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Sagita Displays Hot Air Powered Helicopter

Posted by samzenpus on from the full-of-hot-air dept.

rcastro0 writes "Gizmag reports on the Sherpa, an interesting helicopter design at this year's Paris Air Show. As the article explains 'Rather than driving the rotors directly, the Sherpa's engine instead powers a compressor with an air intake at the rear of the helicopter.' There's no tail rotor. This approach is supposed to be more efficient, more reliable and more affordable than the traditional. A one-fifth scale model was shown to fly. Sagita, the 2008 startup behind the project, has yet to build a full scale prototype. They plan to sell a Sherpa two-seater for around US$ 200k in 3 years."

2 of 73 comments (clear)

  1. Re:What are they up to? by russotto · · Score: 4, Insightful

    I'm wondering if they have separated the compressor and turbine stages in a conventional jet engine in an effort to get a fuel economy or weight improvement.

    I cheated and read the article, and it appears that is what they've done.

    However, they haven't actually built it; they have a 1/5 scale model, but it's using an electric motor (so it's not clear what it proves), and furthermore the laws of aerodynamics are not scale-invariant.

    It's not clear why they're trumpeting the lack of a tail rotor as a new thing; this isn't a NOTAR design (single main rotor with no tail rotor); it's a coaxial helicopter, which is nothing new at all.

  2. Re:What are they up to? by stockard · · Score: 5, Informative

    Coaxial helicopters still have a tail due to the controls on the empennage. Helicopters are a bit odd in that the pilot is basically flying the rotor disk, and the fuselage is kinda just "along for the ride". So, if you wanted to rotate or adjust the pitch of the fuselage, you'd need some sort of controls on the fuselage to do so. (Some adjustment can be made with the rotors, but the standard tail controls are a bit simpler.) So, while coaxial helicopters are more inherently stable and don't need a tail rotor, they'll still have a tail. (See the Ka-50, X2 and Ka-27 among others, as examples.)

    The reason you want controls at the aft end of the the tail is because for things like the elevator, you want as big a moment arm as possible to reduce the force required to adjust the pitch of the aircraft. Similarly, the vertical stabilizers are there to help reduce sideslip at higher speed, since a helicopter can fly in any direction, regardless of the orientation of the fuselage. (Generally for lighter helicopters, the vertical stabilizers are fixed, though the larger ones can have a movable rudder.)

    Additionally, having a tail will help you if you need to do an autorotation, as it will help prevent the rotors from impacting the ground at the rear when you flare it right before landing. (Here are some examples: http://www.youtube.com/watch?v=T-5ARzqF3R4)

    Disclaimer: While I'm a helicopter engineer, I don't work on the controls, so this may be a bit of a simplistic explanation. :)