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Aileron Size Area

Old 08-19-2009, 07:03 PM
  #1  
Octavius
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Default Aileron Size Area

Here's my situation and then the question. 32" wingspan sport plane. I made the ailerons more closer to 3D size with a 2" cord. I'm not looking for 3D flight but more old school sport. Turns out that was way too big so I just used DR to turn them down. From about 1.0+" defection to 0.5" deflection and they work pretty nice.

Now here's the question: Given everything else is equal, is a 2" cord aileron with a 0.5" defection the same as a 1" cord with a 0.5" defection? Same defection but different cord/area.

Basically I want to make my ailerons smaller but don't want to screw myself. Of course I'd like to understand why also.
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Old 08-19-2009, 07:40 PM
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DKNguyen
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I was under the impression that larger area with lower deflection is more effective at low speeds than smaller area with larger deflection. I think it's also more efficient because it deflects a larger mass of air gradually, rather than a small amount of air more abruptly.
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Old 08-20-2009, 02:56 AM
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Sky Sharkster
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Default Aileron Size?

Hello Octavius,
First off, I found two different model aerodynamic references that both quoted the same figure for optimum aileron size. 12% of the wing area.
Next, I agree with DKNguyen, but for a different reason; Aspect ratio. I believe a long, thin (or narrow, take your pick) aileron works better than a short, broad aileron for the same reason that sailplanes have long, narrow wings. Higher aspect ratios are generally more efficient.
Last, there's more to it than that. You've suggested adding one of the two different size ailerons to an existing wing. But then you're not merely changing the aileron size, you're changing the entire size, area and aspect ratio of the wing and the percentage of the aileron to the wing area.
Here's an example; Suppose you had a wing (with no ailerons) that had a 30" span and a 6" chord, alright?
30 x 6 = 180 square inch wing area and a 5:1 aspect ratio.
Now, we add a 1" wide aileron to the entire trailing edge. This wing is now;
30 x 7 = 210 square inches and a 4.2:1 aspect ratio. The 30" x 1" aileron is 30 square inches, or 14.3% of the total wing area.
Or, a 2" wide aileron is added, making a wing of;
30 x 8 = 240 square inches, 3.75:1 aspect ratio. The 30" x 2" aileron is 60 square inches, or 25% of the total wing area.
Disregarding center of gravity, existing wing airfoil, dihedral (if any) and deflection for the moment, the last wing example is short, stubby and has a whopping 1/4 of the wing as an aileron surface. This is somewhat like a 3D model, and the full deflection of these surfaces would be like an airbrake.
So, I'd use the 12% figure as ballpark and adjust the deflection to provide the roll rate or amount of bank you are comfortable with.
JMO,
Ron
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Old 08-20-2009, 05:19 AM
  #4  
Octavius
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Super good info. Thanks.

Sorry if I was unclear, but I didn't mean different wing areas. Both of my examples would be the exact same wing area. The only thing that would differ is the location of the hing line. I'm not going to modify the current plane/wing, but be making another plane. This is already the 2nd version which is much better than the 1st. I just want to add some more tweaks to improve V3.

I can take 12% and run with that.
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Old 08-20-2009, 06:25 AM
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Larry3215
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I think bigger is better as long as the structural issues are handled.

That 12% number is based on heavy, fast flying, glow models that didnt fly as slowly as many of our lightly loaded electrics.

I agree with the other statements - A large surface and a small diflection is always prefered over the opposite.

The trick is to controll twisting and flex in the surface and to keep linkages tight. Larger surfaces can be more prone to flutter so you need to be better at keeping them stiff and sealed. But its worth the effort even if you dont fly 3D.
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Old 08-20-2009, 07:38 AM
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Thanks. BTW, this is the plane. The rainbow color one. The 1st version (green) was almost a complete failure. Next version will be full fuse w/ Hacker A20-20L and 10x3.8 so it won't be going very fast anyway. Ignore that it looks like a 3D plane. hahaha
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Old 08-21-2009, 05:08 AM
  #7  
Larry3215
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Originally Posted by Sky Sharkster View Post
Hello Octavius,
First off, I found two different model aerodynamic references that both quoted the same figure for optimum aileron size. 12% of the wing area.
Next, I agree with DKNguyen, but for a different reason; Aspect ratio. I believe a long, thin (or narrow, take your pick) aileron works better than a short, broad aileron for the same reason that sailplanes have long, narrow wings. Higher aspect ratios are generally more efficient.
Last, there's more to it than that. You've suggested adding one of the two different size ailerons to an existing wing. But then you're not merely changing the aileron size, you're changing the entire size, area and aspect ratio of the wing and the percentage of the aileron to the wing area.
Here's an example; Suppose you had a wing (with no ailerons) that had a 30" span and a 6" chord, alright?
30 x 6 = 180 square inch wing area and a 5:1 aspect ratio.
Now, we add a 1" wide aileron to the entire trailing edge. This wing is now;
30 x 7 = 210 square inches and a 4.2:1 aspect ratio. The 30" x 1" aileron is 30 square inches, or 14.3% of the total wing area.
Or, a 2" wide aileron is added, making a wing of;
30 x 8 = 240 square inches, 3.75:1 aspect ratio. The 30" x 2" aileron is 60 square inches, or 25% of the total wing area.
Disregarding center of gravity, existing wing airfoil, dihedral (if any) and deflection for the moment, the last wing example is short, stubby and has a whopping 1/4 of the wing as an aileron surface. This is somewhat like a 3D model, and the full deflection of these surfaces would be like an airbrake.
So, I'd use the 12% figure as ballpark and adjust the deflection to provide the roll rate or amount of bank you are comfortable with.
JMO,
Ron
Ron, I just realised my reply above came across like I was contradicting what you said. I didnt mean it that way at all. Your comments, calculations and recomendations are quite valid. Probably more so than mine in a general sense.

I should have prefaced mine better and not been so much the knowitall jerk that I sounded like
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Old 08-21-2009, 05:25 AM
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ministeve2003
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I also think that larger surfaces would be more effective at slow speeds... you're for a lack of a better term... "grabbing more air"....

Ps, your model looks great.... Looks like a fun one...

SK
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Old 08-21-2009, 05:29 AM
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ministeve2003
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Ps, here's a video of a Foamy spitfire that kinda resembles your plane... it was built with larger surfaces like yours...

[media]http://www.vimeo.com/1909740[/media]

SK
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Old 08-21-2009, 11:23 AM
  #10  
Sky Sharkster
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Default No Problem!

Hi Larry,
I had no problem with your post. It's true that the 12% area is an old figure, likely from heavier glow planes, but I assumed from Octavius' post that he wasn't looking for 3D performance. So I quoted a general percentage for "Sport" performance. I checked a few of my (electric) planes and it's still a reasonable figure.
You pointed out that lighter, slower models could get by with larger surfaces, and that happens to be a fact.
I guess it just depends on what type of flying he's looking for.
Peace,
Ron
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Old 08-21-2009, 08:37 PM
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Yeah, sport plane performance. I know it looks like a 3D plane but it's too heavy and the CG is way forward to have any characteristics resembling 3D. And no offense but I can't stand the fluttering of 3D. Next version is getting a motor upgrade, but I want to fly it on the wings, not the power.

Currently ailerons are around 22-24%. This gives me a lot to reduce before I get even close to 12%. Given that I won't make any radical changes to the current design since it does fly nice, I might bring it down to 18-20%. Although it's good to know 12% is optimal so I might use that target for any new designs. i.e. the Helldiver I'm also working on.

Rudder won't change because I like the strong knife edge it does now, but elevator might shrink a little too since it's also on 50% DR.
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