Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

Roll Rate vs. Aileron sensitivity

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Old 08-20-2016, 06:31 PM
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dangtaylor
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Default Roll Rate vs. Aileron sensitivity

On my next flight , I'll attempt to alter this condition with 30% exponential but I am looking for suggestions about what might be the aerodynamic reasons for a rather slow roll rate when performing a full roll but overly sensitive reaction when aileron input first given from wings level.

Aircraft is my second Balsa USA Smoothie; weight dry 68 ounces. Center of gravity right now is forward of that specified on plans. I've reduced total aileron throws to first 70% and then 60% called for and am just now putting in the expo noted above.
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Old 08-20-2016, 07:29 PM
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All Day Dan
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You’re not alone. My 50cc powered 20 pound models with strip ailerons react the very save way and I have my exponential and end points set the same way as you. I do believe it’s a function of the strip ailerons because I don’t notice it with the models with barn door ailerons. This does not answer your question. I just live with it. Dan.


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Old 08-20-2016, 08:34 PM
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If you are just trying to balance out the feel so that the response is the same at center as it is at full travel then Expo is a good fix. If you are looking to get more authority at full deflection, there are a few things to look at. If the ailerons are driven by a torque rod arrangement then the ailerons could be flexing and not have the same throw out at the tips as they do inboard. You could be using a servo that is not up to the task. You could have excessive hinge gaps. You could be running expo in the wrong direction.
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Old 08-21-2016, 03:50 AM
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dangtaylor
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I did not consider just being strip ailerons being a cause. You are right, the ailerons themselves are likely flexing . It has been decades since building and flying the first Smoothie and I only noted in my log then that ailerons at first seemed sensitive. A big difference is the age of the pilot and the time past since the first one of this design.

As I noted above, I am intending to fly with Expo on next flight so , no, I have not experienced expo reversed . That would certainly do job of making ailerons sensitive near the center of travel, though, if set up that wrong way.

When I think of aircraft with "barn door" type ailerons that I built in the past and currently, it is correct, I did not experience the slow roll rate vs. sensitive reaction initially.

Thanks for replies.

Dan
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Old 08-23-2016, 06:10 PM
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I don't remember where I saw this, but someone uses carbon veil on strip ailerons to stiffen them. Jim
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Old 09-09-2016, 09:19 AM
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You can try raising both ailerons(reflex) some time depending on the airfoil this can dampen the sensitivity at neutral. Start with just a few mm and try it
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Old 09-10-2016, 06:34 AM
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Couple of things.
Positive expo is opposite for Spektrum and Futaba. Pos. on Spektrum is less sensitive around the neutral point, and of course, neg. on Futaba less sensitive around neutral.
Expo is a personal thing for the amount you use. I use none on my planes with little control throws and a lot on the 3D type planes with a lot of movement.
If you use too much, the controls feel mushy. Just back off on it until you feel comfortable with it.
On the too much flexing of the strip ails, one fix is to move the servos further out on the wings.

Gord.
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Old 09-10-2016, 06:52 AM
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dangtaylor
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I've flown the plane several times with 30% expo (Spektrum, so positive) on the ailerons now. It has been a great help, as expected. Already, I've increased throws via dual rate and see that a lot of my trouble is pilot trouble. Actually, looking back at my flight log comments on my first Smoothie, I see that I experienced the same thing with that airplane, too. Did not have exponential possibilities on the two radios I used in that airplane in 1980-1984 but just got used to things as they were.

It is still an interesting possible cause of the sensitivity around neutral...........strip ailerons.
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Old 09-11-2016, 06:12 AM
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dangtaylor,
Just based on your username, were you in trouble a lot as a kid?
https://www.youtube.com/watch?v=R1hTVtUbhWs
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Old 09-11-2016, 08:55 AM
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dangtaylor
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Not really. I was a goody-two-shoes type. Airplane geek as a kid.

You are making me think about this a little more, however. In sixth grade , an airplane loving friend and I decided to call each other by airplane names. He was Fokker DVII and I was Hellcat.

Last edited by dangtaylor; 09-11-2016 at 09:00 AM. Reason: more needless info
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Old 09-11-2016, 06:29 PM
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Hellcat's good. Much better than Waco.
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Old 09-12-2016, 04:36 PM
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Originally Posted by buzzard bait View Post
Hellcat's good. Much better than Waco.
I have heard it said that there is a song that describes each individual.
Here's mine:
https://www.youtube.com/watch?v=8ecE1UML1q8
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Old 09-22-2016, 08:50 AM
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Flex was mentioned as one possible reason. Another possible cause may be that the strip ailerons are stalling when pushed out beyond a small angle of travel. If they "stall" and form a separation bubble on the "trailing" side they may not be producing the expected change in lift for the airfoil that they produce at the lower angle and operating in a "clean flow" condition.
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