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M&D Flugzeugbau TJ42




M&D Flugzeugbau are a German company based in Friedeburg, Lower Saxony in north-western Germany. M&D Flugzeugbau manufacture the Samburo motorglider and also provide maintenance services for other light aircraft.

In 2007 M&D identified the potential benefits of installing a small jet turbine sustainer in gliders but considered the range of jet turbines available for model aircraft had limitations. Such engines had not been designed from the outset to consider certification or in-flight starting. M&D decided that rather than convert a model aircraft jet turbine into a glider sustainer, it would be better to develop and certificate a new engine.
The key features of the TJ42 engine are:
Single spool jet turbine
Two stage axial-centrifugal stator-less compressor with a compression ratio of 1:3.8
Cannular combustor with multiple fuel injectors and combustion zones contained within a single annulus casing
Glow-plug ignition system (used in start-up sequence only, ignites top combustion zone only)
Single stage axial turbine with stators
Convergent nozzle
Front-mounted, direct drive electric starter motor for initial spool up

The maximum thrust is nominally 42 kgf at 100,000 rpm with an estimated fuel consumption of 66.4kg/hr at full thrust. At the idle speed of 30,000 rpm the thrust is less than 2 kgf. The weight is 3.3kg and overall dimensions 400 mm long and 150 mm diameter.

The TJ42 has a kerosene start-up (as opposed to gas start engines) which eliminates the need for separate gas canisters and long complex start-up procedures.

The start-up sequence is:
Glow-plug heats up for 10 seconds
Electric starter motor spools up engine to 8,000 rpm
Starter fuel solenoid pulses with fuel being injected into the top combustion zone only
Fuel ignited in top combustion zone by glow-plug
Engine spools up to 15,000 rpm
Normal fuel solenoid pulses with fuel being injected into all combustion zones (starter fuel solenoid closes)
Engine spools up to idle speed of 30,000 rpm
Fuel rate controlled by throttle, and matched to density altitude and rpm by ECU

The shut-down sequence is:
Fuel cut off and combustion ceases
With no fuel, the engine speed decreases and EGT decreases

The ECU senses EGT and rpm, and if the engine speed is too low to promote rapid cooling, the electric starter motor runs an automatic cooling cycle (spooling the engine up to 3,000 rpm, then switching off)

Once the EGT has dropped below 50°C the ECU signals that the engine can be retracted

The engine and pylon are enclosed by cowlings manufactured from fiberglass and aluminum (or possibly stainless steel subject to clarification of certification requirements).

The MD-TJ42 is certified for installation on self-sustaining sailplanes only, i.e. it is not intended for take-off operation, EASA Type Certificate EASA.E.099. The first type certificated application was on the Jonker Sailplanes JS-1 Series.

Because of the use of these engines in sailplanes, there are several assumptions to simplify the requirements for certification. These assumptions are:

• the engines will be used for self-sustaining sailplanes only, not intended for take off;

• no bleed air, no reverse functions;

• no flight in icing or hail conditions;

• no aerobatic operation;

• the turbine engine is not used to drive accessories that are essential for any other means than the turbine itself;

• the strike and ingestion of foreign matter can be treated as extremely remote, because the engine is started and shutdown in f1ight. Ground operation will only take place for maintenance purposes.





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