Hi

I got a midwinged plan from a friend who got it as payment for a job. After finish building it I have problem to find were the CG shall be. What I have done is that 1/3 of the wing is balanced with everything in it except fuel. On the maiden fly it wanted about 5 degrees of up elevator. After some reading I try flying inverted and found that I needed down elevator. Applied 10g of lead on the tail with no success after applying 40g more it started to be better but now it wants to go up if I reduce power. This thing is starting to drive me nuts but I hope that some one out there can help me.

Regards

What type of airfoil does it have, and how do the incidences of the wing and stab compare to the thrust line?

Don't know what airfoil it is but it's symetrical airfoil and incidences is 0 degrees (measure with ruler and a cadprogram but I have loaned a meter right now). Thrustline of the engine I placed in the same line as the wing and after all problems with dive I found that stab is 2 centimeters higher than the wing. So my thoughts is that stab wants to be inline with wing and therefor generates a dive. My trim on the elevator is 5 degrees up.

Any idea of what plane it is? Maybe someone can tell you where it is supposed to be for ref. When you say the stab is higher than the wing, are you talking leading or trailing edge?

I don't know what name or anything it has. It has some resemblence that a guy here in Sweden made a drawing to but the wingspan is only 164cm on that and mine is 180cm. On that drawing the engine is mounted in center of firewall and as I say previously in line with the wing. And yes the stab is inline with the wing but offset 2cm higher. I'm charging my homebuild onboard glow right now so I have to wait until I can measure with my friends incidencemeter.

Adding a small amount of down elevator while inverted is OK. Most of my planes are balanced that way. You shouldn't have to put much pressure, though.

Every time I've seen people calculating C of G, it's always been 26-30% or so of the chord.

As MHawker states, the cg should be in that range. Most planes will have to hold a little down when upside down, unless it is a fully symetrical wing and the plane is near perfect. I would be more concerned about the stab being off from the wing.

If I understand correctly, the stab is no problem. I believe jacs is saying that the wing and Stab are at ZERO incidence, but the stab sits slightly higher than the wing. This is not a problem. Many planes actually avoid having them in-line with each other to keep the stab out of the wings wake.

jacs, can you post a picture of this plane?

Oh, I read it wrong. I thought he had 2 CM higher in incidence. Don't know where I was on that one.

Here is comes not the best pictures but tell me so and I will try to get better ones

One more

Last I think

Can't see the thrust on there, but if it trims ok and when you cut the throttle it wants to go up, you may have a thrust problem. Sounds like the engine is pulling the nose down.

Okay measured with a incidence meter right now and stab is 3 cm higher and after aligning wing to zero I moved to stab and that one is also 0 degrees. Have to make a real check with a line from engine to stab as thrust line and go from there.

Made a line from engine to stab and level the plan with that now I have +2 degrees on stab and +1.5 degrees on wing.

Unless I missunderstand, that would make it want to dive the faster it goes. When you pull power off, it would want to climb. Seems like that is the problem you were having wasn't it?

The thing is that I turn the elevator travel a little down and had to trim full up after that the plan wanted to go up when engine was idle. When I used full travel my elevator trim was around 10 clicks with no climb on idle unless you count in that landing was easy as a cake with now up elevator when landing.

Engine was -3 degrees when wing was level so now I changed it to +1 degrees instead but it's easy to grid of material to change. I have to build a small cover for tank area because the old fly away before I can fly again.