Saturday, March 20, 2010


Reader JR sent in these photos of a Luton plane with a J.A.P. flat-twin ohv engine, and wanted some info:
"Hiya Paul, here are some photos of an interesting old airplane hanging in the Miami airport.  I thought you might be interested because it is powered by a JAP boxer twin.  Do you know anything about these? Cheers, JR"

While J.A.P. is better known for pre-WW1 aircraft involvement, they did make a foray into plane engines in 1936.  The Light Aircraft Company of Peterborough, England, bought the rights to make the Aeronca plane under license from the American parent firm, and J.A.P. was chosen to build the engine, which is a flat-twin ohv of 1860cc, producing 38hp @ 2450rpm.  The complete Luton Minor airplane would cruise at 87mph with two passengers and got 28 miles per gallon of aviation fuel.

It is reputed in 'J.A.P. - The End of an Era' (Jeff Clew, 1988, Haynes), that the engine vibrated a bit - surprising given the flat-twin layout - and the fairly low power output meant it had a poor rate of climb, and wasn't terribly popular, with only 50 units sold. Beside the Luton, the engine was also fitted to other light planes such as the 'Currie Wot' and 'Dart Kitten'; both endearing names for pets, but hardly inspiring at 5,000ft.

I imagine that a motorcyclist could find a much better use of the giant flat-twin motor, and find plenty of power within that nearly two liters of capacity!  It is rumored some 'loose' engines still exist, so the project isn't completely far fetched.  Time to hit the aircraft flea market!

It's worth a good look at these close-up photos; aluminum cylinder heads were pioneered in aircraft before being adopted by motorcycles in the late 1930s.  The Aeronca engine clearly has fine-pitched steel cylinders and enclosed rocker gear, with a large faired-in wet sump beneath the crankshaft.  The carb is carried behind the engine, with a cast, bifurcated manifold.  From the angle of trhe rocker gear, I would assume the cylinder head used parallel valves and a flat combustion chamber - perhaps even a 'Heron' head, as used on 80s Morini motorcycles.  I'll have to investigate Heron history now!

(B&W photos from the Clew J.A.P. book - recommended reading!)