I've recently finished building a Great Planes Ultimate 40. I've flown it twice and it does some weird stuff. When I try to make a right turn, as soon as I apply elevator it rolls left and pops up. I've only made right turns with it and therefore I don't know what it would do in a left turn situation. I don't know what the problem is...I was hoping that someone out there could give me some advice as to how to solve the problem.

NoOne:

Sounds like you have some major errors in rigging the plane.

If you do not have an incidence meter buy or borrow one.

Following is general for biplanes, not all are set this way.

Check both wings, at the root and both tips - correct any warps you find, washout should be set approximately two degrees on the upper wing only. Adjust decalage to have the lower wing incidence two degrees more positive than the upper - along with the washout in the upper makes the stall much more gentle.

The horizontal stabilizer should be set between zero and two degrees negative, in other words from neutral to a very slight up elevator position.

Another possibility is having the horizontal stabilizer not level in reference to the wings. Sight from the rear, with the wings level. If the stab is then level to the eyeball it's close enough.

Also, if you have separate pushrods to the elevator halves, or two elevator servos, you might not be getting even deflection. While holding up elevator press the trailing edges down, you might find the "Wyed" pushrod deflecting to one side under load, giving in effect, an elevator only on the left side.

Finally, check the vertical fin. It should be aligned perfectly fore and aft, or angled with the leading edge a little bit to the left, (right rudder) but never angled to the right.

These are all possibilities, but I think most likely you will find your errors in the wing rigging.

HTH.

Bill.

I have checked the incidences of both wings and as far as I can tell, they are correct. I have noticed that the elevators aren't even. They are conntected with a torque rod and the left elevator is slightly higher than the right elevator. I originally thought that was the problem. I'm going to fix that and move the CG a little forward of where it is right now and see what happens.

Check the allignment of the horizontal stab to the wing too. It could be off.

If one elevator is moving up more than the other, it will cause the plane to roll when you pull back. Make sure they come up the same.

Are you sure that you dont have the elevator throws set to high? On my DP Ultimate as moderate speed if I give full delection of the elev the plane will snap violently in a manner similar to what you describe. It just seems to me that if the elevator halves had a lot of differential that you would have trouble climboing on take off (would roll to one side)

Ben in SC

BenW:

That is a definite possibility. Thanks for reminding me.

NoNoe, did you hear Ben?

Yeah, I know, the name is NoOne. NoNoe is what your mother said. Haw.

Bill.

I'll check to see if the horizontal stab is level with the wings. As for the amount of throw the elevator has, I set it up by the intstuction manual. It didn't seem to have any problem with wanting to roll on takeoff, but then again I've only flown it twice and both times were for less than a minute...just long enough to see there was a problem and then fight it back to the ground. Both elevators move the same amount since they operate off the same pushrod. Could misalignment cause the problem that I'm having?

I've got an incidence meter that I've used to set up the plane, but I don't think its too accurate. I may go get one of those lazer incidence meters and see what it says. Next time the weather is good I'm going to try to fly it again and I'll let you know if your advice helped.

thanks

NoOne,

Im not sure what the reccomended throws are on the GP Ultimate but on my DP event the low rate throw listed in my manual resulted in a snap when using full elevator for a loop, banked turn etc. Do you remember ow much elevator input you used whe attempting the turn? As you know normaly on take off you just feed in enough elevator to get a good climb rate. I would try another flight and when you roll right gie very little elevator input, see if this will turn the pane. If it does try thr turn again and give it full deflection. If the snap comes back you either need to dial down the throw or learn where the snap limit is.

Again, all of this is just from the experience I have recently had with my ultimate.

Ben

Yes, misalignment of the elevator will cause the problem you are having. Even out the elevator and fly the plane again.

I've gone over my bipe with a fine tooth comb and I now think that I have everything set up correctly. While doing this I found that a piece of monokote used for trim on the right side of the top wing wasn't ironed down well and was probably acting as a parachute when trying to turn the plane. I've straightened out the elevators and double checked the CG. Tomorrow I'm going to fly it and see what happens. Wish me luck. I'll let everyone know what happens, and once again, thanks for the help.

I flew my Ulitmate this weekend and everything went fine. It didn't have any bad tendencies and didn't do anything like what it did the first time I flew it. Thanks for all the help.