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Copyright © 2004, Emerald Group Publishing Limited
Swapping Lycomings for the Diesel Centurion 1.7
Swapping Lycomings for the Diesel Centurion 1.7
Keywords: Aerospace industry, Engines, Fuel, Aircraft
In May 2002, Meridian Aviation was appointed as the distributor for the German manufactured Thielert Centurion 1.7 diesel aero engine for the UK, Ireland and Spain. Meridian Aviation fought off major competitors in general aviation to gain the distributorship of the engine that will offer private aircraft owners and flying schools the opportunity to reduce the over all operating costs by more than 50 per cent. The engine (first launched as the TAE 125) is a 135 HP 1.7l jet fuel/ diesel engine for general aviation. The engine has four cylinders in line and a turbo charger. In May 2002, the European aviation authorities awarded JAA-certification according to JAR-E, and the Centurion 1.7 is currently certified for jet fuel, but not diesel by the CAA. Diamond Aircraft Industries has installed the Centurion 1.7 in their Diamond DA40 and the modern twin DA42. The DA40 is the first production aircraft that is equipped with a jet fuel engine.
Meridian Aviation converted their first Cessna 172 from its traditional Lycoming to the Centurion 1.7 in November, G-ECON is currently their demonstrator and is said to be proving to private aircraft owners and flying schools just how much simpler, safer and quieter the aircraft becomes to operate, with the added bonus of excellent fuel economy. Because of the fuel efficiency of a diesel, a Piper Warrior aircraft powered by the Centurion with full tanks (burning 17.5 l/h), is reported to be able to fly almost double the distance of a Warrior with its factory fitted Lycoming (at 33 l/h). A range of 1,000 nm is currently obtainable.
According to Meridian, the Centurion 1.7 will challenge the American Lycoming O-320 engine's long established market share of piston powered light aircraft. Meridian believes that the advantages of the Centurion above the Lycoming are many. In Meridian's opinion, the most important is that it runs on the very cheap Jet-A fuel used by airliners and gas turbine aircraft as opposed to the more expensive Avgas. This they believe will offer up to 70 per cent savings on fuel costs.
The engine is also claimed by Meridian to be “greener” than the Lycoming. The Euro III exhaust-gas limits (for diesel cars) have been achieved during the Centurion's development and the engine is currently said to be below any existing exhaust-gas limit worldwide, even for the latest generation of car engines. Noise regulations are also met – even without the use of a muffler.
From the pilot's point of view, the turbo charged Centurion is reported to be easier to operate. It is water-cooled and fuel injected, so the danger of carburettor icing does not exist and there are no magnetos to fail.
The engine is to be supplied to aircraft owners with a three bladed constant speed propeller. The propeller RPM is governed automatically – so there is no prop lever. The Centurion 1.7 is equipped with a redundant electronic motor management. The full authority digital engine control (FADEC) system controls and surveys the engine, and utilises a single lever control for power setting. In addition, the FADEC system logs all engine data for later analysis. Thielert's engine management system automatically guarantees a quality air ratio at all power settings with altitude therefore, no manual mixture control is required. This not only improves performance but is also claimed to be a safety feature, engine damage because of a wrong air ratio is greatly reduced.
Even though it is 3 kg heavier than the Lycoming, the aircraft's take-off performance will reportedly be greatly enhanced by the variable pitch propeller and static thrust of 265 kg.
Tony Wright is Meridian's Centurion Project Manager. He is leading the team of engineers and technicians at Bournemouth who are currently converting the first two client's Cessna 172s. Thanks to the support and visits by German personnel from Thielert during the conversion of G-ECON, and CAA approved JAR 147 TAE course at their recently opened Technical Training Centre, the daunting task of replacing everything forward of the firewall except for the undercarriage assembly and the landing light wiring, is less of a challenge. The old pipes, magnetos and wiring, vacuum pump, engine frame, EGT circuitry, are all redundant.
The most complex element in the conversion is that of the FADEC system. The system monitors 16 sensors and controls nine actuators. The FADEC unit is located on the firewall at the P2 position in the cockpit. The all-monitoring FADEC is also sensing throttle position and manifold pressure. The fuel system, which as Tony Wright points out is crucial to the project, also requires extensive modification with fitment of additional low level and temperature transmitters. A new fuel cock and return lines are also fitted as part of the modification. There are two engine driven pumps, one low pressure which feeds the high-pressure. Not all the fuel pumped to the engine is used so the excess is returned via the return line to the tank. Since the supply fuel is under such high pressure (19,500 psi at max power) it returns to the tank heated, which in turn heats the fuel in the tank selected.
On the subject of fluids – the Centurion has separate oil systems. The gearbox and constant speed prop share one source, whilst the engine has its own. As it is water cooled, good old H20 is mixed (50/50) with antifreeze that also acts as an anticorrosive.
Tony and his team have received encouraging support from the CAA. A good rapport and consultation, both ways, has been vital. Modifications to the original specification have been required. As the FADEC operates the injector electrically, if the FADEC power is cut, injection ceases. The alternator is therefore made the primary power supply to the FADEC. Should the alternator fail, then the battery cuts in. Load shedding is achieved by modifying the circuit breakers on the C172s, so they can be pulled thus giving a minimum power supply of 35 min(AWN 82).
The variants of C172 have also created challenges. The difference between long and short range tanks as well as long or short floor pans have required rethinking.
“We are to start conversions on PA28s from April. There are not so many variations so we do not expect to face any major difficulties with the retrofits”, says Tony Wright. “Avionic installations on both Piper and Cessna aircraft will always need to be treated as a one-off project as the position of additional items required by the modification may need the space occupied by other equipment”.
Meridian Aviation is pioneering the Centurion conversion market although the German and French Thielert distributors also have conversion programs underway. Meridian admits that they are not yet able to complete the conversion within the estimated 110 man hours anticipated by Thielert, but Tony believes that changes to the way the complete modification kit will be supplied in the near future will ensure that the project will reach expected completion targets.
As the UK distributor, Meridian Aviation will be responsible for Thielert parts distribution and importantly, the training of technicians in the UK and the sale of the diagnostic equipment. This includes software, leads for connection between the FADEC and a laptop PC. Metric tooling is also required.
Details available from: Paul Randall, Meridian Aviation's Thielert Sales Manager, can arrange demonstration flights and provide all additional information. Tel: 01202 583200; E-mail: firstname.lastname@example.org; Web sites: www.meridian-aviation.com, www.centurion-engines.com