Influence of Separated Wing Flow on Tail Downwash of Low-Wing Pusher Configuration

Abstract

REVIEW of the various types of airplanes currently in use as ab-initio trainers (e.g., Jane’ s All the World’ s Aircraft, 1988‐89) reveals that these designs predominantly feature a tractor (front-engined ) cone guration with a conventional wing and tail arrangement. However, unconventional cone gurations with a podand-boomfuselage and a pusher engine offer advantages such as reduceddrag,improvedvisibilityforthepilots,andlowernoiselevels. These advantages have been studied by Strojnik 1 and Carmichael. 2 Based on similar considerations, Sharma 3 had proposed a pusherengined, pod-and-boom design for a two-seat ab-initio trainer. Wind-tunnel tests on a model of this airplane showed, 4 as compared to theoretical estimates, much lower lift curve slope, much higher induced drag, and much higher static stability. The tests also indicated a signie cant region of separated e ow near the wing root. Taking clues from this and observations made by Muttray, 5 the lift distribution on the wing was calculated, in the presentinvestigation, withregionsofseparatede ownearlyequaltothoseindicatedbye ow visualization. In this region the local lift-curve slope is assigned a very small value. Calculated lift-curve slope of wing, induced drag, and downwash closely match the experimental values and serve to explain the unusual behavior of the cone guration. The cone guration and results of wind-tunnel tests are briee y described in the next section.Calculationofthelift distribution witharegion of separated e ow and results and discussion are presented subsequently.