D-Motor LF26

D-Motor LF26
Type Piston aero engine
National origin Belgium
Manufacturer D-Motor
Unit cost US $18,500 (2015)[1]
Developed into D-Motor LF39

The D-Motor LF26 is a lightweight liquid cooled side-valve four-stroke flat four, 2.7 litre petrol aircraft engine, produced by D-Motor in Deerlijk, Belgium.[2]

Design and development

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 (flathead) valvetrain. The designer determined that since maximum continuous power output (65.3 kW[3]) was to be developed at only 2800 rpm, the extra weight and complexity of overhead valves (OHV) would be superfluous. The resulting engine is compact and lightweight, with a dry weight of 58 kg (128 lb),[4] and a maximum power-to-weight ratio of 1.09 kW/kg (wet; coolant fluids weigh 5 kg (11 lb)[4]).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 overhead valves to improve engine breathing to aid in power production at higher revs, an advantage of the slow-revving side-valve arrangement is that the engine does not suffer high frictional losses (which increase greatly as engine speeds rise), so the power curve is virtually linear up to 3100rpm.[5] An inherent disadvantage of the side-valve design is the relatively inefficient shape of the combustion chamber, but this is not a real issue at the low engine speeds this engine operates at, since there is plenty of time for complete combustion to occur even with the oddly-shaped combustion chamber, unlike in higher-RPM engines which have a very limited window of space in which to combust the fuel/air charge. In addition, there remains potential for squish to promote turbulence of the fuel/air mix, and the low rpm means that the flame front is able to ignite all the fuel in each power stroke.[6][7]

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 (OHV heads a physically larger and have a higher center of gravity; SOHC/DOHC engines are even more so);
  • the design is simple with no unnecessary complexity, which reduces the odds of mechanical failure and makes repair and diagnosis easier when damage does occur (or when simple rebuilding is required), and the simple nature also makes the engine lighter (considering that it's a liquid-cooled engine)
  • the liquid cooling allows "touch & go's" without thermal shocks (the engine can be shut off/throttled down without the engine cooling rapidly like in an air-cooled design, which can stress the engine if done repeatedly), but adds complexity
  • 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 in a side-valve engine, there is no further expensive engine damage beyond the valve itself, and the engine keeps going (with one less cylinder running); this is unlike interference-type OHV or OHC engines, in which the valve will strike the head of the piston if it is not not closed when the piston reaches top dead center, typically causing serious damage to that piston and the rest of the valvetrain, or more. This is usually caused by a failed timing belt or chain, or a stuck valve that fails to close under spring pressure. A side-valve engine is not prone to this mode of failure, although many OHV and OHC are "non-interference", meaning the valves cannot touch the piston head under any circumstances.[8]

Variants

With the aid of funding from the Belgian government,[9] D-Motor has developed a derivative 4-litre flat-six engine,the D-Motor LF39, which is claimed to produce 125 hp (93 kW) and to have dry weight of 78 kg (172 lb).[10]

Applications

Specifications

Reference: D-Motor[4]

General characteristics

  • Type: horizontally opposed flat four
  • Bore: 103.6mm ( 4.1 in)
  • Stroke: 80 mm (2.91 in)
  • Displacement: 2690 cm³
  • Length: 611 mm
  • Width: 533 mm
  • Height: 382 mm
  • Dry weight: 58 kg with exhaust, radiator & external oil tank

Components

Performance

See also

Comparable engines

Related lists

References

  1. ↑ "Belgium firm offers Light Sport engine". AOPA Pilot: 40. March 2015.
  2. 1 2 3 "Kapelstraat 198 8540 Deerlijk - Recent information". D-motor1.vpweb.be. Archived from the original on 2012-03-28. Retrieved 2012-08-14.
  3. ↑ "D-motor dmotor LF26 specifications". www.d-motor.eu. Retrieved 2016-08-11.
  4. 1 2 3 "LF26 specifications". D-motor. Retrieved 26 June 2012.
  5. ↑ D-motor performance graph
  6. ↑ Speedex, Special cylinder heads, retrieved 3 March 2016
  7. ↑ Second Chance Garage. "Combustion Chambers (and a little engine theory)". secondchancegarage.com. Retrieved 3 March 2016.
  8. ↑ "D-motor dmotor LF26 LF39 ultralight engine concept advantages". d-motor.eu. Retrieved 3 March 2016.
  9. ↑ "Kapelstraat 198 8540 Deerlijk - News". D-motor1.vpweb.be. Archived from the original on 2012-03-28. Retrieved 2012-05-10.
  10. ↑ "D-motor dmotor LF39 specifications". www.d-motor.eu. Retrieved 2016-08-11.
  11. ↑ D-Motor (n.d.). "X-air test plane". Retrieved 2 August 2011.
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