Rotary engine development

Cylinder head of a nine cylinder engine, showing the two valve rockers and the induction pipe from the rear of the engineWhat distinguished the Clerget rotary engine from its rivals (Gnôme and Le Rhône) was that the Clerget had normal intake and exhaust valves unlike the Gnome, and the connecting rod arrangement was much simpler than the Le Rhône.

A source of failure among the British Clerget engines were the special-purpose piston rings, called obturator rings. These were located below the wrist pin to block heat transfer from the combustion area to the lower part of the cylinder and overcome their subsequent distortion. In the British manufactured motors these rings were often made from brass and only had a lifespan of a few hours.

The French built Clerget engines were considered very reliable but they cost more per unit to produce than their rivals. Unlike other contemporary rotaries in which the ignition system was either switched on or off to provide a rudimentary form of engine speed control, the Clerget featured a throttle that allowed the spark to be retarded to individual cylinders.

The Bentley BR 1 and Bentley BR 2 rotaries were designed as improvements of the Clerget, while sharing some of the earlier engine's distinctive design features.

Design features general & specific

The Clerget rotary engines were air-cooled with either seven, nine or eleven cylinders. They were fitted with a double thrust ball race, which enabled them to be used either as a pusher or as a tractor engine. The engines worked on a four stroke cycle. The chief points of difference from other rotary engines were:

A. The pistons were of an aluminum alloy.
B. The connecting rods had a tubular section.
C. The inlet and exhaust valves were mechanically operated by means of separate cams, tappets and rocker arms.
D. The direction of rotation was counter-clockwise as seen from the propeller-end of the engine.
E. Between any two consecutive firing strokes, the engine turned through 80 degrees.
F. Like many other rotary engines of the period they were made chiefly of steel, for strength and strength.
G. Typical external wiring. twin spark plugs on the 9B & 9Bf.

Clerget engine types

Clerget 7Z
(1911) 80 hp (60 kW), seven cylinder.

Clerget 9B
(1913) 130 hp (97 kW), nine cylinder. Seen on Sopwith 1.5 Strutters, Camel F.1

Clerget 9Bf
(1915) 140 hp (104 kW), nine cylinder long stroke version of the Clerget 9B. The most numerous British production engine with 2,350 units being built. Seen on Nieuport fighters and some 2 seaters, Sopwith Camel F.1 and some 2F.1 and late war types fitted for rotaries.

Clerget 9Z
(1917) 110 hp (82 kW), nine cylinder. Redesigned with flat head aluminium pistons, tubular connecting rods and revised valve gear. Tended to be on trainers fitted for rotaries.

Vector Kit motor

Is a fair representation of the 9B used on tractor type aircraft. It could physically pass for the tractor type “9Bf".

Note please! When replacing other kit pieces with the Vector Resin items you will find there may be a need to modify the kit cowling to allow a good fit. Vector tends to be exacting when it comes to overall measurements. Plastic kits tend to have overly thick walls neded to get a kit out of the mold without distorting the freshly poured plastic.

Also when finishing this kit you need to add your own pushrods and wiring.

When contacting manufacturers and publishers please mention you saw this review at AEROSCALE