Power Effects on Stability and Control

The World War II period 1939-1945 coincided almost exactly with the appearance of power effects as a major stability and control problem. Grumman Navy fighters of that period illustrate the situation. World War II opened with the F4F Wildcat as the Navy’s first-line fighter and ended with the debut of the F8F Bearcat. The external dimensions of the two aircraft were almost identical, but the F8F’s engine was rated at 2,400 horsepower, compared to 1,350 horsepower for the F4F.

In unpublished correspondence, W Hewitt Phillips remarks that the appearance of power effects as a major stability and control problem was not entirely the result of growth in engine power:

these effects have been with us since World War I, but weren’t serious then because of the light control forces required to offset these effects, resulting from the low speeds and smaller size of these airplanes. The power effects in terms of thrust and moment coefficients were probably of the same order as in the case of the World War II fighters. These effects would have been somewhat reduced because of the short nose moment arm of these planes, and because of the lower lift coefficients due to the lack of high lift flaps.

The further growth in power and stability effects on military propeller-driven aircraft was of course interrupted by the advent of jets, with a different set of power effects on stability and control, generally of a minor nature. This chapter reviews the history of both propeller and jet power effects on stability and control. Although the days of high-powered propeller-driven military aircraft may be ended, their civil counterparts still exist, with a new set of stability and control problems.