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.
curt [Thu, 22 Mar 2001 23:42:16 +0000 (23:42 +0000)]
David Luff: I've put Phil's temperature correction back in since I'm not
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 !
curt [Thu, 22 Mar 2001 16:27:16 +0000 (16:27 +0000)]
David Luff: Here is an update to the engine model. It now takes
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.
curt [Mon, 19 Mar 2001 13:56:19 +0000 (13:56 +0000)]
Fixed some problems with marker beacon range:
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.
curt [Sat, 17 Mar 2001 21:06:43 +0000 (21:06 +0000)]
Julian Foad: fixes to meters/feet confusion. (Also length of "--vNorth="
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!
curt [Wed, 14 Mar 2001 23:37:50 +0000 (23:37 +0000)]
More tweaks to radios so we can listen to Nav2 and ADF as well.
Fixed a bug which could make a station appear to be out of range when it isn't.
Expanded usable range to 1.3x times the FAA guaranteed service volume.
curt [Fri, 9 Mar 2001 23:35:21 +0000 (23:35 +0000)]
Play the full 4x VOR and 1x DME morse ident sequence at 30 second intervals.
When you tune into a station start at a "random" point in the sequence.
Sped up the words per minute to 13 to which means one sequence per about 4 secs.
This means we get through the whole sequence in about 20 seconds leaving 10
seconds of silence.
curt [Tue, 6 Mar 2001 23:59:08 +0000 (23:59 +0000)]
Patch from Tony so the FDM can trim out a specific starting location for a
joystick input, and then will ignore the actual position of that input
until the user places it in the proper position to match the trimmed position.
At that point the joystick input captures control over the value and the
value will match the joystick position from then on. This is primarily set
up so that the FDM can trim in an initial throttle position.
curt [Tue, 6 Mar 2001 19:11:28 +0000 (19:11 +0000)]
A small patch (a few lines) to add a --file option to
FlightGear, a long-standing request from Norm, and to get the UIUC
--aircraft-dir option working again.
curt [Fri, 2 Mar 2001 23:27:22 +0000 (23:27 +0000)]
Tony's patches to allow you to position yourself at an offset from the
default location (i.e. end of the runway.) This allows you to start
up on final and things like that.
curt [Thu, 1 Mar 2001 16:32:29 +0000 (16:32 +0000)]
Contributed by Dave Luff:
Added fuel-flow and total fuel to the LaRCSim model. Its still a bit
rough for now but it works, except the engine dosn't stop when fuel runs
out at the moment since there's no refuelling capability in the sim just
now. It takes about 4 gallons use before you see the fuel guages begin
to drop since there's 28 gal per tank but the guages go to 26.
curt [Sun, 25 Feb 2001 16:26:48 +0000 (16:26 +0000)]
Fixed a typo preventing the nav2 heading needle from moving.
DG heading bug initializes to a random setting.
Activating heading hold doesn't touch the DG heading bug any more.
Max autopilot decent rate is now -1000.
curt [Fri, 23 Feb 2001 22:25:03 +0000 (22:25 +0000)]
Added support for managing fov via the property manager so the --fov= option
can work again.
Removed a bit of debugging output when reading "native" IO input.
curt [Fri, 2 Feb 2001 20:55:41 +0000 (20:55 +0000)]
David Luff writes:
Basically I've rewritten the prop model along similar lines to how
Jon has done his - using published efficiency and coefficient of
power data. It works *much* better - try pulling the throttle back
to idle and putting the plane into a dive before and after updating
and you'll see what I mean. It doesn't require a fudge factor either
:-)
curt [Fri, 2 Feb 2001 05:25:45 +0000 (05:25 +0000)]
Working on ironing out issues with VOR navigation. It think we are "as
good as we can get" until we find a data source with actual VOR magnetic
offsets. We can use VOR offsets from some fixed date, but not all VOR's
were installed on the same day so no matter what date we pick we will be off on most of them.
projects / flightgear.git / log