Thinking about a Third Autopilot Servo

[svyolo]

I really like the "AY Gain". My guess is that it is adverse yaw gain and it mixes in rudder with aileron, before any yaw is actually sensed. Same as we do, or at least other pilots who still know how to fly without their feet flat on the floor like me.

[Bdflies]

ULet’s see if I can get a couple of videos up here to demonstrate autopilot induced yaw.

https://youtu.be/mEp0VZ4qqd4

https://youtu.be/xYFXxUzwtJs

I suspect there will be questions and comments.

My settings are gain = 1 (on a scale of .5 to 10), torque = 50%

Bill

[jaredyates]

Great data collection Bill, thanks! That is about how mine flies with the YD engaged.
I'll try and collect some similar videos.

[rodsmith]

That's very encouraging Bill. Hopefully the Bearhawk will do as well without a yaw servo. That is a beautiful panel!

[Bdflies]

Thanks for the panel compliment! The most information I've ever flown with, in the most abbreviated panel.

Bill

[Rollie]

I'm not sure what could be that much different in how my Patrol is rigged from Bill's but mine does not act like that. If mine stayed within half a ball of in trim, I would be happy. Mine goes over a full ball out while just making course corrections and forget about it in actual turns. Maybe the better answer would be to get with Bill and compare how all the rigging is set up before I go to the effort, time and expense of adding another servo.

[Bdflies]

From the beginning of this discussion, I struggled with how to demonstrate the induced yaw. The whole concept is subjective, in that some might consider my plane uncomfortable, while I don't think the yaw is an issue at all. It finally occurred to me to just film the slip/skid indicator while commanding turns. That's the only metric I can demonstrate. I can't let y'all "feel it fly", but from the video you can see how it reacts. You do have to endure my rambling babble, however...
Rollie, all I can tell you about rigging is that my ailerons are 3/8" above the wingtips. I did that to lighten the aileron forces. It was really stiff at first, but lifting the ailerons lightened them considerably. I really think setting the servo gain as low as I have mine set, could be the key. If I just shove the stick hard over, it'll slew over pretty badly. If you have any questions about specifics, please ask or PM me. I'm more than happy to help any way I can!

Bill

[svyolo]

Bill;
My first thought with the video (great idea by the way) was the one variable here is how the ailerons are rigged. Mark says that rigging both ailerons "up" reduces adverse yaw, and a couple of builders did it later and confirmed this. I will be sure to rig mine the same way. Sounds like you did the same and are happy with it.

The autopilot should be tuned to be more gentle than when you are hand flying. In moderate turbulence or more, you should have to turn it off because it can't keep up. Fly it like it is for a bit, if you want it to be more responsive, increase the gain only a little at a time. Even airline autopilots can't handle the worst conditions. They are better than 30 years ago now, but when the $hite hits the fan, we still have to click it off and hand fly. It can handle about 1/2 of what the airframe basic limits are, we have to do the rest.

From your video, if it was my plane I would be satisfied without the 3rd servo. Most of the time the autopilot will be flying straight and level, or correctly a few degrees.

My first thought when I clicked on your video was "nice panel".

[Mark Goldberg]

Not that this is for sure relevant, but in my RV8 I could VERY slowly roll into a turn with feet on the floor and see minimal adverse yaw. If I rolled into a turn more aggressively, then had to use rudder. So maybe the speed of entry into the turn affects how much adverse yaw. Mark

[Mark Moyle]

Would be nice to modify or find some sort of add on part to Piper rag and tube Ailerons. If it were not a major alteration I would have modified my PA20 ailerons to mimic the Bearhawk’s reduction in yaw by decreasing the radius on the leading edge of the aileron so that it is below the bottom of the wing when deflected up...thusly creating drag and reducing yah.

[svyolo]

Not that this is for sure relevant, but in my RV8 I could VERY slowly roll into a turn with feet on the floor and see minimal adverse yaw. If I rolled into a turn more aggressively, then had to use rudder. So maybe the speed of entry into the turn affects how much adverse yaw. Mark

Mark;
In smooth air you can use slow and smooth inputs, but as the air gets more active the autopilot (or you) has to work a bit harder. I think my choice would be slow and smooth, and click it off when it can't keep up.

I think the yaw servo would help a lot in bumpy air, especially the yaw damper function. Without it I think the roll servo could easily get into a roll/yaw PIO if you set the gains too high. Or just click it off.

[schu]

The capstain/pulley system I created for the yaw servo seems to be working OK mechanically, but I have not been able to get the system dialed in, only because of a lack of support from Dynon.

I seem to recall you eventually pulled your autopilot, but do you have a picture of how you did the capstain pully system? I'm thinking of putting the yaw servo under the co-pilot seat and tying into the rudder cable there....

Also, for some reason I can't bend my mind around why you need to retain the springs at the rudder pedals if you close the loop. Is it just to give the pedal some give when you hit the brakes?

Thanks

[svyolo]

Maybe "feel".

[jaredyates]

I seem to recall you eventually pulled your autopilot, but do you have a picture of how you did the capstain pully system? I'm thinking of putting the yaw servo under the co-pilot seat and tying into the rudder cable there....

Also, for some reason I can't bend my mind around why you need to retain the springs at the rudder pedals if you close the loop. Is it just to give the pedal some give when you hit the brakes?

Thanks

Here is a link:
https://bearhawk.tips/wp-content/upl...023_143533.jpg

Regarding the spring question, I think the springs are still important from a yaw stability standpoint. Russ had some good points about it in his follow-up to my article about that. The top three articles at this link are all very relevant:

https://bearhawk.tips/?s=autopilot+yaw&submit=Search

Let me know if you have any trouble getting to them and I can send you pdfs.