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;)
+ 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.
