Flying with Autopilot in turbulence

WingedFrog · #1 05-05-2014, 04:02 PM

I did my first flight in turbulence recently (the kind that will have your head hit the canopy if your seat-belt is not tight, don't ask me how I know). I found myself constantly playing with the trim tab as requested by the A/P and pulling the throttle to avoid staying in the yellow only to push it again when the airspeed got too low which only made the trim issue worse. After the flight I concluded that there is no point asking the autopilot to keep altitude when flying through strong thermals. Looking at the expert mode which I have used sparingly so far, there seems to be a possibility to use only the roll servo in order to follow a GPS track and leave the pitch servo alone. In these conditions can I operate the stick for elevator control without interfering with the roll servo? This would solve my trim problem in turbulence and let me keep my altitude with more flexibility than what the pitch servo allows based on its sensitivity calibration. I still would benefit of not having to worry about my heading.
Does all this makes sense or am I missing something?

Paul K · #2 05-05-2014, 04:08 PM

Just so I have a better understanding, what AP are you running and what if anything are you driving it with? Finally, what are you flying?

Thanks

Don Jones · #3 05-05-2014, 04:23 PM

I flew through the conditions of which you speak yesterday. The Skyview was constantly asking for trim changes, roll and pitch slips. I tried to manually fly it in pitch only and I didn't do any better than the a/p. I finally just ignored the trim annunciations and let it ride it's way through. I found as I am sure you did if you change trim it immediately asks for trim the other way, best just ignore it. I sure was glad to get out of that airplane after 3 hours of that. I hit one big bump that bounced me off the canopy and re-arranged all the stuff in the cabin. Showed to be 2.5 positive and 1.7 negative g's

N941WR · #4 05-05-2014, 04:58 PM

You will not harm the AP by turning off one axis and hand flying the other.

As the others have said, let the AP ride the bumps, if you want.

For me, when it gets really bumpy, sometimes I find it more comfortable to hand fly the plane.

kjowen · #5 05-05-2014, 05:30 PM

+1
4500 over the top of Hartsfield Saturday afternoon, could not even get a good shot of downtown out the canopy because of turbulence. I have a constant speed prop so no throttle work needed, but my auto pilot captures VS or Alt, no lateral track only option, so I couldn't set it up that way, even if I wanted.
My suggestion, just ignore Betty.....

Quote:

Originally Posted by Don Jones

I flew through the conditions of which you speak yesterday. The Skyview was constantly asking for trim changes, roll and pitch slips. I tried to manually fly it in pitch only and I didn't do any better than the a/p. I finally just ignored the trim annunciations and let it ride it's way through. I found as I am sure you did if you change trim it immediately asks for trim the other way, best just ignore it. I sure was glad to get out of that airplane after 3 hours of that. I hit one big bump that bounced me off the canopy and re-arranged all the stuff in the cabin. Showed to be 2.5 positive and 1.7 negative g's

BobTurner · #6 05-05-2014, 05:34 PM

The standard recommendation for inadvertent thunderstorm penetration (e.g., strong turbulence) is to turn altitude hold off. Try to maintain nose level attitude and let the plane go up and down, assuming terrain allows it. The idea is to minimize the stress/g-loading.

Mich48041 · #7 05-05-2014, 06:38 PM

I flew a long cross country trip last year. Although it was not turbulent, the scattered clouds caused up and down drafts. The autopilot was constantly fighting the thermals and asking for trim changes. I eventually shut the altitude hold off, but left the AP heading on. I did not try to maintain an exact altitude, just let the plane go up and down with the thermals. I controlled the average altitude using the throttle. The ride was much more comfortable this way.
Having an autopilot is like owning a microwave oven. You wonder how you ever got along without it.
Joe Gores

FORANE · #8 05-05-2014, 07:02 PM

In our 9A I installed a Trio Pro Pilot. It works well in smooth air. In turbulence I find the plane will get off altitude intermittently by a couple hundred feet or more then correct and overspeed. In roll it will track GPS well but the plane will get tossed about to 30 degree roll or more and the autopilot will not correct the unusual attitude fast enough for me to feel comfortable. Thus, in turbulence the autopilot is completely unusable.

I also have a Lancair. By its very nature it does not get bothered much by turbulence. Even with an old Navaid and Altrac it works much better in turbulence than the Pro Pilot does in the 9A.

I wondered if I was alone in these problems. I wondered if the EFIS based autopilots compensated for unusual attitudes better than a non-EFIS based autopilot. I guess not. I guess the RV in turbulence is a challenge for an autopilot.

Jetguy · #9 05-05-2014, 09:20 PM

It's important to keep a certain perspective and understanding about the autopilot. It is not a perfect entity. It is a tool to take out of your pilot bag and use when you would like to reduce fatigue or look at a map or look for traffic or check you flight plan etc. As far as autopilots go the Skyview AP is very elementary but it gives you a lot of bang for the buck.

I think it is about a $2000 add on for the unit with the servos and wiring. If you were putting it into a C-182 or a A36 it would run about $15000 to $20000. Before you turn it on try to establish a cruse trimmed level condition with a fixed power setting. In continuous light chop you will see +-50 to 100 feet in ALT hold depending on what settings you have selected in its software setup. Also +-5 to 10 degrees in heading hold. But in NAV track it does a great job. If you were on a 150 NM x-country this wouldn't be bad at all.

In continuous moderate chop or light turbulence it would be best to just leave ALT hold off. Also understand that you should try to keep you speed as close as possible to what ever it was when you turned it on with Alt hold engaged. Say +-10kts IAS.

even in a climb or descent. Because when your speed changes you are no longer in trim, get it

So try not to chase the up-down trim indicator. Give it time to react to your inputs. Ever heard of CWS (Control Wheel Steering)? If you feel a really big thermal or bump coming on simple press and hold the red button (better known as the autopilot disconnect button) fly the plane through the wave then release the button and the AP will reengage in its previous selections. Or if you feel out of trim you can press and hold the red button and check the trim or adjust it then release the button bingo the AP reengages.

Lets review, pressing the autopilot button quickly disconnects the AP. Pressing it for longer than a second enables CWS.

So get out there and have fun with your AP.

Dave12 · #10 05-06-2014, 05:53 AM

To add to the comparison with the 15k to 20k autopilot, you would probably be getting the Stec which is a different animal. The Stec is a trim based unit that controls altitude by a change of pitch trim. While flying you will see the trim wheel moving to maintain the selected altitude. This is a very good system that has been around a long time. It does require a trim motor to control the trim cables, but works very well. I would like to hear from someone that has an Stec in their RV to see how well it works in that application. These units have altitude pre-select and hold that when properly working, nails it every time. As you can see though, they are pretty expensive. The efis based a/p's are quite a deal for the money.