Modelling the Propeller Slipstream Effect on the Longitudinal Stability and Control

As the aviation industry continues to strive for improvements in fuel efficiency throughout the entire aircraft design, interest has been renewed in propeller engines. New research into advanced turboprop engines, so-called open rotor engines, seems promising as they combine the inherent high propulsive efficiency of ordinary turboprop engines, with the capability of delivering higher thrust. Unfortunately, the implementation of propeller engines does have significant implications on the stability and controllability of an aircraft. These implications are primarily caused by the propeller slipstream, the complex streamtube behind the propeller with strong gradients in various flow quantities both in streamwise and radial direction. The objective of this thesis was to develop, implement, and validate a prediction method for the propeller slipstream effect on the longitudinal stability and control of conventional aircraft configurations in the Initiator. During the investigation of the propeller slipstream effect, an existing prediction method was found which was based on calculating the four major effects caused by the propeller slipstream on the longitudinal stability and control. These four effects are, an additional normal force at the propeller disk, an increase in lift over the wing due to the slipstream, a change in the tail-off pitching moment, and a change in tail contribution to the pitching moment due to increased downwash and dynamic pressure. This method seemed ideal as it not only gives relatively accurate results, but does so with computationaly inexpensive calculations. During the implementation of this method in the Initiator, additional changes were made to calculate aerodynamic variables which were previously estimated using an extended vortex lattice method program. This implemented prediction method was validated using the only available wind tunnel data for the Fokker 50 and a special Saab 340 with T-tail configuration. Through this validation, the prediction method proved to maintain an acceptable accuracy for all configurations with minimal computation time. Further analysis of the results showed that the propeller slipstream effect reduces the tail effectiveness due to an increase in downwash angle at the tail. This was especially the case for the Fokker 50, which due to its low wing configuration, has a further increase in downwash caused by an inflow effect of the outer flow into the streamtube.Flight Performance and PropulsionFlight Performance and PropulsionAerospace Engineerin