Elevator Trim

[plane]

Here's one that's been buggin' the hell out of me.

We trim our planes for hands off upright flight, right? We then settle for having to PUSH down elevator for inverted flight.

Now we go to roll our plane and wonder why it's hard to keep online especially in a 45 degree line.

To me it would make more sense to 'average' upright and inverted trim.

Am I wrong?

[macanaw]

You ned to adjust your CG. you should need very little down pressure inverted , and non on a 45.

[Shawn Berkheimer]

	Quote: Originally Posted by macanaw
	You ned to adjust your CG. you should need very little down pressure inverted , and non on a 45.

I agree, if you are having that much difficulty then the airplane is not properly set up. I set mine up so it takes just a breath of down elevator for level invert. If you aileron differential is off or the aileron travel is not the same left and right it will make rolling manuvers much more difficlt as well.

Shawn

[Stainless Skills]

I always adjust my cg and incidence for that matter so I only have to push and pull a tad.

I always equal my trim out though, when I am upright I like to have to pull a little bit and push a little bit when inverted.

If you only have to push in inverted and not pull in upright then that screws up you nice axial rolls real bad.

Having the trim equaled out between upright and inverted is the only way!

[Andy540T]

Stainless,

If the rolls are getting "screwed" up with the plane trimmed for upright level flight, then you are still holding elevator in the roll. Try adjusting the cg so that you can fly upright hands off and only slightly push to maintain upright inverted flight. You should be able to pull a 45 degree upline and roll to inverted and you plane should pull slightly to level. If you are set up this way, then when you want to roll, you can start by letting go of the elevator and then start your roll.

[Freddy Warbird]

With aerobatic aircraft, I like to think of my flying surfaces like an automoblies wheel alignment. If my control surfaces are not neutral with my appendages in neutral flight, and the plane is not flying straight @ 0, 45, 90, etc...whether inverted, or right side up, something is out of alignment, or out of adjustment. In order for an automoble to track straight down the road, all of it's suspension angles need to be in the correct position. Camber, Caster, Toe, S.A.I, T.O.O.T, all need to be correct, or one will be compensating with the steering wheel all the time while driving down the road. With Too much positive Caster, tracking is very stable, but steering is very difficult. Too much negative Caster, steering is very easy, but stability is lost. If Camber angles are off, either too positive, or negative, the car will pull, or push "drift". The tires will wear out prematurely. All cars require some positive, and negative adjustment to keep the car tracking straight down the road. If one, or more of these angles can't be corrected with factory adjustments, parts need to be replaced. Warped sufaces, incidence, CG, lateral balance, differential, Trustline, trim etc.. are no different. True, some planes require some negative elevator while inverted to keep the plane tracking straight even if the plane is set up correctly. -That- is in their design. On the other hand, other planes feel very neutral inverted. Cars are -no- different. One year, make, and model may need -2 degrees of camber, and +1 1/2 degrees of positive Caster on the right side for correct alignment, while another may not. The point is, all four wheels on the car need to be adjusted for the road, so the car "tracks" straight, and won't prematurely wear out tires. If your plane needs "excess" negative elevator to fly straight/ level while inverted in the sky, check your alignment angles, and CG. If your plane is drifting to the left, or right in a 90 degree upline, check the trustline. -Measure!- Don't guess!- Is the incidence between the main wing, and the horizontial stab correct? No ammount of CG ajustment is going to correct that if its off.

[notorious_benny]

Where is 3Dubya.........

Quite a few of us here in Australia are doing what we call 'vertical trimming'. Where we trim the model so it flies a perfectly vertical downline hands off and a perfectly vertical upline hands off ( adjusting up/side thrust as well as stab incidence if neccessary/possible).

So in upright flight a very small amount of up elevator is required and in inverted flight a very similar amount of down elevator is required. I learnt it from some of the Unlimited pilots here in Aus, and my IMAC flying has improved out of sight.

[notorious_benny]

I explained it as best I can here...... Is it tailheavy?

[OverTemp]

	Quote:
	Where is 3Dubya......... Quite a few of us here in Australia are doing what we call 'vertical trimming'. Where we trim the model so it flies a perfectly vertical downline hands off and a perfectly vertical upline hands off ( adjusting up/side thrust as well as stab incidence if neccessary/possible). So in upright flight a very small amount of up elevator is required and in inverted flight a very similar amount of down elevator is required. I learnt it from some of the Unlimited pilots here in Aus, and my IMAC flying has improved out of sight.

It's how full scale aerobatic pilots do it too.

Your CG has to be in front of the aerodynamic center for a plane to be longitudinally stable. This requires slight downforce when inverted. If I'm any more tailheavy I don't like how the plane handles.

[Dennis C]

Hey where is Kris w when you need him