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Aviation History
1933
1933 - 0471.PDF
FLIGHT, AUGUST 31, 1933 THE NEW BMW Xa LIGHT PLANE ENGINE 54/60 H.P. THE Bayerische Motoren Werke of Munich have now gone into production with a small five-cylinder radial engine developing a normal maximum of 60 h.p. at 2,050 r.p.m. and a continuous output of 54 h.p. at 1,980 r.p.m., while the absolute maximum (for short periods only) is 68 h.p. at 2,300 r.p.m. Already in 1929 the company started work on an engine of this size and kind, and in 1930 the BMW X was brought out, which proved quite capable of sustained heavy service but yet did not quite satisfy the makers. These have in the meantime gained wide expedience with radial air- cooled engines through being licensees of Pratt & Whitney, whose " Hornet " the B.M.W. company has introduced with considerable success in Germany. This experience has been incorporated in the new small BMW Xa, which, among other features, has lead-bronze bearings for the divided crankshaft and the master-connecting rod, and a very small diameter at only 29.05 inches (738 mm.), the total length with hub measuring also only -6.13 inches (664 mm.). The crankcase consists of five separate Elektron cast ings. Steel cylinder barrels with flanged-on light metal alloy heads, which are cast integral with the streamline rocker casings, are employed. Aluminium pistons have two compression and one oil scraper ring. The piston on the master rod has a stroke of 3.54 in. (90 mm.), which also is the bore of all cylinders, while the pistons on the auxiliary rods have a stroke of 3.64 in. (92.5 mm.). There are two valves for each cylinder operated in the usual manner by enclosed pushrods and rockers. Aluminium- bronze valve seats are shrunk in and flanged over. The valve guides are of bronze and two co-axial coil springs are fitted for each valve. Dual ignition by two Bosch magnetos with automatic spark control is furnished. The compression ratio is 5.7 to 1. The engine has proved very economical and does not consume more than 0.52 lb. per h.p.-hour at maximum constant output of 54 h.p. A Sum carburettor type CFV 36 is employed. The engine has completed the full official tvpe tests without a single fault and has fulfilled the Cina conditions so that it is qualified for public use. It weighs 160.6 lb. E. P. A. H. S3 S5 NEW IRVIN PARACHUTE HARNESS A SUCCESSFUL test with a new type of Irvin para chute harness was made by Mr. John Tranum on August 15 at the Irving Company's aero- \vV h v, drome near Baldock, Herts. The new harness, sid w beeT1 deigned DY Mr. Leslie Irvin after con- self H- exPerimenting, embodies almost 100 per cent. ^ • Adjustment, and has no straps to pass between the legs si:-m +t CaSe of the conventional type, which at once s,r"PS the equipment as most suitable for women air pas- .jgers, and very easy to put on. wt n Passen8er sits in the new harness as in a swing, and thr-mK l Parachute opens the straps automatically adjust chut h5 to the Passenger. It is simple to modify a para- iinnorf ».ne5S for eaEe in attachment to the body, but the ti'/n I ^uestion that results is how will the modifica- Obv l n a Jump is made- there f y one cannot delete a strap here or a strap in act°r comfort's sake if it is going to create insecurity Irvin's u Conse<luently the successful test with Mr. have vJlew.narness has proved that simplicity and comfort Tranur? !f^dU"d Yith, Perfect safety. " Puss Moth," owned and In this machine the doors so that they can be dropped off in Cb?Mrdred out °f have hJ Irvm' at 1-2W ft ^e Deen arranged case of an emergency, and on this occasion one door was left off to provide a ready exit. Without intention in this test Tranum incidentally showed how quickly the new harness fitted on when he got into his seat. A seat pack is used with this harness and the latter can be almost completely hidden in the upholstery of the chair, and need not be worn during flight. To attach the equipment to himself the passenger simply moves two short pieces of webbing in the harness across his lap and tightens them with a slight pull. Then he naturally eases his shoulders in shoulder straps in position at the top of the chair, and makes a connection in front. The harness is on. In designing this harness Mr. Irvin has been faithful to the factor that he has followed in his previous harness designs, namely, that the opening shock of a parachute must be distributed over the body, and to obtain this effect the parachutist must sit in a swing which must be held in position so that he does not fall through. It is then essential to provide straps across the back and front to prevent a fall backwards or forwards. Further, the point of suspension should be at the shoulders. These features have been retained in the new harness without the need of adjustment according to the size of the wearer, and without leg straps. 879
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