Modified "Aerostar" Flight Troubles

It could be a balance problem. This would be the easiest to fix. A fully symmetrical airfoil should balance roughly at the 1/3rd point, which is further toward the tail than the original flat bottomed airfoil wing, which balances at the 1/4 point.

It could also be an incidence problem. You want the wing to set at the same angle as the horizontal stabilizer on this model, even if you have to shim the leading edge of the wing up a bit. With the wing and the horizontal stab at the same angle, the engine should have two to three degrees of down and right thrust.

Also, trainers do not generally have large control surfaces. If, after you have made the model conform to the preceding specifications, the model still lacks elevator control authority, you might consider doubling the chord (leading edge to trailing edge dimension) of the elevator. If you do, start off with a modest amount of elevator throw on low rate and more on high rate.

Let us know how you fare.

Ed Cregger

Thanks, I'll verify the setup & post my results. And again thanks for your help.

Frank

(I posted this earlier and it didn't come up on the newsgroup.)

Sounds like it is nose heavy. Have you checked the CG according to the plans? It should appear as a vertical line approximately 25% to 30% of cord aft of the leading edge.

Did you change the cord of the wing? Wider cord requires moving the CG aft. Also, You said you made a symmetrical FLAT wing? Surely not!

If you made a full symmetrical wing, where the airfoil is identical on the top as on the bottom, did you keep the incidence of the wing the same as with the original wing? Incidence can be either positive or negative and is measured from a datum line that usually runs from the center of the crankshaft to the center of the fuselage at the tail end. Typically, the wing might be 1° to 2° positive. I.E., the leading edge is higher than the trailing edge. The horizonal stab is usually set at

A lot of full aerobatic airplanes have everything set to zero.

Hi Frank, Sounds as though it could be a CG problem. Don't know what engine you're using but the .40 is probably considerably heavier than the .20, causing a nose heavy condition. Check the balance and move battery, rcvr, etc aft to correct balance. The comments regarding incidence, etc. are still appropriate.

Hi,

Sorry for the confusion, we decide not to rebuild the totally destroyed semi-symmetrical (which was almost totally flat) with dihedral airfoil and instead built a fully symmetrical with no dihedral.

And yes we made the "incidence of the wing" the same as the original design. And, I agree, I intend to check CG to see if the nose is heavy.

Thanks, Frank

Hi Ed, The .40 is heavier, and I though I made enough of a CG change, however maybe not enough.

Thanks, Frank

Good luck, Frank. I'm sure you'll get it conquered. Let us know how you fare.

Ed Cregger

Hi, Checked plane out... 1/ CG @ 1/3 of airfoil... 2/ Stabilizer & airfoil line up & engine @ 2 degrees of down thrust.

Enough said, next time out to the field I'm going to move CG a little to make tail heavyier ( as a test ) & based on that the next move would be bigger elevator... It might be awhile, weather here in Canada you see, maybe the weekend....

thx, Frank

If you or the son aren't a really good 3D flyer, I wouldn't go back further than one third with the CG (really the balance point). I might be tempted to go right to the increased elevator size.

Of course, I do not know how much elevator throw you are currently using, nor the chord of the current elevator. Perhaps some discussion on that topic should be next?

But, ultimately, this is your decision, so let us know how things go.

Whatever you decide, I wish you the best of luck.

Ed Cregger