Quest for Performance: The Evolution of Modern Aircraft
 
 
Part II: THE JET AGE
 
 
Chapter 13: Jet Transports
 
 
Background
 
 
 
[407] The development and design features of jet transport aircraft from the pioneering DeHavilland Comet of 1949 to the wide-body jets of today are briefly described in this chapter. The particular aircraft discussed were selected because of their significance in the evolution of the modern jet transport, or because they are representative of an important configuration type, or because they are particularly successful. No attempt is made to describe all the jet transport aircraft developed since the end of World War II.
 
Successful jet transports tend to have long operational careers and are usually produced in many versions. Engine changes and improvements, changes in wing area and high-lift systems, aerodynamic and structural refinements, and modernization of onboard systems may take place during the production life of a successful aircraft type. "Stretching" is another modification technique frequently employed. In this case, the fuselage is lengthened by the addition of "barrel sections" so that the passenger capacity of the aircraft is accordingly increased. A description of the sometimes numerous versions of a particular aircraft is beyond the scope of the present discussion. A representative version of a particular aircraft will be described here; information on the different versions may be obtained from the references contained at the end of this book.
 
The aircraft discussed are listed in table VII (appendix A), together with some of their important physical and performance characteristics. Although the terms used in table VII are defined in the list of symbols given in appendix B, clarifying remarks about several of these quantities are in order. The range-payload diagram is so fundamental to the understanding of transport aircraft performance that a brief description is provided at this point. A hypothetical range-payload diagram is given in figure 13.1 in which the range is plotted on the abscissa; [408] and the payload, on the ordinate. Point B corresponds to maximum aircraft gross weight and maximum payload weight with all available seats and cargo space filled but with fuel tanks only partially filled. The gross weight of the aircraft remains the same along the line segment BC, but fuel weight is exchanged for payload weight; that is, payload is off-loaded and the fuel tanks are completely full at point C. Along the line segment D, increases in range are achieved by further reductions in payload although no additional fuel can be carried, and the gross weight is lower than the maximum value. The gross weight of the aircraft along line segment A is less than the maximum value, except at point B, and the fuel load is reduced as the range is reduced. No...
 
 
graph contrasting payload weight with range of flight
 
Figure 13. 1 - Hypothetical range-payload diagram.
 
[409]...increase in payload is shown along line segment A because all payload space is filled. The range at maximum payload, point B, and the range and payload for full tanks, point C, are the two combinations of range and payload given in table VII. The range values given in the table are based on utilization of all fuel onboard the aircraft; thus no allowance is made for necessary reserve fuel to cover such contingencies as diversion to an alternate airport, a missed approach, or holding in the vicinity of an airport. All passenger-carrying airline flights are required to carry a specified amount of reserve fuel. One set of guidelines for determining the necessary amount of reserve fuel is briefly discussed in appendix G. Two cruising speeds are given in table VII. The maximum cruising speed is given by the symbol Vce; the cost-economical cruising speed is denoted by Vce, and is the speed for minimum cost per mile. The landing and takeoff field lengths given in the table are called FAR (Federal Air Regulations) field lengths and contain certain built-in safety margins. A simplified description of these field lengths is given in appendix H. Values of the zero-lift drag coefficient and maximum lift-drag ratio are not given for the aircraft listed in table VII. Such data are not generally available in the open literature because of the highly competitive nature of the modern jet-transport business. Values of these quantities (estimated by the author according to the methods given in reference 176) are quoted in the text for several of the aircraft described, but these values should not be interpreted as necessarily being consistent with company estimates.
 
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