Aircraft

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

The Sagita Sherpa helicopter (Photo: Gizmag)
The Sagita Sherpa helicopter (Photo: Gizmag)
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The Sagita Sherpa helicopter (Photo: Gizmag)
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The Sagita Sherpa helicopter (Photo: Gizmag)
The air intake can be seen at the Sherpa's rear – not a sentence I saw myself writing when I had breakfast this morning (Photo: Gizmag)
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The air intake can be seen at the Sherpa's rear – not a sentence I saw myself writing when I had breakfast this morning (Photo: Gizmag)
(Photo: Gizmag)
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(Photo: Gizmag)
The air intake can be seen at the Sherpa's rear – not a sentence I saw myself writing when I had breakfast this morning (Photo: Gizmag)
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The air intake can be seen at the Sherpa's rear – not a sentence I saw myself writing when I had breakfast this morning (Photo: Gizmag)
Sagita is displaying a 1:1 scale model of the Sherpa in Paris this week (Photo: Gizmag)
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Sagita is displaying a 1:1 scale model of the Sherpa in Paris this week (Photo: Gizmag)
The air intake can be seen at the Sherpa's rear – not a sentence I saw myself writing when I had breakfast this morning (Photo: Gizmag) (Photo: Gizmag)
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The air intake can be seen at the Sherpa's rear – not a sentence I saw myself writing when I had breakfast this morning (Photo: Gizmag) (Photo: Gizmag)
Sagita says theSherpa has no need of a tail rotor (Photo: Gizmag)
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Sagita says theSherpa has no need of a tail rotor (Photo: Gizmag)

Certainly one of the more intriguing things on display at this year's Paris Air Show, the Sherpa by Belgian startup Sagita aims to make the helicopter simpler, more efficient, more reliable and more affordable. The helicopter's rotors are directly driven by turbines which are themselves powered by hot air and fumes from the helicopter's power plant. Sagita claims that this makes the the aircraft approximately 85 percent efficient while doing away with the need for a tail rotor.

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.

Sagita claims that no additional cooling measures are required, and that because fewer moving parts are needed overall, maintenance is reduced.

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

Sherpa 1/5 scale model in flight 1/2

26 comments
Slowburn
Stranger things have worked but that does not make it a good idea.
Anne Ominous
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.
Craig Jennings
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 ;)
Slowburn
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.
The Skud
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?
Pat Pending
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.
BigGoofyGuy
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.
MD
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: http://enzu.bruface.eu/media/filebook/files/Master%20Thesis%20proposal%20BruFacE%20EM%20engineering_Degrez.pdf 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).
Slowburn
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?
Joseph Boe
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.
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