Turbine P120 Graupner 6805 The JetCat P120 model turbine works in a similar fashion to full-size jet aircraft engines. Air is sucked into the engine and compressed by a single-stage radial compressor. The air is then mixed with fuel in the combustion chamber and heated. As the mixture burns, the air mass expands greatly and is forced out of the engine, passing through an axial turbine wheel, which in turn drives the compressor via a shaft. The exhaust gas accelerates to a very high speed (approx. 1100 km/hr) as it leaves the tail end of the turbine, and this produces the thrust required to propel the model. An electric starter motor is fitted at the front of the turbine´s intake trumpet, and this motor spins up the turbine to the speed necessary for it to start running. The procedure for starting the turbine is completely automatic using a highly integrated electronic control unit (Jet-tronic ECU), which also monitors and controls the engine when running by measuring its rotational speed and exhaust gas temperature.
The turbine is started using propane gas which is contained in a refillable miniature tank (lighter gas canister) carried on the model, and the gas is switched on automatically as part of the start-up procedure. When the fuel mixture has been ignited, the ECU automatically switches over to normal fuel operation (kerosene). All the auxiliary electrical components, i.e. fuel pump, glowplug, starter etc., are powered by a single 6-cell battery. The external dimensions of the JetCat P120 model jet engine are approximately the same as the JetCat P80, thousands of which are already in use. The engine´s much higher static thrust compared to the P80 is due primarily to the new compressor and turbine stages, both of which are optimised for greater air throughput. The result is that a JetCat P120 system is around the same weight as a P80 system, butgenerates around 46% more thrust. The engine´s high power output (21 kW!) makes it particularly suitable for larger models (>14 kg take-off weight).
The set also includes a display and programming unit featuring an illuminated alpha-numeric LCD screen (2 lines of 16 characters) plus 10 buttons and 4 monitor LEDs. The GSU (ground support unit) can be plugged in and disconnected when the engine is running, so that you can read off the current operational data and adjust thesettings if necessary. In addition to the momentary operational data such as exhaust gas temperature, rotational speed and pump voltage, the GSU is able to display statistical data including: overall fuel consumption, total turbine running time, maximum rotational speed, number of starts, duration and fuel consumption of the last turbine run, battery voltage etc. A menu control system based on a plain text dialogue is used for all displays and input procedures. The turbine is started and run up to speed fully automatically on command from the transmitter. The pilot then pre-sets the level of thrust he requires using the throttle stick; full proportional control is available.
The ECU is connected to the receiving system using two receiver channels:
channel 1 is used for thrust pre-set (throttle stick), while channel 2 is controlled at the transmitter by a 3-positionswitch (or rotary knob or slider).
The three switch positions are as follows:
Pos. 0 = Turbine OFF, immediate cut-off (switch back).
Pos. 1 = Standby/start, normal operations (switch central).
Pos. 2 = Automatic power-down (switch forward).
Example of a typical start procedure:
1. Disconnect all refueling lines and outboard connections from the model.
2. Switch on transmitter and receiver.
3. Carry model to take-off strip.
4. Set three-position switch on transmitter to centre.
5. Move throttle stick briefly to idle, then to full-throttle position.
6. The turbine now starts fully automatically, and after about 30 seconds the green U READY LED lights up to indicate that the pilot has full control of the running engine. JetCat P120 turbine complete with starter, Jet-tronic ECU (electronic control unit), GSU (ground support unit - display and programming unit), LED display board, miniature fuel pump, electro-magnetic fuel shut-off valve, fuel lines, quick-connect set, refueling and gas refilling fittings, fueltank clunk pick-up and cable set, on-board battery (6 cells, 1250 mAh), miniature auxiliary gas tank, turbine mounting clip (RamTec compatible), comprehensive operating instructions. Turbine power (throttle stick)
Turbine control (Off/Start/Auto-stop)
U 3-position switch or rotary knob/slider. Thrust: 120 N at full load 2.5 N at idle
Weight: 1390 g incl. automatic starter
Diameter: 112 mm
Overall length: 280 mm
Rotational speed: 33,000 - 118,000 rpm
Air throughput: ~ 0.34 kg/s
Efflux velocity: ~ 1230 km/hr
Output power: 21 kW (jet power)
Exhaust gas temperature: ~ 640°C
Fuel consumption: 385 ml/min (full load)
Fuel: Jet A1, kerosene Lubrication: approx. 5% synthetic oil, mixed with fuel
Maintenance interval: 50 hours.
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