Hello,
After fitting the hinges between the wing and the ailerons, I see a thickness difference of approx 1/8 th inch difference between the trailing edge of the wing and the leading edge of the aileron. The trailing edge of the wing is a little over 1/4 inch and the leading edge of the aileron is 3/8 th inch. Do all these kits come like this ? If so does everybody leave it alone, or do you sand it to match the trailing edge of the wing. Or does everybody leave it alone, and how would it affect flight. Thanks in advance.

Regard,

Pat

Pat, the aileron is supposed to be thicker. Do not sand it. Aerodynamically, it is supposed to expand the "flight envelope" i.e. the minimum controllable airspeed is lowered, and also to reduce flutter. I still seal all my hinge gaps with clear monokote to prevent flutter.

I will first state that I have been in this hobby for about 2.5 years now. I have MUCH to learn, but I don't quite understand the reasoning of the answer given by rajul.
I built a 4*120 last winter and the ailerons on it looked like chunks of balsa. (no taper from front to rear). I did read an article, and have been involved in a thread where the flutter-no flutter discussion was discussed. The opinion was divided, as usual. That discussion was mainly directed to the practice of ROUNDING the TE of the aileron. This is my $.02 worth. If the aileron is thicker than the trailing edge, it is not aerodynamicly "slick". Secondly, it looks tacky as h***. I have never seen a full scale plane like that, and don't remember ever seeing models with a "bump" at the wing and aileron. I DID seem to agree with the thread and ideas.... "ROUNDING" the TE of the aileron can promote flutter. I used a razor plane on my ailerons, and shaped them to "flow" with the shape of the wing's TE. I tapered the aileron, from front to rear, to look decent. (instead of a flat piece of balsa). I did NOT round the aileron's TE, but left it square. The 4*120's plans also have the rudder and elevator flat too. I also taperd those too.... nothing drastic, but it looks AND flies great.

PS. As rajul stated... sealing the gaps is a good thing, and sure can't hurt. ...lownslo

I'm building a 4*40, and am assuming the 60 is similarly built. Perhaps you sanded the trailing edge taper too much and left it thinner than designed. Check the drawing on the plans that show the side view of the rib with the aileron and see how it compares to what you have.

flianbrian

lownslo,
I'm with you. I just don't know what to think about all the "theories" about flutter and aileron thickness. So I just follow the plans which specify a bevel on the LE of the aileron.

Tom

"Pat, the aileron is supposed to be thicker. Do not sand it. Aerodynamically, it is supposed to expand the "flight envelope" i.e. the minimum controllable airspeed is lowered, and also to reduce flutter. I still seal all my hinge gaps with clear monokote to prevent flutter."

rajul is correct.

It does expand the "flight envelope".

Don't sand it.

Pat:

Not having access to a wind tunnel and associated gear I can't give you any pictures.

In level flight having the LE of the aileron thicker than the TE of the wing increases drag just the least bit.

Where the real advantage lies is with surface deflection.

With the surface deflected down the top of the aileron is then lower than theTE of the wing, the airflow has to "Step down" to continue following the surface. If the aileron thickness is sufficiently greater than the TE of the wing the air can flow straight to meet the aileron LE.

Maybe Minnflier can give us a graphic.

Bill.

I understand what you are saying Bill, and that DOES make sense. What I don't under stand is this.
Why does every full scale plane and all the models I have seen have a smooth, level, transition between the aileron and TE of the wing. (or stab, etc.). EXCEPT the 4*'s. When I look out the window of the 727 headed for Phoenix, I see a smooth flowing surface at the aileron. I am not trying to be a smart a** here.... I feel I have ask legitimate questions here.
I have only built 3 kits, and 4 ARFs in my 2.5 years in this hobby. All..... except the 4* has had tapered control surfaces. Do any of you fellas out there that fly Caps, Edges, and the like, have chunks of flat balsa, (or built up flat surfaces), for your ailerons, elevators, or rudder??? OR..... do you have a smooth, streamlined, taper of some sort???? I have seen many models and full scale planes in my 62 years, and I just can't accept flat hunks of balsa on my plane's control surfaces.
Of course, I am not an engineer, and I may not have all the equations correct..... but I am happy with the looks of my plane.... AND it really flies
terrific. That's just my opinion.

