walk4718

I am building a 40 size J-3 Cub ARF (China model). The very brief "manual" indicate mounting the airleron servo arm pointing inboard rather than outboard. All of my other models have the servo arm pointing towrd the wingtip. Is this a big deal?

MinnFlyer

My Feedback: (4)

In a word, no. However it could make a difference regarding the servo horn placement

If the horns are pre-installed, they may line up with the horn on the inboard side.

If they are not pre-installed, there may be a plywood hard point built into the aileron specifically for mounting the horn onto - which again, may line up with the inboard side of the servo.

So I would check the aileron to see if the horn has a specific mounting area. If not, do it either way

walk4718

Thank you for the reply. The horns are not preinstalled and the mounting area is wide enough to accept the horn in either mounting application.

opjose

You want the horn closest to the mid point of the aileron.

This spreads out torsional forces more evenly resulting in less effective warping of the surface.

So use whatever orientation gives you this if you have a choice.

MinnFlyer

My Feedback: (4)

Actually, you are better off being off center.

opjose

Why off center?

MinnFlyer

My Feedback: (4)

It has to do with flutter. Flutter is a harmonic vibration. If the two sides of the aileron are equal distances from the horn, a harmonic vibration can occur (providing all other conditions are right) This means that while the center is being held firmly, the two ends of the aileron can start to vibrate in sync with each other.

If it's off center, the two sides will vibrate at different frequencies and cancel each other out.

It's not a HUGH deal as it rarely occurs, but just something to take into consideration. This is why you rarely see a horn located in the center of an aileron - plus it gives you the added benefit of using shorter extensions.

opjose

That makes sense, and I can see how it would help, up to a point...

Beyond that point, say putting the servo close to one side of the aileron, things should get far WORST.

So much so that doing so is more likely to cause flutter than putting the horn smack in the middle.

MinnFlyer

My Feedback: (4)

Yes, you don't want it al the way to one side either. About 2/5 from the inboard side is ideal.

opjose

Heh, let's see... what harmonic would 2/5ths give us?

Thanks.

MinnFlyer

My Feedback: (4)

Hopefully none

K-Bob

My Feedback: (1)

Umm.... we are still talking about a .40 size Cub right? Follow the manufacturers instructions and have a ball.

jship

My Feedback: (4)

Lets keep it real, It's a cub!