[Flightgear-devel] amazing FDM initialization bug

[John D. <js...@av...>]

I've been trying to use the         
    <command>presets-commit</command>
feature ... with less-than-satisfactory results.

All I wanted to do is pop the aircraft into the air, with a
reasonable airspeed, attitude, et cetera.

Note that I set presets/trim {BOOL} = 0 since the trim was 
known to be already OK, and because of numerous longstanding
bugs in the FDM "initial trim" code.

The presets (as shown below) look reasonable to me.  Is 
there something else/different I should have done?

Note that there are two dumps following the presets-commit.
The first one shows that my presets have not been applied.
That's slightly strange.

The second one, taken about half a second later in real time,
shows zero elapsed sim time, and shows that the airspeed preset 
has been applied ... but the attitude has been trashed.  A
roll angle of 179 degrees is more excitement than I really 
wanted.

  Note that if you set presets/trim {BOOL} = 1 the 179 degree
  bank angle is not observed.  (But there are other bugs in
  this case.)

As far as I can tell, <command>presets-commit</command> just
deletes the old FDM instance and creates a new one, using
the basic plain-vanilla constructor.

Let me know if you want to discuss what the dumps below 
seem to be saying.  There's so much weird stuff in there
that I hardly know where to begin.

This is a fairly new bug.  A year ago setting presets/trim=0
worked OK.  It worked much better than presets/trim=1.

Bottom line:  The goal is simple:  being able to initialize 
the aircraft in the air, with position, airspeed, and
attitude specified somehow (preferably via the presets).  
Is there a reasonable way to do that?




sim-time-sec {DOUBLE} = 24.04999999999927
presets {NONE} = nil
presets/airport-id {STRING} = KSFO
presets/runway {STRING} = 
presets/longitude-deg {DOUBLE} = -9999
presets/latitude-deg {DOUBLE} = -9999
presets/altitude-ft {DOUBLE} = 5000
presets/heading-deg {DOUBLE} = 45
presets/roll-deg {DOUBLE} = 10
presets/pitch-deg {DOUBLE} = 1.229999999999999
presets/speed-set {STRING} = knots
presets/airspeed-kt {DOUBLE} = 100
presets/mach {DOUBLE} = 0
presets/uBody-fps {DOUBLE} = 0
presets/vBody-fps {DOUBLE} = 0
presets/wBody-fps {DOUBLE} = 0
presets/speed-north-fps {DOUBLE} = 0
presets/speed-east-fps {DOUBLE} = 0
presets/speed-down-fps {DOUBLE} = 0
presets/onground {BOOL} = 0
presets/trim {BOOL} = 0
presets/glideslope-deg {STRING} = 
presets/fix {STRING} = 
presets/vor-id {STRING} = 
presets/ndb-id {STRING} = 
presets/offset-distance-nm {STRING} = 0.000000
presets/offset-azimuth-deg {DOUBLE} = 110.7116387240434
                                                                    [presets-commit happens here]
Could not open and/or write the state to the initial conditions file.
  Model Author:  Stuart Buchanan
  Creation Date: 2002-01-01
  Description:   Cessna C-182RG

sim-time-sec {DOUBLE} = 0                                            [immediately after re-init]
orientation {NONE} = nil
orientation/heading-deg {DOUBLE} = 27.70999999999999                 [not what was preset]
orientation/roll-deg {DOUBLE} = 0.08095551707843034                  [not what was preset]
orientation/pitch-deg {DOUBLE} = 2.718684952896526                   [not what was preset]
orientation/heading-magnetic-deg {DOUBLE} = 345.6057622845355
orientation/side-slip-deg {DOUBLE} = 0
orientation/roll-rate-degps {DOUBLE} = 0.0005473922565879074
orientation/yaw-rate-degps {DOUBLE} = -0.01218395201758949
orientation/side-slip-rad {DOUBLE} = 0
orientation/yaw-deg {NONE} = nil
orientation/alpha-deg {DOUBLE} = 0
orientation/pitch-rate-degps {DOUBLE} = 7.093092084187309e-05
velocities {NONE} = nil
velocities/uBody-fps {DOUBLE} = 0.003090427771287167
velocities/vBody-fps {DOUBLE} = 0.0005683758212642014
velocities/wBody-fps {DOUBLE} = 0.0005262248631193597
velocities/speed-north-fps {DOUBLE} = 0.001333718179877819
velocities/speed-east-fps {DOUBLE} = -0.002789310675198497
velocities/speed-down-fps {DOUBLE} = 4.824056942942207e-05
velocities/airspeed-kt {DOUBLE} = 0.001832510492080997                [not what was preset]
velocities/mach {DOUBLE} = 2.854210378868731e-06
velocities/vertical-speed-fps {DOUBLE} = -4.824056942942207e-05
velocities/groundspeed-kt {DOUBLE} = 0.00183182522265024
velocities/glideslope {DOUBLE} = -0.01560161773528911

sim-time-sec {DOUBLE} = 0                                             [about 1/2 sec later in Real Time]
orientation {NONE} = nil
orientation/heading-deg {DOUBLE} = 207.71                              huh?
orientation/roll-deg {DOUBLE} = -179.9190444829216                     huh?  ouch!!!
orientation/pitch-deg {DOUBLE} = -0.8938671342377535                   huh?
orientation/heading-magnetic-deg {DOUBLE} = 193.3139562806539
orientation/side-slip-deg {DOUBLE} = 1.430990725275705
orientation/roll-rate-degps {DOUBLE} = 0
orientation/yaw-rate-degps {DOUBLE} = 0
orientation/side-slip-rad {DOUBLE} = 0.02497549972156269
orientation/yaw-deg {NONE} = nil
orientation/alpha-deg {DOUBLE} = 0.01208755310379969
orientation/pitch-rate-degps {DOUBLE} = 0
velocities {NONE} = nil
velocities/uBody-fps {DOUBLE} = 168.6457910316456
velocities/vBody-fps {DOUBLE} = 0
velocities/wBody-fps {DOUBLE} = 0
velocities/speed-north-fps {DOUBLE} = -149.2860547187637
velocities/speed-east-fps {DOUBLE} = -78.41017115482961
velocities/speed-down-fps {DOUBLE} = 2.630923538625738
velocities/airspeed-kt {DOUBLE} = 99.99953147298541                   [approx what was preset]
velocities/mach {DOUBLE} = 0.1510822108137365
velocities/vertical-speed-fps {DOUBLE} = -2.630923538625738
velocities/groundspeed-kt {DOUBLE} = 99.90773989504333
velocities/glideslope {DOUBLE} = -0.01560092456781494