P=39's and flat spins.

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.

Arthur Kramer
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer

"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

"Dudley Henriques" wrote in message
rthlink.net...

"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.

Dudley, do you mean to say that the center of gravity is usually designed
such that the airplane avoids a tail slide in a stall? In other words, the
nose rolls over and airspeed increases?

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!!!

Like being sucked into a black hole?

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!! :-)))

All the thrills of your own airplane out to kill you and people shooting at
you too!

jpt

Subject: P=39's and flat spins.
From: "Dudley Henriques"
Date: 7/14/03 11:44 AM Pacific Daylight Time
Message-id: ink.net


"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

Ah greater wisdom was never spoken The guys I spoke to(1944) had a few unkind
words about sitting in front of the engine as well. Thanks for the clear
rundown. I understand it now and it only took me 60 years... Too bad the AAC
wasn't made up of only Chuck Yeagers. (grin)

Arthur Kramer
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer

Dudley Henriques wrote:
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.

So... what you're saying is, the flat spin recovery technique was to
pull the trigger and start shooting...? :-)


Jeff

Subject: P=39's and flat spins.
From: "Dudley Henriques"
Date: 7/14/03 11:44 AM Pacific Daylight Time
Message-id: ink.net


"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


Thanks Dudley. I got it now, And it only took me 60 years. These guys also had
a lot of bad things to say about sitting in front of the engine. It resulted in
some very gory crash landings.

Arthur Kramer
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer

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
Dynamite paperback re the P39: "Nanette" by Edwards Park, Smithsonian
Institution Press, 1977. Really great.

Quent

"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.

Arthur Kramer

Was this flat-spin condition related in any way to an equally-distressing
condition I've been told about called the "tumble", in which the P-39
allegedly could flip end-over-end (i.e., swap ends, or tumble,
tail-to-front) if sufficient Gs were pulled in turns? Apparently, the
aircraft's wings would completely lose their grip on the air or vice versa.
Ostensibly, this "tumble" was a bugaboo unique to the P-39. At least, I've
never heard of it being associated with its P-63 successor....

Tumblin' P-39s

I've read the factory findings about the in depth testing done to determine
whether this condition actually existed and if so, how to correct it. No
amount of adjustment resulted in the factory test pilots to duplicate the
manuever described by so many combat pilots. Frustrated, the factory asked the
air corps to provide one or more combat pilots who said they had encountered
'tumble' to come to the factory and assist in recreating the situation
necessary to cause it. After several test flights with various data points
matching what the combat pilots reported, no one was ever able to force a P-39
to tumble. I read this in a 'lessons learned'-type report generated after the
extensive testing had been completed.

v/r
Gordon
====(A+C====
USN SAR Aircrew

"Got anything on your radar, SENSO?"
"Nothing but my forehead, sir."

"Gordon" wrote in message
...
Tumblin' P-39s

I've read the factory findings about the in depth testing done to
determine
whether this condition actually existed and if so, how to correct it. No
amount of adjustment resulted in the factory test pilots to duplicate the
manuever described by so many combat pilots. Frustrated, the factory
asked the
air corps to provide one or more combat pilots who said they had
encountered
'tumble' to come to the factory and assist in recreating the situation
necessary to cause it. After several test flights with various data
points
matching what the combat pilots reported, no one was ever able to force a
P-39
to tumble. I read this in a 'lessons learned'-type report generated after
the
extensive testing had been completed.

I think the "tumble" stories were a direct result of what uninitiated and
green pilots encountered when they caused the Cobra to depart while coupled
into accelerated stall and an extreme rearward cg due to the gun cans
problem. An accelerated departure in any fighter can be "interesting".
With the cg aft far enough, the airplane can exhibit some wild antics as it
goes through post stall and develops increasing yaw rates. With roll
introduced as this is happening, I wouldn't be at all surprised with a very
high disorientation factor in a young inexperienced pilot in this airplane.
It would be quite easy for an inexperienced pilot to interpret these wild
antics as a "tumble"!!!
I don't see any way the airplane would have swapped ends though. To do this
requires a tremendous impetus force and a very high energy state, which
would be inconsistent with the aerodynamics found in an ever decreasing turn
radius caused by a decreasing TAS through the arc of the turn as angle of
attack increased up to and past CLmax causing a departure. The resulting
stall from this attitude would most likely have been fairly violent in the
Aircobra with an aft cg, and depending on where the ball was as the stall
commenced, either a high wing roll off or a low wing roll off into the
departure would have been a possibility in the P39, which had positive
static and dynamic stability when in the cg envelope, but with the cg aft
due to ammo expenditure, that roll off could easily have scared the living
crap out of an amateur! In the disorientation through the departure, through
the incipient post stall stage and throwing in a fully developing spin mode
going flat with a coincident extremely high yaw rate associated with this
scenario; a young pilot could easily think the airplane had "tumbled"
Actually, many pilots don't know this, but to get a prop airplane to tumble,
you have to meet specific criteria. Gyroscopic precession from the prop disk
is critical to getting an airplane to tumble, which means power!!! This
means the airplane has to be carefully set up before a tumble potential can
exist. For example, to tumble a Pitts, you set up a 45 degree up line and
slow the airplane below Va with FULL POWER. Then you nail full right rudder
with full left aileron and forward stick all at once!! This causes a 3 axis
inertia coupling that vectors on the gyroscopic precession from the prop 90
degrees ahead of the disk axis as the airplane is being maneuvered in
positive pitch. With all three axis coupled, the damn airplane develops a
mind of it's own and all you do is hang on for dear life as the energy
dissipates through whatever the airplane has decided to do without
consulting you :-))
Now, THAT'S a tumble!!! :-))
Personally, I can see no way that an aircraft configured like the P39 could
be set up to tumble at departure...violent yes...but I seriously doubt end
over end....even with an aft cg. Bell would have picked up on this right
away and they didn't. Hell, this is hard enough to set up in a Pitts, much
less the Aircobra.
My guess is a violent departure, lived through and retold by a VERY
"excited" novice :-)
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/CFI
Retired