LUBRICATING MINIATURE BEARINGS

At Stockholm, recently, the F.A.I. world championship control‐line team race was won for Britain with an aircraft equipped with an Eta 15 Mk. II engine, built by Eta Instruments Ltd., and believed to be the most powerful engine in its class in the world. This is a 2.5 c.c. diesel engine. With an engine of such a diminutive size operating with 15,000 and 20,000 r.p.m. the method utilised to support the crankshaft is obviously of great importance; it must be rigidly held and yet subjected to the minimum rotational constraint. Two Hoffmann miniature ball bearings are used to locate the crankshaft and are mounted at either end of an extended one‐piece aluminium alloy housing that is bolted directly on to the front of the aluminium pressure diecast crankcase. A Hoffmann N6358 ball bearing (⅝‐in. o.d.) is fitted at the front and a Hoffmann S1 V2 (¾‐in. o.d.) at the rear of the housing. The counter‐balanced forged steel crankshaft has a main shaft 0.25 in. o.d.