Innovative Design Produces World's Fastest Helicopter

What is the world's fastest helicopter? The answer to that question has been the same for 25 years. But that is soon to change. In 1986 the helicopter speed record was set by a helicopter which was based on a British military chopper known as the LYNX. With substantial modifications, the helicopter was able to reach a top speed of 249 miles per hour. This happened in 1986. Since then new technology has allowed different types of vehicles to break speed records across the board: there are faster cars, faster trains and faster planes, why has the helicopter record not been broken? The answer lies in a physics problem that has plagued engineers from the beginning.

Helicopters generate lift in much the same way as other aircraft, air passes over the curved blade faster than the air passing under the blade. This creates a low pressure zone above the blade just as you create a low pressure zone underneath a suction cup when you press it to a window. Thus a wing (or a helicopter blade) works in a way very similar to a suction cup. Just as atmospheric pressure holds a suction cup to a window, atmospheric pressure also forces a wing upwards. 

In order for a wing to generate this lift, it must be passing through the air very quickly; the higher the speed, the greater the lift. Airplanes accomplish this task by moving forward quickly, while helicopters accomplish the same task by rotating their blades at enormous velocities. This method of generating lift causes a problem known as dissymmetry of lift and is responsible for limiting the speed at which a helicopter can travel. As a helicopter moves forward, the relative velocity of its retreating blade is reduced and as the velocity of the blade is reduced, so is the lift on that side of the chopper. Conversely, the other blade is traveling through the air more quickly and thus more lift is generated on that side. If this imbalance were not corrected, the chopper would be able to do nothing more than roll over. Fortunately for helicopter pilots, engineers have long compensated for this problem by changing the angle of attack of the blades through methods such as flapping and feathering. Changing the angle of attack changes the speed at which the air flows over the top of the blade (you can see a demonstration of this in the airflow video) and thus changes the amount of lift generated.

Through controlling the angle of attack helicopter engineer’s can account for the different relative speeds of the retreating and advancing rotor blades and accomplish an even generation of lift. This method works well up to a point. However, helicopters have always been limited in that their maximum speed can never exceed the speed of the retreating blade. If this were to occur the speed of the blade would be completely cancelled out by the speed of the helicopter, this would mean there would be no airflow over the blade and thus no lift.

The engineer’s of the Sikorsky X2 have found a unique way to solve this problem. Instead of using a single helicopter rotor, the Sikorsky employs two sets of blades each of which rotate in opposite directions. This opposite rotation cancels out the dissymmetry of lift problem and allows the chopper to fly as quickly as its propulsion systems will allow. This has resulted in the Sikorsky reaching an unofficial speed of 287 miles per hour, more than 45 miles per hour faster than the previous record holder and over 100 miles per hour faster than the average chopper!

The applications for this technology are wide ranging. Greater helicopter speeds will give hospitals greater range and help to save lives, while military helicopters of this type will be better equipped to handle the mountainous terrain of places like Afghanistan. The engineer’s of the Sikorsky have found an elegant solution to an old problem and proved that sometimes the simplest answers are the best.