European research efforts to cut helicopter noise and vibration while improving fuel economy could be realised by building on a 1970s motor racing aerodynamics breakthrough, according to Dutch research into "smart" rotor blades.
Alexandre Paternoster, working at the University of Twente in the Netherlands, has concluded that of the various active blade systems that may improve performance by adjusting the aerofoil shape during its rotation, the most promising is the so-called Gurney flap - named after American motor racing great Dan Gurney, who in the early 1970s discovered that this relatively simple device could dramatically increase the downforce from a car's spoilers.
The Gurney flap is a strip of material placed at a right angle to the airflow at the trailing edge of a wing on the pressure side, to increase lift. They are sometimes used on helicopter stabilisers for aerodynamic balance. But a retractable flap could be used to improve main rotor performance. As fixed-wing aircraft adopt a downward flaps configuration for maximum lift on approach, a Gurney flap on the underside of a helicopter rotor would increase lift - and improve performance if deployed when the blade is retreating, by balancing the greater lift provided by the opposite, advancing, blade.
The width of a typical Gurney flap would be about 2% of the wing chord, or 1.624mm in Paternoster's study. As expected, Paternoster found that such a configuration adds drag, but he concluded that the improvement in lift-to-drag ratio results in a net efficiency improvement.
Further work, he says, must be done to devise a workable activation mechanism, particularly in regards to hinge materials, but a 95V piezoelectric mechanism could deploy the flap within 0.4ms.
Paternoster determined that a retractable Gurney flap was a more practical solution to the "smart blades" problem than trailing edge flaps or morphing blades. His study was supported by the EU Green Sky research initiative.
Source: Flight International
