I am going to be building a scratch build soon and would like to know. I am designing a top wing trainer where the wing panels are going to slide into the fuselage. In doing this the wings are going to be straight (no dihedral), which I guess makes it a sport trainer.

Question is, because it is a wing with no dihedral, does it need to have ailerons? I heard that these type planes do not have the same rudder control as a plane with a dihedral. Is this true? If it has the same rudder control can I get by without ailerons?

Some of the engineers can give you a much better answer but I have a couple of very old 1/2A trainer kits out in the shop with flat bottom wings and no dihedral that are only three channel. The little three channel planes I have built over the years all had the dihedral but these were newer kits.
If I had a good little RC 1/2A engine I would build one of these old kits and find out. I like three channel planes and think they make great trainers so a student lears throttle, rudder and elevator control.

I would think that without ailerons it is going to be very mushy. Any reason why you don't want ailerons?

The airplane must have a means of roll control. Without dihedral, you will want ailerons. You could probably design an aircraft that doesn't have ailerons or dihedral, but you will have to have some other means of adjusting the roll (e.g. cg very far below the ac), but you probably won't like the way it handles. Another option would be a v-tail. Then you would have to mix the elevator and rudder to control roll. Its far simpler to just add ailerons.

Brad

If the CG is quite a bit below the center of lift, there will be some pendulum effect that will provide you some of the righting you get with dihedral but I'm sure you will be far more satisfied if you add ailerons. A slight improvement can be had (if you do not add ailerons) is to cant the rudder hinge line aft at the upper end. I have seen some models of J3 Cubs with no dihedral and no ailerons fly reasonably well.

No reason at all, was just wondering if I should build the ailerons in or not.

I would put them onyou never know it may get you out of trouble sometime.

Wing will be 6 1/4" wide X apprx 38" span (including the width of the fuselage)
Fuselage will be 25" long
Stab will be 12 5/8" length
Will be powered with 450 E-flight electric with 20amp ESC and prob a 1500mAh 11.1v 8C discharge battery pack

Since an aircraft with ailerons is far better to contol I see no reason not to have them.

And if it needs to be known, it is a flat-bottom wing

Build the ailerons. It is just as easy to learn to fly, and will keep you interested in flying.

All of my flat wing planes have rudders and ailerons. Occasionally I practice flying without the use of ailerons to determine what to do if I ever loose the aileron servo (has happened twice with student planes). Some of my planes will NOT change heading with rudder only. I suggest you add the ailerons.

Sounds like you are reinventing the Cessna, Cub, Stick, and about a dozen iother already successful models. All have ailerons and all fly well.

I think you should build the plane however you want. If you decide to go with 3 channels you will want dihedral. If you decide you want a plane with no dihedral, you will want ailerons. I could probably come up with an engineering explanation for you and Gene but I am too tired to think about it right now.

For a flat wing, use ailerons, with dihedral, you will be able to get away w/o aileron. Now, life is a learning exprience, build the flat wing with ailerons, and fly w/o using them. Then you will be thankful you did include them.

If you prefer to learn the hard way, build a flat wing w/o ailerons, fly the plane, and THEN build the ailerons in the wing:-)

Ailerons are a good thing in life!

Good luck

Gerry

I believe that the airfoild shape is irrelevant.

When the tail makes the fuselage go crooked through the air, the advanced semi-wing of a wing with dihedral increases the angle of attack and the lift, inducing an axial roll.

When the tail makes the fuselage go crooked through the air, both semi-wings of a wing with no dihedral keep the same angle of attack and same lift. The fuselage blanks the air reaching the retarded semi-wing, diminishing its lift, inducing an axial roll, but weaker than the produced by ailerons. However, the deflected rudder in the tail is higher than the roll axis, inducing a roll in the opposite direction. Hence, for most of the models, the roll will happen in the direction of the stronger torque. As explained above, the height of the CG also plays here.

Install ailerons if the wing will be straight, I suggest.

Would be nice to have the dihedrals of my Piper Cub (photo) but can not do that with plug-in wing panels, too bad. So will be no dihedral.

If you fly in any significant wind you need ailerons. It's no fun trying to turn an airplane into the wind that constantly wants to roll out of it. Not to mention crosswind landings.

Great question. Trainers with dihedral bank big time with rudder only. Those exact same trainers need a lot of aileron to bank.

Your scratch build, with high lift straight wings needs ailerons to fly decently IMO.

What I am doing is a major bash on a Micro Telemaster. Wider wing panels by about 1" with sheeting and ailerons, fuselage 1/4" wider and 1" longer, stab about 10% bigger, slide in wing panels. Maybe other things during the build. If anyone is interested I am considering doing a build thread in case i need suggestions, ideas, opinions.

QUESTION: How does one determine how much throw ailerons should have on a plane that originally did not have ailerons?
QUESTION: Will the throws change on a stab that is made 10% bigger?

Set high and low rates based on a similar wing.

Throw determination is set by the aircraft designer which is you. Fly it and see.

Your build will be fine with high rates and high throw.

Don't worry about it, it's inconsequential. More stability equates to more latitude on other control surfaces, it doesn't matter IMO.

Yes, You need dihedral, rudder only, its about 5 degrees. airplanes fly in a fairly narrow set of rules. break the rules and they don't fly properly. reinventing the wheel is a waiste of time, spending the time to understand how a wheel works is well worth the time.

No, I am not having dihedral because I want the wing panels to slide into the fuselage like the Something Extra and similar planes. I will be building ailerons into it.

shd3920,
just an idea i have, instead of developing everything from zero why dont you take a proven good working design of a wing like wing of a four star or a mid star (same wing) or anavistar and work from there, the pluses are that you can buy a wing kit and this wing is working very well.

not by mistake there are very similar airplanes from different manufacturers like 4* and dolphin and pulse...

i'm saying this because i tried many years ago to build a cable controlled airplane just out of my head with a profile book and it didnt flew so well.

i'm trying to help and value your time and effort.

Alex