Most of you learned to fly behind a carburetted AVGAS engine with a throttle, a mixture knob and a propeller lever. Forget all three habits here. The DA-42 NG is a diesel — it burns jet fuel by compression ignition, it is run by a computer, and you control the whole thing with one lever. This chapter is about that engine, the gearbox behind it, and the constant-speed feathering propeller in front. Get the RPM and power limits into your memory, because they carry straight through to the limitations paper.
Each nacelle holds an Austro Engine E4-B: a liquid-cooled, four-cylinder, four-stroke, in-line engine with wet-sump lubrication. It is turbocharged with an intercooler, it uses common-rail direct injection, and it ignites by compression — there are no spark plugs and no magnetos. Because it is a diesel, it runs on Jet A-1, not AVGAS, which is one of the type's biggest operating advantages: jet fuel is cheaper and available everywhere airliners fly.
The engine does not drive the propeller directly. A reduction gearbox with a ratio of 1 : 1.69 sits between them, so the propeller always turns slower than the crankshaft. Every RPM figure published for this aircraft is propeller RPM — keep that straight, or the limits won't make sense.
The engine is managed by an Electronic Engine Control Unit (the EECU, often just "the ECU"). It reads the sensors — manifold pressure, rail pressure, temperatures, RPM, power-lever position — and it sets the fuelling, the turbocharger wastegate and the propeller pitch to deliver the power you asked for. You do not manage any of that by hand.
For redundancy there are two ECUs per engine, called ECU A and ECU B. A VOTER switch for each engine normally sits in AUTO, letting the system choose which ECU is in charge. If one fails, the system should switch automatically to the other; you can also force ECU A or B manually, but that is an emergency action only. On the ground, with the power lever at idle and low RPM, an ECU TEST button runs a self-check that cycles between the two ECUs.
These are the numbers the examiner loves. Learn them exactly.
| Setting | Limit |
|---|---|
| Maximum take-off power | 100% (≈ 123.5 kW), at 2300 propeller RPM — 5 minutes maximum |
| Maximum continuous power | 92% (≈ 114 kW), at 2100 propeller RPM |
| Maximum overspeed | 2500 propeller RPM — 20 seconds maximum |
| Reduction gear ratio | 1 : 1.69 |
Each engine drives a three-blade, constant-speed, fully-feathering MT propeller with wood-composite blades. It is hydraulically operated, but the oil is directed by the ECU through the governor — you do not have a separate blue propeller lever to pull. Increasing oil pressure into the hub drives the blades to a finer pitch and higher RPM; reducing it drives them coarser and slower.
On a twin, the deadliest drag comes from a stopped engine's propeller windmilling. Feathering turns the blades edge-on to the airflow so the dead propeller stops and stops fighting you. On this aircraft you feather by shutting the engine down with its ENGINE MASTER switch — that releases the hub oil and lets the blades drive to the feather position.
To restart and unfeather in flight, the ENGINE MASTER is set back ON. A nitrogen-oil pressure accumulator, charged to roughly 22 bar during normal running, pushes the blades out of feather so the propeller starts to windmill and the engine can be restarted. A governor failure or loss of gearbox oil pressure drives the propeller towards feather automatically — a fail-safe that protects you from a runaway overspeed.
One lever per engine sets the demanded power as a percentage of LOAD. Fully forward is MAX (full power); fully back is IDLE. Everything between — manifold pressure, fuel, propeller RPM — is resolved by the ECU. Move the lever smoothly; slamming it produces rapid RPM changes that the light wooden blades respond to sharply.
Being a diesel, the engine uses glow plugs, not spark plugs, and the ECU manages a pre-heat sequence before cranking. Two fuel-temperature gates matter: the engine may only be started above a minimum fuel temperature, and take-off power is only permitted above a (higher) take-off fuel temperature. The maximum fuel temperature is 60 °C.
An overheat detector in each engine bay triggers a fire warning on the flight display if the compartment temperature climbs above about 250 °C. You test it on the ground as part of the pre-flight checks; if the warning does not appear on test, the aircraft needs maintenance before flight.
You now understand the heart of the aeroplane: a computer-run, geared, turbo-diesel twin with feathering propellers. Two threads run out of this chapter — the fuel system that feeds it (next chapter) and the electrical system that keeps the ECUs alive (the chapter after). Both are more critical on this type than on anything you have flown before, precisely because the engine cannot run without them.