Hi Everyone,

I have built a home-made biplane and test flown it this weekend.

The problem is that when it turns to the right, it immediately drops its tail and starts climbing. When turning left the plane does not exhibit this behaviour and it turns perfectly with no climb at all. The plane uses a .90 Super Tigre with a 14x6 prop. The wings are not warped, or in any way twisted. The plane flies level beautifully, turns left beautifully, but on a right turn it just wants to go up and stops turning, just goes up and up and up until stalling....

I have flown it 3 times this weekend and I am trying to figure this out.... The ailerons on the top wing are about 5 degrees up, maybe when I turn the differential between the 2 is cancelled and the plane climbs ?? but why does it not happen to the left ??

I am thinking on working on the CG, maybe move it forward a little and the check my thrust angle, maybe its too much left and when the plane turns right it pulls the plane up....

Any ideas ??

In the picture included its the plane of the left....

Paulo

Could be the differential. Looks like symetrical wings where diff. is not needed. I'd take the diff. out and try it. I'd take the up aileron out of it to. Sort of start from scratch.

I'd start by putting the upper ailerons down to flat. If the picture is any idication you've added a LOT of negative incidence to the upper wing by using that much aileron offset.

How much left thrust does it have? It would need to be a whopping great amount to cause suce a problem. I'm sure there's something else amiss here that is not really aerodynamically related.

Thanks for the suggestions. I will definately make those ailerons flat, but adding negative incidence should make it point its nose down right ?? What is bugging me is that it does it only on a right turn, and not on a left.... it flies perfectly in a straight line.... [:@] I will destroy all my gray matter but this plane will fly better next weekend after xmas.... maybe its waiting for the new year. [:'(]

About the left thrust its almost negligible like 2 degrees.... I had no time to set it exactly straight....

Thanks and keep the opinions coming,
Paulo Poinha

If you're talking about the top wing on a biplane, a flat statement like that isn't taking into consideration:

Where is the center of drag on the airframe as a whole?
Would adding any surface deflection increase the drag on that wing enough to introduce a pitching moment to the airframe?
Changing deflection might actually reduce drag depending on how the original orientation was actually working.
Adding aileron deflection isn't exactly the same as adding incidence to the wing. To get the effectiveness of an incidence change by deflecting flaps/ailerons instead of changing the incidence probably will give the airplane a wing that's throwing a very different L/D at the airframe. You'll probably never be able to get as clean a result as the incidence change gives by deflecting flap/ailerons. And dirty means drag.
And a few more considerations I'm surely forgetting.

BTW, the picture isn't real close, but it really looks like the top left aileron is deflected slightly more than the right. Is that how you flew the model? with the ailerons up? and were they trimmed to keep the model's roll axis horizontal?

The cabane struts have a lot of lateral area. Is there a mis-alignment (left/right deflection, toe-in/out) in any, or all of the cabane struts?

Technically yes. But the first thing you would have done once in the air is trim the elevator to compensate. So it doesn't really count.

From your description, it sounds like you are experiencing adverse yaw when turning right. There are several fixes for this, such as changing aileron differential (more up than down), but a simpler fix is to feed a little rudder in when turning. Works for me.
Left thrust is also not helping your problem.

Thanks guys for all the suggestions, I will definately keep them in mind when trying again after XMAS.... darock, the rons are both deflected the same distance up, maybe the pick was taken with the plane off, when I fly it again I will take a pic of the flight setup closer by, before and after pictures of the rons.... I am going to make them flat with the wing and remove all incidence..

About using the rudder like Herb suggested, I wish I could, I have almost thrown full rudder on this beast when turning and the tail simply will not rise.... I am going to check the CG aswell, it is sounding like a very tail heavy plane, and maybe this airframe doesn't handle that too well..... could those struts be providing enough lift for this too happen ?? well don't think so otherwise this effect would also happen on left turns....

Remember everyone, this only happens when I turn RIGHT, left turns are as gracious and wonderful as a trainer plane. I just had to keep it flying all day long with left turns when I flew it the 1st the times.

Hi everyone, first of all a Happy New Year.... After a few flying tries, I finally corrected the bad tendency, by eliminating the aileron reflexes and adding a positive wing incidence on the top wing to match the bottom wing. The plane flew beautifully, right turn, left turns and all the works, if only my rx battery thought the same, somehow the cable got chafed and down the plane came in a beautiful crash leaving a wing on a tree and the rest splattered on the ground.... Thankfully no1 was hurt and I solved the problem before the crash..... Guess I will try again [:@]

Sorry to hear about your crash. Good luck trying again.

2 degrees is not negligible for a thrust offset. AND it's in the wrong direction (if I interpreted the photo correctly)--it should be right thrust unless your prop rotates counterclockwise as seen from the cockpit. I doubt it had much to do with your problem but it would cause a strong left turning tendency under most flight conditions, assuming everything else is straight and square.