How quick should a plane fall when inverted, hands off the elevator?

I'm carrying .75 positive in the wing and about .25 in the stab to offset down elevator trim. When inverted, hands off the elevator, its diving at a 45 in 3 seconds.

To much positive in the wing?

Todd Schmidt

Todd,

What is the engine thrust line? With 0.75 incidence, I suggest that the T/L should be -0.25 to + 0.5. If you are too much negative could cause that probem. Also the plane could be too much nose heavy. I am sure that you already took care of the CG.

Good luck,

Vicente "Vince" Bortone

It's normal to have to hold in some down stick to maintain level inverted flight. Does it fly level hands off right side up?

Terry in LP

Todd,

Are you mixing low Thr. with down Elev.? I usually do very small amount ~1-2-%. If you have a lot of mixing could cause this problem.

Vicente "Vince" Bortone

Vicente,

The engine is at 0 degree down thrust and I have no throttle to elevator mix.

Terry,

It flys hands off upright and I do realize we have to push to maintain level flight inverted. Just wondering if I'm having to push to much for the norm. To me, it drops faster than it should.

Todd

Hi Todd
your flying wayyyyyy tail heavy,
move you c/g forward probably an inch and your dive will go away ,,, Trust me
remember tail heavy elevator will be sensitive and c/g forward elevator is positive and effective around nuetral
it will require very little elevator to mantain inverted flight ,,,,however you might require more over all throw in the end
when you get way back on the c/g the airplane behaves opposite of what you think it should, very confusing.
make sure your wing inc is 1/2 pos to the thrustline of your model and your motor should be 1/2 neg to the thrustline
your c/g should be around 25% of the MAC not in the 30`S where most models are set up
try this and report back please
P.S.you will find your snaps, spins, knife, up and downlines all improve with this setup
Bryan

certainly all of you guys are more accomplished pilots than i but i fly a ultra sport 60 that flies hands off right side up or inverted.

david

Hi Todd,
Take .25 degrees of positive out of the wing and reset the stab so the elevator flys just a little down trim. When you roll inverted the same thing will happen so you will end up needing to move the CG aft to get the feel you want. I only recommend resetting the wing because it sounds slightly exceesive but will probably not change the feel when inverted, you will end up moving the CG back. I assume also that the .25 of stab was .25 degrees and not 1/4 inch, correct?

The reason I set the stab to run some down elevator trim is I want my plane to be in perfect trim elevator trim from 1/3 throttle all the way to full throttle and at the changing airspeeds. This also makes the plane go straight up, no pitching. Basically I am flying with a cambered stab when setting it this way.

Bill

hi Todd,
Personally, I think you should run the least amount of positive incidence you can - somewhere between 0.25 and 0.5 deg +. Too much positive incidence can double-cross your trim efforts and especially for evaluating inverted flight. I'd go with Bill's suggestion and reduce the incidence for starters, and reset the stab to zero. Down thrust is not a crime and you may end up with a little bit when you are done.

Here is a link to the best trim article I've read, written by Peter Goldsmith. http://www.mini-iac.com/Portals/57ad...20trimming.pdf

Regarding CG, give his method a thought...

This is off of the IMAC website and I hope he doesn't mind the plug. His methodology flat kicks the pants off the "trim-chart", in my opinion, and offers great insight and reasoning into how to get you model flying "right" with an eye towards the complete sequence, versus singled out elements.

Its possible to get combinations of exaggerated incidences or CG settings and still end up with a mildly mixed out model. However, the closer you get to a "stable" model that still carries a tad of the great flying qualities of a near neutral plane, the better you are going to fly. IMHO. You really don't want a plane that flies great upright, then dives like hell towards mother earth when inverted, because no matter how much you play with expos or throws to make it "manageable", the model will still have a setup flaw that will bite you some time. Simply said, the further forward you run the CG, and the more positive incidence you run, the worse the "dive" tendancy is going to be when inverted.

This is a great internet topic because opinions and experience vary so much.
Thanks,
Jim W.

The statement about CG made here is only correct for extreme variances from the recommended CG. The same can be said for the incidence... Half degree positive is an excellent starting point for incidence on modern pattern aircraft. I've seen both in practice and know that what flyincajun recommends works. Of course, it might be easier to help if we understood what kind of airframe we're working with here, as well.

I'd say moving the CG 1.0" forward, as suggested, qualifies an extreme variance. I'm not debating Bryan's methods, mjfrederick, I'm pointing out a fact of airplane life. The further forward you run the CG and the higher the wing incidence goes, the worse its going to dive when inverted. More than one person in the RCUniverse has worked out trim issues before.

