The P-51 known as The Galloping Ghost
that crashed at the Reno Air Races, killing
11 and injuring more than 70.
The Galloping Ghost was equipped with data recorders that stored various parameters and also transmitted engine and GPS information to the ground. Within a couple of days of the accident it was reported that the telemetry had registered an 11 G pitch-up and that the engine was pulling full power — 105 inches of supercharged manifold pressure — in the final moments of the 440-knot dive.
Race speeds are much higher than the indicated airspeeds for which World War II fighters were originally designed, and the airplanes have to carry a lot of nose-down trim to compensate for excessively negative stabilizer incidence. Even the stock P-51H, the final version of the great fighter, could not trim hands-off for level flight at its maximum power. The effect of the nose-down trim — tab deflected upward — was to push the trailing edges of the elevators downward, as if the pilot were pushing forward on the stick. The tab, making use of the very powerful aerodynamic forces at an indicated airspeed around 390 knots, held the elevators down more forcefully than a pilot could. When the tab failed, the elevators would have jumped to their natural trail position and the airplane would have pitched violently upward. The pilot, slammed down and forward, was probably unconscious for the remaining few seconds of the flight.
The same thing had happened once before at Reno. In 1998 a pilot named Bob Hannah, flying the modified Mustang Voodoo, experienced a similar failure, was briefly unconscious and came to bent over, looking at his feet, inverted, and 4,000 feet above the ground. He managed to regain control of the airplane and landed safely.
As speed increases, pitch excursions become harder to manage. One reason is obvious: Aerodynamic forces upon control surfaces increase, but the strength of the pilot does not. Another reason is subtler, and has to do with the behavior of lift coefficient. Lift coefficient is the ratio between the lifting force produced by a wing and the force of air, at the same speed, against a flat surface. The weight of the airplane being constant, the faster it goes the lower its lift coefficient. At very high speed an airplane might have a lift coefficient of, say, 0.1 — one 10th. Lift coefficient increases at a constant rate with angle of attack. That rate varies from wing to wing, mainly as a function of aspect ratio, but for the sake of discussion let’s say that it increases by 0.1 per degree. If an airplane’s lift coefficient is 0.1 in level flight, then all that is needed to generate 2 Gs is to increase the angle of attack by one degree. At a lower speed, however, say the speed for best rate of climb, it might take six degrees’ change of angle of attack to double the G loading. That same six-degree pitch change, occurring at high speed, would generate six Gs.
