FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1969
1969 - 2476.PDF
120 AIR TRANSPORT. the approach. Manual approaches have been made on a number of occasions. Little difference is noted wi<th or without autostabilisation. Manual throttle merely requires more atten tion to speed control. "Redundancy of systems is somewhat revolutionary. For example, there are five electrical systems, four engine-operated and one hydraulically operated. Each has its own battery. There are three hydraulic systems. Cockpit instrumentation provides auxiliary attitude information, as well as back-up raw data altitude and airspeed information. Consideration is being given to providing fuel inerting, but no final decision has been made on this matter. "My overall impression is that the design and engineering have been superlative in every regard." FLIGHT International, 14 July 1969 The report then summarises the structural and fatigue testing and continues with some personal opinions of the author, who says that "the manufacturers and the carriers have taken a very conservative approach to the potential operation of supersonic aeroplanes over land, as indeed they should. However, I would not be at all surprised to see the Concorde operated over the continental United States under certain limited conditions. The sonic boom is still an unknown factor. Even if it is prohibitive in some regimes, it may be possible to operate the aeroplane subsonically under some conditions, without prohibitive economic penalty, and under other condi tions it may be possible to operate supersonically when the aeroplane is high enough and light enough. "Although I am no expert on economics, it appears that the cost per seat-mile in a mixed configuration may be as much as 32 per cent higher than our subsonic, long-range aeroplanes. However, with a modest extra fare and the high load factor which may be expected . . . for the first few years, it may well turn out to be a very profitable aeroplane." QUIETENING THE RB.211 MORE than 200 sq ft of sound-absorbent material will line the inlet, fan and hot exhaust ducts of the Rolls-Royce RB.211 for the Lockheed L-1011. With a high bypass-ratio engine such as the RB.211 there is a drastic reduction in the noise from the jet stream and the major source of noise has now become the fan, with turbine noise secondary in im portance. Although the engine incorporates basic design features to reduce its noise level, the sound-absorbent material greatly lessens this fan and turbine noise. Development of the linings has been done at the Rolls- Royce Flight and Test Establishment at Hucknall. The linings were designed and disposed to reduce the sound pressure level at the peak annoyance frequencies. They consist of a porous material separated from the engine casing by a spacing structure which provides an air gap between the material and the wall of the duct. The noise-attenuation properties are Above, the extent of the noise-absorbent linings for the RB.211 is shown by the heavier lines. Below, RB.211 noise spectrum with and without linings Sound Pressure Level Fan Noise Basic Engine Spectrum Jet Noise Turbine Noise Spectrum application of Acoustic Absorbers VERY CRITICAL AUDIBLE RANGE WHOLE AUDIBLE RANGE ~l 500 1000 5000 10000 Frequency Cycles/second dependent on the porosity of the material, while the depth of the air gap determines the frequency at which peak absorp tion occurs. Small backing depths produce maximum attenua tion at high frequencies and large backing depths at low frequencies, so the linings in the turbine duct have a smaller backing depth than those in the fan duct. A special rig has been built at Hucknall for testing acoustic panels in a duct compatible in size with those of the RB.211. To provide an adequate supply of both air and noise to the test duct, use has been made of a military-type vectored-thrust engine, which has the advantage that the hot and cold gas streams are already separated. Either stream can therefore be fed into the duct to simulate the fan duct or turbine duct on the RB.211, whilst the gas stream which is not passing into the test duct is diverted into) a muffler so that it will not affect noise measurements. The most promising configurations are installed in the RB.211 and evaluated on the new! open-air noise and perform ance test bed at Hucknall. This facility, as well as being equipped for noise measurement, is fully instrumented for performance testing, so that penalties associated with fitting acoustic liners can be rapidly assessed. BAHAMAS WORLD WEIGHS IN THE new airline Bahamas World Transport is planning to operate scheduled services between Nassau and New York, Montreal and London (as reported by Sensor last week, page 77); it has been granted licences by the Bahamas Govern ment, although these are subject to confirmation after objec tions have been heard. One objector may well be Bahamas Airways, which operates one of the four most important routes out of Nassau—to Miami—and which has aspirations towards long-haul routes, although it has not yet got the equipment for them. The matter raises political complications; although the Bahamas is fully independent with regard to internal matters, it still has to consult the British Government on international questions. When these involve bilateral air-service agreements, the Board of Trade in London is called in, and in this case the bilaterals with the USA and Canada are involved. The Nassau-London route is a cabotage matter, again under Board of Trade control. It is to be expected that the Board will spring to the defence of BOAC, which is the designated carrier on the Nassau-New York and Nassau-London routes (the latter is operated in pool with Qantas). But a refusal in London to allow Bahamas World to be designated also could spark off a major political row between the Bahamian and British Governments. BOAC is not particularly popular in Nassau political circles, where officials will point out that the corporation flies only
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
