Date:1 May 2011
Degree of difficulty: 8
Video: To watch a demo of Cottrill’s Lady Anne Boleyn valveless pulse jet, as well as to download the plans for Cottrill’s focused wave pulse jet engine design. [click here]
Bellowing up to 140 decibels, a valveless pulse jet drastically accelerates the speed of bicycles, scooters, skateboards and carousels. “ The most common misunderstandings are the engine’s fuel flow – lots – and the starting air – a trickle,” pulse-jet expert Larry Cottrill says. Here’s how he makes one from scratch in 8 hours – “and I don’t even have a decent workshop,” he says.
Build a chamber
Cut 22gauge mild sheet steel, tracing a pattern with aircraft snips, to fabricate a twopiece combustion chamber. Using a pipe anvil and mallet, roll a long open cone. Use the mallet to form a blunt dome to cap the cone. Weld each cone’s seam. Drill a hole in the dome’s tip and weld on a sparkplug mount nut.
Make a tailpipe
Cut and file an exhaust tailpipe and an intake pipe from lengths of thinwalled tubing. Use a ball-peen hammer to flare each end. Fit the narrow end of the chamber cone into the exhaust.
Weld the dome and the tailpipe onto each end of the combustion cone. Cut a hole in the cone side for a port to fit the intake pipe.
Mount and fire
Fit the rig on a Bukowsky mount (see glossary). Arrange a propane torch so the flame goes across the tailpipe opening. Light it and blow air in.
Bukowsky mount: A simple rack that uses a hose clamp to secure the tailpipe to a rear bracket while the spark plug connects to a front bracket. The mount prevents the engine from moving when ignited, and a built-in heat shield protects the operator.
See for more detailed instructions here.
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