aileron servo placement

[tomp]

This question deals with the case where an aileron servo is directly connected (no bellcrank(s)) to the aileron:

Where should the aileron servo go in relation to the aileron itself?
Middle of the aileron, more towards the wing root, or more towards the wing tip?

And for bonus points ;), why?


Thanks.

tom

[Ollie]

It depends on the stiffness in torsion of the aileron.

If the aileron is long, skinny and not stiff in torsion, then the aileron should be driven from its center in order to minimize twisting due to air loads versus driving torque and to minimize the possibility of flutter.

If the aileron is short, fat and stiff in torsion, then the aileron can be driven from the inboard end so that the mass of the servo is kept inboard to minimize angular momentum in roll and yaw.

[me11owman]

I always just put it out as far as the servo lead will allow.....usally shy of the middle :p

Jim

[tomp]

Thanks Ollie. That's the kind of answer I like: easy to understand!

tom

Originally posted by Ollie
It depends on the stiffness in torsion of the aileron.

If the aileron is long, skinny and not stiff in torsion, then the aileron should be driven from its center in order to minimize twisting due to air loads versus driving torque and to minimize the possibility of flutter.

If the aileron is short, fat and stiff in torsion, then the aileron can be driven from the inboard end so that the mass of the servo is kept inboard to minimize angular momentum in roll and yaw.

[Dereck]

Ideal location is at the aileron's mid-point.

Don't tell that to my Four Star or CAP 232. Both have their aileron servos on the first rib out from the fuselage - the one at the end of the centre section sheeting. That lets me get away without having to buy servo extension leads :)

Don't get excited over ideals - most sports aerobatic oilburners use torque rods with a twistable piece of wire driving the aileron root end from one centrally mounted servo. There's a lot of these built like this, and some of them go very fast and maneuvre real hard without any worries.

D

[feathermerchant]

Speaking of servo extensions I just built a 15oz model and was surprised how much weight I could save by eliminating them.
Get a scale and start weighing stuff. I think it's a good trade to give up a little aileron twist while saving weight.
Also saved 0.2oz by shortening the bat abd motor leads. Metal is heavy!

[Sail 'n Soar]

feathermerchant,

Here, here! While weighing stuff have you compared the weight of two servo's and servo lead extensions with the weight of a single central servo driving pushrods and bell cranks? I'm still trying to sort out the preferred approach for driving conventional ailerons on scale birds. Current design practice appears to favor separate wing mounted servos at the aileron inboard edge.

Gerry

[Ollie]

Where design is concerned it is dangerous to generalize.

The weight of servo extensions can be a significant part of the weight budget of a 15 ounce model but an insignificant part of the weight budget of a 10 pound model. A park flier might fly so slowly that flutter would seldom be a consideration.

Two high quality micro servos with the combined torque of a standard size servo can cost five or six times as much. Cost might be a desiding factor in the aileron drive arrangement.

Where design is concerned, it is a truism that everything affects everything else. How's that for a generalization? ;)

[feathermerchant]

Sail n soar
Yes I actually did weigh all that stuff. And with HS55's the extra aileron weight penalty is not as large as it seems but my Y harness weighs almost as much as a servo! Gonna take out the PCB assuming there are no components on it.
Issue with 2 servos especially on scale - how do you hide them / keep their outputs from hanging on the grass. Most of my planes have no landing gear.

[Sparky Paul]

Originally posted by feathermerchant
Sail n soar
Yes I actually did weigh all that stuff. And with HS55's the extra aileron weight penalty is not as large as it seems but my Y harness weighs almost as much as a servo! Gonna take out the PCB assuming there are no components on it.
Issue with 2 servos especially on scale - how do you hide them / keep their outputs from hanging on the grass. Most of my planes have no landing gear.
.
Use the DAD.... Direct Aileron Driver.
A torque rod from the servo cunningly concealed inside the surface. Works very well!
.
http://home.earthlink.net/~pjburke1/ideas1.htm

[vintage1]

I did the wieghing route as well. By getting rid of extensions (cut wires, use one plug and solder up 'Y' lead yourself) weight is bvery low for 2xHS55 versus metal torque rods. Does leave ugly horns sticking out tho.

I find that in order NOT to flutter (outboard alierons) you need really quite heavy torque rods as well - even in CF, and also with top or center mounted hinges, its hard to get the rod accurately in the center of rotation, and you end up putting stress on the inboard hinge.

Still use rods on full span ailerons tho. There it makes sense

[Sail 'n Soar]

Thanks, all. I appreciate the input. Sparky, your single channel RC experience is showing.