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Aviation History
1949
1949 - 1611.PDF
FLIGHT, 22 September 1949 375 SLOWINC-UP PROGRESS New Dun lop Brake of High Efficiency WHEN one sees a modern multi-engined aircraft taking-off, the enormous power output required to acceleratethe machine from rest and into the air is made readily appreciable. Comparatively few people, on the other hand,seem to realize that very nearly the same amount of energy needs to be dissipated in bringing the aircraft to a standstillafter landing. Certainly, the use of full flaps and airscrews idling in fine pitch offer a certain amount of help in that theyprovide increased drag, but from the point of view of the brake designer this help is so small as to be virtually negligible. Another thing which makes the brake designer's problemmore acute is the continued demand for smaller wheels and tyres whilst, in contrast, touch-down speeds tend to rise. For-tunately, this latter quality is not progressive and it now seems as though landing speeds are rapidly approaching the upperlimit of acceptibility. Perhaps the two most difficult aspects of wheel-brake designare (i) the provision of a shoe, or pad, lining which will main- the initial development installation running was done on anAlbemarle (probably the last one remaining in active service) belonging to the Dunlop Experimental Flight Unit, whilst theother aircraft to be equipped are the Airspeed Ambassador and, most recently, the de Havilland Comet. In addition,there are, of course, plans to convert various established air- craft to the new brake aside from the development of brakesfor new types, and during a recent visit to the Aviation Division factory at Coventry we were, in point of fact, nbleto witness a test run on the inertia machine of one of the new brakes designed for a jet bomber. The Dunlop inertia testing machine is the largest of its kindin this country and, installed in an 8 ft-deep pit, comprises a 250 h.p. D.C. induction motor driving a shaft on which fly-wheels varying in weight from one to eight tons can be mounted to provide the requisite amount of kinetic energy.The wheel to be tested is mounted on the flywheel shaft be- neath an easily removable safety cage. For the test we wit- These views of the new brake show (right) the compact design and excellent ventilation qualities whilst the exploded view (left) makes the operating principle clearly understandable. tain its mechanical properties substantially unimpaired at veryhigh temperatures and pressures, and (ii) the adequate ventila- tion of the whole assembly so that the greatest possible areais presented for direct heat radiation to the air. Just how efficient a job can be done in meeting all the conflicting require-ments is to be seen in the new plate-type brakes developed by the Dunlop Aviation Division. The accompanying illustra-tions clearly show the structural-form of the design. Two concentric pairs of high-production copper rings, aninner and an outer, are respectively keyed to the inside dia- meter of the wheel rim and the outside diameter of the wheelhub. These rings, or plates, are given a hard-chrome surface- finish, and braking action is provided simply by squeezing therings between pads of an especially developed composition. The pads and actuating cylinder assemblies are mounted indiametric opposition at the ends of a torque plate which is bolted to a flange on the undercarriage axle and is, therefore,a stationary component. Each cylinder contains two pistons —the second provides duplication, as a safety measure, incommon with duplication throughout the whole of the brake operating system—these pistons being subjected to hydraulicpressure on their under-sides and the consequent movement transmitted by means of a draw-bar to a back-plate. The back-plate is faced with pressure pads bearing againstone pair of inner and outer rings, and spaced between these and their complementary pair of rings is another set of pressurepads; a further set of pressure pads between the torque plate and adjacent brake rings completes the assembly (which per-haps can best be likened to a double-decker sandwich with the pressure pads as the bread and the rings as the filling).Actuation of the brake is essentially simple in that the pressure pads are anchored to the torque plate which is bolted to theaxle, whilst the rings rotate with the wheel and then, when pressure is applied under the pistons, the pressure pads aresqueezed against the rings and the wheel thus brought to rest. So far the new brake has been fitted to three aircraft: all nessed, a 3^-ton flywheel was used, the kinetic energy storedin this when rotating at 880 r.p.m. being the somewhat con- siderable figure of 6,300,000 ft lb. The brake under test hasbeen designed to decelerate the aircraft at loft/sec/sec, repre- senting a time-to-rest of about 14 seconds. Converted intoheat units, 6.3 million ft lb of energy represents 8,100 B.Th.U. and the dissipation of this in 14 seconds, i.e., 578 B.Th.U./sec, is equivalent to the absorption of 818 h.p. The demonstration of such a test as this makes very clearthe magnitude of the job a modern brake has to do. Heat generation is far more rapid than could be obtained in eventhe most efficient furnace, for the brake rings are brought to a bright red heat in about five seconds and, although on thisparticular occasion the time-to-rest was 26 seconds, instead of the normal 14, the pressure pads showed no signs of distressnor, despite the glowing brake rings, was there any sign of flame. It was a singularly convincing demonstration of theefficiency of what the manufacturers quietly and confidently believe to be the most advanced design of aircraft wheel brakevet devised. FORTHCOMING EVENTS Sep:. 24. Helicopter Association : "Helicopter Economics," L. S Wigdortchik, A.F.R.Ae.S. Evening : Annual Dinner. R.N. Air Station Yeovilton : Air Display. R.Ae.S. (Weybridge) : "Do Scientists Know Anything >" C. G. Grey. British Interplanetary Society : Conversazione. R.Ae.S. (Luton) : Film Show. R.Ae.S. ; " Design Analysis Methods in Research Division o! Bureau of Aeronautics, U.S.N. Department," I. Driggs A.E., F.I.Ae.S., F.R.Ae.S. R.Ae.S. Graduates ; " The Time Scale in Aeronautical Engineer- ing," Sir John S. Buchanan. College! of Automobile and Aeronautical Engineering ; Dance. R.Ae.S. Section Lecture ; " Flutter Problems " E. G. Broadbent, M.A., F.R.Ae.S. Oct. 19. R.Ae.S. (Reading): "Atomic Energy," A. G. Salmon, B.Sc, A.lnst.P. Sept. Sept. Oct. Oct. Oct. Oct. Oct. Oct. 24. 28. 1. 5. 6. 13. 14. 18.
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