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Getting started with Route Manager  Topic is solved

Using the autopilot is an important thing when flying airliners.

Getting started with Route Manager

Postby macnab » Tue Oct 11, 2011 5:24 am

There is plenty of information on planning a route, enetering waypoints, etc., but there doesn't seem to be an overall guide to using Route Manager. Or have I just not found it?

For example, using the Citation X, I use RM to set departure and destination airports only. A simple test. I click Actvate. The idea being that I will be turned automatically to the correct heading to overfly the destination airport. As I said, just a simple test to get started.

Now what? Do I need to set NAV1 to the destination airport's VOR? So I open up the throttle, maintain my path down the runway and then rotate. Now what? When do I "let go of the controls"?

Sorry if I seem dumb.
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Re: Getting started with Route Manager

Postby skyop » Wed Oct 12, 2011 2:09 am

You don't sound dumb at all; in fact you're asking a really good question. :)

The short answer is that the way to use the Route Manager with the autopilot will vary by the aircraft flown. For the Citation X, that means setting the autopilot to "NAV" mode and then pressing the "FMS" button above the PFD. For most other aircraft with a standard autopilot dialog, you would set the heading mode to GPS/FMS course hold.
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Re: Getting started with Route Manager

Postby macnab » Wed Oct 12, 2011 2:54 am

Thanks.

There seems to be one final step to do. After take-off, what do I do to make the RM/AP take over?
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Re: Getting started with Route Manager

Postby clrCoda » Wed Oct 12, 2011 5:19 am

Like Skyop said, it's different for each plane, but for most planes you just hit F6 and if you look in the F11 autopilot dialog to see that it is set to TRUE or GPS/FMS course hold.

MUCH LUCK!
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Re: Getting started with Route Manager

Postby macnab » Wed Oct 12, 2011 5:54 am

Citation X. Flying EHAM to EHRD via LOPEK, TOLEN, DIBRU.
Autopilot Settings - click NAV. Lateral Mode NAV-ARM.
Route Manager - create route (altitude 4000ft at all Fixes) - click Activate.
Autopilot settings now say Lateral Mode LNAV.
Click FMS above PFD.
Take off, climb to 3500ft, hit F6. No effect. RM shows LOPEK as next waypoint/ current leg, but no course change.

EDIT: The PFD shows me the heading to the next (first) waypoint, so RM is programmed. The heading is correct if I cross-check on Map. The top of the PFD shows LNAV --> VNAV, but my point is that the AP does not take control of the aircraft. There seems to be one more button that must be pressed.
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Re: Getting started with Route Manager

Postby skyop » Wed Oct 12, 2011 7:06 pm

Oh, press the AP button in the dialog.
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Re: Getting started with Route Manager

Postby macnab » Thu Oct 13, 2011 4:06 am

Got it. AP/YD buttons in the cockpit as well. Flies the route, but altitude settings ignored, even if I set AP to VNAV. Tends to lose height slowly. All the way to the ground. AP not programmed fully yet?

Should be able to manage most aircraft now. Thanks for all inputs.
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Re: Getting started with Route Manager  

Postby zakalawe » Thu Oct 13, 2011 12:03 pm

I don't think any aircraft AP supports vertical route navigation yet - and the route-manage itself only has partial support for editing waypoint altitude. There's no real obstacle - waypoints store an altitude (and speed), and the AP can read it, but nobody spent time making it work yet. (Vertical modes also tend to depend more on fuel/load and performance data from the FMS, which is an area that's been lacking, so hard to model the climb and descent profiles meaningfully)
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Re: Getting started with Route Manager

Postby macnab » Thu Oct 13, 2011 12:46 pm

I understand the problem of vertical-change programmimg. Hence the disappointment for the person who wanted FG to implement terrain-following. That must be a significant part of the cost-price of modern-day military planes.

But if I set the vertical mode of the AP to altitude hold, it does not work. Maybe not implmented fully yet. The tutorial does have a caveat that "not all modes may be implemented" without saying which ones.

I guess I will just have to learn to trim the Citation X for level flight. I don't actually want to use the AP for flying as such - want to program the RM for an interesting, winding course around a place of interest, and then use FRAPS to record videos.

