Sunbeam Manitou
| Industry | Aero-engine manufacturing, Automotive engineering |
|---|---|
| Founded | 1917 |
| Founder | Louis Coatalen (designer) |
| Products | Sunbeam Manitou aero-engine, Sunbeam 350HP racing car engine |
The Sunbeam Manitou was an aero-engine created by the Sunbeam. While it did not achieve success in aviation, it is recognized for its role in powering the Sunbeam 350HP racing automobile.
Development
The Manitou was developed as an evolution of the V-12 Maori III, with design efforts led by Louis Coatalen beginning in 1917. It incorporated aluminium cylinder blocks cast as three-cylinder monobloc units, a distinctive feature of Sunbeam engines. The bore was enlarged to 110 mm, while the stroke remained at 135 mm. The engine employed a 60° V configuration with dual overhead camshafts per cylinder bank, actuating four valves each. Fuel delivery was managed by two Claudel-Hobson carburettors, and ignition was provided by dual British Thomson-Houston (BTH) magnetos. For aviation applications, a reduction gear was fitted. Initial output was rated at 300 hp at 2,000 rpm, subsequently improved to 325 hp.
Only a single unit was completed before the conclusion of World War I, as attention shifted to resolving problems with the Arab engine. Similar to many Sunbeam aero-engines, the Manitou underwent testing in only one aircraft model—a Short 184 seaplane—and did not proceed to mass production. Post-war economic challenges and an oversupply of aero-engines diminished demand. Consequently, Sunbeam repurposed the Manitou for marine use, installing four engines in the racing powerboat Maple Leaf V. Although wartime orders totaled 840 units, only 13 were delivered before cancellation.
Sunbeam 350HP
The engine gained wider recognition when installed in the Sunbeam 350HP racing car in 1920. This vehicle was later purchased by Malcolm Campbell, who achieved multiple land speed records with it and designated it as one of his famous Blue Bird cars.
Consistent with his typical methodology, Coatalen undertook significant modifications to the engine despite its one-off nature and absence of production intentions. The original twin-camshaft four-valve cylinder head was replaced by a single-camshaft three-valve design, likely adapted from the Arab. To accommodate larger valves, the bore was increased to 120 mm.
A key engineering alteration involved changing the stroke length, also inspired by the Arab, where this dimension had previously contributed to engine failures. Due to spatial constraints on connecting rod length within a multi-cylinder V engine layout, Coatalen implemented articulated connecting rods, wherein one connecting rod attaches directly to the crankshaft journal and the second connects indirectly through a journal on the first rod. This configuration results in slightly different piston strokes on each bank—135 mm on one side and 142 mm on the other—potentially leading to imbalance and vibration challenges.