SV autopilot losing the GS if to fast...

[rlallen1]

Hello...


I am in in the beginning stages of IFR training. I am curious as to what airspeed others shoot ILS approaches at. I realize there are many varibles and probably not always the same airspeed is used.

The reason I ask is the when I have my SV autopilot tracking the ILS, autopilot coupled, I have noticed that if my airspeed is to high then it will lose the GS lock. Same thing if I change power settings to much.

I have been able to successfully shoot the ILS with autopilot locked in on GS and LOC, but I have found I need to stay around 90 kts.

Is this norm or is there a sensitivity setting I can adjust?

 

[dlloyd]

I think the install guide states following a glideslope takes much more torque than maintaining level flight. Check to see if you can increase torque to 100%. Otherwise you may need a stronger servo.
My RV7 will follow the glideslope at my usual 90 to 100 knots but faster than that the servo will slip. I do not have the auto trim function. What are you flying?

 

[Dynon]

If by "lose the GS lock" you mean that the servos are slipping that is annunciated by SkyView, then that needs to be resolved by either torque setting, or, if it's already turned to 100%, with either mechanical changes to the installation or a larger servo. If it just doesn't seem to be tracking the GS, but isn't slipping, then yes tuning may help. The Autopilot In-Flight Tuning Guide is the gold standard for this. If you haven't been through that during your initial installation / tuning, that would be step one. One thing to look at in particular is if you're running into your autopilot speed limits. Not likely unless they're set really tight, but worth looking at nonetheless.

 

[rlallen1]

Ok, spent 90 minutes tuning and the flying four ils approaches. I did further tune in pitch sensitivity using the ias guide. Pitch gain was already maxed at 3.0, I moved pitch sensitivity from 9 to 19. The AP works great in IAS and level flight, but flying the glide slope is another story. LOC is locked in. GS not so much. I am getting a lot of pitch servo slipping. What else can i do or does this mean I need a stronger servo. Mine is maxed out at 100% torque. Flying rv7, manual trim...heavy angle valve IO 360.

Thx

 

[rfazio1951]

Ryan, I'm flying an RV6 with the dynon autopilot. I have been flying with it for a few years and it works great. Recently I'm taking IFR lessons and have been shooting approaches. One problem I am having, which may be what you are experiencing, is that once I'm on the glide slope or approaching it an on AP, and then try to add flaps it messes up the AP in pitch. There is too much pitch pressure down for the AP to over power it. It slips and the plane dives. My next flight the plan is to hit autopilot disconnect, add flaps, adjust trim, and re-engage the AP. Does your problem occur when adding flaps?

 

[rlallen1]

Richard... Yes, to an extent. I also have manual trim and the further down the glideslope I get the more AP slips. Another pilot here said I was shooting the approaches to fast too. I was shooting them around 90 kts, (that may be true, but the AP should still be able to keep up)... So I am going to slow next time to around 65 -70 KTS. Another thing that may be causing my issue is that my minimum airspeed on the AP setting is set at 80 KTS, so I believe I will have to lower that down to about 60.

 

[dpbarnes]

I had trouble with the autopilot holding glide slope while adding flaps also.  What I do now is add a notch of flaps near the faf while in altitude hold mode before intercepting the gs.  I don't try to add additional flaps until at decision height and after I have disconnected the autopilot.  I fly the approach at about 100 to 110 kts.  It flys it very nice.  I didn't want to lower the stall speed to allow the autopilot to fly slower.  I am flying a Lancair ES so this may not work as well for you.

 

[rfazio1951]

I like Dan's procedure also. I think that could work. Either way you need to trim for the amount of flaps you are putting in. 60 might be a bit slow for the autopilot. I have mine set to 70 kts as the slowest. With version 13 in the skyview you can hit the disconnect button once and hand fly, trim, then hold the disconnect and she will re-activate the autopilot and continue down the glideslope. that is my next try.