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Transportation Technology

Sagita Displays Hot Air Powered Helicopter 73

Posted by samzenpus 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."
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Sagita Displays Hot Air Powered Helicopter More

Sagita Displays Hot Air Powered Helicopter

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  • Comment removed (Score:4, Funny)

    by account_deleted ( 4530225 ) on Thursday June 20, 2013 @08:24PM (#44066557)
    Comment removed based on user account deletion

  • It is not energy efficient to run the main rotor based on simple compressed air. Thermodynamically compressing the air and then letting it decompress results in a great deal of waste heat energy. Mechanical systems are significantly more energy inefficient.

    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.

    • Re:What are they up to? (Score:5, Insightful)

      by russotto ( 537200 ) on Thursday June 20, 2013 @08:49PM (#44066687) Journal

      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.

      • What bothers me is that if this is a counter-rotating coaxial design, they why does it have a tail at all? Are we too used to seeing helicopters with tail booms that we can't imagine one without one?

        • Re: (Score:3, Informative)

          by m0n0RAIL ( 920043 )

          The tail provides stability during forward motion. A helicopter without one would need constant corrections to maintain its orientation during forward flight.

        • Re:What are they up to? (Score:5, Informative)

          by stockard ( 1431131 ) on Thursday June 20, 2013 @10:26PM (#44067219)
          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 [wikipedia.org], X2 [wikipedia.org] and Ka-27 [wikipedia.org] among others [wikipedia.org], 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 [wikipedia.org], 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 [youtube.com])

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

          • No disclaimer needed (Score:1)

            by Anonymous Coward
            No disclaimer is needed. This is precisely the reason I still come to this site. Bravo!

          • "...you want as big a moment arm as possible to reduce the force required to adjust the pitch of the aircraft."

            This.

            As well as improve stability, I would think. While main-rotor adjustments might be sufficient to control yaw, having that "moment" probably smooths out that control by adding some inertia.

      • Re: (Score:2)

        by Jeng ( 926980 )

        but it's using an electric motor

        Yes, apparently the helicopter that is suppose to run on hot air does not, which makes this just a bunch of hot air.

        What are they up to?

        Seeking venture capitol.

      • Re: (Score:3, Interesting)

        by modecx ( 130548 )

        As far as I can see, their innovation can be accurately summed up thus:

        They've decoupled the power turbine (the one which provides power to the rotors via a gears and such) from the engine, and mix cooler air into the exhaust stream. They've done away with the transmission and drive train by forcing this much cooler exhaust stream through a power turbine directly coupled to the main rotors, and they have also eliminated all of the complexity of a tail rotor and associated drive train by going with co-axial

    • It seems to me that if they directed the exhaust downward, rather than using it to drive a turbine to spin the rotors, they'd be ahead of the game. As it is, this seems like a glorified turboprop engine.

      • ... this seems like a glorified turboprop engine.

        Which it is.

        But without the fancy gearbox of a turboprop or the transmission of an engine-driven rotor. It should be WAY simpler mechanically, much lighter, and need far fewer moving parts. Eliminating the gearbox losses should gain them far more efficiency than plumbing the fast, hot, gas around costs.

        • Without the "turbo" part either. "Turbo" implies a gas turbine engine. Turbojets are nothing more than a gas turbine. Turbofans have a gas turbine at their core. A turbocharger is a gas turbine wrapped around an internal combustion engine. This is a piston powered helicopter with a fluid dynamic transmission. It's merely different from the typical fluid dynamic transmission in that it is an open loop. Anyone in the automotive world will tell you a fluid dynamic transmission is lossy and inefficient.

  • TFA says "the helicopter's performance is theoretical". They only flew a 1/5 scaled prototype.
  • Hot Air Powered Locomotion; This new technology will ensure the hyperpower status of the USA for the 21st century; given plentyful resources located in the north americas politician deposits.
    • What we need is a generator that runs on bullshit. Washington DC could be the Saudi Arabia of bovine excrement power with ample reserve in Wall St. in the unlikely event that DC should ever prove insufficient.

    • This new technology will ensure the hyperpower status of the USA for the 21st century; given plentyful resources located in the north americas politician deposits.

