Ridges on helicopter blades could help to improve future agility

Specially designed ridges placed on the leading edge of helicopter blades could allow the aircraft to travel at higher speeds and with greater agility, writes Andrew Czyzewski.

Researchers at the German Aerospace Centre (DLR) took inspiration from ridges found on the pectoral fins of humpback whales.

Helicopters owe their ability to vertically take-off and land to their main rotor, but this contributes to aerodynamic instabilities – as Dr Kai Richter of DLR explained to The Engineer. ’The main problem is that on the advancing blade the rotational speed and the flight velocity of the craft itself combine, so locally on the blade there are very high flow velocities – you even get supersonic flow on the outer part of the blade. But on the retreating blade it’s the other way round, the rotational speed and the flight speed of the helicopter subtract and you have low flow velocities.’

The result of this asymmetry is that the inclination of the rotor blade changes so that the advancing side has a low ’angle of attack’ and the retreating side, a high angle of attack. ’Typically if you increase the angle of attack of the rotor blade, the lift you generate increases as well, but at some point when your angle of attack is too high, the flow separates and your lift drops – this is called dynamic stall. This phenomenon occurs especially when you fly at high speed and when doing narrow turns,’ said Richter.

In an effort to delay this stalling, the researchers came across work modelling humpback whales, which due to their large pectoral fins with bumps along the front edge, are quite agile in the water.

Since flow phenomena in water are similar to those in air they were able to adapt these bumps for the latter, taking into account the greater density of the water. The results was a series of leading-edge vortex generators (LEVoGs) with a diameter of 6mm and a weight of just 0.04g.

After performing wind-tunnel testing to get the right configuration, researchers are now essentially gluing LEVoGs to helicopter blades.