Coaxial Propeller Mechanism – Counter-Rotating Shaft Transmission

Coaxial Propeller Mechanism

Coaxial Propeller Mechanism Explained

The coaxial propeller mechanism is a mechanical transmission designed to drive two propellers along a single axis in opposite rotational directions. This system is commonly found in aviation, UAV propulsion, and marine engineering.

Coaxial Propeller 1 - Motion

Why Counter-Rotation Matters

A single rotating propeller creates reaction torque that can destabilize the vehicle. A coaxial system balances this by spinning a second propeller in the opposite direction, which:

• Cancels torque reaction

• Increases thrust efficiency

• Reduces swirl energy loss

• Improves directional stability

Coaxial Propeller 1 - Motion 2

How the Mechanism Works

The system relies on concentric shafts:

• Inner solid shaft drives one propeller

• Outer hollow shaft drives the second propeller

A gear train inside the transmission splits torque from the engine or motor. One path keeps the rotation direction, while another path uses additional gears to reverse it before driving the outer shaft.

Main Components

• Spur or bevel gears

• Hollow outer shaft with internal bearings

• Central solid shaft

• Thrust bearings to handle axial loads

• Independent propeller hubs

Engineering Challenges

• Precise alignment of concentric shafts

• Managing axial thrust forces

• Gear load distribution

• Vibration control

Applications

• Coaxial helicopter rotors

• Counter-rotating drone systems

• Marine dual-propeller drives

• High-efficiency experimental aircraft

The coaxial propeller mechanism is a powerful example of how gear systems can manipulate direction and torque within a compact and efficient design.