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Sagita's hot air-powered Sherpa rethinks the ultra-light helicopter


June 18, 2013

The Sagita Sherpa helicopter (Photo: Gizmag)

The Sagita Sherpa helicopter (Photo: Gizmag)

Image Gallery (6 images)


The Sherpa's propulsion system bears explaining a little more fully. Rather than driving the rotors directly, the Sherpa's engine instead powers a compressor with an air intake at the rear of the helicopter. That compressor feeds some of its air to the engine to aid combustion, while the rest draws heat from the Sherpa's cooling system before being mixed with engine exhaust fumes to heat the air to 100º C (212º F). The compressed hot air drives two turbines which directly drive the Sherpa's two contra-rotating rotors.


The two-seater's distinctive bullet-shaped fuselage comes as a result of the air intake to the rear, needed to supply the compressor with air. The cockpit is about 1.45 m (4.8 ft) wide and 1.26 m (4.1 ft) high. The Sherpa's nose-to-tail length, excluding rotors, is just under 4.8 m (15.8 ft).

The 1:1 scale Sherpa on show in Paris is just a model, and at this stage the helicopter's performance is theoretical. However, Sagita says that the 260 kg (573 lb) helicopter can lift an additional 171 kg (377 lb) of load. It has an expected cruise speed of 158 km/h (85 knots), range of 400 km (250 miles) and a maximum flight time of 3 hours. Its ceiling is 2,000 m (6,600 ft).

Talking to Gizmag in Paris, Sherpa inventor and Sagita Director, Hubert Antoine, suggested that the technology is applicable to much larger helicopters. He also suggested the Sherpa has the potential to become a UAV platform.

It's hoped that the aircraft, in development since Sagita's founding in 2008, will make its debut flight in 2 years, and go on sale in 3. It's target price is €150,000 (US$200,000).

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.

Source: Sagita

About the Author

Stranger things have worked but that does not make it a good idea.

18th June, 2013 @ 10:17 am PDT

I have to agree with Slowburn, at least to some extent. While the powerplant might in fact be efficient, putting the intake at the rear seems like a really weird thing to do. The video shows that the thing has a definite tendency to fly backward, and for pretty obvious reasons.

Maybe not such a bad idea, but at the very least I would put the intake(s) somewhere else.

Anne Ominous
18th June, 2013 @ 02:44 pm PDT

85% efficient of what?

I was expecting the rotors to be driven by the compressed air via jets at the tips at first, why else compress air etc.

Looks cool so it's 90% there ;)

Craig Jennings
18th June, 2013 @ 02:46 pm PDT

re; Craig Jennings

I agree blowing warm air through the blades and out nozzles at the tips would have provided the NOTAR performance with a single rotor and as a result fewer bearings and prevented blade icing as well.

I don't like the idea of loosing power to just one rotor either but that can happen with a gear driven system as well.

18th June, 2013 @ 04:10 pm PDT

I agree the air intake(s) placement seems strange, why not, say, at the top of the fuselage where the rotor's downforce could help ( even if a tiny amount)? Even if at the front, with the airflow path under the cabin floor, at speed surely the increase of air pressure would "turbo" the efficiency?

The Skud
18th June, 2013 @ 08:16 pm PDT

Presumably the exhaust gasses exit through the slot around the saucer shaped rotor head possibly providing extra lift due to the Coandă effect?

Always liked the idea of coaxial rotor helicopters (not a new idea; Henry Bright patent 1859) lets hope it fares better than the Sikorsky X2.

Incidentally, if you blow air through the blades and out nozzles at the tips you get no torque reaction so you only need one set of rotors.

$200,000 makes it cheaper than a Robinson R22 ($260,000) so affordable as a trainer, although the CAA/FAA would probably have to create a "limited" licence specially for it.

Pat Pending
19th June, 2013 @ 05:19 am PDT

I think it looks like a ducted fan gyrocopter.

I also think the compressed air should run the main rotor with 'jets' at the tips. It would - IMO - simplify the mechanicals of it.

19th June, 2013 @ 05:57 am PDT

Get a real scale model working before parading in Paris.

Seems they have described a direct drive, dual free-power-turbine, high bypass gas (low temperature) ?? engine...... but what is the powerplant driving the compressor..

Hard to see how they can reach even moderate efficiency (thermodynamically) given the small scale.

Um... High thermodynamic efficiency needs high temperatures the best they can ever hope for is to approach Carnot efficiency....

