High altitude thunderbolt

Air Classics, Mar 2002 by O'Leary, Michael

DISPLAYED AT YANKS AIR MUSEUM, THIS SOLE SURVIVING P-47M HAD AN ABORTED CAREER A AS A BENDIX AIR RACER

As the war moved into 1944, United States Army Air Force Republic P-47 Thunderbolt units moved towards Japan as America's war doctrine of island-hopping began capturing more and more enemy islands. The fighter preferred for lengthy Pacific over-water missions was the Lockheed P-38 Lightning, whose twin Allison engines offered a considerable margin of safety, but the plane was not available in as large numbers as the Thunderbolt and the P-38 did not really begin to proliferate until a bit later in the Pacific War.

Thunderbolt range was a problem due to the hungry P&W R-2800 radial but some unique modifications were undertaken to cure the problem. One of these was the installation of a huge 300-gallon tank under one wing with a 165-gallon unit under the opposite wing - this let P-47s fly from Morotai to Balikapapan, a distance of nearly 1000 miles, so that 5th Air Force bombers could be protected while they hit the enemy's important oil production plants in Borneo.

With the outsize fuel load, the Thunderbolts were hard to fly and the effect of flying long hours at high altitude was physically very trying for the pilots. Only a few missions of this type were undertaken but they greatly helped the 5th's fleet of Consolidated Liberators pound the enemy refineries into ruin.

As the American military effort moved closer to Japan, the enemy's aerial forces were literally blown out of the air as USAAF and Navy fighters scrambled for the relatively few remaining targets. Unknown at that time was the fact that the Japanese had pulled back many of their combat aircraft to prepare them for the suicide attacks that would take the Americans by surprise. Back home, Republic was rapidly moving forward with variants of the basic design that would make the P-47 an even more potent weapon.

In Europe, many of the P-47 Groups were having their aircraft replaced with Mustangs and, by the start of 1945, only the 56th Fighter Group still had the P-47 and they were going to get a brand-new version - one that promised much superior performance.

The last four aircraft in the P-47D27-RE production line were pulled from the line for rework. Three of these aircraft would become YP-47Ms and the final craft would become the XP-47N. The YP-47Ms were fitted with the Pratt & Whitney R-2800-57 "C" radials that at WEP rating could produce 2800-hp at 2800 rpm. For some time Republic was considering making a "hot-rod" Thunderbolt and the XP-47) was one such attempt. By taking the new radial and mating it to a production airframe, the M Model would be a relatively simple expedient that could be useful in chasing the new generation of Luftwaffe fighters and V-I robot bombs.

Testing indicated that with the CH-5 supercharger and Curtiss Electric paddle-- blade propeller, the M could hit 473 mph at 32,000 feet which was a very impressive figure. Even though the airframe was basically stock D27, numerous improvements were incorporated including new turbosupercharger, modified ignition harness, and more efficient fuel controls that would improve the engine's fuel specifics.

Using the WEP setting meant that P-47M pilots would be able to pass the fastest Mustangs at altitude but it would be at a distinct price since the engine at that setting would be consuming an astonishing 330 gallons per hour! The late D Model Thunderbolts could carry 370 gallons of fuel internally so it did not take a genius to figure out the range. The new engine controls in the M would, however, aid the pilot in reducing the aircraft's fuel consumption at cruise to about 100 gallons per hour which was an improvement over earlier models.

The P-47M would be a limited production aircraft and enough were ordered to equip two fighter groups. Only 130 P-47M-1-REs were built and virtually the entire production run was assigned to the Eighth Air Force's 56th Fighter Group.

With the constant rush of wartime production, complete testing was sometimes not undertaken. What worked under hasty factory testing would not function under operational conditions. This, unfortunately, was true of the P47M. Combat pilots were horrified to find their engines stopping completely or cutting in and out once they reached cruising altitude. Missions were hastily aborted and maintenance men were puzzled. Other engine problems began to manifest themselves, including corrosion and low cylinder head temperatures which affected the correct operation of the engine. There were also many piston and piston ring failures.

Republic rushed vice-president Hart Miller to England to aid in the problem-solving but this soon grew to nightmare proportions when it became obvious that every P-47M operated by the 56th was stricken with some form of problem. Since this was a major problem, the USAAF and P&W assigned their best maintenance crews. Ignition leads were suspect and they were replaced with a different type but the problem would not go away and it seemed that the -57 powerplant was an engine fated not to run.