Aircraft Factfile and Recognition Guide - P-47 Thunderbolt

Background

In 1939, the Republic Aviation Company designed an AP-4 demonstrator powered by a Pratt & Whitney R-1830 radial engine with a belly-mounted turbocharger. While the resulting P-43 Lancer was in limited production, Republic had been working on an improved P-44 Rocket with a more powerful engine, as well as on a fighter designated the AP-10. The latter was a lightweight aircraft powered by the Allison V-1710 liquid-cooled V-12 engine and armed with a pair of 0.50 caliber (12.7 mm) machine guns. The United States Army Air Corps (USAAC) backed the project and gave it the designation XP-47.  As the war in Europe escalated in the spring of 1940, Republic and the USAAC concluded that the XP-44 and the XP-47 were inferior to the German fighters. Republic unsuccessfully attempted to improve the design, proposing the XP-47A.

Alexander Kartveli subsequently came up an all-new and much larger fighter which was offered to the USAAC in June 1940. The Air Corps ordered a prototype in September, to be designated the XP-47B. The XP-47A, which had almost nothing in common with the new design, was abandoned. The XP-47B was of all-metal construction, except for fabric-covered tail control surfaces. The cockpit was roomy, and the pilot's seat was comfortable, "like a lounge chair" as one pilot would later put it. The pilot was provided with every convenience, including cabin air conditioning. The canopy featured doors that hinged upward. Main and auxiliary self-sealing fuel tanks were placed under the cockpit, offering a total fuel capacity of 305 US gallons (1,155 L). Power came from a Pratt & Whitney R-2800 Double Wasp two-row 18-cylinder radial engine producing 2,000 hp (1,500 kW) and turning a four-bladed Curtiss Electric constant-speed propeller 146 inches (3.7 m) in diameter. The loss of the AP-4 prototype to an engine fire ended Kartveli's experiments with tight-fitting cowlings, so the engine was placed in a broad cowling that opened at the front in a "horse collar"-shaped ellipse. The cowling admitted air for the engine, left and right oil coolers, and the turbo supercharger intercooler system. The engine exhaust gases were routed into a pair of wastegate-equipped pipes that ran along each side of the cockpit to drive the turbo supercharger turbine at the bottom of the fuselage about halfway between cockpit and tail. At full power, the pipes glowed red at their forward ends and the turbine spun at 60,000 revolutions per minute. The complicated turbo supercharger system with its ductwork gave the XP-47B a deep fuselage, and the wings had to be mounted in a relatively high position. This was problematic since long landing gear were needed to provide ground clearance for the propeller. To reduce the size and weight of the long landing gear, it was fitted with an ingenious mechanism by which it telescoped out 9 inches (230 millimeters) when extended.

The XP-47B was a very large aircraft for its time with an empty weight of 9,900 pounds (4,490 kg), or 65 percent more than the YP-43. Kartveli is said to have remarked, "It will be a dinosaur, but it will be dinosaur with good proportions." The armament consisted of eight 0.50 caliber machine guns, four in each wing. The guns were staggered to allow feeding from side-by-side ammunition boxes, each with a 350-round capacity. Although the British already possessed eight-gun fighters in the form of the Hurricane and the Spitfire, these used the smaller .303 inch (7.7 mm) guns. The XP-47B first flew on 6 May 1941 with Lowry P. Brabham at the controls. Although there were minor problems, such as some cockpit smoke that turned out to be due to an oil drip, the aircraft proved impressive in its first trials. It was eventually lost in an accident in August 1942.

Refinements of the Thunderbolt continued, leading to the definitive P-47D, of which 12,602 P-47Ds were 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 US gallons (1,421 L), and the bomb racks under the wings were made "wet" (equipped with fuel plumbing) to allow a drop tank to be carried under each wing, in addition to the belly tank. A variety of different drop tanks were fitted to the Thunderbolt during its career — following the early conformal 200 US gallon (758 L) ferry tank and the lozenge-shaped flat 200 US gallon belly tank, teardrop-shaped 75 US gallon (284 L) and 150 US gallon (568 L) metal underwing drop tanks were developed. The P-47 could also carry British-designed 108 US gallon (409 L) and 200 US gallon tanks made of plastic-impregnated paper. These tanks were cheap and were useless to the enemy if found after being dropped, though they could not store fuel for an extended period of time. With the increased fuel capacity, the P-47 was now able to perform escort missions deep into enemy territory.

The P-47D-16, P-47D-20, P-47D-22, and P-47D-23 were similar to the P-47D-15 with minor improvements in fuel system, engine subsystems, a jettisonable canopy, and bulletproof windshield. The Curtiss propeller was replaced by new and bigger propellers, with the Long Island plant moving to a Hamilton Standard propeller with a diameter of 157.875 inches (4.01 m), and the Evansville plant switching to a new Curtiss propeller with a diameter of 156 inches (3.96 m). With the bigger propellers, Thunderbolt pilots had to learn to be careful on takeoffs to keep the tail down until they obtained adequate ground clearance. Failure to do so damaged both the propeller and the runway.

Even with two Republic plants rolling out the P-47, the USAAF still was not getting as many Thunderbolts as they wanted, and so an arrangement was made with Curtiss to build the aircraft under license in a plant in Buffalo, New York. Most of the Curtiss Thunderbolts were intended for use in 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 the just before the leading edge of the wing to provide twin tandem seating, and designated TP-47G. 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). Curtiss built a total of 354 P-47Gs.

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. 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 US gallons (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 P-47D-25.

It was followed by similar bubble-top variants, including the P-47D-26, P-47D-27, P-47D-28, and P-47D-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 ten "zero length" stub launchers for 5 inch (127 mm) High Velocity Aerial 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 reticule to compensate for the required deflection.

Recognizing the P-47

The P-47 is an easy aircraft to identify on the ground as well as from the air.  Here's tips on how you can identify the Warhawk.

Wings: Very straight wing with curved wingtips.
Engine(s): Single engine with gigantic cowling and massive four-bladed propeller.
Fuselage: Bubbulous fuselage with a greenhouse canopy (later models featured a bubble canopy), hence the "Jug".
Tail: Low, rounded tail fin.  Elevators mounted mid-high on fuselage.

Specifications

Sources: Aviation History Online - P-47 Thunderbolt, Wikipedia P-47 Thunderbolt

© 2004-2007 Steven Holzinger