The P-47 Thunderbolt
Republic Aviation's P-47 Thunderbolt, also known as the "Jug", was the largest, heaviest, and most expensive fighter aircraft in history to be powered by a single reciprocating engine. It was heavily armed with eight .50-caliber machine guns, four per wing. When fully loaded, the P-47 weighed up to eight tons, and in the fighter-bomber ground attack roles could carry five inch rockets or a significant bomb load of 2,500 pounds—over half the weight the famous B-17 bomber could carry on long-range missions. The P-47, based on the powerful Pratt & Whitney R-2800 Double Wasp engine, was to be very effective as a short-to-medium range escort fighter in high-altitude air-to-air combat and when unleashed as a fighter-bomber, proved especially adept at ground attack in both the WW-II European and Pacific Theaters.
The P-47 was one of the main United States Army Air Forces (USAAF) fighters of World War II, and served with other Allied air forces such as France, the UK and the USSR. Mexican and Brazilian squadrons fighting alongside the U.S. were equipped with the P-47.
The sturdy and rugged aircraft was designed by Alexander de Seversky and Alexander Kartveli, emigres from the Russian Empire. The armored cockpit was roomy inside, comfortable for the pilot, and offered good visibility. A modern-day U.S. ground attack aircraft, the Fairchild Republic A-10 Thunderbolt II, takes its name from the P-47.
Production changes gradually addressed the problems with P-47B, and on balance, with experience the USAAF decided that the P-47 was worthwhile, quickly following the initial order for P-47Bs for 602 more examples of a improved model, named P-47C, with the first of this variant delivered in September 1942. The initial P-47Cs were very similar to the P-47B.
Initial deliveries of the Thunderbolt to the USAAF were to the 56th Fighter Group, which was also on Long Island. The 56th served as an operational evaluation unit for the new fighter. Teething problems continued. A Republic test pilot was killed in the fifth production P-47B when it went out of control in a dive on 26 March 1942, and crashed due to failure of the tail assembly, after fabric-covered tail surfaces ballooned and ruptured. The introduction of revised rudder and elevator balance systems and other changes corrected these problems. In spite of the problems, the USAAF was interested enough to order an additional 602 examples of the refined P-47C, with the first of the variant delivered in September 1942.
Essentially similar to the P-47B, the initial P-47C featured strengthened all-metal control surfaces, an upgraded GE turbosupercharger regulator, and a short vertical radio mast. After the initial manufacture of a block of 57 P-47Cs, production moved to the P-47C-1, which had a 13 in (33 cm) fuselage extension forward of the cockpit at the firewall to correct centre of gravity problems, ease engine maintenance and allow installation of a new engine mount. There were a number of other changes, such as revised exhausts for the oil coolers, and fixes to brakes, undercarriage and electrical system as well as a redesigned rudder and elevator balance. The 55 P-47C-1s were followed by 128 P-47C-2s which introduced a centerline hardpoint with under-fuselage shackles for either a 500 lb (227 kg) bomb or a 200 U.S. gal (758 l, 167 Imp gal) fuel tank that conformed to the underside of the fuselage. The main production P-47C sub-variant was the P-47C-5 which introduced a new whip antenna and the R-2800-59 engine with water-methanol injection with a war emergency power rating of 2,300 hp (1,716 kW). With the use of pressurized drop tanks, the P-47C was able to extend its range on missions beginning 30 July 1943.
By the end of 1942, most of the troubles with the P-47 had been worked out and P-47Cs were sent to England. The 56th FG was sent overseas to join the Eighth Air Force, whose 4th and 78th Fighter Groups would be equipped with the Thunderbolt as well.
Refinements of the Thunderbolt continued, leading to the P-47D, which was the most popular version with 12,602 built. The "D" model actually consisted of a series of evolving production blocks, the last of which were visibly different from the first.
The first P-47Ds were actually the same as P-47Cs. Republic could not produce Thunderbolts fast enough at its Farmingdale plant on Long Island, so a new plant was built at Evansville, Indiana. The Evansville plant built a total of 110 P-47Ds, which were completely identical to P-47C-2s. Farmingdale aircraft were identified by the "-RE" suffix after the block number, while Evansville aircraft were given the "-RA" suffix.
The P-47D-1 through P-47D-6, the P-47D-10, and the P-47D-11 successively incorporated changes such as the addition of more engine cooling flaps around the back of the cowl to reduce the engine overheating problems that had been seen in the field. Engines and engine subsystems saw refinement, as did the fuel, oil and hydraulic systems. Additional armor protection was also added for the pilot.
The P-47D-15 was produced in response to requests by combat units for increased range. The internal fuel capacity was increased to 375 U.S. gal (1,421 l) and the bomb racks under the wings were made "wet" (equipped with fuel plumbing) to allow a jettisonable drop tank pressurized by vented exhaust air to be carried under each wing, in addition to the belly tank. Five different auxiliary tanks were fitted to the Thunderbolt during its career:
200 U.S. gallon (758 l) ferry tank, a conformal tub-shaped jettisonable tank made of paper, which barely cleared the ground on grass airfields, was used as an interim measure between 30 July and 31 August 1943
75 U.S. gal (284 l) drop tank, a teardrop-shaped steel tank produced for the P-39 Airacobra, was adapted to the P-47 beginning 31 August 1943, initially carried on a belly shackle but used in pairs in 1944 as underwing tanks
108 U.S. gal (409 l) drop tank, a cylindrical paper tank of British design and manufacture, used as a belly tank beginning in September 1943 and a wing tank in April 1944
150 U.S. gal (568 l) drop tank, a steel tank first used as a belly 20 February 1944, and an underwing tank 22 May 1944
215 U.S. gal (810 l) belly tank, a wide, flat steel tank developed by VIII Service Command that allowed performance-degrading wing pylons to be removed, was first used in February 1945.
