Board index FlightGear Support Flying

Turbulence with AP  Topic is solved

Controlling your aircraft, using the autopilot etc.

Turbulence with AP  

Postby tfreriks » Sat Jun 15, 2019 3:42 pm

Question 1: When flying the Citation (actually most of the aircraft) I get severe turbulence when the Altitude Control is engaged. There's no turbulence setting in weather. Is that normal? It seems to calm down occasionally, but is normally pretty rough.

Question 2: How do I shut off the ground haze. The Weather reads clear/clear/clear but I can't see the great scenery at altitude.

Thanks.
tfreriks
 
Posts: 79
Joined: Mon Dec 31, 2018 9:52 pm

Re: Turbulence with AP

Postby V12 » Sat Jun 15, 2019 9:44 pm

Are You using Advanced weather and ALS render with Realistic visibility checked ON ?
What is Your Maximal visibility limit and LOD ranges ? Have You check ON terrain effects and presampling ?
Fly high, fly fast - fly Concorde !
User avatar
V12
 
Posts: 1441
Joined: Thu Jan 12, 2017 4:27 pm
Location: LZIB
Callsign: BAWV12

Re: Turbulence with AP

Postby legoboyvdlp » Sat Jun 15, 2019 9:49 pm

The former would indicate a badly tuned autopilot.

As for the second a screenshot would help tell of it's due to LOD, visibility, or advanced weather?
User avatar
legoboyvdlp
 
Posts: 6928
Joined: Sat Jul 26, 2014 1:28 am
Callsign: YV-LEGO
Version: 2018.3.1
OS: Windows 10 HP

Re: Turbulence with AP

Postby Thorsten » Sun Jun 16, 2019 7:54 am

How do I shut off the ground haze. The Weather reads clear/clear/clear but I can't see the great scenery at altitude.


A visibility of 10 km is actually enough to be reported as a clear day. It's fairly common to have that kind of clear air on the ground and just see a whitish haze from aloft in reality. In fact, also larger values are frequently reported as 10 km or 10 nm by stations (presumably because the precise value is hard to measure).

Anyway, if you want a large ground visibility, it needs to be set in the METAR string, if the string reports 10 km, you'll get 10 km.
Thorsten
 
Posts: 10820
Joined: Mon Nov 02, 2009 8:33 am

Re: Turbulence with AP

Postby tfreriks » Sun Jun 16, 2019 1:38 pm

Thanks for the comments. I know that ground haze is common in the 'real' world, but I want to see the scenery. In 'Advanced Weather Configuration', I have 'realistic weather' set, Terrain Effects and Terrain Presampling checked. Max Visibility is 250 km. turbulence is set to weak. If I set Tile Selection Mode to METAR, I get more ground haze. Rendering is set to default in the main menu.
Here's one I don't understand: LOD. Scenery Ranges are Detailed, 1500; Rough, 9000; Bare 30000 (meters). AI/MP Detailed is 3000 and Rough is 10000 (distance). What???
tfreriks
 
Posts: 79
Joined: Mon Dec 31, 2018 9:52 pm

Re: Turbulence with AP

Postby tfreriks » Sun Jun 16, 2019 1:54 pm

Quick note: I changed the value in LOD to zeros (I think it turns LOD off) and ground visibility is much better. THANKS!!

Now: how do I fix a 'badly tuned autopilot'?
tfreriks
 
Posts: 79
Joined: Mon Dec 31, 2018 9:52 pm

Re: Turbulence with AP

Postby legoboyvdlp » Sun Jun 16, 2019 2:28 pm

You'll see detailed objects (e.g. high detail OSM buildings and stuff) at max 1.5km, medium detail up to 9km and up to 30km just terrain (as far as I know).


For the autopilot you need to adjust the PID controllers. Unfortunately I don't really know how.


If you turn atmospheric light scattering on it will look better and quite possibly work much faster than default renderer?
User avatar
legoboyvdlp
 
Posts: 6928
Joined: Sat Jul 26, 2014 1:28 am
Callsign: YV-LEGO
Version: 2018.3.1
OS: Windows 10 HP

Re: Turbulence with AP

Postby Johan G » Sun Jun 16, 2019 2:48 pm

tfreriks wrote in Sun Jun 16, 2019 1:54 pm:Now: how do I fix a 'badly tuned autopilot'?

