• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Help! determining control surface area

Hi everybody,

I'm doing a project where we need to design an rc airplane. Now we have some trouble figuring out how much control surface we will need. At first we also needed to build the plane and our plan was to make a estimated guess and then test it out before the competition day and make changes where needed. (it is a competition of which group can built the plane that can lift the most weight) But because of Covid19 our university decided to replace the building by us delivering set parameters to our coach who will moddel it into a flight sim. So now we can't test beforehand if our control surface will be enough. Do you guys have anny tips?


Old and Bold RC PILOT
I agree with the previous posts in that the larger the control surface the greater amount of control. There are a couple of things to be aware of though. Very large control surfaces normally require to be constructed much stronger so that the control surface itself does not flex under load. If insufficiently strong the control surface can bend and flex under load causing some very interesting manoeuvres in flight and the faster the plane flies the worse it gets!

Large control surfaces, moved aggressively at slow speed, can cause a stall of the control surface or the wing, (in the case of ailerons), this can also cause a control reversal effect as well as unwanted yaw effects. On a heavily loaded plane, large control deflections should be used with caution at very low speeds.

For large control surfaces in FB I use a balanced control surface approach where the hinge line in at around 50% of the Stabiliser cord with a balanced tip design. I try to avoid large cord ailerons but I definitely use the balanced tip approach. With ailerons a full span aileron or a combination of Ailerons and flaperons for the full wing span is more effective than "Barn door" ailerons.

Finally do not forget that control surfaces that are "Blown" by motor thrust / propwash are far more effective at take off when the actual airspeed can be too low to give fully effective flight controls.

Just what works for me!

Have fun!


Elite member
Figured I'd throw this in for comparison. This is taken from Basics of R/C Model Aircraft Design by Andy Lennon.
The book is a very by the numbers math-based approach to airplane design.
If you have questions about what anything means I'd be happy to clarify.

Click the thumbnail for a larger picture.