Fuselage geometry is determined from the designed passenger capacity (see Chapter 6). There are two parameters to size (i. e., fuselage width [W] and fuselage length [Lf]), which determine the constant-section fuselage-barrel length. In turn, this depends on the seat pitch and width for the desired passenger comfort level. Table 4.2 lists the statistics for existing designs – a new design would be similar. The width and length of the fuselage must be determined simultaneously, bearing in mind that the maximum growth potential in the family of variants cannot be too long or too short and keeping the fineness ratio from 7 to 14 (a good value is around 10). Boeing 757-300 records the highest fineness ratio of 14.7. A seating arrangement with two aisles results in more than six abreast (average diameter, Dave = [H + W]/2; see Figure 4.14).
4.7.1 Fuselage Width
The first parameter to determine for the fuselage average diameter is the number of abreast seating for passenger capacity. There is an overlap on choice for
Table 4.2. Number of passengers versus number of abreast seating and fineness ratio
* More than 450-passenger capacity, the fuselage cross-section becomes a double-deck arrangement due to current restrictions of fuselage length to 80 m (262.5 ft). In the future, this restriction could be relaxed.
the midrange capacity in the family of design; for example, an A330 with 240 to 280 passengers has seven-abreast seating whereas the same passenger capacity in a B767 has eight-abreast seating. When seating number is increased to more than six abreast, the number of aisles is increased to two to alleviate congestion in passenger movement. Because of the current fuselage-length limitation of 80 m, larger – capacity aircraft have a double-deck arrangement (e. g., the B747 and the A380). It would be interesting to try a two-aisle arrangement with six-abreast seating that would eliminate a middle seat. A three-aisle arrangement with ten-abreast seating would eliminate the cluster of four seats together. A BWB would have more than two aisles; there is no reason to not consider a triple-deck arrangement.
Although a circular cross-section is the most desirable relative to stress (minimize weight) and manufacture (minimize cost), the market requirements for the below-cabin floorspace arrangement could result in a cross-section elongated to an oval or elliptical shape. The Boeing 747 with a more narrow upper-deck width is a unique oval shape in the partial length that it extends. This partial length of the upper deck helps cross-sectional area distribution (see Section 3.23) and area ruling.
Figures 4.12 and 4.13 show various options for aircraft fuselage cross-sections to accommodate different seating arrangements. All fuselage cross-sections are symmetrical to the vertical plane. In general, aircraft with four-abreast seating and more have space below the cabin floor for baggage and cargo.
vung partially through fuselage
Unpressurized propeller-driven aircraft operating at lower altitudes can have rectangular cross-sections to reduce manufacturing costs, as well as offer more space (e. g., Shorts 360 aircraft). A pressurized fuselage cross-section would invariably be circular or nearly circular to minimize weight from the point of hoop-stress considerations. A two-abreast circular cross-section would have cramped legroom; a better option is a slightly widened lower lobe (e. g., Learjet 45) to accommodate legroom. In general, with a three-passenger capacity and more, the midsection fuselage has a constant cross-section with front and aft ends tailored to suit the requirements. The wing box arrangement for smaller aircraft should pass over (e. g., high-wing DO328) (Figure 4.13) or under (e. g., Learjet 45) the fuselage.