What About Those Diesels? Part 2

Today’s aero-diesels


Diesels (compression-ignition piston engines) have a long history in aviation, but their numbers have never been impressive. After my first article on this topic appeared in the May 2012 issue of AMT, I was bombarded by diesel historians, and I promised to mention some of what they told me.

Dr. Hugo Junkers built successful aero-diesels as early as 1913; by 1916, these oil-injected (for fuel) beasts were making 500 hp. They powered Lufthansa airliners by 1935, and by WWII, they were making one horse for every 1.4 pounds of weight – better than most modern private-aviation gasoline engines. BMW made a water-cooled radial (with radiators between the cylinders); Daimler-Benz’s diesels powered the Hindenburg. The first USA-built Packard diesel-powered airplane flew in 1929. A Ford Tri-motor so equipped famously flew for a fuel cost of three cents a mile. Guiberson took up the mantle in the U.S., equipping prototype Navy airplanes (and then battle tanks).

In Britain, the Bristol Phoenix, the unsuccessful and heavy Beardmore Tornado, and the Jumo-designed Napier Culverin also flew, some with better-than-gas-engine performance. Even Rolls-Royce tried converting a Condor to diesel power. The Czech ZOD, Italian Fiat, Russian Charomski, and French diesels (Clerget, Salmson, Jalbert-Loire, and Jumo-licensed C.L.M.) also flew in the pre-war period, with varying degrees of success.

Thielert, Centurion, and Austro

Recent history recalls the Thielert 1.7-liter unit, originally (2002) used in the Diamond DA42. This breakthrough powerplant, based on the Mercedes OM640 car engine but with an aluminum block, became notorious for its maintenance requirements: its 600-hour (later 1,000 hour) TBR (time before replacement) was interrupted every 300 hours by a mandatory clutch and gearbox rebuild. But local mechanics could do nothing but the swap-outs; only the factory was authorized to perform the overhauls and repairs.

The second generation (135 hp, 2.0 liter) had a longer TBR and longer-lived gearbox, but the company hit hard times and emerged under new ownership and management to build the Centurion, whose engineers looked at every weak point to improve it; it now has a 1,500-hour TBR (1,200 for the more-powerful 155 hp 2.0s version) and gearbox improvements that have also doubled that unit’s TBR to 600 hours. All the 1.7-liter engines have either been replaced by the 2.0, or are set to be replaced at their next service. The Thielert Mercedes-based 4-liter V-8 shown in 2007 received a TC (Type Certificate) and STCs for the Cirrus SR22 and Cessna 206, but has not been heard from since the reorganization.

While Diamond was sweating out the Thielert situation, another aircraft engine (using the original iron Mercedes block) came to life, closely allied with the Diamond company’s ownership. The four-cylinder, 180-hp 2-liter Austro AE300 comes into the Austro Engine Factory and is stripped practically bare; and rebuilt with new components — electric controls, alternator and starter, a proprietary turbocharger, wastegate, sump, torsional damper (Thielert/Centurion uses a clutch in its gearbox), and countless other details have brought the Austro into volume production. Today, all heavy MRO work is done at the factory.

Austro Engine has offered EASA Part 147 maintenance training for the AE300 (E4-series) in cooperation with Diamond Aircraft Industries since 2009. All maintenance procedures are specified in the maintenance and overhaul manuals. Austro Engine recently received its first extension of the TBO to 1,200 hours; the target is 2,000 hours. The formerly limited TBO on the alternator and torsional damper were also extended to “on condition,” and the TBO on the high pressure fuel pump went up to 600 hours. In 2011, Austro and Steyr Motors entered an agreement to develop the Steyr M-1 Monobloc, a 280-hp six-cylinder design, for aviation use, but little has been heard since the announcement.

SMA and Continental

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