Low speed wind tunnel test of the jet trainer model at high angles of attack

Abstract

The article discusses the results of the wind tunnel test of the model of the highly manoeuvrable jet trainer, in the wide range of angles of attack. The main objective of this work was to modify the geometry in order to achieve the assumed properties (stability, control and dynamic behaviour in terms of high angles of attack), and possibly reliable verification of characteristics. In order to control the geometry of subsequent variants of aerodynamic models during the test, the full parametric representation of the CAD geometry was used (applying Siemens NX system) and the modular construction of the models. This enables to change the various components (e.g. the front part of the fuselage, the air inlets, wings, tail, strakes etc.). The wind tunnel models were produced using 3D printers, based on the FDM (Fused Deposition Modelling) method. This allows for relatively fast model prototyping while maintaining full control of geometry and very low cost. Studies were conducted using several models differing in geometry as well (in order to determine the effect of blockage) model scale implementation. Studies carried out in a low speed wind tunnel using an internal balance mounted on bent sting (to enable measurement at high angles of attack). The measurements were carried out in the range of angles of attack -2° to 56° and slip angles +/20°, with different deflections of leading edge flaps, trailing edge flaps, elevator, rudder and ailerons. The static aerodynamic characteristics of final version of the model indicates the correct properties in the entire range of flight conditions: the ability to ensure a longitudinal balance with appropriate longitudinal moments necessary to control (reduce the angle of attack), the correct dynamic characteristics at high angles of attack (no pro-spin trend) and the ability to lateral and directional control. Some interesting novelty that will be presented in the paper is a preliminary evaluation of the dynamic properties of the aircraft at high angles of attack, carried out on the model in the tunnel, providing three degrees of freedom (rotation about all three axes).