Popular belief says the cleaner the leading edge of an airfoil is, the more efficient it becomes. But scientists are now looking into how strategically placed bumps on the main rotors of helicopters may boost performance. Researchers at the German Aerospace Center (DLR) in Göttingen, Germany, claim they got the idea of using the concept on helicopters from humpback whales, which are able to attain great speed under water with help from their oversized, bumpy-edged pectoral fins. “Research has shown that these bumps cause stalling to occur significantly later underwater and increase buoyancy,” said Holger Mai from the DLR Institute of Aeroelasticity.
This concept has been used on airplane wings with vortex generators (VGs), which effectively delay the separation of airflow over the wing. This change in the airflow around the airfoil can improve control surface effectiveness and decreases the stall speed, depending on the installation.
But the benefits for helicopters may be significantly different.
Kai Richter from the DLR Institute of Aerodynamics and Flow Technology hopes the addition of Leading-Edge Vortex Generators (LEVoGs for short) will decrease the dynamic stall of the aft moving main rotor blade during maneuvers and fast forward flight, which diminishes maneuverability and speed and causes unwanted vibration. If the concept proves successful, Richter says the rubber pieces could easily be retrofitted to existing main rotor blades at little expense. He also claims LEVoG contours could be milled into the propeller blades for new helicopters.
After conducting wind tunnel tests on the concept, DLR is now in the process of flight-testing LEVoGs using a Messerschmitt-Bölkow-Blohm Bo105 helicopter with 186 rubber LEVoGs attached to each of the four main rotor blades. The purpose of the initial flight tests is to prove the safety of the concept and so far the new technology looks promising. “The pilots have already noticed a difference in the behavior of the rotor blades,” Richter said. The next flight-test phase will record the effects of the LEVoGs.
