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Autopilot general

Using the autopilot is an important thing when flying airliners.

Autopilot general

Postby Frieder » Fri Apr 03, 2020 10:07 pm

Hi there!
I'm a beginner in FlightGear and I mostly finish to take off the plane. But then I try to activate the Autopilot. For example I got information via YouTube about the MD-11F. I downloaded that plane and started from Hannover Airport (EDDV), because I live near Hannover. I reached the runway and successfffully took off. From the video I knew the key to turn on the Autopilot. The route was already shown in the display. Then I clicked this key. But first nothing happened. No sound, no steering, nothing. Then the plane steered left. First I thought, it was the Autopilot which did that. But suddenly the angle went greater and greater and the curve became smaller. The plane turned more left than the route would afford. Then I heared: "Bank angle! Bank angle!" The plane started falling - and then the plane crashed.
I had such things with very many kinds of planes. I also tried the generic autopilot, also nothhing happened. Switching on the autopilot isn't included in a tutorial. Planning the route also not. So please answer the following questions for me:

1. I don't know right, how to plan route (setting and moving waypoints) and how can I use the Generic Autopilot? From the instruction I read that there is a generic autopilot, which works even with those planes, which don't have one normally. How can I plan the route for this one? The Autopilot menu then is faded off (for example in the Cessna 172P, which is installed within the program).
2. What are the conditions to activate the autopilot? How can I activate it?
3. What do I have to do, that the auto-flight proceedes correctly? What doesn't the Autopilot do?
4. The same questions for the automatic landing system.
I would look forward, if someone sends me a saved route from Hannover (EDDV) to Frankfurt am Main (EDDF), which works with the autopilot. I don't care about which runways to start and land.
Greetings
Frieder
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Re: Autopilot general

Postby Johan G » Sat Apr 04, 2020 7:37 am

Autopilots can differ a lot between aircraft. Try look for in-sim aircraft help by pushing [ ? ]. In addition a lot of aircraft comes with readme files and handbooks in the aircraft directory. A lot of aircraft are also documented on the wiki, in particular airliners (see Category:Airliners on the wiki).

While there is a generic autopilot with a route manager, some aircraft, where the real life aircraft lack autopilot features or an autopilot at all, the autopilot and route manager might be disabled and unavailable. For a lot of aircraft the generic autopilot is not tuned to the aircraft and may be very unstable. In addition a lot of aircraft, in particular airliners, have custom autopilots very different from the generic autopilot and often with the route manager disabled. Routes are for those are instead entered though displays in the cockpit emulating the functionality of FMS displays.

Frieder wrote in Fri Apr 03, 2020 10:07 pm:1. I don't know right, how to plan route (setting and moving waypoints) and how can I use the Generic Autopilot? From the instruction I read that there is a generic autopilot, which works even with those planes, which don't have one normally. How can I plan the route for this one? The Autopilot menu then is faded off (for example in the Cessna 172P, which is installed within the program).

See the FlightGear wiki articles:

Frieder wrote in Fri Apr 03, 2020 10:07 pm:2. What are the conditions to activate the autopilot? How can I activate it?3. What do I have to do, that the auto-flight proceedes correctly? What doesn't the Autopilot do?

That can differ a lot between aircraft, see above.

Frieder wrote in Fri Apr 03, 2020 10:07 pm:4. The same questions for the automatic landing system.

See above. Also, in real life only some very few aircraft, typically airliners, have autopilots with autoland capacity. If the autoland system would fail the aircraft would very likely have a fatal accident. Thus extra redundancy of navigation equipment (instrument landing system, radar altimeters etc) are required. In addition the equipment requires more certification testing. However, except from visibility, the autoland systems still have more stringent weather minima when it comes to for example crosswind and wind gusts. In essence an autoland system is very expensive, yet still can not always be used.

If I understand it correctly, an autopilot would typically disconnect at decision height (DH) and the landings would be flow manually. On approach you will pass a published DH at which the pilots, depending on the weather, decide to land, go around of divert to another airport. For landings airports have published weather minima in a few classes that depends on the equipment available on the aircraft, typically depending on runway visual range (RVR) and cloud base. In addition the aircraft have published weather minima. These would typically include crosswind.
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Re: Autopilot general

Postby Frieder » Sat Apr 04, 2020 11:21 am

Hi Johan G.
thanks for the information. But at some aircraft I can't open the Autopilot menu, so I can't open the Autopilot Settings ore the Route-manager. Then I can't plan a route for the generic autopilot. Can you or someone else tell me, how I can plan the route, if the menu is disabled? And what do I have to activate/deactivate in the Autopilot Settings to activate the Generic Autopilot?
Greetings,
Frieder
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Re: Autopilot general

Postby V12 » Sat Apr 04, 2020 1:19 pm

This is simulator, not game. If real aircraft has basic autopilot for wing level, heading hold and altitude hold without ability follow route, You would not expect that simulated aircraft can use route manager. Route manager in FG is workaround for aircrafts without completly implemented A/P controlled via buttons in cockpit. For example - default C172 has only very basic autopilot without route follow mode and this is reason, why is AP panel and Route manager disabled. Other example - development version of A320 family has MCDU with own "flightplanner" and ignore route manager. It is much more realistic enter route into MCDU than into route manager. And this is simulation.
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Re: Autopilot general

Postby Frieder » Sat Apr 04, 2020 2:25 pm

Yes, I know that it's a simulator. But untill now I don't understand what you mean. What does it mean? In the instruction is written that Flightgear supports a generic autopilot that works with ALL aircraft (even those
that would not normally have an autopilot). (getstart.pdf, p.44)
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Re: Autopilot general

Postby Thorsten » Sat Apr 04, 2020 2:44 pm

In the instruction is written that Flightgear supports a generic autopilot that works with ALL aircraft (even those
that would not normally have an autopilot). (getstart.pdf, p.44)


That probably by and large used to be the case 10 years ago when this document was written - but these days there's some fairly realistic craft in which the generic AP causes nothing but trouble - or is intentionally disabled by the craft maintainer.

