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Aerospace Power failure on helicopter

  1. Aug 4, 2004 #1
    Can a helicopter that has lost power to the main rotor blades land slowly enough so that nobody gets hurt? What would the terminal velocity of a freefalling helicopter be?
  2. jcsd
  3. Aug 4, 2004 #2


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    Probably not. Depends on the altitude the thing was flying before it lost power.

    Probably the same as a freefalling rock. If you have enough time to hit terminal velocity, you have enough time for the rotors to stop spinning entirely. You also will be going fast enough to leave a crater upon impact, so you definitely will not survive.
  4. Aug 4, 2004 #3


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    Hasn't anyone here ever heard of autorotating?
  5. Aug 4, 2004 #4
    I thought that autorotation was one of the skills that helicopter pilots have to practice in order to qualify as liscenced pilots?

    Basically, the helicopter will fall with the engine off, so the pilot will try to keep energy in the blades. I think what pilots do in this case is decrease collective (decrease the pitch of the blades) so that the helicopter drops fast. This causes lots of air to rush into the blades, accelerating them and storing kinetic energy in their rotation. When a proper "flare" altitude is reached, the energy is dumped out of the blades (increasing the pitch so that the blades produce much more lift than before), slowing the descent of the helicopter so that it's vertical speed is low enough to land without damage.

    A freefalling helicopter would probably fall pretty fast with it's blades locked and nose pointed down. If it's blades were free to rotate, however, I imagine a skilled pilot could nurse some energy into the blades and safely recover, given enough altitude.

    I have seen this move demostrated multiple times in real life with remote controlled helicopters, and in videos with full-size helicopters. The cheap remote-controlled helicopters, however, do not have a one-way bearing in their mechanics, however. If this is the case, and if the engine seizes or quits, the blades will stop moving entirely (or break) and the helicopter will fall to the ground.

    Helicopters can do some things that you would never expect. I believe that apaches can do loops and barrel rolls with enough altitude. Remote-controlled helicopters (expensive ones made for stunts and excessive amounts of power) can do CRAZY tricks. I've seen people in real life fly loops in an RC helicopter while spinning continuously. (the tail rotor is shut off or given enough power to cause the helicopter to rotate along the main rotor axis, and then the helicopter does a loop while this is going on) Some pilots even fly their helicopters upside-down within inches of touching the ground! (The pilots tell me that the helicopter is actually more stable upside-down. The reason for this is the downwash from the main rotors doesn't have to flow around the body of the helicopter this way. Instead, it makes almost a perfect cylinder of air, making it very stable)
  6. Aug 4, 2004 #5
    How likely is it that a rotor blade will break into pieces while rotating - they must be under a lot of stress.What are rotors made from? I know they get hot and are hottest at the tips - doesn't heating and cooling encourage fatigue?
  7. Aug 4, 2004 #6


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    My father worked for a company that the clutch that makes autorotation possible. Before the invention of that clutch, if power went out on a helicopter, the blade froze in place like the tires of a car when the engine dies and the clutch is not engaged. The chances for survival in these early power failures was almost nill. Now, a power failure is even a cause for injury or damage (necessarily).
  8. Sep 17, 2004 #7

    A helicopter is designed to autorotate, which means that the rotors keep rotating at powerloss. This enables the pilot to make a smooth landing, although the engine has shut down.

    The design of the helicopter's gearbox ensures that the antitorque rotor (tail rotor) is detached if powerloss occures, so the antitorque force will stop, which keeps the yawspeed of the fuselage neutral.
  9. Sep 17, 2004 #8

    oops , sorry, there have been enough qualified answers ...
  10. Sep 17, 2004 #9
    Main rotor blade design and materials

    • Each rotor blade is manufactured as a composite, with foam or honeycomb materials forming the core of the blade, covered with one or more layers of fibre reinforced plastics. For further reinforcement, carbon, kevlar or glass fibres are used. In highly stressed areas, such as the front edge of the blade, metallic layers provide additional reinforcement.
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