I have some questions on flaps. I guess I really don't understand how they work, where they are located, I hear people say sometimes that the ailerons may double as flaps, can you add them on any plane? I guess I am just looking for general information about them. I appreciate your help.

SLO

Flaps are on the trailing edge of the main wing. Usually, the center is a flap and the outboard is an aileron. Some people leave the whole surface as one and use it as ailerons, and couple them so they both go down the same amount. That is called flaperons.

They are good in some cases for slowing the plane. I have used flaperons and they are good for some planes, bad for others. My glider has flaps that go out about 1/2 way to the tip. The ailerons go the rest of the way. That plane can drop the flap almost 90 degrees and the flaps are very effective. I can also raise them some to give the plane lots of speed in the air.

There are lots of ways to do the flaps, just depends on what the plane is and what you want them to do. Approx the first 20 degrees will provide some lift, any more is drag for slowing the airplane.

Flaps alter the wing's camber and angle of attack, both of which change the lift coefficient which changes flying speed - A glider's trimmed flying speed depends only on its lift coefficient and wing loading.

When used as ailerons, the inboard location of flaps limits their effectiveness in generating a roll-axis moment for a given amount of drag created, compared to ailerons. Therefore, when flaps function as ailerons, they generally aren't deflected as much as the ailerons (50% of aileron throw is common).

Full-span camber control (ailerons also functioning as flaps) is preferable, in order to avoid an abrupt change of camber and AOA at the flap/aileron junction.

If you have a plane that you want to be able to slow down and land in tight quarters I guess the answer would be to add flaps? I am assuming that with flaps you can drop a plane on a dime?

Let's say that the plane that you want to add flaps onto has ailerons that run near the whole length of the wing.

1. Can you just shorten the length of the ailerons closest to the fuselge and add 2 flaps one on each side of the fuselage?

2. If you were to do this how long would you want each flap to be?

3. Is it a percentage or ratio of the aileron, or the wing?

4. If you were to do this how much maneuervability of the plane would you lose?

I am sure that the information provided is probably a little insuficient to make super accurate statements. I am just trying to figure out ideas. I don't really have any particular plane in mind. I am just thinking. I appreciate your help given the lack of information.

Thanks for the feedback!

SLO

http://www.rcgroups.com/forums/showt...threadid=88642

IMO, the most effective glide slope control is flaps in combination with traditional (pop-up fence) spoilers which destroy lift more effectively than reflexed ailerons in crow, while also preserving aileron authority at low speed. The drawback of spoilers is that they require at least one more servo, and can sometimes (read "usually") be a hassle to install.

It's not realistic to predict how much roll control you'll sacrifice without knowing several other things: the plane's inertia about the roll-axis, aspect ratio, flying speed, dihedral, airfoil, etc. ==> Yuk. Avoid the headache and just look at several models similar to yours and go from there. I think you'll be safe with ailerons as short as 1/3 of span, flaps the remainder (2/3) of span and flap chord = 15% - 20% of wing chord. It would also be easy to just temporarily tape-hinge flap/aileron stock of different lengths and see the real-world effects.

Narrow long control surfaces are generally better than wide short ones, since a wide surface alters lift coefficient only slightly more than a narrow one, but the load on the servo will increase by the square of the width. Flaps are a high-load application, so servo torque needs to be considered.

If you're intent on using flaps, it would be wise to invest in a programmable transmitter if you don't have one. Deploying flaps almost always causes a pitch-up situation requiring down trim to maintain level flight - a pain to deal with manually.

When flying, one thing to be careful about is rapidly bringing flaps up, especially during landing approaches - A rapid reduction of Cl when the plane is already flying slowly can cause a nasty stall; the last thing you want at low altitude Similarly, large flap deflection can cause a plane to fly so slowly that it becomes prone to tip stalling or sluggish control response - Find out how your plane responds to these things when it's up high!

The flaps that FLYBOY mentioned (90 degree down) work very well for speed control. I would say 50 to 60% of span and 10 to 15% of chord is workable. I have set-up a few gliders this way with mechanical elevator compensation. Building the mechanical mixer is fun and easy. Either mechanical or electronic, you'll need some down elevator mixing to prevent a sharp up pitch.

I have never been a fan of full span flapperons. For gliders, it doesn't provide speed control, deteriorates aileron effectiveness, and makes tip stall more likely. I see guys use full span flapperons at my power model club for no apparent reason. It usually causes a trim change, tip stall, and crash. For a glider, I would stick to the old formula.