Hi All,

When flying my Scanner (low wing sports) I find that I need a lot of down elevator when flying inverted. Does this mean that the plane is nose heavy? The plane is trimmed well when flying normally and there is no noticeable deviation from a neutral position in any of the control surfaces.

Can anyone help on this one?

Thanks

Langfire

it could be the aerofoil, of the C of G
check these both

Langfire, that is usually the first indication of a forward CG. Try moving the CG back in NO MORE than 1/8 inch increments and see if things get better. CAUTION as the CG moves aft the aircraft will be less stable in pitch!

As others said, check CG , and also the engine thrust line.

Thanks for the feedback,

I'll look at each of these points and start with small changes to cg.

Cheers

Langfire

Langfire,
Is there any throttle related pitch change when flying upright? If the plane tends to gain altitude at full throttle (upright) it could be an engine thrust issue.

If its a "Pattern Style" model www.nsrca.org has a trimming guide.

The guide assumes a 0-0-0 (0 deg downthruts, 0 deg wing incidence, 0 deg stab incidence) symetrical airfoiled everything in a straight line setup. If the model deviates from the setuyp... its usually in wing placement. airfoil and "decalage" (angle between main wing and tailplane incidences) that will throw the trim chart off. These being different usually void the dive test, and can void the inverted flight tests.

If you have an angle between the main wing and stab ncidences.. you will 99.9% of the time need down elevator for inverted flight. (about 90% of the stick travel for a typical trainer...) moving the CG back MIGHT be the answer for your model... but I'm not familiar with your model.

Ok I see the logic in the arguments put forward. I will test on the weekend for any thrust related issues before making any cg changes. Will also check the 0 deg wing incidence & 0 deg stab incidence on the bench before then.

Thanks

Langfire

I don't know that plane but if it's a low wing sport plane (not low wing aerobatic or pattern) it almost for sure isn't 0-0-0.

Even for trainers, moving the CG back does reduce the amount of down elevator you need when inverted. If the plane doesn't have any snap rolling tenancies and otherwise flys like you want it, I'd move the CG back, a little at a time. When you test fly with the CG moved, get high first, then try out the elevator and stall handling. You will likely find that the elevator rate should be turned down as the CG goes back. That's normal.

I agree with post #9. Unless it is a scale aerobatic or pattern plane, it's not likely to be built at 0-0-0 incidence. Any dihedral at all would be a good indication that it's not.