Recently we drove over to Croydon Aerodrome—an historic place which, as Brooklands was, is in grave danger of being destroyed by bureaucracy–to see the Ardent 4C02 sera engine which the well-known and long-established firm of Rollason Aircraft and Engines, Ltd., is supplying for installation in the promising Druine Turbulent single-seater ultra-light monoplane.
The basis of the Tubulent’s power plant is a Volkswagen industrial engine which, except for a stiffer crankcase and the latest, more heavily webbed crankshaft, is virtually identical with the normal VW car engine. After the French had found the VW engine suitable for the original Turbulent which was built in France two years ago, Rollason’s bought a crashed VW, removed the engine and, after stripping it, decided that it was indeed splendidly made and ideal for conversion into a light aeroplane engine. They purchase new industrial engines from VW Motors, Ltd., in London and find very few modifications necessary to produce a reliable and inexpensive engine developing 30.9 b.h.p. at 3,000 r.p.m. with the propeller normally fitted to the Turbulent.
It is significant, and a tribute to VW workmanship, that standard components are retained almost entirely. The compression-ratio is normal and pistons, valves and ports unaltered. Cylinder ducting is unnecessary and flywheel and starter ring are likewise removed. A new fabricated inlet manifold is used, incorporating hose-joints to accommodate expansion between it and the cylinder barrels. As the oil-cooler is not appropriate to aeroplane installations oil-heating of the inlet manifold is substituted, which obviates icing-up and also keeps the engine lubricating oil cool. With this arrangement the engine opens up without trace of fiat-spot from idling to maximum speed. A Soles P.B.I.C. 32 downdraught carburetter is used with the choke reduced to 20 mtn. and the cam-type petrol pump is replaced by a Peugeot car-type fuel pump. The generator bracket is removed and where the generator is normally mounted a crankcase breather with simple one-way valve and U-pipe is fitted. As dual ignition is compulsory for aircraft the ignition distributor is not required, so the tachometer drive is taken from this point. Ignition is by a dual B.T.H. magneto hung from a plate below the crankcase and driven at engine speed from the crankshaft by a duplex chain. It fires two plugs per cylinder, the V W cylinder heads being drilled to take the extra plug, at an angle which was found after careful experimentation, space being restricted by the radius of the combustion chamber, the holding-down studs and the push-rod tubes. This dual ignition is purely precautionary, little or no extra power being attributable to it and the drop in speed when running on one plug per cylinder usually being in the region of a mere 20 r.p.m.
The faith which Rollason’s have in the VW engine is reflected not only in the fact that ‘capacity, compression-ratio, valve tinting and engine intervals remain unaltered but that no reason has been found to increase the oil capacity. The engine exhibits the low oil consumption enjoyed by owners of VW cars, which tends to result in over-filling of the sump at routine checks after a few hours’ flying ! The weight of the Rollason conversion is 133 lb. inclusive of exhaust tubs and propeller and the price is £272. No doubt the power output could be raised to 34 b.h.p. or more for racing purposes.— W. B.