There’s a change going on in the way military aircraft carry out stealth surveillance. Rather than risk the lives of pilots, small unmanned aerial vehicles (UAVs) carrying camera systems, sensors and other electronics are being sent out on an increasing number of missions. To put this into context, the U.S. Air Force presently trains more UAV operators than pilots.

But there’s one big problem with the majority of these small UAVs, the ones carrying these multi-million dollar systems of equipment over battlefields, as well as the ones in non-military uses like border surveillance and monitoring forest fires: the engine. That’s because instead of developing engines specifically for small UAVs, integrators have worked with off-the-shelf engines to deploy the aircraft more quickly. While there is something to be said for accelerating time to market—or in this case, time to mission—that’s not always the optimal solution.

That’s because some of these “off-the-shelf” engines are modified versions of those that you find in model airplanes and garden appliances like weed whackers or lawnmowers. These engines aren’t designed to fly at high altitudes, nor are they optimized for weight or silence, so you can imagine their unreliability when trusted to carry expensive surveillance equipment or conduct a stealth mission beyond enemy lines.

That’s where Ricardo, Inc. (ricardo.com), a company that knows a thing or two about developing engines for vehicle systems integration (especially in the case of the military), comes into the picture. Engineers have been developing a family of purpose-built engines for small UAVs at its Detroit Technology Center over the past six months. The first in Ricardo’s family of “Wolverine” engines is an air-cooled, 88-cc, three horsepower, two-cylinder, two-stroke hybrid. It runs on the military’s JP-8 heavy fuel, which is delivered via a mechanical fuel pump to the cylinders and ignited by spark plugs. It also carries 500 watts of onboard power from an integrated starter-generator. Crafted from aluminum alloys, steel and titanium, it weighs only five pounds, lightweight enough to allow for extended range and altitude when installed in a UAV.

“Taking something for a military application that’s been designed for a different usage is always doomed for failure,” says Stephen Cakebread, unmanned services project director for Ricardo. “We’ve taken a clean sheet design over a six month period. Everything is optimized to meet performance.”

In developing the engine, Ricardo sought input from military and civilian UAV experts, specifically those at the University of Dayton Research Institute’s Center for UAV Exploitation. For instance, relying on gasoline engines, as was the case for many of the off-the-shelf type, can create obstacles in military use. This is because military vehicles typically use heavy fuels, so a gasoline engine means fuel would not only have to be imported—which is expensive—but the fuel quality could be questionable in an application where there’s little margin for error.

“Probably the biggest benefit is the heavy fuel capability,” Cakebread says of the Wolverine engine, adding, “The majority of engines in this class are gasoline. It does cause significant logistic issues as well as safety issues. We’ve taken all the good points needed for that application and applied them into a very small package.”

A team of 30 worked on the project, developing the engine from the inside out while designing and simulating key parts relative to its desired size. Investment casting was chosen as the method to form the crank cases, enabling flexibility and ease in conducting running changes as the engine was being developed, minimizing tooling costs.

The engine’s “first fire” was completed in May 2010, and its first flight is scheduled for Q3 2010, when it’s set to be installed in the Nightwind 2 (NW-2), a next-generation tactical UAV developed by Unmanned Aerial Systems (uasnw.com). With the Wolverine powering it, the NW-2 won’t be able to be seen or heard (or tracked on radar) above 1,000 feet. The engine will double the UAV’s altitude ceiling to 20,000 ft and allow the craft to be operational for over three hours, compared to 30 minutes.