Object StatementAircraft engine, Clerget-Blin Type Z7 World War I radial aero engine, serial No. 1104, air cooled, 7 cylinders, 80 hp, 1200 rpm, steel and aluminium, designed by Pierre Clerget, France, 1911, made by Gordon Watney and Co Ltd, Weybridge, Surrey, England, 1918
Physical DescriptionAircraft engine, Clerget-Blin Type Z7 World War I radial aero engine, serial No. 1104, air cooled, 7 cylinders, 80 hp, 1200 rpm, steel and aluminium, designed by Pierre Clerget, France, 1911, made by Gordon Watney and Co Ltd, Weybridge, Surrey, England, 1918
Single row rotary with poppet valves. Bore/stroke 4.72 x 5.91 in. Vol. 722.75 cu.in. (120 x150mm.). Compression ratio 4.3:1. Direct RH tractor/LH pusher drive. Bloctube carburettor, one magneto normally fitted. Diameter 36 in.
The Clerget-Blin 7Z rotary aero engine comprises seven finned cylinders radially disposed around the crankcase to which the propeller was attached. The crankshaft is hollow and fixed to the body of the aircraft while the cylinder assemblage rotated together with the propeller. The pipes at the rear of the engine transferred the air/fuel mixture from a chamber at the rear of the crankcase to each of the cylinders. The intake and exhaust valves were operated by separate push rods driven from two cams in the crankcase.
A single bloc tube carburettor, with a simple fuel jet, attached at the rear of the crankcase, supplied fuel to the air intake. Since the crankcase volume did not vary as the engine rotated there was no pumping action to force a fresh mixture into the cylinders. Instead, the cylinder fills due to the suction generated inside it as the piston travelled down after the exhaust stroke. Because the only forces moving fuel/air mixture through the engine were centrifugal in the transfer passages and the suction generated in the cylinders, rotary engines used a pressurised fuel system to spray petrol into the carburettor. The cams operated the inlet and exhaust valves were set so that the inlet valve opened 4 degrees before top dead centre (TDC) and closed 56 degrees after bottom dead centre (BDC) while the exhaust valve opened 68 degrees before BDC and closed 4 degrees after TDC. Ignition commenced 22 degrees before TDC.
Since it is impossible to fit an exhaust system to a spinning engine, the exhaust valve on each cylinder opened directly into free air inside the cowling. Even so, they were relatively quiet in operation as there was little pressure in the cylinder by the time the exhaust valve opened.
As in most radial engines one of the connecting rods, designated the ?master rod', connects with the crankshaft in a conventional manner. The remaining connecting rods are pivotally connected to the big end of the master rod. This configuration means that the pistons do not follow the exact dynamics of the master piston.
The engine operated on the four-stroke cycle where air was drawn first through the carburettor then through the hollow crankshaft to an annular chamber behind the crankcase and finally to the engine cylinders. An inherent problem in rotary engines was that this tortuous passage of the air/fuel mixture limits the power which could be developed. A single magneto, connected to a spark plug mounted on the side of each cylinder, initiated ignition which occurred in alternate cylinders during each revolution of the engine. The engine was started manually through the propeller. The engine normally ran at full speed which could only be varied by cutting the ignition via a 'blip' switch on the control column.
Lubrication was a total loss system. Castor oil was injected into the carburettor by an engine-driven pump, with the unburnt residue forming part of the exhaust. The fuel/oil/air mixture flowed through the crankshaft into the crank case, where it lubricated the bearings before being transferred into the cylinders.
Height: 915 mm
Length: 915 mm
Cylinder diameter: 120 mm
Piston stroke: 150 mm
Weight: 234 lbs (106.1kg)
Compression ratio: 4.3:1
MarksCLERGET Blin 7 Z TYPE No 1104