Autorotations

What happens when you’re in a helicopter and the engine fails?  Now, well maintained helicopter engines don’t fail every day.  In fact, I know a 10,000+ hour R22/R44 pilot who has NEVER experienced an engine failure!  But say yours fails; then what happens?  Do you drop out of the sky?

Not exactly.  An experienced helicopter pilot can safely land a helicopter without engine power with an autorotation.

When is a good time to do an autorotation?  Engine Fire, Engine Failure, Tail-rotor failure, and practice autorotations with an instructor.  Applicants for the helicopter certificate are required to perform autorotations.

In normal powered helicopter flight, air is drawn into the main rotor system from above and exhausted downward, but during autorotation, air moves up into the rotor system from below as the helicopter descends.

How can a helicopter possibly descend safely following an engine failure?  Two things contribute:

  1. A freewheeling unit called a sprag clutch, which allows the main rotor to continue turning even if the engine is not running, and
  2. Aerodynamic forces of relative wind maintaining rotor speed, rushing up through the rotor and spinning it much like a pinwheel or windmill.
  • These two features allow a helicopter to land safely in the event of complete engine failure.

Watch this excellent video below on the SpragClutch by DCCDanny

The aerodynamics of the relative wind driving the blade are largely affected by main rotor blade twist and the pilot manipulating the controls. In general, the portion of the blade which drives the rotor RPM is only a portion of the rotor disc.

How to perform an autorotation?

You can see my detailed lesson here.

In the event of an engine failure, lowering the collective and keeping the aircraft level on the entry are super important.