Ground-based warfare in World War 2 (1939-1945), with its heavy reliance on massed formations of tanks and other armored fighting vehicles, showcased to American warplanners the need for air services to field competent ground attack / support platforms. Various fighters were pressed into the fighter-bomber role and a few dedicated attackers mixed in-between. In the post-war world, with the jet age taking a greater hold with each passing month, there proved a "blank canvas" of sorts for engineers to develop all-new aircraft types. Because of the limitations inherent in early jet technology, "mixed powerplant" aircraft (combining a prop engine with a jet or rocket powerplant) were considered for a time and one entry into this field became the "AP-47" (AP = "Army Project") by Republic Aviation.
During the war, Republic was best known for its classic and versatile P-47 "Thunderbolt", a single-engine, single-seat aircraft affectionately known as the "Jug" for its deep fuselage appearance. This platform held 8 x 0.50 caliber heavy machine guns for standard, fixed armament and was soon found to possess exceptional qualities as a light bomber, carrying either drop bombs or rockets into the fray. In time, this fighter-bomber was supplanted in the U.S. inventory as more advanced aircraft began to take center stage. Unlike other wartime prop-driven aircraft seeing continued combat service in the upcoming Korean War (1959-1953), the Thunderbolt was not given an extended lease on life and eventually retired.
Back in September of 1948, during a decade when mixed-powerplant aircraft were en vogue, Republic attempted to interest the United States Air Force (USAF) in a new ground attack platform as the aforementioned AP-47. This aircraft was designed for the ground support mission and borrowed some of the proven qualities of the original P-47 including a four-bladed propeller unit and primary armament comprised of 8 x 0.50 caliber heavy machine guns. A tear-drop canopy was to provide exceptional vision around the aircraft with the cockpit fitted well-forward of midships. The prop engine was fitted to the nose ahead of the pilot and the turbojet seated within the aft fuselage, taking in air through a chin-mounted scoop and exhausting thrust through a port under the tail unit. The tail incorporated a single rudder with low-set horizontal planes. The wing mainplanes were reminiscent of the P-47, straight in their general appearance (from a top-down perspective) with rounded tips.
The fuselage was well-contoured with a sleek appearance as it tapered from nose to tail. The canopy was of a low-profile design to decrease drag at the frontal area and its position was to give the pilot a good view during attack runs, particularly when diving in on a target / target area. Unlike more modern jet-powered fighters types of the period (and today for that matter), the AP-47 was to feature an old-school "tail-dragger" undercarriage for ground-running.
The powerplants of choice became the Pratt & Whitney R-2800 "Double Wasp" installed in the nose and the Westinghouse 24C turbojet installed in the fuselage aft. The prop engine could output up to 2,500 horsepower and the jet was rated up to 3,000lbs of thrust. The aircraft should have been able to fly with one powerplant off but the Combined power promised exceptional performance - limited primarily by technology, fuel and the airframe.
The aircraft was to hold a wingspan of 41 feet, 6 inches but few other numbers were known such as range - which was to rely on three large internal fuel tanks taking up space within the fuselage to feed both the prop engine and the jet, the latter being the thirstier of the two.
In the end, USAF authorities were not convinced of the merits of this mixed-powerplant attacker and held little interest in pursuing the design, leaving it to the pages of military aviation history instead. The United States Navy (USN) found slightly more success with a mixed-powerplant design in the Ryan FR "Fireball" detailed elsewhere on this site. Some seventy-one of this aircraft were completed. The follow-up XF2R "Dark Shark" did worse with only a single prototype built but by this time pure jet-powered thoroughbreds had become the way of the future.
There were certainly other mixed-powerplant designs entertained during this period but advancements to jet technology soon made the prospects for such aircraft poor.
Performance specs on this page are estimated on the part of the author.
- Close-Air Support (CAS)
- X-Plane / Developmental
40.03 ft (12.2 m)
40.03 ft (12.2 m)
13.94 ft (4.25 m)
7,716 lb (3,500 kg)
11,684 lb (5,300 kg)
404 mph (650 kph; 351 kts)
43,143 feet (13,150 m; 8.17 miles)
1,553 miles (2,500 km; 1,350 nm)
4,500 ft/min (1,372 m/min)
8 x 0.50 caliber Browning M2 heavy machine guns in wings (four per wing element).
Most likely provision for drop bombs and air-to-surface rockets.
AP-47 ("Army Project 47") - Base Project Designation