The Rationalization of Load Factors for Airplanes in Flight 320027
CONSTANT improvement in airplanes involving increased speeds and increased maneuverability permits of their performing evolutions that were not contemplated when present strength requirements were established. Additional data and experience, however, make possible the breaking down of some of the problems involved into components that can be treated rationally and others that must still be handled empirically. A method for determining load factors in the high-angle-of-attack condition by the use of two rational variables and one empirical coefficient is described and applied to some 19 airplanes, the results being compared with the factors established by current practice. An effort is also made to coordinate wing and tail-loading conditions by establishing limiting velocities for various maneuvers, these depending on the magnitudes of such factors as have been established by experience, the factors being dependent on velocities where new conditions require diving and pulling out from dives at speeds in excess of those formerly considered necessary.
All limitations established must be based on experience and good judgment, hence empirical or approximate procedures can frequently be substituted for more tedious theoretical processes. Because of the empiricism involved in certain factors and the lack of data concerning variables affecting others, complete rationalization of load factors and design conditions is not yet possible, although a number of steps can be taken to advance the art in that direction.
Remarkable unanimity of opinion is expressed by the various discussers regarding the need for rationalizing the load factor, but there agreement ceases. One discusser suggests two formulas including an arbitrary factor of safety multiplied by the speed range squared and multiplying the cube root of the wing-loading:power-loading ratio by a constant respectively. Physiological resistance of the pilot and the strength of the airplane are stressed by another. A third considers that linking the nose-dive and tail-loading conditions with the angle of attack offers the best solution of the problem and points out that the safe pull-out speed should be determined and posted in the cockpit for the pilot's guidance. Piloting technique, more than any other influence, says another, determines the load factor in a given functional group.