Blow me up, blow me down

LOOKING out from a window seat in the midsection of an airliner, you can see clearly that the wing is made up of many moving parts. Although its aerofoil shape provides lift, a pilot needs to regulate the airflow over it in order to control the aircraft. The Wright brothers did this using a system called wing warping, which relied on pulleys and cables to twist the wings into a different shape. That approach was quickly abandoned, though, in favour of ailerons—hinged moving parts that provide more subtle control and place less stress on the structure.

But ailerons add weight and complexity to a wing. They also generate a lot of the radar reflections that designers of stealthy aircraft wish to eliminate. Finding a way to do without ailerons while avoiding the tedious business of having to warp the whole wing would thus be a good idea. And a group of researchers in Britain think they have one.

FLAVIIR, the Flapless Air Vehicle Integrated Industrial Research project, is a consortium of Cranfield University and nine other British universities, working in conjunction with BAE Systems, a defence contractor. Its pioneering effort, an aircraft called Demon, is a remote-controlled, delta-winged drone, 2.7 metres (106 inches) from wingtip to wingtip, that is powered by a small jet engine. Nothing particularly odd about that. But, in addition to ailerons, the wing is fitted with what the project's engineers refer to as fluidic controls.

Instead of moving a physical surface, fluidic controls divert the airflow over a wing by blowing compressed air out of narrow slots. Each side of Demon's delta wing has one row of these slots in the upper part of its trailing edge and another on the lower part. When one row on one side blows air at a higher pressure than the other it causes the airflow over the trailing edge on that side to bend up or down, in exactly the way that an aileron would, and the plane rolls accordingly. The ailerons, fitted as a back-up, in case the fluidic controls did not perform as hoped, are thus redundant.

FLAVIIR's researchers have come up with a range of designs for these fluidic controls. Philip John, the technical director of the project, says the version used on Demon has the compressed air entering a single chamber within a wing's trailing edge. This chamber contains a slightly eccentric cylinder which can be rotated to make either the upper or the lower slots bigger. On Demon, the air is produced from a seperately powered compressor, but in a production version it could be drawn from the engine.

Once enough data have been gathered from Demon, either a larger demonstration aircraft will be built or the system could be tested by converting an existing plane. The Demon system's success in controlling roll, one of the three axes of movement of a body in free space, is also leading engineers to wonder if the other two axes, pitch and yaw, might similarly be transferred to fluidic systems from, respectively, the elevator flaps on the tailplane and the rudder on the tail. The result, they hope, will be aircraft that are lighter and easier to maintain—and invisible to the enemy.