hope, with earlier versions as well)
- support for the new LONG value type
- gear support for UIUC (updated for the newly renamed SG_* stuff;
otherwise identical to what I sent you before)
- fixed reported MSVC problem in src/FDM/flight.cxx
I have created a set of patches to provide configurable landing gear
for the UIUC models. The patches (including four new files) are
available at
http://megginson.com/private/fgfs/uiuc-20010309.tar.gz
A modified UIUC configuration file for the Twin Otter (DHC-6) is
available at
http://megginson.com/private/fgfs/aircraft.dat
It should be possible to configure appropriate gear for all of the
UIUC models now. As a bonus, the models also support braking, both
absolute and differential, as well as nose-wheel steering (all of
which are currently missing from the UIUC models) -- when you land,
you don't have to keep rolling off the end of the runway anymore, and
you don't have to bank to steer in a taxi.
My sample configuration file contains absolutely bizarre, wild
guesses, and many places that I didn't even bother to guess properly.
The only actual data I had was the wing-span of the DHC-6 (65ft),
which I used for positioning the wing tips. The wing-tips for this
model actually work now -- I hit the aileron hard while accelerating
for take-off, and the wingtip noticeably strikes the ground and
bounces up (quite dramatic in external view using the DHC-6 model from
Wolfram's site).
Details
-------
The UIUC models now support up to 16 gear points each where a gear
point is anything in the aircraft that can come in contact with the
ground, including the tail and wing-tips. I have added the following
new fields to the UIUC configuration files, where <index> is an
integer between 0 and 15, and <value> is a real number:
gear <index> Dx_gear <value> # x offset from CG [ft]
gear <index> Dy_gear <value> # y offset from CG [ft]
gear <index> Dz_gear <value> # z offset from CG [ft]
gear <index> cgear <value> # spring damping [lbs/ft/sec]
gear <index> kgear <value> # springiness [lbs/ft]
gear <index> muGear <value> # rolling coefficient
gear <index> strutLength <value> # gear travel [ft] (not yet used)
Most of these names were already pencilled into the UIUC documentation
(as TODO items), but I had to make up Dx_gear, Dy_gear, and Dz_gear --
if those are inappropriate, I'd appreciate suggestions for better
names.
It will be necessary to modify the other UIUC configuration files to
include some kind of gear support as well, or the planes will sink
nose-first into the ground down to their CG's (it's actually quite
funny to watch with an external view).
Background
----------
As I frequently remind everyone here, I have no math background worth
spitting at, so I will not even pretend to have done the hard stuff.
The UIUC code uses a copy of a very old version of the LaRCsim
c172_gear.c -- I wanted to update it with Tony Peden's excellent newer
version, which includes differential braking among other goodies (the
UIUC models don't support brakes, period).
I copied the newer code into uiuc_aero.c, and it compiled and ran, but
all of the planes ended up sitting on their tails with their noses in
the air. Since Tony made his gear code nicely parameterized, I
experimented with different values, and found that it wasn't too hard
to balance the Twin Otter by moving the gear back a bit. At first, I
used properties to set different values, but then I decided to
integrate the whole thing properly into the UIUC configuration
framework. Thanks to Tony Peden, who did the real modelling work -- I
can take credit only for two or three hours of integration. It turns
out that Tony's code is generalized enough to deal with a wide range
of different gear structures -- I suspect that it will even work for
the 747, when I get around to trying some values.
implicitly correcting for that yet. The plane now makes it to 11000ft on
autopilot *slowly*. I think I'll have to look at the prop parameters
next - altering the diameter and blade angle just slightly can have
quite an effect. If you want to play then try changing the values
prop_diameter and blade_angle in FGNewEngine::init. Keep blade
angle between 20 and 25 (since those are the only values for which
I've entered data and I interpolate between them) and ignore
FGProp1_Blade_Angle since that's an old variable that isn't used. I
really ought to read all the engine and prop parameters from file to
avoid recompilation when tweaking !
the actual air pressure and temperature from the LaRCSim model
instead of assuming that it is at sea level as before. This has
reduced the ceiling from over 60000 ft to about 9000 ft. This is a bit
low (should be around 13 - 14000 ft I think) but I still have some
stuff to do with the engine power correlation and its ignoring the
temperature at the moment so I'm not panicking yet :-)
I've also changed the mixture-power correlation to one from a
published paper since the curve from the IO360 manual seemed to
be a load of rubbish, and didn't have any numbers on the mixture
axis anyway.
I've also knocked the full rich mixture down a touch in line with
Riley Rainey's recommendation, and cleaned up the code a bit.
a) I was compairing feet vs. meter (making the range 3x too. big)
b) I was using the diameter in place of the radius (making the range an
additional 2x too big.)
c) Updated the equation for calculating range to model the weak transmitter
not being picked up at upper altitudes.
We still might need some additional tweaking, but I think we are starting to
get in the right ball park.
is 9 not 8.) Note that the initial altitude setting was placing us way below
the ground, but as it doesn't seem to have caused us problems, it's probably
redundant!
