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Implementing VNAV support in FlightGear (view source)
Revision as of 22:12, 30 November 2013
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== Problem == | == Problem == | ||
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. | {{cquote| 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 (VNAV) also tend to depend more on fuel/load and engine performance data from the FMS, which is an area that's been lacking in FlightGear, | Vertical modes (VNAV) also tend to depend more on fuel/load and engine performance data from the FMS, which is an area that's been lacking in FlightGear, | ||
so hard to model the climb and descent profiles meaningfully.</ | so hard to model the climb and descent profiles meaningfully. <ref>{{cite web |url=http://forum.flightgear.org/viewtopic.php?f=40&t=13777&hilit=performance+vnav#p140230 | ||
|title=Getting started with Route Manager | |||
|author=Zakalawe |date= Thu Oct 13, 2011 6:03 am}}</ref>|Zakalawe}} | |||
{{cquote|I've seen the use of simple simulation within a simulation, where | |||
performance data is being calculated. It was not within JSBSim, however. | 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 | This is an interesting prospect. Nobody has ever done this, up to now. My | ||
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functions. So, my guess at this time is, yes, you should be able to set up | 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 | JSBSim to calculate *some* performance data. It may be a lot of work, but | ||
it should be possible. | it should be possible. <ref>{{cite web |url=http://sourceforge.net/p/jsbsim/feature-requests/29/?limit=10&page=1#8ce6 | ||
</ | |title=JSBSim Issue#29: performance database/prediction | ||
|author=Jon S. Berndt |date= Thu Oct 13, 2011 6:03 am}}</ref>|Jon S. Berndt}} | |||
{{cquote|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 | 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. | is the bounds on the integrations. A simulator will integrate over a frame; a flight planner much longer.<ref>{{cite web |url=http://forum.flightgear.org/posting.php?mode=quote&f=6&p=51952 | ||
</ | |title=flight path trace in autopilot mode | ||
|author=MAKG |date= Thu Nov 05, 2009 11:55 am}}</ref>|MAKG}} | |||
{{cquote|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!<ref>{{cite web |url=http://forum.flightgear.org/viewtopic.php?f=6&t=6290#p52637 | |||
|title=flight path trace in autopilot mode | |||
|author=Jon S. Berndt |date= Wed Nov 11, 2009 8:48 pm}}</ref>|Jon S. Berndt}} | |||
It is 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. | |||
So far, the general consensus has been that it simply isn't yet possible in FlightGear to properly implement VNAV. | |||
It is one of those "holy grails" in FlightGear, I am not aware of any aircraft that currently support a proper FMC/CDU "progress" page - creating the page is trivial, but making it functional requires some more work - look for threads with the keywords "performance database", and you'll see that this has been talked about for over half a decade meanwhile. (computing remaining fuel vs. fuel consumption per hour is fairly trivial, but once you want to compute range, you need to be fully aware of the flight plan (speeds, altitudes) and weather/configuration (and aircraft/engine performance in particular) to make a reasonable guess at remaining range). | It is one of those "holy grails" in FlightGear, I am not aware of any aircraft that currently support a proper FMC/CDU "progress" page - creating the page is trivial, but making it functional requires some more work - look for threads with the keywords "performance database", and you'll see that this has been talked about for over half a decade meanwhile. (computing remaining fuel vs. fuel consumption per hour is fairly trivial, but once you want to compute range, you need to be fully aware of the flight plan (speeds, altitudes) and weather/configuration (and aircraft/engine performance in particular) to make a reasonable guess at remaining range). | ||
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Supporting VNAV/LNAV still is tricky for other reasons, and currently not on anybody's agenda - it's not just something that can/should be tackled by a single aircraft developer, it requires lower-level changes in FlightGear's architecture and the way FDMs are used. | Supporting VNAV/LNAV still is tricky for other reasons, and currently not on anybody's agenda - it's not just something that can/should be tackled by a single aircraft developer, it requires lower-level changes in FlightGear's architecture and the way FDMs are used. | ||
<references/> | |||
== VNAV for the 777 == | == VNAV for the 777 == | ||
First part of VNAV is the control of vertical movement of the aircraft. | First part of VNAV is the control of vertical movement of the aircraft. | ||