The tanks made of plastic-impregnated (laminated) paper could not store fuel for an extended period of time, but they worked quite well for the time it took to fly a single mission. These tanks were cheaper, lighter, and were useless to the enemy if recovered after being dropped—not only did they break apart, but they did not provide the enemy with any reusable materials that could be scavenged for their own war effort. With the increased fuel capacity, the P-47 was now able to perform escort missions deep into enemy territory. A drawback to their use was that fighters could not land with the tanks in place because of the hazard of rupture and explosion. Fighters recalled from a mission or that did not jettison for some reason were required to drop paper tanks into a designated "dump" area at their respective fields, resulting in substantial losses of aviation fuel.
The P-47D-16, D-20, D-22 and D-23 were similar to the P-47D-15 with minor improvements in the fuel system, engine subsystems, a jettisonable canopy, and a bulletproof windshield. Beginning with the block 22 aircraft, the original narrow-chorded Curtiss propeller was replaced by propellers with larger blades, the Evansville plant switching to a new Curtiss propeller with a diameter of 13 ft (3.96 m) and the Long Island plant using a Hamilton Standard propeller with a diameter of 13 ft 2 in (4.01 m). With the bigger propellers having barely 6 in (152 mm) of ground clearance, Thunderbolt pilots had to learn to be careful on takeoffs to keep the tail down until they obtained adequate ground clearance, and on landings to flare the aircraft properly. Failure to do so damaged both the propeller and the runway. A modification to the maingear legs was installed to extend the gear legs via an electric motor (un-extending before retract) to accommodate the larger propeller diameter. The P-47D-25 was a model with increased range, firepower, and maneuverability.
Even with two Republic plants rolling out the P-47, the USAAF still was not getting as many Thunderbolts as they wanted. Consequently, an arrangement was made with Curtiss to build the aircraft under license in a plant in Buffalo, New York. The Curtiss plant experienced serious problems and delays in producing Thunderbolts, and the 354 Curtiss-built fighters were relegated to stateside advanced flight training. The Curtiss aircraft were all designated P-47G, and a "-CU" suffix was used to distinguish them from other production. The first P-47G was completely identical to the P-47C, the P-47G-1 was identical to the P-47C-1, while the following P-47G-5, P-47G-10, and P-47G-15 sub-variants were comparable to the P-47D-1, P-47D-5 and P-47D-10 respectively. Two P-47G-15s were built with the cockpit extended forward to just before the leading edge of the wing to provide tandem seating, designated TP-47G, essentially to provide a trainer variant. The second crew position was accommodated by substituting a much smaller main fuel tank. The "Doublebolt" did not go into production but similar modifications were made in the field to older P-47s, which were then used as squadron "hacks" (miscellaneous utility aircraft).
All the P-47s to this point had a "razorback" canopy configuration with a tall fuselage spine behind the pilot which resulted in poor visibility to the rear. The British also had this problem with their fighter aircraft, and had devised the bulged "Malcolm hood" canopy for the Spitfire as an initial solution. This was fitted in the field to many North American P-51 Mustangs, and to a handful of P-47Ds (and far more on P-47Bs and P-47Cs). However, the British then came up with a much better solution, devising an all-round vision "bubble canopy" for the Hawker Typhoon. USAAF officials liked the bubble canopy, and quickly adapted it to American fighters, including the P-51 and the Thunderbolt. The first P-47 with a bubble canopy was a modified P-47D-5 completed in the summer of 1943 and redesignated XP-47K. Another older P-47D was modified to provide an internal fuel capacity of 370 U.S. gal (1,402 l) and given the designation XP-47L. The bubble canopy and increased fuel capacity were then rolled into production together, resulting in the block 25 P-47D (rather than a new variant designation). First deliveries to combat groups began in May 1944.
P-47 D (Blocks 25-30)
It was followed by similar bubble-top variants, including the P-47D-26, D-27, D-28 and D-30. Improvements added in this series included engine refinements, more internal fuel capacity, and the addition of dive recovery flaps. Cutting down the rear fuselage to accommodate the bubble canopy produced yaw instability, and the P-47D-40 introduced a dorsal fin extension in the form of a narrow triangle running from the vertical tailplane to the radio aerial. The fin fillet was retrofitted in the field to earlier P-47D bubble-top variants. The P-47D-40 also featured provisions for 10 "zero length" stub launchers for 5 in (127 mm) High velocity aircraft rockets (HVARs), as well as the new K-14 computing gunsight. This was a license-built copy of the British Ferranti GGS Mark IID computing gyroscopic sight which allowed the pilot to dial in target wingspan and range, and would then move the gunsight reticle to compensate for the required deflection.
Read More about the 365thThunderbolts of the Hell Hawks
(Barnes, Crump and Sutherland)
320 pages, 500 photos and 98 illustrations of the group's P-47s.
(Dorr & Jones)
The story of the band of young American fighter pilots, and their gritty, close-quarters fight against Hitlers vaunted military. The "Hell Hawks" were the men and machines of the 365th Fighter Group.