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Aviation History
1949
1949 - 0635.PDF
APRIL 14TH, 1949 FLIGHT 431 Air Horse means of sprockets with which engage the chain inserts in the control transmission. For the inner shaft governing cyclic pitch, the sprocket can be mounted direct on the heel of the shaft, since the total turning motion involved is but 180 deg, i.e., 90 deg from cast to north, and 90 deg from east to south. For the collective-pitch shaft, how- ever, the matter is somewhat more difficult, in that rotary motion at the sprocket must be converted into vertical motion in the shaft: the obvious method is to employ a screw jack. The sprocket is splined to a nut sleeve engag- ing threads cut in the skirt of the shaft. Above the nut is a keyed sleeve, the keys of which engage ways cut through the screw jack threads in order to prevent rotation of the shaft and ensure vertical movement only. The keyed sleeve is bolted to the base plate of the hub gearbox, and in its mouth houses the ball race in which the nut sleeve is located and rotates. In turn, in the mouth of the nut sleeve is a needle roller bearing in which the cyclic- pitch shaft rotates. At the head, the cyclic-pitch shaft is steadied in a plain Tufnol bearing in the mouth of the collective pitch shaft, ^between the jaws. With the survey of the mechanical design of the control system, and the fundamental rontrol actions behind us, we can now revert to a consideration of blade articulation and movement. To take the flapping hinges first: these are embodied to allow the blade to take up a compromise position between the directions of centrifugal and lift forces. When any collective pitch-change is being im- posed, the tip-path plane will be normal to the hub axis. When, however, cyclic pitch is imposed, the blade tends to flap upward under the influence of an increased angle of attack, and subsequently to flap downward as the angle of attack is reduced. Thus, although the lift of the rotor as a whole remains substantially the same, the flapping action of the blades as they rotate has the same effect as tilting the whole rotor, and, by virtue of this action, the thrust axis is tilted and so provides a couple about the air- craft's centre of gravity, which leads to directional motion imposed on the aircraft as a whole. Azimuthai Variation The drag hinges accommodate variation in the angular disposition of the blades one to each other. When the air- craft is in directional flight, there is a relative air speed across the rotor as well as the flow through the rotor. For purposes of illustration, we can visualize the aircraft as flying northward and, thus, there will be a relative airflow across the rotors from north to south. If, as in the case of the Air Horse, the blades rotate anti-clockwise when seen from above, in moving from south through east to north a blade will encounter greater relative airflow than it will in rotating from north through west to south. For this reason, the former is said to be an " advancing " blade, whilst the latter is referred to as a "retreating" blade. Obviously, the drive imparted by the engine must be re- garded as of constant angular velocity and, therefore, the rotor hub must similarly be regarded. Even without the complication of cyclic pitch-change, however, it is readily apparent that the drag of an advancing blade is greater than that of a retreating blade, and thus the advancing blade tends to lag and the retreating blade to accelerate relative to their nominal angular dispositions. The drag hinges in the blade articulation linkage are embodied to accommodate this tendency, but the oleo-pneumatic snubber units are fitted to provide some restraint to these azimuthai variations and damp out what might otherwise be dangerous cumulative accelerations. C. B. B.-W. HONOUR FOR D.H. ENGINEER MR. W. T. WINTER, A.M.I.A.E., chief development engineeron the Ghost engine, has been awarded the President'sGold Medal of the Society of Engineers for his paper The Development of the Jet Propulsion Engine, which he read before the Society on May 3rd last year. This is the premier award for all papers read" during the 1948 session and, in the President's own words, its winning represents a most note- r.worthy achievement. PROTECTIVE PLASTIC COATING OF particular value for the protection of highly finished light-alloy and other metal sheet during assembly, and for theprotection of parts in transit, an improved form of Avigel pro- tective coating has been evolved. The earlier substance of thisname required a hot-dipping process of application, which naturally limited its usefulness, but the new material, known asAvigel '' 100," can be applied cold by brushing or spraying. The transparent coating formed is thin but tough, with arubbery consistency, and can be peeled off without difficulty when no longer required. Six colours are available. It isstated to be proof against water oxidation, mineral acids and alkalis in any strength, and most greases, oils and solvents,and to be unaffected by extremes of ambient temperature or by fungi, bacteria and moulds. Sold in one- and five-gallon tins,and capable of covering 250 sq in for one penny, it is claimed to be the cheapest form of such protection at present available. Avigel " 100" is obtainable from Clear Glass Products, Ltd.,16-18, Malvern Road, Southampton. A.R.B. NOTICES THE Air Registration Board has made a third issue of No. 3in the series Notices to Licensed Aircraft Engineers and to Owners of Civil Aircraft. It points out that the Air NavigationRegulations (which came into force on April 1st) require that the certification of an aircraft before flight shall be made inrespect of the airframe by an aircraft engineer licensed in Category "A" and in respect of the engines by one licensedin Category " C." The respective duties of engineers licensed in the two categories are given in an appendix. A second issue has been made of Notice No. 8; it concernsthe Air Navigation (Radio) Regulations, 1949, which require all matters relating to the maintenance of radio apparatusinstalled in aircraft to be certified by radio-maintenance <! 17 engineers licensed by the Ministry of Civil Aviation. Theintroduction of these radio engineers' licences does not affect the present duties of licensed aircraft maintenance engineers.Enquiries regarding the new licences should be addressed to the Secretary, the Ministry of Civil Aviation. SWIFTLY SUNWARDS LAST Friday Mr. John Derry, the de Havilland experimentaltest pilot, won the Coupe Montana, a prize offered for the first flight from Paris to Cannes in under one hour. In astandard Vampire Mk. 5, powered by a de Havilland Goblin 2 turbojet, Mr Derry had flown from Hatfield to the airport atLe Bourget on the previous day. Taking off from Le Bourget, he flew the 440 miles to Cannes in 44 min 51 sec, at an averagespeed of 589 m.p.h. After crossing the finishing line, the Vampire landed at Nice airport. KING'S CUP AND NATIONAL AIR RACES 'TMrlE Royal Aero Club announces that His Majesty the King-*- has graciously approved the revival of the King's Cup Race; the event will take place on July 30th, as part of alarge-scale air race meeting, to be known as the National Air" Races and to be held over the August Bank Holiday week-end.The Ministry of Civil Aviation has granted permission for the event to be held at Birmingham Airport. There will be eleven races, each race a short closed-circuitcourse. Prize money of at least ^1,500 has been guaranteed. The provisional programme is as follows: —Friday, July 29th.—Arrival of competing aircraft. Saturday. July y>lh.—(i) Heats and final of a handicap racefor aircraft constructed within the British Empire and restricted to certain speed limits. (2) An international high-speed handicapfor aircraft with a minimum handicap speed of 300 m.p.h. (3) The King's Cup Kace.Sunday, July 31s/.—Aircraft demonstrations. Monday. Angus! ist.-(i) International race for ultra-light air-craft. (2) Inter flying-club race. (3) International handicap re- stricted to aircraft fitted with reciprocating engines and having aminimum handicap speed of 300 m.p.h. (4) International handicap limited to aircraft with a certified all-up weight between IOOI and1750 kg (2,206-3,858 lb.). (5) International handicap for jet aircraft. (6) International handicap race for aircraft with a certified all-up weight of between 501 and 1000 kg (1,104-2,205 lb).The Royal Aero Club hopes to announce the arrangements for spectators, and full details of the programme, and to haveentry forms for competitors available, by about May 18th.
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