For instance, what do you expect does the generic 'altitude hold' do with a glider?

What do you think it does with a helicopter in hover?

What's the use of a generic 'heading hold' AP aboard the Space Shuttle?

The generic AP is a generic tool to which some aircraft (usually those with mild flight characteristics) respond reasonably well, other aircraft marginally and several not at all. If the option has been disabled, you're not supposed to use it for your own good.

And that's the end of this story.

If you're interested in flying by AP, use a plane that has one implemented at the level of sophistication you need (I believe the 777 would have a working airliner-type AP, but I'm really not flying airliners much), learn to operate it properly, enjoy the results.

Be aware that APs in FG are not FAA certified devices - they're what hobby-programmers wrote, and in many situations they may be out to kill you if they're out of their depth :evil:
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Re: Autopilot general

Postby Frieder » Sat Apr 04, 2020 2:57 pm

Thank you. :) That means, that the "generic autopilot" isn't a plane-independend autopilot.
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Re: Autopilot general

Postby Thorsten » Sat Apr 04, 2020 6:30 pm

It is - which is precisely why it doesn't work with every plane.
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Re: Autopilot general

Postby Frieder » Sat Apr 04, 2020 10:44 pm

But I didn't only try the generic autopilot, I also have the MD-11, which has a supported autopilot. But until now I don't really know how to activate it. As I press the Autoflight kesy nothing happens. Can somebody help me there? I read through the wiki, but it doesn't work already.
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Re: Autopilot general

Postby Thorsten » Sun Apr 05, 2020 7:22 am

As I said, I am not into airliners, the only ones where I've tried a good while ago with AP are the 777 and the Concorde, both did what I expected of them after I learned.

A realistic AP implementation might be just that - realistic. For instance some expect you to properly trim the plane before connecting the AP, others react weird of they don't have a signal on the VOR.

Most of the problems I've had have been me misunderstanding how the system is supposed to work.

Having said that, designing a good AP is really hard work, so there's plenty of planes which have marginally working systems. If you assume that every plane in the FG reporitory works great, you're in for a disappointment, there's ~ two dozen really highly developed craft which take a lot of time to learn, then there's a bunch of good ones and then there's hundreds which sort of fly, but not with any degree of realism.

I can't tell you off-hand what the situation with the MD-11 is (not into airliners, remember) - if you want to learn an AP, pick a plane which someone else flies regularly under AP, try to learn it, ask specifically someone who operates the plane successfully what the trick is.
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Re: Autopilot general

Postby Hooray » Sun Apr 05, 2020 9:05 am

regarding crashing planes (under AP control), the other possibility is that regardless of the quality of the aircraft/autopilot implementation, you're seeing autopilot oscillations - that would be the case if frame rate/spacing are "stuttering".
In that case, the autopilot basically isn't getting enough computing time to update the flight controls. So that it is literally lagging behind with its inputs.
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Re: Autopilot general

Postby Thorsten » Sun Apr 05, 2020 9:40 am

In that case, the autopilot basically isn't getting enough computing time to update the flight controls. So that it is literally lagging behind with its inputs.


The generic AP and most other APs should be running at FDM rate though - only if you write it in Nasal it has this problem.
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Re: Autopilot general

Postby Hooray » Sun Apr 05, 2020 11:02 am

yes, but even in the early days of the project (in fact, even pre-Nasal/pre 2003), some FlightGear aircraft exhibited such problems, despite their PIDs execution being interleaved with the FDM rate - but I agree that given how computers have evolved since then, this is unlikely to be the case here.
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Re: Autopilot general

Postby SE-HK » Tue Nov 03, 2020 1:33 pm

Hello!

I have a question related to the Autopilot and Route Manager. I know the AP is quite basic for some aircraft, for example the default C172p, still I would like to use the Route Manager "manually". By "manually" I mean to have it as a checklist only for IFR, not to fly the plane for me. Even though AP menu is disabled I can open the AP dialog with F11 key. Is it possible to open the Route Manager or enable the AP menu by some key or through Nasal?

Thanks!
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Re: Autopilot general

Postby Frieder » Wed Nov 04, 2020 8:44 am

No, this isn't, because the AP from that plane doesn't have as many functions as for example the AP from the MD-11. The AP of the C172p doesn't have the full ability to guide the plain along a certain route. You need to set the heading, speed and height manually with some buttons in the cockpit. You can find an AP-instruction for the C172p in the FlightGear instruction (getstart.pdf in the FlightGear\Docs directory). If you want to fly a plain with full AP-function I'd recommend the MD-11.
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