Pitch-up

In aerodynamics, pitch-up is a severe form of stall in an aircraft. It is directly related to inherent properties of all swept wings, and seen primarily on those platforms. Unlike conventional low-speed stalls, pitch-up can occur at any speed, and are especially dangerous when they take place in the transonic; at these speeds the aerodynamic loads can become so high as to break up the aircraft, as occurred in 1964 when a F-105 Thunderchief of the USAF Thunderbirds broke up in mid-air.

Pitch-up problems were first noticed on high-speed test aircraft with swept wings. It was a common problem on the Douglas Skyrocket, which was used extensively to test the problem.

Before the pitch-up phenomenon was well understood, it plagued all early swept-wing aircraft. In the F-100 Super Sabre it even got its own name, the Sabre dance. In aircraft with high-mounted tailplanes, like the F-101 Voodoo, recovery was especially difficult because the tailplane was placed directly in the wing wake during the pitch-up, causing deep stall (although the T-tail was meant to prevent pitch-up from starting in the first place). Deployment of the braking parachute and a considerable height above the ground were essential for a chance at recovery.

Wings generate a relatively complex pattern of forces at different points on their planform. These are usually described as lift and drag components, using vector decomposition. If these vectors are added up for the entire wing, the result is a single force acting at some point on the wing. This point is known as the "center of pressure", or CoP, and is normally located somewhere between ⅓ and ½ of the way back from the leading edge. The exact location changes with changes in the angle of attack, which leads to the requirement to trim aircraft as they change their speed or power settings.

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