Subject: Number Thirty-Nine in the Series--Bell P-39 Airacobra (2 of 9)

From: [email-masked] (Joseph F Baugher)
Date: 10 Dec 92 17:27:27 GMT

>From Joseph F Baugher <[email-masked]>

All of the media hype surrounding the spectacular performance of the 
XP-39 prototype had caught the attention of the British Direct 
Purchase Commission which had visited the USA in 1940 in search of 
combat aircraft.  Seduced by promises of 400 mph top speed, a tricycle 
undercarriage, heavy cannon armament, and high climb rates, the 
British ordered 675 examples of the Airacobra.  Unfortunately, Bell's 
glossy advertising brochures did not distinguish between the 
performance of a lightly-loaded, unarmed, highly-polished 
experimental prototype and a production fighter heavily-loaded with 
military equipment and armament, and the British were to rue the day 
that they ever looked at an Airacobra.  

In 1940, the British were desperate for combat aircraft and were 
willing to consider just about anything that had wings, irrespective 
of how poor its performance might be.  Consequently, when Bell 
submitted specifications to the British Direct Purchase Commission for 
a fighter with a top speed of 400 mph, a ceiling of 36,000 feet, and a 
range of 1000 miles, the Commission literally salivated on the spot 
and ordered 675 Bell Model 14s sight unseen on April 13, 1940.  

The RAF model was at first named Caribou, but the American name of 
Airacobra was adopted in July 1941.  The British Airacobra was 
virtually identical to the American P-39D, but the 37-mm cannon was 
replaced with a Hispano 20-mm cannon with 60 rounds.  Two 0.50-inch 
machine guns were mounted in the fuselage, and four 0.30-inch machine 
guns were mounted in the wings.  The engine of the Model 14 was the 
1150 hp Allison V-1710-E4 (-35).  The British serials of the 
Airacobras were AH570/AH739, AP264/AP384, BW100/BW183, and 
BX135/BX434.  

Bell began test flying the first Model 14 Airacobra I in April 1941.  
It carried the British serial number AH570.  Tested on the second 
British Airacobra (AH571) was a revised rudder of more angular shape 
and less area.  Although the aircraft was delivered to England in this 
form, this rudder was not adopted as standard.  A very small dorsal 
fin just ahead of the rudder became a standard feature of the RAF 
Airacobras and was also a distinguishing feature of the American P-39D 
and subsequent versions.  

President Roosevelt signed the Lend-Lease Act on March 11, 1941, 
permitting large quantities of war supplies to be transferred to the 
Allies.  Among the early requisitions under Lend-Lease were three 
P-39Cs intended for "war tests" plus a batch of 150 Airacobra IAs--the 
A suffix being used to distinguish between Lend-Lease and Direct 
Purchase machines, which were otherwise identical.  In the event, only 
the three P-39Cs were ever delivered as British machines, and were 
assigned the serials DS173/DS175.  The P-39Cs could be distinguished 
from the British Airacobras by the four machine guns in the nose and 
the lack of wing guns.  

The first of these P-39Cs actually arrived at RAF Colerne on July 3, 
1941, followed by the other two the next day.  It made its first test 
flight in England on July 6.  However, during trials at Duxford, the 
performance proved disappointing.  Although the test pilots praised 
the general ease of handling of the aircraft, the maximum speed was a 
shocking 33 mph lower than that anticipated.  The fighter proved to be 
definitely inferior to the Hurricane and Spitfire in climb rate and 
ceiling, and the 750-yard takeoff run of the Airacobra excluded its 
operation from some smaller fighter airfields.  There was universal 
shock and dismay among the RAF personnel.  What had gone wrong? Bell 
Aircraft executives later sheepishly admitted that their performance 
figures had been based on the unarmed and unequipped XP-39 prototype, 
not on the armed and equipped P-39C.  

The first British-purchased Airacobras began arriving at Colerne 
before the end of July, joining the three P-39Cs already there.  
Deliveries of the Airacobra to Britain had to be made by sea, since 
the Airacobra lacked the range to make the Atlantic crossing.  By the 
end of September, eleven machines had been received.  No.  601 "County 
of London" Squadron was selected to be the first Fighter Command 
squadron to equip with the Airacobra.  

