POWER PLANT: One Kayaba Model 1 ramjet engine rated at 750 kp thrust at 457 mph and four solid fuel rocket boosters for take-off, rated at 7.200 kp thrust
PERFORMANCE: 559 mph (estimated)
COMMENT: The Kayaba “Katsuodori” (“Booby Gannet”) was the result of the endeavor to design a single-seat, ramjet-powered interceptor-minded platform which utilized a short, tailless fuselage configuration with swept-back wing main planes. The cockpit would be held well-forward and offered exceptional vision for the pilot. The mid-mounted main planes were affixed ahead of midship with each tip capped by small vertical stabilizers. The ramjet propulsion system was buried within the tubular fuselage and a rocket-assist scheme (consisting of four externally-held rocket pods) was to be used. The rocket pods were installed under the wing roots and jettisoned once their usefulness had run out. Having achieved the required speeds, the aircraft would then continue on under ramjet power with a flying window of about 30 minutes being estimated. To aspirate the ramjet, the nose section featured an air intake. No conventional undercarriage was provided. Instead the aircraft would glide back home powerless and land on a belly-mounted skid. The ramjet under consideration for the project became the Kayaba Model 1 which promised 750 kp thrust output.
Since the aircraft never achieved prototype form, performance specifications were estimated and this included a maximum speed of 560 miles per hour with a rate-of-climb around 11,000 feet-per-minute. The latter would prove a good quality to have in interception sorties. The service ceiling was listed at 49,215 feet
As an interceptor attempting to tackle very large, slow-moving (but well-defended) targets, it was seen to arm the fighter appropriately through 2 x 30mm Ho-301 series cannons – this was a suitable arrangement to counter even the high-flying and technologically advanced Boeing B-29 “Superfortress” which had made its presence known since mid-1944. The cannons would have been embedded in the sides of the nose.
Design work on the “Katsuodori” progressed into 1943 and plans were underway to begin construction of a working prototype for the following year. However, Japan’s fortunes in the war had worsened into 1944 and the attention of authorities turned to more viable military weapons such as the Rikugun (Mitsubishi) Ki-202 “Sharp Sword”, based on a rocket-powered interceptor developed by Mitsubishi as Ki-200 “Shusui” for the IJAAF and J8M-1 for the IJNAF on the basis of the German Messerschmitt Me 163 “Komet” (Ref.: 24).
POWER PLANT: One Lycoming XH-2470-1 liquid-cooled engine, rated at 2,300 hp
PERFORMANCE: 381 mph at 28,500 ft
COMMENT: The Vultee Company had submitted a proposal in response to a US Army Air Corps request for an unusual configuration. The Vultee design won the competition, beating the Curtiss XP-55 “Ascender” and Northrop XP-56 “Black Bullet”. Vultee designated it Model 84, a descendant of their earlier Model 78. After completing preliminary engineering and wind tunnel tests, a contract for a prototype was awarded on January 1941. A second prototype was ordered on March 1942..
The XP-54 was designed with a pusher engine in the aft part of the fuselage. The tail was mounted rearward between two mid-wing booms, with the 12-ft propeller between them. The design included a “ducted wing section” developed by the NACA (National Advisory Committee of Aeronautics) that enabled installation of cooling radiators and intercoolers in the inverted gull wing. The Pratt & Whitney X-1800 engine was initially proposed as the power plant but after its development was discontinued, the liquid-cooled Lycoming XH 2470 was substituted.
In September 1941, the XP-54 mission was changed from low altitude to high altitude interception. Consequently, a turbo-supercharger and heavier armor had to be added, and the estimated empty weight increased from 5,200 to 8,200 kg.
The XP-54 was unique in numerous ways. The pressurized cockpit required a complex entry system: the pilot’s seat acted as an elevator for cockpit access from the ground. The pilot lowered the seat electrically, sat in it, and raised it into the cockpit. Bail-out procedure was complicated by the pressurization system and necessitated a downward ejection of the pilot and seat in order to clear the propeller arc. Also, the nose section could pivot through the vertical, three degrees up and six degrees down. In the nose, two 37 mm T-9 cannon were in rigid mounts while two .50 cal. machine guns were in movable mounts. Movement of the nose and machine guns was controlled by a special compensating gun sight. Thus, the cannon trajectory could be elevated without altering the flight attitude of the airplane. The large nose section gave rise to its whimsical nickname, the “Swoose Goose”, inspired by a song about Alexander who was half swan and half goose: “Alexander was a swoose.”
Flight tests of the first prototype, Serial Nr. 41-1210, began on 15 January 1943. Initial trials showed performance to be substantially below guarantees. At the same time, development of the XH-2470 engine was discontinued and, although it appeared possible to substitute the Allison V-3420 engine without substantial airframe changes, the projected delay and costs resulted in a decision not to consider production buys.
The prototypes continued to be used in an experimental program until problems with the Lycoming engines and lack of spare parts caused termination. The second prototype, 42-108994 (but mistakenly painted as 42-1211) equipped with an experimental General Electric supercharger, only made one flight before it was relegated to a “parts plane” in order to keep the first prototype in the air (Ref.: 24).