With successes in the 50-shp class gas turbine engine class for unmanned aerial vehicles (UAVs), UAV Turbines has reached an agreement with the U.S. Army’s Reliable Advanced Small Power Systems (RASPS) program to design, manufacture and test a 200 shp class advanced technology turbine engine.
The goal of the RASPS program is to get the turbine to technical readiness level 6 (TRL 6): testing a prototype in a relevant environment. The next steps involve operational testing and qualification through testing.
“The RASPS program is targeting performance goals that include higher power-to-weight ratio and lower brake specific fuel consumption (BSFC), using advanced concepts, materials, and system optimization,” according to UAV Turbines Chief Design Engineer Dan Mikkelson. “A special focus will be on technology that greatly improves reliability over conventional engine systems.”
Company officials point to the development of the UT50R turbine for UAVs and performance and efficiency gains compared to the conventional engine in the AAI Corporation RQ-7 Shadow as reason for the development’s progress. The U.S. Army uses the UAV for intelligence, reconnaissance, and surveillance (ISR) missions and it is currently powered by a 38 bhp AR741-1101 Wankel rotary engine.
UAVs in Group 3 and 4 with an engine rating of less than 400 horsepower currently rely on intermittent combustion engines entirely. Mikkelson says that there are issues with them regarding noise, inability to use heavy fuels, and shorter lifetimes. Microturbines face high fuel consumption rates and cost more upfront.
UAV Turbines say the UTP50R and the future 200-hp class recuperated powerplant help to solve both sets of issues because of the recuperation of exhaust gases with a design similar to that of a turbocharger. Company officials note that the design adds some weight compared to the RQ-7’s existing powertrain in the 50-shp class. However, it offers several key advantages, according to program engineers.
For one, the engineers leveraged experience working on the Sikorsky UH-60 Blackhawk and various engines to create a system that incorporates the turboprop, a variable pitch propeller, and split-stage gearbox to improve efficiency in different flight modes.
Specifically, the turbine uses a single-stage centrifugal compressor mated to a compact high speed, radial inflow turbine. The gearbox uses a split-torque load path design and integral oil passages and a high-offset output shaft. With a variable-pitch propeller, the small turboprop can improve efficiencies during climb and loiter scenarios.
In a testing program comparing their UTP50R to an existing intermittent combustion engine, engineers at UAV Turbines noted the following benefits of their system:
- At 9,000 feet, the UTP50R was able to loiter for 11.3 hours, a two-thirds increase over the existing platform’s 6.8 hours.
- Time at 18,000-ft. loiter nearly doubled, from 5.2 hours to 10.3 hours.
- Rate of climb is 11 percent higher at 1,350 feet per minute (fpm)
- Dash speed is 136.5 knots to the baseline RQ-7’s 99 kts.
The UTP50R would also be a significant development for the U.S. Army, if successful, because of its use of JP-8. The diesel variant is used in everything from tanks to heaters to other ground vehicles. As part of the Department of Defense “One Fuel” goal, it would reduce logistical issues compared to the current need to supply UAV units with aviation gas and oil in addition to the other fuel needs.
With the goal of a TRL 6, there are likely to be some kinks the company will work out, but the engineers behind the first-in-class UAV turboprop remain optimistic.
“It’s always simpler to scale designs up rather than down with things like wall thicknesses and passages; it all either gets larger or simpler to make,” says UAV Turbines Senior Vice President Fred Frigerio. “It’s easier to make a grandfather clock than a Swiss watch. We expect to have some challenges in scaling up to bigger engines, mostly related to having to deal with larger airflows and power, but the engineering in many ways is simpler.”Continue reading »