No.  601 Squadron pilots found numerous flaws and weaknesses during 
their initial work-up with the the Airacobra.  Some of them were a 
question of improving operational efficiency and pilot comfort, but 
others were considered essential to make the aircraft operational.  
Numerous modifications were made in the field in an attempt to make 
the aircraft suitable for combat.  A master valve was introduced to 
allow oxygen to be turned on from the cockpit.  The gunsight mas 
modified to improve forward visibility.  Changes to the ammunition 
tanks for the wing guns were made.  Modifications were made to the 
cockpit harness release in order to simplify the operation.  The IFF 
(Identification, Friend or Foe) set was removed from behind the pilot, 
where it obstructed aft view.  A throttle control quadrant friction 
damper was introduced.  

The Air Fighting Development Unit received a British Airacobra I on 
July 30.  They subjected it to tests and completed their report on 
September 22.  They found the aircraft to be pleasant to fly and easy 
to takeoff and land.  Controls were well balanced and although heavier 
than those of the Spitfire at normal speeds, did not increase 
appreciably in weight at high speeds as they did in the Spitfire.  It 
was difficult to hold the aircraft in a dive at high speeds unless the 
aircraft was trimmed nose-heavy.  During a turn, the Airacobra would 
give ample warning of a high-speed stall by severe vibration of the 
whole airframe.  Handling in formation and formation attacks was good, 
although deceleration was poor because of the plane's aerodynamic 
cleanliness.  Take-offs and landings in close formation were not 
considered safe, since there was considerable difficulty in bringing 
the aircraft back to its original path after a swing.  

The Airacobra I was powered by an Allison V-1710-E4 twelve-cylinder V 
in-line engine rated at 1150 hp for takeoff.  Weights were 5462 pounds 
empty and 7845 pounds normal gross.  Maximum speeds were 326 mph at 
6000 feet, 343 mph at 10,000 feet, 355 mph at 13, 000 feet, 341 mph at 
20,000 feet.  Initial climb rate was 2040 feet per minute.  With an 
internal fuel capacity of 100 Imp gal the Airacobra had an endurance 
of 1 hour 20 minutes at maximum continuous cruising speed at 6000 
feet, 1 hour 5 minutes at 12,000 feet, and 1 hour 35 minutes at 20,000 
feet.  The true airspeeds at these altitudes were 287 mph, 327 mph, 
and 308 mph, respectively.  Under most economical cruise conditions, 
the endurance increased to 3 hours 20 minutes, the relevant speeds 
being 183 mph at 6000 feet, 217 mph at 12,000 feet, and 215 mph at 
20,000 feet.  Under maximum continuous climb conditions, it took 15 
minutes to reach 20,000 feet.  The operational ceiling was considered 
to be about 24,000 feet, although there was a marked decrease in 
performance above 20,000 feet.  At the Airacobra's rated altitude of 
13,000 feet, it was 18 mph faster than the Spitfire VB.  However, the 
speed fell off rapidly above that height, and the two planes were 
almost exactly matched at 15,000 feet.  At 20,000 feet, the Spitfire 
VB was 35 mph faster and at 24,000 feet it was 55 mph faster.  The 
ground run of the Airacobra during takeoff was 2250 feet, as compared 
with 1470 feet for the Hurrican II and 1590 feet for the Spitfire V.  

The AFDU also did some comparative dog-fighting tests with the 
Airacobra against a Spitfire VB and a Messerschmitt BF 109E.  

The Airacobra and the Bf 109E carried out mock dog-fighting at 6000 
feet and 15,000 feet.  The Bf 109E had a height advantage of 1000 feet 
in each case.  The Bf 109, using the normal German fighter tactics of 
diving and zooming, could usually only get in a fleeting shot.  The Bf 
109 could not compete with the Airacobra in a turn, and if the Bf 109 
were behind the Airacobra at the start, the latter could usually shake 
him off and get in a burst before two complete turns were completed.  
If the Bf 109 were to dive on the Airacobra from above and continue 
the dive down to ground level after a short burst of fire, it was 
found that the Airacobra could follow and catch up to the Bf 109 after 
a dive of over 4000 feet.  When fighting the Bf 109E below 20,000 
feet, the Airacobra was superior on the same level and in a dive.  

A similar trial was carried out against a Spitfire V.  Although the 
Airacobra was faster than the Spitfire up to 15,000 feet, it was 
outclimbed and out-turned by the Spitfire.  Unless it had a height 
advantage, the Airacobra could not compete with the Spitfire.  If on 
the same level or below, at heights up to about 15,000 feet, the 
Airacobra would have to rely on its superior level and diving speeds 
and its ability to take negative "G" without the engine cutting out.  
Above 15,000 feet, the Airacobra lost its advantage in level speed.  

