When these HL-devices are stored during cruise-flight, they disrupt the smooth aerodynamic shape of the wing by their resulting gaps and seams. This precludes a possible cruise drag-reduction through a technology called Natural-Laminar Flow (NLF).
For NLF to work, especially the leading edge region of a wing needs to have a very smooth surface. In order to still be able to take-off and land at reasonable airspeeds and to allow drag-reduction in cruise, new smooth HL-devices are a prerequisite.
This research aims at evaluating a set of candidate structural technologies that allow for a smooth variation of the airfoil’s shape between the cruise and landing configuration.
A design trade-off that must be made in applying such HL-devices is the selection of the stiffness of the deformable nose part. Too low a stiffness results in a skin that will deform to a large extend under aerodynamic loading, while too high a stiffness makes it impossible to deform the nose into its HL configuration.
Another design aspect that is taken into consideration is the noise that an aircraft will generate with these novel HL-devices in take-off and landing. In comparison with traditional HL-devices, the proposed novel concepts will produce less lifting capability, which results in higher take-off and landing speeds. Although the novel devices are smoother and inherently less noisy than the traditional slats and flaps, this is offset by the fact that the generated noise power scales with the fifth power of the airspeed. The reduction of lifting capability therefore has to be brought to a minimum.
Since the envisioned application of these HL-devices is not limited to the standard â€œKansas-cityâ€ aircraft configuration, also the application to novel configurations will be investigated. Configurations that are under consideration are Blended Wing Bodies and Prandtl-planes.