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Aviation History
1918
1918 - 1091.PDF
SEPTEMBER 26, 1918. employed, as far as possible, for specially urgent work. The Committee are glad to note also that many firms in this country have recognised the value of experiments on models in relation to design, and have constructed wind channels for their own use ; a number of requests for details of the National Physical Laboratory channels have been responded to within the past year. Equipment for Experimental Work at the National Physical Laboratory.—As above indicated, proposals for additions to the buildings and equipment for experimental work at the National Physical Laboratory have recently been made; — the construction of these is in hand, and will, it is hoped, be completed at an early date. Two new channels are to be provided, one similar to the existing 7-ft. channels and one of special type. The design which has been adopted for the latter has been completely worked out by experiments on model channels, and while based on the same principle as was applied in designing the earlier channels, exhibits some interesting modifications in detail, which may be found generally valuable in future in channel construction. The buildings to be provided will contain also additional work- shop and office accommodation. Modifications of the existing equipment made during the past year embody the results of experience as regards the most accurate and the most expeditious methods of con- ducting the experiments. New methods have been perfected for measuring the drag on models in cases where this is very small and where consequently the highest accuracy is neces- sary if the results are to be of value, especially when a con- siderable change of scale is involved in passing from the model to the full-sized aircraft. Special apparatus has been designed for vertical force measurements, and for experiments on propellers and propeller interference. New apparatus has been constructed for the determination of rotary derivatives. Improvements have been introduced in existing methods of measurement, and every effort has been made to secure ease and rapidity of working, consistently with the maintenance of the requisite accuracy. In the Engineering Section special ., apparatus has been constructed for dealing with particular problems, among which may be mentioned the apparatus for impact tests at high temperatures of specimens of alu- minium alloys. Experimental Work in Aerodynamics.—In April, 1917, a Sub-Committee was appointed to consider the relation between full scale and model results, and to examine into certain special questions which appeared to present difficulty. This Sub-Committee held r 1 meetings and received 31 special reports. In the course of their investigations they found it necessary to arrange for a considerable amount of experi- mental work both at the National Physical Laboratory and at the Royal Aircraft Establishment, while valuable assistance was also derived from reports made of the performance tests at other air stations. The information available was not sufficient to enable general conclusions to be reached as to scale effect, for which investigation extending over a long period will doubtless be necessary, but the results brought out were of great interest, and to a large extent cleared up existing difficulties. The Sub-Committee reported in Decem- ber, 1917, and their report will shortly be ready for issue among the confidential papers of the Advisory Committee circulated by the Technical Department (T. 5). Following a recommendation made by this Sub-Committee, the Aero- dynamics Sub-Committee, to which reference has already been made, was appointed in the same month and now sits regularly for the discussion of aerodynamics problems of special importance which arise in relation to aircraft. This Sub-Committee includes among its members representatives of the Technical Department and of the Services as well as of the National Physical Laboratory and the Royal Air- craft Establishment. Reports will be submitted to them of experimental work carried out at Service Air Stations, and arrangements have been made for securing the attendance at meetings of the officers in charge of such experimental work, in order that the Sub-Committee may have the fullest possible information on the matters dealt with. A large amount of interesting and valuable work has been carried out during the year both at the National Physical Laboratory and at the Royal Aircraft Establishment, but it is not now proposed to give any detailed summary of in- vestigations completed. The experiments have ranged over the whole field of practical aeronautics, including tests relating to aeroplanes, airships, kite balloons, propellers, radiators, wind screens for aircraft, aeroplane carrying ships, bomb dropping, pressure distribution, stability, &c. A considerable number of experiments have been made on models of complete aeroplanes, and the work done for the Scale Effect Sub-Committee included an analysis of the resistance of a complete model and comparison of the whole resistance with the sum of the resistances of the component parts. The investigations relating to propellers have been of special value and importance. The question of flight at high . altitudes has received attention. In existing circumstances it has not been possible to concentrate attention on general aerodynamical theory, but some consideration has necessarily been given to general questions arising in connection with the experimental work, and the study of eddy motion has been advanced. The Air Ministry has formed a special Committee to investigate certain questions relating to airscrew design. Dr. Stanton, the Superintendent of the Aerodynamics and Engineering Departments at the National Physical Laboratory, is a member of this Committee, and experiments to obtain information desired by the Committee will be carried out at the Laboratory. Strength of Construction.—Continued attention has been given to questions connected with strength of construction. Early in .the year a series of calculations was carried out for various enemy machines to investigate the factor of safety allowed in German design. It is of interest to note that the conclusion resulting from these calculations was that neither in performance nor in strength were the German machines equal to the British. Other things remaining the same, an increase in the factor of safety necessarily involves some reduction in performance and manoeuvring power, which, not less than strength, are of vital importance for safety in air fighting ; it is clear, however, that the strength factor adopted in British design, which has in earlier years been the subject of much careful consideration by the Committee, has been wisely maintained at a high level. Specific questions relating to strength have arisen, chiefly in connection with engines, and propellers in relation to engines, and have been dealt with by the Engine Sub-Committee. Valuable papers relating to methods of stress calculation and measurement have been received from both the National Physical Laboratory and the Royal Aircraft Establishment. Engines.—The Engine Sub-Committee has held 29 meetings during the year 1917-18, and has received 131 reports and memoranda on various matters. The work has been of very varied character. The advice of the Committee was invited by the Air Board on several occasions with regard to the engine programme, and the selection of engines for future development. In order to arrive at a decision on questions submitted to them the Sub-Committee has visited works and inspected engines under test conditions. Among other matters which have been before them for discussion may be mentioned the methods of engine testing, engine design for high altitudes, the causes of failure of crankshafts and other parts, gearing, methods of cooling, methods of preventing freezing at high altitudes in water-cooled engines, special fuels, &c. Considerable attention has been given to matters connected with magnetos and ignition, and a large amount of experimental work in this direction has been carried out at the National Physical Laboratory and at the Royal Aircraft Establishment. At the latter also numerous in- vestigations have been carried out for the Committee on engines and engine cylinders, which are referred to more particularly in the section ol this report which deals with the experimental work done at the Establishment. A series of reports giving the results of experimental investigations undertaken for the Sub-Committee has been prepared for confidential issue, as explained. The Sub-Committee desires to acknowledge the assistance which has been given it on many occasions, in the considera- tion of special matters, by the technical representatives of manufacturing firms who have attended its meetings and have communicated valuable papers and reports on questions under discussion. Light Alloys.—The Light Alloys Sub-Committee was formed in February. 1917. Since that date it has held 18 meetings and has received 93 reports and communications. Experi- mental work has been carried out for the Sub-Committee at the National Physical Laboratory, the Royal Aircraft Establishment, Birmingham University, and Manchester University, as well as by the Aeronautical Inspection Directorate and at works foundries. The result has been to secure, and to disseminate, a large amount of valuable information with regard to both cast and wrought aluminium alloys suitable for use in the manufacture of engines and aircraft parts. Experiments have been made with a number of new alloys, and every effort has been made to accumulate systematic data with regard to alloys in common use, as well as to the newer alloys which appear to exhibit valuable characteristics. The volume of work on light alloys dealt with at the National Physical Laboratory has been very large, and it has been necessary to ask for additional staff to enable it to IO9I
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