earned a rare LIKE from Wolf Hollow Tech.
One man shoots a .45 while standing on a treadmill while another shoots 9mm while standing on roller skates. The treadmill will move backward to match the velocity of the bullet. Which man is wearing the more effective camo pattern?
Discuss.
Because ice cream got no bones
Heavy jet driver here with almost 30 years of flying under my belt... Given the treadmill is as long as the standard runway for control purposes...
As long as the jet is not tied down/back and the wheel brakes are off, it will accelerate forward under it's own power. The wheels will spin faster than normal though. Regardless how fast the treadmill spins, the plane will accelerate to a certain point until the wheels explode... The maximum tire speed on most large transport category aircraft is 195 knots. Assuming the plane gained enough "air speed" to generate lift before the tires blow up, she'll fly.
Your explanation was spot on, especially about the tire speeds and overcoming friction of the gear assemblies.
I had to sit in bed and stare at the ceiling for awhile before I realized ya’ll were correct.
I shall go forth now and eat some humble pie.
Thanks Will for the brain teaser.
stuff
Remind me never to get in an airplane with you . . . .
john armond
10-20-20, 11:23
Because ice cream got no bones
WoW.... middle school memories right there!!!!
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