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72 A number of other new features were added to improve airflow inside the heat exchanger, but the company is not providing details of them for now. One side effect of having the exhaust gas flow through the heat exchanger’s dense network of pipes is that its speed and density are greatly reduced before exiting the engine, which helps to lower the noise and vibration being produced.  “The two noisiest aspects of any turbine engine are typically the compressor, with its high-frequency sound – which can easily be muffled – and the exhaust gas density, which in our engine is suppressed through friction with all the microtubes,” Fauvet explains. Less vibration extends the engines’ lifespans, while producing less noise is a benefit for UAVs that might operate near populated areas. “An additional result of the exhaust heat being re-absorbed by the Inconel tubes is that the gas leaves our engines at about 350 C, compared with 700 C or thereabouts for most smaller commercially available turbine systems,” Fauvet adds. “It’s worth noting as well that this greatly shrinks the engine’s infrared signature, potentially opening up applications for its use in stealth and reconnaissance UAVs. It also means the outer hull of the engine doesn’t get hotter than 150 C – that is important for mounting it in UAVs made from carbon fibre, which isn’t good at withstanding excess heat. “The design of the exhaust system can also be customised according to users’ requirements. Some will want rear- pointing exhaust outlets, while others may want side-mounted or underbelly- mounted exhaust ducts.” Generator As discussed, the primary idea behind the development of the TG-R55 is for the turbine’s shaft to directly drive a brushless, permanent magnet generator, in order to recharge an electric aircraft battery during flight. “The direct drive maximises the power we get from the generator; a gearbox is unnecessary here,” Fauvet says. “It also keeps the mechanics very simple, with just a single shaft and spool, and just two bearings, which have been custom- designed to accommodate the high speed of the shaft.” Although much of the key information on the generator (including the number and type of coils and magnets in the stator and rotor respectively) could not be disclosed, CTO of mechatronics Marc Nguyen says, “We’ve done essentially all the April/May 2020 | Unmanned Systems Technology Dossier | Turbotech TP-R90 and TG-R55 The design of the exhaust system can be customised to a user’s needs – a rear-pointing one, side-mounted or on the underbelly TP-R90  Turboprop Fuels: Jet-A1, diesel, avgas, UL91, biofuels Power output: 90 kW Weight: 74 kg Dimensions: 1084 x 412 mm Turbine speed: 80,000 rpm Propeller speed: 2272 rpm TBO: 3000 hours Fuel consumption: 18-25 litres/hour TG-R55  Turbo-generator Fuels: Jet A-1, diesel, avgas, biofuels Power output: 55 kW Voltage: 400-900 DC Weight: 65 kg Dimensions: 1015.5 x 412 mm Turbine and rotor speed: 80,000 rpm Synchronous brushless generator TBO: 3000 hours Fuel consumption: 15-22 litres/hour Some key suppliers CFD simulation: Ansys CAD software: Catia Castings: Zollern Microtubes: Le Guellec Housings: GCA Groupe Shafts: GCA Groupe Combustion chamber: Alsenam Gears: MTA Industrie Groupe Jogam Bearings: Cerobear Variable-pitch propellers: Airmaster Assembly: in-house Testing rigs: in-house Data acquisition: National Instruments Seals and gaskets: undisclosed Ignition system: undisclosed Fuel system: in-house Starter/generator: in-house Pumps: in-house Oil filter: undisclosed Fluid lines: in-house Wiring loom: in-house Engine management system: in-house Additional technical consultation: Safran Specifications