Get to the Choppa! Understanding How Helicopters Work

Written by Dabney B. on Wednesday, August 1st, 2012

Helicopters are a common sight in many places throughout the world. They’re used to transport important people, catch news footage, pursue criminals in high-speed chases, and airlift injured people to hospitals — and that’s in addition to the thousands of military helicopters that are currently in service.

As common as helicopters are, most people don’t have a very solid grasp of how they work. The blades spin and that makes the helicopter go up — we get that much, but past that it’s all a big mystery. Today, we’re going to dive into the mechanics of rotary flight by figuring out just how these noisy contraptions work.

The first and most important thing to understand about helicopters is that they operate under fundamentally different principles from conventional fixed-wing aircraft. Planes and jets use an airfoil, which causes lift as wind passes over wings. Harry Reasoner, a US broadcast journalist who covered the Vietnam War, famously described helicopters, “An airplane by its nature wants to fly. … A helicopter does not want to fly. It is maintained in the air by a variety of forces and controls working in opposition to each other, and if there is any disturbance in this delicate balance, the helicopter stops flying, immediately and disastrously. There is no such thing as a gliding helicopter.”

That rather grim description is obviously supposed to be kind of funny, but that doesn’t make it any less true. Fixed wing aircraft can lose engines and still glide for a while — in fact, the X-37B spaceship glides all the way from orbit down to the tarmac without engines or turbines. A helicopter that stops working will promptly become a $7m hunk of explosive metal.

That’s because a helicopter’s only source of lift comes from the constantly spinning main rotor blades. As long as these blades are generating more lift than the weight of the helicopter, the chopper will move upward. That very simple mechanism gives you an aircraft that can travel vertically up and down.

Now comes one of its trickier dimensions: side-to-side movement. Helicopter pilots control turning with foot pedals that influence the tail rotor, which is located at the back of the aircraft. Its primary purpose is to provide anti-torque force. You ever hear of Newton’s Third Law of Motion, that every action has an equal and opposite reaction? Well, it’s a big deal for helicopters. If you gave a helicopter a single buy antibiotics in uk rotor, the main fuselage would quickly spin out of control in the opposite direction of the blades.

The tail rotor provides enough anti-torque force to prevent that spinning. All it needs to do is slow down and the helicopter fuselage will begin to spin in the direction it wants to spin (thus turning to the right), or it can speed up and create more anti-torque than torque (thus turning left).

All that’s left is the ability to move forward. It might surprise you to learn that the rotor at the top of the helicopter is not fixed so that it’s perfectly level with the ground. It can lean forward or backward slightly. Changing the orientation of the main rotor also changes the direction of the lift. By pointing it forward, lift pushes backward to generate forward movement. A helicopter pilot can similarly orient the rotor backward to create forward thrust and slow down the aircraft.

Does it sound complicated? Well, it’s about to get even messier. Helicopter engineers and pilots constantly have to worry about vibration. Plane’s aren’t so bad — every part of a plane is moving at the same speed in the same direction. Helicopters are a completely different story because the advancing blades can actually surpass the speed of sound, thereby creating an incredible amount of drag and vibration.

And yes, vibration is a big deal. If a helicopter isn’t properly calibrated, it can vibrate so much that it literally tears itself apart midair. This vibration puts a ceiling on the max speed of helicopters. Helicopter pilots and engineers must respect the sacred limitation of VNE, Velocity, Never Exceed. Crossing that threshold could cause the rotor blades to stall out and send the helicopter plummeting back to Earth. Manufacturers have gone to great lengths to stabilize the vibrations as much as possible by developing vertical stabilizer bars on the rotors, and vibration dampeners for height and pitch.

Helicopters: a marvel of modern science or a terrifying flying death trap that’s constantly on the brink of disintegration? It might be a little bit of both. I’ll leave you with this: an anonymous helicopter pilot once said, “A helicopter is an assembly of forty thousand loose pieces, flying more or less in formation.” If that doesn’t make you excited to begin a career as a helicopter pilot, I don’t know what will.

If you want advice about the world of military aviation, there’s no better people to turn to than men and women who have sat in the cockpit and flown some of the world’s most advanced aircraft. With over 50 current and ex-warfighters on call, Strike Fighter Consulting Inc. can give you access to up-to-date, first-hand technical and tactical expertise.