  • Read up on the basics of PID regulators and/or view some basic YouTube tutorials. Just enough to get a grasp of the differences between what the P (proportional), I (integrating) and D (derivative) gains do. And maybe the basics of trimming an PID regulator (there are several ways to approach this problem though). You may not need all of those.
  • Skim through the Howto:Design an autopilot (permalink) and Autopilot configuration reference (permalink) articles on the FlightGear wiki.
  • Trial and error. :wink:
Low-level flying — It's all fun and games till someone looses an engine. (Paraphrased from a YouTube video)
Improving the Dassault Mirage F1 (Wiki, Forum, GitLab. Work in slow progress)
Johan G
Moderator
 
Posts: 5480
Joined: Fri Aug 06, 2010 5:33 pm
Location: Sweden
Callsign: SE-JG
IRC name: Johan_G
Version: 3.0.0
OS: Windows 7, 32 bit

Re: Turbulence with AP

Postby tfreriks » Sun Jun 16, 2019 3:26 pm

Cool! Thanks, everybody.
tfreriks
 
Posts: 79
Joined: Mon Dec 31, 2018 9:52 pm

Re: Turbulence with AP

Postby Octal450 » Sun Jun 16, 2019 3:53 pm

Johan, it's not nearly that simple. The design of the system is wrong (I had a look at a few). Lots of them are based on the horrid generic autopilot, and others are designed as an ideal system and not an actual one. Of you want to fix this, essentially the whole A/P needs to be redesigned.

Kind Regards,
Josh
Octal450

Lead Programmer, IDG (Join our Discord!)
Download High Quality Aircraft from Octal450 Hangar
User avatar
Octal450
 
Posts: 4284
Joined: Tue Oct 06, 2015 12:51 pm

Re: Turbulence with AP

Postby tfreriks » Sun Jun 16, 2019 9:10 pm

Oh. For a moment there I was encouraged. Well, at least it won't make me sick. BTW: which ones are the best, and can I swap them for the AP in my 337G and Citation II?
tfreriks
 
Posts: 79
Joined: Mon Dec 31, 2018 9:52 pm

Re: Turbulence with AP

Postby Octal450 » Mon Jun 17, 2019 12:38 am

I built a few modular autopilots

GA: http://wiki.flightgear.org/S-TEC_55X
Jet/Prop Airliner: http://wiki.flightgear.org/IT-AUTOFLIGHT

Happy to help you install them if you wish.

Kind Regards,
Josh
Octal450

Lead Programmer, IDG (Join our Discord!)
Download High Quality Aircraft from Octal450 Hangar
User avatar
Octal450
 
Posts: 4284
Joined: Tue Oct 06, 2015 12:51 pm

Re: Turbulence with AP

Postby Johan G » Mon Jun 17, 2019 10:04 am

Octal450 wrote in Sun Jun 16, 2019 3:53 pm:Johan, it's not nearly that simple. The design of the system is wrong (I had a look at a few).

Oh. What are the typical pitfalls to avoid?

Octal450 wrote in Sun Jun 16, 2019 3:53 pm:Lots of them are based on the horrid generic autopilot [...]

So basically those are just tweaks of one that is not that well suited to a specific aircraft to begin with?

Octal450 wrote in Sun Jun 16, 2019 3:53 pm:[...] others are designed as an ideal system and not an actual one.

As in as if it was just a simple industrial process (like controlling voltage of a heating element in a water heater), rather than an aircraft with a lot of external perturbations (like shifting winds and turbulence)?
Low-level flying — It's all fun and games till someone looses an engine. (Paraphrased from a YouTube video)
Improving the Dassault Mirage F1 (Wiki, Forum, GitLab. Work in slow progress)
Johan G
Moderator
 
Posts: 5480
Joined: Fri Aug 06, 2010 5:33 pm
Location: Sweden
Callsign: SE-JG
IRC name: Johan_G
Version: 3.0.0
OS: Windows 7, 32 bit

Re: Turbulence with AP

Postby Octal450 » Mon Jun 17, 2019 3:27 pm

Here is the most common issues I've seen:
* PID where no PID should be used
* Using integrators to try and catch up on lagging systems
* Duplicated controllers for the same thing (can cause handoff instability between modes
* Totally missing filters for when A/P is disabled, makes the PID initialize in a bad place
* Poorly tuned

Yes, correct. The generic A/P really needs to be redone. I would correct it and offer one if I had the time, but I just don't have time right now.

Essentially, think of it something like this: the ideal system (or theoretical system) has no turbulence, no weight inbalence, no disturbances, and possibly even reduced aerodynamics or mechanics of the system. But the actual system is much more less "ideal". So to have to build the system with all that in mind. What may work theoretically may not always work that well in actual aircraft FDM even if you tune it.

Plus, tuning your control loops is a complex process. If you want good results, don't just throw number at it and see what happens. Especially with PID elements. The entire system has to be carefully designed to achieve it's purpose. It also helps to learn the math and theory behind the PID and various components.

Kind Regards,
Josh
Octal450

Lead Programmer, IDG (Join our Discord!)
Download High Quality Aircraft from Octal450 Hangar
User avatar
Octal450
 
Posts: 4284
Joined: Tue Oct 06, 2015 12:51 pm


Return to Flying

Who is online

Users browsing this forum: No registered users and 3 guests