All I could find was this link:

Mentions using a diesel engine for compressor power... and

direct embedded turbines attached to each coax rotor...

Back in the old days they called the set-up a motor jet.

85% thermodynamic efficiency is Not likely given the most efficient combined cycle power plant is around 60% efficient.. Unless their gas generator is a solid oxide fuel cell.. and the compressor is electrically driven....

Also, don't forget that tailrotor helis also drift (sideways instead of backwards)

Wouldn't a better bet be using electric drive at the hub, and whatever higher efficiency generator they can come up with (even batteries for short duration UAVs).

19th June, 2013 @ 06:11 am PDT

re; Pat Pending

The Sikorsky X2 was built as a proof of concept/technology demonstrator that fulfilled its design roll and was retired on schedule while also providing data for the development of higher capability production vehicles.

How is that not faring well?

19th June, 2013 @ 07:53 am PDT

Is it me or is every claim they have made "in theory"?

They claim to have "proven the concept" yet they didn't. They built a scale model...that doesn't use the same technology....and have no working prototype.

Also, it can only lift 377lbs (in theory -ha!) ... two full grown men and some gear won't even get off the ground.

Verdict: Ridiculous, speculative, nonsense that will never see the light of the marketplace.

Joseph Boe
19th June, 2013 @ 09:13 am PDT

It sounds like someone wants to put a turbo charger at the hot end of a jet engine and use the shaft from the turbo to spin the rotors. The whole idea seems foolish to me but perhaps i'm not getting it right.

Jim Sadler
19th June, 2013 @ 09:25 am PDT

If I understand correctly, this is a brilliant evolution of the french 60' djinn concept.

The engine that powers the compressor feed the rotor with a double landstrom type turbine. Easy and effective.

Mouammar K
19th June, 2013 @ 11:12 am PDT

James Holloway writes:

"because fewer moving parts are needed overall, maintenance is reduced."

But, fewer moving parts relative to what? Even the simplest diesel or petrol engine has about 5 times as many moving parts as the gas turbine/gearbox combination in use with the majority of large helicopters today. More importantly, the number of non-bearing RUBBING parts in any multicylinder reciprocating engine is also much higher than in a turboshaft. As documented, the design seems to have swapped a diesel engine, compressor, and rotor turbines for a (much simpler) gas turbine and planetary gearbox.

Can somebody show how this design has fewer moving parts than a conventional turbine coax helicopter like the KA50?

Also, unless the diesel engine spins at tens of thousands of RPM, a further gearbox would be needed to drive the main compressor. Either that, or perhaps the compressor is directly driven from the diesel's exhaust, with no mechanical connection whatsoever.

The backwards flight of the model was probably not due to it being "sucked backwards" by the rather unfortunate choice of air intake location, but most likely due to the CG being slightly behind the main rotor mast. Happens all the time with models, even real helis.

See "Feynman Sprinkler" if in doubt.

But as others have stated, almost any other location for the intake would be more helpful.

If the model really was being "sucked backward" with any useful force, the solution would be very clear! Mount the compressor air intakes on the blades' leading edges! ;-)

@ Slowburn


Good point! Having redundant and completely independent rotors is a plus, but comes at some efficiency cost. Autorotation is a very viable alternative for helicopters.

19th June, 2013 @ 11:16 am PDT

@Jim Sadler


Agreed, that would be foolish. You basically just described the power mechanism that all turbine helicopters have used for nearly the past 70 years. They don't call it a turbo charger, but a "power turbine" and it doesn't have a separate impeller, as that would serve no purpose, and waste some of the valuable mechanical energy needed by the rotors.

19th June, 2013 @ 11:37 am PDT

"Everything works on paper." Now put a live person in a full size helicopter and then blow the exhaust fumes back down on the pilot and it will be a short flight!

19th June, 2013 @ 11:39 am PDT

All been done before look up Fairey Rotodyne, Compressed Air Plus Jet fuel was fed to rotor tip engines for vertical take off and landing, during horizontal flight the turbo props drove the aircraft forward and the blades auto rotated for lift.

This design was not theoretical it was in commercial service in the late 50's but it was loud, which forced it out of the market for city to airport shuttle service.

Robin McCabe
19th June, 2013 @ 02:08 pm PDT

How about improved pilot training, since NO tail rotor to mess with & upsize to 4, 8., 10, 20 place model & for Cargo alone.

