Martin Spott wrote:
"Vivian Meazza" wrote:
Hmmm, this behaviour is consistent with the wing stall angle being (far) too
small - the wing is stalled on the ground. Having the twist angle greater
than the incidence won't help either. If you want to try, change the wing
stall angle in the YASim config file to 17.5, [...]
You mean the
stall aoa="7.5"
entry in b1900d.xml ? I'll try that tonight when I'b back to a computer
that is capable of running FG ....
I will make a very bold statement here. Any time you see a YASim
aircraft make a sharp break and drop a wing and roll quickly, you are
seeing a stall condition ... both in positive aoa regimes and especially
in negative aoa regimes.
Even at top speeds, if you pull hard up elevator in most YAsim planes
(especially the ones that are higher performance than the cub) it's
pretty easy to get the wing angle of attack into the stall regime. What
you then see is a sharp roll and loss of altitude. If you are trying to
push the nose over and lose altitude quickly (especially if you have any
amount of flaps lowered) it's even easier to induce a negative aoa
stall. This seems to affect the bigger, heavier planes more than the
smaller nimbler planes.
These are all real world effects and YASim's stall and negative aoa
stall modeling are plausible but perhaps not always scaled right for any
particular aircraft, and the assumptions that yasim makes may not always
scale correctly with size and speed?
One thing that you should check is how many positive/negative g's you
are pulling to induce a high speed stall such as people are complaining
about. Then think about real life. A real pilot in a real airplane
will feel the g forces on their body and will have real control loads to
deal with on their stick/yoke. That naturally limits how much elevator
input they will give in some configuration.
In flightgear you might be able to pull the stick all the way back in
the middle of a high speed dive, full flaps dive; and then complain that
YAsim doesn't behave like you expected. But if you did the same thing
in real life, you might have just pulled 15 g's and be dead, with a
shower of aluminum bits floating out of the sky. And in real life you
would have stopped pulling the stick back much sooner because you felt
the g forces building.
This is an area that is all but impossible to simulate on a PC. So I'm
not saying that yasim always scales it's stall/aoa effects just right,
but do pay attention to how many g's you need to pull/push in order to
get yasim to stall/snap/spin.
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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