FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1926
1926 - 0169.PDF
MARCH 11. 191:6 installation in machines of the single-engincd and twin- engined bomber class. Materials The Sub-Committee on Aircraft Materials is further sub- divided into three sub-committees, one dealing with metals, a second with woods and glues, and a third with coverings, dopes and protective coatings. During 1925 the Sub-Committee on Metals recommended a programme of research for the study of intercrystalline embrittlement of Duralumin. The outline of this programme was as follows : (a) the study of acceleration of this type Of corrosion for testing purposes ; (ft) the effect of permanent deformation on material hardened by spontaneous ageing; (c) the effect of deformation on fully hardened material hardened by accelerated ageing at a higher temperature ; (d) the effect of protective coatings ; (<••) the effect of gas during casting; (/) the effect of heating and quenching mediums • (g) the effect of the composition of the Duralumin tested. Intercrystalline attack and embrittlement in material received from two American companies was produced experi- mentally, both in aged .material, and-in material cold-rolled after ageing. Material which had been greatly deformed by rolling after ageing and slightly deformed by stretching, is stated to be under test. Preliminary results indicate that stretching prior to test hastens the initercrystalline corrosive attack. The Bureau of Standards has continued to examine speci- mens found in service. These all confirm the conclusion that material cold-worked after ageing and subjected to corrosion is especially susceptible to embrittlement, although if the condition's are severe material which has not been worked after ageing is also attacked. Material which had been attacked in service by calcium chloride, cleaned, and re- varnished, was recently examined to see whether the inter- crystalline attack had progressed. No proof was found that the attack had progressed further since the previous examination. These results indicate that a coating which is actually imper- vious to such agents as water vapour and " salt air " prevents the corrosion. The material was in " notch brittle " con- dition after cleaning, and was still in that condition, although apparently no worse. The report states that the information now in the possession of the Committee does not justify a pessimistic outlook in respect to the use of Duralumin as a structural material for aircraft, unless in very thin sheets. It is believed that research on the embrittlement problem will ultimately show how to prepare, protect and use this material to ensure reliability in service. Concerning airship structures, the report states that previous tests of girders for the " Shenandoah " showed that the strength of these girdeis was determined by the elastic properties of the channels and the type of restraint offered by the lattices. The principal clastic constants of the channel are their two flexural stiffnesses (moments of inertia Young's modulus) and their torsional stiffness (torsion constant shear modulus). The object of the modern investigation was to determine by tests the relative importance of these three constants in determining the strength of the girders. According to the report the measurements so far made are consistent with the assumption that with the present construction the coefficient of torsional stiffness of the channels is the controlling factor in determining the load which these girders will carry. The report points out that the Forest Products Laboratory of the Department of Agriculture conducts practically all the investigations on the application of woods and glues to aircraft construction. A lengthy scries of tests is reported by the Sub-Committee on Woods and Glues, to which we are unable to refer in detail, owing to lack of space. A brief list of the subjects dealt with may, however, serve to give an indication() f the class of work that has been undertaken. A study of the effects of the attachment of metal parts and fittings to wood members was undertaken and the results of the tests'have been presented in the form of charts which give the most efficient size of bolt for given conditions. A series of tests has been made on box spars of various dimensions and on I-section spars having plywood webs. The results lead to the conclusion that in the design either of plywood box or I-section spars a web thickness 25 per cent, greater than that calculated to give equal likelihood of failure by shear or compression will give the best results. A preliminary study was made on the use of screws for fastening three-ply wood to spruce and ash frame members. As a result of the tests a table of screw sizes for different thicknesses of three-ply wood has been prepared for general design use. Concerning waterproof glues, the report states that no adequate study has been made of the durability of glued joints under long periods of time. Experience indicates that in many places where glued joints are used, any change in strength or water resistance is very slow. Tests-will be'uarried on over a long period of time with different water-resisting glues to determine the conditions under which glues will retain their original properties. An investigation has been carried out in an effort to produce a grade A plywood with casein glues. The report states that satisfactory results have been secured on a laboratory scale and that plans are now being developed for one or more demonstrations on a factory scale. It is believed that by proper control of the glue and the glueing conditions it will be practicable to produce a satisfactory product in quantity. Investigations have also been carried out on air seasoning of aircraft woods, on the effect of fungus infection on the mechanical properties of wood, and on the cause and detection of brashnes.s of wood. The Sub-Committee on Coverings, Dopes and Protective Coatings reports that at the Bureau of Standards extensive investigations have been conducted in the developments of experimental gas-cell fabrics for rigid airships. It is believed that a certain type of fabric which has been developed will, when fully developed, be the most satisfactory substitute for the goldbeater's skin now used in rigid airships. A coating for Duralumin produced by anodic deposit of the metal in a plating bath has been developed. The deposit is stated to be a luminum oxide, which is said to be a distinct protection. The process is understood to be patented. Usually the articles are lacquered after the plated coating is applied. At the suggestion of the Bureau of Aeronautics, Duralumin sheets such as are used for seaplane floats, were alternately exposed to sea-water and to air under tropical conditions. A coating has been developed which, it is stated, will prevent the growth of barnacles and be durable in air. It is made from plastic resin, coal tar, and toxic poisons. At the Naval Aircraft Factory, the report states, excellent results have been obtained, by using an inexpensive bituminous paint for floats and hulls, and it is stated that if the surfaces are enclosed this paint probably gives the best protection against under-water corrosion. The disadvantage is that the coating is heavy. The paint can be greatly improved by the addition of 10 to 20 per cent, of asbestine, a crystalline pigment showing a rod-like structure under the microscope. On the subject of coatings for magnesium to prevent corrosion, preliminary exposure tests of magnesium sheets have been made and it was found that uncoated magnesium sheets corroded slightly and the colour became dark if exposed so that moisture dried off, but that they became deeply pitted in six months if the surface did not dry off. Sheets coated with silicate of soda resisted corrosion better than uncoated sheets, although if the surface did not dry off they did corrode. Two coats of aluminium spar varnish appeared to give perfect protection. Six months' tests showed about equal corrosion in magnesium and in steel sheets. Changes at Supermarine's THE London office of the Supermarine Aviation 'Works, •td., has been removed to Bush House, Aldwich, London,1 C. 2. The telephone number is now Central 7262, and •>e telegraphic address is " Supermarine, Fstrand, London." e are also informed that Mr. H. Leigh Mossley, formerly the board of directors, and London representative, has longer any connection with the Supermarine Aviation >rks, Ltd. A.F. Flying Accidents THE Air Ministry regrets to announce that as a result of an accident at Calshot to a Fairey III.D., of the Royal Air Force Base, Calshot, on February"26, 1926, Flight-Lieut. Geoffrey William Hemming, the pilot of the aircraft, and Flying Officer Robert Collins were seriously injured. Flight- Lieut. Hemming died of his injuries shortly afterwards, and Flying Officer Collins died in hospital on February 28. As a result of an accident at Karachi, India, to a Bristol Fighter of the Aircraft Depot, Karachi, on March 5, Plying Officer Camille Percy Maurice Benjamin Caillard, the pilot of the aircraft, was "killed, and No. 111099 L.A.C. Andrew Barron, was seriously injured and died shortly afterwards. 149
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
