The P39 verus the P47

[Seeker]

From some one who flew both:
*************************
Any amateur historians who are sharp enough could find the writer's identity from this; it ain't me!)
*******************************

About the airacobra versus the thunderbolt--it is a rather
complex story and the differences are difficult
to assess in a few words.  I think the main point to keep in
mind is that the two fighters represented two
very different technological periods--though only some three
to four years apart as start up projects.
The power plants of the two represented the maximum engine
capability achievable at the time.  The
P-39 was designed around a 1000 horsepower engine, not yet
available in 1936, when it's design
began.  The P-47 was designed around a 2000 horsepower
engine, also just coming on stream,
development wise, in 1939-40, when the aircraft design took
shape.  (note, I might be off a bit, time
wise, on the latter date(s)).  Obviously the two powerplants
offered very different challenges and
opportunities for the two design teams.  One was highly
constrained by weight and size while the other
had the power to lift a great deal more weight, providing
the possibility of achieving not only more range
but greater armament striking power in the design.  It was
conceived as a long range fighter
interceptor--no one dreamed that the the fighter, a
"defensive" weapon, would ever be used as an
offensive weapon, in the prewar period.  Bombers were the
only offensive air weapon and they would
be able to carry enough defensive armaments to take care of
themselves, thank you.  Fighter escorts
would not be required.  Both concepts being 'gospel' in the
ranks of the senior bomber generals running
the prewar Air Corps.
 
At the time the P-39 was developed the concept was to build
an interceptor capable of operating near
top speed at 20,000 feet.  All fighters of the time had
engines with at least a single stage supercharger
to allow the engine to produce maximum power somewhere
around seven to ten thousand feet.  This
enabled the engine to be effective near sea level, seven
thousand feet below max power, and also at
some seven thousand feet higher than the max power altitude,
or, up to some 14 or 15 thousand feet, as
an example.  But the only way to achieve full power at
20,000 feet, or higher, was to provide the engine
with a two stage supercharger.  That could be achieved by
two means, either a second stage mechanical
system, or via exploiting the exhaust gasses of the engine
to drive a turbo supercharger to gain the
added 'boost' for the second stage.  
 
When push came to shove, the Air Corps punted, on the P-39
design.  Originally, the Air Corps had
opted for a turbo supercharger, in line with the P-38 engine
decision.  But the design of the P-39
airframe made it difficult to bolt an experimental turbo
supercharger to the P-39 engine.  Unlike the
German and British approach where their Daimler-Benz and
Rolls Royce engines were modified, as
possible, to accomodate the tight designs of the Me-109 and
the Spitfire, the Air Staff did not insist that
Allison modify an engine to make it easier to integrate a
turbo charger into the specific design of the
Airacobra--or demand that they take the time to produce a
second stage mechanical supercharger.
With the outbreak of WW II in Europe the US was desperate
for all the fighters that could be produced
in 39-40 , and the Air Corps chose to concentrate on numbers
over technological cutting edge design.
As a result, Allison (part of GM) was directed to gear up to
build all the 'standard' engines they could,
as fast as they could, and Bell was, in effect, told to
forget about a two stage supercharger for the
Airacobra.  Thus, both Bell and Curtis were committed to
produce large numbers of P-39s and P-40s
and to stick a standard Allison engine into each.  As a
result both of these aircraft reached their
maximum horsepower capability in the mid altitude range of
something under 10,000 feet.  As indicated,
Allison did produce an engine with a turbo supercharger for
the large P-38 Lightening design.  
 
