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Aviation History
1951
1951 - 1590.PDF
FLIGHT, 17 August 1951 203 THE DESIGN-STUDY ... q.1.2 Fuselage percentage structure weight; (WilW) per cent=ioox —+5.0, where <SF=fuselage surface area (Ref. 9). vAlternatively, per cent=336 x P +5.0, where a.u.w.P=payload required, pounds. 3.1.3 Empennage and controls weight: (WJW) per cent=ioo/tti, where zu=wing loading (simplified expression derived from Ref. 9). 3.1.4 Undercarriage structure weight: (WJW) per cent= 1.5 + 0.04 x v2, where v in ft/sec is the design vertical velocity, usually 8 to I2ft/sec. It must be emphasized in this connection that the nosewheel- type undercarriage need not necessarily be any heavier than a tailwheel installation, provided that the aircraft is designed for it from the beginning. (Ref. 1.) 3.1.5 Nacelle structure weight: (Wn/W7) per cent*= *°h where IT/b.h.p. is the take-off power loading. Having decided on certain constants, we can now express our structure weight in terms of the coefficients we have derived, and can thus draw curves of all-up weight versus aspect ratio and wing loading, or any other values made variable. These weight curves will form the minimum obtainable weight pattern. On the Other hand, the aerodynamic requirements listed above and discussed in detail hereafter will form the pattern of permissible maximum weight. The intersection of these two nests of curves will give us the ideal aircraft within the framework of the specification. Let us, there- fore, now turn to the aircraft dimensions required to meet the aerodynamic performance demands. 3.2 Computing wing area required for the demanded take-off distance to Soft: The following very simple expression (first suggested, I believe, by Mr. T. P. Wright) gives a good approximation: (/T-O) yd—iCx'.' *X ' * - where K—a constant depending onb.n.p. o TABLE II: MODERN CIVIL AIRCRAFT TAKE-OFF DISTANCES Aircraft 1. Rapide ... 1 Consul ... 3. Beech 18 4. Dove ... 5. Avro XIX 6. Prince ...7. Lodestar 8. DC-3 ... 9. Scandia... 10. Viking ... 11. Martin 202 12. Wayfarer 13. Convair 240 14. Bellatrix 15. Ambassador I , 16. Marathon 17. Northrop Pioneer, 18. Viscount 19. Languedoc161... 20. S. Marchetti SMS5 21. BoeingStratolinei 22. Lancastrian 23. York 24. DC-4 25. Tudor IV 16. Canadair 4 27. Hermes IV 28. DC-6 29. Breda Z308 ... 30. Constellation 649 31. Constellation 749 32. Stratocruiser 377 33. S.E. 2010 34. Constitution ... T-O wing load- inglb l 16.5 23.7 24.4 25.4 22.5 29.2 33.5 25.6 35.1 36.9 44.4 26.9 49.6 44.2 39.1 33.0 25.0 53.0 43.0 38.3 36.3 50.0 55.7 50.1 56.3 55.1 58.2 66.7 46.5 57.0 63.7 78.5 62.551.0 T-O powaiload- ingIb7 b.h.p. 13.9 9.4 9.45 12.5 12.4 10.2 8.4 11.5 9.8 9.4 9.5 11.8 9.6 10.25 8.712.5 10.0 10.7 11.0 11.251 9.9 10.8 12.4 11.5 11.4 9.75| 11.1 10.35 9.40 10.50 9.65 12.10 13 20 Flaptyp Split Split Split Plain Split Slot'd Fow- Split Slot'd Splitp'ble slot'd Split Fow- ler Slot'd Split Fow- • ler11.46|D'ble slot'd D'ble slot'd lot'd Slot'd Split Split Split ilot'd Split D'blelot'd Slot'd D'ble slot'd Split Fow- ler Fow- ler Fow- ler lot'd Fow- ler T-O to 50ft (ft) 1.535 1.440 1,650 2,370 2,100 1.836 1,700 2,000 1.935 2,550 1,565 2,310 2,980 2,640 2,440 1,170 3,090 2,870 3,000 2,950 3600 5,640 3,900 5.250 2,900 4,200 3,060 3,850 4,000 5.900 4,320 ICAO T-O 4,290 3,060 3,690 3,600 3,510 3,6904,250 5,575 3,900 4.840 4,000 5.500 5,000 5,830 4,600 4,200 5.200 5,380 2.23 2.15 2.39 Z492.5 2.06 2.01 2.26 1.9 2.46 1.42 2.43 2.19 2.59 1.97 1.36 1.94 2.08 2.37 X41 2.22 3.18 2.09 2.78 1.71 2.46 1.90 1.92 1.54 2.36 1.92 K ICAO 4.51 3A4 3.62 3.47 3.18 3.88 3.37 4.10 3.83 3.51 3.27 255 2.95 2.48 Z87 2.35 2.33 2.37 Remarks Small-span flap 0.75 span flap Full-span flap and spoiler