Lately I’ve really noticed my SW1900 climbing out in a pronounced slip. The HUD shows level on the ground and wind minimal. The plane flies perfectly level at low power settings. I believe this is being caused by P-Factor, Torque, and Spiraling Slipstream. (my student pilot days are coming back to me slowly)
Although the plane is tuned very nicely in all other respects, I have not changed any of the yaw parameters other that .35 RDDRMIX for turn coordination.
What do you recommend I try? After reading the parameters I’m thinking this:
Sidelslip control integrator (YAW2SRV_INT)
This is the integral gain from lateral acceleration error. This gain should only be non-zero if active control over sideslip is desired. If active control over sideslip is required then this can be set to 1.0 as a first try.
Also, what is the difference between KFF_RDDRMIX and YAW2SRV_RLL? They both pertain to turn coordination.
I can upload a log when I return from my travels if that helps.
Thanks.
[quote=“iskess”]Lately I’ve really noticed my SW1900 climbing out in a pronounced slip. The HUD shows level on the ground and wind minimal. The plane flies perfectly level at low power settings. I believe this is being caused by P-Factor, Torque, and Spiraling Slipstream. (my student pilot days are coming back to me slowly)
Although the plane is tuned very nicely in all other respects, I have not changed any of the yaw parameters other that .35 RDDRMIX for turn coordination.
What do you recommend I try? I can upload a log when I return from my travels if that helps.
Thanks.[/quote]
Enable the yaw damper and its integrator. It is incredibly effective and an important safety device (it makes it nearly impossible to spin as your aircraft will never be uncoordinated) plane.ardupilot.com/wiki/roll-pi … er-tuning/
Of note: RDDRMIX does NOT coordinate the plane. In fact, it will have the opposite effect. RDDRMIX exists to counteract adverse yaw from the ailerons. As most aircraft have an overbanking tendency requiring opposite aileron during a turn, this will tend to make coordination worse during turns.
[quote=“iskess”]Thank you for being so fast!
You responded while I was editing my post.
I’m confused about RDDRMIX. Countering aileron adverse yaw and turn coordination are the same thing, right?[/quote]
No! Adverse yaw is a yawing force applied by your ailerons. Coordinated flight is keeping the relative wind parallel to the fuselage. Counteracting adverse yaw can be done with a simple mix - keeping the plane coordinated is done by “stepping on the ball,” so to speak.
Edit: to clarify what I said before, counteracting adverse yaw will help to coordinate the plane while the plane is rolling, but once you’re trying to maintain your bank angle (by fighting overbanking tendency with opposite aileron) it will input opposite rudder and make things worse.
I think I’m starting to grasp the distinction, but it’s not an easy concept for me. I understand that RDDRMIX is a simple dumb linear mix. If Yaw2srv_rll is stepping on the ball, then why do we need RDDRMIX? Stepping on the ball should resolve any sideslip whether it’s caused by Adverse Yaw, Proverse Yaw, P-Factor, asymmetrical thrust (twin), etc…
Thanks for taking the time to talk through this with me.
[quote=“iskess”]I think I’m starting to grasp the distinction, but it’s not an easy concept for me. I understand that RDDRMIX is a simple dumb linear mix. If Yaw2srv_rll is stepping on the ball, then why do we need RDDRMIX? Stepping on the ball should resolve any sideslip whether it’s caused by Adverse Yaw, Proverse Yaw, P-Factor, asymmetrical thrust (twin), etc…
Thanks for taking the time to talk through this with me.[/quote]
A feedback controller like the YAW2SRV_* controller, has to “see” the yaw rate error caused by adverse yaw before it can do anything about it. The RDDRMIX feedforward controller, on the other hand, doesn’t have to. It knows that the ailerons cause adverse yaw and it fixes it before it gets to the YAW2SRV controller.
Today I put together a new plane and found that the RDDRMIX was reversed in relation to the ailerons when bench testing roll upsets in FBW. The strange thing is that the Yaw Damper was the correct direction. If I reversed channel 4 in the Radio Calibration page, the RDDRMIX would be correct, but the Yaw Damper would be the wrong direction.
Finally I tried inputting a negative RDDRMIX number, in this case -.35, and to my surprise it worked! I didn’t even know this could be a negative number.
This isn’t documented, is this an appropriate solution?
[quote=“iskess”]Today I put together a new plane and found that the RDDRMIX was reversed in relation to the ailerons when bench testing roll upsets in FBW. The strange thing is that the Yaw Damper was the correct direction. If I reversed channel 4 in the Radio Calibration page, the RDDRMIX would be correct, but the Yaw Damper would be the wrong direction.
Finally I tried inputting a negative RDDRMIX number, in this case -.35, and to my surprise it worked! I didn’t even know this could be a negative number.
This isn’t documented, is this an appropriate solution?[/quote]
Something must be reversed. Ailerons? Are you sure yaw damper is correct? When you turn the plane it should deflect the rudder in the direction that it is rotating. RDDRMIX should be deflecting the rudder towards the upward aileron. The upward aileron should be on the side that you want the plane to roll towards.
I’m sure. I’ll make a video when I get home from traveling.
Edit: I’m sorry, my mistake. Since I was checking RDDRMIX using FBW and physically banking the plane, I was stupidly referencing the banked attitude rather than the aileron deflection trying to “right” the plane.