Lateral-directional wind tunnel tests of the PROSIB 19-pax aircraft model

This paper presents the power-off, lateral-directional wind tunnel tests on the fixedwing, 19-passenger aircraft model developed within the Italian PROSIB project. The concept is an innovative small air transport airplane with distributed propellers and hybrid-electric powerplant. By measuring the aerodynamic forces and moments, the experimental investigation focused on the estimation of the power-off stability and control derivatives, highlighting the effects of the aerodynamic interference. Tests included a belly-mounted pod, simulating a battery storage unit, and two distinct empennage configurations: a body-mounted(low) horizontal tail and a T-tail(high). Numerical analyses were also used to further highlight the role of aerodynamic interference in the generation of forces and moments. For instance, wind tunnel data have shown a beneficial effect of the belly pod on the aircraft directional stability(+13%), but were in contrast with the results of numerical analyses(-30%). The measured sidewash depends also from the empennage layout, not only from the vertical tail planform area. Simulations confirmed an excessive directional stability with respect to the directional control in the ratio of 1.65, suggesting that such class of airplane should have a larger rudder chord ratio or a horn balance. Combined tests at different angles of attack and flap deflections revealed some issues on the lateral stability of the model, which are related to the velocity circulation on the wing in high-lift conditions counteracting the effective dihedral of the model's layout. The collected dataset of aerodynamic derivatives will serve as reference for a next experimental investigation on the aero-propulsive effects and provide useful information to researchers and professionals involved in similar design studies.