I have been making the mistake of using words "propeller" and "rotor" interchangeably when they are not the same thing. What is the difference between a propeller and a rotor?
Rotor is the generic name for something in rotation. It can be used for a propeller, the rotating wing of an helicopter, the rotating elements of a compressor or a turbine, etc. Rotor (rotating) is the antonym of stator (stationary).
Propeller blades are airfoils (small wings) which accelerate air to create lift and thrust. Sometimes a propeller is referred as a propeller disc to designate the whole disc swept by the blades, and the inner cone.
Propeller blades are fixed on the rotation axis, except for the pitch angle.
Rotor blades (rotorcraft) are not fixed, they have some freedom in flapping and leading-lagging.
These freedom degrees are necessary to prevent vibrations due to varying forces encountered by a blade during a full turn.
Rotor blades of a gas turbine are like propeller blades, though for the turbine itself they may work by "impulse" and by reaction (acceleration by converging nozzle), and more generally by a mix of both principles.
Often the inner part of a rotor holding the blades is referred as the rotor disc.
Blades of a turbine engine are fixed like blades of a propeller, though in some cases they are not locked on the disc mechanically, but dynamically by the centrifugal force.
The distinction between rotor and propeller is more a matter of custom.
- Rotor is quite generic, you can't be wrong using it for a spinning device.
- Propeller is rather specific to the mean of creating horizontal thrust within a fluid and with the objective to move an object. A house fan is not a propeller.
You may find a similar distinction between (aerodynamic) lift (and drag) and thrust, created by the same phenomena: Fluid acceleration. The distinction is here in the way the aerodynamic force is symbolically broken down into geometrical components.
- Rotor is a generic term for a rotating part of a mechanical device.
- Fan is a rotor that creates a flow within a fluid (i.e. gas or liquid).
- Propeller is a fan with the purpose to create thrust.
According to these definitions, it is not wrong to name propellers as rotors and vice versa.
In aviation language usually helicopters have rotors and planes have propellers, because:
- A plane propeller creates (mostly) thrust, and the lift is created (mostly) by the wings.
The air flow from a helicopter rotor generates both, lift and thrust.
Helicopters are differentiated from planes by rotary wings versus fixed wings.
- Propeller is getting lift from the wing and thrust from the propeller but helicopter gets both from the rotor.
- propeller aircraft can not hover over a spot but helicopter can.
- Propeller aircraft can not perform vertical landing but helicopter can do.
- Propeller blade is pre-twisted but helicopter blade are symmetrical.
- Propeller aircraft has two hard/re-enforcing point such as: Wing root and Engine mount but helicopter has only one hard point that is "ROTOR MAST" and more differences are there.