Thanks,
Jim W.

WOW three responses
three different fixes ,,
how confusing can that be ?
Let us know what works Todd,
Bryan

The microwave just beeped, popcorn at the ready....LOL

I'm interested to see what ends up being the fix as well. My advice would be the same as has already been offered here, so I'm in curious mode....I know that the actual design of the plane sometimes plays a LARGE part in this, but I have a hunch you already got the right advice.

-M

Hey Mike,
the design has very little to do with Todd`s problem.
tail heavy is tail heavy
once you get too far back it will act nose heavy inverted and dive . thats why I want him to move the c/g forward one inch
inc. has nothing to do with this , the only thing that plays in to this problem could be airfoil thickness,
the thicker the airfoil the worse the effect on diving inverted at an aft c/g location.
I have felt what what Todd is discribing recently with an experiment
so I know his problem well.

As you know there aint much we have not run across helping every one else fix trim problems and working on our own.
The root problem is c/g more nose weight, elevators are more effective around nuetral,,
and tail heavy airplanes ,,, have no controlable effect around nuetral
they are just sensitive,sowe expo it out to make it "feel" good
I just fixed this problem recently Soooo,

Todd you have three ways of doing this ,,,it`s your move
let us know what happens
Bryan

Hey, this is a great forum. Now I have some things to try. Thanks Bryan, Bill, and Jim for your input. First I'm going to reduce the incidence and reset the stab to -0-, then play with the CG. I be sure to let you guys know what happens. Again, thanks for all your input.


Todd

That's what I was thinking.....

-Mike

Hi
Okay now I am confused. I am trying to set up my Angel S and at the moment I have it in a tail heavy configuration. I have no control over the incidence just the CG. To my simple understanding Tail heavy is Tail heavy regardless of what way the plane is up. So how does it suddenly become nose heavy when inverted if you move the CG too far back??

M

I am suprised that no one has mentioned the difference in lift when inverted and upright if you have a semi semetrical airfoil section, over to you.

Mike

If you cannot move the wings don`t move the c/g forward, you have to fly it tail heavy,
if you go forward with the c/g on a zero wing inc. setup your airplane will require uptrim and then it will pull in the downlines to the canopy and may`be in the uplines also
This will require engine down thrust and right thrust to correct,
your right rudder knife will require down elevator mix your left rudder will need up elevator mix
your inverted flight will need too much elevator input,
your 45`s upright and inverted will fall off line, your take off`s will be very hard to perform smoothly
and rudder will feel heavy
some of this is already the case I`m sure ,,,except the inverted part, and right rudder knife is probably ok the way you have it setup now...Am I correct ?

When you put the c/g too far back you won`t actually be nose heavy But it will feel like it ,,,,"only with the inverted elevator"
as soon as you let go of the stick it will go straight down.
ever tried to fly a hand glider tail heavy ? same effect except you don`t have a motor pulling foward.
your airplane will fly ok o-o except in the wind and upline snaps it will wander off line
you will have to lead the 45 down line snap with elevator to show a break
and the spins will be hard to hit the exit, you will have to lead the rotation and stop a little before your ready

To correct this move the c/g forward say 25% of the M.A.C.
put your wing 1/2 deg pos to thrust line
stab start at zero inc.
keep moving the c/g forward till up and downlines are straight and everything else will be fixed.
Yes putting nose weight with the wing at a 1/2 pos will actually make the airplane go straight up and down.
Bryan

Mike!
Microwave!?!?
[X(]
You've GOT to have one of these!

JLK

So if an aircraft is too nose heavy then it's too tail heavy?????? Whatta...

This I gotta see [sm=spinnyeyes.gif][sm=spinnyeyes.gif][sm=spinnyeyes.gif][sm=spinnyeyes.gif][sm=spinnyeyes.gif]

Todd,

As you were told before, adjust all the incidence first! this can be very deceving, second, the airplanes are not always suppose to fly inverted hands off, unless you are flying 3D, and for some manouvers this is bad anyway, fly a loop or reversed cuban 8, if at the exit and you progressibly release up elevator the aircraft pitches up and you have to push, then is tail heavy, this is one of the methods I use, it really works well, as many people try only one manouver, like the inverted 45 dg climb, to me the manouver exit is the most important.

Remember, the CG is also a personal adjustment to your way of flying, try to find the one you are comfortable with.

Hope this helps.

Had the pleasure of practicing with Todd, Joe, and Vince this weekend. Both Defiants looked great and locked in. Thanks for all the great feedback guys. Looking forward to the Nats. Even survived a trip to the "Defiant Dungeon".

Steve Ford