AJ MacLeod wrote:
On Thursday 03 November 2005 11:28, Shelton D'Cruz wrote:
Anyone else notice a strange problem with the Citation II - after a while
flying her, she will all of a sudden go up and down in a yo-yo fashion -
only happens to the Citation.
Yes, I noticed it before. It's a known problem, I think - a pity too because
the 3d model and cockpit are so nicely done...
Is this with the autopilot on?
YAsim has a 'feature' such that when a wing gets in a negative aoa
regime, it stalls *far* more quickly than in the positive aoa regime.
This is my analysis based on my observation (lacking any formal
aeronautical engineering training.) So what happens is as you speed
goes up, the aoa required to maintain level flight gets lower. At
really high speeds the aoa gets really tiny, and then small disturbances
or small control input can put you in a negative aoa situation and
<WHAM> you get a "negative" incidence stall (or whatever that might be
called.) If the autopilot is engaged, the wing leveler can often hold
the wings level during a hard negative stall, but your pitch obviously
goes a bit crazy. If you have the altitude hold on when this happens,
it really has to chase to catch up and level things back out.
So far no one has been able to spot the reason why negative aoa stalls
happen so much earlier than positive aoa stalls ... maybe a sign
someplace that should be flipped?
This is my biggest beef with the yasim flight model. It works great in
most regimes, but if you ever get in a situation where you are over
speed (very low aoa) or if you are trying to push the nose down to drop
altitude on an approach (for instance) you can get these wild negative
aoa stalls when you least expect them. Adding flaps seems to change the
nature of the wing and make this problem happen at slower speeds.
Curt.
--
Curtis Olson http://www.flightgear.org/~curt
HumanFIRST Program http://www.humanfirst.umn.edu/
FlightGear Project http://www.flightgear.org
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