Pitch-Rate Induced Abrupt Wing Stalling of Straight Wing Aircraft

Abstract

An initial flight investigation into the effect of pitch rate upon stalling characteristics ha s been conducted , in the context of a comprehensive programme of transport aeroplane dynamics . For this study, the NRC Harvard straight -wing aircraft was used. A number of stalling manoeuvres w as conducted in free air and straight flight, at a variety of different stall -entry pitch rates. The results showed a variation of rigid body roll acceleration and roll rate with pitch rate. In addition, the post -stall motion profile also varied with pitch rate. The nature of the pitching and rolling characterist ics is discussed in terms of the flow physics of pitch -rate induced coupling effects determining the leading edge boundary layer state, including viscous fluid/ motion coupling . Generally, the stall -onset incidence varied directly with stall -entry pitch ra te; in other words , it was delayed by increasing pitch rate. The experimental data from the aircraft flight tests are correlated with dynamic stall data for airfoil sections using a stall onset delay similarity parameter . The favourabl e correlation obtai ned demonstrates the universality of this parameter and provides confidence in predictions of pitch -rate induced stall of aircraft .