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servo placment

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Old 01-16-2014, 07:36 AM
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69 roadrunner
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Default servo placment

When building a wing is there a formula to where the servo goes. Like one third of aileron or just as close to wing root as possible. Thanks Steve
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Old 01-16-2014, 03:51 PM
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Bump,
Anybody? I too would like to know !!!


Mike
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Old 01-16-2014, 07:07 PM
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As a rule I place mine 25 to 30% outboard of the aileron root in a single servo scenario.

Bob
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Old 01-17-2014, 09:32 AM
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Thanks Bob!
I have followed several of your threads over the years, Mostly at the other forum sites, LOL. Your willingness to help others and this hobby is greatly appreciated and I know my building skills have improved as a direct result of your work.

Mike
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Old 01-17-2014, 11:04 AM
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I've seen references to the idea that you don't want to put the control horn where the inboard and outboard portions are evenly divisible. So don't put the control horn at the 50% point or the 1/3 point. Instead make it an oddball number like 45% or 28%.

The theory being that exactly even or related divisions can promote flutter. Sort of like the old Tacoma suspension bridge. By putting the control horn at some oddball location along the span length you break that possibility.

And of course at that point you put the servo just ahead of the horn if using outboard servos with one on each surface.

To avoid high mass moments in the wing I like to put the servo as inboard as possible within reason. So I look to put the horn at around 27 to 30% out from the inboard end of the surface. That puts the servo out far enough that I don't need to worry as much about flex and I avoid the 4:1 ratio of putting the horn at 25%. But the outboard mounted servo is not so far out that it builds on making the tips heavier too badly.
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Old 01-17-2014, 02:00 PM
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A good rule of thumb is to place it at an odd multiple of the span; i.e. 1/3, 1/5, 2/5 2/3 etc. This minimizes the chance of flutter as it tends to cancel out some of the possible flutter frequencies. For best use of the forces required of the servo, the farther out on the wing the better.
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Old 01-17-2014, 03:08 PM
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Put the servo wherever it's convenient and keep the linkage tight. Most issues are caused by poor linkage choices or poor mechanical set up.
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Old 01-17-2014, 05:51 PM
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Quote:
Originally Posted by Rodney View Post
A good rule of thumb is to place it at an odd multiple of the span; i.e. 1/3, 1/5, 2/5 2/3 etc. This minimizes the chance of flutter as it tends to cancel out some of the possible flutter frequencies. For best use of the forces required of the servo, the farther out on the wing the better.
1:3 can still set up a strong resonance. 1:4 is better but still possible. 1:5 is better again but still possible. The problem is that you're still using evenly divisible ratios. The higher the ratio the less strong any resonance will be but it can still achieve a size based resonance.

What's needed is a real oddball like 1:3.2. The surface may still flutter but with a non integer based ratio such as this it'll be due to other factors than resonance due to the horn location.
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