rigging flaps on unconventional wing

Reading all the stuff on intermediate RTF (or ARTF) and went to looking at corehouse page. Looking at the RC Trainer and go to thinking..... http://home.earthlink.net/~philcartier/rcpsychokit.html

Could a person easily make these ailerons work as flaps. Because the trailing edge is not straight, I'm wondering how it could be done without creating a bind. Im sure it has been done before, maybe separate rods with individual control horns on each flap?

Mitch:

Yes, flaps with swept hingelines are possible, even fairly common. But the question begs:WHY?

The Corehouse Stunter as well as the Ukey are terrific Intermediate planes as planned.

See Ya

>Mitch:
>
>Yes, flaps with swept hingelines are
>possible, even fairly common.
>But the question begs:WHY?
>
>The Corehouse Stunter as well as
>the Ukey are terrific Intermediate
>planes as planned.
>
>See Ya
>
>Peabody

I assume you have modified both these airplanes and found that they perform no better with working flaps?

catdaddy

>>Mitch:
>>
>>Yes, flaps with swept hingelines are
>>possible, even fairly common.
>>But the question begs:WHY?
>>
>>The Corehouse Stunter as well as
>>the Ukey are terrific Intermediate
>>planes as planned.
>>
>>See Ya
>>
>>Peabody
>
>
>I assume you have modified both
>these airplanes and found that
>they perform no better with
>working flaps?

Probably not, but it doesn't necessarily take an actual test. When you add flaps, you need a larger tail volume. The flaps, while they increase the maximum coefficient of lift, also tend to torque the airplane in the opposite direction. This means that when you drop the flaps for an inside corner, the airplane tends to nose in the opposite direction. More tail volume is required to overcome this tendency.

In general, just putting flaps on otherwise unflapped airplane doesn't work out so well. They need more changes than that to work properly. Much better to get an airplane that was designed for this from the beginning.

If you still want to try it, use R/C Aileron fittings with a "y" shaped pushrod, or a conventional horn with a "sandwich" box that allows the free end of the horn to move relative to the flap. If/When it doesn't turn so good, you can always lengthen and enlarge the tail.

Anyway, to answer the question, You use split flap horns. Easier to do in a full fuse than a profile but that is how yo do it. The push rod from the bellcrank is two pieces assembled to look like the letter Y. This is also how you can rig a V tail stunter. That look so cool.

The mechanical aspects aren't as much trouble as the effects of the aerodynamics on trimming. Many of the more accomplished stunt pilots have averred that this type of flap hinging on a wing is a great deal more difficult to work with than the usual setup. Al liked his scale planes and thus had several with the flaps hinged to forward swept TE's, I think, but Al is in some kind of class of his own at surmounting design and trim problems.

Kiwi

>Anyway, to answer the question, You
>use split flap horns.

If a good flying competitive stunt ship is the goal, split flap horns are to be avoided if at all possible.

There is no way short of a mechanical system that would weigh entirely too much that will keep the flaps flexing differentially due to the assymetrical loads on the flaps. You will end up a model that has all sorts of nasty habits that simply cannot be trimmed out. Yes, I have had and I know others have had models with split flap horns that have placed at the Nats. These have been on airplanes with dihedral and flap hinge line sweep. And I am familier with some fairly elaborate attempts to minimize the free play (slop) and flex from one flap to the other using split horns. But I have built another airplane of one of those designs with a single horn and it was immediately a better flying airplane.

Al Rabe has incorporated split flap horns in his earlier designs, but I believe he is using single horns now.

There are several ways to use a single horn on a wing that has dihedral and/or flap hinge line sweep. Unless there is an excessive amount of dihedral or hinge line sweep, the single horn can be mounted just as you normally would on a wing with a straight flap hinge line. One might think that there would be a bind as soon as the flaps are deflected but this does not happen. Apparently, there is enough flex in the hinges and the wood surrounding the flap horn to allow for plus or minus 30 to 40 degree flap deflection. There is probably a limit to the absolute TE angle that this approach can be used, but for a "typical" design like in a semi-scale Bearcat, Mustang or Focke-Wulf, the single horn works fine.

Another method is the use of the "lucky boxes" like those sold by RSM. These allow the ends of the flap horn freedom to move inside the lucky box as the flap moves up and down, yet allow little or no differential "play" from one flap to the other.

I will let Al describe another method he and Frank McMillan have used where the hinges of the single horn are lashed to the trailing edge of the wing, allowing the horn wire to flex to the curvature needed to match the dihedral/hinge line sweep. This means that the flap horn wire is required to flex longitudinally. It still resists any torsional twisting (sort of like a really stiff speedometer cable). This requires a fairly sturdy trailing edge and a substantial method of lashing the horn hinge tubing to the TE. Sounds like it could not work, but it does. Al has won the Nationals and took second at the World Championships with this sort of flap horn.

I have not found any kind of a flexible cable or connector that could be adopted satisfactorily for a flap horn. I know there have been several people seriously explore this to a great extent and have examined some fairly exotic shaft connectors, but I am not aware of any successfull ideas or applications.

There is the extreme example of special hornsand shafts required like on the fabulous F4U Corsair that Kirk Mullinnex had at the Nats last year. He had full span flaps across the inverted gull wing of the Corsair. He machined his own universal joints for all of the connecting shafts between the flaps. He used very close tolerances in the universals and had very little free play (slop) in the flaps. I think there was a penalty for the weight of these things, but it is a large airplane with plenty of power and it flies extremely well.

We will probably hear something in the near future about what Windy is using on his B-25.

Split horns on a V-tail are not so critical, but that is another subject.