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D Motor LF39

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The D-Motor LF39 is a lightweight liquid cooled side-valve four-stroke flat six 4 litre petrol aircraft engine, produced by D-Motor in Deerlijk, Belgium. It is a derivative of the flat four D-Motor LF26.

Contents

Design

The LF39 produces 125 hp (93 kW) and has a dry weight of 74 kg (163 lb). Just like its smaller sibling, the LF26, this direct-drive aero-engine is unusual in two respects: it is very oversquare with a bore:stroke ratio of 1.295:1, and it has a side-valve valvetrain. The designer determined that since maximum continuous power output was to be developed at only 2800 rpm, the extra weight and complexity of overhead valves would be superfluous, so the resulting engine is compact and lightweight. The engine uses fuel injection, so carburetor heat is unnecessary. Lubrication is by dry sump, with an external oil tank. Dual ignition is used, each cylinder having twin spark plugs sited between the valves and the piston crowns.

Unlike an engine which uses ohv to be capable of high revs, a feature of the slow-revving side-valve arrangement is that the engine does not suffer high frictional losses, so the power curve is virtually linear from 50 kW @ 1920rpm to 91.55 kW @ 3100rpm. An inherent disadvantage of the side-valve design is the relatively inefficient shape of the combustion chamber; but there remains potential for squish to promote turbulence of the fuel/air mix, and the low rpm means that the flame front is able ignite all the fuel in each power stroke.

In its page,"Concept and advantages of the D-motor", the company claims:

  • they chose a sidevalve design over an ohv to keep the engine compact, despite its large capacity;
  • the design was simple with no unnecessary complexity, so "there is not much that can go wrong";
  • despite having liquid cooling, the simple design kept the engine light;
  • the liquid cooling allows "touch & go's" without thermal shocks, and gives efficient fuel use and low emissions;
  • a large engine running at low revs is "strong";
  • Nikasil liners, while not strictly necessary on a low-revving engine, add to reliability;
  • if a valve seizes, there is no expensive engine damage, and (unlike an ohv motor) the engine keeps going.

    • Development

    With the aid of funding from the Belgian government, the D-Motor LF39 was developed from the LF26. The company encountered problems with the casting of the flat-six cylinder block and there were further problems with the flywheel/alternator, but these were solved using a lighter flywheel with neodymium magnets.

    The 2014 expected price was €17800.

    In September 2014, EDM Aerotec announced the results of test flying the engine in their EDM Aerotec CoAX 2D/2R coaxial rotor helicopter, saying, "We are glad to present the 6 cylinder in action. After more than 100 hours testflying ... the coax helicopter equipped with the 6 cylinder... (proved) a perfect combination according to the test pilots." and added, "Another 6 cylinder has been installed in a test plane in Belgium".

    Applications

  • EDM Aerotec CoAX 2D/2R
  • Niki Lightning

    • Specifications

    Reference: D-Motor

    General characteristics

  • Type: horizontally opposed flat six
  • Bore: 103.6mm (4.1 in)
  • Stroke: 79 mm (2.91 in)
  • Displacement: 3,900 cc (238 cu in)
  • Length: 648.7 mm (25.54 in)
  • Width: 566 mm (22.28 in)
  • Height: 423.4 mm (16.67 in)
  • Dry weight: 74 kg (163 lb) with exhaust, radiator & external oil tank

    • Components

  • Valvetrain: none (tappets only)
  • Fuel system: fuel injection
  • Fuel type: 100/130 Avgas or auto gas 91 Octane Minimum
  • Oil system: Dry sump
  • Cooling system: liquid cooling

    • Performance

  • Power output: 125 hp (93 kW) at 3,000 RPM
  • Compression ratio: 8:1
  • Fuel consumption: x litres/h at 75% power
  • Power-to-weight ratio: 1.26 kW/kg

    • References

    D-Motor LF39 Wikipedia
    (Text) CC BY-SA