U.S.A.
TYPE: Interceptor fighter
ACCOMMODATION: Pilot only
POWER PLANT: Wright R-3350-17 Cyclone, rated at 2,300 h.p.
PERFORMANCE: 488 m.p.h.
COMMENTS: Only two prototypes ordered
TYPE: Dive bomber, ground attack aircraft
ACCOMMODATION: Pilot only
POWER PLANT: One Pratt & Whitney R-4360 radial engine, rated at 3,000 hp
PERFORMANCE: 363 mph
COMMENT: The Vultee XA-41 was originally ordered as a dive bomber. After combat experience led the U.S. Army Air Corps to believe dive-bombers were too vulnerable to enemy fighters, the contract was amended to change the role to low-level ground attack. Although the XA-41 was a potent weapons system, the design was overtaken by more advanced technology, and never entered production.
The Vultee engineering team decided early in the design process to build the XA-41 (company Model 90) around the 3,000 hp Pratt & Whitney R-4360 “Wasp Major” radial engine. The large wing resembled that of the two-seat attack aircraft/dive bomber Vultee A-31/A-35 “Vengeance including a straight leading edge, forward-tapered trailing edge and pronounced dihedral on the outer wing panels. Designed to carry both a large internal load and external stores, the XA-41 was large for a single-engine aircraft. The single-place cockpit, set in line with the wing root, was 15 ft off the ground when the airplane was parked. As operational priorities shifted during its development phase, the original order for two XA-41 prototypes was cancelled, although the USAAF pressed for the completion of one prototype as an engine testbed for the R-4360, the same engine used by the Boeing B-50 “Superfortess” bomber.
Flying for the first time on February 1944, the sole XA-41 proved to have good performance with a maximum speed of 354 mph reached in testing and superb maneuverability, being able to out-turn a P-51B “Mustang”. However, with the reduction in military orders due to the approaching end of the war, no production contract was placed, and the aircraft was used as an engine testbed for the USAAF as well as being evaluated by the U.S. Navy in comparison with other contemporary attack aircraft, especially the Douglas AD-1 “Skyraider” and Martin AM-1 “Mauler”. After its Navy trials, the XA-41, bearing civil registration, was consigned to the Pratt & Whitney division of United Aircraft to continue engine tests. These continued until 1950 before the XA-41 was scrapped (Ref.: 24).
TYPE: High-speed medium bomber
ACCOMMODATION: Crew of three
POWER PLANT: Two General Electric J35-GE-3 turbojet engines, rated at 1,835 kp each
PERFORMANCE: 507 mph
COMMENT: USAAF leaders in the Air Material Command began to consider the possibilities of jet-propelled bombers as far back as October 1943. At that time, Douglas Aircraft was just beginning to design a promising twin-engine bomber designated the XB-42 “Mixmaster”. Reciprocating engines powered this aircraft but they were buried in the fuselage, leaving the laminar flow-airfoil wing clean of any drag-inducing pylon mounts or engine cowlings. The airframe appeared ideally suited to test turbojet propulsion. Douglas confirmed the feasibility of the concept and the USAAF amended the XB-42 contract in March 1944 to include the development of two turbojet-powered XB-43 prototypes, reduced from an initial order of 13 test aircraft. The Douglas design team convinced the Army that modifying the XB-42 static test airframe into the first XB-43 was a relatively straightforward process that would save time and money compared to developing a brand new design. Douglas replaced the two Allison V-1710 engines with a pair of General Electric J35 turbojets, then cut two air intakes into each side of the fuselage, aft of the pressurized cockpit. Removing the propellers and drive shafts freed enough space for two long jet exhaust ducts. Without any propellers present, there was no chance of striking the blade tips on the runway, so the entire ventral fin/rudder unit of the earlier XB-42’s full four-surface cruciform tail was omitted. Douglas compensated for the loss of yaw stability by enlarging the dorsal fin/rudder unit. The end of World War II caused a general slowdown within the aviation industry and General Electric was late delivering the engines. So America’s first turbojet bomber finally flew for the first time on 17 May 1946. Douglas Aircraft was keen to mass-produce the new bomber and the USAAF considered ordering 50, but these plans never became realized. The USAAF was already moving ahead with a new bomber, the North American XB-45 “Tornado”, designed from the outset for turbojet power and promising a quantum leap in every category of performance (Ref.: 24).