Aerodynamically, the P-39 was a very slick design, however,
and still had enough power at some 1100
to 1200 horsepower, (by 1940/41 the engine power had
achieved this range) to be a serious
contender, up to 15,000 feet.  In tests conducted by the
RAF's Air Fighting Development Unit in July
1941, they determined that the P-39 could out run and out
dive their Spitfire Mark V , the latest version
reaching combat units, below 15,000 feet.  However, the Spit
was superior to the Cobra in both turning
radius and in the climb.  More important, they flew a
captured Me-109 E, the Battle of Britain
fighter, against the P-39 and found that it could outrun,
out dive and out turn the Messerschmitt at
15,000 feet and below.  Though the document I have seen does
not mention it, I assume that the
mechanically driven two stage supercharger of the Me-109
enabled it to easily out climb the P-39 at all
altitudes, as the latter was both heavier and had less
horsepower than the 109.  Unfortunately,
this important performance information about the relative
strengths and weaknesses of the P-39 versus
the Me-109 was never shared with the P-39 pilots in
combat.

[Seeker]

cont/d
**********

The E model of the Me-109 was not the latest version in
1941, the F had reached some Luftwaffe
units but its mid and lower altitude performance was not
materially improved over that of the "E".  When
I tested an Me-109 G against the P-39 in February 1944, I
came to the same conclusions the RAF had
reached, two and a half years earlier.  I had no knowledge
of the earlier tests, of course.  But above
some 15,000 feet the single stage supercharger of the
Airacobra's power plant caused its horsepower
to drop off steadily with every increase in altitude.  So,
in summary, the P-39 was quite advanced,
aerodynamically, at the time, but limited by its engine
design.  The Germans and the British, were, of
course, confronted with the same engine design problem for
their two small fighters, the Me-109 and
the Spitfire, both about the same size as the P-39.  It
should be noted that the Germans succeeded in
adding a two stage supercharger to their bird first,
followed by the Spitfire (I believe I have the order
right) by 1939 or 40.  The Airacobra never achieved that
capability though its follow-on, redesigned
as the P-63 Kingcobra, was equipped with a mechanical two
stage boost system which gave it a
competitive speed capability at 20,000 feet and above.
However, the US never fielded the P-63 in
combat--almost all the production going to the Red Air
Force, which had achieved high scores with the
P-39 in air to air combat on the Eastern front, against the
same enemy we faced in the MTO.  
 
In the summer of 43 each Squadron in the 350th Group was
equipped with two P-38s to augment their
P-39s so that we could intercept the high flying Luftwaffe
reconnaissance flights being sent down to
surveil the fleet gathering for the invasion of Sicily.  We
kept a flight of two P-39s and a single P-38 on
5 minute scramble alert at the end of the runway of the
airfields we occupied on the Algerian coast.  On
scramble, we usually got all three aircraft off in 3
minutes, the two 39s usually going first as the P-38 had
to start two engines.  The P-39 could hold its own with the
P-38 up to some 13 to 15 thousand feet,
but above that the 38 pulled away steadily.  I flew both
aircraft on these scrambles and of course was
highly impressed with the 38's climb at higher altitudes and
its range capabilities.  But I was not
impressed wih the design; for a single engine fighter pilot
it was too big to be nimble, though it could turn
with, or almost with, the P-39, when we rat raced.  But it
had too much wing and fuselage on each side
of the cockpit capsule to be an ideal design for detecting
approaching enemy fighters.  However, none
of the early designs gave the pilot a view to the rear,
certainly not the P-39, Me-109, P-40 or the early
P-47 and P-51.  The Hawker Typhoon and Fw-190 showed the
advantage of the bubble canopy
design, adopted for all subsequent fighter aircraft.  
 
I did not fly the P-51.  It was a racer, with  range enough
to escort bombers to any target in Europe,
when they added the fuselage tank.  It was not nearly as
survivable as the Jug but was a fine aircraft for
escort duty, once the Allison engine was replaced with the
higher performing, two stage supercharged
British Rolls Royce mill.  
 
