Whales inspire rotor blade efficiency study

After studying humpback whales, scientists working for the German Aerospace Centre (DLR) have discovered and flight tested a way of making helicopters more manoeuvrable, it has been revealed.

The scientists had been studying the issue of 'dynamic stall' created when lift separates from a blade moving backwards. The stall creates turbulence resulting in increased drag, and putting loads on rotor head control rods. The issue limits the speed of helicopters and their manoeuvrability, while vibration levels make the flight uncomfortable for passengers.

'Stalling is one of the most serious problems in helicopter aerodynamics – and one of the most complex,' said Kai Richter from the DLR Institute of Aerodynamics and Flow Technology in Göttingen, Germany.

The scientists looked to nature in a bid to solve the dynamic stall issues and fell upon pectoral fins on humpback whales. These fins, according to the scientists, feature bumps along the front edge. Research found that the bumps 'cause stalling to occur significantly later underwater and increase buoyancy'.

The DLR team translated the idea of using bumps for delaying the onset of stalling to helicopter rotors, and patented it as Leading-Edge Vortex Generators (LEVoGs).

Experiments on the LEVoGs conducted in the wind tunnel proved so successful that the team fitted them to the DLR's Bo105 research helicopter. As part of the DLR SIMCOS (Advanced Simulation and Control of Dynamic Stall) project. Some 186 rubber LEVoGs were glued to each of the helicopter’s four rotor blades.

'The pilots have already noticed a difference in the behaviour of the rotor blades,' explained Richter.
'The next step is a flight using special measuring equipment to accurately record the effects.'

If the idea proves successful, the researchers hope that existing helicopters could be retrofitted at little expense. For new helicopters, LEVoG-like contours could be milled into the front edges of existing titanium blade designs during the manufacturing process.


Source: By Tony Osborne in London, 02 February 2012 - Rotorhub News (www.shephardmedia.com)

Photo: German Aerospace Centre (DLR) Bo-1085 Helicopter (Photo by Shephard Group)

(1.02.2012)