Board index FlightGear Support Flying

C172 autopilot

Controlling your aircraft, using the autopilot etc.

C172 autopilot

Postby approxdec » Mon Oct 22, 2018 1:10 pm

gday.

why is the C172 autopilot altitude set at 20000' on the ground?

j
approxdec
 
Posts: 6
Joined: Mon Oct 22, 2018 2:37 am

Re: C172 autopilot

Postby stuart » Mon Oct 22, 2018 2:20 pm

Hi approxdec,

That looks like a bug. According to the KAP-140 manual (https://bendixking.com/en/~/media/bendi ... -guide.pdf, page 84), it should set to the current altimeter pressure altitude when pressed.

Could you raise it using the Bug Tracker (link at the top of the page), and I'll take a look?

Thanks,

-Stuart
G-MWLX
User avatar
stuart
Moderator
 
Posts: 1629
Joined: Wed Nov 29, 2006 10:56 am
Location: Edinburgh
Callsign: G-MWLX

Re: C172 autopilot

Postby Octal450 » Mon Oct 22, 2018 2:54 pm

That KAP140 is fully of issues and such, I'm in the process of making new one, ijce I find all the data I need.

Kind Regards,
Josh
Skillset: JSBsim Flight Dynamics, Systems, Canvas, Autoflight/Control, Instrumentation, Animations
Aircraft: A320-family, MD-11, MD-80, Contribs in a few others

Octal450's GitHub|Launcher Catalog
|Airbus Dev Discord|Octal450 Hangar Dev Discord
User avatar
Octal450
 
Posts: 5583
Joined: Tue Oct 06, 2015 1:51 pm
Location: Huntsville, AL
Callsign: WTF411
Version: next
OS: Windows 11

Re: C172 autopilot

Postby wkitty42 » Mon Oct 22, 2018 3:41 pm

approxdec wrote in Mon Oct 22, 2018 1:10 pm:why is the C172 autopilot altitude set at 20000' on the ground?

specifically, to avoid the AP altitude alarm going off when you don't set the altitude properly... the team decided to set the AP to 20000 specifically and do so explicitly in the code of the c172p...

i generally only set the AP once i'm airborne and that only after i turn it on to level out and hold current climb rate... climb rate is the first i adjust... then i worry about the other settings as i climb out of the airspace...
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
User avatar
wkitty42
 
Posts: 9148
Joined: Fri Feb 20, 2015 4:46 pm
Location: central NC, USA
Callsign: wk42
Version: git next
OS: Kubuntu 20.04

Re: C172 autopilot

Postby Octal450 » Mon Oct 22, 2018 4:09 pm

Why not model it like the real one? Doesn't that make more sense?

Kind Regards,
Josh
Skillset: JSBsim Flight Dynamics, Systems, Canvas, Autoflight/Control, Instrumentation, Animations
Aircraft: A320-family, MD-11, MD-80, Contribs in a few others

Octal450's GitHub|Launcher Catalog
|Airbus Dev Discord|Octal450 Hangar Dev Discord
User avatar
Octal450
 
Posts: 5583
Joined: Tue Oct 06, 2015 1:51 pm
Location: Huntsville, AL
Callsign: WTF411
Version: next
OS: Windows 11

Re: C172 autopilot

Postby stuart » Tue Oct 23, 2018 10:30 am

Indeed. That's absolutely not the correct thing to do here. I'll have a look and attempt to fix the underlying bug so that it at least sets to the current pressure altitude when it is pressed.

Josh - I wasn't aware that the KAP-140 implementation was so poor. It's been a while since I've used it, but I've used it for instrument approaches in the past, and whenever I've found issues they've always been with my assumption as to how it works, rather than bugs. If you haven't done so, it's well worth reading the manual I linked above, as you do have to use it in the right way and the way in which the modes changes is not obvious.

-Stuart
G-MWLX
User avatar
stuart
Moderator
 
Posts: 1629
Joined: Wed Nov 29, 2006 10:56 am
Location: Edinburgh
Callsign: G-MWLX

Re: C172 autopilot

Postby Octal450 » Tue Oct 23, 2018 2:09 pm

Hi Stuart,
My opinion is based in reading it! :D

I've been collecting info on it with intention to right a new one that works more accurate.

Josh
Skillset: JSBsim Flight Dynamics, Systems, Canvas, Autoflight/Control, Instrumentation, Animations
Aircraft: A320-family, MD-11, MD-80, Contribs in a few others

Octal450's GitHub|Launcher Catalog
|Airbus Dev Discord|Octal450 Hangar Dev Discord
User avatar
Octal450
 
Posts: 5583
Joined: Tue Oct 06, 2015 1:51 pm
Location: Huntsville, AL
Callsign: WTF411
Version: next
OS: Windows 11

Re: C172 autopilot

Postby wkitty42 » Thu Oct 25, 2018 3:24 pm

it0uchpods wrote in Mon Oct 22, 2018 4:09 pm:Why not model it like the real one? Doesn't that make more sense?

you'll have to ask the team on the dev site issue tracker... i know that giliberto was involved in the discussion as was wlbragg and onox IIRC... it was several years ago when it was done...
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
User avatar
wkitty42
 
Posts: 9148
Joined: Fri Feb 20, 2015 4:46 pm
Location: central NC, USA
Callsign: wk42
Version: git next
OS: Kubuntu 20.04

Re: C172 autopilot

Postby wlbragg » Thu Oct 25, 2018 6:45 pm

I have nothing to contribute other than I vaguely recall a conversation about shutting the alarm off. I wasn't involved in any of the details or the tech behind the AP.
Kansas and Ohio/Midwest scenery development.
KEQA, 3AU, KRCP Airport Layout
Intel i7/GeForce RTX 2070/Max-Q
User avatar
wlbragg
 
Posts: 7588
Joined: Sun Aug 26, 2012 12:31 am
Location: Kansas (Tornado Alley), USA
Callsign: WC2020
Version: next
OS: Win10/Linux/RTX 2070

Re: C172 autopilot

Postby wkitty42 » Fri Oct 26, 2018 1:52 am

yeah, exactly... that's me, too... which is also why i pointed to the dev site and the issue tracker ;)
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
User avatar
wkitty42
 
Posts: 9148
Joined: Fri Feb 20, 2015 4:46 pm
Location: central NC, USA
Callsign: wk42
Version: git next
OS: Kubuntu 20.04


Return to Flying

Who is online

Users browsing this forum: No registered users and 5 guests