MistWolf
10-06-13, 01:26
Hooked up the Chadwick-Helmuth Model 177M-6A balancer to the R-22 after replacing the main rotor blades to check the track & balance.
http://i115.photobucket.com/albums/n289/SgtSongDog/Whirlybird/20131005_181815_zps537a4d61.jpg
I was going crazy because the balancer was showing a vibration of only .2 ips (inches per second) which is within specifications, yet the helicopter was shaking like rat caught by a terrier. All the symptoms- Excessive aircraft vibration, Excessive Cyclic Vibration and Intermittent Blade Track Picture while checking blade track with the strobe- all had one source in common according to the Troubleshooting chart : Bad Teeter Bearing, which meant waiting till Monday to order the needed parts AOG so we could have them in by Tuesday, another four days of downtime. "Pleasepleaseplease," begged. "Don't let it be a bad teeter bearing!" I needed this helicopter in the air yesterday!
Turns out, the ips wasn't .2, it was 2 and the Vibration was so bad the machine was giving confused data. Vibration was along the blade chord (the width of the blade). Fortunately, it was the 1:30 o'clock position which meant I needed to remove weight, not add it. Looking at the chord arm where the weights are attached, it became obvious whoever had balanced the previous set of blades had used far too much- so much that they used a second point not designed to hold weights! The head should have been shifted instead.
After peeling off some of the excess weight, the ips dropped to 1.5, still at 1:30. Good, that meant the change moved everything towards the target. Removing all the chord weights brought the vibration down to .6 ips, still at 1:30. Good news was we made good progress and changes moved the balance towards the center. Bad news was, I still needed to shift weight but had no more weights to remove. That meant a head shift.
Called in another pilot (already had one helping me, I don't know how to fly) to cone the blades (stand on ladders and lift the blade tips upward) so I could pull the teeter bolt (the center bolt that holds the hub, or head, to the mast) and change the shims to shift the head .008". Another test hover showed we were now down to .4 ips but the position changed to 3 o'clock. That was a good thing, because I didn't have the right shims to shift the head further. The vibration was now along the span, or the length of the blades. We removed a couple washers from the blade tips and our vibration dropped to .1 ips and our hover track & balance is finally done. All that's left is a test flight to check tracking in level flight and during auto rotation...
....and I to think- I had hjmpanzr laughing at me in the morning because the M&P-10 was short stroking with under-powered CAVIM surplus ammo and had to figure out how the turrets work on a NF 2.5-10x32 :jester:
http://i115.photobucket.com/albums/n289/SgtSongDog/Whirlybird/20131005_181815_zps537a4d61.jpg
I was going crazy because the balancer was showing a vibration of only .2 ips (inches per second) which is within specifications, yet the helicopter was shaking like rat caught by a terrier. All the symptoms- Excessive aircraft vibration, Excessive Cyclic Vibration and Intermittent Blade Track Picture while checking blade track with the strobe- all had one source in common according to the Troubleshooting chart : Bad Teeter Bearing, which meant waiting till Monday to order the needed parts AOG so we could have them in by Tuesday, another four days of downtime. "Pleasepleaseplease," begged. "Don't let it be a bad teeter bearing!" I needed this helicopter in the air yesterday!
Turns out, the ips wasn't .2, it was 2 and the Vibration was so bad the machine was giving confused data. Vibration was along the blade chord (the width of the blade). Fortunately, it was the 1:30 o'clock position which meant I needed to remove weight, not add it. Looking at the chord arm where the weights are attached, it became obvious whoever had balanced the previous set of blades had used far too much- so much that they used a second point not designed to hold weights! The head should have been shifted instead.
After peeling off some of the excess weight, the ips dropped to 1.5, still at 1:30. Good, that meant the change moved everything towards the target. Removing all the chord weights brought the vibration down to .6 ips, still at 1:30. Good news was we made good progress and changes moved the balance towards the center. Bad news was, I still needed to shift weight but had no more weights to remove. That meant a head shift.
Called in another pilot (already had one helping me, I don't know how to fly) to cone the blades (stand on ladders and lift the blade tips upward) so I could pull the teeter bolt (the center bolt that holds the hub, or head, to the mast) and change the shims to shift the head .008". Another test hover showed we were now down to .4 ips but the position changed to 3 o'clock. That was a good thing, because I didn't have the right shims to shift the head further. The vibration was now along the span, or the length of the blades. We removed a couple washers from the blade tips and our vibration dropped to .1 ips and our hover track & balance is finally done. All that's left is a test flight to check tracking in level flight and during auto rotation...
....and I to think- I had hjmpanzr laughing at me in the morning because the M&P-10 was short stroking with under-powered CAVIM surplus ammo and had to figure out how the turrets work on a NF 2.5-10x32 :jester: