I have a home built stick plane with 1/4" deheral, flat bottom wing, 2 deg down on engine; my problem is at full thottle the plane wants to climb so i give it down elevator then when i slow down i have to give it up elevator the cg is nose heavy can anyone help me.

change the incidence of either the wing or the elevator.

which way pos. or neg.

I would personally start by putting a small piece of balsa under the trailing edge of the wing..

But thats just me..

You may also as an alternative.. Check for drooping ailerons.. or bring them up just slightly.

Another thing to check is the engine's thrust line.

It sounds like you may need some more down thrust.

Flying at full throttle, and trimmed for level flight. Quickly pull back the throttle to minimum and observe the result right after you do that. If the plane climbs breifly, then you have too much down thrust on the engine. If it quikly dives then you have to much up thrust.

What it should do is go straight ahead, and slowly enter a gliding dive.

It sounds like yours will dive quickly.

The incidence and CG also factor into the equation. You may have to fiddle with each to get the plane well trimmed out.

Trim charts such as the one linked below are useful:
http://www.tracyskyliners.com/AirplaneTrimChart.htm

thanks for all your help. I will give it a try.

An airplane naturally climbs with an increase in speed/throttle. The lift on the wing(s) increases with speed, but your weight stays the same (ignoring fuel consumption).

The result... the aircraft climbs.

If pitchup is the problem, that is different... heed the advice of the other posters.

It can be hard, sometimes, to tell if the problem is too much wing incidence or if it's a thrust line issue.

What I do is take the plane up high, pull back the power, wait for the plane to slow down, then push in to a dive. The idea is to see if the pitch trim changes too much with airspeed with out changing the engine power output.

Compre the results of dive testing to what happens when you increase and decrease throttle, and you should be able to decide if the problem is due to the engine thrust line or the wing incidence.

JimTrainor's test of quickly pulling back the power is aimed at determining the same thing, unless I'm mistaken somewhere.

Do check the ailerons as suggested above. It's common on flat bottom wings with strip ailerons for people to set them as a continuation of the top of the wing, which can lead to problems like you describe. Raising the ailerons a bit will help. At the very least, they should continue the bottom surface of the wing instead of the top.

a Tail heavy airplane will also do the same thing, might not neccasarily be an incidence problem. Just a thought.

> The lift on the wing(s) increases with speed, <

Actually, the lift increases with the square of the speed and that makes a big difference.

Dave Segal

True... it's also influenced by air density, but I was trying to keep it simple

I would add some shim under the top side of the motor mount to get some down thrust. The way I see, if in the exact moment you cut the power the plane tend to go down, even though it still carries some momentum (airspeed), it should be a engine thrust issue IMO.

Your post contains the solution. You said that the “cg is nose heavy". The forward cg makes the airplane very stable in pitch so that any increase in speed produces a drastic pitch up. Move the cg aft a little at a time until it flies like you want it to. As you approach neutral stability (rear cg limit) it will just go where it’s pointed with little pitch change at any speed. Just ahead of the this neutral point is where aerobatic pilots like, but depending on your experience level, you may want to keep a little greater stability for ease of flying. If you want it to fly well inverted, take out the down thrust and mount the engine level. You won’t need the down thrust when you get the cg right.

With a flat bottom wing, the stabilizer should be set at zero incidence, as well as the wing.

What ken, and dsegal said.

Jetts