New Range of Pobjoy En ines
Page 51
If you've noticed an error in this article please click here to report it so we can fix it.
Three Geared and Ungeared Radial Units Suitable for Employment in Civil Aircraft
THE well-known Pobjoy R-type, seven-cylindered, radial engine was fully described and illustrated in this paper dated May 12, 1933. Pobjoy Airmotors, Ltd., Hooton, Wirral, Cheshire, has now produced a new range of three engines of the same form and having common cylinder dimensions and many common components.
Speaking ' generally, • the Niagara 90 b.h.p. engine is a new model having totally enclosed valve gear and cowling as part of its standard equipment. The Cataract 80 b.h.p. 'unit resembles the 1933 R-type, but has the redesigned ignition system; improved cylinders, • reduction gear and exhaust collectors, and is cheaper than the Niagara.
The Cascade 70 b.h.p. unit is of interest as the first direct-drive Pobjoy engine._ It resembles the Cataract, but by a sacrifice of about 10 b.h.p., it can be sold at a rather lower price. It incorporates the fourpole magnetos, which are a feature of the two bigger engines, but hand-starting gear is, in this case, an extra.
The cowling of the Niagara consists of a nose piece supported on a tubular ring stayed from the r,yankcase, and supports the bonnet. All air entering the nose piece is forced by cast helmets to circulate over the cylinder heads or around the barrels, and air speeds in these passages are higher. than the speed of the aircraft, giving increased cooling efficiency. A sheet aluminium guard completely surrounds the rear of the engine, and in a serious crash the exhaust pipes would be trapped between two layers of cold aluminiu m. Accessibility of the engine is not impaired by the presence of the
cowling. The bonnet is easily opened. An improved feature of the Niagara is that the valve gear is completely enclosed, the crankcase having around its circumference an oil-tight chamber which envelops the tappet guides, so that oil working out of them drains back into the crankcase.
The advantage of the four-pole magnetos is that they run at only seveneighths crankshaft speed instead of that speed, as in the preldous models. An arrangement is incorporated to facilitate starting, in conjunction with the handturning gear operated by cable from the pilot's seat. • The die-cast aluminium finned cylinder heads are screwed to the steel barrels by the maker's patent process, which has survived the test of eight years without a single leak. The valve seatings are inserted by a new process claimed to eliminate all familiar troubles. The reduction gear is of the double-helical type, and the well-tried crankshaft bearings, pistons, cam-drive gear, oil pump, etc., are retained as in previous engines. The exhaust collectors are of improved design.
The Niagara engine is to be employed in the Short Scion monoplane described elsewhere in this supplement, giving improved performance over the R type.