How a Helicopter Flies: Rotors, Pedals and Sticks
A helicopter's spinning blades are wings. Three controls change their pitch to climb, move and turn, and a tail rotor balances the spin. Here is how each part works.
In this article
A helicopter flies because its main rotor blades act as rotating wings. The pilot changes the angle of those blades with two hand controls and a pair of foot pedals, and a small rotor at the tail stops the body from spinning the other way. This article walks through each control and what happens if the engine fails.
The rotor is a wing that spins
An aeroplane wing makes lift as air flows over it. A helicopter gets the airflow by turning the blades around a mast. The more the blades are tilted into the air, the more lift they make, up to a limit. The tilt is called pitch.
Collective: all blades together
The collective lever sits by the pilot's left hand. According to the flight-controls article on Wikipedia, it changes the pitch of all main blades by the same amount. Raising it adds lift and the helicopter climbs. Lowering it reduces lift and the helicopter descends.
Extra pitch also means extra drag on the blades. Migflug's explainer notes that the throttle, or an automatic governor, must add power to keep the rotor turning at a steady speed.
Cyclic: tilting the disc
The cyclic is the stick between the pilot's knees. It changes each blade's pitch as it goes round, so a blade has more pitch on one side of the circle than on the other. The result is that the whole spinning disc tilts. Lift acts at right angles to the disc, so tilting it forward pulls the helicopter forward, and tilting it sideways moves the helicopter sideways. In forward flight, Wikipedia says, the cyclic changes the nose attitude and rolls the helicopter into turns.
Migflug adds a detail: because a spinning rotor behaves like a gyroscope, the linkages apply the pitch change about a quarter of a turn ahead of the place where the tilt is wanted.
The swashplate
The controls reach the spinning blades through a swashplate, which is a pair of plates around the rotor mast. Migflug explains that the lower plate does not rotate and is moved by the pilot's controls, while the upper plate turns with the rotor and passes movement to each blade through pitch links.
The tail rotor and the pedals
When the engine turns the main rotor one way, the body tends to turn the other way. This is called torque. Most helicopters counter it with a tail rotor that pushes sideways. According to Migflug, the anti-torque pedals change the pitch of the tail rotor blades and so control heading, especially in a hover.
The collective affects torque, so a pilot who raises or lowers it normally adjusts the pedals as well. Wikipedia notes that some helicopters use a design called NOTAR, which replaces the tail rotor with air blown through vents in the tail boom. Helicopters with two main rotors turning in opposite directions cancel torque between them and need no tail rotor.
Autorotation: landing without power
If the engine fails, a helicopter does not fall like a stone. A freewheeling unit disconnects the engine from the rotor, and the pilot lowers the collective at once. Air then flows up through the rotor as the helicopter descends, and that airflow keeps the blades turning, according to the autorotation article on Wikipedia.
- Entry: lower the collective straight away so the rotor keeps its speed.
- Glide: hold a steady forward speed; the article gives a typical glide angle of about 17 to 20 degrees.
- Flare: at roughly 50 to 100 feet, raise the nose and apply upward collective to slow the descent.
- Touchdown: land with a short run-on or, in some helicopters, stop and settle without forward movement.
Pilots practise this manoeuvre. Which procedure applies depends on the helicopter type and its manual.
Where the layout came from
Migflug states that Igor Sikorsky's VS-300 made its first tethered flight on 14 September 1939, and that its single main rotor and tail rotor arrangement is used by almost all helicopters today.
Limits of the design
In forward flight, one blade moves into the oncoming air while the opposite blade moves away from it. Wikipedia says that at certain speeds this can cause the retreating blade to stall, which can make flight unstable. This is one reason helicopters have speed limits that are lower than many aeroplanes'. This is general information; real limits are set in each helicopter's flight manual.
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