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PAGE FOURTEEN \ Helicopter Experiments May Provide Additional ~ Submarine Protection Lao By E. COLSTON SHEPHERD have often been con- sidered for convoy protection work submarines, Like the air- het bmarines in 0x a ter has the TL i 538 Ln 1 own disk ares, w 3 causing it to move, 10° ft. roll and 20 ft. in pitch. | Trials in still heavier wedther are to be made Ed Ir these trails succeed, the heli- copter can be considered as an alternative to the light aircraft has About the same duration as an ordinary aeroplane but it can- not cover the same area because of its lower speed (85 mph. as compared with 300 m.p.h.). In its present form it carries a& smaller load than the orthodox aeroplane and it has a shorter flying life be- tween overhauls, It also requires more replacements, 'particularly for allowing the blades to flap slightly as they rotate, for altering the angle at which they meet the air and for tilting the whole rotor head forward or back. Stil hy Process Until recently, the rotor head had to be stripped and examined for wear at the end of about 100 hours of flying. The périod has now been increased to 300 hours but the pro- cess still remains a lengthy one, for in one type of helicopter, there are 30 working parts in the rotor head. Improvement in the rotor is most desirable if thé helicopter is to take its place among military and naval aircraft on specialist tasks. 'The short working life of the rotor head is explained in the main by the vibration transmitted through the long flapping wings. Simple as the whirling wings may seem, théy do in fact perferm - some strange manoeuvres. They go fast- ér as they retreat than they do as théy come forward. They undulate as they make their circuit, rising as they advance and drooping a little 45 they Yetréat. . To sets Of -hinges are required to allow for this hurrying down wind and this flapping in the course of the circuit, and through those hinges a good deal of vibra- tion is communicated to the bear- ings and also to the contrpl mé- chanisms which twist the blades at their roots and tilt the rotor head to determine the amount of forward speed. This last motion permits the rotor head to be used to generate thrust as well as lift. Among thé sources of vibration is the large differénce in the speed at which thé blade tip will, and the base of thé blade pass through the alr. These blades are wings and at slow turning speeds, the root may be stalled while the outer part con- tinués to develop lift. There is then the inevitable conflict be- | tween the two parts and vibration | develops. At fast turning speeds, | thé trouble can be reversed. The , tips, moving at the speed of sound, can run into shock waves ond be- have erratically so that more vibra- tion is- communicated to the rotor head. These troubles are of special in- terest because of the work which | has been done by the Bristol Aero- | plane Company and is still being done at Bristol by the old heli- copter designer, Raoul Hafner, to improve the technique. The under- lying principlé is best understood by considering what happens to a slow-moving rotor. If the tip of the blade is moving at a speed of 300 mph. and thé helicopter is moving forward at 90 m.ph. the total speed of the air over the blade tips as they advance is 390 mph. but as the blade retreats, the air speed over the tip is only 310 mp.h. This is a difference of about 45 percent and stalling of the root as the blade retreats is like- ly. Raising the tip speed would reduce the difference. Suppose the tip speed is made 500 mph, and the forward speed 110 mph. then the total tip speed on the advance would be 610 m.p.h. and on the retreat 300 mph, The reduction in this case is only about 30 percent, and the rick of root stalling is lessened. Therefore the likelihood of serious vibration is reduced. Such high tip speeds have been, generally avoided by de- signers. Hafner satisfied himself that a tip speed of 615 m.p.h. could be used without meeting shock waves. A Bristol helicopter em- bodying this fast-turning rotor has been flown and is being further developed. It is most promising, because Hafner said that another benefit could be combined with it. He chose to make his fast-turning rotor a heavy rotor and so gave it sbme of the qualities of a fly- wheel capable of storing a certain amount of energy. This is invaluable, in the four or five seconds after an engine fails, for altering the angle of the blades so that they can be turned by the pressure of the air instead of by engine power and so continue to develop some lift and to pre- serve control. That 1s a critical period. If control is lost at en- gine failure a crash may result. The fly-wheel type of rotor gives a margin just about sufficient for the change-over. With it, in the Bris- tol model goes a much simplified form of rotor head. Gradually the helicopter is becoming a safer and more practical aeroplane, The Royal Navy's handling experiments should yield an operations! tech- nique in readiness for the improved helicopter. 