Major Andras wrote:
> When I try to take off with the dc3-yasim, the model seems to drag to
> one side, make the aircraft slide off the runway, and almost
> impossible to get into the air. I think that the side to which the
> drag occurs is the one whose engine was started second. It appears
> that the engine that was started first is stronger, even after waiting
> for some time with the brakes engaged after starting the engines.
Are you sure it's not just that your rudder control doesn't center
properly? You can check the engine power being developed in the
property system; the same code is used in both cases, so I'd be really
surprised if this was the case.
What I think you're seeing is the feature that *everyone* who tries
the DC-3 discovers: the DC-3 is a taildragger, and is really, really,
really (!) hard to handle on the ground. I've had zillions of
complaints about this, and have investigated every one thoroughly.
Really, there's nothing unphysical going on. The instability is an
actual feature of the real aircraft.
The reasons I can think of that the real aircraft is "easier" are:
(1) Real aircraft have feedback in the controls, so you can notice the
yaw as it happens instead of after.
(2) Real aircraft controls are far more sensitive than PC joystics
(even the best have only ~7 bits of resolution or so).
(3) YASim doesn't model prop wash, so rudder authority is lower at
slow speeds than it should be.
(4) You don't have toe brakes. At slow speeds, the only useful way to
control yaw is with differential braking. Flapping the rudder is
exactly like swinging open your car door -- it's a poor way to
turn.
(5) Really taildragger pilots are much better than sim jockeys.
> Another issue is that, on landing with the dc3-yasim at a rather
> high speed (so that the angle of attack is near 0), the tail
> instantly falls onto the runway, but the aircraft nevertheless
> doesn't take off again, although the angle of attack just increased
> rapidly. Although I haven't ever been in a real-world taildragger, I
> don't think this is normal behaviour.
This one sounds weird and buglike. I'm not sure I can reproduce it,
however. The reason that the tail falls "instantly" onto the runway
is that the gear are forward of the c.g., and you didn't set it down
gently enough. :) Neither JSBSim nor YASim have any special case
ground handling, so if your intuition is to look for this kind of bug
as you do in some consumer sims, you're likely to be misled.
When I land the plane, I routinely get many bounces (I'm not very good
at landing taildraggers). Are you absolutely sure you're seeing zero?
Is it possible you're just not hearing the tire squeal sound being
played? The sound code has gone through some changes lately and I've
seen some sounds being missed, I think.
Andy
--
Andrew J. Ross NextBus Information Systems
Senior Software Engineer Emeryville, CA
[EMAIL PROTECTED] http://www.nextbus.com
"Men go crazy in conflagrations. They only get better one by one."
- Sting (misquoted)
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