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Aviation History
1944
1944 - 0354.PDF
184 FLIGHT FEBRUARY 17TH, 1944 CORRESPONDENCE until amplified by some electronic apparatus which must exist at the site where it is intended to receive the " signal." Now, a fair or average amplifier will give an output of, say, about 20 watts for a weight of roughly 20 lb.; also 746 watts = 1 h.p. Thus we should need an output of 1,641,200 watts to equal the power developed by the "Sabre" engine, i.e., 1,641.2 kilowatts. I believe 1 am correct in stating that the total radio power transmitting stations in this country generate 5,000 kilowatts, and so, according to my admittedly Heath Robinson analysis, we should need an aircraft with a wing area about the size of Surrey, and even then our radio set would not generate enough power to move it. I would like to add that I obtained most of this information from your sister journal. Wireless World, to which I am also a regular subscriber F. WRIGHT. Present Known Principles Not Applicable HESITANT as one is to-day to use the word '' impossible '' when discussing future invention, I think one may say that none of the present known physical principles are applic able to the problem of effective power transmission by radio. Even foreseeing, with "Typhoon," a beam system so per fected that all the transmitted power is put to full account by the consumer aircraft, full efficiency could only obtain if the supply were just equal to demand. This equality must assume either a constant consumer load or the pilot's control of station output. Neither condition is easy to imagine, particularly when several aircraft are routed on a common beam. Normal electrical traction is effective and efficient partly because of the negligible transmission losses and partly because the supply to the rails is never more than the demand. It may be said that here the fuel consumption of the power station is virtually linked to the control levers in the drivers' hands. I recall, with "Typhoon," the newspaper account of the hypothetical "magnetic currents" adduced by an American experimenter. Details were lacking, but it would appear that the electrolysis encountered at the poles of a magnet, immersed in acidulated water, might well be ascribable to an electric current resulting from normal electro-magentic induction. The need of an intense magnetic flux is quoted, and it may well be that a sufficient movement of the electrolyte, due to bubble formation and other causes, would occur and would produce a "cutting of lines of force" with a generation of current. The necessary closed circuit would be provided by the iron core of the magnetic system and the electrolyte itself. It would be interesting to know the result of interrupting this circuit by an air-gap small enough to retain the high flux density. In my own view (and "Typhoon" does invite opinion) the present practice of carrying the "fuel" on the aircraft will continue for a long time yet with further progress in the design of the prime mover and the means for converting its power to useful thrust. The recently publicised success of jet propulsion masks an historical and logical step in this direction both by the elimina tion erf reciprocating parts of the normal I.C. engine and by the elimination of an airscrew. It has also led to a widening of the range of useful fuels. Aircraft have never really been other than jet-propelled, and we witness now a potential substitute for the airscrew which was fast approaching the limits of its usefulness. FRANK A. GOODLIFFE. (Director, Science Films, Ltd.) From Lord Ventry. When the Airship Scores TF I may, I would like to add a little to Major Robertson's -*- most interesting article in Flight of February 3rd. The pilots of the raiding airships of the last war liked clouds to escape into, and many a Zeppelin unfortunately escaped from our aircraft in this manner. Again, in October, 1918, the Italian Army airships were going aloft under such visibility that H/A were grounded, and yet managed to make useful raids on German communications. The same is true of to-day, for the U.S. Naval airships are often able to go out on anti-submarine operations when, owing to bad weather conditions, the H/A machines are not able to go out. Perhaps I might also be allowed to blow our own L/A trumpet just once! H.M.A. Delta, piloted by the late Major E. M. Maitland—as he was then—and afterwards by Captain C. M. Waterlow, later killed as a Wing. Cmdre., R.N.A.S., went aloft in the Army manoeuvres of 1913 when ths clouds were about 500 feet, and mist stopped the H/A from operating. Mr. Churchill was taken for a flight in No. 3 command by the late Wing. Cmdre. N. F. Osborn, R.N., when the fog was so thick at Farnborough that it was hardly possible to see the length of the ship, and yet she arrived on time. VENTRY. CIVIL AVIATION Room for the Competitive Spirit W ITHIN American aeronautical circles it is confidently assumed that post-war civil aviation will continue to run on a private enterprise basis, and, in comparison with our own hazy conception of a Government-controlled organisation, their outlook is a happy one. It is my candid opinion that competition is essential for the continued progress of civil aviation. One has only to look at the slow rate of development of combines like the British rail ways, which has been eclipsed time and time again by the revolutionary strides of the airline companies, to appreciate that accumulative control can, and usually does, have a marked bearing of a detrimental character upon large con cerns. There is not the same fighting spirit for business supremacy and expansion, since they have the tendency to be independent. It does not necessarily imply that certain Government ser vices may not be required in order to benefit sections of the British Empire, or for various reasons of State, due to receipts not being able to balance expenditure. But, on the whole, the post-war civil aviation reconstruction programme should T0t drawn up without delay by a special committee representing parties interested in airline operations, and an earnest en deavour made to establish some worth-while details on which to base future developments. ERIC LORRAINE ADLEM. THEORY OF FLIGHT Up and Down Wind J" REFF^R again to the subject of optimum gliding speeds, in -*• case no one else has by the time this reaches you given the simple explanation which seems to be required. If an aircraft is gliding upwind its resultant path over the ground is the difference between the distance flown through the air and the distance the air as a whole was moving over the ground during the time of the aircraft's flight. The latter distance depends, for a given wind velocity, solely on the time of flight. In gliding downwind- the resultant path over the ground is the sum of the two distances. It is therefore clear that anything which tends to reduce the time of flight without affecting gliding angle (and therefore distance flown through the air) is beneficial in a glide upwind, and anything which tends to increase the time of flight is beneficial in a downwind glide. Therefore, as a correspondent has already stated, hang on to everything you have got in gliding upwind and lighten ship when gliding downwind. Secondly, there is the question of departing from the SQJJJI which gives the best gliding angle with the particular lop^lP board. If an aircraft gliding upwind increases its speed aoove the optimum it may, for example, get down ten minutes earlier but lose five miles on the glide. But if the wind velocity was 30 m.p.h. it will have saved five miles of wind drift, and in a higher wind it would have saved more than it lost. There must therefore be a certain wind velocity which justifies a given increase in speed, and it follows that there must be a certain optimum speed for any given wind velocity. The same argu ment can be applied conversely to downwind flight; useful decrease of speed being limited naturally by the rapid change of characteristics around the stall. There is in fact only one condition of wind in which optimum speed for ground distance covered coincides with optimum speed for gliding angle, namely, a calm (and possibly also in true cross-wind flight, but this is rather complicated). It would be most interesting if an expert with the necessary information would produce a graph for any particular aircraft showing optimum gliding speeds for ground covered, plotted against wind velocity (head and tail winds), with speeds for best gliding angle and minimum rate of sink also shown. It would also be interesting to know the mathematical result of jettisoning 100 lb of equipment from any particular type of aircraft gliding at the resulting optimum speed with and against a wind of, say, 30 m.p.h j The figures are likely to be small for high-speed aircrart, but there may be all the difference in the world in a couple of feet for an aircraft in distress. R. E. PEARS, Capt., R. Signals.
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