Control of Tailless Aircraft
Flying wings, or tailless aircraft, can be designed to have very low radar signature. The particular shape, and especially the absence of a vertical tail, require rather unconventional concepts to ensure that the aircraft is laterally controllable in all flight conditions.
A common approach to generate yaw control moments without a vertical fin is to create asymmetric drag by means of differential flap deflections, that is, by deflecting two flaps on only one wing in opposite directions. In contrast to a conventional rudder deflection,
the resulting yaw moment is not linearly dependent on the deflection angle. Furthermore, the efficiency of this technique depends substantially on the flight condition, notably the angle of attack.
As part of this research project, extensive wind tunnel experiments are performed in order to evaluate the effectiveness of aerodynamic control surfaces in a variety of flight conditions. For this purpose, two light carbon-fibre composite wind tunnel models have been developed and built. One is equipped with electronically actuated control surfaces and can be mounted in different rigs allowing model rotation, while the other will be used for unsteady pressure measurements.
The image below shows two photographs of oil-flow visualization experiments, where oil with a fluorescent agent is used to visualize the characteristics of the flow near the surface. From the pattern of oil accumulation on the surface, conclusions can be drawn with respect to the location of flow separation lines and the local magnitude of skin
Defence Materiel Administration (Försvarets materielverk, FMV)