I had a low-wing aerobatic plane and crashed it. I bought a new one, the Pole Cat. I really like the way it looks and it is faster, but at full throttle it points up, and at low power it wants to drop the nose.My old plane stayed straight no matter what throttle setting. I have it figured out, the center of drag is higher on my new plane (being a high-wing) than the center of thrust. I have an idea, raise the engine. That will help put power inline with drag. But my fiberglass cowling wont't let me go more than about three-sixteenths of an inch. I have another idea, angle the engine downward. my cowling would allow that. the down thrust should counter the tendency to point up, and at lower speeds will be more neutral. It really bothers me because I keep thinking the elevator trim is all wrong. I have to trim in between both extreemes. Does anyone have this problem?

You are describing the classic, normal airplane behaviour. You do have a trim lever on elevator. Learn to use it. If you can, go for a flight in a full size at your local pilot training school, and just see how much trimming the full size guys do, you will be surprised at just how much is done. there is a trim for takeoff and climb, one for cruise, another for descent, and another for just about every flap position you use. Models and modellers are lucky, we have one and just put up with what happens at other times.
Evan, WB #12.

hey

your trusthline have to be 2 or 3 degrades down

that means that you engine pull a bit down at full speed and that get the plane to go level and when you drossel you still go level

very simple

best regards oy6689

Louis9624,

If the down thrust angle is like specified by the designer, it is possible that your middle wing model has a different problem than what you suppose.

If the CG is located too forward, you may be trimming the elevator up to compensate.

This may introduce a decalage for which your neutral model has not been designed.

That incidence difference between wing and tail may make it sensible to speed changes.

Just try a shallow dive with no engine and see if it noses up when it picks speed.

Check this link out:

http://www.charlesriverrc.org/articl...GMarkDrela.htm

Regards!

You can get the COG right on ..from a good COG calculator.... That leaves wing & horz. stab. at the wrong angles....A high cliff will prove that in a hurry. not joking. Remember the amount of tail trim lever needed to do a short level flight. Reenter that into the plane on landing. Does it look minor ?
Adjust wing / tail till acceptable........Here is were the time gets boring. The final adjusting of surfaces level and moving COG weight to get a ALMOST flat glide. A small amount of below level angle is OK. A few degrees. Lots of short flights needed by me.

Now coach ?.......OK You can play with motor angles. I do this with all planes. Some were designed perfectly. Others by Brick Layers.

Rich

Well, I raised the engine about three sixteenth's inch and put two washers behind each upper engine mount and the problem has been reduced by one-half. I put one more washer in and will fly it soon. I definintely can not go more than that. If it is not enough, I am thinking of lowering ther horizontal stabilizer about an inch. Or take dehydral out of the wing. (the wingtips are about three quarters inch higher right now), making it straight across. Anything to lower the center of drag. But I don't want to fix one problem and create another.

Not a good idea, I believe.

That would locate the stab closer to the downwash of the wing, reducing its authority for high AOA and slow flight.

Creating drag is never good, but it will be better in the landing gear (better leverage), for a nose down moment.

I still recommend re-checking the trimming.