POWER PLANT: One General Electric XT31-GE-1 turboprop, rated at 2,300 h.p. and one Allison J 33-GE-5 turbojet, rated at 703 kp
PERFORMANCE: 507 m.p.h. at 30,000 ft
COMMENT: For the long distances in the Pacific Area a long-range fighter was needed. The combination of a turboprop in the nose and a turbojet in the rear fuselage was promising: The turboprop would be used for endurance cruising and the turbojet to boost performance in the action area. Two prototypes were ordered but only one completed and flown
Power Plant: One × Allison V-3420-23 liquid-cooled engine, rated at 2,885 hp driving three-blade contra-rotating propellers
Performance: 433 mph at 20,000
Comment: The disappointing results of the test program with the General Motors/Fisher XP-75 “Eagle” led to a complete re-design of the aircraft. Furthermore, in mid-1943, the need for long-range escort fighters became more urgent than fast climbing interceptors so a decision was made to order six more XP-75 airplanes modified for the long-range role. At this time, an order for 2,500 production aircraft was also let, but with the stipulation that if the first production version P-75A was not satisfactory the complete order might be canceled.
At the time, General Motors was busy in several projects towards the war effort, including the mass production of several different aircraft types, among them the Grumman TBM “Avenger”. Redesigns of the P-75A “Eagle” were introduced including a new outer wing section from the North American P-51 “Mustang”, a modified tail assembly, new “bubble” canopy, and a V-3420-23 engine that corrected most of the deficiencies by the time the first P-75A “Eagles” entered flight test in September 1944.
By this time, the Army Air Forces decided to limit the number of combat aircraft types in production and not enter into large-scale production of new types that might not be available before the war ended. As the twin-engine Lockheed P-38 “Lightning” and North American P-51 “Mustang” demonstrated excellent long-range capabilities the production run of the P-75A “Eagle” was substantially terminated on October 1944. Although the “Eagle” was given extensive media coverage prior to its first flight, being trumpeted as a “wonder plane”, it was decided to use the six completed production aircraft for experimental work and development of the V-3420 engine. As a result of these events, the P-75A did not complete formal performance trials due to termination of the production contract. Ultimately, only eight XP-75s and six P-75As were built (Ref. 24).
Power Plant: One × Allison V-3420-19 liquid-cooled engine, rated at 2,600 hp, driving three-blade contra-rotating propellers
Performance: 433 mph at 20,000
Comment: The General Motors/Fisher XP-75 “Eagle” was a fighter aircraft designed by the Fisher Body Division of General Motors. Development started in September 1942 in response to USAAF requirement for a fighter possessing an extremely high rate of climb, using the most powerful liquid-cooled engine then available, the Allison V-3420.
In October 1942, the contract for two prototypes was signed. The design concept was to use the outer wing panels from the Curtiss P-40 “Warhawk”, the tail assembly from the Douglas A-24 (SBD) “Dauntless”, and the undercarriage from the Vought F4U-1 “Corsair” in a general layout much as in the Bell P-39 “Airacobra” with the engine located amidships with the propeller driven through an extension shaft.
In mid-1943, the need for long-range escort fighters became more urgent than fast climbing interceptors so a decision was made to order six more XP-75 airplanes modified for the long-range role. At this time, an order for 2,500 production aircraft was also let, but with the stipulation that if the first P-75A was not satisfactory the complete order might be canceled.
Powered by a V-3420-19 24-cylinder engine rated at 2,600 hp driving co-axial contra-rotating propellers, the XP-75 flew for the first time on 17 November 1943. The second XP-75 flew shortly thereafter, with all six long-range XP-75s entering the test program by the spring 1944. The test program brought up numerous teething problems, including miscalculation of the fighter’s center of mass, failure of the engine to produce its expected power, inadequate engine cooling, high aileron forces at high speed, and poor spin characteristics. These failures led to a complete redesign of the aircraft to a long-range escort fighter with the unchanged designation P-75 “Eagle” (Ref. 24).
POWER PLANT: One Pratt & Whitney R-4360-13 Wasp Major engine, rated at 3,450 h.p.
PERFORMANCE: 490 m.p.h. at 25,000 ft
COMMENT: At the time when the famous Republic P-47 “Thunderbolt” was not ordered by USAAF for mass production, Republic worked on a completely different fighter, the Republic XP-69. But in 1943 this project was cancelled in favour of a less radical design, the XP-72, and two prototypes were ordered. The first flew on 2 February 1944 with a four bladed propeller; the second XP-72 prototype had Aero Product contra props. An initial production contract for 100 aircrafts was ordered, which were foreseen as being useful for combat with V-1s, being launched in Europe at that time. But the need for long-range escort fighters declined, so the order was cancelled
POWER PLANT: 2 x Westinghouse 19B (J30) jet engines, rated at 650 kp each
PERFORMANCE: 547 mph
COMMENTS: In 1942 John K. Northrop conceived the XP-79 as a high-speed rocket-powered flying-wing fighter aircraft. In January 1943, a contract for two prototypes with designation XP-79 was issued by the United States Army Air Forces. To test the radical design, glider prototypes were built, designated MX-324. Originally, it was planned to use a Aerojet XCALR-2000A-1 liquid-fueled rocket motor rated at 920 kp thrust supplied by monoethylanilin and red fuming nitric acid. Because of the corrosive and toxic nature of the liquids, the XP-79 was built using a welded magnesium alloy monocoque structure to protect the pilot if the aircraft was damaged in combat with a 3 mm skin thickness at the trailing edge and a 19 mm thickness at the leading edge. However, the rocket motor configuration using canted rockets to drive the turbopumps was unsatisfactory and the aircraft was subsequently fitted with two Westinghouse 19-B (J-30) turbojets instead. This led to changing the designation to XP-79B. The nickname “Flying Ram” is attributed to the unusual fighting tactic. It was planned to fly with high speed direct towards the enemy and to hit it with wingtips or fuselage. Due to its extreme stability the fighter and its pilot should survive. The XP-79B was lost during its first flight on 12 September 1945. Shortly thereafter, the second and the overall project was cancelled (Ref.: 23).