A Study Of The Army Standard Hot Day

A study was made of the Army hot day standard design hover criterion through the development of analytical models representing hovering aircraft, cost, climatology and various features of the operational environment. Design pressure and altitude and temperature were treated as input variables, and their effect was evaluated using a rotorcraft's probability of hover in nineteen countries/regions contiguous or nearly so to the Soviet-Sino block. It was concluded that although the probability of hover provided insight into various factors affecting design and operation of aircraft, it did not exhibit any inherent feature that would allow the selection of a design hover criterion. The inclusion of cost in the evaluation revealed that an aircraft exhibits a maximum in effectiveness/ cost with increasing design altitude (at constant temperature). Because this maximum effectiveness/cost point is sensitive to factors causing operational performance degradation (power losses, weight growth and so forth) and aircraft type and weight class there is no optimum design hover criterion, but rather a range of best design hover points. It was concIuded that if a rotorcraft is to have any tolerance for performance degradation then a design point of 5500 feet, 95°F represents the low end of the range of design hover conditions. The best point within the range is a matter of judgment, however, there appears little justification for lowering the present 6000 feet, 95°F design hover criterion.