kerrydel

My Feedback: (2)

I'm building a Carl Goldberg SU26M kit. As designed, the kit has flat tail surfaces. This plane has a wing span of 72" which scales at about 22%. I felt like the tail is big enough to deserve airfoiled surfaces. What I did was to 'sheet' the horizontal stabilizer with 1/4" balsa on the top and bottom. I marked the 25% span as a rough guide, then I planed/sanded the surface to an airfoil. The elevator I made with a straight taper. For reference, the elevator has about the same cord length as the stab.

So my question is, will this cause problems? The biggest concern I have is with different lift side-to-side causing the plane to want to roll. I'd also like to do the same thing with the vertical stab/rudder.

Any info is appreciated.

Kerry

jamie_duff

If you've made it fairly symmetrical I can't see there being much of a problem [8D]

rmh

rest easy --on any of these - the ONLY thing which really counts is that the left and right sides are the same -and operate in exact unison
flat , diamond , streamlined shape , make no detectible difference in flying
The best thing you can do at this point is figure out how to drive both with one servo - in perfect travel.
a well made forked pushrod and a servo on it's side are best for this and far better than any dual servo setup .
there has been a lot of conjecture on flat surfaces and "airfoiled " surfaces
as long as the entire tail group is stiff and deflects evenly -it makes no difference.
For what it's worth, the rigidity of a curved or a diamond shape is th best reason to choose these over flat surfaces - which deflect far more easily than you may imagine .
The sensitivity or improved "lift " are of no real benefit. Looks good tho----

cyclops2

I Have always made all verticals a symmetrical shape, winged the shape.
Horizontails are Clark Y's, same as the wings. As a result they are 4 to 5 times thicker than the flaties. I have found the planes have VERY slow stall speeds and when flying with the wind they have much less tail wiggling.

Much better control in winds during a landing.
I have never swaped a Clark Y to a flat one to actually document the % improvement.

Flying wings + a flying tail has been my logic.

I believe the front and back surfaces should have the same foil in sport planes.

BMatthews

My only thought is that there are lighter ways to produce an airfoiled shape.

There's some tricks you can use to help guide your shaping efforts. Some lines drawn on the wood and then plane or sand down to the lines produces a series of facets that roughly reproduce the airfoil with a high enough degree of control that you can rest easy about any small differences. Once you have a rough shape with 4 to 6 bevels or facets you then smooth the high points down to blend it all into a nice curve. At that point you're quite sure it's as close to symetrical top to bottom and side to side as you could ever need.

But by far a lighter method would have been to make the falt surface, add on some airfoil shaped riblets top and bottom and then to bend some 1/16 sheet over the whole thing to form the airfoil shape.

kerrydel

My Feedback: (2)

Thanks for the input guys. As far as weight goes, I'm thinking it might need it in the tail. Reason I say this is because the ARF uses 2 servos in the very tail to drive the elevator halves. This kit puts the elevator and rudder servos both up under the cockpit. I hung an OS 160 on the ARF and it balanced with no additional weight. That's why I did it the way I did. I'll keep my fingers crossed that I don't end up adding lead to the nose.

Kerry