Autopilot approach troubles

[Taipan]

Hi Guys,

I've been practicing some approaches by GPS since I bought the RXP. I have read the RV-7 manual including the autopilot section

The autopilot on the RV-7 though as I get close it starts a fast warning sound and autopilot goes off. Even after shutting down the plane (landed by hand) the warning sound is still going (and autopilot is still lit up, but disengaged).

What I was doing was an approach with the little GPS icon next to it, so it is a GPS approach I think should work...
Then I set the autopilot to GPS mode.

It follows the approach quite nicely for a while. I am on altitude hold as per the original ATC request.

So for the approach I start to increase descent rate on the altitude hold to bring myself down. Now this may be where I am making a mistake.. maybe I descend too fast for the autopilot or I need to adjust trim?

But it's during this descent that the AP goes off, and no matter what I do I cannot turn the AP back on again.

The RXP GPS I haven't read all of the manual yet, I've done the tutorial from Santa Maria to LAX and back though. That didn't cover VNAV, maybe VNAV is something I need to look into as well.

So I'm hoping to figure this out you guys can help me with some questions:
1. What am I doing wrong to cause the autopilot to stop responding and sound a warning tone?
2. Does the autopilot have a minimum altitude?
3. I haven't mapped a trigger button I'm just using the middle mouse click on the autopilot which turns it on and off, I assume they do the same thing though is this correct or does an autopilot trigger operate differently to clicking on the control?
4. Can the autopilot be made to follow altitude VNAV from the GPS?
5. Can I control the vertical component with the stick, with autopilot still contolling roll? autopilot seems to turn off when I do this..

Any tips would be appreciated.

Cheers

[maherd]

Hi Taipan, I can go over the LPV procedures and help get your approach working



First I'll just post this section from page 9 of the DigiflightIIOperatingManual...DigiflightIIOperatingManual.pdf

FYI...
CDI = HSI Course Deviation Indicator
VDI = HSI Vertical Deviation Indicator (aka Glide Slope Indicator)
GPSV Button = ALT Button (3)

...To use the GPSV mode with the
GNS 430/530/480, the aircraft
must be below the virtual glide
slope and the autopilot must be
in altitude hold. When
approach is initiated and the
CDI becomes active, the GPSV
button can then be pushed and
the unit will enter the GPSV
mode. The first screen will
show as below:


The screen will oscillate
between GPSV FLG and GPSS
HLD. When the VDI is no
longer flagged, the unit will
enter GPSV hold, and the
display will show as below:


Once the VDI has been above
the center by one dot for at least
5 seconds the GPSV mode will
ARM, and the display will
show:


As the VDI passes through
center, the autopilot will couple
to the virtual glide slope, and
the display will show that the
autopilot is now coupled to the
virtual glide slope as below:


Missed approach
Once the Glide Slope is coupled
press any button to activate the
Go Around mode. The
autopilot will pitch up to +500
fpm and will engage TRK mode
on the current track.

...I'll be back soon...

[Taipan]

Looking back at the documentation there is certainly more there than I remember

Probably doesn't help that I read it all 2 weeks before using the autopilot! I need to retread this and print it out to try while flying the approach.

Looks like quite a powerful module I just need to use it properly.

Will do some more approaches on Saturday

[Taipan]

Well I tried tonight, couldn't wait.

This autopilot is very hard to use

I managed to get it through to GPSV-> (the final stage) with the arrow, but it turned off before landing when I lowered flaps.

Would this be because my speed dropped outside it's range?

Other approaches I was coming in on altitude hold as per the manual, and when I hit the Alt button to try to move it to GPSV mode as the manual states "once in the GPSS mode, pushing the ALT button will enter the GPSV". However that turned off the autopilot and violently pitched the nose forward and straight down.

Also often the autopilot just starts making the fast clicking noise and will not turn back on no matter how stable I have the wings. The manual doens't mention any warning tone, do you know what this is?

My other problem is the vertical speed mode. It might be something like 800 or 900, and when I try and mousewheel it up or down it just jumps 100 or so and goes back to what it was. It won't let me adjust the vertical speed. Is it ever supposed to not respond like that?

Same with the middle mouse on the dial to turn autopilot on/off. Sometimes I cannot turn it on or off, and I have to jerk my stick to get out of the autopilot. This sometimes starts the fast clickign sound but not always.

[maherd]

Hey Taipan just so you know the trouble you’re experiencing isn't the normal operation.
So we'll need to figure out just what the trouble is and fix it.
I suspect something is interfering with the autopilot's control.
Do you have a hardware controller for your elevator trim?
If you do, can you describe it
Danny

[Taipan]

Hi,

Yes I've got a rotary wheel on my throttle base, assigned via normal FSX assignments to elevator trim.

So this could be overriding the vertical navigation limits?

It's possible, I have used altitude hold and vertical speed changes with other autopilots. But never on approach or with trutrack.