Can a jet on a treadmil fly?

[Renegade]

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!

[Skyyr]

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.

[Chubbs103]

Explain to me how a conveyor belt can leave an aircraft stationary.

[Skyyr]

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).

[Skyyr]

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.

[Renegade]

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.

[WillBrink]

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...

[Skyyr]

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?

[WillBrink]

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?

[Skyyr]

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....