The Airacobra was considered to be very suitable for low altitude 
operations because of the excellent view and controllability, and it 
was fully maneuverable at speeds above 160 mph.  It was not difficult 
to fly at night, but the exhaust flames could be seen by another 
aircraft flying three miles to the rear.  The flash from the nose guns 
was blinding, and could cause the pilot to lose not only his target 
but also his night vision.  Firing of the nose guns caused the buildup 
of carbon monoxide contamination in the cockpit, and this could reach 
a lethal level very quickly.  The guns were fairly inaccessible, and 
maintenance was troublesome.  

By the end of September, No. 601 Squadron had received permission to 
take its Airacobras into action.  On October 9, two Airacobras took 
off from RAF Manston and flew across the Channel on a "rhubarb"--a 
code name for a small-scale raid by fighters against targets of 
opportunity.  On this raid, they shot up an enemy trawler near 
Gravelines.  The next day two Airacobras visited the same area, but 
found no targets.  On October 11, two aircraft flew to Gravelines and 
Calais and hit some enemy barges and then three Airacobras flew to 
Ostend, but no targets were found.  

After these four missions, the RAF Airacobras were taken off 
operations because of difficulties encountered with the compass.  The 
compass was too close to the guns in the nose, and when the guns were 
fired, the compass got thrown out of alignment.  Deviations of 
anything from 7 degrees to 165 degrees were recorded.  Without a 
reliable compass, pilots tend to get themselves lost.  In December of 
1941, the Airacobra was officially withdrawn from operational service 
with the RAF.  

In spite of the problems with the compass and the need for flame 
dampers for the exhaust and flash suppressors for the nose guns, the 
RAF concluded that the Airacobra would make an excellent day fighter 
at altitudes below 20,000 feet and was well suited for the 
ground-attack role.  However, before these plans could be implemented, 
a decision was made to divert the bulk of the British Airacobra 
contract to Russia.  

By the time this decision was made, production of British-contract 
Airacobras had reached four a day at Bell's Buffalo plant.  The 
initial contract for 170 planes (RAF serials AH570 thru AH739) had 
been completed before the end of September, and all but six of these 
planes had actually been shipped to Britain.  However, many of them 
remained in their crates and were shipped directly to the Soviet Union 
without being opened.  Somewhere between 80 and 100 Airacobras were 
assembled and flown in Britain by the end of 1941.  They were gathered 
at maintenance units for final modification before being re-crated and 
shipped to the Soviet Union during 1942.  Some In all, the Soviet 
Union received 212 of the British Airacobras (some of them shipped 
direct from the USA), but 49 more were lost at sea en route.  

No 601 Squadron relinquished its 13 Airacobras in March of 1942 in 
favor of Spitfires.  One Airacobra was fitted with an arrester hook 
and was used for deck landing trials at the RAE at Farnborough.  

After Pearl Harbor, the USA found itself in desperate need of aircraft 
to stem the Japanese onslaught in the Pacific.  Consequently, nearly 
200 of the British direct-purchase Airacobras still in the USA were 
promptly requisitioned by the USAAC.  Although they were similar to 
the USAAC's P-39Ds, they were not identical and were known by the 
USAAC under the non-standard designation of P-400.  The P-400 
designation had, in fact, been associated with the British Airacobras 
for contractual purposes as early as August 1941.  The USAAC P-400s 
retained their original British serial numbers.  Most of these planes 
were used for training stateside, but some of them were rushed to the 
Southwest Pacific in an attempt to stem the onrushing Japanese 
advance.  

The P-400s also saw some use closer to Britain.  179 of the Airacobras 
sent to Britain were re-acquired by the USAAF and were sent to North 
Africa to join the Twelfth Air Force.  

Sources:

  War Planes of the Second World War, Fighters, Volume Four, William Green,
  Doubleday, 1964.

  The American Fighter, Enzo Anguluci and Peter Bowers, Orion Books, 1987.

  United States Military Aircraft since 1909, Gordon Swanborough and Peter 
  M. Bowers, Smithsonian Institution Press, 1989.

  P-39 Airacobra in Action, Ernie MCDowell, Squadron/Signal Publications, 
  1980

  The Calamitous 'Cobra, Air Enthusiast, August 1971.

Joe Baugher       AT&T Bell Laboratories    2000 North Naperville Road 
		  Naperville, Illinois 60566-7033.   (708) 713-4548