The Jug was a huge beast, twice the loaded weight of the
Cobra, but with its turbosupercharger it had
an excellent high altitude capability and was an easy and
honest bird to fly.  A pilot had to be a bit more
skillful to get the maximum out of the P-39 design.  Any
fighter of the time could be forced into a snap
roll if the pilot was ham handed enough and exceeded the
lift of the airfoil by overcontrolling the
aircraft.  However, the Airacobra was easier to slip into
this condition when on its back and with its
nose up.  In such cases, the aircraft sometimes snapped into
a wicked rotating action before ending up
in a spin that was harder to break than with most fighters
of the time.  With experience in the bird, spins
were no problem, you could rack the bird around just as hard
as any fighter, you simply kept the bird
flying and stayed out of spins.  This did not require any
conscious "thought" on the part of the pilot, any
more than a race driver "thinks" about getting through an
up-coming curve.  The experienced pilot
sensed where the max limits were and controlled the bird
accordingly.  Any pilot in any fighter who over
controlled and ended up in a spin quickly became vulnerable
in the recovery maneuver to any
opponent alert to take advantage of the opportunity.  But
that was still the era when it
was deemed desirable for pilots to familiarize themselves
with spins in a fighter.  The Air Force
abandoned that approach 30 or 40 years ago and has trained
its pilots to stay out of spins ever since.  I
think we lost 4 P-39 pilots to spins and, off the top of the
head, I can recall only one lost in a Jug.

[Seeker]

cont/d
**********

The P-47 turned well, climbed poorly--in comparison with the
Spitfire, for example-- and almost
certainly relative to the Me-109, an excellent climbing
machine--at least up to an altitude above 20,000
feet.  However, it reputedly gained the advantage over the
Me-109 at the highest operating altitudes of
WW II.  In September and October 44 we often encountered
thunderstorms over the Apennines,
blocking our entry into the Po valley.  We routinely
attempted to fly over these storms and I have led
flights loaded with the belly tank and two 500 pound bombs
to 27,500 feet, over the top of the
'bumpers' and on to our target in the Po.  We could only
admire a machine with that capability.  The
P-47 could out dive anything in the sky, constrained only by
compressibility, a high speed condition at
high altitude that resulted in the stick being frozen in
place with the pilot losing any capability of pulling
out of the dive until the aircraft reached  denser air at
some 10 to 15 thousand feet.  On reaching the
lower altitude where the pilot could regain control, he had
only a few seconds to pull out and avoid
impact, of course.  However, as the word got around on
compressibility, pilots simply avoided the
condition by throttling back in a dive, as necessary.  The
jug's speed on the straight and level was
competitive but not outstanding--our pilots lost some long
chases with the Luftwaffe reconnaissance
birds.  It had great survivability and dished out a
withering fire with 8 fifty caliber machine guns which
had a long firing capability with 800 rounds per gun.  The
P-39 had adequate fire power with a 37 mm
canon and two fifties in the nose, and four 30s in the
wings--but it had a short firing time with its cannon
and fifties.  On the other hand, each of the 30s had a
thousand rounds capacity.  The only time we
carried the full load of 30s was on strafing missions--for
air defense operations we normally loaded only
4 or 5 hundred rounds for each wing gun.  The Me-109 had a
20mm canon and two 30s in the nose, in
the straight air to air fighter version.  The 30s were
replaced by 50s with the G version, the model with
the largest production run.  Again it had a short firing
time.  A Bell Technical Representative in the
Soviet Union during the war stated in correspondence to the
factory that some of the Red Air
Force units had removed the four 30 caliber guns from the
wings of their P-39s to lighten the bird for air
to air combat.  Their highest scoring pilots claimed up to
60 kills total, double the highest scoring
American pilot on the Western Front.  Some of the top
scoring pilots flew the P-39 with some claiming
up to 40 kills in the Airacobra.  By contrast, I had an
opportunity to shoot down two Me-109s with the
P-39, apparently the only Airacobra pilot to do so in the
MTO.  So you can see that we had drastically
different missions--they used the bird as a counter-air, air
superiority fighter over some of the largest
battles on the Eastern Front in the 42-43 period, when it
was one of the top performing fighters in their
inventory.  We, on the other hand, used the bird primarily
in a defensive role in the MTO
and secondarily as an offensive fighter-bomber, and never in
an air superiority role.  Our Group shot
down two Fw-190s, and five Me-109s, with P-39s, all
confirmed in the post war, and lost four P-39s
to Fws and Mes.  Henry Nelson was also shot down in a P-39
on the flight from England to Africa on 5
February 43, after his flight broke up in a severe storm,
out over the Bay of Biscay.  A German pilot,
Hermann Horstman, in a Ju-88 fighter version, stumbled
across him while on patrol and probably
ambushed him.  Not a real fighter to fighter aerial combat,
as we envision such actions, but none the less
a loss to an enemy fighter.  In addition to the fighter
kills, our pilots in Airacobras, shot down another six
bomber and reconnaissance aircraft.   But our total P-39
kills are so few in number that they seem
appaling in comparison to claims made by P-39 aces in the
Red Air Force.  
 
