Helicopter Lift and Forward Flight Explained

What is the term for the difference in lift between a helicopter's advancing and retreating blades during forward flight?

Choices: 1. Dissymmetry of lift 2. Angular momentum conservation 3. Blade flapping 4. Tail rotor thrust

Answer:

Dissymmetry of lift is the term for the difference in lift between a helicopter's advancing and retreating blades during forward flight.

When a helicopter is in forward flight, the difference in lift produced by the forward-going and aft-going blades is known as dissymmetry of lift. This phenomenon occurs due to the relative airflow difference over the advancing (forward-moving) blade and the retreating (aft-moving) blade.

To balance the dissymmetry of lift, helicopters utilize a mechanism called 'blade flapping'. This mechanism allows the advancing blade to rise while the retreating blade lowers, ensuring that the lift is distributed evenly across the rotor disc.

Helicopters store a significant amount of rotational kinetic energy in their blades, which is crucial for takeoff and maintaining flight. The conservation of angular momentum plays a key role in stabilizing the helicopter's body from rotating in the opposite direction, with additional support from the tail rotor's thrust.

Understanding the concept of dissymmetry of lift is essential for comprehending the aerodynamics of helicopters and how they achieve stability during forward flight.