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Author Topic: Lateral bellcrank location matter?  (Read 1497 times)

Offline Matt Brown

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Lateral bellcrank location matter?
« on: August 21, 2018, 06:40:29 AM »
Iím thinking about a sport flying profile design more in the stunt trainer arena. Structure would require the bellcrank be somewhat inboard. Pretty much most designs Iíve looked at have the bellcrank pretty well on the centerline of the plane. With a 4Ē crank, the bearing will need to be roughly 2Ē, maybe 2 1/2Ē inboard of centerline.  Other than the pushrod being a bit farther away from the fuse side, are there any other considerations?

Thanks, Matt


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Offline Dave_Trible

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Re: Lateral bellcrank location matter?
« Reply #1 on: August 21, 2018, 06:59:17 AM »
It shouldn't matter a great lot given the type of airplane.  If it had flaps you would want to try to keep the drive hole location on the bellcrank close to the centerline so that you aren't driving the flap horn from an angle which might cause flex, binding and higher wear, along with some distortion of the travel arc.  If it doesn't have flaps this wouldn't be much of an issue.  Just be sure the pushrod is supported so it doesn't flex under load.

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Offline Tim Wescott

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Re: Lateral bellcrank location matter?
« Reply #2 on: August 21, 2018, 08:49:02 AM »
I'm not sure exactly what your concern is.  There have been statements made about the bellcrank pivot needing to be at the CG, which aren't borne out by actual theory or practice -- leadout positions with respect to CG matters, the relationship between leadout movement to elevator movement matters, and the amount of slop, friction, and flex in the control system matters.  But  once the leadouts and control surfaces are in the right place, the actual bellcrank position only matters to the extent that the control system works right.

Having said that, your throwaway comment about the pushrod being further away than normal from the fuselage does matter.  Profile fuselages flex from side to side.  They do so because of wind, and from varying loads during maneuvers.  The further away the pushrod is from the fuse centerline (assuming a straight pushrod), the worse this effect will be.
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Offline Matt Brown

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Re: Lateral bellcrank location matter?
« Reply #3 on: August 21, 2018, 08:59:13 AM »


Having said that, your throwaway comment about the pushrod being further away than normal from the fuselage does matter.  Profile fuselages flex from side to side.  They do so because of wind, and from varying loads during maneuvers.  The further away the pushrod is from the fuse centerline (assuming a straight pushrod), the worse this effect will be.

Actually, the main reason Iím thinking about this project is to reduce flex and the all too common breaking the fuse at the nose and/or at the trailing edge of the wing. After many years of flying RC 3D profiles, they have pretty well eliminated these failure points. My plan is to build a Re-structured Twister to see how it holds up to accidents that would normally break a profile fuse. Reducing the flexibility of the aft fuse would reduce the pushrod issue you mentioned as well.

Matt

Online Ken Culbertson

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Re: Lateral bellcrank location matter?
« Reply #4 on: August 21, 2018, 11:22:35 AM »
Actually, the main reason Iím thinking about this project is to reduce flex and the all too common breaking the fuse at the nose and/or at the trailing edge of the wing. After many years of flying RC 3D profiles, they have pretty well eliminated these failure points. My plan is to build a Re-structured Twister to see how it holds up to accidents that would normally break a profile fuse. Reducing the flexibility of the aft fuse would reduce the pushrod issue you mentioned as well.

Matt
A much simpler solution is two carbon fiber arrow shafts embedded in the top and bottom of the fuselage from mid wing to mid stab.  They add very little weight, in fact one of mine was actually lighter than the balsa it replaced.  Fuselage flex all but eliminated.

Ken
« Last Edit: August 22, 2018, 11:30:29 AM by Ken Culbertson »
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