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Aviation History
1954
1954 - 1375.PDF
604 FLIGHT Artist's impression of the whirling arm at Teddington. The"claw" which carries the model under test is mounted on a 30ft arm on the central rotating assembly. SCIENCE ON SHOW Whirling Arms and Aching Feet) at the N.P.L. Open Day THE notice stated simply "stand clear when the hooter sounds." The hooter sounded and obediently we stood clear. In the centre of the low, wide, circular building was a cylindrical wooden wall reminiscent of the "Rotor" (Battersea Fun Fair type), inside which a large framework of metal girders began slowly to rotate. Only the absence of strident organ music over a distorting loudspeaker—and the fact that it was an arrowhead wing which whistled round a few feet from the spectators' faces—indicated that this was not, in fact, a fairground attraction. It was the National Physical Laboratory's whirling arm, whirling for the first of innumerable times on Friday last, the Laboratory's open day. At Teddington, there was litde in the atmosphere to show that the occasion was at all different from any number of similar open days held annually by other establishments, colleges or organiza tions. Only in the programme of exhibits—"of scientific work and apparatus"—was the incredibly wide scope of the establishment's work apparent. Certainly, the entire range of physics, electricity, electronics, mathematics, aerodynamics, metrology, metallurgy, light, etc., could not be observed first-hand by any one person in one day alone, for there was a total of 207 separate exhibits. What follows, then, is simply an account of the impres sions of one student of aeronautical science whose duty it was to report mainly on the aerodynamic aspects of N.P.L.'s work. As mentioned, the Laboratory's famed whirl ing arm was our starting point, Flight artist R. E. Poulton and the writer being the day's first customers for Dr. A. S. Halliday, B.Sc, Ph.D., who is in charge of its operation. The determina tion of rotary derivatives LR, NR and NQ (rolling SODIVM LIQHT SOURCE BEHIND SLOT IN SCREEN. FLOW INDICATED BV ALUMINIUM PARTICLES SWEPT WINC- SECTION The water tunnel, in which the aluminium-particle tech nique is being used for the study of low-speed flow. and yawing moments due to yaw, and pitching moment due to pitch) have formed the major part of the work carried out. Some type of whirling arm—this installation is N.P.L.'s third—has been found essential for the study of stability, since this type of accelerated motion cannot be reproduced in a wind tunnel. An idea of die general arrangement of the arm may be obtained from the heading sketch on this page. The radius of the model's path is 30ft, and the maximum rotational speed is 31.8 r.p.m., giving the model a linear speed of lOOft/sec, and subjecting it to a radial acceleration of 10.35g. The model is mounted between two vertical aerofoil vanes, in what is known as the "claw," counter-weights being fitted at the opposite end of the arm. At the time of our visit, the series of measurements of stability derivatives for the arrowhead swept wing had not been com menced. During the last year, pitching moment measurements have been made on the whirling arm for a rectangular wing, and have compared well with lifting surface theory. Attempts have been made to obtain two-dimensional flow conditions, using end- plates, so that the pressure distribution measured on the arm can be used to check camber derivatives. As we moved on from the whirling-arm building, trade was brisk. The hooter hooted, the arm whirled, and spectating rows of heads clicked regularly, Wimbledon-fashion, from side to side. Nearby, a closed-circuit water tunnel was in use for the visualization of flow at low speeds. A darkened room with a tank apparently containing a golden-rain firework display turned out to be a demonstration of one method of visualizing flow. Fine particles of aluminium had been added to the water; a semi-span swept-wing model was mounted in the working section; and a movable narrow slit of light was projected through the glass walls of the section to illuminate as a bright trace the flow across and behind any particular chordwise section of the wing. It has been found that certain flow phenomena, such as vortex cores and separated regions, can be located by the introduction into the water flow of a stream of air (through a small movable tube) just ahead of the leading edge. The air tends to move into regions of low pressure, giving a clear indication of the extent of vortices and separated flow. A third method used is to study the movement of a film of oil over the surface of a body. Each of the three methods is well suited to photographic recording. A stranger to N.P.L. with a misguided sense of humour, if asked to guess what the 7ft low-turbulence tunnel contained, might, we imagine, conceivably answer "the Runcorn-Widnes suspension bridge." And we have to record that this would be absolutely correct. At least, a l/32nd scale model of the proposed Runcorn- Widnes suspension bridge is in there, being subjected at present to aerodynamic oscillation tests—just one of many industrial applications of aerodynamic techniques described (we were told with quiet pride) in N.P.L. Notes on Applied Science, No. 2, price 3s 6d, H.M.S.O. Suitably impressed, we passed on. In the building housing the 13ft x 9ft tunnel, we came across two most interesting projects. One was the "porous body of
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