Curtiss XF15C Mixed-Propulsion Navy Fighter Prototype
The Curtiss XF15C was born during the fighting of World War 2 but suffered cancellation in the immediate post-war period.
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World War 2 (1939-1945) showcased both the pinnacle of the propeller-driven aircraft design and the rise of jet-powered aircraft. The former would be embodied by such aircraft as the late-war Grumman F8F "Bearcat" U.S. Navy (USN) fighter while the latter appeared through several progressive types that ultimately became fighting forms - the British "Gloster Meteor", the German Messerschmitt Me 262 "Schwalbe", and the American Lockheed P-80 "Shooting Star".
The road to dedicated turbojet aircraft was itself a long and arduous one that claimed the lives of many and further the careers of a select few. There stood a bridge design between the piston-powered forms that dominated the air battles of the war and the true turbojet-powered designs - the mixed-propulsion, or composite fighter, aircraft.
Because early turbojet designs were thirsty and generally seen as unreliable, early fighter forms were often fitted with two or more jets and these mounted under the wings for ease-of-maintenance and repair/replacement. Even the earliest of jet fighters - such as the famous Me 262 - actually flew under prop-power for a time in its testing phase. As such, engineers began drawing up plans for the short-term future of the military fighter aircraft flight and this led down the path of the combination propulsion system - a propeller-driven engine coupled with a force-producing rocket or turbojet installation.
Curtiss Aeroplane had been a longtime supplier of military and civilian aircraft even prior to World War 2 but its true claim to fame would only ever be its prewar P-40 "Warhawk" fighter which made a name for itself fighting over China against the Japanese. The company put together many other projects - some that were adopted and others that fell by the wayside before the end, the Curtiss XF15C becoming one of the latter investments.
The United States Navy was somewhat convinced about the short-term gains in utilization of a combination propulsion scheme and commissioned for several designs - one becoming the Ryan FR-1"Fireball" which first flew in June of 1944 and saw production reach 71 examples. This aircraft was evolved into the XF2R "Dark Shark" which flew in 1946. For its second composite fighter aircraft, the USN looked at a capable airframe powered by a Pratt & Whitney R-2800-34W of 2,100 horsepower coupled with the Allis-Chalmers J36 turbojet of 2,700 pounds thrust output (the Allis-Chalmers was a license-production copy of the British de Havilland Goblin engine). A four-bladed propeller would be driven by the former installation which also benefitted from use of a single-stage supercharger element.
A design review ensued which involved Curtiss and their Model 99 write-up which was put together in 1943. The USN liked what it saw and selected it for development as the "XF15C" which forced Curtiss engineers to abandon work on the high-performance XF14C aircraft - another navy-minded fighter design attempting to find a buyer (just one prototype of this design was completed). In April of 1944, the USN officially ordered three prototypes to fill its XF15C development commitment.
For the new aircraft Curtiss engineers adopted a low-wing monoplane form with the piston engine installed in the nose of the fuselage in the usual way. The fuselage was deep and well-contoured with the cockpit set well-ahead of midships. The pilot's position was over and ahead of the turbojet installation which ran across the belly and was fed by intakes in the wingroots. This jet exhausted through a port held under the tail. The tail itself and of a traditional design with a single vertical element and low-mounted horizontal planes. The wing mainplanes were straight with clipped tips and were mounted ahead of midships. The pilot maintained a commanding view of the surrounding terrain thanks to a relatively uncluttered view. The undercarriage was retractable and of a rather modern-looking tricycle arrangement.
The XF15C-1 - the designation afforded to the prototype group - was a large aircraft for one considered to enter carrier service. The type was intended to be fielded from the USN's new Midway-class which could accept larger types. Dimensions included a length of 13.4 meters, a wingspan of 14.5 meters and a height of 4.6 meters. Empty weight was 5,740 lb versus a gross weight of 7,545 lb.
Proposed armament became 4 x 20mm cannons - a definitive shift away from the American norm of multiple 0.50 caliber heavy machine guns featured so prominently in other fighter designs to date.
First flight of the XF15C prototype was on February 28th, 1945 though this was accomplished without the required turbojet engine and the intended Pratt & Whitney 34W engine - instead a Pratt & Whitney 22W radial was used. It was not until early May that the aircraft flew with its turbojet in place though this aircraft was lost in a crash later that month. During the short flying phase, some issues with handling and control became apparent and attempts followed to remedy them.
Despite the program's setback (the test pilot died in the crash) the program continued through a second prototype which went airborne for the first time on July 9th 1945 - this time it featured both of the intended powerplants which provided more of a finalized look and feel for the aircraft. Handling issues persisted and additional engineering was called into play which led to a new tail unit being fitted - this with a T-style arrangement and an extended dorsal section along the base of the vertical fin.
The war in Europe had ended back in May of 1945 which forced the review of many in-development aircraft and some inevitably fell to naught while others were allowed to gestate a bit longer. The latter proved the case with the XFC15-1 as the American commitment to the war in the Pacific was still ongoing. However, when this phase of the war drew down in late August and the USN beginning to focus more heavily on dedicated turbojet-powered forms, the Curtiss composite fighter was left with no takers. A last gasp for the project was briefly seen when the U.S. Army moved in to evaluated the large plane but this initiative was ultimately abandoned. The XF15C was formally cancelled in October of 1946 with three prototypes for show for itself.
Known performance specifications of the XF15C included a maximum speed of 470 miles per hour, a range out to 1,385 miles and a rate-of-climb nearing 5,020 feet per minute.