Main Landing Gear Flutter ?
04-08-2002, 10:54 PM
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Main Landing Gear Flutter ?
I have a Global 40 size PT-19 powered by a FA-56 that I have been having a ball flying for the past few seasons.
It is in for "overhaul" in preparation for the upcoming spring flying weather, and I am racking my brain to come up with a solution to the one minor quirk of this airplane:
The main landing gear is the typical 5/32" steel rod ... bent and strapped to wing blocks in a torque bar arrangement. Everything has remained "ultra tight" with none of the sometimes occuring "wallering out" of the vertical hole. This is one strong and secure fixed landing gear.
How-some-ever: Upon landing this very nice flying warbird trainer, both struts start to oscillate back and forth (fore and aft) just as soon as the main wheels touch down. As the plane slows down and the tail settles (if a wheel landing) the oscillation stops and all is normal. I do not lose any control during the oscillation, and there doesn't seem to be any adverse structural effects from these "duck paddling" gyrations.
But BOY do I get a ribbing from my flying buddies every time I land. "Come see Bob's centipede"; "Don Knotts is in Bob's trainer and making a twitch-i-wee touch down again"; "Go around, I wanna see it scramble one more time"; "Is that Daffy Duck or an airplane ?"; etc
Very embarassing.
The struts are 4 3/4 inches in length from the bottom of the wing to the center of the 2 1/2" Dubro wheels. I have thought of going to heavier struts or attaching some spring loaded "shock absorbers" that I have sitting in my "round tuit" box. Both would add undesired weight, possibly changing the nice flying characteristics of the airplane. And I am not sure the shock absorbers wouldn't make the oscillations worse, since they would add the weight at the end of the struts.
Any thoughts and/or advice will be appreciated and welcomed with open arms.
.
It is in for "overhaul" in preparation for the upcoming spring flying weather, and I am racking my brain to come up with a solution to the one minor quirk of this airplane:
The main landing gear is the typical 5/32" steel rod ... bent and strapped to wing blocks in a torque bar arrangement. Everything has remained "ultra tight" with none of the sometimes occuring "wallering out" of the vertical hole. This is one strong and secure fixed landing gear.
How-some-ever: Upon landing this very nice flying warbird trainer, both struts start to oscillate back and forth (fore and aft) just as soon as the main wheels touch down. As the plane slows down and the tail settles (if a wheel landing) the oscillation stops and all is normal. I do not lose any control during the oscillation, and there doesn't seem to be any adverse structural effects from these "duck paddling" gyrations.
But BOY do I get a ribbing from my flying buddies every time I land. "Come see Bob's centipede"; "Don Knotts is in Bob's trainer and making a twitch-i-wee touch down again"; "Go around, I wanna see it scramble one more time"; "Is that Daffy Duck or an airplane ?"; etc
Very embarassing.
The struts are 4 3/4 inches in length from the bottom of the wing to the center of the 2 1/2" Dubro wheels. I have thought of going to heavier struts or attaching some spring loaded "shock absorbers" that I have sitting in my "round tuit" box. Both would add undesired weight, possibly changing the nice flying characteristics of the airplane. And I am not sure the shock absorbers wouldn't make the oscillations worse, since they would add the weight at the end of the struts.
Any thoughts and/or advice will be appreciated and welcomed with open arms.
.
04-08-2002, 11:23 PM
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Main Landing Gear Flutter ?
It sounds as if the airplane has Character. Why not just leave it.
On the other hand you could check to see if the wheels are aligned. Too much toe in or out could cause this.
Ed S
On the other hand you could check to see if the wheels are aligned. Too much toe in or out could cause this.
Ed S
04-09-2002, 04:36 AM
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Main Landing Gear Flutter ?
Do they have a single loop spring in them?
You could remove them from the plane and put them in a vice to carefully and slightly increase the angle of attack.
I had an aircraft do this too. (But not so bad! LOL) By increasing the angle of attack more force will be transferred up the leg instead of against it. Worked for me.
Jeff
You could remove them from the plane and put them in a vice to carefully and slightly increase the angle of attack.
I had an aircraft do this too. (But not so bad! LOL) By increasing the angle of attack more force will be transferred up the leg instead of against it. Worked for me.
Jeff
04-09-2002, 01:40 PM
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Main Landing Gear Flutter ?
And it doesn't do it on take-offs also ? I've seen it on several of
the same planes and 1/4 scale too. It does give character to the
plane. The only fix I could see would be to move up to 3/16"
wire. Eventually the flex will weaken the block mount to the ribs.
the same planes and 1/4 scale too. It does give character to the
plane. The only fix I could see would be to move up to 3/16"
wire. Eventually the flex will weaken the block mount to the ribs.
04-09-2002, 02:20 PM
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Main Landing Gear Flutter ?
Originally posted by rreiss
And it doesn't do it on take-offs also ?
And it doesn't do it on take-offs also ?
Going to 3/16" struts is certainly an option that I have considered, and will continue to. As mentioned previously, added weight is what makes me hesitant to install them.
Before going that route, I may try Jazzy's suggestion of bending the struts further forward ... assuming I have enough propeller clearance to do so.
And as far as "character" goes: I know that I "are one", it's just that my poor little PT-19 gets flustered when they laugh at him/her. Perhaps some consoling discussion sessions with the cute critter will reconcile his/her station in life as a landing clown.
.
