Bob Maddox's Jet Bicycle.

By Chuck Squatriglia Via: Wired

"If skydiving doesn't quite do it for you, you could always strap a jet engine to your chest. That's what Bob Maddox did until discretion got the better of him and he decided a jet-powered bicycle might be a little safer.

Maddox, an artist and cabinetmaker in Medford, Ore., has been tinkering with
pulse jet engines for seven years now. He's recently started bolting them to old-school cruiser bicycles and selling them on eBay, and a video of him riding one is bouncing around the blogosphere.

We got ahold of him at his workshop, where he's wrapping up a sweet purple jet bike for a customer in the Netherlands. He's only built two so far. He got the first one up to 50 mph but backed off when visions of catastrophic wheel failure danced in his head. He figures the bikes will hit 75 if anyone's got the guts to do it.

"When you're on a motorcycle going 50 mph, you don't think anything about it," he told us. "But on a bicycle, it feels way too fast."
And loud. Way too loud.

"It's loud like a top alcohol dragster loud," he says. "It'll pop your ear drums if you aren't wearing protective gear. That's a drawback to the engines."
No kidding.

Pulse jet technology dates to the beginning of the 20th Century when they were developed in Sweden. Germany used them during World War II to propel the V-1 "buzz bombs" they hurled at England during the Blitz of 1944. The exceedingly simple internal combustion engines that will run on just about anything and remain popular with hobbyists.
"It'll run on propane, gas, kerosene, absolutely anything except cryogenic fuel," he says. "They'd run on peanut oil if you want."

He discovered turbine jet engines are expensive. But pulse jets are as cheap as they are simple, so Maddox set to work building one. "All I started with was a schematic out of an encyclopedia," he says. The engines are basically a long tube with a fuel pump, a spark plug and a reed valve. Air and fuel are mixed at the front and ignited in a process that repeats - or "pulses" - about 70 times a second.


Maddox soon had a working engine and he developed a throttle that allowed him to control the level of thrust - something he says is rare on a pulse jet. He made three jumps from a plane (that's him in the pic) but quit because "the fuel system was a little scary" and he worried about setting the plane on fire. But Maddox was hooked.

He started refining his pulse jet engines, which he fashions from aluminum and stainless steel in his workshop. He's sold about 50 of them. The smallest are used to power model airplanes. The largest - two monsters producing 500 pounds of thrust apiece - have joined the beastly nitro-methane engine in Wally Larson's Top Gun Groundfighter show car.

The thought of bolting a jet engine to an old Schwinn cruiser came to him about six months ago when "I wanted to throw the engine onto something that would get me around." The bike engines provide 50 pounds of thrust. They weigh 13 pounds apiece, but Maddox says you hardly notice it when you're on the bike. Get it going, though, and things get interesting.

"It accelerates pretty quickly," he says. "It'll hit top speed in about 7 seconds. But even at high speed, it feels very stable. You're just being pushed along on a column of air."
A column of air being produced by a red-hot tube howling at 150 decibels. Besides being hot and loud, pulse jets aren't very efficient. They'll suck down half a gallon of fuel a minute at full throttle, and the bikes carry just six to eight quarts.

With his bikes starting to, er, take off, Maddox is looking to his next project - a pulse jet motorcycle that he'd bring to drag races or maybe the Bonneville Salt Flats. If you think riding a jet bike is crazy, give a jet motorcycle a whirl. Maddox says, "you'd be straddling the engine with a fork out front and a tire in the back."