Flying P-38s, it appears from German records that our pilots
shot down seven reconnaissance birds
over a three month period.  I have not counted any claims
for which there is no confirmation, at least so
far, in Luftwaffe records.  Like all organizations of all
Nations, pilot claims exceed opponent losses.  As
for the Jug, our pilots shot down some 20 Italian pilots
flying Me-109s in the last eight months of
operations over northern Italy--without a direct loss.
However, one P-47 was lost when it's tail wheel
would not come down for landing at Pisa after having taken
several 20 mm rounds in the tail.  The pilot,
Tomlinson, of 346 Sq. landed on the tail and was able to get
the bird almost all the way off the landing
strip.  However, before it could be moved, an 86th Fighter
Group pilot landed and failed to see
Tommy's aircraft in time to avoid it, crashing into it and
wiping out both birds.  So, in fact, the record
was 20 versus 1, or 2, depending on how one wishes to scores
it.

 
The P-39 had only one external shackle, while the Jug had
three.  As we had only the one hanger, when
we carried a bomb, either a 500 or a 1000 pounder, we were
severely restricted in our strike range.
We carried out strikes across the 80 to 140 mile run from
Corsica to coastal targets along central Italy
but had little endurance for carrying out extended strafing
forays after dropping our bomb.  The P-47
had a 110 gallon drop tank and could carry two 500 pound
bombs to most targets in the Po Valley,
from Pisa.  We had enough ammunition and fuel after dropping
bombs to spend considerable time
hunting for strafing targets, on most missions. In the final
battle of the war in Italy, in April 45, some of
our sorties were flown without the centerline drop tank and
two 1000 pounders were carried to the Po
by our P-47s.  
 
With its up front cockpit and abbreviated nose, the P-39
gave the pilot the best strafing platform of the
WW II fighters. From near zero altitude you could see every
thing in front of you in a 180 degree arc,
pop up to two or three hundred feet and push over to execute
a quick firing pass, minimizing exposure
to enemy flak.  The Jug had a huge nose that the pilot had
to look over, requiring flight at a few hundred
feet to enable an effective strafing pass.  I found the nose
gun tracers of the P-39 far more effective as
an aiming aid than the spread out tracers fired from the
wing guns of the P-47.  Though only some 10
feet out on each side from the pilot's line of sight, the
wing guns simply did not provide the direct contact
with the target that the tracers did when eminating from a
few inches below the pilot's eyes.  You could
look straight down the string of tracers right into the
target and had an instantanious feed back on how
to adjust your aim to correst any error in your bullets
impact.  You got a similar imput from the wing gun
tracers but their off set position and converging pattern
was simply not equal to the nose gun feed back.
With its rugged radial engine the P-47 was much more
survivable than the P-39 with its glycol plumbing
system, though the little bird was structurally quite
strong.  
 
That's some of the story, off the top of the head.  If I had
the time to restudy some of the dates and
other numbers, I'm sure I would have to change some of the
above, a bit--but its close enough to give
you some idea of the strengths and weaknesses of the two
birds.  I enjoyed flying both aircraft--but
was terribly disappointed in the missions we drew most of
the time with the P-39--as were all the
Group's pilots.  C'est la guerre.

[oboe]

Nice post, Seeker.  Thanks!

Hoping to see a P-39 in AH soon.

[Grizzly]

Actually two WW2 fighter vets, from Hugh Dow via Earl Miller. BigWeek is a good place  =o)