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Flaperons

Old 11-08-2005, 05:15 PM
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rcrmel
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Default Flaperons

Please help. On the small cap with flaperons. [strip ailerons that work with flaps]. When the flaps are deployed even very slightly with or without elevator input the airplane actually dives instead of lifting. The speed was slow enough to keep the plane airborne. Why??? What is happening??? I hope I have explained this correctly if not please let me know. Thanks. Mel.
Old 11-08-2005, 06:14 PM
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britbrat
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Default RE: Flaperons

Which way are they moving? They should flex downward, rather than reflex upward.
Old 11-08-2005, 08:25 PM
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rcrmel
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Default RE: Flaperons

Yes it moves both ailerons down just slightly about a 1/4" and with down elevator [about 1/4" also] the plane dives. Without elevator the plane still dives when the flaperons are deployed. Other wise the the plane flies fine. I hope this helps. Mel.
Old 11-08-2005, 08:45 PM
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exeter_acres
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Default RE: Flaperons

you normally need to mix in a bit of up elevator with flaperons.......IIRC


Or am I backwards...my radio is downstairs[:@]
Old 11-08-2005, 08:55 PM
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Default RE: Flaperons

If you are using them to assist 3D flying, program them coupled to the elevator. Coupled 180 degrees out of sync with the elevator is my definition of flaperons in the 3D context, or in sync with the elevator I term as spoilerons. Either mode will add to your bag of tricks if the plane is up to it,
Old 11-08-2005, 10:25 PM
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rcrmel
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Default RE: Flaperons

We were trying to use the flaperons to see if we could improve the ease of landings. What both of you are saying is that I should use [UP] elevator trim so to speak with [down] aileron trim. Is this correct?? another words when I flip the switch to land the ailerons will come [down] and the elevator will go [up] the 1/4" I talked about. That seems to be backwards of what true flaps acts like. I hope I am explaining this correctly. Thanks Mel.
Old 11-08-2005, 10:49 PM
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B.L.E.
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Default RE: Flaperons


ORIGINAL: rcrmel

Please help. On the small cap with flaperons. [strip ailerons that work with flaps]. When the flaps are deployed even very slightly with or without elevator input the airplane actually dives instead of lifting. The speed was slow enough to keep the plane airborne. Why??? What is happening??? I hope I have explained this correctly if not please let me know. Thanks. Mel.
When you deploy the flaps, you change the wing's airfoil into one that has more positive pitching moment than it had with the flaps up. This makes the plane pitch down. Take a look at the pitch control for tailless flying wing aircraft. There is no difference between your flaperons and a flying wing's elevons. They do the same thing.
Old 11-08-2005, 11:08 PM
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rcrmel
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Default RE: Flaperons

Thank you So in essence I need to put in down ailerons and up elevator . Could you explain why the difference in a regular flap type aircraft or what causes the different actions between using ailerons and seperarate flaps VS the combined aileron/flap. Thank you.
Old 11-08-2005, 11:09 PM
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rcrmel
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Default RE: Flaperons

Thank you So in essence I need to put in down ailerons and up elevator . Could you explain why the difference in a regular flap type aircraft or what causes the different actions between using ailerons and seperarate flaps VS the combined aileron/flap. Thank you.
Old 11-08-2005, 11:39 PM
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Default RE: Flaperons

I think we are in an area where you have to say that "it depends".

I know that flaps on sailplanes will lift the nose unless some down trim is mixed in or inputed. Other modelers have reported neutral pitching. And now you are saying that it wants to tuck.

I think it's a case of how wide the wing chord is relative to the tail length and area. Any airfoil with positive flap in going to show some negative pitching moment at the same time it wants to lift. If the chord is narrow the tail has the leverage to resist the nose down pitch and the extra lift lifts the nose. If the chord is wide the extra lift is overpowered by the pitching moment of the airfoil if the tail and tail length are not sufficient to counter the pitching action.

At least that's my story and I'm sticking to it...
Old 11-09-2005, 12:27 AM
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Default RE: Flaperons

There is also a small contribution from the increased drag due to the deployed flaps and for lack of better terminology, the location of the added drag vector relative to the vertical location of the C.G. In other words added drag below the CG will increase the nose down pitching moment, and increased drag above the C.G. will reduce the nose down pitching moment. This component of the moment would be small relative to the added camber and the longitudinal location of the C.G.
Old 11-09-2005, 01:25 AM
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Default RE: Flaperons

rcmel,

As B.L.E. points out, you can expect flaperon deflection to change the "pitching moment" of the wing. Looking just at the WING, deflecting a flaperon down will almost always have a nose-down effect. BMatthews is correct in pointing out that the OVERALL effect of flaperon deflection "depends". Unlike your plane, some aircraft pitch up rather than down with flaperon deflection (this is often because the flap/flaperon reduces the tail's effective angle of attack). Such aircraft pitch up even though their wing experiences a nose-down pitching moment (you have to consider the whole aircraft).

If I read your initial post correctly, the thing that was making you scratch your head was: "by deflecting the flaperons down I've added lift, and that should make me go up, not down". If you held speed and angle of attack constant, deflecting a flaperon would normally increase lift, but in your case the nose-down moment discussed above reduces the angle of attack, and the net effect is a reduction in lift (a purist could point out that the CG initially makes a small upward excursion before starting down, but that's a very minor detail). As exeter_acres mentions, you can mix elevator in with flaperon deflection. You would probably want a combination that gave no change in lift as the flaperons are deflected (meaning your plane continues on the same flight path).