PS. Again... I do not taper the TE it to a point. I only reduce the rear thicknes by about 25 to 30 percent, and I don't round the TE, but leave it squared off.

...lownslo....... Bob

Bob:

The difference is in the hinging, and the gaps.

If you use Robart Hinge points, or similar, the surfaces can be hinged in a manner such that the surface LE has no effective drop on deflection, and then the thicker control surface gives only more drag, and not more effective control. To do this the hinge pivot line is behind the LE of the control surface.

Using "Skin" hinges, and a stiff skirt over the gap on the bottom, a la RC racing planes, again there's no advantage.

You mentioned the full scale planes. I don't know of any jets or fast prop planes that don't have the leading edges of the control surfaces in front of the hinge pivot line, this keeps the LE pretty much even with the TE of the wing.

You also have to remember that the gap on the full scale planes, with the inset hinges, is a very small fraction of one percent of the wing chord. On our RC planes, with conventional CA hinges, the groove in the surface is huge in comparison.

Or for an example of a full scale plane using the surface "Bump" trick, look at the vertical fin and rudder on a FW-190. Note the notches for the rudder hinges. When deflected to the right, the LE swings out, just a bit, to the left.

Bill.

Bob:

I noticed I did not address the tapered/nontapered surfaces.

A nontapered surface with a sharp edged blunt TE is almost as low in air drag as a tapered surface with that same hard edged blunt TE.

If you can make the taper greater than a 4:1 ratio, and have a genuine knife trailing edge, you will get minimum drag in level flight from the control surface. The 4:1 ratio means, of course, if the surface is 3/8" thick it would have to be 1 1/2" chord.

But even if you start with a knife edge, it wont be that way long. Or you will spend all your time protecting it.

With the knife edge, the upper and lower boundary layers separate evenly, with minimum vortex generation.

A rounded TE aggravates turbulence, giving lessened control effectiveness.

A sharp cornered blunt TE greatly decreases the induced turbulence and vortices affecting the control surface.

So. If you want to taper the surfaces for appearance's sake, do it. I do it too, and for the same reason. But if you build two planes. identical except having tapered surfaces on one and flat surfaces on the other, you wont tell any difference flying them. As long as you have the hard corners on their trailing edges.

Bill.

Bob:

Just one more note, airflow vortices affect big planes too. Loook at this picture.

That's not ice. It is moisture condensed by the pressure induced temperature change fliying at high alpha.

Bill.

Bill, Thanks for a VERY good explanation!! You guys out there are loaded with knowledge.
Bill wrote:You won't believe this..... I almost wrote the same basic thoughts in my last post!! (the statement about NOT being able to tell the difference on our models). I did taper the surfaces for looks and kept the TE blunt because of what I had heard about turbulance. Thanks again for your time and detail. And I shouldn't forget the mention of the cool picture of the jet!! ......lownslo

I looked at my 4*60 and I don't see this thickness difference. Seems that the aileron is 1/4" stock and the wing TE thickness is the same.

I didn't have a chance look at the 4*60 plans, but they should show what the design thicknesses should be. You may have wrong lumber for the aileron stock.

Bob and Bill:

Just one more note on the blunt trailing edges.

Look at the pictures of the X-15. Specifically the vertical fin.

Its thickest point is the trailing edge, and no one can deny it was a fast plane.

Bill.

Better late than never.

I believe that this is what Bill was referring to earlier. Note the relationship of the aileron to the red lines depending on where the hinge's pivot point is.

(Did I get it right Bill?)

Minn:

You got the idea. Now everyone else can, too.

Thanks.

Bill.

Just a couple more notes.

When a control surface is hinged to protrude on the side away from the deflection, as on the FW-190 rudder, the protrusion works as a turbulator.

You can do a search on the term for more information, they are commonly used on sail planes for boundary layer control.

Attached picture shows blunt TEs on the X-15

Bill.

Minn: Terrific diagrams as usual!!
My Robart hinges are installed close to what you have on the diagram at the bottom. My hinge points are "not quite" as deep as the ones pictured, but the bevel has to be completly notched out in the aileron for the hinge to flex. I should cover my gaps..... but this method works great, and the gap is very narrow. Thanks again to all....
lownslo... Bob

Thanks for all your replies. And a special thanks to Bill and Minnflyer for the diagrams and photos. This is by all means the most interesting hobby I ever got involved in.

Thanks again,

Pat