I've added reheat to the engines to simulate water injection and then tweaked
it so that it's just about possible to take off with the full fuel load/ferry
configuration (a little under the mtow - 420,000lbs vs 450,000lbs).
It's interesting to note that the normal combat tow for the F model was
291,570lbs - equivilent to a fuel load of about 0.46 (this would actually
leave you with more fuel than in real life because some of that weight would
be the weapons load but here it's fuel)
Anyway, I've added all this info to the readme and explained some of the
reasoning behind the fdm there.
It still doesn't reach the correct altitudes, and certainly not with a full
fuel load, but it starts getting into the right ball park at combat tow.
Here's an update to the yf23. I've added a couple of small details to the
model and played with the textures a bit:) Still no response from the chap
at NASA about sticking their logos on it yet.
I've also been fiddling with the fdm. It had been bugging me that I couldn't
find any sign of air/speed brakes but just recently I found that braking is
done by moving the ailerons up and the flaps down, in opposition to each
other, which I thought was pretty neat really.
This was actually pretty easy to mimic - although there are no spoiler
surfaces defined in the YASim wing entry I was still able to map the spoiler
control input to the ailerons and flaps, and once I'd got the directions
right it seems to work - hit the spoilers and the ailerons move up, the flaps
drop and the energy worm shows that I'm losing speed.
The downside is that the flaps and the ailerons have to have similar lift and
drag characteristics, to balance each each other, and this means that it ends
up with the flaps not giving much lift and the brakes not having much affect
at low speeds. If I could change the deflection rates then I could balance
them that way (and improve the rudder control too) - as it is, the deflection
for the flaps and ailerons is the same, just in opposite directions. This
sounds like a job for interpolation tables but I haven't tried them yet and I
don't know if I can use them in this way in YASim.
The opposing flap/aileron techique is also used for manuevering e.g. by using
it on just one side but I haven't tried to incorporate that yet;)
Landing it is proving to be tricky - it gets down smoothly to about 20ft then
what I presume is ground effect kicks in and upsets the trim. The only
answer appears to be to force the nose down at this point. What's more, it
needs to be held down untill you trim the elevator out otherwise it'll
happily roll along on it's main gear, with it's nose in the air:) There's
definitely not enough drag either.
I've been messing with the yf23 some more. I think it flies a bit better now
and has more reasonable auto-pilot take-off characteristics - just apply full
power and go, and it doesn't go into such a steep climb.
Out of curiosity, I've also taken the rudder control input and linked it to
the stabilators/elevators and ailerons. Now, with some slick joystick
manipulation it's possible to fly it at about 30 deg off-axis in more or less
level flight (actually, with full 'rudder' input, it looks nearer to 40 deg
to me and you end up tracing a very long curve).
If no rudder input is used it flies 'normally'.
I'd like to be able to 'tune' it so that it's more stable while transitioning
but I'm not sure if that's going to be possible. It's also high-lighted some
problems I'm having with my Sidewinder joystick - when I use the rudder
control, the engine No.2 throttle jumps to 50% unless auto-throttle is
engaged (this also happens with the b52 too), and there seems to be some
interaction between the different axis if all three (roll, pitch and rudder)
are changed at the same time - difficult to be sure on that one though.
I'll probably un-map the throttle control from the joystick as I tend to use
the keyboard for engine control anyway, especially for landing.
Here's a quick update to the yf23 fdm and auto-pilot settings. It flies and
takes-off reasonably well - still haven't tried landing it yet;) It can
still be a bit wobbly at times though and It's not very good at terrain
following either.
Taking off on auto-pilot is quite fun. Set full flaps and CTRL-a (assuming
you're near sea level), hit F6 to make it go straight and apply power - about
50% until it rotates then apply full power. Retract the gear as soon as it
gets off the ground and by the time you#ve done that, retract the flaps.
Quite entertaining from a tower view:)
It's not really an ideal a/c to model but apart from the aesthetics, which
appeal to me, I was curious about not having a rudder.
There's a new texture sheet too but it only makes the a/c a paler shade of
grey.
I've attached an update for the yf23 and I think I've included all the right
files - the model is unchanged (I think I'll eventually paint it in an
imaginary NASA scheme, perhaps a bit like the HIDEC F-15, until I can get
some newer pictures and see what they've done with it) so I've not included
it again.
The fdm still needs quite a bit of work - it can be a bit twitchy and wobbly
at times, and the auto-pilot roll-out and smooth need tightening up, but it's
flyable. Haven't tried landing it yet though;)
here's an update to the b52 - it's just some relatively minor changes to the
fdm and panels.
I've been trying to improve the take-off and landing characteristics, or at
least get them to fit the pictures and film I've seen.
The best way to take off is by using the autopilot - at sea level just extend
the flaps, punch in the altitude hold on the autopilot (and heading if you're
lazy), and apply full power. It'll also take of with the default the default
elevator trim of -0.07 but it 'staircases' a little bit - the auto pilot
smooths that out.
I've included some notes and observations about taking-off and landing in the
readme.
While I wouldn't claim any sort of accuracy for it, I hope it manages to get
some of the characteristics right.
much what i've seen p-51d's do. Be careful of spins.