For a different reason I have found using flaperons to improve landing qualities a dicey proposition. When you apply "aileron" to a flaperon, you will obviously reach full downward deflection sooner if you have also applied "flaps". Once you reach full downward deflection your roll authority is essentially cut in half. Not only that, the "break" in roll response when you reach full deflection can lead to unpredictable roll behavior, and that can be more detrimental to your landings than a little extra speed. That said, it does make for interesting tinkering. Good luck, hope this helps.

Shoe
Old 11-09-2005, 09:55 AM
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britbrat
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Default RE: Flaperons

Uh -- guys, you are over-complicating the problem. This is NOT a tailless aircraft & flapperon deployment in a tailed aircraft normally increases the effective AOA --- UP pitch. However, in this particular case the pilot has overcompensated for the anticipated (correctly) pitch-up with too much elevator down-trim mixing.

Remove the elevator mixing & try again -- carefully & at a safe height. It will pitch up -- work from there.
Old 11-09-2005, 10:48 AM
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Flypaper 2
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Default RE: Flaperons

Big problem is, the flap,elevator deflection is proportional to airspeed. As a scenario, drop flap to 15 degrees. take off. as the plane accelerates flap affect starts to lift the plane.Lift off say, to 20 ft. Now to maintain that height, as the plane accelerates you would have to keep adding more down el. because of the added lift with speed. Now throttle back you will have to gradually back off on the up el. till it slows down enough to the point where el. is at neutral. as it slows down more you would have to add up el. to maintain flying speed just before touchdown. When we used maneuvering flaps on controlline yrs. back, rule of thumb was flaps would move 1/3 of el. travel.
Old 11-09-2005, 11:06 AM
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Default RE: Flaperons


ORIGINAL: Flypaper 2

--- Now throttle back you will have to gradually back off on the up el. till it slows down enough to the point where el. is at neutral.
You mean back off on the DOWN elevator as you slow down.

You are correct that a bit of "up" elevator will eventually be needed to flare, however, not as much up as you would if the flapperons were not deployed. These are flapperons -- not flaps -- they are (or should be) only deployed at a shallow angle -- not like true flaps in landing configuration.

This is a simple case of over-compensation -- the mixed-in down elevator trim is excessive.

Shoe's comments about the relative effectiveness & associated risks of using flapperons are right on the money.
Old 11-09-2005, 11:17 AM
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Flypaper 2
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Default RE: Flaperons

Right, just another old age brainfart The 1/3 travel is a good place to start as to much flaperon can overpower the elevator. Sort of a trial and error setup. They do make nice square corners.
Old 11-09-2005, 11:39 AM
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Default RE: Flaperons

over complicating the problem here may be right. as i recall, in real aircrafts, it made a difference whether the airplane was a low wing or high wing. low wing with flap deployment lowered the nose -- you had to anticipate and correct for that. high wing did the exact opposite. perhaps it's the flaperon combo that is not making me understand the whole conversation here but that is how i know flap operation to be in the real world (not flaperon) and i am sticking to it...........
Old 11-09-2005, 12:07 PM
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britbrat
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Default RE: Flaperons

Often enough, the use of flaps is concurrent with the extension of landing gear. The gear will assuredly cause a pitch down.

Again these are flapperons, NOT FLAPS. Unlike flaps (particularly in landing configuration), flapperons are most often full span & only deployed at a shallow angle -- this causes an immediate increase in angle of incidence, & results in pitch-up, regardless of wing configuration. The pitch-up is speed sensitive. The pilot can manually compensate for the pitch-up, or as in this case, he can mix in some down elevator. The down-mix is also speed sensitive -- it is also not in-flight adjustable.

Rcrmel has mixed in too much down trim.
Old 11-09-2005, 12:27 PM
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Default RE: Flaperons

It makes no difference whether the control surfaces in question are separate flaps, or is a set flaperons. The best way to check is to remove all elevator mixing. Set the model up for your normal approach speed and add the amount of down flap you wish to use. Compensate with normal elevator stick movement. You'll very quickly see which direction and how much compensation you need to keep your holding of the elevator to a minimum. Now set your transmitter accordingly. The amount may be much more or less than you thought, and it may not. You may be surprised.

It doesn't really matter wheter the model pitches up or down with flap deflection. You just have to find out which way it does, and then adjust for it. As a general rule of thumb, though, low-wing aircraft tend to pitch down with flap deployment, and high-wing aircraft tend to pitch up.

Work with the model up high so that you can play with varying amounts of flaps. See how the model flies at various speeds. Fly faster, fly slower, climb, descend, turn. Adding down deflection to ailerons may make your model stall more easily, and may even give you a nasty tip stall...it depends upon the exact planform, wing loading, and amount of flap. Find this out high enough so that you can take out the flaps and fly normally. Again, you may be greatly surprised...one way or another.

Enjoy finding out how your model handles with the flaperons. That's one of the more fun aspects of R/C flying...finding out how the model flies and then flying it to the limits and getting good while doing it.
Old 11-09-2005, 01:09 PM
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britbrat
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Default RE: Flaperons

Actually it does make a difference whether we are discussing flaps, or flapperons. Flapperons cannot (dare not) be deployed at the steep angles that flaps use in landing configuration.

While some full scale AC do indeed pitch down with flap extension (particularly full extension), in very many years of modelling I have never seen a model pitch down with strip ailerons used as flapperons.
Old 11-09-2005, 05:30 PM
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rcrmel
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Default RE: Flaperons

Well gentlemen I will try to digest all of this support. I really appreciate it.
Thanks very much. Mel.

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