Flame Fly

Hybrid Thermoacoustic-Stirling engine with articulated wings

The Kontax Flame Fly Thermoacoustic engine features anodised aluminium body, a borosilicate glass cylinder and resonating tube, a solid graphite piston and striking brass flywheels. This is a BIG engine, weighing over 1.6kg and measuring 310mm in length. It has an interesting double cam linkage driving the articulated wings. The engine uses a resonating tube to generate high‑amplitude acoustic pressure waves. These oscillations drive a piston connected to a crank and flywheel, converting acoustic power into smooth rotary mechanical output. The system delivers Stirling‑like performance with no displacer, no valves, and minimal moving parts.

How does it work?

This thermoacoustic engine converts a steady temperature gradient into powerful acoustic pressure oscillations inside a tuned resonator. Heat applied to the stack region drives periodic compression and expansion of the working gas, creating a standing wave that amplifies until it reaches a stable operating amplitude. The resonator geometry and stack configuration are engineered to maximise acoustic power generation with no valves, displacers, or complex moving assemblies.

The oscillating pressure field drives a mechanical piston at the resonator’s operating frequency. This reciprocating motion is transferred through a crank to a flywheel, smoothing the alternating acoustic power into continuous rotary output. The piston behaves similarly to the power piston of a Stirling engine, allowing the system to deliver familiar Stirling engine performance while retaining the simplicity and reliability of a thermoacoustic device.

Magnetic burner

The burner features a magnetic connection to the base, which holds it firmly while allowing for small movements to fine-tune performance.

Operation

Once the burner is lit and placed on its magnetic coupling on the base, allow 30-60 seconds for the engine to warm up and then spin the flywheels in either direction. The engine will increase in speed over the first 2 minutes of operation before reaching its steady operational speed, which is between 600-800rpm. The position of the burner can be adjusted backwards and forwards to fine-tune performance.

Main features:

• Spoke design flywheels
• Stainless steel resonating stack
• Runs on a methylated spirits or denatured alcohol flame
• Extremely low friction self-lubricating graphite piston
• Precision ball-race bearings
• Forever wicks included (never burns down)
• Easy to adjust burner

Materials

• Aluminium connecting rod
• Stainless steel ball-race bearings
• Micron precision borosilicate glass cylinder
• Borosilicate resonating tube
• Stainless steel resonating stack
• Micron precision graphite power piston
• Aluminium base and legs
• Brass flywheel rims
• Aluminium body
• 3D printed wings

Dimensions

• Base - 155mm x 110mm x 4mm thick (6.1in x 4.3in x 0.18in)
• Flywheels - 57mm diameter x 7mm thick (2.24in x 0.27in)
• Power piston - 22mm diameter (0.87in)
• Resonating tube - 24mm x 200mm (0.94in x 7.87in)
• Overall height - 120mm (4.72in)
• Overall length - 310mm (12.2in)
• Overall weight - 1.6kg (3.5lb)
• Burner - 34mm diameter x 34mm high, 9.8cc (1.4in x 1.4in)

Assembled and Kit

The engine will initially be available fully assembled, with self-assembly kit form to follow.