Hello, I read somewhere were the TE of the control surfaces should be squared off. The "rounded off" TE creates some kind of turbulance that helps create flutter, and eventual failure of that surface. I have started my Sig 4* 120 and it has 3/8" thick control surfaces. They say to: sand angles on the LE for the hinge movement..... and ROUND OFF the trailing edges of all control surfaces. What do you experienced builders out there think???
PS. These ailerons have NO taper anyway, and look like a block of balsa hanging on the wing etc.
While I have your attention.... .... I read somewhere about a "trick, or jig", to sand and
even taper down the length of control surfaces. Anybody familar with that?
Thanks in advance.... lownslo....

The trailing edge should be squared off, for the reasons you cited.


Vince

I was taught to square the edges to help prevent flutter,on some planes I have rounded, some I have squared,neither way has fluttered. Knock on wood.

I have done it both ways and haven't noticed any differences.

I don't see how it would matter one way or another with a non-tapered control surface. Squared or rounded, they are all aerodynamically dirty anyway. Power planes can get away with this because you have a big ol' tractor on the nose to overcome all that drag. Can't see how squaring off would be any more flutter prone.

Having come from a sailplane background, I just can't stand these slabs of wood they pass off as powerplane control surfaces. The ideal trailing edge, control surface or not, is as sharp as you can practically get. It is the most aerodynamically effcient and leaves the least amount of wake and turbulence behind the wing.

Squared edges are not necessary.

However, there are several other areas that you need to concentrate on to avoid flutter.

1. Tight, slop-free linkages.
2. Very small hinge gap, or taped hinge line.
3. Ailerons should not extend all the way to the wingtips.

If these 3 things are taken care of, you will not have an issue with flutter.

To help with your question of the jig for sanding, I use a peice of aluminum "T" stock with sandpaper applied with Scotch spray adhesive.

Square them off. If your ever on the skating edge for flutter, the rounded ones will take your plane out first. It's all in the aerodynamics of how the air breaks away from the trailing edge during flight.

But by all means, Definitely do what Daven says. This is most important, but you might as well cover all the angles up front.

Cheers!

Whether they ask for sqare or round, If I have a kit with a straight elevator, I always taper it.

If nothing else, it LOOKS so much nicer!

I tapered some ailerons once... then I discovered aileron stock at the LHS
Way too much work to do it by hand, for my tastes.

Well, a belt sander helps

How does one round off or square the Trailing Edge ?

As I am about to build my first kit , I'm tryingto assimilate all info before I can .

I am buildign the PH 3 D & Edge Profile by Ohio Models.

Request ur Info.

Regards.

Arjun Chopra

A popular method is to laminate a piece of 1/64 ply in between 2 pieces of balsa. This allows a very fine edge that is also resistant to hangar rash. Others have achieved the same thing by impregnating the trailing edge with cyano.
There is a weight penalty however.
Any other variations?
--
Merlin

Hi arjunchopra,most trailing edges are square out of the box,to round the trailing edges is the same for the leading edge,get sandpaper on a sanding block then sand the square edges to a rounded shape.

I am going to try and explain one of my orignal questions a little better. Some of the fellas are asking about "how to" round or square the edges. That is a fairly simple deal. What I read a while back was a "jig" of sorts. (this is not used to round off or square edges). Instead, this simple apparatus helped you TAPER the aileron from LE to TE, keeping the sanding bar or razor plane at the correct angle and depth. This removal of stock was along the whole length of the aileron, from inboard to outboard tip.
I know it was simple and cheap, just can't remember!!!
I wish I would have printed off that posting. My memory is not the best.. lownslo

See the attached picture. Is this where the direction are trying to tell you do round?

lownslo,

Squared off or rounded trailing edges could both cause flutter, in theory, since you could have oscillating flow behind either. This situation might be a little worse with rounded edges, but only if the radius were big enough. In any case, aerodynamically, Volfy has it right: sharp is where it's at. Anything else is second best.

banktoturn

lownslo,
I will agree with most all of what has been said above, but you have to look at each use. On a fast sail plane you would want a sharp pointy trailing edge, but when these get damaged then all that work is down the drain. If you are flying large 3D style aircraft, you want a tapered surface, but the trailing edge will still be square. If round, you just don't get the same control athority due to aerodynamics. On a slow flying 4-star model you will be just fine with round trailing edges, you don't need to taper them either. The plane has been designed to be a great second airplane/first tail dragger. I used a 4-star to get back into flying gas after spending 4 years racing cars and doing a bit of slop flying. I have now moved into giant scale aerobatics and having a blast. Be careful not to over power this model, it doesn't need the extra power and if you get the plane going too fast the flight will become very harry before you ever flutter the surface.

Mo

What exactly do you mean by "very harry" ?

Not real sure about the term HAIRY. (I always thought it was spelled this way). Anyway....when I was growing up as a teen in the late 50's, this was a slang term used then. We seemed to relate it to a wild ride in a car, a car getting "loose" in the corners, or basically on the EDGE of being out of control in anything. I think this is what Madmoc means.... lownslo

spell it the way you want, slonlow got my point. The airplane gets squierly, like a car out control. it changes directions erractically, and just gets "hairy". When you get out of the power everthing goes back to normal great flying.

Madmoc