Added vstab incidence (real ones have it) thus improving takeoff behavior.
Reduced turbo-mul to what it probably should be.
Returned wing camber to Andy's estimate.
Increased flap drag. And tried making adjustments to get the thing to not
glide so impossibly far.
Corrected empty + pilot aircraft mass to 7190.
Upped "cruise speed" to maximum operational speed of 380 knots.
Reduced prop pitch at cruise to 0.8 (3000 rpm is only for takeoff).
Changed camber to 0.01 (found reference that said 1%)
Decreased tail surface effectiveness slightly just to get better numbers.
Changed turbo-mult to 2.5 and wastegate-mp to 30
Changes:
Fit the solver to the known stall speed instead of an abstract
approach configuration. That is, specify stall AoA and speed as
"approach" values. At approach weight (20% fuel) I can now just
barely hold the aircraft in the air without losing it at 87 kias.
Note that the IAS guage seems to have a slight calibration error, it
was reading something that looked more like 95 knots; I got the real
value out of the property browser.
Change the sign of the incidence value for the wing. It specifies a
rotation about the axis pointing out the left wing, so positive values
are "nose down".
Increase the "effectiveness" of the tail surfaces quite a bit.
Smaller surfaces do actually need higher values. YASim scales surface
force coefficients with their areas, which is correct within a single
wing. But between wing-like devides, generated forces kinda/sorta
scale linearly with their spans. This is particularly important for
tail draggers, since YASim's lack of prop wash modelling needs to be
offset by extra elevator authority.
Add a camber value to the wing. Most wing airfoils are asymmetric,
and produce non-zero lift at zero AoA. I picked 0.1 (10% of stall
lift at zero alpha) as a reasonable guess. If someone has airfoil
data for the Mustang we could look this up exactly. This was the
biggest change, which allows the cruise AoA to be much lower than
approach or stall.
Reduced the compression value for the tail wheel to 20cm. These
things are very stiff; they "compress" only as much as the tires do.
Even 0.2 is too much motion, but the numerics tend to go wacky when
you give them very high spring coefficients. This helped the ground
handling a little bit.
Removed the extra damping from the main gear. My impression of tail
draggers is that they tend to have "squishy" main gear. Again, this
(subjectively) seemed to improve ground handling to me. I also tried
reducing the spring constants to 0.5, but that ended up being too
squishy -- you could see the ship (stopped on the ground) bank to the
left by 2-3° when you pushed the throttle forward.
Ground handling is still pretty difficult; I get the best results by
holding the tail down until 90 knots or so and then very gently
lowering the stick. The aircraft bobs once or twice and then lifts
off. I don't think this is proper procedure, though.
Andy
Changes:
Fit the solver to the known stall speed instead of an abstract
approach configuration. That is, specify stall AoA and speed as
"approach" values. At approach weight (20% fuel) I can now just
barely hold the aircraft in the air without losing it at 87 kias.
Note that the IAS guage seems to have a slight calibration error, it
was reading something that looked more like 95 knots; I got the real
value out of the property browser.
Change the sign of the incidence value for the wing. It specifies a
rotation about the axis pointing out the left wing, so positive values
are "nose down".
Increase the "effectiveness" of the tail surfaces quite a bit.
Smaller surfaces do actually need higher values. YASim scales surface
force coefficients with their areas, which is correct within a single
wing. But between wing-like devides, generated forces kinda/sorta
scale linearly with their spans. This is particularly important for
tail draggers, since YASim's lack of prop wash modelling needs to be
offset by extra elevator authority.
Add a camber value to the wing. Most wing airfoils are asymmetric,
and produce non-zero lift at zero AoA. I picked 0.1 (10% of stall
lift at zero alpha) as a reasonable guess. If someone has airfoil
data for the Mustang we could look this up exactly. This was the
biggest change, which allows the cruise AoA to be much lower than
approach or stall.
Reduced the compression value for the tail wheel to 20cm. These
things are very stiff; they "compress" only as much as the tires do.
Even 0.2 is too much motion, but the numerics tend to go wacky when
you give them very high spring coefficients. This helped the ground
handling a little bit.
Removed the extra damping from the main gear. My impression of tail
draggers is that they tend to have "squishy" main gear. Again, this
(subjectively) seemed to improve ground handling to me. I also tried
reducing the spring constants to 0.5, but that ended up being too
squishy -- you could see the ship (stopped on the ground) bank to the
left by 2-3° when you pushed the throttle forward.
Ground handling is still pretty difficult; I get the best results by
holding the tail down until 90 knots or so and then very gently
lowering the stick. The aircraft bobs once or twice and then lifts
off. I don't think this is proper procedure, though.
Andy
I've done a new Sea Hawk. Well, the model and the fdm aren't new, just
slightly modified, but I've incorporated some more animation stuff and tried
a different way of texturing it.
The animation additions are things I worked out for the YF23 (still can't get
it to fly again) - mostly u/c related stuff.
