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Aviation History
1931
1931 - 1082.PDF
FLIGHT, OCTOBER 9, 1931 Report, are now bearing fruit. A single sleeve-valve petrolengine has already been constructed to aircraft engine scantlings, and the results of preliminary tests hold outgood promise that this first of its type may lead the way to an important new line of development. It has been known for some time that multi-cylinderengines consume far more fuel than would be expected from experiments on single cylinders, and that this is dueto the uneven distribution of the mixture of fuel and air to the various cylinders. This uneven distribution is nowalmost accepted as inevitable in practice, in spite of many empirical experiments which have been made to improvethe distribution of particular engines. The Committee be- lieve, however, that the whole subject has never beenthoroughly attacked in the light of existing knowledge, and a Panel has therefore been appointed to go into thequestion and review, with the aid of the industry, the present position regarding carburation and air intakeproblems, and to make recommendations as to the most promising lines of investigation. The behaviour of lubricating oils in service is anothermatter of first importance. The life of many aircraft engines before overhaul mainly depends on the length oftime that piston rings and valve stems remain perfectly free from gum or hard carbon produced by the oxidationof lubricating oil. There are various indications that a further scientific inquiry will reveal methods either ofinhibiting the formation of gum in lubricating oils or avoiding its bad effects by simple methods. Another problem in connection with lubricating oils isthat it has hitherto been found extremely difficult to de- vise physical and chemical tests which will form a realguide to the qualities of an oil for use in aircraft engines. The Committee have had evidence that the present speci-fications do not meet practical needs. A Panel has there- fore been set up to inquire into these matters in consulta-tion with the industry. Spinning of AeroplanesAn outstanding problem bearing on safety relates to the spinning of aeroplanes. This is receiving the full atten-tion of the Committee, and four lines of research are proceeding. The full-scale experiments have continued, and a de-tailed report is expected shortly on trials of the Bristol Fighter under a great variety of conditions of flight.In the wind tunnel, models with a fuselage deepened near the tail and with different positions of the tailplaneunit have been tested to find out the characteristics that assist in bringing aircraft, otherwise dangerous, out of aprolonged spin. Certain modifications have been suggested which are intended to reduce the wash from the tailplaneon the rudder during a flat spin, and these will be shortly tried out on an aeroplane. The model tests on the Fairey III.F seaplane have beencompleted at the N.P.L. The floats have a marked effect, and it would appear that if a landplane does not comeout rapidly from a spin, then when the same type is fitted with floats, its behaviour should be carefully studied beforeit is flown in prolonged spins. Full-scale spinning experi- ments on seaplanes are proceeding.The fourth method of experiment has been the dropping tests on light balsa wood models in the R.A.E. BalloonShed. These have been successful in developing a good technique for such free flight experiments, using a cinemato record the whole motion in the air, and in confirming the conclusions reached from model experiments ondeepened body and a displaced tailplane carried out at the N.P.L. Owing to the success of the method, sug-gestions have been put forward for a more effective mea^s of experiment, using a vertical upward airstream of abc'i-'12 ft. diameter, in which the models can continue spin- ning for some time without appreciable change in heightSmall-scale experiments on this novel idea have proved successful, and, as this type of experiment has obviousadvantages over the dropping method, the construction of the apparatus for producing a vertical upward airstreamof large diameter has been put in hand. Load Factors The strength of an aeroplane has an obvious bearingon its safety. The Load Factors Sub-Committee were appointed to examine generally the assessment of loadfactors for modern aircraft and to pay special attention to the question of the stresses that might be produced byhigh accelerations. At one of their meetings the Sub- Committee had the advantage of the presence of SirThomas Lewis to discuss physiological problems. It appears that, if a pilot experiences an acceleration of5 g. or over, he is liable temporarily to lose his physical senses, particularly that of sight. An acceleration of thisorder may be experienced in a rapid pull-out from a dive or in very tight turns such as occur during races for theSchneider Trophy. Some discomfort is also experienced at lower accelerations if they persist for an appreciable lengthof time. The present load-factor scheme allows for an accelera-tion of 7-8g under the worst conditions of flight, and the Sub-Committee have not felt it necessary to recommendanv increase of the load factor for the acrobatic type of aeroplane, either service or civil. In fact, the generalscheme at present in use appears to be satisfactory, with the exception of the conditions for inverted flight. Regard-ing this, the Committee have proposed modifications in the methods of calculating for airworthiness purposes thestresses imposed on the acrobatic aeroplane in inverted flight. To ensure a satisfactory application of the calcu-lations for airworthiness for this type of flight, certain wind-tunnel data have been obtained on a number of wingsections. This information has been published as R. & M. 1383. For civil aeroplanes not in the acrobatic class, it hasbeen felt that the terminal nose dive condition should now be replaced by other conditions more nearly approachingthose met with in flight. The original condition, though shown by considerable war experience to be safe, wasarbitrary and did not in any way represent modern civil use. The proposed new conditions are given in detail ina supplement to this report. There is still a lack of knowledge of the accelerationsexperienced, both by military and civil aircraft, under all conditions of flight, and, with the aid of accelerometers,it is hoped gradually to collect information on this subject from which the airworthiness conditions may be moreaccurately laid down. It is also desirable, as the enquiry into the accident at Meopham has shown, to have informa-tion on the amount of turbulence and the magnitude and sharpness of the boundaries of up and down currents inthe atmosphere. A special Panel is dealing with these questions. (To be concluded.) <3> <$> PRESENT PRACTICE IN AERIAL SURVEY PEAKING before the Society of Engineers at Burling-ton House, W.I, on Monday, October 5, Major C. K. Cochran-Patrick, D.S.O., told his audience,in clear and concise terms, a very great deal of the " how and why " of aerial survey. He described some of the difficulties which are metwith when making an aerial survey of a certain territory, but compared them very favourably indeed with the diffi-culties incurred in making a survey of the same, area from the ground. The processes necessary before the photographs takencould be made into maps were explained at some length, and the use of both oblique and vertical photographs forthis purpose for maps of such widely differing scales as 1/250,000 and 1/1,000 was further elucidated with anumber of lantern slides. As an example of the work necessary, many slides of Northern Rhodesia were shown,and the whole method, starting from the taking of a series of vertical photographs along lines running E. to Vv.across the area, clearly shown. The co-ordination, by stereoscopic means, of the subsequent oblique views, whichwere taken on lines running N. and S., was then explained, and so on down to the final plotting of the map^themselves. The methods by which accuracy is obtained when mapsof large scale from vertical photographs are made, was the next subject of discourse, and the lecture wound upwith a number of very interesting slides showing the many other uses, such as archaeological, forestry and purfengineering projects, to which aerial photography may be put. The lecturer did a great deal to dispel the ider.that aerial survey was an inexact science, and we expect that increasing interest will be shown, by all engineerswho require surveys, in the extent to which the Aircr.iit Operating Co., of New Square, Lincoln's Inn, can solvetheir problems. 1012
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