A dirt bike is a tool for getting a person to a place they shouldn’t be. Lightweight, made for rough terrain, and fast, motorcycles allow special forces to slip through woods, navigate narrow canyons, sneak through alleyways, or hurtle down footpaths. There’s only one problem: dirt bikes are really, really loud, so any secrecy gained by using a bike is lost to the engine’s roar. Which is why DARPA, the Pentagon’s future projects wing, is funding the development of a versatile electric dirt bike, so that special forces can have as silent a ride as possible on two powered wheels. The bike is called “Silent Hawk,” and after receiving the first prototype, DARPA liked to so much they asked for two more.
Silent Hawk is a collaboration between Logos Technologies, which makes military tools like drones and sensors, and Alta Motors, which makes electric dirt bikes. Creating a silent motorcycle meant starting from an electric bike. As designed, one modification of the Silent Hawk uses a hybrid engine, so it can run on gas most of the time, and on electricity when it needs to be quiet. And it’s not limited to gas: It’s can run on diesel, as well as JP5 and JP8 jet fuels, so that the special forces using it in the field can power it with whatever fuel they might encounter. When running on fuel, the Silent Hawk recharges its own batteries and any electronic devices the troops might have, like radios, GPS receivers, or tablets.
“Because they’re motorcycles and they’re relatively small, you can put several of these in the back of a V-22 and they could be dropped off somewhere,” said Doug Rombough, VP of Business Development for Logos Technologies. “They could go 50 miles, and when they get within 10 miles of an objective, they could shut off that multi-fuel engine, and go all-electric—the only noise [they] will produce at that point will be the noise of the tires on the surface and or the chain of the motorcycle.”
Running on fuel with the generator activated, the bike is about 75 decibels, or the sound of a garbage disposal. Switched to all-electric, Silent Hawk lead engineer Alex Dzwill says it produces less than 55 decibels, or about the sound of normal conversation. Is it possible to make it quieter?
“Literally the loudest thing is the chain, and it’s possible for us to outfit a belt, though there’s a whole host of reasons for why you wouldn’t want a belt on a dirt bike,” said Dzwill. “If you get a rock in there, it’s very likely that you’ll rip the belt up, but if you’re in a sandy location like the desert, it’s possible you could use a belt and be fine.”
So 55 decibels may be as quiet as a dirt bike gets. Competition dirt bikes are regulated to stay under 113 decibels, so compared to the roaring engines that normally come with such vehicles, the Silent Hawk represents a world of improvement.
The soon-to-be-signed follow-on contract with DARPA will produce these new prototypes within a year. If DARPA likes what it sees, the next stage would be more of a production model, and then after that it’s possible special forces could get a brand-new bike for moving undetected wherever they may need to go. Just don’t expect them to make a big noise about it.