FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1945
1945 - 1305.PDF
1*4 FLIGHT BRISTOL CENTAURUS ; cylinder and head finning is interesting. By experiment has been shown that the optimum pitch for fin location in the region of o.iin.-^the pitch on the Centfturus is [izin. and the cooling area of finning to each cylinder id head is no less than 32.47 sq. ft. Not the least novel feature of the cooling arrangements the fact that, unexpectedly enough, the front,row of flinders, due to the amazing control of the cooling air- low, actually runs a trifle hotter than the rear row. pressure drop in the cooling air through, or, rather, across he cylinders is the rather high figure of 10 inches of water, 3d, very shrewdly, this is put to incidental, yet none the useful, advantage in cooling the rear-swept front-" ylinder exhaust pipes. These are shrouded' with tubular jufis, open at each end, which extend nearly to the trans-. jterse centre plane of the engine, and the pressure differ- ential between front and rear open ends induces an air- Bow through the muffs which effectively cools the exhaust Wipes whilst, at the same time, isolating their cooling ajf prom the ordinary flow to the rear cylinders. Limits of Cooling The cooling efficiency of the Centaurus is nearly as high it is possible to get. There are for the future the addi- tional refinements of a geared cooling fan running at higher [speed so inducting a greater mass flow,'and also the closer pitching of the cooling fins. Nevertheless, it would appear that the ultimate is at- least within sight, and from this aspect it is a reasonable assumption that some limit will sooner or later enforce a barrier against the use of more potent fuels and increase of engine rating by stepping up the b.m.e.p. This reflection excludes consideration of the (use of water/methanol injection and kindred devices which conceivably might have an increasingly large part to play. The reduction gear is the well-tried Bristol-Farman type I bevel epicyclic which is so well known as to render a [further description superfluous. One element is, however, [worthy of note; the rear driving bevel and the front [stationary (sun) bevel ring are both located on annular Iseatings, the bearing faces of which are spherically curved. I This measure ensures that the«driving and sun bevels can- [each rock slightly and so permit the load to be distributed I equally among all three planet pinnions. The three ["spokes" on which the planets are carried are integral [with the airscrew shaft, the tailpiece of which is supported" I in a bearing-in the forward end of the crankshaft. Airscrew' — thrust is carried by a large-diameter ball-bearing housed in the" front of the r.g. casing forward of the gear itself. The crankcase of the Centaurus is unorthodox in that it is composed of three sections—front, centre, and rear— the mating faces of which are disposed on the transverse , centre planes of the cylinder banks..' Each section has a diaphragm, those of the front and rear supporting the sleeve drive bearings and isolating the gear trains from the crank throws, and that of the centre provides a sup- port for the main central crankshaft bearing. The front and rear sections of the casing are secured to the central section .by hollow bolts on each side of each cylinder. Mating faces are metal-to-metal, there being no gaskets, this in itself being a tribute to the Bristol production efficiency. Both sets oi sleeve drives are composed of spur gear trains powered from a common input gear mounted on the crankshaft. A description of one set suffices for both, as front and fear Urives are identical. Meshing with the central input gear are three equispaced intermediate gears each of which drives the middle wheel of a separate train of three, each of the three wheels driving a sleeve crank ; he three sleeve-driving wheels are connected in a train by dler wheels^one between adjacent pairs. ' A built-up, nitrided crankshaft—also in three sections— 6 employed,-the front and fear sections, which include the balance weights, being attached to the central section by WWmB •i*J\\.--:\ ••'•• :T: BALANCED ' *%£- mum two-bolt maneton joints. Each of the balance weights .contain two 2.875m. dia., 3.52 1b. Saloman ball-type vibration absorbers which have proved to be very effective in de-tuning both torsional and flexural vibration. Ex- amination of the double curvature seat track of the ball enclosures has established that'the ball movement cither longitudinally or transversely does not exceed 0.75111. Big-end bearings carry-on the unique Bristol precedent of employing white-metalled sleeves shrunk on to the crankpins, in contrast to the more usual floating-bush type bearing. Each crankpin carries a master connecting rod to which the other eight very slim con-rods are articu- 31 i
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
