Considerations in Configuring the Fuselage

Following are general considerations important for the fuselage layout. Section 3.23 provides definitions of associated fuselage geometries.

Geometry

(1) diameter (e. g., comfort level, appeal)

(2) abreast seating

(3) length, fineness ratio

(4) upsweep for rotation angle and rear door, if any

(5) cross-section to suit under floorboards and headroom volume and space

Structure (affecting weight

and external geometry)

(1) doors and windows

(2) wing and undercarriage attachments

(3) weight

Section 6.4 describes typical fuselage layouts from two-abreast seating to the current widest seating of ten abreast.

The important considerations for civil aircraft fuselage layout are as follow:

1. The current ICAO limit on fuselage length is 80 m. This is an artificial limit based on current airport infrastructure size and handling limitations.

2. The fuselage fineness ratio must be from 7 to 14 (see Table 4.3). Section 4.7.3 lists front – and aft-fuselage closure shapes. Section 6.3.1.2 describes how to make the fuselage closure. There is aft luggage space in front of the pressure bulkhead, especially in smaller aircraft.

3. Seat and aisle dimensions are obtained from Table 4.5.

4. For a fuselage with four-abreast seating or more, the cross-section could use space below the floorboards. If the bottom half is elongated (i. e., oval), then the space can be maximized. Full standing headroom is easily achievable for a fuselage with four-abreast seating or more. Cargo container sizes are described in Section 4.7.8.

5. Two aisles are provided for a fuselage with seven-abreast seating and more (the current maximum is ten). In the future, if a wider cabin is designed (e. g., with a BWB), then more than two aisles will be necessary.

Figure 6.4. Fuselage upsweep angle

6. The minimum number of cabin crew depends on the maximum passenger capac­ity that the airframe can accommodate. Although not required for up to 19 pas­sengers, a cabin crew is provided by some operators.

7. A pressurized fuselage is invariably circular or near circular to minimize weight. Unpressurized cabins for aircraft operating below 4,300 m (14,000 ft) need not be circular in the cross-section. Smaller utility aircraft demonstrate the ben­efits of a rectangular cross-section. A box-like rectangular cross-section (see Figure 4.14) would not only offer more leg space but also is considerably less costly to manufacture (e. g., the Short SD360).

8. The FAA and CAA have mandatory requirements on the minimum number of passenger doors, their types, and corresponding sizes dependent on the max­imum passenger capacity for which the fuselage is intended to accommodate. This requirement ensures passenger safety: certification authorities stipulate a time limit (e. g., 90 s for big jets) within which all passengers must egress if an unlikely event occurs (e. g., fire). The larger the passenger capacity, the more doors are to be installed. Not all doors are the same size – emergency doors are smaller. Passenger doors have several categories and are described in Sec­tion 15.7. All doors are kept locked while airborne.

9. The fuselage provision typically includes a toilet, a galley, and cabin crew seat­ing – the extent depends on the number of passengers and the duration of flight. Chapter 4 describes toilet and galley details. For smaller aircraft with a shorter duration of flight, it is desirable that at least a toilet be provided. To reduce cost, smaller aircraft with a low mission range do not have a toilet, but these aircraft can therefore be uncomfortable.

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