      Nah. The U.S. has no monopoly on government bombast.

  • Something isn't adding up... (Score:4, Interesting)

    by wagnerrp ( 1305589 ) on Thursday June 20, 2013 @09:40PM (#44067003)
    According to the article, the air is compressed, then heated by the engine's cooling system, then mixed with exhaust gasses, and the resultant flow into the turbine is only 100C? Something doesn't seem right here. That temperature difference implies such a low boost that it won't even operate effectively as a supercharger, much less provide anything like enough power to those turbines. There's a reason gasoline engines with worthwhile turbochargers and superchargers all have intercoolers, and that's because compressing air makes it really damn hot.

    • Re: (Score:2)

      by b4upoo ( 166390 )

      You are correct. The design sounds fishy. Just for a start why the heck would you put an air intake at the rear of the bird? Even if the machine has an 80 mph top end the ram air effect of a forward mounted air intake would be a huge advantage. Maybe they should take a clue from every jet fighter ever built and notice not a single design mounted the air intake in the tail. Designs like that should be designed with deep thinkers like Glen Beck signing the blue prints.

      • Just for a start why the heck would you put an air intake at the rear of the bird?

        I'm not an aviation engineer, but wouldn't a rear-facing inlet reduce the likely hood of something, like an actual bird, getting sucked in?

      • No. Ram air at 80mph will not produce any meaningful difference. You're talking about maybe one psi difference between forward facing and rearward facing at that speed, while your compressor is going to have to be producing several tens of psi to power that rotor. The only value of ram air on a car is that you're feeding the engine fresh, cool air, as opposed to air entering through the grille and heated by the radiator.
        • Or you could just go calculate it with 1/2 rho v^2 and realise it's 0.1 psi...
          • Yeah, or look it up in the table in the back of one of the books on my shelf behind me, but it's morning, and my first day off in two weeks. Forgive my laziness.

    • According to the article, the air is compressed, then heated by the engine's cooling system, then mixed with exhaust gasses, and the resultant flow into the turbine is only 100C? Something doesn't seem right here

      IANAP[hysicist] and I'm bad with math so I'm possibly not even capable of doing the numbers, but gases do cool when they expand. If they're letting them out through some kind of control aperture, then perhaps the flow is only 100C at the point at which it reaches the turbine blades. Or maybe that's a lot of bunkum, because as I said, I haven't done the numbers. However, you don't seem to have accounted for this in your complaint.

      • Huh? By expanding and cooling, you mean decompressing. You're right back at the same point I described, too low of pressure ratio above atmospheric to do anything useful.

    • Re: (Score:3)

      by dywolf ( 2673597 )

      This is actually not new technology.
      In fact, most turboshaft helicopters already use this sort of system, eg: Hueys and Cobras (my background)

      What you have here is a non-physical or indirect link between the engine and rotor transmission.
      In some helicopters the link is direct or physical. IE, the transmission gearbox is directly attached to the engines output shaft, just like a car with a direct connection. This means the transmission must input must therefore spin at the same RPM as the engines output.

      What

      • Re: (Score:2)

        by dywolf ( 2673597 )

        when i say "some helicopter have a direct link" its referring more to much older designs using piston engines.
        i dont know of any turboshaft powered helos that have a directly linked xmission....since as stated thats wher ethe name of the powerplant type comes from!
        so..there.

      • Re: (Score:2)

        by dywolf ( 2673597 )

        damn we need an edit button. "and im sure some other types as well"...dont know why i typed that. damn stream of thought typing.

      • I understand how a helicopter engine works (no offense taken by the explanation). My problem with this design is two fold.

