The Challenge

UMS SKELDAR, a joint venture between Saab and UMS AERO Group, develops advanced Rotary Unmanned Aerial Vehicle (UAV) platforms. The company is Europe’s leading provider of Remotely Piloted Aircraft Systems (RPAS) across maritime, military and civilian markets where dependable and affordable systems are required.

For the maritime industry, coverage of the Earth’s oceans is a significant task, and one that cannot be easily completed by manned aircraft. To support this, UAVs are being deployed on a growing scale to carry out missions quickly, efficiently and cost-effectively.

Fixed-wing UAV’s have been around for many years in the maritime domain. However, Vertical Take-Off and Landing (VTOL) systems are now maturing to enable maritime operators to patrol and monitor borders with ease. Some of the key challenges facing UAV operation – particularly in the maritime sector – include safety, endurance and reduced logistical footprints.

Historically, the maritime and military sectors have largely used fixed-wing UAV’s. However, these systems require significant resources in terms of ground crew and equipment to launch and recover the system, not to mention the space required on a naval vessel to house it. Rotary UAV’s, on the other hand, allow operators to make significant reductions in their logistical footprint and resource requirements, which is especially important for navy ships where space is at a premium.

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From a maritime perspective, it is critical that the UAV runs on heavy fuels. The major reason for this is safety; gasoline is not permitted onboard a navy vessel due to its combustibility. Mostly kerosene based, heavy fuel is one of the primary fuels used in the maritime domain and is desirable due to its strong performance and lower volatility. Heavy fuels are very hard to ignite, increasing their ability to be safely stored for long periods of time without risk of degradation. Most importantly, heavy fuels reduce the danger of fires on a ship or base, which is a must for naval operators.

The kerosene based JP8 is one of the primary fuels used in the maritime domain. JP8 supports NATO’s one-fuel policy, which has been in existence for over 30 years and was designed to maximise equipment interoperability using a single fuel for all, be it on land or sea.


The Solution

Hirth Engines has been a pioneer of the two-stroke engine for over 60 years, with a track record of more than 30 years in the UAV sector. To meet the requirements UMS SKELDAR had set it, Hirth needed to design an engine no other manufacturer could offer at the time. Able to operate on heavy fuels, Hirth designed a variant of its 35 series, already a proven engine in other markets.

Hirth’s 35HF is a market-leading two-stroke engine that delivers an exceptional power-to-weight ratio and extreme operational range in all conditions.

Pairing this unique engine with UMS SKELDAR’s main platform, the V-200, was the perfect match and is the only heavy fuel rotary VTOL capable of flying extended missions for up to five hours.

At sea there is no margin for error. The SKELDAR V-200 heavy fuel engine is precise and reliable, making it the UAV of choice for navy commanders or any maritime installations. The 35HF engine provides landing and take-off assurance where conventional fuels are prohibited. Hirth’s two-stroke engines include advanced sensor and actuator technologies giving manufacturers the confidence the system can operate in a wide range of environments and conditions.

The 35HF is able to operate on both JP5 and JP8 fuels (NATO code F-34), providing a safe solution for maritime applications that do not require heaters and has a high time before overhauls (TBO) – something that is typically a challenge for other spark ignition heavy fuel engine technologies.

Hirth have been instrumental in enabling UMS SKELDAR to engineer the very best offering for the UAV sector in terms of a heavy fuel powered rotary VTOL, advancing the V-200 platform to become the first in its class to meet NATO’s one-fuel policy to eliminate gasoline for safety and logistics reasons.

The 35HF is an excellent choice for maritime operations due to its high flight performance and easy to maintain design. This is a powerful engine that allows operators to fly for longer and requires less maintenance than four-stroke or Wankel alternatives. The unmatched flight endurance, power-to-weight ratio and TBO make the system the first choice for navy commanders.

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The Future

The SKELDAR V-200, powered by Hirth Engines’ 35HF, has flown extensive missions around the globe and is becoming the leading platform for navies the world over. Engineered with a meticulously proven heavy fuel two-stroke engine, the V-200 boasts endurance; rapid maintenance turnaround; and the ability to integrate into land or sea-based command and control centres.

The ever-growing reputation of the SKELDAR V-200 has been proven in major contract wins with the German Navy, the Royal Canadian Navy and most recently, the Belgian and Royal Netherlands navies. Thanks in part to the integration of Hirth’s 35HF engine, UMS SKELDAR has secured a position at the forefront of the global maritime UAV market.

Looking to the future, UMS SKELDAR are working with Hirth on a continued program of enhancements to improve sensor technology and endurance capabilities of the SKELDAR V-200. The partnership with Hirth in developing the 35HF further is now looking to advance the V-200’s endurance beyond the five-hour mark while carrying a full payload. Furthermore, the recently launched SKELDAR V-150 also operates on a Hirth turbine engine propulsion system that uses heavy fuels.

Considering that naval operators are required to patrol lengthy borders and extreme environments, Hirth believe that advancing the capabilities of its VTOL offerings will be enabled by further advancements to the propulsion system of choice, the Hirth 35HF.

Many areas of the aviation industry are currently focussed on future technologies such as electric and hybrid engines, the latter combining both a combustion engine and an electric propulsion system. However, these alternatives do not have the payload and endurance requirements that a heavy fuel powered VTOL can provide, especially considering the expanding requirements of navies worldwide. For this reason, Hirth aims to advance its VTOL heavy fuel system to the height of its capabilities.

The need for longer endurance, more efficient engines, reduced logistical footprints, lightweight platforms and safer operations are all at the forefront of customers’ minds, and will continue to be into the future.

To meet these needs, engine manufacturers such as Hirth are continually looking to build highly efficient and effective two-stroke propulsion systems. The reason is simple: the performance, durability, reduced energy requirements and ease of maintenance for two-stroke engines is unbeatable and provides an ideal platform for the future of aviation.

Overall, Hirth’s goal for the future is to provide the military, maritime and civilian markets with an advanced and robust VTOL engine that can compete with their fixed wing counterparts on endurance while providing major advantages in terms of logistical resources and minimising the impact of space and manpower needed to operate and maintain the platform.