Republic P-47D Thunderbolt

The "Jug" (short for Juggernaut) was built in the later part of the war as a multipurpose fighter. Numerous production difficulties arose in creating this mammoth aircraft, and when it did appear it took some time before tactics evolved to meet its capabilities. Weighing almost half as much as some of the bombers it escorted, the P47 was built around the famous Pratt & Whitney R-2800 18 cylinder engine that served in so many U.S. planes. While it was fast, carried ample armament, and was incredibly tough, the Jug was initially met with little enthusiasm. It would be fair to say the RAF hated it - it was dramatically different from most of their designs and didn't fit most engagement tactics of the time. Eventually the Jug found a home as the premier ground attack fighter of the war. It could carry a wide array of weapons and was the terror of retreating armor columns, trains, and the like. With the addition of an external fuel tank P47s could easily range to the target and back with their bombers, and several squadrons (notably the famed 56th) rang up impressive air to air success with the plane some thought would never fight against the sleek designs it often countered.

The P-47D was the first version of the Thunderbolt to undergo really large-scale production. The first USAAF order for the P-47D took place on October 14, 1941, when 850 examples were ordered. However, it was to be followed by many, many more. In its initial form, the P-47D differed very little from the P-47C. The P-47D had some changes in the turbosupercharger exhaust system which incorporated an adjustable duct and redesigned vents for the engine accessory section. Additional cowl flaps were fitted to improve engine cooling airflow. More extensive armor protection was provided for the pilot. Generally, however, early P-47Ds can be distinguished from Cs only by their serial numbers.

All early Thunderbolts used the R-2800-21 engine. Water injection capability was added to this engine during the P-47D production run and retrofit kits were also made available for earlier models at that time. Provision was made for the mounting of a 15-gallon tank carrying a water-alcohol mixture to the bulkhead just aft of the engine. A line from this tank was plumbed directly into the fuel intake. When injected into the combustion chamber, the water checked a dangerous rise in cylinder head temperature while manifold pressure was boosted. For brief instants, a 15-percent increase in engine power could be obtained, giving a maximum war emergency power of 2300 hp. This happened when the throttle was pushed forward into its last half-inch of travel. Shackles for a belly tank or a 500-pound bomb were added and later blocks and underwing pylons were introduced. These enabled a drop tank or a bomb to be carried underneath each wing in addition to the stores carried on the belly shackles. Fuel changes had to be made to incorporate plumbing for the underwing tanks. Bomb selection increased to two 1000-pound or 3 500-pound bombs, with maximum bomb load being 2500 pounds. Alternatively, a 108-gallon drop tank could be carried underneath each wing, adding 150 miles to the P-47's range. Earlier P-47C and D models could be modified in the field to accommodate underwing racks, but the amount of work required many man-hours of effort by maintenance personnel. The underwing pylons had a detrimental effect on performance, and their air resistance cut 45 mph off the maximum speed. However, a redesigned, more streamlined pylon cut the loss to about 15 mph.

Toward the end of 1943, Eighth Air Force Thunderbolts began returning from escort missions over the Continent "on the deck", seeking out enemy ground targets of opportunity as they made their way back to the Channel. Somewhat surprisingly, it was found that the Thunderbolt was rather well-suited for this new role. This led to perhaps the most successful adaptation of the Thunderbolt as a fighter bomber. Subsequently, P-47Ds were fitted with underwing pylons and stronger wings which permitted them to carry two 1000-lb bombs, three 500-lb bombs or a combination of bombs and drop tanks. Either six or eight machine guns could be carried, and the maximum ammunition capacity was 425 rpg. However with the full ordinance load, ammunition capacity was reduced to 267 rpg. Then, a number of Thunderbolts suffered mysterious engine failures during these return missions over the Continent that could not be ascribed to enemy action. It was eventually discovered that the addition of the bombs and drop-tanks added so much weight to the aircraft that the Thunderbolt was able to build up excessively-high speeds during bombing attacks. During the recovery from these high-speed dives, g-forces got so high that a surge or vapor lock was produced in the fuel lines which the fuel pump was unable to overcome.

Further modifications and improvements continued on the P-47D and a "universal" wing which could carry a variety of drop tanks or bombs was introduced. Also introduced was the R-2800-59 engine with an improved ignition system. The power was the same as that of the -63, with a war emergency power output of 2300 hp. The length of the tail wheel leg was increased and a larger (13- foot diameter) paddle-bladed propeller was fitted to make full use of the additional power provided by water injection. It added 400 feet per minute to the climb rate, but during landings and takeoffs there was only a scant six inches of clearance between blade tips and the ground. P-47Ds were also provided with a jettisonable cockpit canopy which was activated by the pilot pulling a ring. The hood would then be pushed backward, and the force of the slipstream would then do the rest of the job of pulling the canopy free of the aircraft. A bulletproof windshield was fitted, and internal fuel capacity was increased.

The first 5,000 or so Thunderbolts all had the original framed sliding canopy that was first used on the P-47B. However, combat experience indicated that the rear fuselage decking on these Thunderbolts provided a serious blind spot aft which was a real hindrance in air-to-air battles. In an attempt to improve rearward visibility, a few P-47Ds were fitted in the field with the RAF "Malcolm hood", a Spitfire-like bubble canopy made in England which was made famous by its application to the P-51B and C Mustangs flown by both the RAF and USAAF. In search of a more lasting solution, the USAAF fitted a standard P-47D airframe with a bubble canopy taken from a Hawker Typhoon. In order to accommodate the bubble canopy, the Republic design team had to cut down the rear fuselage. This conversion was redesigned XP-47K, and was tested in July 1943. This modification was immediately proven to be feasible, and was promptly introduced to the P-47D production lines. Ordinarily, the USAAF would have given such a radical modification as that which produced the bubble-canopy Thunderbolt a completely new variant letter (or perhaps even a new type number). However, the USAAF chose instead to designate it simply by giving it a new production block number in the D-series. These batches also had the R-2800-59 or -63 engines, the paddle-bladed propeller, and the "universal" wing first introduced on the "razorback" P-47D-20-RE. Stronger belly shackles capable of carrying a 91.6 Imp. gal. drop tank were fitted. This tank, together with the 170.6 Imp. gal. main fuselage tank, an 83-gallon auxiliary fuel tank and two 125-gallon underwing tanks, made it possible to carry a total fuel load of 595 Imp. gal., providing a maximum range of 1800 miles traveling at 195 mph @ 10,000 feet.

The early "bubble-canopy" Thunderbolts suffered from some directional instability as a result of the loss of aft keel area. So a dorsal fin was fitted just ahead of the rudder. This innovation successfully restored the stability. Underwing zero-length launching stubs were also added at this time for a total capacity of ten five-inch HVAR rockets. The high diving speeds of which the Thunderbolt was capable pushed the aircraft into the edge of compressibility, and new blunt-nosed ailerons were fitted to improve controllability at these high speeds. In order to help in dive recovery an electrically-operated dive recovery flap was fitted on the under surfaces of each wing.

Republic's Farmingdale plant produced a total of 2,547 bubble-canopy P-47Ds and their Evansville factory built another 4,632.

US Planes and Specifications