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(For the Blade 400 and Blade CX2 helicopters, see E-flite).

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A pair of Align 325 PRO blades

Also known as a "rotor" blade, as it relates to a helicopter, a blade is basically a small wing. Like all wings, a blade's purpose is to generate lift when air is moved across its surface. However, a blade makes its lift in a slightly different manner than a traditional airplane wing, which is held stationary in relation to the fuselage as the aircraft moves forward through the air. Rather than relying on the forward motion of the entire aircraft to generate airflow over its lifting surface and therefore, generate lift, a helicopter spins its rotor blades rapidly around a central point (the main shaft or mast) in a circular fashion and the blades generate lift as they move through the air. Therefore since the helicopter's wings are always moving through air, a helicopter can fly while stationary in space (or hover). What's more, a helicopter can also fly in any direction, regardless of where its nose is pointed.

Blades are also used in a similar fashion on the tail of most helicopters, to generate lift in the horizontal plane to counteract the helicopter's tendency to rotate opposite the main rotor as a result of torque. If a helicopter does not have some method of counteracting this torque reaction, it will not be controllable. This is where a tail rotor comes in. There are other methods of counteracting torque in use on modern helicopters, such as the Fenestron tail and the NOTAR system, and even counter-rotating coaxial helicopters, but the simplest and most common method in use is the tail rotor.

A helicopter's main and tail rotors can be made up of anywhere from two to 5 blades, and in some case many more. A majority of RC helicopters use two blades on their main rotor and two blades on their tail rotor. Generally, as the number of blades in a rotor system increases, so does the complexity of the system needed to control them in a stable manner.

Blades can be:

  • Symmetrical
Having identical profile on the top and bottom surfaces, and so working just as well inverted as right side up. Commonly used for collective pitch helicopter main blades, and for tail blades.
  • Semi-symmetrical
Having slightly asymmetric profile, improving their performance in upright flight at the expense of inverted performance. Not very common now, used sometimes on large scale helicopters.
  • Asymmetric
Intended only for upright flight, but offering far higher efficiency, including more lift at lower speeds. Fixed pitch helicopters and coaxial helicopters often use highly asymmetric blades.

Blades are traditionally measured in millimetres from the bolt hole in the blade root to the very tip of the blade. Blades can vary from under 10cm for very small electric helicopters, to 80cm for the larger nitro and gasser machines, and over 1 metre for specialist and scale helicopters.

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