Redrup - Radial
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Redrup D2-492-50-08
Photo ou archives : F-M. Dumas

Capacity : 309
Model : Radial
Production : 1919 - 1920
Category : (R) Street Bike


309cc Radial Three-Cylinder -1919

Odd-ball power unit

Just after WWI, the lack of demand for new aircraft grounded many aviation specialists.

Among them was the Briton Charles Redrup, who had been working on radial engines since 1903. Around 1912, he had devised a rotary three-cylinder motorcycle engine that

drove the rear wheel through two shafts, one linked to the crankcase and the other to the crankshaft, which rotated in the opposite direction. After the Armistice, Redrup resurfaced at Burmantoft, near Leeds, in partnership with a man named Boyle.

Modern Design

Charles Redrup's three-cylinder engine was now a fixed radial; it was modern by 1919 standards of motorcycle design, with pressure lubrication, fully-enclosed valve gear and

aluminum pistons.

Aesthetic Failure

But Redrup's highly-personalized aesthetics and odd-ball power unit failed to advance his career, whereas other aviation engine makers like BMW and Gnome-Rhône prospered when they turned to motorcycle manufacturing. Redrup even built a six-cylinder motorcycle engine by coupling two of his radial threes side-by-side. He had vanished from the scene by 1922. Three-cylinder radials have never been common: the layout next appeared on the British-built Eta of 1921 (which had its engine set across the frame and a longitudinal crankshaft, airplane fashion). The German Pax designed in 1922 by Fritz Cockerell had a three-cylinder engine in the rear wheel. Cockerell subsequently created the Megola (which had a five-cylinder rotary built into the front wheel!).


Engine: 309cc (5lx5lmm) air-cooled three cylinder four-stroke; Runbaken magneto

Valves: side

Fuel System: carburetor

Transmission: 3-speed, chain primary drive; belt final drive

Suspension: girder (front); rigid (rear)

Brakes: rim (front); belt rim (rear)

Wheels: 26x2.50 inch clincher (front & rear)


Redrup's aim of adapting aviation techniques to motorcycle construction was a noble one, but be fatally ignored the aesthetic aspect; only three Redrup Radials were built and this one, is visible in the Sammy Miller Museum

Motorcycle encyclopedia Moto Passion, realised by François-Marie Dumas, include almost 2000 photos presented with an exhaustive history of the motorcycles exhibited.

This unique collection has been realised with the participation of many specialists. With many thanks in particular to Yves Campion, Michael Dregni, Didier Ganneau, Jean Goyard, Helmut Krackowizer, Michel Montange, Christian Rey, Bernard Salvat, Mick Woollett, etc

One can order here

  • Original cards on paper (in french)
  • High resolution scans or original documents presented and signed with my name.

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François-Marie Dumas

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