The alternative is to use the c172 (which has nice large windows), make a note of the headings and turning points on a piece of paper (and then at least I'm not limited to existing waypoints). I can then fly individual legs and then use the repeat flight mode to do the video-capture. Just takes a lot longer, but at least I won't fly past the Eiffel Tower at 0.8 Mach!
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Re: Getting started with Route Manager

Postby Hooray » Thu Oct 13, 2011 12:59 pm

macnab wrote:I understand the problem of vertical-change programmimg. Hence the disappointment for the person who wanted FG to implement terrain-following. That must be a significant part of the cost-price of modern-day military planes.


Regarding terrain following, you may want to read this (which still holds true as of 10/2011) : http://www.flightgear.org/forums/viewto ... 513#p89686

In that thread, I also outlined how you could start simulating this by using some clever Nasal code, interacting with the autopilot PID controllers by using some intermediate properties. Basically, you'd need a "gradient hold" mode and a way to do proper "energy/performance management", as zakalawe mentioned already.

Computing required and actual gradients would be a no brainer in Nasal, and could be easily done using "geodinfo()" calls, given that this particular function is heavily used by the local weather system, and given that it has been optimized to be 50 times faster than it used to be, that should be a promising route.

zakalawe wrote in Thu Oct 13, 2011 12:03 pm:(Vertical modes also tend to depend more on fuel/load and performance data from the FMS, which is an area that's been lacking, so hard to model the climb and descent profiles meaningfully)


This is VERY true and probably the single most important reason why this isn't yet supported by FlightGear, which boils down to a lack of support by the FDMs (JSBsim/YaSim) actually.

If you are truly interested in the technical details: there has been a rather lengthy discussion over at the jsbsim issue tracker here: http://sourceforge.net/tracker/?func=de ... tid=369399

So far, the general consensus has been that it simply isn't yet possible in FlightGear to properly implement VNAV.

This discussion took place almost 6 years ago, and Jon (JSBsim) mentioned in 2008:
Jon wrote:I've seen the use of simple simulation within a simulation, where
performance data is being calculated. It was not within JSBSim, however.
This is an interesting prospect. Nobody has ever done this, up to now. My
initial reaction was pessimistic. However, the flight control components
within JSBSim are fairly capable, and you are permitted to define arbitrary
functions. So, my guess at this time is, yes, you should be able to set up
JSBSim to calculate *some* performance data. It may be a lot of work, but
it should be possible.


Also, 2 years ago there was an interesting discussion that took place here on the forums:

http://www.flightgear.org/forums/postin ... =6&p=51952
MAKG wrote in Thu Nov 05, 2009 5:55 pm:
flameout wrote:As far as guessing the path the autopilot will take, that will be very difficult. It tries to fly to the given parameters, but guessing where it will go on its way will be difficult.


Without being very familiar with the FG source code, the usual way to do this is to call the FDM. Isn't that sort of thing exactly what JSBSim is for?

The distinction between a flight planner and a flight simulator is the bounds on the integrations. A simulator will integrate over a frame; a flight planner much longer.



Back then, Jon mentioned that it might be possible to use some cascaded <system> controllers in JSBsim to accomplish this:

http://www.flightgear.org/forums/viewto ... 290#p52637
jonsberndt wrote in Thu Nov 12, 2009 2:48 am:
MAKG wrote:Without being very familiar with the FG source code, the usual way to do this is to call the FDM. Isn't that sort of thing exactly what JSBSim is for?

The distinction between a flight planner and a flight simulator is the bounds on the integrations. A simulator will integrate over a frame; a flight planner much longer.


Yes, this is an interesting problem. I worked on the Shuttle Abort Flight Management project several years ago. At each second during the shuttle ascent, several simulations were run quickly to determine viable abort locations at that instant and given the vehicle configuration. It has occurred to me that a JSBSim control <system> could be created that would use a simplified approach to predicting where the aircraft would be in ten, twenty, and thirty seconds into the future, based on current velocities, rates, and accelerations. I think it's possible. It would be a good exercise for someone!

jb


zakalawe is the one currently working on this, and he mentioned plans to provide the required infrastructure so that it becomes accessible from Nasal space:
viewtopic.php?f=14&t=12499#p128052
zakalawe wrote in Tue Jun 21, 2011 11:48 am:
scotth1 wrote in Tue Jun 21, 2011 9:35 am:One thing I would add is that the existing waypoints don't seem to contain enough information, I've written some more Nasal classes to handle SID/STAR/IAP, Top of Climb and Top of Descent pseudo waypoints and Altitude constraints versus FMS calculated altitudes etc.

