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Aviation History
1947
1947 - 0238.PDF
162 FLIGHT .FEBRUARY 13TH, UNIVERSAL POWER PLANTS peratures, this cap is designed to prohibit removal under conditions that might be dangerous to the service engineer. A 30: 70 pei cent ethylene-glycol water mixture is used in normal climatic conditions, and separate systems with separate engine-driven circulating pumps are used for main cooling and for the intercooler. Civil Merlin installations have in the cockpit low-flow indicators which include warning lights automatically switched on should leakage or pump failure reduce the capa- city or circulation of engine coolant to a dangerously low level. Rolls-Royce are now tackling the problem of pipes and hoses and the design of connections which are thought to be in need of improvement to keep pace with other com- ponents. A satisfactory all-metal flexible pipe with screwed connection is one of the aims. Exhaust System For the original U.P.P. as fitted to the Linclon night bomber, exhaust flame damping was essential and, as has been mentioned, the air-cooled manifolds and fishtails, which project independently from the cyunder blocks into the two louvred exhaust panels, are very efficient in this matter. The exhausts terminate in curved fishtails with £in slits. Flame damping is achieved in this manner with minimum loss of power due to back pressure, but at the expense of some exhaust thrust. On civil installations the fishtails were replaced by round stubs to regain thrust, but they proved to be noisy. The answer to the silencing problem may be long pipes carried below the wing and acceptance of loss of thrust and in- crease of weight, although on the D.C.4M this is imprac- ticable because of the engine position in relation to the leading edge. A modified fishtail may still be used for this installation. . Since a fuel supply failure may stop an engine even more quickly than a mechanical failure, Rolls-Royce have made themselves responsible for testing the whole fuel systems except for the tanks. As with other services, tanks, pumps, filters, lines and cocks are all assembled as an installation on a test rig, and fuel supply is checked in all attitudes and under extreme conditions of temperature and pressure. Fire Extinguishing Rolls-Royce, Ltd., have made a special study of fire prevention and extinguishing, and all civil power plants now meet world requirements A multi-bottle system of spray nozzles at strategic points around the engine have proved satisfactory on many full-scale tests conducted at Hucknall. Accompanying illustrations give a good idea of such a test in progress, although the second Lancaster, standing just in front of the burning engine and providing slipstream from its engines at full throttle, is not shown. Several important changes have taken place among the minor components of the power plants, and in some in- stances these must also be mentioned as differences between the D.C.4M and Tudor plants. First, the actuators on the D.C.4M are all of the Rotax and Miles electric screw type because the Canadians believe these are better suited to operation in extreme cold. Engineers at Hucknall support this contention, but believe that the alternative electro-pneumatic rams can be made satisfactory for very low temperatures with the use of suitable natural rubber. T.C.A. require their D.C.4MS to operate at —40 deg C, and synthetic rubber washers become hard and may cause air leaks at less than —30 deg C. Elec- tric screw actuators are somewhat heavier than pneumatic ones, and must be covered by safety devices to provide automatic opening or closing as appropriate in the eve of failure. Another Canadian modification is the fitting of stainless steel pipes in place of copper ones, which might eventually fatigue and crack. In addition, all plants are to have new semi-rigid ignition conduits of nickel-plated steel. These will give better protection against oil, moisture and vibra- tion, and will improve the appearance considerably. With oil absorption and fire risks in mind, a new type of flexible pipe is being used which is rubber-covered and asbestos-lagged. A small engine modification which gives much improved accessibility is the side-mounting for the airscrew C.S.U. An additional advantage of this modification is that it per- mits the use of a simple rod control in place of a remote system. The foregoing description will, it is hoped, have indi- cated something of the enormous amount of thought and research which goes into the preparation of a modern uni- versal power plant. As a result, engines are equipped to meet almost every climatic emergency and are capable of very long running periods before overhaul, followed by only a few hours of aircraft unserviceability for power plant change. The overhaul period for the Merlin engine varies according to the air service on which it is used, and a representative figure is 650 to 750 hours. Many of the accessories and services now have overhaul periods up- wards of 1,500 hours. • M. A. S. DATA SUMMARY Engine weight (net dry) Take-off power Max. cruising (at 23,500 ft, consumption 68 g.p.h.) Power plant weight ... Diameter Length overall Merlin tO J 1,700 Ib. 1,725 b.h.p. 1.160 b.h.p. 2,790 Ib 55.8 in 83.5 in. Merlin 620 1,740 Ib 1,725 b.h.p. 1,160 b.h.p. 2,606 Ib 55.8 in 83.5 in Merlin 621 (D.C.4M) 1,740 Ib 1,725 b.h.p. 1,160 b.h.p. 2.830 Ib 60 — 55.8 in (tapering) 84.25 in NOT SO HOT SEEKING COLD FACTS : An Fi 103 flying bomb (V-i) on test at " 50-below " in Alaska where the U.S.A.A.F. Task ForceFrigid is testing modern air equipment, including jet fighters. On the right is a pre-heating unit for the impulse duct power unit
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