By : Anthony Smith

I recently attended an aerospace engineering conference in Melbourne. It was very informative, but tended to lean towards the larger commercial aircraft in its topics. However a number of items were discussed which we may see appearing in gliding in the not too distant future :

This has been an area of research by universities and NASA for some time. Rather than have conventional ailerons and flaps with a sharp change in airflow at the hinge line, they are looking at having the whole wing (or at least the near half) change its shape to provide more or less lift.

This would be significantly better aerodynamically, but is proving difficult to engineer using current materials and technology. The most successful so far is NASA who were using an F-111 with a modified wing that has a uni-directional elastomeric skin 9ie a skin that can stretch in only one direction), but the skin currently has only a short life span.

A very interesting paper was presented on a new direction in wing tip design. It researched why some birds of prey with relatively mediocre aspect ratio wings have similar glide performance to the Albatross and similar birds with very high aspect ratio wings. The author’s conclusion was the wing tip finger feathers on eagles significantly reduced the induced drag of their wings. He carried out flight tests on a glider by cropping the outer wing and replacing it with four slender parallel winglets in the same plane as the wing. His results were an increase in wing efficiency to around 2 (considering most glider wing currently are around 0.97!).

However I will have to research his calculations a bit better as I thinks he was a tad optimistic. The winglets were also the last part of the wing to stall as they behaved like a multi-slatted wing. What the high speed performance was like was not made clear in his presentation.

Two similar papers talked about the use of grooved surfaces to control airflow and control separation. You can now get adhesive plastic film in which grooves have been produced in the direction of optimum airflow for your aircraft. You carefully stick these sheets to your wings and fuselage. The grooves encourage the air to flow in an optimum pattern around the aircraft and hence improve the aircraft’s performance. Unfortunately the groove pattern only works best at one speed.

The other idea was to use grooves angled at 30 to 60 degrees across the airflow to control laminar separation. The idea is that the upstream end of the groove is closed and the downstream end is open. The airflow across the groove generates a vortex in the groove which flows out the open end. This vortex has low pressure and hence sucks away the boundary layer and has enough suction to prevent laminar separation. It was shown that even in unseparated flow, the grooves had less drag than a smooth surface! Is this goodbye to turbulator tape?

Lastly was a paper on continuing research at the Australian Defence Force Academy on castellated trailing edges. The theory is that square bites out of the trailing edge of a wing produce small vortices. These vortices are used to control the airflow near the trailing edge of a wing and hence reduce drag. Early results have shown a significant drag reduction on a range of wings (including helicopter rotors) in wind tunnels, including laminar and turbulent airflow.

My prediction is that if only a number of these prove successful, the shape of wings to come will be very interesting indeed! Enjoy your flying.

(Reprinted from Uni Gliding)