20,741
edits
Implementing VNAV support in FlightGear: Difference between revisions
Jump to navigation
Jump to search
m
Implementing VNAV support in FlightGear (view source)
Revision as of 19:23, 3 December 2013
, 3 December 2013→YaSim
m (→YaSim) |
|||
| Line 158: | Line 158: | ||
== YaSim == | == YaSim == | ||
{{cquote| | {{cquote|VNAV stuff-- An interesting problem. | ||
<ref>{{cite web |url= | |||
|title= | A large part of what the YASim solver does is pre-calculate an elevator incidence such that the aircraft can fly at "cruise" with neutral elevator and also have sufficient elevator throw to meet the "approach" criteria. Lift/weight and drag/thrust are held in static equilibrium, and the solver plays with stabilizer and elevator settings to meet the constraints. Essentially it's looking to balance pitching moments at both approach and cruise ends of the flight envelope. This is why in a YASim aircraft you do not set the elevator incidence-- the solver sets it in order to guarantee an aircraft that is more-or-less controllable. | ||
|author= |date= }}</ref>| | |||
Since the solver is essentially validating the aircraft at two predicted flight attitudes (approach/cruise), this suggests that someone could probably create similar routines to specify top-of-descent and bottom-of-descent parameters, feed in some additional constraints for wind vector, time, and desired flight economy profile, and have the revised solver return pitch and thrust requirements. Where the current solver assumes weight/lift at equilibrium, I'm going to guess it would probably iterate to find the appropriate weight/lift ratio that results in the correct altitude change over the time period. Once it finds one it returns the pitch/thrust settings used, else it aborts. It would be a messy little project, but I think it would be doable. | |||
I would not envy anyone trying to do this. The YASim code base is, um, a bit challenging and has very little documentation. | |||
I suspect this wouldn't work well as a run-time flight predictor, the YASim solver has to crunch a lot of numbers, but I'm guessing it could be used to build a database of profiles. | |||
Assuming YASim elements could be hacked/revised to do this, I suspect such solutions would at best be ballpark approximations compared to the same profile flown in the actual simulator. They'd need to be verified with actual flight tests, and if someone is going to bother to properly conduct and log such tests, it makes the point of the solver a little questionable. Maybe I under-rate the possibilities or it could be refined over time, I dunno. | |||
Also, VNAV profile data for any particular YASim aircraft would have to be re-built every time someone made a change to the YASim FDM. Seemingly minor FDM tweaks can have major YASim impacts, particularly if the developer isn't very experienced or knowledgeable with YASim. So VNAV data and the YASim aircraft FDM version would have to be tightly coupled. If someone commits a Git change to the aircraft's FDM, then the VNAV DB for that plane is hosed until it's re-calculated.<ref>{{cite web |url=http://forum.flightgear.org|title=YaSim vs. VNAV (by PM) | |||
|author=Buckaroo |date=Mon Dec 02, 2013 9:38 pm }}</ref>| | |||
}} | }} | ||
== JSBSim == | == JSBSim == | ||