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Building Tips and technical articles. => Building techniques => Topic started by: Larry Wong on January 05, 2007, 08:39:18 PM
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Has anybody tryed Bob Palmers differential flap control? and Vertical plane lead outs? if so what are your views on it , and why not more flyers are not using it? It seams to have work for him at the 58 Nats with his THunderbird. #^ HB~>
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Hi Larry,
Vertical LOs work fine. Someone posted a vertial LO set up that is adjustable.
As to the differential flaps, Tom Dixon REVERSED the differential on his last Thunderbird and it flew great.
Plus, 1958 (it was really 1959) was almost 50 years ago! **)
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I have trouble understanding the advantage of a larger (area) outboard flap. Consider an inside loop as an example.To my way of thinking, if the outboard flap area is large than the inboard then the wing center of lift moves farther outboard as the flap is deflected. This outward shift creates an outboard tip up rolling moment that can only be tamed by adding more tip weight. So it seems to me to be one of those design features that requires compromise. Then again as I think about it, it could be a chicken and egg situation. Did this concept of larger outboard flap area result as a means to tame the hinging from large tip weights which do have benefits of among other things, improved line tension in the overheads?
It seems to me that today's designs are carring more tip weight in than in the "old days".
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Hello Dick,
It is good to talk to you again.
I have tried the differential flap idea published by Palmer years ago. They did not work for me and the consensus of those that have tried the differential flap is that they do not work. Even Bob Palmer has since stated that if anything, the differential flap, if used should be connected to have the opposite differential than his article showed.
I have tried the larger outboard flap and will always incorporate some variation of that in my airplanes. They work. The consensus of many top flyers is that they work. Many of the top designs that have appeared in recent years show the larger outboard flap. This includes the Saturn and the Impact. There must be a reason.
I will not try to explain why they help, but they do. That is good enough for me to use them. It is one of those things, like on Bob Whitely's list of things that work: if the idea works, I do not need a technical explanation nor do I need to pay much attention to those who reach for reasons why the idea should not work.
Keith Trostle
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Can we get this list of Bob Whitely's shown on this web site ? I sure would like to see it.
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Hi Gordon, the following is a list of the “Things That Always Work” from an article written by Bob Whitely in the July/August 1998 Issue of Stunt News.
Positive stab incidence
Rudder Offset
Engine Right and Down Thrust
Square control edges may be coming to the list.
So what do you think?
Added - Larry Cunningham had an excellent article on "Non-linearities in CL Stunter Control Systems". I would like to see this series run in CLW.
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The first (positive stab incidence) and the third (engine out and down thrust) have benifited my planes most. I am going to try a full on Rabe rudder on a profile mustang powered by Saito 30. Havn't had great allaround results with fixed rudder offsets. The square trailing edge stuff, I will try later. The thing that comes close to the square trailing edge thing that makes me feel uneasy is on my Strega kit the Stab trailing edge is mutch thicker than the leading edge of the elevator. That set up doesn't give me warm fuzzie feelings downunder. I think I might just make the leading edge of the elevator match the trailing edge of the stab. And no I do not have a graduate degree in aerodynamics, just seat of the pants, and an eye for when things look hinky.
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HI Gordon,
The undersize elevator has been a feature on several top level planes. Bob Baron used the smaller elevator many times as well as the Pattern Master, etc..
My understanding is that it allows the plane to groove better, and reduces the control inputs around neutral. Another way of reducing sensitivity??
Bill <><
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My Magnum flew great with smaller elevators than the Stabalizer.
Jim Pollock ;D