Propulsion means creating force leading to the movement. It consists of two Latin words: pro + pellerr. Pro means forward/before and pellere means to drive.

Propulsion System

The propulsion system is a source of mechanical engine or motor power and some means of using this power to generate force.

There are following propulsion systems are –

  1. Air Propulsion
  2. Ground Propulsion
  3. Marine Propulsion
  4. Space Propulsion

Propulsion system is required because it generates thrust –

  1. To balance the drag. (When aircraft is moving with constant velocity or cruising)
  2. To exceed the drag of the aircraft to accelerate.

Check out books for the aircraft propulsion system


Propeller provides thrust for flight of the aircraft. Propellers develop thrust by the virtue of rotation of blades.

Materials for the Propeller

Initially, propellers were made of wood in order to shape them easily. Wood propellers are the lightest and smallest load to the engine, assuming all else to be equal (diameter, picth and shape). These propellers are capable of turning higher RPM as compared to the heavier propeller. Also, these propellers are prone to damage.

Fibre glass filled Nylon propeller are the heaiest and also the most durable. These are less efficient than carbon fibre propeller. However, Carbon fibre peopeller are rigid and extremely expensive.

Nylon propeller are so flexible that they get twisted while using. These propellers constanly change the pitch but produce high vibrations.

Later on, different materials were introduced for the manufacturing of propellers like Aluminium alloys, Titanium alloys & modern composites. The advantage of such propellers is that it allows the propellers to operate at high speeds (supersonic and transonic). Blade used in such propellers are called transonic blades.

Fundamentals of the Propellers

  • A propeller is an interface between an engine & an aircraft.
  • In all the propellers, moving in air produce a propulsive force called thrust.
  • Thrust is propduced by affecting the net change in momentum to a propulsive fluid in the air of motion. Propellers create thrust by introducing a small change in velocity to a relatively large mass of air.
  • Propellers have two or more exactly similar plates, each of which is built up by stacking of sirfoil sections, radially from root to tip.
  • A propeller blade consists of tip, leading edge, trailing edge, root and hub.
Propulsion system - propeller blade labeled diagram
Propeller Blade
  • Number of blades in a propeller can be 2, 3, 4 or more as per the need of an aircraft. Propeller with more than ten blades is called Profan.
  • The performance of a propeller depends upon the local aerodynamics of the blade elements integrated over blade length.
  • For efficient operation, each blade element should be at an angle of attack (α) optimised to the value near maximum elemenral lift to drag ratio.

α varies with radius, since α is between chord line and free stream velocity.

While manufacturing a blade, why is it twisted with the changing raditaion?

While manufacturing, a blade is twisted in order to achieve different angle of attack (α). The blade shaping gives a radical twist, which gives a local air angle of attack for each blade section.

Quad Angle/Blink Setting Angle

Quad Angle is the angle between the root and the plane surface. The angle reduces as we move towards tip. This angle is also called Blink Setting Angle.

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