Helicopters are the actions heroes of the sky. With the ability to take off and land in small and confined spaces, hover in the air travel at any speed in any direction they are the perfect vehicle for military action, search and rescue operations, and medical emergencies.
Helicopter blades spin at between 400 and 500 RPM, are between 40 and 60 ft long, and are attached to the helicopter by a rotor hub which allows the pilot to control the aircraft by changing the blades’ angle and pitch of rotation.
The defining feature of the helicopter is, of course, its rotor blades. Since their invention in 1936, these wonders of engineering have made possible the most versatile flying machines the world has ever known.
When was the rotor blade invented?
The rotor blade is the defining feature of the helicopter and, interesting, the helicopter rotor seems to have been thought of earlier in history than the propellor. This may be because nature has produced its own little helicopters that fall to the ground slowly and can travel far on the wind because they have evolved into little helicopter rotors.
Most people credit Leonardo Da Vinci with the invention of the helicopter. In the 1480s, Da Vinci drew schematics for an ‘air screw’ which used the principles of an Archimedes screw to show how verticle flight might work.
In fact, the idea of a helicopter was first mentioned some 2000 years earlier in China in 400 BC. The author Ge Hong wrote about a child’s toy comprised of a bamboo stick and paper rotor which children would spin in their hands causing it to fly vertically up in the air.
Ultimately, though, these were just ideas and it wasn’t until the 1930s that true helicopters took to the air. Heinrich Focke and Igor Sikorsky competed to create the helicopter as we know it today.
How do helicopter rotors work?
Helicopters and airplanes use the exact same principles of flight to create two very different kinds of flying machines.
An airplane’s wing is a curved surface called an airfoil which causes air moving over the wing due to the propellor to travel at different speeds and therefore at different pressures. The lower air pressure above the wing causes uplift which pulls the wing up and causes the airplane to fly.
Helicopter rotors are long thin airfoils that work like both a propellor and a wing by spinning very fast directly above the center of gravity of the helicopter fuselage. Just like in an airplane, the spinning rotors have a lower air pressure above them and this uplift creates the vertical flight which defines a helicopter.
Rotors alone will only allow the helicopter to move up and down so some very clever engineering is needed to all changes in vertical speed and changes in direction.
Each rotor connects to the engine-powered hub by a feathered hinge which is controlled by link rods, allowing the pitch of the rotor to change and consequently rise or fall in the air. A pair of swashplates under the hub change the angle of the rotors allowing the helicopter to move in any horizontal direction.
Why are helicopters so noisy?
There’s no denying that helicopters can be very noisy, contributing to noise pollution in urban areas and annoying the innocent who are trying to sleep while the police hover and search for wanted criminals.
Helicopters are so noisy because of the vortices created by constantly shifting rotors spinning at high speed a few feet above the helicopter’s engines and fuselage. Air vortices are essentially turbulent, noisy air which creates the distinctive but loud ‘whop whop’ sound.
Understandably, there is a high demand for helicopters that do not disturb wildlife, criminals, or the enemy. Advanced rotor designs on the Bell 429 and the Airbus H130 are making helicopters quieter than ever before.
What’s next for the helicopter rotor?
Although the helicopter has not changed the basics of rotor design much in the last century, there is always room for improvement in the way rotors are engineered and designed.
Recent developments in the field of Computational Fluid Dynamics (CFD) allows for enhanced and speedier design and testing of helicopter rotors, without the need for expensive prototyping and testing. CFD allows computer simulations to accurately predict the viscous airflow around rotors, especially in the most challenging area, the rotor tips.
As a result, Bell has been able to patent a split-tip rotor design which promises a new generation of helicopter rotors that are quieter, more stable, and more energy-efficient.