Civil Aircraft Fuselage: Typical Shaping and Layout

Passenger-capacity and seating-arrangement requirements dictate the layout, which is generally limited to the constant cross-section midpart of the fuselage. Options for various types of fuselage cross-sections are described in Section 4.7.1. Typical geometric and interior details for aircraft with 2- to 10-abreast seating accommo­dating from 4 to 600 passengers with possible cabin width, fuselage length, and seating arrangement are described in this subsection and shown in Figures 6.5 and 6.6. The figures are from the stabilized statistics of market demand, which varies slightly among cases. The public domain has many statistics for seating and aisle dimensions relative to passenger number, cabin volume, and so forth. The diagrams in this section reflect current trends. Figures 6.5 and 6.6 show the spaces for toi­lets, galleys, wardrobes, attendant seating, and so forth but are not indicated as such. There are considerable internal dimensional adjustments required for the

Toilet, galley, wardrobe, attendant seat provided Family variants not shown

Figure 6.6. Wide-body, double-aisle fuselage layout (not to scale)

compromise between comfort and cost. The fuselage fineness ratio is kept from 7 to 14 (in the family of variants; the baseline design can start at around 10). Table 4.2 lists the typical relationship between the number of passengers and the number of abreast seating.

The first task is to determine the abreast seating for passenger capacity. The standard practice for seat dimensions is to cater to the 95th percentile of European men. Section 4.7.6 describes typical seat and aisle dimensions. Elbowroom is needed on both sides of a seat; in the middle seats, it is shared. Typical elbowroom is from

1.5 to 2 inches for economy class and double that for first class. In addition, there is a small space between the window elbowrest and the fuselage wall, larger for more curved, smaller aircraft – typically, about an inch (see Figure 3.50). A wider cabin provides more space for passenger comfort at an additional cost and drag. A longer seat pitch and wider seats offer better comfort, especially for oversized people. Air­craft with a seating capacity of 150 to 200 passengers and as many as 6 abreast with a single aisle is known as a narrow body. With more than six abreast, a two-aisle arrangement is the general practice. Fuselage width is the result of adding the thick­ness of the fuselage structural shell and soft wall furnishings to the cabin width (see Figure 3.50). During Phase 2 (i. e., the project-definition stage), when sufficient struc­tural details emerge, the interior-cabin geometric dimensions are defined with bet­ter resolution; the external geometry remains unaffected. The number of abreast seating and total passenger capacity determine the number of rows. Table 4.5 lists typical dimensions of seat pitch and width.

When the interior arrangement is determined, the constant cross-section mid­fuselage needs to be closed at the front and aft ends. The midsection fuselage could exhibit closure trends at both the front and aft ends, with diminishing inte­rior arrangements at the extremities. The front-end fuselage mould lines have a favorable pressure gradient and therefore are blunter with large curvatures for rapid

Table 6.1. Fuselage seating dimensions – narrow body (in inches) 2-Abreast (1-1) 3-Abreast (1-2) 4-Abreast (2-2) 5-Abreast (2-3) 6-Abreast (3-3) Seat width, B (LHS) 19 19 2x 18 2 x 18 3 x 18 Aisle width, A 17 18 19 20 21 Seat width, B (RHS) 19 2 x 19 2x 18 3 x 18 3 x 18 Total elbowroom 4 x 1.5 5 x 1.5 6 x 1.5 7 x 2 8 x 2 Gap between wall & seat, G 2 x 1.5 2 x 1 2 x 1 2 x 0.5 2 x 0.5 Total cabin width, Wcabm 64 85 102 126 141 Total wall thickness, T 2 x 2.5 2 x 4 2 x 4.5 2x 5 2 x 5.5 Total fuselage width, Wfuselage 69 93 111 136 151 Cabin height, Haabin 60 72* 75 82 84 Typical fuselage height, Hfus 70 85 114 136 151 * Recessed floor.

front-end closure. Basically, a designer must consider the space for the flight crew at the front end and ensure that the pilot’s view polar is adequate. Conversely, the aft end is immersed in an adverse pressure gradient with low energy and a thick bound­ary layer – therefore, a gradual closure is required to minimize airflow separation (i. e., minimize pressure drag). The aft end also contains the rear pressure-bulkhead structure (see Section 4.7.3 and Figure 4.16 for closure shapes). The longer aft-end space could be used for payload (i. e., cargo) and has the scope to introduce artistic aesthetics without incurring cost and performance penalties.

An important current trend is a higher level of passenger comfort (with the exception of low-cost airlines). Specifications vary among customers. Designers should conduct trade-off studies on cost versus performance in consultation with customers (i. e., operators) to satisfy as many potential buyers as possible and to maximize sales. This is implied at every stage of aircraft component sizing, espe­cially for the fuselage.

Dimensions listed in Tables 6.1 and 6.2 are estimates. The figures of seat pitch, seat width, and aisle width are provided as examples of what exists in the market.

Table 6.2. Fuselage seating dimensions: wide body (in inches) 7-Abreast (2-3-2) 8-Abreast (2-4-2) 9-Abreast (2-5-2) 10-Abreast (3-4-3) Seat width, B (LHS) 2x 19 2 x 19 2 x 19 3 x 19 Aisle width, A 22 22 22 22 Seat width, B (Center) 3 x 19 4 x 19 5 x 19 4 x 19 Aisle width, A (RHS) 22 22 22 22 Seat width, B (RHS) 2x 19 2 x 19 2 x 18 3 x 19 Total elbowroom 9 x 1.5 10 x 1.5 11 x 1.5 12 x 1.5 Gap between wall and seat, G 2 x 0.5 2 x 0.5 2 x 0.5 2 x 0.5 Total cabin width, Wcabin 192 212 232 253 Total wall thickness, T 2x 6 2 x 6.5 2 x 7 2 x 7.5 Total fuselage width, Wfuselage 204 225 246 268 Cabin height, Hcabin 84 84 84 to 86 84 to 86 Typical fuselage height, Hfus 204 225 246 268

The dimensions in the tables can vary to a small extent, depending on customer requirements. The seat arrangement is shown by numbers in clusters of seats, as a total for the full row with a dash for the aisle. For example, “3-4-3” indicates that the row has a total of 10 seats, in a cluster of 3 at the 2 window sides of the fuselage and a cluster of 4 in the middle flanked by 2 aisles.

Variants in the family of aircraft are configured by using a constant cross-section fuselage plug in units of one row of pitch. The changes in passenger numbers are discreet increases in the total number of passengers in a row (an example of six – abreast seating is shown in Figure 6.5). An increase in capacity results from adding plugs as required. If more than one, they are distributed in front and aft of the wing. When in odd numbers, their distribution is dictated by the aircraft CG posi­tion. In most cases, the front of the wing has the extra row. Conversely, a decrease in passenger numbers is accomplished by removing the fuselage plug using the same logic. For example, a 50-passenger increase of 10-abreast seating has 2 plugs distributed as 3 rows in a subassembly in front of the wing and a subassembly of 2 rows aft of the wing. Conversely, a 50-passenger decrease is accomplished by removing 3 rows from the rear and 2 from the front. For smaller aircraft with smaller reductions, unplugging may have to be entirely from the front of the wing.

Readers are required to work out dimensions using the information provided in the following subsections – intensive coursework begins now. However, read­ers should be aware that the worked-out examples demonstrate only the proposed methodology. Designers are free to configure aircraft with their own choices, which are likely to be within the ranges defined herein.