Sikorsky counterrotating helicopter takes flight

Sikorsky flew its prototype counterrotating helicopter yesterday (press release).  Typical helicopters, however expensive, are limited to about 165 knots of cruise speed.  When the helicopter is moving faster than that, the “retreating blade” is not getting enough airflow, i.e., the blade is going backward about as fast as the helicopter is going forward.  This results in a loss of lift on half of the disk.  With two rotor systems rotating in opposite directions you still get retreating blade stall but it happens to both rotors at the same time and on opposite sides of the helicopter.  Instead of the helicopter pitching and rolling it should just keep flying.  The goal with this style of helicopter is to achieve cruise speeds closer to 250 knots, albeit probably at Sikorsky prices starting at $20 million.

How new is this idea?  The U.S. military tried this around 1970 and gave up due to uncontrollable vibrations.  The Russians built and flew some helicopters like this, also around 1970, but never went into large scale production.

What makes it practical today when it wasn’t practical in 1970?  Better computer systems that can run active vibration dampening (like noise-canceling headsets but for vibration).

3 Comments

  1. Brandon

    August 28, 2008 @ 10:45 pm

    1

    850 Kamov Ka-26s, and at least a couple hundred Ka-25s and variants isn’t large scale production?

  2. philg

    August 28, 2008 @ 11:00 pm

    2

    Brandon: I don’t think that the helicopters you cite get into retreating blade stall or cruise especially fast. They look like the Kaman (Connecticut designed and built) heavy lift helicopters where the counter-rotating main rotors are there to maximize power available. Wikipedia has the maximum speed on a ka-26 as 100 mph, i.e., slower than a Robinson R22!

    Maybe
    http://en.wikipedia.org/wiki/Kamov_Ka-50 is the interesting one, with a cruise speed of 204 knots.

  3. SuperCorgi

    August 29, 2008 @ 2:39 pm

    3

    And there is also the unloaded / slowed rotor at cruise type helicopters, that Jay Carter has done a lot of promising work with. With our tax money. For a good return.

    http://www.cartercopters.com/

    I rather like the weighted rotors, gives obviously lots of sustained energy in an autorotation event, or the neat *hop off*
    takeoff these sort of gyro designs have.

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