VNAV coupling

ackselle

I love flying!
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Jul 5, 2016
Messages
21
Location
Winnipeg, Manitoba, Canada
I have a Skyview Touch, RV-7A, Avidyne IFD440..for the most part, the combination works well.

Tuning the autopilot for reliable IMC flight seems elusive, sometimes I think I’ve got it, then not.

9 times out of 10, the glide slope is captured and autopilot flies the glide slope just fine. Sometimes it ignores the glide slope altogether even though VNV has gone from armed to active! I can not reproduce the ignore at will... but I watch for it on each approach.

I saw this as a discussion a while back....but haven't seen any answers. Anyone else have this issue? Any resolution?

Cheers,
Ackselle
 

DBRV10

Member
Joined
Jun 15, 2008
Messages
755
Location
Brisbane, Qld. Australia
A few things to consider.

Trim speeds, These need to be reasonable so the auto trim is practical. Something like 100% trim speed at or below 100 knots, and 40% speed at say 135 knots.

Next your pitch servo numbers can be set to these to see if they help.
Torque 100%
Sensitivity 16 or 17
Pitch Gain 1.6
Alt Gain 0.9
Pull rate 2.0
VSI gain 1.5
G Error Gain 1.2
G Error limit 0.70-0.75

When the next version of firmware comes out, there will be some specific GS tuning parameters.

I have what I feel works well, but still tweaking them (along with those above) but you will need to wait for that.

Give them a try and see how you go.

Also make sure your shear pin is not broken.
 

ackselle

I love flying!
Joined
Jul 5, 2016
Messages
21
Location
Winnipeg, Manitoba, Canada
Thanks David...

Like many, I'm waiting (impatiently) for the next release with GS tuning/parameters.

My pitch servo numbers are VERY similar...I keep playing with them, but I think I have them set well for the most part.

My shear pin is not broken....like I said, Glide Slope is USUALLY captured, but sometimes it misses, and it seems I'm flying the same on any of the approaches. It's just one of those things I've learned to watch for on the approach, and it's relatively easy to control and get back on slope manually.
 

ackselle

I love flying!
Joined
Jul 5, 2016
Messages
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Location
Winnipeg, Manitoba, Canada
So I think I have the VNAV coupling issue resolved. I've made the changes recommended by David...and then some adjustments as per below. I've flown at least 8-10 LPV and/or ILS approaches since I last posted and the autopilot coupled and flew each approach nicely. Changes I made as follows:

1) Updated Skyview software from 15.3.4 to 15.4.7....no change from that upgrade. Autopilot usually worked well, but still flew through the glide-slope on occasion.

2) Changed my Trim speeds as folllows (as per David's advice):
100% trim speed at or below 100 knots
40% speed at 135 knots.

3) Changed my Autopilot pitch servo numbers as per David's advice as follows:
Torque 100%
Sensitivity 16 or 17
Pitch Gain 1.6
Alt Gain 0.9
Pull rate 2.0
VSI gain 1.5
G Error Gain 1.2
G Error limit 0.70-0.75

.....with these changes, the autopilot caught the glide-slope, but the plane always porpoised through the glide-slope (bounced up and down) very aggressively. So..... I changed the Pitch Gain to 1.2 from the recommended 1.6 which eliminated the porpoising. However, at straight and level flight, the pitch was still swimming through the assigned altitude (very gentle but noticeable bouncing over then under then over etc the assigned altitude). So I adjusted the Pitch sensitivity to 10 and my Trim

My current configuration (the numbers I settled on and are working):
Trim speeds
100% trim speed at or below 100 knots
40% speed at 135 knots.

The pitch numbers:
Torque 100%
Sensitivity 10
Pitch Gain 1.2
Alt Gain 0.9
Pull rate 2.0
VSI gain 1.5
G Error Gain 1.2
G Error limit 0.75

I believe I have resolved/tuned my autopilot so it works very well....it catches the glide-slope and is very smooth during all phases of flight.

Thanks for your help David!

Cheers,
ackselle
 

DBRV10

Member
Joined
Jun 15, 2008
Messages
755
Location
Brisbane, Qld. Australia
That is good news. Glad I could help. The sensitivity and pitch gain need playing with, they vary from aircraft to aircraft.

Do you have a fixed pitch or CSU prop? This actually has an effect too.
 

ackselle

I love flying!
Joined
Jul 5, 2016
Messages
21
Location
Winnipeg, Manitoba, Canada
David,

Couple questions on the new release:
1) When is it to be expected?
2) Will it include GS tuning on Skyview Touch systems?...or do we need to upgrade to the HDX?
3) Do you have a list of new features available?

Cheers,
Ackselle
 

Dynon

Dynon Staff
Staff member
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Jan 14, 2013
Messages
13,583
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Woodinville, WA
1) We don't have a date, but some features are in beta
2) AP improvements should be across the board. The core subsystem is pretty model-agnostic.
3) The features have ebbed and flowed, but some of the major ones are support for the new ADS-B wx products, improvements to vertical navigation (this one may be HDX-only, because it's UX-heavy), and refinements to autopilot.
 

steve m

New Member
Joined
Feb 10, 2020
Messages
10
Location
Asheville NC
VNAV coupling question

- Today on RNAV approach, ATC brought me in high so I came in above the glide slope. My question is, in this condition, will VNAV arm (not couple but arm) and if so, what will flight director show. If the flight director does become active, will it give pitch down guidance to match my default VS down speed (I think mine is 800 fpm)


- Any updates on when new AP software may be available? I love the functionality of this system but my Trutrak AP was sooo rock solid on approaches, no overshoot\hunting. To be honest, I have gotten a bit leary\lost trying to adjust gain\sensitivity up\down trying to find magic numbers\setting for RV10
 
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