The engine we used in our jet-powered go-kart is a modified Allied Signal JFS-100/13A gas turbine starter. Through a number of modifications, we converted the engine from a jet fuel starter to a pure turbojet engine. Click here to see specs for the JFS-100 gas turbine starter.

The unmodified engine is originally designed as a starter motor for a military jet engine, for example, the Pratt& Whitney TF-30 engine in the Navy A7 Corsair. The JFS-100 is designed to mount directly to the TF-30’s accessory gearbox. When the pilot hits the cockpit start switch, the JFS-100 automatically spools up and lights off, immediately accelerating to full power. The JFS-100’s free power turbine drives a reduction gearbox which accelerates the main engine up to lightoff speed. Once the TF-30 jet engine has accelerated to idle speed, an overspeed sensor is tripped on the JFS-100, and the little jet fuel starter automatically shuts down, only to run again the next time the big jet engine needs to be started.

Pratt & Whitney TF-30 Turbofan Engine, not for use on a go-kart.

Because of this extremely narrow scope of usage, the JFS-100 has many operating limitations as a turboshaft engine. First of all, there is no throttle. The engine spools up to full power immediately. Secondly, because it is only designed to run for short spurts at a time, it is very prone to overheating if run for more than five minutes. Fuel consumption is terrible, the nature of its electric starter engagement means that it must idle at a high speed if equipped with a throttle, and if the power turbine overspeeds even slightly, the engine is automatically shut down.

Because of these limitations, we decided to modify the engine as a turbojet to power our first turbine go-kart. Here is a list of the modifications we made to transform it into a turbojet:

1. Removed the free power turbine, containment ring, and nozzle.
2. Had a starter control unit and tachometer made.
3. Modified the oil system to run an external oil cooler, to prevent overheating.
4. Modified the fuel system to install a throttle control.
5. Installed a jet pipe in place of the power turbine.
6. Bolted mounting brackets to the engine.
7. Fabricated a frame to mount the engine.

Here are some stats for the resulting JFS-100 Turbojet:

• Thrust: 100 lbs. thrust @ 104% N1.
• Weight: 55 lbs.
• Thrust to weight ratio: 1.8:1
• Specific Fuel Consumption: 1.17 lb/lbt-hr.
• Fuel Consumption: 117 lbs/hr, 17 gallons/hr.
• Compressor Speed: 75,000 rpm

            The JFS-100 Turbojet is a single spool turbojet engine, with single stage centrifugal compressor, annular through flow combustor with five fuel nozzles, and single stage axial turbine. The exhaust nozzle is a fixed area convergent nozzle with straightening vanes and no afterburner.

Before

After

Garrett/Allied Signal JFS-100 Jet Fuel Starter

• Type: Dual spool, free shaft turbine
• Inlet: Axial
• Compressor: Single stage centrifugal
• Burner: Annular with 5 fuel nozzles
• Turbine: Dual spool, single stage axial gas producer turbine, single stage axial power turbine
• Exhaust: downward facing, single exit scroll diffuser
• Power Rating: 90 shaft horsepower at 3,000 rpm
• Peak Torque Output: 290 lb/ft at stall rpm
• Weight: 84 lbs.
• Power/weight: :1.07:1
• Air mass flow: 1.6 lbs/sec
• Compression Ratio: 3.5:1 at 73,000 rpm
• Maximum TIT: 1850 degrees F
• Specific Fuel Consumption: 1.3 lb/shp/hr