Buka, that question is better answered by Bryan, but from what I understand, yes, you will reduce the incidence angle on the stab to get rid of the up elevator trim.

Triangulation: pull to canopy on up/down lines is understood but how come the pull to belly in left rudder KE?

Brdgs
Guttorm

Your CG is still too far aft. (I think, I haven't read the article in a while)

Edit: CG is too far aft, this is causing the tuck on knife. Need a little more incidence, this will fix the uplines. These will both probably cause a need to change the stab incidence again to remove the elevator trim, sounds like you're getting very close though.

CG/ince yes, but why more tuck to belly in LEFT rudder KE than on right rudder (assuming a 'tail-heavy' 0-0 setup)?

Brdgs
Guttorm

The left rudder tuck to belly being more pronounced than right rudder tuck is normal . Almost all pattern planes exhibit this tendency (at least on my planes). Probably has to do with prop wash not being symetrical in a knife edge attitude.

Woodie

Nice thread. May be the left KE tendency is due to P-Factor?

I would appreciate Bryan's input here.

Thanks,
Nikos

i guess the tucking tendancy is more severe with left rudder for the same reason you always need right thrust and not left... its not like the plane knows where up and down left and right is .

by the way.
as i have been stting up my model. moving cg forward as per instruction. i realised that tail heavy airplanes ho stall turns better...
whats the word on that?

I've never had a problem with stall turns, and I use Bryan's setups exclusively. I do use a rate switch for the rudder, though, because the snaps are way too fast with the rudder deflection I use in stall turns. As far as the tuck on left rudder KE, I don't know if Bryan has gone as far as figuring out why it is more prounounced than the right. Bryan states in his article that he doesn't claim to be an aerodynamic guru, he leaves that to Nat Penton. What Bryan has done is come up with a method of trimming to deal with the problems, knowing what causes them is not important. You may want to pose that question in the aerodynamics forum and see if they can come up with a consensus answer (they probably won't).

Edit: BTW, Bryan is in the final stages of finishing his latest project. I'm not sure if he has time at the moment to check the forums. I can't wait till he finishes this project either. This one is gonna turn some heads!

Yes, the left tuck is directly related to the prop and thrust.

Stall turns are not easier with a more rearward CG in my experience. Might seem so depending on the design, but generally, no. But you can't wait until the plane stops and then force it....it may not go

-M

Hi Buka.

Please take a look at this:

Nat Penton Trim without Mix Drawings
http://nsrca.us/all/flying/254-pento...-drawings.html

Regards,

Federico

Spiral airflow would seem to be the culprit. On many airplanes, the difference in pitch trim in knife edge can be eliminated by changing the incidence of the right stab relative to the left stab. Decrease the incidence of the right stab (lower the leading edge) or increase the incidence of the left stab (if you do both, the elevator trim for level flight will not change). This type of change is more effective on some planes and setups, and I have never seen it cause any problems so far as loop tracking. This type of change is generally less effective when the plane is tailheavy.

Regards,

Dave

I'll second what Dave suggested....I do that trick myself, and I think it was Dave that told me about it a long time ago?

It also works somewhat with tweaking one elevator half. As long as pushes and pulls stay clean, you're all set.

I'f you're carrying 20% mix, obviously it isn't the answer. But if it's a small number and it's the only mix you have, try it. I'm a believer [8D]

-M