P=39's and flat spins.

"ArtKramr" wrote in message
...
I ran into quite a few guys who flew P-39's. The all said the same thing.
It
had dangerous flat spin characteristics. . Benig bombardier I asked,
"what the
hell is .that?" They explained. I don't remember what they said so I
can't
explain it here. But I am sure guys like Ed and Dudley can.

Flat spins are an aft cg scenario for the P39. Generally, in an airplane
with positive stability , a flat spin has to be entered deliberately and
HELD with power and aileron; the exact amounts of each differ with each type
spun flat. The P39, had a problem with aft cg movement along a very narrow
in range parameter with ammunition expenditure. If the airplane exceeded
critical angle of attack when the ammo cans were at a certain level, the
departure could easily cause an out of envelope spin mode that could go
flatter as autorational velocities and moments of inertia changed as the
spin progressed into ever increasing yaw rates.
Departure in a P39 while in this configuration was a very difficult thing to
handle. Pilots like Tex Johnston had little trouble with recoveries under
controlled conditions, but a low time pilot on operational flying could find
himself in a world of hurt if getting caught this way. It usually happened
if the airplane went defensive and turning after an initial extended firing
run air to air. If engaged and going defensive, as the speed bled due to
radial g and the angle of attack increased, a departure was imminent if you
went deep enough into the turn, especially if the turn was being forced down
by an aircraft with a lighter WS and lower corner. You could easily be
pulled into departure city in a situation like that, and this is indeed what
nailed a lot of 39 drivers. If you departed and went flat in this airplane,
recovery was NOT where the amateurs should be!!!
I should say also that most of the 39 pilots I have talked to through the
years liked the airplane after flying it for a protracted period...and that
includes Yeager! The trick was to fly it right the first time through to the
last time....and I could say THAT about every airplane I've ever flown at
least!! :-)))
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/CFI
Retired