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Mönch talks to Peter Lietz, Head of International Business Development for Hirth Engines (acquired last year by UMS Skeldar), about the new hybrid Unmanned Aerial Vehicle (UAV) engine application the company will be demonstrating for the first time at AUVSI Exponential in Chicago next week.

Fixed wing UAVs can be very demanding from a logistical point of view,” Mr Lietz told Mönch, “as they require systems such as a catapult for take off and nets or parachutes for landing.” Catapults are quite bulky and though they are relatively easy to set-up on a ship, they add considerably to the logistical footprint of the UAV brought on-board. Similarly, nets need to be installed on the ships deploying the UAVs whereas parachutes add to the weight of the UAV, something that most customers would rather avoid to be able to save that weight for payloads. Finally, landing in a net or at sea is not only inconvenient but also runs the risk of damaging the UAV.

Developed to include both internal combustion engine and electric propulsion motor, Hirth Engines’ new engine has been designed so that the propulsion unit can select either the combustion engine or the electric motor to drive the Vertical Take Off and Landing (VTOL) UAV’s propeller. “Our system allows customers to select the electric motor for vertical take off, then switch to gasoline for the rest of the operation,” Mr Lietz specifies. “Once the mission is over, the customer can switch to the electric motor again for a smooth landing on the desired spot,” whether on land or on-board a ship. This not only reduces the footprint of the UAV system, but it also increases safety.

Hirth Engines’ new hybrid system can be run in three different functions: the gasoline engine drives the generator that powers the system; run the system purely electrically with the batteries, which brings enormous advantages in relation to noise levels and CO2 emissions; or, as a booster, equipping the UAV with a small gasoline engine and its generator, which can be used to give a boost during take off. “Most customers use the first option, which is more conventional, but the others are available for customers who are interested,” added Mr Lietz.

This hybrid application can also bring significant benefits to UAV manufacturers, such as extended ranges and longer endurance levels, increased fuel efficiencies and a significantly improved power-to-weight ratio. Indeed, the hybrid application means that the engine can be set-up from the start on the best economy RPM point, meaning the engine will need less fuel and therefore will benefit from an extended range.

Hirth Engines currently has four on-going contracts for its new hybrid system: two customers in North America, Israel and China. There is also one potential customer in Germany. Speaking to the future of UAV engines and the next challenges that need to be tackled, Mr Lietz concluded: “The biggest challenge on the horizon is the ability of UAVs to fly purely on electrical engines, because battery technology development at the moment is quite slow. The power per kilogramme (kg) - battery compared to the power intensity per kg - fuel is still 1/20-1/30.”

At AUVSI, Hirth Engines will introduce its new UAV hybrid engine (Photo: Hirth Engines)

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