Search results

CONSTANT frequency 400Hz 3 phase, aircraft main electrical power is mostly obtained by employing a main engine driven constant speed drive (C.S.D.) of cither the pneumo or hydromechanical type. The latter, in the form of the Sundstrand (USA) pattern, is the most used and over the years has been improved so that it is at present a very reliable unit. It is, however, very costly to buy and maintain and the quality of the governing it gives is not outstanding.

IN VARIABLE SPEED constant frequency (VSCF) generating systems for aircraft, the variable frequency generator, usually six phase, is directly coupled to a main propulsion engine. The output of this generator is converted to three phase constant frequency, usually 400Hz, for general aircraft use by a cycloconverter using thyristors as switching devices.

CURRENTLY it is usual to demand that the entire electrical power for proposed super‐sonic airliners should be generated at a constant (400c/s) frequency. In order to do this a device called a constant speed drive (C.S.D.) is used to couple the shaft take‐off from the main propulsion engine to the electrical generator. These constant speed drives are extremely expensive items requiring specialised maintenance. On current subsonic airliners they absorb approximately 80 per cent of the time and expense required for the maintenance of the entire generating and distribution system on the aircraft. If these constant speed drives could be dispensed with a great step forward in simplification would result.

THE term ‘mixed frequency generation’ is of American origin and refers to an electrical generating system for an aircraft where the main generators are directly coupled to the engines and deliver a variable frequency over the engine speed range. A part of the generator output is used directly for such loads as de‐icing and galley loads which are not at all frequency sensitive. Other loads which require a constant frequency of supply (generally 400 Hz.) are supplied by rotary or solid state inverters (called ‘converters’ in the U.S.A.). Direct current loads (generally 28 V.) are obtained from transformer rectifier units.

The first part of this feature which appeared last month, covered dynamics of the throttle, the electro‐hydraulic governor, governor internal loop stability and alternative methods of stabilisation.

AN ALTERNATOR directly coupled to a spool of a jet propulsion engine produces a variable frequency of ac supply depending on the speed range between ground idle and take‐off rpm.

Remote power control basically means control at a distance of major switching operations in a generating and distribution system.

Independent of the size of the company, an Enterprise Resource Planning (ERP) system can either boost or doom a company, if implemented successfully or unsuccessfully. There is a great deal of supporting evidence from the literature, mainly from large manufacturing and service organisations. This article adopts a case study approach to investigate the selection and im plementation activities in a manufacturing company in Greece focusing mainly on production management aspects. The goal is to provide insight into the ERP functionality with respect to production and thus the selection of an actual business case proves how the enterprise successfully implemented and integrated such a system, highlighting the processes used, the obstacles faced and how they were overcome, as well as the gains achieved. Finally, it provides useful information and practical suggestions that may help production managers and users to get a better understanding of how to deploy such systems.

William Blackwood, the founder of the firm of the name, saw service in Edinburgh, Glasgow, and London before opening in 1804 as a bookseller at 64 South Bridge, Edinburgh. Blackwood continued in his bookselling capacity for a number of years, and his shop became a haunt of the literati, rivalling Constable's in reputation and in popularity. His first success as a publisher was in 1811, when he brought out Kerr's Voyages, an ambitious item, and followed shortly after by The Life of Knox by McCrie. About this time he became agent in Edinburgh for John Murray, and the two firms did some useful collaborating. Blackwood was responsible for suggesting alterations in The Black Dwarf, which drew from Scott that vigorous letter addressed to James Ballantyne which reads: “Dear James,—I have received Blackwood's impudent letter. G ‐ d ‐ his soul, tell him and his coadjutor that I belong to the Black Hussars of Literature, who neither give nor receive criticism. I'll be cursed but this is the most impudent proposal that was ever made”. Regarding this story Messrs. Blackwood say: “This gives a slightly wrong impression. Scott was still incognito. William Blackwood was within his rights. He was always most loyal to Scott.” There has been some controversy as to the exact style of this letter, and it has been alleged that Lockhart did not print it in the same terms as Sir Walter wrote it. Blackwood came into the limelight as a publisher when he started the Edinburgh Monthly Magazine in 1817, which was to be a sort of Tory counterblast to the Whiggish Edinburgh Review. He appointed as editors James Cleghorn and Thomas Pringle, who later said that they realised very soon that Blackwood was much too overbearing a man to serve in harness, and after a time they retired to edit Constable's Scots Magazine, which came out under the new name of The Edinburgh Magazine and Literary Miscellany. [Messrs. Blackwood report as follows: “No. They were sacked—for incompetence and general dulness. (See the Chaldee Manuscript.) They were in office for six months only.”] Blackwood changed the name of The Edinburgh Magazine to Blackwood's Edinburgh Magazine, and became his own editor, with able henchmen in John Wilson, Christopher North, John Gibson Lockhart, and James Hogg as contributors. It was a swashbuckling magazine, sometimes foul in attack, as when it told John Keats to get “back to the shop, back to plaster, pills, and ointment boxes”. Lockhart had a vigour of invective such as was quite in keeping with the age of Leigh Hunt, an age of hard‐hitting. The history of Blackwood in those days is largely the history of the magazine, though Blackwood was at the same time doing useful publishing work. He lost the Murray connexion, however, owing to the scandalous nature of some of the contributions published in Maga; these but expressed the spirit of the times. John Murray was scared of Blackwood's Scottish independence! Among the book publications of Blackwood at the period we find Schlegel's History of Literature, and his firm, as we know, became publisher for John Galt, George Eliot, D. M. Moir, Lockhart, Aytoun, Christopher North, Pollok, Hogg, De Quincey, Michael Scott, Alison, Bulwer Lytton, Andrew Lang, Charles Lever, Saintsbury, Charles Whibley, John Buchan, Joseph Conrad, Neil Munro—a distinguished gallery. In 1942 the firm presented to the National Library of Scotland all the letters that had been addressed to the firm from its foundation from 1804 to the end of 1900, and these have now been indexed and arranged, and have been on display at the National Library where they have served to indicate the considerable service the firm has given to authorship. The collection is valuable and wide‐ranging.