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The F/A-22 Raptor performs aerial maneuvers during the Aviation Nation airshow on Nellis Air Force Base in November 2007. (U.S Air Force Airman Stephanie Rubi)

Birth of the Kulbit

Not just maneuverability. Supermaneuverability.

airspacemag.com

The idea of Wolfgang Herbst of the German aerospace group Messerschmitt-Bölkow-Blohm (MBB) envisioned a new class of aircraft that could maintain complete control while flying at airspeeds and angles of attack that would stall most aircraft. Such “post-stall maneuvers” could, in theory, be achieved with raw thrust alone when the airplane no longer had lift to fly in the conventional sense.

Normally, even the best-designed wings can stall at angles of attack above 20 degrees because normal control surfaces lose their effectiveness. The ability to rear up like a cobra in mid-flight would offer a huge tactical advantage to a fighter aircraft, predicted William Siuru in a paper published in 1988 by Airpower Journal.

“Let us look at an engagement between two fighters, one with post-stall maneuvering capability and one without it," he wrote. "The supermaneuverable fighter could turn much faster and dissipate much less energy in the process. Quite conceivably, it would have the adversary in its weapon system field of view several critical seconds before the other has completed its turn and is in firing position.”

Siuru warned that state-of-the-art Soviet fighters such as the Sukhoi Su-27 Flanker, the MiG-29 Fulcrum, and the MiG-31 Foxhound were nearing the capability of the U.S. fleet. “To give our pilots the edge, new designs incorporating advanced technologies are needed as well as revised tactics to get the most out of the improvements,” he suggested. “Enhanced maneuvering is high on the list.”

Early research for U.S. fighters centered on the Rockwell-MBB X-31 enhanced fighter maneuverability (EFM) program at NASA’s Dryden Flight Research Center in California. The first flight came in April, 1992. Within a year, the X-31 could fly a 180-degree turn in the minimum radius, a trick well beyond the aerodynamic limits of a conventional aircraft. The maneuver was called the Herbst, to honor the German scientist. The X-31 was soon joined at NASA Dryden by an F-18 and an F-16, which continued research on thrust vectoring in more than one axis.

In the U.S., research focused on Lockheed Martin F-22 Raptor, while designers in Russia used a circular nozzle for the Su-37.

Thrust vectoring may someday give pilots the edge in actual dogfights, but in the meantime the technology has become a top crowd-pleaser at airshows. One move possible only with thrust vectoring is the Kulbit, a somersault performed with the airplane at a full stall, and executed in the smallest possible forward and vertical distance. Russian pilots introduced it, but today every self-respecting thrust-vectoring airplane, including the MiG-29, the Sukhoi 30MK, and, of course, the Raptor has incorporated the sequence into its routine. When it comes to wowing the audience these days, "supermaneuverability" is all but required.

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