How does a helicopter manage to fly?

Watch a fixed-wing aircraft and the physics is intuitive: forward speed pushes air over the wings, the wings make lift, the aircraft flies. Watch a helicopter hovering in still air, with no forward speed at all, and the same intuition says it should fall out of the sky. The fact that it doesn't is one of the cleverer pieces of engineering in twentieth-century aviation, and the explanation is a great deal simpler than the cockpit ever lets on.

Look at a helicopter's main rotor blade end-on and you'll see the shape of an aircraft wing: a curved upper surface, a flatter lower surface and a leading edge that's rounder than the trailing edge. It's an airfoil — and like every airfoil, it generates lift when air flows over it.

The clever part is where the airflow comes from. A fixed-wing aircraft generates airflow by moving the whole aircraft forward. A helicopter generates it by spinning the wing — typically at around 350 to 500 revolutions per minute, depending on the type. The blade tips of a modern executive helicopter travel at about 450 knots even when the aircraft itself is stationary in the sky. That's where the lift comes from. The helicopter doesn't need to be moving for the wing to be moving.

Sitting in the cockpit of a helicopter, the pilot has three flight controls — and unlike a fixed-wing aircraft, none of them is a steering wheel or a yoke that directly tilts the aircraft.

• The collective — a lever to the pilot's left, raised and lowered. Lifting the collective increases the pitch angle of all the rotor blades simultaneously, which increases lift. Pull up to climb; push down to descend.
• The cyclic — a stick between the pilot's knees, moved in any horizontal direction. The cyclic tilts the rotor disc as a whole. Tilt forward and the helicopter accelerates forward; tilt left and it slides left. The cyclic is what gives the helicopter its direction of travel.
• The anti-torque pedals — under the pilot's feet. These control the tail rotor, which we'll come back to in a moment. The pedals are how the pilot rotates the helicopter around its vertical axis — pointing the nose in a different direction without changing where the aircraft is in space.

Coordinating the three is the entire skill of flying a helicopter. They interact constantly — lift the collective and the aircraft tries to yaw, requiring a pedal correction. Push the cyclic forward and the aircraft accelerates but also starts to lose altitude, requiring a collective input. A good helicopter pilot is doing all three more or less constantly, with feet, both hands, and a refusal to look surprised about it.

Newton's third law of motion says that for every action there is an equal and opposite reaction. Spin a rotor one way, and the aircraft body wants to spin the other way. Without something to counter it, a helicopter would simply rotate underneath its rotor while going nowhere.

The tail rotor solves this. It is a small rotor mounted vertically on the tail boom, generating a sideways thrust that exactly counters the torque of the main rotor. The pedals control how much sideways thrust the tail rotor produces. Add power on the main rotor and you need more anti-torque from the tail; reduce power and you need less. The pedals are constantly being adjusted to keep the nose pointing where the pilot wants it.

Some larger helicopters use two main rotors that spin in opposite directions — the Boeing Chinook is the obvious example — and don't need a tail rotor at all. The Eurocopter EC135 and EC145 family use a Fenestron, which is a tail rotor enclosed in a shrouded duct. Smaller and quieter, same job.

When the pilot pushes the cyclic forward, the rotor disc tilts forward, and the lift the rotor produces now has a forward component as well as an upward one. The helicopter accelerates. Above about thirty knots, the aircraft enters something called translational lift — the rotor system starts behaving more efficiently because it's now also flying through air, like a fixed-wing aircraft does. Cruise feels noticeably smoother than hover for this reason.

There is one quirk of forward flight worth knowing. As the rotor spins, half the disc — the advancing side — is moving in the same direction as the aircraft, so the relative airspeed on that side is high. The other half — the retreating side — is moving against the direction of flight, so its relative airspeed is low. This asymmetry would tip the aircraft over without correction, so each blade is hinged to flap up and down independently, evening out the lift across the disc. The hinge is the reason a stopped rotor droops at the tips.

The first question people ask about helicopters is what happens if the engine fails. The answer is autorotation, and it's the part of the system that's hardest to believe until you've seen it demonstrated. If the engine quits, the pilot lowers the collective immediately, which reduces the pitch of the blades to near flat. The aircraft begins to descend. The descending airflow now drives the rotor from underneath, keeping it spinning. The pilot then uses the cyclic to control the glide path, and at the last moment flares to slow the descent and lands — engine off, on the rotor's stored energy alone.

It is taught from the first day of every commercial helicopter licence. Every type-rated pilot is required to demonstrate it to maintain currency. It is the reason engine failure in a helicopter is a recoverable event, not a catastrophic one — and one of the reasons twin-engine helicopters, with redundant power on top of autorotation, are the standard for executive charter.

The short version: the wing spins so the helicopter doesn't have to. Everything else — controls, tail rotor, autorotation — is what it takes to make a spinning wing controllable.

Modern executive twins are remarkably refined places to sit. The vibration that defined helicopter travel for decades has been largely engineered out by active rotor dampening and modern blade design. The noise inside an Agusta A109 or Airbus H145 cabin, with the door seals fresh and ANR headsets, sits closer to a luxury car than a turboprop. Cruise is steady. The helicopter does what you actually wanted it to do, which is to land directly where you needed to be — and the engineering that allows that to happen, hovering in still air, is genuinely some of the best of the last hundred years.

Next time you're in one of ours, watch the pilot's left hand on the collective and the constant small inputs on the cyclic. None of it looks like work. All of it is.