D-Motor LF26

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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, 2.7L petrol aircraft engine, produced by D-Motor in Deerlijk, Belgium.[2]

Design and development[edit]

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 (65.3kW[3]) was to be developed at only 2800 rpm, the extra weight and complexity of overhead valves 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 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 up to 3100rpm.[5] 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 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;
  • the design is simple with no unnecessary complexity, so "there is not much that can go wrong";
  • despite having liquid cooling, the simple design keeps 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.[8]


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



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



See also[edit]

Comparable engines
Related lists


  1. ^ "Belgium firm offers Light Sport engine". AOPA Pilot: 40. March 2015. 
  2. ^ a b c "Kapelstraat 198 8540 Deerlijk - Recent information". D-motor1.vpweb.be. Retrieved 2012-08-14. 
  3. ^ "D-motor dmotor LF26 specifiactions". www.d-motor.eu. Retrieved 2016-08-11. 
  4. ^ a b c "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. Retrieved 2012-05-10. 
  10. ^ "D-motor dmotor LF39 specifiactions". www.d-motor.eu. Retrieved 2016-08-11. 
  11. ^ D-Motor (n.d.). "X-air test plane". Retrieved 2 August 2011. 

External links[edit]