TYPE: High-speed medium bomber
ACCOMMODATION: Crew of three
POWER PLANT: Two Allison V-1710-125 liquid-cooled engine, rated at 1,325 hp each, driving three-bladed, contra-rotating propellers
PERFORMANCE: 410 mph at 23,440 ft
COMMENT: The XB-42 was developed initially as a private venture; an unsolicited proposal was presented to the USAAF in May 1943. This resulted in a contract for two prototypes and one static test airframe, the USAAF seeing an intriguing possibility of finding a bomber capable of the Boeing B-29 “Superfortress” range without its size or cost. The aircraft mounted a pair of Allison V-1710-125 liquid-cooled V-12 engines behind the crew’s cabin, each driving one of the twin propellers. Air intakes were in the wing leading edge. The landing gear was tricycle and a full, four surface cruciform tail was fitted, whose ventral fin/rudder unit prevented the coaxial propellers from striking the ground. The pilot and co-pilot sat under twin bubble canopies, and the bombardier sat in the extreme front behind a plexiglass nose. Defensive armament was two 0.50 in machine guns each side in the trailing edge of the wing, which retracted into the wing when not in use. These guns were aimed by the copilot through a sighting station at the rear of his cockpit. The guns had a limited field of fire and could only cover the rear, but with the aircraft’s high speed it was thought unlikely that intercepting fighters would be attacking from any other angle. The first XB-42 was delivered to the Army Air Force and flew at on 6 May 1944. Performance was excellent, being basically as described in the original proposal: as fast or even faster than the de Havilland “Moquito” but with defensive armament and twice the bomb-load. The end of World War II allowed the Air Force to consider possibilities with a little more leisure. Although with the second prototype additional Westinghouse 19XB-2A jet engines were mounted under the wings to enhance performance (XB-42A) it was decided to wait for the development of better jet bombers rather than continue with the XB-42 program (Ref.: 24).
TYPE: Experimental pusher fighter. Project
ACCOMMODATION: Pilot only
POWER PLANT: One Allison V-1710 liquid-cooled engine, rated at 1,100 hp at 30,000ft, driving contra-rotating propellers via extension shaft
PERFORMANCE: Data not available
COMMENT: Work on this unusual design started in in 1939. In order to keep the fuselage aerodynamically as clean as possible the engine was mounted in the mid-fuselage, driving counter-rotating three bladed pusher propellers via an extension shaft. Another advantage of the buried engine was enough room for heavy cannon armament in the nose. Thus the pilot had an excellent view and a wide field of fire. Although this fighter project was never realized it was the basis for many other pusher-type aircraft e.g. Bell XP-52, Vultee XP-54 Swoose Goose, Curtiss-Wright XP-55 Ascender, Northrop XP-56 Black Bullet, and Douglas XB-42 Mixmaster.
Type: Long-range escort fighter
Accommodation: Pilot only
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).
Type: High-altitude interceptor fighter
Accommodation: Pilot only
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).
TYPE: Long-range Escort Fighter
ACCOMMODATION: Pilot only
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
TYPE: Long-range escort fighter
ACCOMMODATION: Pilot only
POWER PLANT: Pratt & Whitney R-2800-77 ‘Double Wasp’ radial engine, rated at 2,800 hp
PERFORMANCE: 460 mph at 30,000 ft
COMMENT: The Republic P-47N was the last Thunderbolt variant to be produced. It was designed as an escort fighter for the Boeing B-29 Superfortress bombers flying raids on the Japanese home islands. Increased internal fuel capacity and drop tanks had done much to extend the Thunderbolt’s range during its evolution, and the only other way to expand the fuel capacity was to put fuel tanks into the wings. Thus, a new wing was designed with two 50 U.S. gal fuel tanks. The redesign proved successful in extending range to about 2,000 miles, and the squared-off wingtips improved the roll rate. The P-47N entered mass production with the uprated R-2800-57 engine, with a total of 1,816 built. The very last Thunderbolt to be built, a P-47N-25, rolled off the production line in October 1945. Thousands more had been on order, but production was halted with the end of the World War II in August 1945.
