For the thrill of it
Craftsman Bob Maddox admits his creations aren't practical. That's the whole point.
In his Griffin Creek Road shop outside Phoenix, Maddox creates pulse-jet engines and gleaming motorcycles propelled by them for enthusiasts looking for a thrill.
A recent visit to Maddox's shop finds a dragster, several bikes, go-karts and what may be the world’s fastest skateboards. There’s a stunning blue motorcycle with thrust engines on each side that’s available for $54,000. At the other end, a simple plywood go-kart has basic mechanicals such a cable steering and brakes that rub against tires.
Relying on Newton's principle that for every action there is a reaction, a pulse-jet engine produces thrust via 60 to 75 explosions per minute in the cylinder. The engines are pretty much a simple tube with a spark plug igniting fuel.
“It’s just like a cannon,” says Maddox.
When running, the entire engine glows at 1,200 degrees and roars at up to 140 decibels. Shielding provides protection from the heat. The engines go through fuel quickly: A 600-pound-thrust engine consumes from 2.5 to 3 gallons of gasoline per minute at full throttle.
“They don’t have any practical purpose,” Maddox says of his creations.
Maddox has sold more than 400 pulse-jet engines around the world, he says. Sales are split about evenly between the United States and overseas, with many coming from Europe. Top countries are Australia and Sweden, where enthusiasts run pulse-jet vehicles on skis.
Maddox also has sold about 100 engine kits with components ranging from $310 for basic pieces to $650 for rolled pipes. Builders can also download engine plans from Maddox's website (maddoxjets.com) for $29.95.
Views of his videos on YouTube several years ago were bringing in $3,000 to $4,000 per month to the business, he says. In some months he was getting 30,000 or more views.
Over the past couple of years, Maddox has been developing valveless engines and working to create an event in northeast California that would gather thrust- and other nonmechanically-powered vehicles for several days of fun.
Maddox hopes to use dry lake beds that total 20 miles long and 2 miles wide in the Cedarville, California, area for his “Thrust-o-Rama” event. He visits the beds three to four times per year to test his own creations. He hopes to hold the event in mid-August.
Also in development is a show for a YouTube channel that would be supported by subscribers. Maddox plans to do a show every two weeks and would make creations in each episode.
A 50-pound-thrust engine sells for $725, while 100-pounders go for $1,750. He also develops higher thrust engines for special applications.
Current engines use reed valves which require a machined head, but the valveless engines he’s perfecting wouldn’t need those.
“Most of them don’t make as much power," Maddox says. "They all run on propane.”
Maddox recently created a thrust-powered, streamliner motorcycle anticipated to hit 300 mph for an Australian. Renowned vehicle craftsman Randy Grubb of Grants Pass did the compound-curve aluminum body work for the bike.
When Maddox takes on a custom project, he prefers to work from general concepts rather than following the dictates of the customer.
“If you let me do what I want, you’ll get something a lot better than you are envisioning,” Maddox says. “It’s always one of a kind.”
— Tony Boom is an Ashland freelance writer. Reach him at firstname.lastname@example.org.