This actual aircraft (WV908) is in the Royal Navy Historical Flight and so is
kept unusally clean;) In the photographs I looked at, hardly any fuseage
panel lines were visible so I've not tried to include any. Instead of the
normal fuselage side views and wing plan textures I've just used fairly
high-res detail 'patches' for the markings, applied to 'carrier' objects.
This is much more like the way I'd do things if I was working on a picture in
my 3d software - there I'd apply multiple textures to an object, as required,
using scope and priority settings to get what I want. With .ac format models
you can only apply a single texture to an object - hence the need for the
carrier objects. These are sections of the underlying 'real' object that
have been moved out/away from from the original object surface so that they
cover them.
The pros are 1) the resolution of the details is much higher - have a close
look at the Ace of Diamonds art on the nose and on the bit that sticks out of
the front of the tail-fin (I don't know the proper name for this), and 2)
less texture space is needed.
The most obvious con is that there's more potential for z-buffer problems. I
notice that whilst on the ground (in chase view), there appears to be
z-buffer fighting for the texture patches but once the a/c has taken off and
has got to about 200ft or so, it clears up. I've no idea why this should
happen as I'm not changing any of the view settings.
There are a few things I still need to figure out in this respect - I think
there's an issue with graduated textures - they seem to get reduced to 16bpp
and show a lot of banding that's absent on the texture and the model appears
inverted from tower views, at least in 16bpp, but ok from the chase view, and
stuff like that.
I said that the model and fdm aren't new but they have been modified a bit.
I've only reduced the approach aoa in the fdm but the model, whilst basically
the same, has had quite a few changes to accomodate the new u/c and texture
patches. It also got into FG by a slightly different route - I found that
AC3D would support polys with > 3 sides and after looking at and comparing
.ac and .obj file formats (I can export from RS3D in .obj format) I wrote a C
prog to convert .obj format files into .ac format files. It's a nasty bit of
hackery that even uses a temporary workfile (LOL), and it will only work with
the simplest of .obj files (e.g. no vertice normal or texture info) but it
allows me to export the model geometry in .obj format, convert it, and load
it straight into AC3D without turning everything into triangles or flipping
face normals.
The funny thing is that objects that consist of just a single rectangle (e.g.
an aileron or flap surface) are not recognised by FG and they have to be
split into two triangles, and once the model's loaded up into FG I can see
from some of the rendering artifacts that it's all still reduced to triangles
prior to display anyway. Still, it saves me from having to do a lot of face
flipping.
Really, the texturing method is experimental and I hope I get some feed-back
on it regarding display and performance issues. Ultimately, I'd like to try
to reduce the texture size down from 512x512 to 256x256 - nearly half of the
current texture 'space' is unused.
+ The wing stall angle was weird, as mentioned earlier. Values
greater than 45° don't have much physical meaning. I changed it to
25, which should be closer to a realistic value.
+ The lift="1.1" on the elevator flaps wasn't quite enough to get the
aircraft into the approach AoA. I changed it to 1.2, and it works.
It's still not as responsive as I'd have expected (then again, this
is a big aircraft...).
+ The hstab effectiveness was negative. This is wrong, as this is a
multiplier for all force generated by the surface. A surface with a
negative value will produce thrust instead of drag. :) Maybe this
was needed because the elevator was rigged backwards somewhere else?
I changed it
+ The wing and hstab had very small stall widths (very sharp stalls).
Low aspect wings should have gentle stalls, not sharp ones. I
changed it to 15 as a guess.
+ There's no rudder input mapped. This can be done with a "split"
input to the tails in exactly the same way that the aireron works on
the wing. It will simply add to the elevator input. V-tail
Bonanzas will require the same treatment.
elevator and trim give ridiculously high airspeeds.
Increase the elevator effectiveness slightly.
Increase the vertical stabilizer effectiveness, and give it a 1.5
degree incidence angle, to compensate for asymmetric propeller
effects.
Increase the rudder effectiveness to help with cross-wind takeoffs and
landings.
Here're some updates for some of the instruments, the TSR2 and the B52.
The instruments are just parameterised/non-specific versions of the engine
and fuel gauges. The old gauges will still be used by the a10s and the sea
hawks until I get them done.
There're a couple of tweaks to the tsr2 yasim config and amendments to the
model file to change the angle at which the airbrakes operate, correct the
direction that the nose gear retracts/extends and to rotate the main-gear
carts during retraction/extention. There're also new panels, using the new
instruments.
The b52 yasim config has some big changes due to finding some more info i.e.
wing incidence of 6 degrees, fuel capacities and aileron changes (removed
from G & H versions!). It's now based on an 'F' model and I've put some
comments in the yasim config about it. The b52-readme.txt includes a
suggested method on getting airborne;). I've included an amended model -
B52-F.3ds, which is the default in the new model file, and a couple of panels.
I'm quite pleased with the b52 - the take-offs resemble the photographs I've
seen and I think I've got reasonable values where I've had to guess at stuff,
but the results from the yasim solver look as through the model is
approaching the limits of acceptability for yasim. By this I mean that the
model is probably a bit dodgy, not that the yasim solver is limited.
speed/cruise speed setting was better and I've reverted to that - they were
too fast at altitude:) They are closer using Andy's figure.
They don't quite have the required range though:(