Be huge if size of HH53 copter or Marine 1.

Stephen N Russell
19th June, 2013 @ 05:31 pm PDT

@ Robin McCabe "All been done before look up Fairey Rotodyne, "

Yes, the Rotodyne was a brilliant design with all the boxes ticked. Its top speed was only a bit below the recent Eurocopter record mentioned on this site, and was achieved 60 years ago with much greater payload capacity.

It was proven to be quieter than Sikorsky's Skycrane, a similar sized machine, and FAR quieter than current short-haul airliner takeoffs. But it seems the habit in Britain (and sometimes the US) in those days was to scrap perfectly good, novel, inexpensive, and proven aircraft designs due to unrealistic concerns, often politically amplified by special interests.

(Boeing SST, for example)

I suspect it was too good, and someone with connections didn't want it competing with their vested interests, but that's only a theory.

Technically, though, it has almost nothing to do with the design mentioned here.

Firstly, it was well proven and flyable. Secondly, it wasn't coaxial, thirdly, its rotor was not powered with a local turbine, but a sort of hybrid subsonic ramjet collection. And fourth, the main rotor was designed to spend most of its service life in autorotation, unlike the design here.

And finally, the power source of the Sherpa is apparently a diesel engine, rather than a pair of Napier Elands which double as forward flight turboshafts.

Now, for an incredibly cheap, and incredibly noisy ultralight helicopter, a system with no internal engine and tip pulsejets would be the go. Completely portable, very low cost and low tech, and guaranteed to annoy the neighbors with a truly unique sound, when you take off from the backyard! :-P

19th June, 2013 @ 05:48 pm PDT

It never really states what the primary power source is.

It is not likely to be a Turbine-

Turbocharging a Turbine is not advisable.

Is it Rotary?

If they are doing vapourware,

where's the flux capacitor?

An electric model proves nothing.

Many R/C helicopters can cut grass-

try that with a "real" helicopter....

19th June, 2013 @ 10:46 pm PDT

re; Griffin

It depends on the helicopter and takes tall grass but precobra huey gunships Did a good job if you keep the blades flat; the leading edge could take it the bottom of the blades couldn't.

20th June, 2013 @ 07:37 am PDT


Remember that when Sikorsky upgraded from the X-wing to the X2, the DARPA stopped all funding for the new concept -- probably because of the X2's potential to evolve into a highly popular mass-produced civil ultra-light electric VTOL aircraft eligible as a substitute for the motor car outside urban areas...

The same is of course true for the AW-609 civil tilt-rotor prototype which will remain grounded indefinitely in Italy since AW has bought out Bell from the project... under an agreement granting Bell the exclusive right to conduct any new developments (e.g. reversible-twist rotor blades for auto-rotation capability, as is mandatory for civil certification)!

Yet don't count either on Bell to transfer forthcoming reversible-twist blade technology to its former partner AW!

And don't count on AW for claiming access to said technology to get their baby off the ground -- because both Bell and AW are serving the interests of their main customers, i.e. the military who don't like the idea of the civil society challenging global military control of the airspace with myriads of personal aircraft...

20th June, 2013 @ 04:19 pm PDT

The only sherpa unable to make it even to the bottom of Mt. Everest... unless it's on the back of a truck. :P

Lance Alladin
20th June, 2013 @ 07:32 pm PDT

re; euroflycars

What are "reversible-twist rotor blades"?

There is nothing special about the rotor heads used it tiltrotors.

In vertical flight mode conventional auto rotating rotors work conventionally. In horizontal flight mode you feather the blades putting the minimal cross section into the wind and glide. If you loose power to a rotor in conventional flight and have the ability and desire to convert from horizontal to vertical flight mode you still need the rotor to spin in the normal direction so you will have the rotor windmill at more or less the same pitch that it would be in under power until the direction of airflow over the blade shifts from forward to backward.

DARPA not funding something that uses already proven technology is not exactly evidence of a conspiracy to limit the availability of private aircraft.

It is not the military that has the motive of limiting the personal mobility of the people. In fact Having large numbers of private aircraft that match their need is to their advantage in an emergency.

21st June, 2013 @ 04:52 pm PDT

Rear intake, sounds backwards. It has a nice streamline look to it, but not practical. By the time the new design is out and manufactured we'll all be dead anyway. No one designs transportation fast enough to free us from big oil :/

22nd August, 2013 @ 08:41 pm PDT
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