2 Avon Jet Powers Canberra The Rolls-Royce Avon jet engine i. obviously a remarkable piece of engineering, furthermore, it is the power plant of an, at least, equally remarkable airplane--the English Electric Canberra bomber, says a British release. "The "Oanberra" (being tested in the U.S. after a flight from Brit- ain) is-now to be made at four of Britain's biggest aircraft factories --Handley Pages, Avros, Short and Harlands, and, of course, at its parent factory of the English Elec- tric Company at Preston, Lanca- shire. Engine Output The production of the Aven en- gine, obviously, has to keep pace with this three-fold expansion; so now we have the news that Avons are to be made at the Rolls for- mer "shadow" factory in Glasgow; at Bristols, and possibly at Napiers. Certain details of this jet--which is one of the most powerful in the' world--are still classified as secret. Other facts, however, are known. We can reveal, for instance, that on a "do-rated test," an early version of the engine registeréd 6,000 pounds of thrust, whieh, at 600 miles an hour is the equivalent of nearly 10,000 horse power. A Meteor fighter, fitted with Avons of unspecified power, climb- éd to 40,000 feet in under three minutes, and, furthermore, the said Meteor could only use the available power from the Avons when in a steép climb, To have opéned the throttles when flying straight and level would have brought the plane against the compressibility (or speed of sound) limits of the air- frame. Fitted in the two-enginéd Can- berra itself, the Avon has helped to : produce such a lively long- range, high-flying and load-carry- ing medium bomber, that men who know its secrets describe it as the most outstanding military airplane of the jet era. Lower Fuel Use One of the advantages the Avon offers is that it is an "axial flow" enigine--which means that it has a higher compression ratio, and therefore a lower fuel consumption than the centrifugal engines such as the Derwent, Ghost, Néne, and Goblin, now in such general use. The disadvantage of axial flow is thit several stages of compressipn are. needed, and therefore, many more compressor blades have to be made, and %1so that the éngine is sensitive to icing. These are engi- neering or production problems, and presumably had been ever- come or planned out before such bulk orders for the engine were placed. ; There is, however, one aspect of the Avon engine in particular, and of axial flow in general, which Should be stressed. It has nothing to do with bombers, or fighters, but is one of everyday civilian interest. It is simply that, with the help of such engines, the Comet jet air- liner could become a really long range airplane, capablé of flying the North Atlantic serviée without mid-air refuelling. . In other words, an "Avon" Comet would be able to tackle any of the main line long-haul routes of BO.AC. and halve journey times all over the world. I a mhappy to report that thére is, indeed, now to be such an air. puant, Sapphire Engine ) It is not yet 100 pércent certain that it will be an Avon Comet. The planning is that it will be, but that depends upon engine availability, with defence needs as the top pri- oriority. But even so, the héalthy state of the British jet industry is such that there are other "axials" to choose from. These include the new Armstrong Siddeley Sapphiré which, on test, has produced 7,200 pounds of thrust, and, as far 4s of- ficially released figures go, is the most powerful jet in the world. A long range Comet could com- plete Britain's battery of airliners for many years to come. Say De Havillands: "We have been examining such a develop- ment for a long time. The project- ed new plane will be complement- ary to the present Ghost-engined Comet, which is suitable for all but the longest routes, The Comet II would tackle those longer hops by virtue of reduced fuel consump- tion. It might be a bit faster than the Comet I--but not much." Crown Ends Evidence In Shotgun Slaying 8t. Thomas, March 8--(CP)--The Crown concluded its cise Wednes- day in the murder trial of Law. rence William Jones in the shot. gun slaying of his common-law wife, Mrs, Sarah Ann Evans. ; The final evidence was a' state- ment Jones had given to police after the slaying in their one- room cabin-trailer at nearby Yar- mouth Centre last Nov. 21. In the statement, Jones said he had no recollection of shooting Mrs. Evans and didn't realize she was shot until he found her body Some time later and placed it on & bed. The defence offered no evidence, FORCE LIMITED TO 4 MILLION Washington, March 8 -- (AP) -- The Senate voted Wednesday for a manpower limit of 4,000,000 on America's armed forces. 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