I have A 66" extra 300S and it flies great except when I do a knife edge it wants to
go toward the belly....do I need to adjust something other than the pilot!?
Also Its just a bit on the balancing of being tail heavy (lightly).
2 others flew it and one says add weight to the tail & the other said add nose weight?
I am Stuck?

it has a 90 2 stroke and weights in arount 8.5 to 9 pounds.
Here is a pic of the model..

Thanks
Catfish

That is typical for the Extra. If you have a computer radio you can mix it out with a Rudder -> Elevator mix (try 10% for starters and work from there). If you do not have a computer radio, now may be a good time to get one.

Craig.

CrashMeister is right, mix it out on your radio, slaving elevator to rudder . This will get rid of the pitch coupling and make the rudder more correct in all manuevers. On my Extra's I have done this. It took a little more elevator one way than the other. The radio handles that flawlessly. I think I'm 10% on left, maybe 15% on the right.

I have the Futaba 8UAPS.
So it shouldn't be a problem doing this!


THANK YOU !

Planes like Extra and Cap by design will go to belly at knife edge. When the thrust line is high above and center of drag (close to the wing leading edge) is down below, it will naturally pull it downward. When in level flight, the weight will help compensating for the downward moment. But in knife edge flight, the weight vector is no longer working against this downward moment, but rather causing pitch moment (if left side fuse is up, it will roll to the right) because the center of mass is closer to the canopy than the center of lift of fuse side. I had both of the low wing Extra and Cap, and my findings support this theory.

Conversely, a high wing plane will pitch to the canopy and roll to level during knife edge.

With the Dave Patrick Ultimate, the center of drag is about co-axial with the thrust line, so they advertise "no pitch coupling in knife edge". But its up-down center of mass is closer to the canopy than the fuse center of lift, so it will have pitch coupling at knife edge, rolling toward inverted. It sorts of makes sense. Same with the true mid wing planes (with mid thrust-line).

For your Extra, to reduce pitching to the belly during knife edge, reduce down thrust. I am not sure about adding nose weight or tail weight. I haven't gotten the theory behind that figured out yet.

I wouldn't recommend ajusting the thrust line to get your knife edge better. Set the thrust line so that the elevator trim is constant across the speed range and then use the mixes in the radio to eliminate the pitching effect.

It is a characteristic of this type of plane that it will not naturally perform knife edge, and the only way round it is to use the mixes.

Also bear in mind that when you are using large amounts of mixes (10%+) it will only work properly at one speed, so for instance if you have to use a lot of rudder at slow speed when you have trimmed it for fast knife edge it will not behave properly.

p.s.

also check your C of G. It should be set so that you need little or now down elevator to maintain inverted. If you need to hold in a lot of down then it is too far forward and it won't be helping you in knife-edge.

We did find it uses about 1/3 stick of down elevator while inverted...So my next step is to get the CG straightened out...

Cat

Ummmmm...........How about FLYING the airplane. Once you get your CG set right if it needs up or down elevator well ....... do it. I know you can "fix" it with the radio but isn't that kind of like .......I don't know .............cheating?

I personally enjoy doing my own inputs and adjustments just like you would in a scale aircraft. It seems to be a "purer" method of flying. It also improves your flying skills.

I guess it all depends on the pilot. It seems the guys who pre-program manuevers into the radio aren't really flying the plane, their computer radio is.

HEY! Who are these guys under the bridge with me. YIKES! they're trolls!

Fair enough comment, it's entirely up to the pilot as to how they want to overcome the problems. As to whether it is cheating or not, I don't think so, you are simply using all of the tools available to you to improve your flying. It's a bit like saying a bigger plane flys better than a smaller plane but that's cheating so I'll fly a 50 size model at the world champs...

Seriously though, don't think that you'll be "cheating" by mixing out the rudder coupling, just go to any aerobatics comp and ask the competitors if they use mixes or not and I'll guarantee that all of them will. All you are doing is making the plane fly better so that you can concentrate on flying the manoeuvres better rather than fighting the model to keep it straight all of the time.