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The XP-39E was an experimental version of the Airacobra originally produced as a test bed for the Continental V-1430 engine. This engine failed to appear, and so the three XP-39Es were powered by the Allison V-1710-47 (E9). This engine was one of a number of versions of the V-1710 to be given a two stage mechanical supercharger (the same technology as used in the Rolls-Royce Merlin). As a result the XP-39E had much better high altitude performance than any version of the P-39 apart from the turbo-supercharged XP-39, with a top speed of 393mph at 24,000ft.
The XP-39E is often said to have had a laminar flow wing, as used in the P-63 Kingcobra, but this does not appear to have been the case. Instead each of the three XP-39Es used a slightly different wing. The XP-39E was significantly heavier than standard P-39s, with a gross weight of 9,000lb.
Originally two XP-39Es were ordered. The first aircraft made its maiden flight on 26 February 1942, but was lost in a crash on 26 March 1942 (from which the pilot escaped). After this crash a third prototype was ordered. The second aircraft made its maiden flight on 4 April 1942, and itself suffered serious damage on 11 May 1942.
Two days before the XP-39E made its maiden flight an order was placed for 4,000 of the new aircraft, with the designation P-76. This order was cancelled on 20 May 1942 before any aircraft had been built, and the factory space saved was used to built the B-29 Superfortress.
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How to cite this article: Rickard, J (7 July 2008), Bell XP-39E Airacobra , http://www.historyofwar.org/articles/weapons_XP_39E.html