Directional Flight Handling Evaluation of the DUUC Using a Mobile Wind Tunnel

Abstract

Directional flight handling and stability characteristics of the Delft University Unconventional Configuration (DUUC) were assessed by means of an inhouse designed and built mobile wind tunnel setup. The DUUC aircraft features an integrated ducted fan propulsive empennage (DFPE) that replaces the entire horizontal and vertical tails for stability and control. For flight evaluation the DUUC was mounted on top of a pick-up truck and allowed only one degree of freedom around the z-axis. Testing was done by driving the pick-up truck on a 2.4km long runway at 15m/s and 20 m/s with thrust settings of 50% and 100%. The performed tests include one-engine-out trimming manoeuvres, step inputs, frequency steps and tests with an optional nose fin that reduces directional stability with 훥퐶푛훽 = 0.035. This thesis focusses on the static on-engine-out experiments. Testing has revealed that the directional stability and rudder efficiency of the DUUC are inversely proportional to the advance ratio. Nevertheless, the DUUC retains ample directional stability regardless of flight conditions. Validation of the experimental results was done by developing a semi-analytical model based on the linearized asymmetric
equations of motion and supplementing it with CFD data as well as previously obtained experimental data on the DFPE. The model is able to account for the observed phenomena and can reliably simulate different scenarios. Comparing the nominal directional stability of the DUUC with that the Boeing 747-200, Boeing 727-200, Cessna Citation II and Fokker F-27 reveals that it is by far the most stable aircraft with a minimal 퐶푛훽 = 0.34. OEI testing has revealed that the rudder alone is able to trim the aircraft at low advance ratios. At high advance ratios the rudder saturates in order to trim the aircraft. The aircraft remains controllable nonetheless given the option of using roll inputs to continue manoeuvring. Finally, the mobile wind tunnel setup employed for this project is a cost-effective alternative to a full scale wind tunnel and can gather adequate data but is susceptible to external disturbances currently limiting its usability.