I have a plane that always starts a rolling circle towards the belly of the first knife edge when rolling with rudder corrections. In other words if I roll left and add top side rudder when at 90 degrees the plane will push to belly. Funny thing is the next knife edge (270 degrees) does not push to belly. In other words, once the plane pushes to belly at 90 degrees into the roll the plane continues on a rolling circle path regardless of how many rolls I do. I have this problem with both left and right rolls. I can of course correct with elevator while passing through the first knife edge potion of the roll but was hoping for a mix to resolve the issue.

I have the rudder -> elevator mix set for knife edge just fine. Also, the plane rolls very axial (i.e., no heading change) if I don't add rudder corrections. Throttle setting seems to make some difference but not a lot (the problem is worse at high throttle settings.) Thrust angles check out fine, incidence is fine, might be a smidge tail heavy. I've double checked to be sure I'm not pushing down elevator when I start the roll... I'm pretty sure I'm not doing that. I figure the smidge tail heavy part could be causing the push to belly at KE if I'm behind the curve a bit on my top side rudder, but why dosen't the second KE push to belly? Any ideas on what is causing this? Thanks.

MBoy,

Getting the trim just right for aerobatics is a very personal matter. No two people will agree on exactly the best settings.

First, I am confused at why you are using rudder, since you said it rolls perfectly axial without rudder correction? At any rate, I suspect the mixing you set up for knife edge is interferring with your rolling.

As you reach the first knife edge in a roll, you would normally be easing forward on the stick so the wing lift becomes zero. If it turns to the belly at this point, you are pushing forward too fast. When you get inverted, you will push more on elevator to produce negative lift. If it doesn't turn to the belly at the second knife edge, then your timing is perfect for that segment.

Personally, I don't use any mixes. I just watch the plane and add whatever corrections are needed for each manuever.

Tom

Well, for slow rolls I must add top side rudder or I drop altitude. Don't need much rudder... just a smidge. For standard rolls I also drop altitude if I do multiple rolls. I've tried adding just elevator for standard rolls but I don't like how the correction looks. I'm sure it's a pilot thing as I have a hard time finding just the right amount of elevator. I may set a lower rate for elevator to see if that helps.

I'm feel the opposite way on mixes. Mixes won't fly the plane but I feel they can make the plane easier and more predictable to fly. As for the R->E mix, I have mixed about 3% up elevator to rudder (required for KE tracking.) If anything the mix should have helped prevent the push to belly when rudder is added. I have attempted the rolls with the mix off and even with the mix set as high as 10%. It was pretty gusty the day I tested this but as best I can tell there was't much change. This is probably because I'm not adding much rudder so the slaved elevator just barely moves regardless of the mix setting.

You mentioned easing off the elevator in the first knifeedge. I guess I never really thought about needing to push some down elevator at that point but I must have been doing it unconsciously. I had someone watch my thumbs on the plane in question and they said I always push down just after starting the roll. I worked on stopping that which is why I mentioned in the first post that I don't think I am pushing down (anymore.) However, you may be very right that I am still over correcting on the first roll.

I just wanted to be sure that this issue was a pilot issue as opposed to a trim issue. I'm leaning toward "pilot issue" because I can't think of any trim issue that would cause the rolling circle. Thanks for you input Greenboot.

If it's trim/speed dependent, maybe you've bled off some speed by the time you get to the 270 position.

I'm glad that you understand why the rudder is needed and are using it.

You might try stopping after the first 1/4 of the roll. If you are doing everything properly, it should continue flying straight ahead in knife edge.

If all else fails, just be proud you can do a rolling circle, as it's a very difficult manuever!

Tom

Coupling during KE may not be linear. I mixed out the couple with rudder->elevator like you did but it only works perfect at one speed. If the plane is slow and I add more rudder the mix is too much; fast plane, too little rudder and the mix is not enough.

Like Scott said, maybe you bled off too much speed.

I don't think I'm bleeding off much speed in the rolls, but maybe... I'll try to see if I can detect that. I flew last night when it was calm (a rare event in Nebraska) and I actually can roll axial with the elevator and rudder corrections, but I have a hard time reproducing it. It did seem speed dependent. I had to enter at just the right throttle setting for my mixes to work. My R->E mixes are linear at the moment (running two mixes one for 3D and one for normal flying) but I have enough data now I can tell the R->E mix should NOT be linear. I may fiddle around some with setting up a curve for the R->E mix. Does that make sense to you?

Considering Chip Hyde won the XFC in a borrowed Carden 35% Edge, I figure at this point most of my problem is the pilot and probably not the plane or even the mixes for that matter. However, I still want a mix set up if possible. I'm light years away from being a Chip Hyde, but I figure if he can win the XTC with the exact plane I'm having the issue with ... it must be the pilot, ya know what I mean?

Greenboot: THANKS for the encouragement on rolling circles! Problem is I learned rolling circles two years ago and have been working hard on two roll rolling loops this year. Now if I could just learn those really difficult axial rolls