How do helicopters fly and hover?

1. The engine spins the main rotor. Each blade is shaped like a long, thin wing. As it whirls around, it slices through the air and pushes it down.
2. To take off, the pilot pulls up a lever called the collective. All the blades tilt more steeply, push more air down, and the helicopter rises straight up.
3. When the push from the rotor equals the helicopter's weight, it hovers, hanging in one spot. Airplanes can't do that!
4. When the engine spins the rotor one way, the body gets pushed to spin the other way. The tail rotor blows air sideways to stop that spin and keep the nose pointing straight.
5. To fly forward, the pilot pushes the stick called the cyclic. The spinning blades tilt forward, so the rotor pulls the helicopter forward as well as up.
6. To land, the pilot lowers the collective a little at a time, so the lift is just less than the weight. The helicopter sinks gently until the skids touch down.

Tap each part to see what it does. Many of them move when you find them!

• Main rotor. The main rotor has long, thin blades shaped like wings. Spinning around, they push air down, and that lifts the helicopter.
• Swashplate. The swashplate is a ring around the rotor mast. Moving it up tilts all the blades more. Tipping it makes each blade change its tilt as it goes around.
• Engine. Most helicopters have a turbine engine. It sucks in air, burns fuel and spins very fast to turn the rotors.
• Gearbox. The engine spins much too fast for the rotor blades. The gearbox uses gears to slow the turning down and make it stronger.
• Tail drive shaft. A long shaft runs inside the tail boom. It carries spinning power back to the tail rotor.
• Tail rotor. The tail rotor blows air sideways. That push stops the body from spinning the opposite way to the big rotor, and it lets the pilot turn left or right.
• Pilot's controls. The collective lever makes the helicopter go up and down. The cyclic stick tilts it to go forward, backward or sideways. Foot pedals turn the nose left and right.
• Skids. Many helicopters land on skids instead of wheels. They are light and work on grass, snow or rooftops.

Use the lift lever to take off and hover. Tilt the rotor to move. What happens to the body if the tail rotor stops?

Experiment: What happens to a flying helicopter if its tail rotor stops pushing?

1. Raise the lift until the helicopter takes off, then find the hover.
2. Switch off the tail rotor and watch the body.
3. Switch it back on. What does the tail rotor do?

What we found: Without the tail rotor, the body spins the opposite way to the big rotor. When the engine pushes the blades around, the blades push back on the helicopter. The tail rotor's sideways push stops that spin.

Turn on JavaScript to try it yourself.

Turn the helicopter around, fly over the hill and land softly on the hospital roof.

A helicopter's rotor blades are wings that go around in a circle instead of moving straight ahead. Because the blades are always moving through the air, a helicopter can make lift even when it isn't moving at all. That's why it can take off straight up, hover and land almost anywhere.

The pilot has three main controls. The collective lever tilts all the blades more or less steeply at once, to go up or down. The cyclic stick tips the spinning rotor so the helicopter moves forward, backward or sideways. Foot pedals change the push of the tail rotor to turn the nose.

Spinning the big rotor has a side effect. When the engine pushes the blades one way, the blades push the helicopter body the other way. Without a tail rotor, the body would spin around and around. Some helicopters use two rotors spinning in opposite directions instead.

Hovering takes a lot of power, so helicopters use more fuel than airplanes to carry the same load. In return they can rescue people from mountains, ships and rooftops where no airplane could land.

Key words

Rotor

The spinning set of blades that makes a helicopter's lift.

Collective

The lever that tilts all the blades together to go up or down.

Cyclic

The stick that tips the spinning rotor to move forward, backward or sideways.

Torque

A twisting push that makes something spin.

Hover

Staying still in the air because lift exactly equals weight.

Downwash

The air pushed down by a spinning rotor.

Check your thinking

1. How does a helicopter's main rotor lift it?

   Show the answer

   Its spinning blades push air down. The blades are wings that spin. Pushing air down makes an upward push on the helicopter.

2. Why does a helicopter need a tail rotor?

   Show the answer

   To stop the body spinning the opposite way to the main rotor. Spinning the rotor pushes the body the other way. The tail rotor pushes back.

3. Which control makes the helicopter go straight up or down?

   Show the answer

   The collective lever. The collective tilts all the blades together, making more or less lift.

4. When does a helicopter hover?

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   When the rotor's push up equals its weight. Balanced forces mean no speeding up or slowing down: it stays put.

5. A helicopter's rotor makes 12 kN of thrust at a blade pitch of 6°. In this simplified model thrust is proportional to pitch. About how much thrust at 9°?

   Show the answer

   18 kN. 9° is 1.5 times 6°, so thrust is about 1.5 × 12 = 18 kN.

6. Why do helicopters struggle to hover very high up?

   Show the answer

   The air is thinner, so the blades push less air. Thin air has less air to push down, so the rotor makes less lift.