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Aviation History
1957
1957 - 0152.PDF
20O aooo S5OO 5000 4.5OO 4,(300 3.500 3.000 2.5OO 2,000 1,500 1P00 500 AIRCRAFT _^INDUSTRY ^^ / y N.LJ-. / /J 1 154 FLIGHT, 1 February 1957 1946 1948 1950 1952 1954 1956 1946 1948 1950 1952 1954 1956 An indication of the scale of Dutch aeronautical effort is provided by these curves taken from Prof, van der Maas' paper. On the left, aeronautical-research expenditure; right, personnel available to .:-; ._• .. the Dutch aircraft industry and the N.L.L. A briefly recorded last week, on January 24 Professor Dr.Ir.H. J. van der Maas, F.R.Ae.S., of the department of aero-nautical engineering at the Technological University of Delft, was due to read a paper on Aeronautical Research in theNetherlands before the Royal Aeronautical Society. The author prefaced his account with the reminder that, after World War 2,his country had virtually to rebuild an aviation industry from scratch, and also had a considerable amount of research leeway tocatch up. After ten years the rebuilding stage was more or less complete.Curves of annual governmental expenditure on aeronautical research and man-power in the Dutch aircraft industry [publishedhere] gave an idea of the overall magnitude of activity, and on the latter graph was plotted the personnel strength of the NationalLuchtvaart Laboratorium, i.e., national aeronautical research institute. The total vote for current expansion of N.L.L. facilitieswas approximately £2.1m. At present the N.L.L. employed 65 graduates, 105 other technical staff, 65 workshop personnel and65 administrative and internal-service workers. For the past 15 years the backbone of N.L.L. aerodynamicshad been a pair of low-speed tunnels, one with a 5ft-square work- ing section running at up to 130ft/sec and the other 7ft by 10ftwith a maximum speed of 260ft/sec. The bulk of the latter tunnel's time in recent years had been devoted to research for the FokkerF.27 Friendship These facilities were now being supplemented by high-speed tunnels. Of the new tunnels the major installation was a transonic (origin-ally designed as subsonic) variable-pressure tunnel with a Mach range up to 1.3, a working section 5ft by 7ft and a 20,000 h.p. drive.It was hoped to start calibration runs on this tunnel in the spring of this year. A smaller (1,200 h.p.) tunnel, originally planned as apilot design for the 5ft by 7ft unit and with a test section 1.4ft by 1.8ft, was completed as a subsonic facility in 1955. Earlier, in1947, a small l|in-square supersonic tunnel was commissioned; it had reached Mach numbers up to 6 and had been instrumental inthe development of the Erdmann interferometer. A new project, said Prof, van de Maas, provided for the con-struction of a pair of supersonic tunnels. One would have a test section 5ft wide and a height changing from 4ft at Mach 1.4 to 3ftat Mach 4. The second would be a much smaller unit, capable of reaching Mach 6 with a 12in by 7in section, and fed from themain tunnel's 20,000 cu ft storage for runs of several minutes. The N.N.L.'s tunnel equipment is summarized in the table. The lecturer went on todiscuss problems of flutter, and noted in particular theinvestigations completed on the rotor of the Kolibrie ram-jet tip-drive helicopter. These led to the development of atheory considering flow about a cylinder co-axial with therotor. Unrolling the cylinder generated a train of aerofoilsand the corresponding two- dimensional flow was evalu-ated. The programme had established reduced rotor-blade damping which might be an important factor in con-sidering blade vibration caused by the varying down-wash along the disc circum- ference. Other investigationsfor the Kolibrie had led to the self-adjusting blade systemnow employed, with greatly Development , in the Netherlands Points from an R.Ae.S. Lecture enhanced stability characteristics, and had also determined thebehaviour of the tip-mounted ramjets. Succeeding sections of Prof, van der Maas' paper dealt with theextensive Dutch investigation into three-dimensional laminar boundary layers, gust loads and stability derivatives. The authorthen turned to actual flight testing and pointed out that, largely as a result of the work done by the Centre d'Essais en Vol atBretigny, it was now practicable to measure performance in non- steady flight. The N.L.L. had evolved special instrumentation—a photo-recording pendulum inclinometer and a normal acceler- ometer, a vane-type angle-of-attack indicator and a longitudinalaccelerometer, the latter pair both with electric servo or synchro indication—and had conducted non-steady tests with an Si204. Prototype testing had required further development of special-ized instruments and techniques. Investigation of the forces and moments on the wing of the Fokker S.14 at transonic speeds wasundertaken with 49 equally spaced orifices around a representative wing section coupled to potentiometer-type transducers. Very extensive research had also been undertaken by the N.L.L.into structure and material testing. In particular a great deal had been done in increasing fundamental knowledge of fatigue inriveted and Redux-bonded structures, and in the investigation of cumulative damage and crack-propagation. Special programmesof testing concerned the static and fatigue properties of com- ponents made from glass-fibre-reinforced plastics, and ultrasonictesting (which might be applicable to bonded joints). In conclusion, Prof, van der Maas outlined the work done bythe Technical University at Delft. Extensive in-flight readings had been taken during basic boundary-layer research, duringwhich a method had been evolved for estimating the transition point without disturbing the flow around the wing. The authordescribed the method adopted in some detail. The principal Delft wind tunnel was a 4ft by 6ft low-turbulencefacility with a maximum speed of 400ft/sec. It had been used, inter alia, for an investigation into the problems of boundary-layer control by suction. To obtain experience in this field a simple two-dimensional model was built, which could be provided withslots at one per cent and 40 per cent chord, or a porous surface from 30 per cent chord to the trailing edge. It was in the courseof investigations with this model that the method for predicting the boundary-layer transition region was determined. Delft employed an Auster J.5B Autocar for general flightresearch, and the author produced the results from a series of measurements of stick-fixed, constant-power position of e.g. forneutral stability. Two methods were employed, derived from the moment curve and the slopes of the trim curves. Also availableto the University was a structural-test laboratory, and a small blow-down supersonic tunnel was being completed. For generalflight-dynamics research a modest analogue computor had been designed and built. One of its particular features was the low-drift of its amplifiers, permitting computations of relatively long duration on a true time-scale. . . . Working section ,. size ,, length R (chord of A.R. = 5) Max. ft/sec or Mach number Turbulence level Available h.p. Pressure (ata): settling chamber Speed control Date WIND TUNNELS OF THE N.L.L. In Operation Low-speed Closed 7ft x 10ft 13ft 2.2 x 10« 260 3-4 per cent 600 Word Leonard 1940 Small low-speed Open 5ft x 5ft 7ft 0.5 x 106 130 4-5 per cent 50 Ward Leonard 1940 Small Supersonic Closed 1^in x 1^in 1 Jin M = 0.5to6 25 1-170 1948 Pilot tunnel Closed 1.4ft x 1.8ft 3ft 0.8x105 Max.M = 1.0(empty work- ing section) Low (8 screens) 1200 1 Variable pitch and frequency 1954 Building Transonic Transonic5ft x 7ft 28ft Max. M = 1.3 Low (25 screens) 20,000 Variable:1/8-4 Variable pitch and frequency Expected to be ready for opera-tion: 1957 In^Design Stage Supersonic (1) Free jet 10-7in x 12in 1ft M=1.4 to6 Low (5 screens) 6,200 Max. 40 Flexible nc Supersonic (2) Free jet 4-3ft x 5ft 5ft M =1.4 to 4 6,200 Max. 14 Tiles Expected to be ready for operation: 1958
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