Slashdot Mirror
Sagita Displays Hot Air Powered Helicopter
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."
Just put one of these helicopters over Washington D.C., and you'd have an unlimited supply of hot air.
The thing would be able to run forever!
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.
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.
The fluid coupling between the compressor and the rotor can't be efficient.
SURE it can.
What makes you think it can't? It's just a rotating joint with a seal on a hollow shaft. Nothing new here, move along.
In fact there is nothing new here anyhow, unless there's some aspect of it they're not telling us. "Water sprinkler rotor"-style helicopters have been played with for half a century or so.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
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.
You've got that backwards. Work is power done over a period of time.
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 and a turboshaft - 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 pretty fast.
TL:DR version: Two old ideas mashed together, unlikely to be 85% efficient
Everything in the world is controlled by a small, evil group to which, unfortunately, no one you know belongs.
I research and teach physics, and even I think you're being kind of stupid here. Yes, that is a stab at the physics definition of power, but it should be pretty obvious to anyone with some basic understanding of English that there is a non-jargon meaning to the word, and usually it is quite clear from context which is meant. Many words have more than one meaning, get used to it, unless equivocation is a hobby of yours.
No disclaimer is needed. This is precisely the reason I still come to this site. Bravo!
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 let alone a real possible model of a full scale craft that could work.
Adjust the relative speeds of the contra-rotating blades...
I have determined that my sig is indeterminate.
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", 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 performance and, mainly, to the difficulty of designing reliable multi-engine configurations which pretty much limits this technology to small helicopters (and over-land operation only). Additionnally, a lot more power is lost in the compression and transport system than in a conventional gearing system, which eats away quickly any weight-saving. For one, the Djinn had double the fuel consumption of a similar-size chopper. That's why they disappeared.
Here, the Sagita's description from the article claims that the two contrarotating main rotors are driven by a pair of turbines which are driven by a compressor which is itself driven by the main engine and its turbine. That makes it a hybrid between a conventional turboprop helicopter where a turbine in the engine drives the main rotor through a gearbox, and a jet tipped helicopter where the engine's turbine drives a compressor which blows air (usually with added combustion, as in the ramjet-tip configuration used on the Djinn) through the rotor's blade tips.
In a way, it can be understood as the application to helicopters of a somewhat modern-ish turbopropeller tech used in airplanes, where different sets of turbines each drive the main propeller and the engine's inner compressor at different rotation rates. However, in an airplane this design is streamlined and integrates in a very straight-forward way inside the engine because the main propeller IS the "additional compressor", whereas on the Sagita, the main rotors are not aligned nor even integrated with the main engine, requiring a whole compressor added to the mix. That implies more mass, more complexity and some transmission losses that mitigate the efficiency of the whole thing, so I doubt their efficiency gains figures.
Maybe we deserve this world ?
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.
"No fear. No envy. No meanness." Liam Clancy
They didn't go into the "green hybrid" detail about the copter utilizing hose fed flatulence from the pilot and passengers, either.
*Repent!Quit Your Job!Slack Off!The World Ends Tomorrow and You May Die!
Or rather... power = work / time....
Because fluid couplings are inherently inefficient. You use them in a turboshaft engine because of the very nature of your gas turbine core, releasing all of its energy as large volumes of exhaust air. You use them on cars and heavy industrial vehicles because they continue to produce significant torque even when stalled out at zero RPM, allowing you to move heavy loads from a standstill without burning up a mechanical clutch. When you don't have good reason to use a fluid coupling, you use a mechanical one for the efficiency gains.
It's like a turboshaft with a free power turbine?
https://en.wikipedia.org/wiki/Fairey_Rotodyne https://en.wikipedia.org/wiki/Tip_jet
There is nothing wrong with yr Internet. Do not attempt to adjust the picture. We are controlling the transmission - NSA