ailerons Very small chord flap Large- span flap the type of flap to be used, and the take-off parameter. The I.C.A.O. take-off parameter, for example, requires the aircraft to be accelerated up to take-off safety speed, whereas the 1.2F3 parameter permits take-off and climb at 1.2 x stalling speed with flaps and undercarriage in the take-off configuration. The values of K have been evaluated as mean terms from Table 2, and are presented below in order to enable the wing area to be calculated if the all-up weight and take-off b.h.p. are known. TABLE 111: MEAN VALUES OF T-O para- meter 1.2V I.C.A.O. ... Engines 24 24 Split flap 2.42.65 3.93.3 TAKE-OFF DISTANCE CONSTANT, K Slottedflap 2.12.25 3.73.2 Double- slotted flap 1.81.85 3.62.7 Fowler flap 1.71.85 3.4Z3 Full-spanflap, double- slotted orFowler type 1.4 3J The importance of efficient flap design is exemplified by applying the above formula to a twin-engined aircraft where, by using a large-span Fowler or double-slotted flap, instead of a plain, split-type flap, the all-up weight of the aircraft can be increased by 31 per cent for the same take-off distance to 50ft. Alternatively, for the same weight, power and take-off distance, the wing area can be reduced to 60 per cent of the standard. A much better approximation to the take-off distance can,1 however, be obtained by the following formula, the so-called "mean speed" method. The total take-off distance consists of the ground run, transition distance and climbing distance to 50ft, all distances being expressed in feet. „ W Vj-oGround run j t= — x - -2 E (i — D) Where FT-O=take-off safety speed, ft/sec. T, lb,=thrust at mean speed_F= 11^2 x FT-o D, ft,=drag at mean speed V=ij\/2X Fr-o ( S ) = ground incidence CL=n x n x A for best ground run (Ref. 1). [i = ground friction coefficient, 0.03/0.10 Transition period run .?2=(FT-O> ft/sec). A transition time of one second has been assumed. Climbing distance to 50ft 53=50 x W T-D Where T=thrust at take-off safety speed (from airscrew thrust curve). D=drag at take-off safety speed t This method gives excellent results even when compared with the step-by-step integration method, the accuracy being, in fact, within 2 per cent for conventional aircraft. If the all-up weight variation with wing area can be approxi- mated, then the take-off distance to 50ft can be calculated and plotted with the wing area as a variable for different flap and airscrew arrangements. In this way, the wing area required for a specified take-off distance can be found. 3.3 Computing wing loading for a demanded landing distance from If the maximum landing distance from 50ft is included in the specification, the wing area determined from para. 3.2 should be checked against this requirement. This check can be done by either of the two methods given below. The first is simple, but is very approximate, and relates landing distance to wing loading, namely: Where w=landing wing loading, then 1 = const x w const=24.4 for split flaps • =23.8 for slotted flaps = 17.3 for double slotted or Fowler flaps The above coefficients have been based on statistical data given in Fig. 1, where required landing-field lengths have been plotted against wing loadings for 47 different types of aircraft and 91 different landing wing-loadings. If a greater accuracy is required for computing the landing distance, the following method is recommended as giving close results. The total landing distance is assumed to comprise the gliding distance from 50ft, the flare-out distance and the touch- down-to-stop distance. Gliding distance si=50 xJL where L = Cj. at approach safety D D CD speed FA FA=I.I to 1.3FS depending on requirements.
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