Sagita Sherpa very light helicopter

[UpForce]

Sagita is a Belgian consortium of some sort, founded in 2008. They're showing a full scale mockup of their Sherpa very light helicopter at Paris this year. The powertrain is pretty unconventional, starting from the compressor inlet being pointed towards the rear. The rest of it seems to have something to do with hybrid boundary layer driven turbines, but that's more or less a guess on my part. Contra rotating lifting props, so no need for a tail rotor. Not too much to be found online about the Sherpa, but a cursory search did return a link to a Flightglobal story from 2009, so at least there's that. Might be worth a little buzz.

Two images from Sagita's website, and one of a "Ljungström turbine" CC attribution share alike by "Lidingo" from Wikimedia Commons.

Quote from "How does it work?" Tech section:

• The engine drives a compressor that takes in air at the rear of the fuselage.
• Part of the compressed air feeds the engine, the balance bypasses the engine, collects the heat of the cooling system and is eventually mixed with the engine's exhaust gases in order to raise the temperature to 100°C (212 °F).
• The hot compressed air is then sent to the rotor and expanded in two contra-rotating Ljungström type turbines.
• Each of these turbines drives directly one of the two contra-rotating coaxial rotors. The air exits the turbine through a circumferential gap between the two rotors.
• The transmission system requires no lubrification (sic), no cooling and no tail rotor drive. Its efficiency is about 85%.

 

[ouroboros]

Basically a warm cycle helicopter without the hollow rotor tip jets then, or would this be more accurately described as a direct drive turbine rotor?

 

[Matej]

.

 

[hesham]

Welcome your return my dear Matej,


and a nice helicopter design UpForce.

 

[hesham]

And;

 

[jsport]

Sagita is a Belgian consortium of some sort, founded in 2008. They're showing a full scale mockup of their Sherpa very light helicopter at Paris this year. The powertrain is pretty unconventional, starting from the compressor inlet being pointed towards the rear. The rest of it seems to have something to do with hybrid boundary layer driven turbines, but that's more or less a guess on my part. Contra rotating lifting props, so no need for a tail rotor. Not too much to be found online about the Sherpa, but a cursory search did return a link to a Flightglobal story from 2009, so at least there's that. Might be worth a little buzz.

Two images from Sagita's website, and one of a "Ljungström turbine" CC attribution share alike by "Lidingo" from Wikimedia Commons.

Quote from "How does it work?" Tech section:

• The engine drives a compressor that takes in air at the rear of the fuselage.
  
• Part of the compressed air feeds the engine, the balance bypasses the engine, collects the heat of the cooling system and is eventually mixed with the engine's exhaust gases in order to raise the temperature to 100°C (212 °F).
  
• The hot compressed air is then sent to the rotor and expanded in two contra-rotating Ljungström type turbines.
  
• Each of these turbines drives directly one of the two contra-rotating coaxial rotors. The air exits the turbine through a circumferential gap between the two rotors.
  
• The transmission system requires no lubrification (sic), no cooling and no tail rotor drive. Its efficiency is about 85%.

Whatever happened this superior means to engineer a helicopter along with a disk rotor system.

 

[FXXII]

The green and grey circular cilinders in the drawing do not seem to have any aerodynamic shape, so how does the air get transported to the circumference and why would it be compressed? Or is there more to the principle drawing than is depicted? Anybody an idea?

 

[riggerrob]

Dear FXXII,
The only way that turbine makes sense - to me - is if the two Ljungstrom turbine discs have a series of axial turbine blades installed parallel to the main shaft. That way radial escaping steam turns turbine blades. Each ring of turbine blades/buckets serve as inlet guide vanes for the next outer row of blades/buckets.
This counter-rotating turbine was invented in 1906 by Swedish brothers Fredrick and Birger Ljungstrom to generate electricity. Ljungstrom turbines also powered a huge oil tanker. The Ljungstrom brothers were eventuauly bought out by Brown Boveri who built the first electric-generating turbine in Switzerland.

 

[jsport]

Paper

 

[UpForce]

Ha, didn't remember starting this topic ... guess this externalized memory makes me (us?) a kind of a cyborg entity, individual recollection depending on community demand. Alas, the Sagita website seems to have vanished.

 

[jsport]

Ha, didn't remember starting this topic ... guess this externalized memory makes me (us?) a kind of a cyborg entity, individual recollection depending on community demand. Alas, the Sagita website seems to have vanished.

The helicopters are for sale on another website.

 

[jsport]

Sagita is a Belgian consortium of some sort, founded in 2008. They're showing a full scale mockup of their Sherpa very light helicopter at Paris this year. The powertrain is pretty unconventional, starting from the compressor inlet being pointed towards the rear. The rest of it seems to have something to do with hybrid boundary layer driven turbines, but that's more or less a guess on my part. Contra rotating lifting props, so no need for a tail rotor. Not too much to be found online about the Sherpa, but a cursory search did return a link to a Flightglobal story from 2009, so at least there's that. Might be worth a little buzz.

Two images from Sagita's website, and one of a "Ljungström turbine" CC attribution share alike by "Lidingo" from Wikimedia Commons.

Quote from "How does it work?" Tech section:

• The engine drives a compressor that takes in air at the rear of the fuselage.
  
• Part of the compressed air feeds the engine, the balance bypasses the engine, collects the heat of the cooling system and is eventually mixed with the engine's exhaust gases in order to raise the temperature to 100°C (212 °F).
  
• The hot compressed air is then sent to the rotor and expanded in two contra-rotating Ljungström type turbines.
  
• Each of these turbines drives directly one of the two contra-rotating coaxial rotors. The air exits the turbine through a circumferential gap between the two rotors.
  
• The transmission system requires no lubrification (sic), no cooling and no tail rotor drive. Its efficiency is about 85%.

Google--The hover efficiency ("figure of merit") of a typical helicopter is around 60%. The inner third length of a rotor blade contributes very little to lift due to its low airspeed.

 

[robunos]

I read this to mean that the transmission efficiency is 85%, not the rotors . . . of course this figure is probably over-optimistic, too . . .

cheers,
Robin.

 

[jsport]

I read this to mean that the transmission efficiency is 85%, not the rotors . . . of course this figure is probably over-optimistic, too . . .

cheers,
Robin.

Generally, a direct drive turbine is going to be more efficient than hard geared mechanical. Likewise, the turbines can spin faster than the gear system thus higher lifte faster. Losses which CRW suffered from are overcome in a more compact system..

Likewise, drag air is expressed at the rear of the craft which itself feeds the intake, therefore drag air assists the propulsor.

 

[jsport]

Paper

The VLR-class TDR helicopter, using either an Avgas or a Diesel reciprocating engine of approximately 90 kW, exhibits a performance gain of circa 10% over the conventional helicopter. The NH-90-class TDR helicopter benefits from an impressive coefficient of performance margin of 47% while using a turbofan with a thrust potential of 22.5 kN, which makes the concept attractive in the heavy helicopter category. For both configurations, a RELT geometry is proposed yielding adequate turbine polytropic efficiencies between 85% and 90%