THUNDERBOLT

Air Classics, Oct 2004 by O'Leary, Michael

THE BIGGEST SINGLE-SEAT COMBAT AIRCRAFT OF WORLD WAR TWO, AND ONE OF THE BEST, THE P-47 COULD TACKLE SEVERAL DIFFERENT MISSIONS AND PERFORM ALL OF THEM WELL

Seversky's (and later Republic's) experience with the P-35 and P-43 series of fighters had led to the conjecture that an improved version of the P-43 could supply the Army with a heavyweight fighter that would be capable of performing ground attack as well as interception duties. Alexander Kartveli, Seversky's chief designer, felt that there could be several avenues down which the new design could proceed. First, a basic redesign and modernization of the P-43 was an easy possibility. secondly, since the Army was so drawn to the Allison inline, Kartveli reasoned that a major redesign of his basic fighter concept could be undertaken so that the Allison could be accommodated. However, there was the possibility of sweeping the design board clean and coming up with an entirely new prototype.

The Army had shown some interest in the idea of using an Allison but Kartveli, studying the results of the early aerial fighting over Europe, decided that it would be wise to mate a new, slimmed-down air-frame to the Allison. However, during 1939 Kartveli came up with drawings and projected performance figures for the new Allison-engined project which was given the company designation of AP-10 but, when it was time during August 1939 to submit the design, now envisioned as strictly an interceptor, to the Army some problems arose. The Army did not think the new aircraft was suited to mass production techniques. However, the projected performance estimates were very encouraging so the data was submitted to the Army's experimental flying section at Wright Field in Ohio where the design was given a complete going over.

Army engineers had several helpful suggestions that increased the AP-10's chances for production. Kartveli's initial design work had attached the Allison to the smallest air-frame he could design. His reasoning was that superior performance could be achieved by keeping the frontal area as low as possible, the overall weight low and the armament fairly restricted to decrease space and save weight. Wright Field had a few other ideas to make the aircraft more suitable to the Army. They enlarged the design slightly, increasing weight and wing area. Oddly, since current battlefield reports were flowing in from Europe, Wright kept Kartveli's restricted armament of one .30- and one .50-cal machine gun housed in the upper section of the cowling. However, they did add two pylons under the wing that could , carry small bombs.

At this point, one of those strange twists that makes aviation history such a fascinating subject took place. With a projected top speed of 415-mph, the Army wanted to get the revised AP-10 into production as soon as possible. Accordingly, the Army issued the project with two designations: XP-47 for a fully combat furnished prototype and XP-47A (to be delivered before the XP-47) which would be an experimental prototype that would not be fitted with military equipment and would be used strictly to prove that the design was airworthy and suitable for production.

The company was thus faced with a very ambitious project: Build a relatively lightweight (something Seversky could not have been accused of previously doing) new fighter with a liquid-cooled engine and have it flying in the very short space of nine months. Problems quickly arose when the Army tried to obtain final permission for contract funding. An investigation into the type quickly showed some major deficiencies that were of serious concern to the contract makers. The rather primitive armament was immediately rejected in the light of European experience, while wing loading (the wing was a tiny 115-sq-ft in area) was felt to be much too high and the top speed, based on the projections from other manufacturer's new designs, was felt to be too low. These considerations led the design team back to the drawing board where the new design was hacked about, the wing area increased, the armament uprated with the addition of one .30- and one .50- cal machine gun and the weight increased to accommodate the various modifications. Kartveli felt that he could hold the top speed figure but he knew that the climb rate, a prime consideration for an interceptor, would decay with the additional size and weight.

By the start of 1940, the combat situation was changing so rapidly in Europe that American manufacturers were almost overwhelmed with design changes to keep up with what the foreign air forces wanted, Seversky had become Republic by the end of 1939, and the new company was continuing to modify the basic AP-10 design to satisfy Army requests. More weapons were to be added along with armor protection and self-sealing fuel tanks. More work was, of course, needed to complete design drawings and the final completion date of the XP7 -47A kept slipping. Republic could probably see that the idea of producing the new fighter was rapidly fading. The old Seversky company always favored big radial engines and, despite the change in name and the reshuffling of top management, the idea that a big radial was better than the Allison was still very popular.