FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1961
1961 - 1336.PDF
440 FLIGHT, 14 September 1961 ROUND THE STANDS ... \1 Propulsion IN last week's issue we reported upon most of the major newdevelopments in gas turbines, and upon VTOL propulsion in particular. Yet there is at least as much to say about the develop-ment of powerplants for relatively low and very high flight speeds —namely, piston engines and rocket motors. In the former fieldthe pre-eminent names are Alvis and Rolls-Royce, the latter company having undertaken to manufacture light horizontallyopposed units designed by the US Continental Motors Corporation. Outwardly, there is seldom very much to report upon the aero-engine work of Alvis Ltd, and this year the only exhibit that could really be discussed in detail is a superbly sectioned Leonides 531.But behind the scenes both the single-row Leonides and the double- row Leonides Major continue to fulfil arduous requirements underevery conceivable type of operating condition. Probably the most severe duty of all is the propulsion of ASW helicopters, in whichvery high powers must be sustained for hours at a time during dunking duties, with the helicopter hovering at 50ft or below. Thesalt-water environment, lack of forward speed and absence of substantial angular momentum in the output (so that any loss ofpower is likely to be very serious, if not catastrophic) are most difficult to match with the demands for extreme reliability andmaximum overhaul life. The diagram above suggests some of the possible ways in which existing Bristol Siddeley rocket chambers might be disposed, in order to provide a wide range of powerplants with thrusts ranging from 50 up to 100,0001b. Chamber hinge axes are indicated Bristol Siddeley's diminutive PR.37 rocket engine, with an inset above illustrating its installation in the Jindivik: A, HTP input; 6, kerosine input; C, nitrogen input; D, kerosine stop valve (non-electric): £, HTP jettison valve; F, HTP jettison pipe; G, HTP stop valve; H, mixture-ratio trimming valve; J, thrust chamber with inner and outer walls fabricated from steel sheet; K, HTP control valve; L, HTP feed to annular space between chamber walls In last week's issue the first details were given of the de Havilland Spartan I pre-packaged liquid rocket, developed under a technical agreement with Thiokol Chemical Corporation. The sketch above shows its simplicity: A, igniter; 8, booster charge; C, pressurizing cartridge; D, burst band; E, fuel (amines); F, oxidant (nitric acid); H, area in which propellants mix and ignite hypergolically; J, combustion chamber Principal helicopter engine is the Leonides Major 755, with amaximum continuous rating of 695 b.h.p. For the difficult ASW mission in the Royal Navy's Whirlwind HAS.7 this engine is atpresent pulled every 300hr; elsewhere the same installation is currently overhauled on a 600hr basis. Whirlwinds powered bythis engine are in wide service outside the UK, and both the helicopter and its powerplant are made abroad under licence. Alvis feel that the long-stroke Leonides 531 single-row enginehas been sold with surprisingly little effort, particularly to both the Ministry of Aviation and existing owners of Twin Pioneeraircraft, for conversion of those machines originally built with the jower-powered Leonides 514. Overhaul life of the Mk 531 engineis at present of the order of 600hr. It is difficult for this to be rapidly extended, in view of the relatively low aircraft utilization;but it is anticipated that the ARB will not have to see very many units before the life can be increased at least to the levels reachedby earlier Leonides. Incidentally, Alvis remain an entirely independent company,reflecting the character of their managing director. Rumours concerning possible take-overs or mergers have been prolific duringthe past year, but do not at present appear to have much founda- tion. Roughly 45 per cent of the firm's business is aeronautical,and this includes substantial sub-contract production of high- precision machined parts for gas turbines by Rolls-Royce andBlackburn Engines. Most of the components are steel shafts and gears, but one contract covers all aluminium-alloy castings for theBlackburn Nimbus. The only other engine company suffering under the strains ofASW dunking is Napier Aero Engines Ltd, whose Gazelle 161 is in full Royal Navy service as the powerplant of the Westland WessexHAS.l. This engine has a one-hour rating of 1,430 s.h.p., and more powerful versions (described in Flight for August 31) are underdevelopment for later marks of the same helicopter. Discussions with Naval personnel at Farnborough leave a clear impression ofpreference for turbines, on the grounds of reduced in-flight vibration and aircrew fatigue; and to some extent it may be reasonable tohope that the newer powerplants may lead to a reduction in the number of failures of various airborne systems. Napier have had to take special precautions to fit the Wessexinstallation to the salt-water environment. It is not entirely fortuitous that the intake velocity of the Gazelle is relatively low,and this substantially reduces ingestion problems (not only of sea- water but also of sand and any other foreign material). As isgenerally the case with Napier gas turbines, the compressor rotor blades arc of aluminium-bronze. This has good resistance tocorrosion, but it is impossible to avoid progressive coating with salt and other matter, which is periodically removed by purgingthe engine with special cleaning fluid injected at the intake during
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
