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!)


J.N. Heath said...

Always wondered why I hadn't seen a bike or outfit using a Lycoming flat 4 aircraft engine. Must be one out there someplace . . . Lycoming has a bicycle-making history too.

Thanks for the above, didn't know about JAP aircraft engines. Part of the glorious era when machines were all interchangeable, the same guys raced and fixed cars and bikes and boats, flew airplanes, and built their own radios. Machine-age boys, who grew up on horses but turned into Burt Munroes casting their own pistons, etc. My grandfather was one of them, not intimidated by anything machine, although not a motorcyclist. During the Second World War he built a tractor out of used components, using multiple gearboxes in series. It may still be plowing out near Pocatello, Idaho.

marticelli said...

Hi Paul. Martin Shelley aka Marticelli writing again. This item on early aero engines reminds me that you should buy a copy of a new book which is a definitive history of such things. Take a look at and you will find it on Amazon. Written and researched by an old bike enthusiast, Brian Thorby, it not only covers the products of the Douglas factory and their heirs and successors, but also covers all similar productions including those made by JAP. It's a remarkably thorough piece of work, and I think is very good value for money too, a must for any vinatgent's library shelf.

Keep up the good work,


Rodney Rushton said...

There is an airworthy Luton Minor owned by Mr. Richard Webber at Eggesford Airfield, Devon. He bought the parts unassembled and finished it off - just because it had the JAP Engine! He also part owns the sole Luton Duet- a two seater, powered by the 65hp Continental Motor, and kept at the same place along with several Austers of various vintages.

John Leak said...

Back in the 60s a friend dumped an ammunition box of parts in one of the garages at my parents' home. He averred that they were for a JAP flat twin as used in target drones. True or false?

That added to the clutter of an MGA Twin Cam engine (intended for my TVR) and, believe it or not, a Daimler 2.5 V8 mounted on an Austin 1800 gearbox. All unrealised projects. I fear they all went for scrap when my parents moved to Jersey.