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Aviation History
1949
1949 - 0054.PDF
FLIGHT JANUARY 13TH, 1949 The Modern Autopilot matical terms and concludes with the demonstration that thetransfer function of the aircraft has a phase lag of 90 deg at resonance, so that below this frequency the phase lags in theautopilot and the rest of the system may safely be allowed to approach 90 deg. As a result of tests made with phase-advancing network, Smiths have decided to incorporate it as standard in both the rudder and elevator channels of the newS.E.P.iC. The lecturer further suggests that every effort should be made to eliminate the '' threshold '' lags and to keepthe main lags down to a standard which he would like to see set at 0.025 °f the highest resonance frequency of the aircraft.On the subject of radio guidance, Mr. Meredith observes that his company have been simulating the problem of closingand holding a beam in the laboratory, and have found con- clusive evidence for the need of making the whole processautomatic. It is difficult enough to hold the beam with suffi- cient precision, but the problem of closing in a reasonablyshort time using the information provided by compass and beam indicator is far too difficult to impose on the pilot in thetrying circumstances of a blind approach. Mr. Meredith observes that it is really illuminating to attempt to execute themanoeuvre using the pilot's controller of the autopilot and then, when feeling frustrated, to switch in the autopilot radioswitch and see one's mistakes being immediately corrected and the beam signals subsiding cleanly to zero.' The lecturer con-cludes with the expression of a purely personal opinion: that perfectly safe blind approaches will, before long, be a matterof simple routine, using ILS in conjunction with the autopilot, simultaneously with a GCA system supplying a running com-mentary to give extra confidence to the pilot, and to provide a standby in case anything should go wrong with the neces-sarily complex sequence involved in the auto-approach system. AIR LEAGUE BALL T TNDER the patronage of H.R.H. Princess Elizabeth, thev Air League of the British Empire and the Guild of Air Pilots and Air Navigators are jointly holding a ball at theSavoy Hotel on Friday, February nth. The proceeds will be shared between the Guild's Benevolent Fund and the AirLeague's flying scholarships fund which provides scholarships for young people in general, under schemes organized by theAir League branches, and also for A.T.C. Cadets who have obtained proficiency certificates. The estimated cost for theA.T.C. scheme for 1949 is £12,000 and it is hoped to provide 100 scholarships up to private pilot's licence standard forsenior cadets in 1949. The Air League's plan for branch scholarships is to double whatever funds a branch may raisefor flying scholarships, up to a limit of ^100. The objects of these scholarships are to stimulate recruiting for the A.T.C.and also to increase interest in private flying, and in the latter case they are likely to be of some assistance to the flying clubs.Tickets for the ball which can be obtained from the Guild of Air Pilots or from the Air League, at Londonderry House,19, Park Lane, are priced at three guineas single and five guineas double; these prices include supper. The ball com-mences at 8 p.m. and continues until 2 a.m. CABLING GOOD NEWS IN addition to the standard range of aircraft cables whichBritish Insulated Callender's Cables, Ltd., have produced for many years, a new range, given the brand prefix " Pren,"has recently been introduced. During the war, the rapid increase in the physical size ofaircraft and the increase in the number of sendees, brought forth an urgent demand for a decrease in the weight of cablesinstalled. Up to that time the orthodox cables conformed to a common pattern, comprising a copper conductor shroudedwith a rubber insulation sheath which was in turn bound with oil-resisting tape and cotton braid and finished with afinal coating of cellulose lacquer. This form of cable, although perfectly efficient and suited to its purpose, was both heavyand non-flameproof. Research showed that, by using a polychloroprene sheathover a braiding of woven glass-fibre surrounding the conduc- tor, the insulation characteristics remained unimpaired, whilstadditional advantages were accrued in effecting relative flame- proofing, inertia to petrols, oils and hydraulic fluids, etc. (whichattack natural rubber) and considerable saving in weight. This latter quality is due not only to the reduction in insula-tion bulk but also to the fact that, as polychloroprene has a higher temperature resistance than rubber, it allows the con-duction core to be proportionately smaller for a given current flow, since temperature is a function of the square of the flowfor a constant resistance. Thus, for a given duty, not only are the Pren-type cables smaller and lighter in bulk of insula-tion but also in core size. By virtue of the outstanding resistance to burning, it hasbeen possible to specify tests for Pren cables of an order of severity which is new to the aircraft field of application. Testsamples of cable, after soaking in hot lubricating oil, are exposed for 15 seconds to the hottest part of a Bunsen burnerflame: the cable does not support combustion, and burning or charring is confined to a length not exceeding 6in. Furthersamples, without immersion in oil, are subjected to electrical break-down tests after similar exposure to flame until theinsulation and covering are incinerated. One minute after removal of the flame, the instantaneous break-down voltagebetween conductors is greater than 500 v (RMS) 50 c/s. Pren cables are made in a series of unicell (i.e., a singlecore element) and multicell versions; the latter are individual unicell cables bound together with a glass-braid sheath andlacquered with a polyvinylchloride final coating. Alternatively, multicell cables are available, in 6-amp size, in a polychloro-prene outer sheath instead of the glass-braid, in order to afford greater physical flexibility. There are also versions with anouter metal-braid sheath over the glass-braid to afford earth screening characteristics. These new cables are the only types of general-purpose air-craft cables which are designed for compliance with the offi- cially specified requirements of 208 v between phases, equiva-lent to 120 v to earth at 400 c/s A.C. They will, of course, cater more than fully for the hitherto orthodox standard 24 vA.C. system. SUCCESS OF SMITHS AIRCRAFT INSTRUMENTS SIR ALLAN GORDON-SMITH, K.B.E., D.L., Chairman ofS. Smith and Sons (England), Limited, presided at the annual general meeting of the company which was held onDecember 31st. Reporting a successful year, Sir Allan said that Smiths instruments were being fitted to practically allcivil aircraft manufactured in this country. The Smiths auto- matic pilot was now in production and considerable orders forthe Government and for the British aircraft industry were in hand. Reference was also made to this division's entry intothe field of aircraft equipment for foreign constructors who are being supplied with instruments and equipment in increasingnumbers. Speaking of the progress achieved by the aircraft instru-ment division during the past few years, Sir Allan declared that this had fulfilled the company's expectations of a fewyears ago which were for Smiths instruments to achieve the same position in the aviation field as Smiths motor accessorieshad reached in the automobile industry. Sir Allan also stated that the Smith factories now made a larger variety of theseinstruments and ancilliary equipment than any other company in any part of the world. Great credit, he said, was due tothe management of the Division—Mr. Morgan on the admini- strative side, W/C. Samuelson, Technical Sales Director, Mr.Meredith, inventor of the automatic pilot, and Mr. Watson, who controls the aircraft instruments factory. " Sorry old man. You must pretend you haven't seen it" B 10
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