stunthanger.com
General control line discussion => Open Forum => Topic started by: Zuriel Armstrong on November 19, 2009, 06:24:27 AM
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For years I have built planes with a stab that is thicker than the elevators, i.e. 1/2" stab and 3/8" elevators. With all of the adjustablilty we have in our planes now, is this necessary? I believe the logic was to help reduce hunting. It seems it would be easier to build the stab and elevators out of one piece, shape, and separate. Just curious.
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I've always preferred to make the stab thicker than the elevs. It just
works for me. Bob G's Gieseke Nobler had airfoiled stab/elev construction
with both the same thickness. But, as he began to builld bigger planes
he changed to the big/small method you described. My brother and I have
always lived by the "if it's good enough for Bob, then it's good enough for
me" theory.
Steve
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Well, a lot of pilots build them that way. I used to until the last several years. We started using down thrust, and a lot of the hunting problems went away. Without having to use much, if any down elevator bias, the turns became more even between insides and outsides. we noticed that we were having a slight hesitation at the intersections of the eights. If we didn't anticipate, we wound up with a flat spot.
So trying to use logic, it was decided that if we made the stab and elevator the same width, we might get rid of that hesitation.
It seems to work.
The idea behind having a thinner elevator is to blanket the elevator a little, reducing its efficiency in level flight, and helping tame the hunting. Using down thrust helps offset the causetive problem that contributes a lot to hunting.
I prefer the downthrust solution, but use what floats your boat.
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An elevator thicker than the stab can reattach the boundary layer and make it more effective and also reduce drag.
With the large movements we use it may be meaningless.
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Well, a lot of pilots build them that way. I used to until the last several years. We started using down thrust, and a lot of the hunting problems went away. Without having to use much, if any down elevator bias, the turns became more even between insides and outsides. we noticed that we were having a slight hesitation at the intersections of the eights. If we didn't anticipate, we wound up with a flat spot.
So trying to use logic, it was decided that if we made the stab and elevator the same width, we might get rid of that hesitation.
John, I'm curious who the "we" is in your comments above...??
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My old flying buddy. You know who I mean don'tcha? H^^
He's kinda short.
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For years I have built planes with a stab that is thicker than the elevators, i.e. 1/2" stab and 3/8" elevators. With all of the adjustablilty we have in our planes now, is this necessary? I believe the logic was to help reduce hunting. It seems it would be easier to build the stab and elevators out of one piece, shape, and separate. Just curious.
I build them as a single part and then cut them apart. Making the elevator smaller than the stab probably, kind of, does what is intended, but it's unnecessary and even if it worked perfectly, it causes the control response to be non-linear - nothing much for the first little bit of travel, then all of a sudden, a lot. I have had the best luck trying to keep the turbulence and flow as smooth as possible over the entire tail.
Brett
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Randy Powell's Slider:
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I once asked that question of Dick Johnson, former world soaring champion and professional aerodynamicist, back when I was flying full scale sailplanes. He said the general rule is to make the control surface slightly larger, with a rounded entry, to reattach the boundary flow. He said it was also true of hatches, doors and other openings.
I'm writing this from memory. Dick was killed in the crash of his sailplane last year, a very pleasant and knowledgeable guy.
John W
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My old flying buddy. You know who I mean don'tcha? H^^
He's kinda short.
It would definitely be a good idea to give him credit by name.
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Are you being serious Bill? Gordy and I are always poking a little fun at each other.
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What would a shorter elevator and longer stab do to an airplane?
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Confusion.....
Lets get back to using
Span
Chord
Thickness(or %)