The first fighter ‘Swinger’

As discussed earlier, with the advent of jet propulsion, the variable sweep “swing wing” appeared to offer military aircraft many advantages, notably the ability to land at low speeds like a straight wing aircraft but fly very fast like a swept wing aircraft.

Most of the research in the variable sweep area was done in World War II Germany by the Messerschmitt company for its uncompleted P.1101 fighter, and the prototype that never flew was recovered by U.S. forces in Oberammergau, Germany, and taken back to the United States for exploitation. It was given to Bell Aircraft, the builder of the ill-fated XP-59.

Bell used the P.1101 as a basis for the Bell X-5 research aircraft, which had a three position wing and became the first “swing wing” aircraft to fly. The good news was the swing wing worked well; the bad news was that other than that, the X-5 had terrible flying characteristics and was soon discarded.

The swing wing remained especially intriguing to the U.S. Navy for carrier operations, so after the relative success of the X-5 the Navy asked its most reliable aircraft supplier, the Grumman Aircraft Company of Bethpage, Long Island, to develop a swing wing fighter.

Grumman took the innovative assignment to heart, perhaps too much so. The company produced a fighter, the XF10F Jaguar (Grumman named all its fighters after cats), that not only had a swing wing but a new type of horizontal stabilizer, a new fuel transfer system and a brand new engine, the Westinghouse J-40.

The Jaguar turned out to be a large, portly – actually fat – fighter with an empty weight of more than 20,000 pounds – almost twice as much as the USAF F-86, a rough contemporary.

The XF10F had a shoulder mounted “swing” wing that could be put in two positions – a 13.5 degree sweep for takeoff and landing and 42.5 degrees for high speed flight. The wings had only very small ailerons and lateral control was provided mainly by eight paddle spoilers on each wing. These were not hydraulically powered, which was very usual for a jet fighter.

The Jaguar had “cheek” air intakes on both side of the nose, which gave it a hamster-like appearance,  and a “T” tail – a “double delta” horizontal stabilizer on top of the vertical stabilizer. The large rear delta stabilizer was free floating and moved by the small delta foreplane controlled the by the pilot. The small delta would, in theory, move the larger stabilizer. Wind tunnel tests had shown this design was wildly unsatisfactory, but this was chalked off as “model effect” and the stabilizer was included on the aircraft.

The J-40 engine on the Jaguar only produced 6,800 pounds of thrust, so a taxi test was made to see if the aircraft could fly from Grumman’s relatively short 5-000-foot-long runway. At 70 knots, the test pilot, “Corky” Meyer, pulled up the nose until the tail bumper hit the ground, then pushed the nose back down, only to find that stabilizer did not respond. As the wind tunnel tests had predicted, Meyer had a “control surface he could not control.”

Meyer had to hit the brakes to pull the nose down and stop, and the XF10F was sent to Muroc (now Edwards) Air Force Base, Calif. Muroc had a 7-mile-long “runway” on the salt flats that was used for flight tests on underpowered aircraft, and Meyer used it on every flight.

At Muroc, the large XF10F was derided by Air Force personnel as “The Navy Blue B-52,” and the test program went no better. On the Jaguar’s first takeoff try, Meyer recalled there was a long delay in elevator response, “it felt like it were made of very soft rubber” and “the airplane and I lurched up and down like one or the other of us was drunk.”

Meyer was not amused. After a week of taxi runs and brief liftoffs, he still did not feel the Jaguar was safe to fly more than 10 feet off the ground. When he finally made the first flight on May 9, 1952, the wing slats would not retract, limiting the aircraft to 180 knots, and an attempt to test low speed handling led to violet yaw and oscillations.

As the flight tests progressed, another disturbing characteristic emerged. The J-40 shuddered violently at start up and occasionally would send out a large puff of black smoke in flight. These were eventually accepted as “normal” and the test program continued, but the engine did not produced anywhere near the advertised thrust.

More challenging was the J-40’s slow acceleration – 21 seconds from idle to 100 percent, as opposed to other jet engines’ 10 seconds – and an as yet unexplored characteristic of the “T” tail, the deep stall. The innovative spoiler also fluttered at high speed with the wings swept back. Despite many attempted fixes, the control problems across the envelope were never solved.

On the other hand, the raison d’être for the Jaguar, the variable sweep wing, worked perfectly.

With the wings swept, the underpowered Jaguar could go supersonic in a dive with no compressibility or critical Mach number problems, and with the wing swept forward, the stalling speed was less than 90 knots, amazingly low for a fighter capable of Mach 1.

But at the end of a year, during which Meyer said “we tried to break all the rules of aerodynamics and common sense,” Grumman gave up on the Jaguar and the Navy used the two prototypes for arresting gear tests.

Grumman kept the swing wing idea, however, and used it on the F-14 Tomcat of “Top Gun” fame.

Dr. Michel is currently deployed downrange.