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Aviation History
1942
1942 - 1604.PDF
3L 126 FLIGHT FIGHTER TAKE- Rapid and Accurate System for / By W. NICHq a? [stimating a New Design t.Ae.S. Class A B C 1) E Crew One One Two One Two Engines One One One Two Two Average Gross Weight (lb.) 6,900 10,500 8,300 10,000 20,500 THE estimation of weights and/the ultimate take weight offers more difficultiei probably thanyftny other branch of aircraft design\_ Geoinetrica^imi larity and theoretical considerations are rtwiletl inyppHcj tion, and average data from similar existing tjjpe^xan only be applied up to a point and can also be very^nisleading in certain fauna In searching for a system or method whereby at the commencement of a new design a rapid and accurate esti mate can be made, it was found convenient to classify existing types, including foreign aircraft of which details are available, into groups according to the purpose for which they were de signed. This article Pig. 1. " FIGHTER " TYPES deals exclusively with the fighter class. To avoid con fusion fighter type aircraft must again be regrouped accord ing to the table in Fig. 1, which shows the variation in types of the fighter class The most common type of fighter is, of course, the single-seater with one engine ; in view of the data available it was decided to investigate the problem of this class first. It became apparent at once that, while average data applied with a reasonable degree of accuracy to unit and component weights, it gave no reliable indication to the final take-off weight. Fig. 2 is a tabulated weights distribution chart for a complete aircraft, and as a percentage of the take-off weight each main weight, unit and component weight has Jjeen assessed. This chart has been compiled from average data of existing types of similar aircraft and is sufficiently accu rate to be of practical use when allotting the weight distri bution for a new design. Basic Operational Equipped Weight It should be noted that change-over of the power unit from a liquid-cooled engine to an air-cooled radial engine does not make any appreciable difference to the total for the power unit. If anything, the liquid-cooled installation is a little superior from the weight point of view. Apply ing average data in an attempt to find the take-off weight, a.s previously stated, was found unreliable, and a curve plotting known values of average load carried, against take-off weight for a number of apparently similar types proved to be inaccurate up to 8 per cent, and over. A most noticeable fact, however, was that the basic operational equipped weight (see Fig. 2) remained at or very close to 89 per cent, of the take off weight in every case, and as a matter of fact this particular weight remains closely constant as a percentage of the take-off weight for all military aircraft, though not, of course, necessarily 89 per cent, as in this case. At this point average data no longer applies due to the great variation in the fuel load in what otherwise appear to be similar aircraft. Tackling the problem practically, however, it is assumed that an estimate for the take-off weight is required for a new S.S. fighter design. From the specification the range and performance will be stated, and from the specified engine data the fuel and oil load for this range or endurance can be calculated. Likewise the removable load, which includes guns, ammunition, removable equipment and crew. In this case one yil be stated, and again the weight for the removable loajjl^xan be calculated. - As the basic operational weight averages more or less constant, it was assumed that some relation between these two loads should give a reasonably accurate estimate of the take-off weight. This proved correct, and as a result the curve in Fig. 3 was evolved. This curve shows the Removable Load value of „, . , ,—r-p;—-, , .-,. ,.— which can be referred Weight of Fuel and Oil Max. to as /8 plotted against a weight coefficient O/io3 or C*xi ,000 for a full load of from 80 to 200 gallons, includ ing the equivalent weight of oil which covers the '' full supply '' load carried for all aircraft within this category. Practical Application As to the practical value of the use of the Curve in Fig .3^ assume from the specification for a new design the fuel and oil required for the necessary endurance are: Fuel 88 gallons, oil 8.5 gallons, giving a weight for these two items of 757 lb. Also from the specification the "removable load" is found to be 605 lb. Incidentally, these weights actually apply to the Messerschmitt fighter Me.iogF. 605 From Fig. 3 the above fi =—-=0.8, and from the curve 757 for (8 = 0.8 0 = 7,600 .'. Take-off weight = 7,600 x 0.8 = 6,080 lb. OB TAKE-OF F WEIGH T BASI C OPERATIONA L EQUIPPE D WEIGH T TAR E WEIGH T RE FU! 01 BAR E WEIGH T STRUCTUR E POWE R PLAN T PROTECT &. FIXED L( .MOVABLE LOAD TOTA 1 AND L LOAD NG S =£ I TAI SELAG E U_ WINGS INCLUDING CENTRE SECTION MAIN UNDERCARRIAGE UNIT TOTAL-WING UNIT TAILPLANt & ELEVATORS FIN 1 RUDDER TOTAL-TAIL UNIT FUSELAGE COMPLETE TAILWHEEL UNIT ENGINE MOUNTING &. COWLING TOTAL-FUSELAGE UNIT FLYING CONTROLS-TOTAL TOTAL FOR STRUCTURE WE R UNI T K EL SUPPL Y ENGINE (DRY) AIRSCREW COMPLETE RADIATOR .PIPING, COWLING. COOLANT ACCESSORIES TOTAL-POWER UNIT > FUEL TANKS FUEL SYSTEM OIL TANKS OIL SYSTEM FUEL SUPPLY UNIT-TOTAL TOTAL FOR POWER PLANT TOTAL BARE WEIGHT ON DAD PROTECTIVE ITEMS FIXED ARMAMENT L FIXED LOAD TOTAL TARE WEIGHT REMOVABLE ARMAMENT ' REMOVABLE EQUIPMENT j CREW TOTAL-REMOVABLE LOAD . BASIC OPERATIONAL EQUIPPED WEIGHT FUEL OIL TOTAL- FUEL & OIL TAKE-OFF WEIGHT % 15-0 A--1 19-7 1-27 0-55 1 8E 7-12 0-52 2-42 10 06 123 32-8 21-2 4-96 5-8 1-92 55 88 0-96 0-56 0-17 0-61 2-1 360 «-8 2-4- 4-6 75-8 13-2 13 2 BP C 100 vol 11 Oj 100 U Fig. 2. Average weight distribution as percentage of take-off weight for fighter aircraft, Class A.
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