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The Stirling Hot-Air engine was invented by Robert Stirling, a Scottish clergyman, in 1816.  His engine gave a high thermal efficiency and had some inherent advantages, such as flexibility in the choice of fuel, which could make it as important as the internal-combustion engine.

The Stirling-cycle engine differs from the internal-combustion engine in that the working fluid - in this case, air - remains in the working chambers. The heat is applied from an external source, so anything from wood to nuclear fuel can be used. It also means that combustion can be arranged to take place under the best possible conditions, making the control of emissions considerably easier. The burning of the fuel is continuous, not intermittent as in an internal-combustion engine, so there is less noise and vibration.

Stirling engines generally use two pistons to push the working fluid between two working spaces. One space is kept at a high temperature by the heat source and the other at a low temperature. Between these two spaces is a regenerator which alternately receives and gives up heat to the working fluid. The pistons are connected to a mechanism which keeps them out of phase (usually by 90°). It is this differential motion that moves the working fluid from one space to the other. On its way to the hot space, the fluid passes through the regenerator, gaining heat. In the hot space it gains more heat and expands, giving power. After the power stroke the fluid is pushed back through the regenerator, where it gives up its residual heat into the cold space and is ready to start the cycle again

The pictures on this page show a wide range of working Hot-Air motors designed and constructed in the Kimberly Clark training workshop. A few are my own work but most have been made by KC Trainees as engineering projects for their Modern Apprenticeship. NVQ's


Hot-Air Engines..




A very nice Stirling Engine designed and built by Paul, one of my Apprentices from a few years ago.  It was the success of this motor that renewed my interest in these fascinating machines. 




A small and very decorative Stirling Motor. The engine has very good performance and is virtually silent in operation. This motor has exceeded 2500rpm - the highest speed of all my engines.

I have to admit that this motor is based on a commercially available German model 




A Stirling engine of my own design employing a bell-crank operating mechanism. The flywheel was machined from solid & the engine has a Butane gas burner and tank housed within the anodized aluminum base


I built this motor to explore the benefits of the 'Ross' crank linkage system. This ingenious mechanism was tricky to build but has a great influence on cylinder phasing and consequently this engine has very good performance and will achieve 2000rpm. One of my favorite machines.


An early attempt at an L.T.D. (Low-Temperature-Differential) engine.
 This motor never quite achieved the performance I was expecting although it does run quite well off a Table Light. The rather crude counterbalance was added in an attempt to improve the performance.




 A Flame Gulper designed & built by Phil Rigg, one of my 1st year Apprentices as his Foundation-year project in 2000.  The engine now runs beautifully but Phillip had many problems to overcome before achieving this fine result



A magnificent Stirling Engine designed and built by Sean Minnican, one of my 1st year Apprentices. The name 'Lizzie' was Sean's choice and he refuses to reveal the reason for the name!



 Another really nice Stirling Engine built by Ryan Marsland, a 2000 1st year Apprentice.  The spirit lamp is machined from solid bronze with the two parts silver-soldered together.



 Yet another version of the popular brass motors.  Richard Crewdson followed the original design plans but added his own individual touches to complete an excellent 1st Year Project

  Hayley's Kommet

A beautiful machine built by Hayley Forbes, a 2003-1st Year Apprentice.  Her aim was a machine that looked 'busy' when running.  The basic layout was reasonably straightforward but the actual construction was much tougher than she anticipated - the flywheel alone took more than 20hrs on a manual milling machine!  The completed motor is a joy to see and is a smooth and silent runner.


 Yet another excellent example of determined effort.  Designed and built by Mike Ray, a 2003 1st Year Apprentice, the motor proved to be extremely difficult to construct and he had many hours of frustration before successfully completing an excellent 1st Year Project.


A twin-cylinder Flame Gulper based on an engine called 'Dos Pyros'.  The machine was relatively easy to build although the cam-groove around the flywheel was difficult to produce on a manual milling machine. Getting the machine to run successfully was quite another problem. It took many patient and frustrating weeks before the motor ran acceptably.  It now performs well and makes a most delightful pop-pop-pop sound when running.


 Yet another 'Brassie' this one was recently built as a gift to my youngest grandson Jordan. He is fascinated by these machines and always wants to see my engines running. I hope he will have many hours of fun with this motor


 A really nice Stirling Engine built by Steven, one of my 2004, 1st year Apprentice. The motor uses the Ross linkage system and the spirit lamp was fabricated from a piece of stainless steel tube.


Minno's Chopper

 An interesting machine based on the glass tube 'Brassie' motor.  Small bevel gears drive the rotor blade which also acts as the flywheel. It took a great deal of patient work to get this one to run.


Gill's Gulper

 A really nice Flame Gulper built by Ben Gilbert. It was based on Phil Rigg's Phrapper and employed a similar valve mechanism. It ran well but never quite achieved the same steady performance as the original Phrapper. 

Big Burner

Designed and constructed by Chris Turner in 2005, this motor follows the basic idea of the first engine on this page (Hot-Tube) with some refinements to the design. A very nice motor which performs well.


It is not known why Mark Morgan gave this wonderful exercise in brass a name which apparently  means 'smelling strongly like an animal'.  Built in 2005 this superb creation achieved 2400rpm during the testing and development process - one of the highest speeds ever recorded by one of our Hot Air Motors.

If you would like more information regarding these fascinating machines please visit

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