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#11
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It is done by pulling in and out of landing flap enough to flex the wing tips up and down as the mixer moves the ailerons between positive and negative settings
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#12
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ASH-25 flutter
On Saturday, June 27, 2015 at 7:07:58 AM UTC-7, JJ Sinclair wrote:
Time for another JJ story. We were finishing at Ephrata at 50 feet and 140 knots in our ASH-25 (with 2 meter wing extensions). As I crossed the finish line, I pulled up and rolled left,. At about 45 degree left bank, I applied right stick to stop the left roll............IT KEPT ROLLING LEFT................I then applied full right stick and rudder and the left roll stopped, but by then we were in a 75 degree left turn. The nose was up, so as airspeed slowed, the ship slowly responder to right stick commands. After landing, I talked to the guy running the finish gate who was looking right down our wing as we flew through the gate...........He said it was the scariest thing he had ever seen! The wing tip leading edge, twisted down and doug-in, resulting in the un-commanded left turn, the rest of the wing looked like a sign wave. The wing extension had been somewhat blessed by Schleicher who had us install some 12# of lead in the outboard leading edge.. I believe it was to prevent flutter, but probably aided the twist problem.. Any aerodynamic experts explain why the lead was placed in the leading edge? Didn't it help twist the wing leading edge down? Not too long after that, I sold the ship and retired to the peace and tranquility of the finish cylinder in sports class. JJ Happened to my Dad doing Max Q pull-ups while flight testing an F-86. The aileron acted like a trim tab for the entire wing. Not fun at transonic speeds. I don't have a precise answer for the lead in the leading edge. Aeroelastics are complex, but presumably they want the leading edge to twist downward under loading so that there is a restoring force from whatever input perturbs the wing. Make sense that this could increase the resonant frequency and delay the onset speed for flutter and/or add some damping effect, but obviously it had a second consequence for you. 9B |
#13
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ASH-25 flutter
On Sun, 28 Jun 2015 06:18:29 -0700, Andy Blackburn wrote:
On Saturday, June 27, 2015 at 7:07:58 AM UTC-7, JJ Sinclair wrote: Time for another JJ story. We were finishing at Ephrata at 50 feet and 140 knots in our ASH-25 (with 2 meter wing extensions). As I crossed the finish line, I pulled up and rolled left,. At about 45 degree left bank, I applied right stick to stop the left roll............IT KEPT ROLLING LEFT...............I then applied full right stick and rudder and the left roll stopped, but by then we were in a 75 degree left turn. The nose was up, so as airspeed slowed, the ship slowly responder to right stick commands. After landing, I talked to the guy running the finish gate who was looking right down our wing as we flew through the gate...........He said it was the scariest thing he had ever seen! The wing tip leading edge, twisted down and doug-in, resulting in the un-commanded left turn, the rest of the wing looked like a sign wave. The wing extension had been somewhat blessed by Schleicher who had us install some 12# of lead in the outboard leading edge. I believe it was to prevent flutter, but probably aided the twist problem. Any aerodynamic experts explain why the lead was placed in the leading edge? Didn't it help twist the wing leading edge down? Not too long after that, I sold the ship and retired to the peace and tranquility of the finish cylinder in sports class. JJ Happened to my Dad doing Max Q pull-ups while flight testing an F-86. The aileron acted like a trim tab for the entire wing. Not fun at transonic speeds. I don't have a precise answer for the lead in the leading edge. Aeroelastics are complex, but presumably they want the leading edge to twist downward under loading so that there is a restoring force from whatever input perturbs the wing. Make sense that this could increase the resonant frequency and delay the onset speed for flutter and/or add some damping effect, but obviously it had a second consequence for you. It also helps delay flutter onset if the wing CG is in front of the torsional axis. Adding lead in the LE or putting weights in front of the LE on stingers are both ways of moving the wing's CG forward. I heard that years ago from a fellow who worked at the Royal Aircraft Establishment at Farnborough and have seen the stingers used to sort out flutter problems on models. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#14
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ASH-25 flutter
On Sun, 28 Jun 2015 10:05:01 +0100, Ventus_a wrote:
;905822 Wrote: You've got to be kidding. It is done by pulling in and out of landing flap enough to flex the wing tips up and down as the mixer moves the ailerons between positive and negative settings Well spotted. Its clear from the video that the flaps are in landing setting during the initial part of the flypast. You can see them clearly during the initial approach and the fact that the wings are almost straight is another clue. Watch the next ASH-25 approach and landing when you're at the field and you can easily see the usual curve in the wings flatten out as landing flap is selected and the mixer moves the ailerons to a negative setting. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#15
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Quote:
Colin |
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