Propeller Rotation Effects on Pitching Moment for Transport Aircraft with Conventional Tail

The effects of the propeller rotation direction on the pitching moment characteristics for a typical twin-engine turboprop aircraft with a conventional tail at low and moderate angles of attack under high-power conditions are investigated through unsteady Reynolds-averaged Navier-Stokes simulations. The numerical method is validated using wind-tunnel data for a twin-engine T-tail turboprop aircraft. The computational results of the conventional tail configurations indicate that the corotating propellers significantly degrade the longitudinal stability at low angles of attack in the takeoff configuration. By comparison with corotating propellers, counter-rotating inboard-up propellers not only increase the lift but also lead to a notable improvement in longitudinal stability, especially at low angles of attack. In contrast, the counter-rotating outboard-up propellers further reduce the negative pitching moment curve slope of the airframe. Analysis of the flowfield demonstrates that the effects of the propeller rotation direction significantly alter the downwash gradient at the horizontal tailplane by affecting the vertical location of the high-downwash region. The effectiveness of the horizontal tailplane and the longitudinal stability of the aircraft are therefore changed.