Right, and that's the next question - I don't want to hard-code that kind of logic in C++, if I can avoid it - but we need to work out a way for Nasal to set the values into the route-manager or GPS data, so the ND can pick it up - especially all the cruise/phase-of-flight/altitude/energy stuff. I apologise for being lazy, but can you remind me where the relevant Nasal code is? Then we can have a discussion (possibly involving some other people) about which parts can be in C++, and some standard locations the ND can look for Nasal-computed value, and so on.

BTW, I'm lacking a good set of photos of the Airbus displays - the sooner I know what I need to cover, the happier I'll be - do you know of any suitable resources?



As you can see, there have been lots of discussions on this topic, doing a forum or mailing list search, you should be able to find even more pointers: viewtopic.php?f=46&t=2577&p=35664&hilit=performance+database#p35664

I guess that is one of those feature requests that really deserves its own wiki page eventually...
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Re: Getting started with Route Manager

Postby HHS » Thu Oct 13, 2011 1:23 pm

zakalawe wrote in Thu Oct 13, 2011 12:03 pm:I don't think any aircraft AP supports vertical route navigation yet - and the route-manage itself only has partial support for editing waypoint altitude. There's no real obstacle - waypoints store an altitude (and speed), and the AP can read it, but nobody spent time making it work yet. (Vertical modes also tend to depend more on fuel/load and performance data from the FMS, which is an area that's been lacking, so hard to model the climb and descent profiles meaningfully)


Look into this thread and you will see that people already tried to make the AP using vertical route navigation. The 777 makes use of the waypoint altitudes as well, unfortunately not with the VNAV-button.

Regarding climb and descent profiles: how many aircraft fdm are tuned so that act like the real one?
Last edited by HHS on Thu Oct 13, 2011 1:47 pm, edited 1 time in total.
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Re: Getting started with Route Manager

Postby Hooray » Thu Oct 13, 2011 1:34 pm

In the CRJ7000 thread, skyop came up with a neat idea to provide an advisory vnav mode, which merely displays a vertical deviation indicator for the profile to be flown. We actually exchanged a number of messages about this, and we concluded that it might be possible to come up with a working vnav implementation by combining Nasal, geodinfo() calls and some clever PID controllers.

I never looked myself into using JSBsim for this, though.
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Re: Getting started with Route Manager

Postby macnab » Thu Oct 13, 2011 1:43 pm

I'm actually only interested in altitude hold, together with fly from waypoint to waypoint. Just tried again using only ALT in the AP. Can't find any method that makes it work. Aircraft just climbs to 11000ft, noses over, and dives into the ground.
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Re: Getting started with Route Manager

Postby HHS » Thu Oct 13, 2011 1:49 pm

macnab wrote in Thu Oct 13, 2011 1:43 pm:I'm actually only interested in altitude hold, together with fly from waypoint to waypoint. Just tried again using only ALT in the AP. Can't find any method that makes it work. Aircraft just climbs to 11000ft, noses over, and dives into the ground.


Interesting how many people suddenly are interested in the Citation X.....strange :x

That's an issue with the AP of the Citation X and the author is already working on. With the link I gave there is one possible solution, some others which works as well by cascade can you find in the mentioned thread as well
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Re: Getting started with Route Manager

Postby HHS » Thu Oct 13, 2011 1:57 pm

Hooray wrote in Thu Oct 13, 2011 1:34 pm:In the CRJ7000 thread, skyop came up with a neat idea to provide an advisory vnav mode, which merely displays a vertical deviation indicator for the profile to be flown. We actually exchanged a number of messages about this, and we concluded that it might be possible to come up with a working vnav implementation by combining Nasal, geodinfo() calls and some clever PID controllers.

I never looked myself into using JSBsim for this, though.


I must admit I'm a bit confused about what people here understand under "VNAV".

VNAV is, as I understood, and wikipedia also says, just an autopilot function which controls the aircraft vertical movements.
In cruise it takes the flightplan(aka the route typed in our routre-manager), on approach and landing it follows the ILS glideslope. So a lot of aircraft including the 777 indeed doesn't simulate the right behavior, though it should be easy.

FMS just controls how this vertical movements in cruise will look: fast climb rate, thrust and engine settings, speed...
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