The jet engine made its way into operational service in the latter stages of WWII, first with the German Luftwaffe, then the Royal Air Force, and finally with the United States Army Air Forces, who fielded the rather disappointing Bell P-59 Airacomet. By 1943, the US Navy wanted to develop their own turbojet fighter, but the early jet engines couldn’t provide the acceleration required to take off from short aircraft carriers, and the steam catapult was still about ten years away. So Admiral John S. McCain, Sr. proposed the development of a hybrid aircraft that would make use of a proven propeller engine for takeoff and landing, and a jet engine for high-altitude cruising and bursts of speed. Eight companies proposed such a plane, but the first one to fly came a company that was not known for producing military aircraft.

Ryan FR Fireball (US Navy)

The Ryan name became famous in 1927 with the Ryan NYP, better known as the Spirit of St. Louis, though the company that bore the Ryan name by WWII actually had nothing to do with Charles Lindbergh’s airplane. Ryan Aeronautical was founded in 1934, and the company had made most of its money building civilian sport planes. Its only experience with military aviation was the successful PT-22 Recruit trainer. Nevertheless, the Navy awarded Ryan a contract for the delivery of three prototypes, designated XFR-1. Ryan nicknamed the aircraft the Fireball, and the Navy adopted the name.

The arrangement of radial and jet engines in the Fireball (US Navy)

Unless you saw the Fireball from the rear, it was hard to tell that it was actually a modern hybrid fighter, as it bore the outward appearance of a traditional piston-powered fighter. Even without its jet engine, the Fireball was quite advanced for its era. It featured a tricycle landing gear, a laminar flow wing, and flush rivets over the entire aircraft, a first for the Navy. The nose of the Fireball housed a Wright R-1820 Cyclone nine-cylinder radial engine providing 1,350 hp, and the fuselage was wrapped around a General Electric I-16 (J31) turbojet which provided 1,600 lbs of thrust. The radial gave the Fireball plenty of power and speed at lower altitudes, while the thrust of the jet helped improve high-altitude performance. At maximum speed, the Fireball managed just over 400 mph. The maiden flight was taken on June 25, 1944 with just the radial engine, and the jet engine was installed a few days later.

The FR-1 Fireball’s jet exhaust. Note the larger vertical stabilizer than the original Fireball. (US Navy)

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The Fireball was not without its teething problems, including trouble with radial engine overheating and structural weaknesses. When pilots exceeded 7.5 Gs in a dive, the wings had a nasty habit of breaking off. It was also known to break in half after particularly hard carrier landings. Despite these shortcomings, the Fireball entered service with Navy squadron VF-66 in March 1945, and the fighters were sent to the Pacific to combat the Japanese Ohka piloted suicide rockets, which were too fast for the Navy’s piston-powered fighters. However, the Fireballs arrived in the theater after the Japanese surrender and never saw combat service. Still, the Fireball earned the distinction in November 1945 of being the first Navy aircraft to land on a carrier under jet power alone, but it only did so because the radial engine had failed. The Navy originally ordered 1,000 Fireballs, but only 66 had been delivered when the contract was canceled with the end of the war.

Ryan XF2R Dark Shark. It’s lineage to the FR Fireball is evident. (San Diego Air and Space Museum)

Though it never flew in combat, the relative success of the Fireball prompted Ryan to improve on it. One production Fireball was modified to receive a General Electric TG-100 (T31) turbojet engine in the nose to complement the I-16 turbojet, and the newly named XF2R-1, called the Dark Shark, became the first US Navy aircraft aircraft to fly with a turboprop engine. Not only did the turboprop offer better overall performance, its use of a variable pitch propeller turning at a constant speed allowed instant acceleration and deceleration and shortened carrier landing distances. The Dark Shark also benefitted from 550 lbs of extra thrust from the turboprop engine, which helped it attain a top speed of nearly 500 mph. Though the Dark Shark performed well, it was clear that mixed propulsion was not the wave of the future as the Navy had hoped, and only a single prototype was built before the program was canceled.

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Ryan X2FR Dark Shark engine arrangement (San Diego Air and Space Museum)

Ryan wasn’t the only company to develop a mixed propulsion fighter for the Navy. Curtiss proposed their own hybrid fighter in the hopes that the aircraft manufacturer might score a lucrative Navy contract to prop up the struggling company. Curtiss had been working on such a fighter for some time and, when the Navy approached them to provide three prototypes, they told the Navy they could deliver one the next day. The XF15C, unofficially nicknamed Stingaree by Curtiss, was powered by a Pratt & Whitney R-2800 Double Wasp radial in the nose and an Allis-Chalmers J36 centrifugal flow turbojet, a license-built version of the de Havilland Goblin, installed amidships. The central location of the turbojet allowed for a shorter tailpipe which increased the thrust of the jet engine.

Curtiss XF15C-1 with modified T tail. The first XF15C had a tail similar to the FR Fireball. (US Navy)

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The XF15C took its maiden flight without the turbojet on February 27 (or 28), 1945, and tests with the jet engine commenced three months later. With at top speed of 469 mph, the XF15C was slightly slower than the Dark Shark, though it had a better rate of climb. Following the crash of the first prototype, Curtiss completely redesigned the tail, enlarging the horizontal stabilizer and adopting a T tail configuration, but problems with the hybrid fighter continued, including significant issues with vibrations that were never solved. Of the two remaining prototypes, one was scrapped after the war and the other was placed in storage. It is now part of the collection of the Hickory Aviation Museum in North Carolina.

The XF15C with its original tail design (US Navy)

In the end, the idea of mixing propeller and jet engines never really took off. Rapid advances in jet engines technology led the Navy to adopt its first pure jet fighter, and the first to be specifically designed for carrier duty, in the McDonnell FH Phantom in 1947. In the 1950s, The Air Force experimented with adding props to existing jet fighters, such as the McDonnell XF-88B and Republic XF-84H, and turbojets were retrofitted to existing propeller aircraft to augment power and increase speed. But the true hybrid fighter, which had one wheel in the past and one wheel in the future, was left behind.

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