Design > Engineering board
New log flap drive crank idea
Mark wood:
--- Quote from: Dennis Toth on November 09, 2021, 02:40:27 PM ---Not to criticize development work just want to understand what it is trying to advance. So does this system reduces the amount of flap input to elevator as you apply more control? Or is it adding more flap as the amount of control is increased? And we can't do this with different mechanical ratio variations why? Does this allow a more rearward CG for tighter corners? What is it doing that is different from the basic Nobler flap/elevator setup? How much better is it?
Best, DennisT
--- End quote ---
As Tim suggests I am not creating a new concept only building upon one. Actually, I am bringing three together. The first is the log crank, second readily modifiable ratios and third complete adjustability. Perhaps another one is easily achieved. I could send you one of these tomorrow.
The reason for making the flap ratio changeable is because of the other work I am doing with regards to increasing the flap size. A larger flap deflected less has the potential of doing the same job with less drag. Igor's flap drive slows flap deflection down to about 27 degrees which is about where I am going to start. By changing out the second lever in the mechanism I can change the resulting drive ratio. A large flap deflected 18 degrees for instance wouldn't work correctly with the current ratios. Notice that the elevator to BC ratio doesn't necessarily change but can be done.
I have intent on changing the flap size and or hinge offset on the airplane. To do this the drive horns must also move and therefore the linkages need to be adjustable. The nice part is 100% of the trim adjustments will be accessible via a hatch most likely on the bottom as the connections change the sense of the motion.
Istvan Travnik:
Dear Mark,
In my album you can find some photos on my variable mechanism.
https://www.flickr.com/photos/171504164@N04/48094388683/in/photostream/
(Some 5-6 pictures about the mechanism)
My preferred measures: narrow wing with 30% flap at the core, 20% at the tip, concave flap, moving not more than 20°. Movement is linear, or slightly exponential.
Horizontal stab+elevator is round 1/4 area of the (complete) wing, elevator moving 45°, strongly exponential. (That means it is more than 2 times faster at the end, related to the neutral position. )
I fly with this arrangement from the mid-eighties, only the material and outfit of mechanism altered.
The full album is connected to my "old" topic here:
https://stunthanger.com/smf/building-techniques/the-bluefoam-model-or-how-to-build-a-stunt-plane-without-a-bit-of-balsa/msg471991/#msg471991
Istvan
Dennis Toth:
Istvan,
Interesting that you have the elevator moving exponentially faster at the high deflection end. I assume this is to give crisper corners, correct? Does it cause the round maneuvers to be harder to keep round? From what has been posted here in other threads as our ships go through round maneuvers we need to ease off at the top a bit since gravity is helping hold the flight path. This is usually a very small amount of control movement. With the conventional system the control surface movement slows as it gets more deflection because of the arch angle of the the bellcrank and control horns.
For you arrangement do you use a longer tail moment to smooth out the movement?
Best, DennisT
Mark wood:
--- Quote from: Istvan Travnik on November 09, 2021, 05:33:42 PM ---Dear Mark,
In my album you can find some photos on my variable mechanism.
https://www.flickr.com/photos/171504164@N04/48094388683/in/photostream/
(Some 5-6 pictures about the mechanism)
My preferred measures: narrow wing with 30% flap at the core, 20% at the tip, concave flap, moving not more than 20°. Movement is linear, or slightly exponential.
Horizontal stab+elevator is round 1/4 area of the (complete) wing, elevator moving 45°, strongly exponential. (That means it is more than 2 times faster at the end, related to the neutral position. )
I fly with this arrangement from the mid-eighties, only the material and outfit of mechanism altered.
The full album is connected to my "old" topic here:
https://stunthanger.com/smf/building-techniques/the-bluefoam-model-or-how-to-build-a-stunt-plane-without-a-bit-of-balsa/msg471991/#msg471991
Istvan
--- End quote ---
Istvan
Thank you very much for that input. It sound like a point of confirmation to me on this path. I've done some work on the exponential mechanisms and I couldn't solve the equation properly for the elevator drive. What is desirable, in my mind, is that the slope around neutral should be less than that of a linear drive arrangement and increasing during deflection to reach a similar angle at around 30 degrees elevator then increasing from there. Seems like you might have something like that. I think I saw another variation of what you have here and I never sat down and worked out the equations for it, yet. I decided to work on the flap drive first and the flap proportions. I think that 30% flaps full span would not be unreasonable but maybe 35% tapering to 25% at the tips if there is any "tip stall" indications.
Istvan Travnik:
Dear Mark,
My "love story" with exponential elevator began that time, when I realized that I am too "wooden-handed" to fly without hunting, and without wobbling after the corners. Les McDonald in his article (in M.A.N.) advised "a bit of slop" in the elevator mechanism, against hunting. As a mechanic engineer I did not like this idea. (Chance of flutter, etc.)
My friends advised against wobbling closer distance of connection points of the handle. I found myself too slow-handed to fly sharp corners with this arrangement. But...
...That time advanced R/C transmitters appeared with so-called (analogue) "exponential knob", and I simply tried to model this function in the mechanics, and symmetrically. It needs a luffing arm (made of slippery plastic, as nylon, Textolite (textile-bakelite), or now ZX-100 ), plus a polished hard steel standing pin. When this arm has several input- and output holes, plus maybe more positions for standing pin, the ratios and charecteristics are nearly limitlessly variable.
I never started to stand up the equation with many sin, tan, arcsin and arctan parameters, it looked more friendly to solve it on paper, with liner, compasses, bevel and pocket calculator... :)
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