Hi all,

I had seen a Chip Hyde plane in a catalog. It said that the trailing edges were left square for responsiveness. So I am wondering what the aerodynamics are of a tapered and rounded trailing edge on a rudder/elevator, vs just leaving it squared off?

Thoughts?

I do not recall the sources but this has been discussed many times. The consensus of all, if I remember correctly is, if high speed then a very sharp tapered but stiff trailing edge is best; for normal sport flying the square edge is best and worst in all cases was the rounded trailing edge. Since it is very difficult to get a sharp and stiff trailing edge, most RC craft benefit best with the square trailing edge.

Years back we fussed over the shape of tips and the thicknes of edges and sharp vs rounded LE on n on
Once we finally had time to do purely objective comparisons we found most of these "facts" including trick turbulaors and such were mostly just wistful thinking
The typical small glo engined models were never light enough - and when it was all said n done - only two things were really worthwhile

make it lighter if any choice is presented
keep it as stiff as possible without adding weight

Once you get down to slower smaller models - the entire model can just be flat slabs -if you can keep the weight off.
Don't believe it?
buy some 1/2" thick EPP an make some models -in say 400-600 sq in range - make things as sharp or rounded as you want - - the differences ?
you tell me.

I would say that the shape of the LE is less important than the volume of the vacuum formed aft anything but a perfectly sharp edge.
That empty volume is what draws molecules of air into a turbulent flow within it, which cost extra energy.

Measurable?
Not really for our models and their speeds.

Observe, however, the TE of commercial and war planes, as well as the TE of any propeller.
They are as sharp as practical (there is a point beyond which the part becomes fragile or too flexible).

For some reason, whatever is easy to do, seldom has the best results.

I don't buy the "square for responsiveness" statement.

I flew a toilet seat CL when I was a kid.

I was under the impression that square trailing edges in aerobatic airplanes was to reduce break-out pressure for the pilot.
Brad

I got to test that on a Stryker that needed new ailerons. The stock one are flat with a rounded trailing edge, and I made balsa ones with a pretty sharp trailing edge. I couldn't tell any difference in speed, but I did notice that the controls were softer at the middle, which would indicate that they are less effective/ sensitive at low throws. Obviously, that's just one plane but I actually was able to reduce the exponential in my radio a bit and keep the same feel in the center.

As a bunch have noted already it really doesn't matter in some ways. In others it matters a lot.

If you're building a racing or high speed model you want the trailing edge to extend back to a razor like sharpness. A blunt trailing edge produces more drag than a razor sharp one. It may not matter as much in models as with full size but if you're racing where a single tenth of a second can be the difference between first and second then it pays to hone that trailing edge to where you can thin slice deli meat with your wing.

On aerobatic models there's no need. But if you round the trailing edge instead of leaving it sharp edged blunt then you increase the chance of inducing aileron flutter. And this is a very real danger even at our model sizes. The thicker and more blunt the more likely that it'll flutter if you round it instead of leaving it sharply squared off.