Rollercoaster ride on autopilot approach
Posted: 03 Apr 2020, 11:33
My recently purchased Cessna 182 is equipped with a RXP GTN 750. I tried a RNAV (GPS) RWY 34 approach at Arlington Airport (KAWO), and she flew the outbound, teardrop reversal, and the approach just fine. I hit the APR button on the autopilot and started slowing the airplane down, checking fuel, mixture, prop, etc. The glideslope pointers started coming down, and... YES! The nose dropped as the glideslope was captured! Woah, Nelly, we're picking up some speed here - time to select 10 degrees of flaps. That's when the rollercoaster ride began. The airplane began to hunt for the glideslope, and the up and down action wasn't dampening out at all. I turned off the autopilot and hand flew her in, referring to the PAPI lights and the glideslope pointers which were still available on the HSI even with the autopilot off.
I figured that the oscillations were due to a combination of low pitch authority of the autopilot and a significant trim change in the 182 when even 10 degree flaps are selected. I'm going to play around with this some more, but I read something by Scott that you guys are going to be doing more real-word testing, and thought maybe you could check this out in a real 182 sometime.
Maybe I should select 10 degree flaps before the glideslope is captured? Or maybe plan on no flap landings in IFR conditions? Yeah, I know - real men don't fly IFR by the autopilot, but I enjoy exploring the gadgetry aspect sometimes.
Thank you
ATB
I figured that the oscillations were due to a combination of low pitch authority of the autopilot and a significant trim change in the 182 when even 10 degree flaps are selected. I'm going to play around with this some more, but I read something by Scott that you guys are going to be doing more real-word testing, and thought maybe you could check this out in a real 182 sometime.
Maybe I should select 10 degree flaps before the glideslope is captured? Or maybe plan on no flap landings in IFR conditions? Yeah, I know - real men don't fly IFR by the autopilot, but I enjoy exploring the gadgetry aspect sometimes.
Thank you
ATB