Mach Tuck - History

History

World War II fighters with high power engines capable of producing extremely high airspeeds were the first aircraft to experience Mach tuck. Because research with supersonic airfoils was in its infancy, there were no wings with the design elements that aid in slowing the onset of the Mach tuck effects. Instead, the shock wave would engulf the entire wing, making recovery much more difficult.

The P-38 was the first 400 mph fighter and it suffered more than the usual teething troubles. It had a thick, high-lift wing for fast climb characteristics and for holding a large fuel supply. It also had three fuselages: the central weapon and pilot nacelle or gondola, and the twin booms containing engines and turbosuperchargers. Finally, it was a very densely weighted fighter for its day, and accelerated quickly to terminal velocity in a dive. Bernoulli's effect worked very strongly on the thick wing, and was even more pronounced where air was pushed out of the way by and compressed between the central nacelle and the engine booms. Mach tuck would occur when the aircraft attained Mach 0.68 at which point the air flow over the wing roots would go transonic. The wing would lose lift and the normal loading of the tail's horizontal control surfaces would move aft, leaving the elevator unloaded, bringing the nose further down in a Mach tuck. Lockheed engineers eventually found a solution whereby a small 'speed bump' flap on the underside of the wing would be engaged by a pilot initiating a dive. The flap changed the center of pressure distribution so that the wing would not lose its lift.