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Old 01-28-2010, 05:59 PM   #1
copeab
 
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Join Date: Mar 2005
Location: near Houston
Default [WWII] Bell P-39 Airacobra, fighter/ground-attack (USA)

I originally did this design eight years ago. After watching a TV program on the P-39, I decided to take a look back. I decided the write-up needed to be beefed up and that there were errors that needed to be fixed. Therefore, I present again ...
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Bell P-39 Airacobra, fighter/ground-attack
Copyright 2002, 2010 by Brandon Cope

The sleek P-39 started as an interceptor in April 1938. However, as armored systems began to be added, without any increase in engine power, its speed (initially 390 mph) and maneuverability rapidly dropped. However, the P-39 proved quite capable in the role of ground support, especially in Russian hands. While the P-39 has poor performance at high altitude and climbed slowly (largely due to lack of a supercharger), it was quite effective at 10,000 feet and below. which was just fine for North Africa, the Eastern Front (where it often protected the Il-2) and the Pacific (for the most part). While the P-39 was at a severe disadvantage dogfighting the Zero, Russian use showed this was quite not the case against German fighters (nine Soviet pilots were credited with at least 20 kills flying the P-39). Despite the limitations, the P-39 (along with the P-40) were the primary USAAF fighters in 1942 and most of 1943.

The P-39 introduced several new features to US combat aircraft. First, it used tricycle landing gear instead of the more standard tail-dragger arrangement. Second, to place the engine at the airplane's natural center of gravity it was necessary to place it behind the pilot, with a 8' shaft to the propeller running under the pilot's legs. Pilots new to the P-39 were quite concerned; it didn't take much to imagine what damage a broken shaft could do whipping around in the cockpit. However, the system proved quite reliable in service, even in crash landings. The mid-mounted engine also allowed the plane to concentrate armament in the (relatively empty) nose; no wing guns meant the wings could be made smaller, creating less drag. The plane also used car-like door to enter and exit the cockpit, complete with roll-down side windows! Although the cockpit gave excellent visibility, the pilot's hated the door. Some 4,900 P-39Qs were built, with a total of about 9,600 of all types. Nearly 5,000 went to Russia.

The P-39Q uses 40.3 gallons of aviation fuel per hour.

Subassemblies: Medium Fighter Body with Good streamlining +3, Medium Fighter Wings +2, three retractable wheels +1.
P&P: 895 kW HP gasoline engine w/895-kw aerial propeller, 120 gallons aviation gasoline in self-sealing fuel tanks (body and wings)
Occ: 1 NCS Cargo: 1.6 Body, 0.6 Wings

Armor
All: 3/5
Cockpit: FBU 0/+30, RL 0/+15

Weaponry
2*Long Aircraft HMG/Browning M-2 [Wings:F] (300 rounds each)
2*Long Aircraft HMG/Browning M-2 [Body:F] (200 rounds each)
37mm Medium Aircraft AC/M-4 [Body:F] (30)

Equipment
Body: Medium radio receiver and transmitter, IFF, navigation instruments, autopilot, 1,000-lb hardpoint.

Statistics
Size: 30'x34'x12'
Payload: 0.65 tons
Lwt: 3.7 tons
Volume: 200
Maint.: 40 hours
Price: $24,900

HT: 10
HP: 180 [body], 120 [each wing], 18 [each wheel]

aSpeed: 370
aAccel: 7
aDecel: 23
aMR: 5.75
aSR: 2
Stall: 80

Design Notes
Design speed was 402 mph. 40 rounds of 37mm ammo were purchased. The historical values have been used. Wing and chassis cost, weight and HP were increased by 50%. Loaded weight does not include a loaded hardpoint (which could carry a bomb or 120 gallon drop tank). A loaded hard point drops aSpeed by 7 mph.

Some subvariants of the -Q carried only 87 gallons of internal fuel, while others had less armor (no side or belly).

The 37mm cannon was not terribly reliable early in the war (Malf 15).

The wing guns were technically in underwing pods, not in the wings. The Russians often removed the wing guns to reduce drag (aSpeed 376).

Variants
The P-39C (1940) was the initial Army version, originally listed as P-45. It lacked pilot armor and self-sealing tanks. Drop wing guns and add two .30-cal M-2 MGs (Aircraft LMG) in nose; reduce cannon ammo to 15. aSpeed 379 with a 858-kW engine. 20 built.

The P-39D (1940) moved the two .30-cal MGs to the wings and doubled them (with 1,000 rpg), as well as adding the pilot armor and self-sealing tanks. It carried 30 rounds of 37mm ammo. It could carry a 60-gallon drop tank or up to 600 lbs of bombs. aSpeed dropped to 360 mph. 60 built.

The P-400 (1941) was an export version built specifically for the British. It differed from the -D primarily in replacing the 37mm gun with with a 20mm Hispano cannon (20mm Long Aircraft AC) with 60 rounds and having .303-cal rather than .30-cal guns. aSpeed was 355 mph. Although less agile than a Spitfire, it showed it could outmaneuver the Bf 109 at low and medium altitude. About half those sent to Britain ended up in Russia and around 200 were taken over by the US in December 1941 before they could be shipped to England. Nearly 200 British planes were transferred back to the Americans in North Africa. American P-400's were also used quite extensively in the Pacific in 1942. 675 built.

The P-39D-1 and D-2 (1941) were similar to the P-400, but built for Lend-Lease. They used .30-cal rather than .303 MGs. The D-2 replaced the 20mm gun with the 37mm gun and upgraded the engine. 336 D-1 and 158 D-2 planes were built. Most went to Russia but some were used in combat by the US at Guadalcanal and in North Africa. The D-3 and D-4 were 37 recon aircraft used in Italy.

The 229 P-39F were basically the same as the P-39D. The twenty-seven P-39F-2's were converted for the ground attack role by adding belly armor (DR 20) and downward-facing recon cameras. The last 25 P-39F's had a slightly different engine and were designated P-39J.

The P-39K had a 988-kW engine (aSpeed 360) but was otherwise the same as the -D. 210 were built.

The 250 P-39L's (1942) were similar to the -K. They added underwing rocket racks.

The P-39M (1942) was an attempt to get better high-altitude performance with a new prop and engine (895-kW) . aSpeed was only 370 mph. 240 built.

The P-39N (1942) was the first version to be built in really large numbers (2,095). Most had wing tankage reduced from 120 to 87 gallons (although these tanks could be reinstalled in the field if needed). They were otherwise similar to the -M. Over 160 were converted in a similar fashion to the P-39F-2 for ground attack.
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Brandon Cope

GURPS 3e stuff: http://copeab.tripod.com
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