Aileron size relative to flaps - RCCanada - Canada Radio Controlled Hobby Forum
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Old 11-20-2010, 01:31 PM   #1
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Aileron size relative to flaps

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Am working on an unfinished 1/4 scale, low flat bottomed 80" wingspan model that I purchased from an estate sale.......I noticed the flaps occupy approx three fifths of the span of each wing and the ailerons the remaining 2/5ths......However, I noted on the full scale version of this kitted plane that the flap to aileron ratio is 50/50.

My question is...(and I'm close to its maiden flight) how will the smaller aileron to flap ratio (on my model) affect the flight characteristics of the plane..i.e slower turns etc ?....what can I expect on take off with these shorter ailerons, should I be programing more aileron differential due to their shorter length ?

Is there an aerodynamically "written in stone" formula for calculating the length ratio of these two control surfaces on any model?

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Old 11-20-2010, 06:14 PM   #2
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Re: Aileron size relative to flaps

Hi Joe,
There is no written in stone formula. It depends what capabilities you want the plane to have.

The smaller the aileron surface area, the slower the roll rate, given the same degrees of throw.
Increasing degrees of throw, will cause the aileron to have more effect.

The slower the plane is flying, the less effective all control surfaces become, more so for ailerons that aren't in the prop wash.

Might be a good idea to have an experienced RC pilot, test and trim the plane for you. Posting some pictures, would help others help you. Hope this helps.
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Old 11-21-2010, 09:41 AM   #3
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Re: Aileron size relative to flaps

The ailerons are sized by their relation to the wing, not their relative size to the flaps. It is their effectiveness in rolling the wing that counts. I know that in your case, unless you want to increase their chord, the sizes are linked. That is increase one decrease the other. On a plane like that you don't need flaps, it's just fun to have them. I put them on a Kadet, just for fun. If you are concerned about how effective your ailerons will be, switch the flaps for the aileron. I mean move the parts used for flaps to the outboard position and use them as ailerons.
With your plane itís more important to have roll control that for the flaps to work well. On a flat bottom wing you might need differential throw, more up than down.
Since all of this is guess work, the maiden flight may be a wild one, be ready for it. make sure you have lots of rudder incase you don't have enough roll with the ailerons.
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Old 11-25-2010, 11:30 AM   #4
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Re: Aileron size relative to flaps

As others have already noted, the ailerons and flaps are independent of each other because they perform completely different functions.

One thing to note is that on a "flap bottomed" wing with relatively large flaps, your airspeed can be brought nearly to a crawl because of the high lift and drag. With the significant loss of airspeed, the effectiveness of the ailerons will decrease dramatically.

In a nutshell, deploy the flaps with care. I'd suggest first flights be without flaps and then increase the amount of flaps as you get more comfortable with the model.

If your transmitter is capable, you could program the flaps to act as flaperons, meaning they deflect downward (principally), but also deflect up and down slightly as ailerons (secondarily). That's another whole complication though.............
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Old 11-26-2010, 12:16 AM   #5
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Re: Aileron size relative to flaps

Thanks guys... I am a fairly competent pilot but never too proud to seek advice or draw from the experiences of others..... this was just one situation I hadn't come across before.

Thanks again
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