        First, according to the article, the air they're feeding into the turbine is around 100C, and they even made a point of saying it was low temperature so no special cooling measures would be needed. In a turboshaft engine, the exhaust coming out of the gas turbine into the secondary is closer to 1000C. Temperature and pressure are intimately linked. You can't have one without the othe

        • Re: (Score:2)

          by dywolf ( 2673597 )

          i can explain the mechanics of the engine, but the physics/thermodynamics of the heat and flow etc is not something im expert on so i actually cant really speak to how they could get it working at 100C, though i do recognize that its unusually "cool". i guess it would just depend on how much energy they need to drive the rotors themselves, and i'd just be guessing.

          mechanically, it did seem odd that the power turbines are seemingly integral to the rotor mast/housing, no reduction gearbox. as for getting rid

          • one reason jets are hot is because its a consequence both of the required pressures need to both keep the reaction self sustaining and not escaping out the front (essentially a pressure wall from the compresor stage so it can only go rearward), and combustion itself.

            Really, it's all due to efficiency. The higher your pressure ratio, the higher the thermodynamic efficiency of your cycle. The trouble comes down to scaling issues. In order to reach high pressure ratios, you necessarily end up with high temperatures, those high temperatures require exotic mechanisms to keep the hot sections within reasonable operating conditions, and those exotic mechanisms require lots of room to implement. The largest aircraft and industrial gas turbines run upwards of 40:1 pressure

        • Re: (Score:2)

          by dywolf ( 2673597 )

          (really really need an edit button)
          although...one reason jets are hot is because its a consequence both of the required pressures need to both keep the reaction self sustaining and not escaping out the front (essentially a pressure wall from the compresor stage so it can only go rearward), and combustion itself. the heat itself isnt necesarily required, it's "just there". so if they could get the required pressures and airflow for their power turbines to work without as a much heat, so much the better for t

  • An engine drives a compressor, heat is added to the compressed air and it's used to spin a turbine that isn't hooked up to the compressor? In that case it's the bastard child of a motorjet [wikipedia.org] and a turboshaft [wikipedia.org] - and looking at the temperatures involved it's unlikely to be terrible thermally efficient. They might be able to coax enough power out of it to drive a small chopper, and it might be cheaper and/or easier to maintain than a pure turboshaft engine... but somehow I think this will vanish into obscurity pr

  • It looks and sounds like the 1/5 scale prototype is electric and very crudely controlled... only 8 throttle settings? The blades are counter rotating, so no tail rotor is needed except to rotate the craft (which it can't, it seems). Any cyclic adjustments to one of the lift rotors looks like it could cause a catastrophic collision with the other. It seems to me the demo in the video was basically completely uncontrollable except for the throttle.

    I don't think this could really be a real scale prototype le

    • Re: (Score:2)

      by Ksevio ( 865461 )
      The prototype also stayed within a foot of the ground which makes me wonder if it can even fly or was just able to hover. Most toy electric helicopters flying around in the mall are more impressive than this demo.

      • Re: (Score:1)

        by Anonymous Coward
        I own a counter rotating RC helicopter [amazon.com]. The GP post implies they can't turn, but they can, by varying the relative speed of the blades. It's really fun to fly. Hard, because it's so light any draft moves it fast. Flying it around the house is like paying a very complex video game. It's my first RC aircraft and well worth the $50. You correctly noted that the toy model didn't get more than a foot off the ground. They are using the ground effect [rchelicopterfun.com]. It allows you to hover with less power. It feels like

  • There is hardly anything new in here to see, except maybe for a new take on jet tip rotor.

    Jet-tip rotor helicopters are old technology, especially in France where the only successful model of such an helicopter, the Sud Ouest SO.1221 "Djinn" [wikipedia.org], has been designed and commercialized over 50 years ago.

    Jet tip rotors had a lot of issues, from the thrust-control, failure-mitigation and temperature-control mechanisms that have to fight the huge centrifugal force at the end of blades, to the poor autorotation perfor

  • The very definition of vapor ware (Score:3)

    by bdwoolman ( 561635 ) on Friday June 21, 2013 @05:17AM (#44068707) Homepage

    FTFA "Though a full-scale working prototype is yet to be built, Sagita claims to have proven the concept (albeit with an electric motor) with a one-fifth scale model. You can see the video of it in flight below.">

    And it actually uses vapor. But not the good kind.

    As for me? I am developing a teleportation device. I don't have a working prototype, but I have a proof of concept using my automobile. Any VCs out there can reach me on my FTL communicator. Also in development.

  • It's like a turboshaft with a free power turbine?

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