288 October, 1929 AIRCRAFT ENGINEERING Recen t Important Air Ministry Announcements No . 12 of the year 1929.—The atten (b) Expansion chambers which are too small Aero Engine Magnetos. tion of all owners of and ground engineers or too stiff to cope with the temperature B.T.H. Types. concerned with the undermentioned "Avro " range experienced. A.V.14. S.C.12-7A, S.C. 12-7B. aircraft is called to Leaflet D. 3, paragraph 6 (c) Inadequate de-aeration of the compass S.V.14A. A.C.12-1, A.C.12-10. (ii) of A.P. 1208, the Airworthiness Handbook liquid before the bowl is finally sealed A.V.12D, A.V.12E, S.C.9-1, S.C.9-1A, for Civil Aircraft, in which it is laid down that up . A.V.12F. S.C.9-1B. the petrol supply from all tanks is to be such S.V.12A, S.V.12F. S.C.7-1. "3 . Attention is particularly drawn to 2 (c) tha t it is not affected by the collection of S.V.9. S.G.5-1. above, owing to the fact that alcohol normally foreign matter in th e sump, and that a method S.C.14-1. holds in solution a considerable volume of air, of draining the sump must be provided. Watford Types. and if the pressure on the liquid is gradually The following are the types of "Avro " air C.6.S.M. S.T.5-1. S.P.9-1. decreased, some of this air will be liberated and craft affected:— will form a bubble. Such conditions occur Hand Starter Magnetos when aircraft climb to high altitudes where the Type 504 K. Type 548. B.T.H. Types. air pressure is low. Aircraft compasses should, S.S.-l . A.S.-l . Type 504 N. Type 548 A. therefore, be guaranteed by their makers to be The following have received "limited" "Gosport. " "Avenger. " free from bubbles if placed in a chamber in approval only. These are early-type hand- "Baby. " "Avian " (all types). which the air pressure is reduced to 3 lbs. to starte r magnetos, and are only capable of Provisions to meet the above requirements th e square inch." dealing with the capacity effect of a very short are to be incorporated in all "Avro " aircraft length of metal-braided cable:— of the above-mentioned types before Septem CAV. type. No . 15 of the year 1929.—(1) The modifica ber 1, 1929, or when the aircraft is submitted CAV. (modified). tions described herein must be satisfactorily for inspection for issue or renewal of a Certificate Lucas (Thompson-Bennett) type. incorporated in all existing D.H.50 and D.H.50A of Airworthiness, whichever is th e earlier date. A.M.S. (modified). aircraft with "Puma " engines before any such Unless the above-mentioned requirements aircraft is submitted for inspection for renewal have been satisfactorily complied with, no No . 17 of the year 1929.—The attention of of the Certificate of Airworthiness. Certificates of Airworthiness will be issued or all ground engineers is directed to the impor renewed in respect of any "Avro " aircraft (2) The modifications consist of altering the tance of maintaining cockpits, windscreens, etc., of the above-mentioned types, and after present position of the petrol filter to a position in watertight condition so as to ensure pro September 1, 1929, any Certificates of Air above the level of the carburettors. A "Y " tection of instruments and other equipment worthiness already issued will become invalid. piece is fitted on the filter outlet, and separate under adverse weather conditions. branches ar e led from this "Y " piece t o elbow Leakage of water through defective joints in connections on the bottom of the carburettors. cowling and windscreens may seriously impair No . 13 of the year 1929.—The attention A ¼-in. vent pipe is led from the highest point th e efficiency of the aircraft and must be of all ground engineers is directed to the of the filter to above the top level of the fuel prevented in order to maintain the aircraft in fact that corrosion is found to take place tank. an airworthy condition. under the brass identification clips of stream (3) These modifications are introduced to line wires and tie-rods. These parts, No . 18 of the year 1929 The spruce bot overcome the likelihood of fuel starvation due therefore, should be immediately examined by tom front centre section spar in the fuselage of to air locks, which are probably caused by the moving the clips from their position, and should "Avian " Mark III, IIIA, and IV aircraft is hea t of the exhaust pipe vaporising the petrol corrosion be found, the wire or rod must be liable to split along the line of the bolt holes. in the lead from the tan k to th e filter. replaced. Where frequent examinations are This member should be frequently inspected, difficult, e.g., within covered components, the (4) The modifications are shown on D.T.D. and at the first sign of splitting, Modification wires and rods may be protected under the clips Drg. No. 16/1098, copies of which can be No. Avian/25, which consists of replacing the by a coating of good varnish, care being taken obtained on application to the Drawings existing spruce spar by a birch multi-ply spar not to damage this protective coating when Library, Air Ministry, Kingsway, W.C.2, on of identical cross-sectional dimensions, should replacing the clips in their final position. If prepayment. be embodied. No Certificate of airworthiness the clips are a slack fit, they should be lightly (5) No Certificate of Airworthiness will be will be issued or renewed in respect of "Avian " closed to prevent their sliding on to the un issued or renewed in respect of any D.H.50 and Mark III , IIIA, or IV aircraft unless the above- protected parts of wires or rods. To prevent D.H.50A aircraft with "Puma " engines unless mentioned modifications have been satisfac the above-mentioned corrosion, new materials th e above-mentioned modifications have been torily incorporated. The above information is are being introduced for the clips on wires and satisfactorily incorporated. substituted for that contained in Notice to rods of future manufacture. Ground Engineers No. 11 of 1929, which is hereby cancelled. No . 16 of the year 1929.—Certain types of No . 14 of th e yea r 1929.—In view of th e fact magnetos fitted on aero engines have been tha t trouble has recently been experienced approved and are suitable for use only with No . 19 of the year 1929.—The attention of through the formation of bubbles in liquid plain rubber H.T. ignition cables. The fitting all ground engineers is draw n to the necessity of compasses installed in Service and civil air of metal distributor screens and metal braided strict compliance with paragraph 20 (g) of craft, the attention of all concerned is directed H.T . ignition cables thereto, for the purpose of A.N.D. 7, which requires that operations such t o the following report on this subject:— overcoming interference where wireless is as doping must be carried out by methods installed in an aircraft, may seriously affect approved by the Secretary of State. "1 . The presence of a bubble in a liquid their correct functioning owing to the increased The "approved" doping schemes normally compass renders the liquid liable to disturbance load imposed due to capacity effect, and result require the dope to be applied in an atmosphere whenever the movement of the aircraft changes in engine failure or defective running. The absolutely free from draughts and a t a minimum in any way. These movements of the liquid attentio n of ground engineers is, therefore, temperatur e of 65° F . affect the magnet system and usually render directed to the necessity of ensuring tha t metal When such conditions are not attainable, th e compass completely unreliable. For this distributor screens and metal braided H.T. doping is not permissible unless recourse is had reason it is essential that aircraft compasses ignition cables are not fitted to any magneto t o special "approved " doping schemes which should be constructed so that they will remain unless it is of a type which has been type-tested cater for wider ranges of temperature and free from bubbles under all normal flying con and approved for use under these conditions humidity. The manufacturer concerned issues ditions. on the particular type of engine in question. full instructions as to the manner and condi "2 . The formation of bubbles may be due to The following is a list of the types of magnetos tions of application, and such instructions any of the following causes:— must be strictly adhered to. which have been type-tested and approved for (a) Leaking at one or more places where use with metal screens and metal braided H.T. All instructions for the application of joints have been made, e.g., filling plug, ignition cables and is appended for guidance. "approved " doping schemes bear a reference verge ring, expansion chamber. Additions will be made as and when necessary. t o the approval authority.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Aug 1, 1929