passengers have free choice in seating, cargo and fuel-loading are done in prescribed sequences, with options.

It has been observed that passengers first choose window seats and then, depending on the number of abreast seating, the second choice is made. Figure 8.2 shows the window seating first and the aisle seating last; note the boundaries of front and aft limits. Cargoand fuel-loading is accomplished on a schedule with the locus of CG travel in lines. In the figure, the CG of the OEM is at the rear, indicating that the aircraft has aft-mounted engines. For wing-mounted engines, the CG at the OEM moves forward, making the potato curve more erect.

For static-stability reasons, it must be ensured that the aircraft has a static margin at all loading conditions. With the maximum number of passengers, the CG is not necessarily at the aftmost position. Typically, the CG should be approximately 18% of the MAC when fully loaded and approximately 22% when empty. The CG is always forward of the neutral point (i.e., the aircraft’s aerodynamic center, established through CFD and wind-tunnel tests). The aerodynamic center is assumed to be 50% of the MAC and must be iterated until the final configuration is reached.

Figure 8.2 represents a typical civil aircraft loading map, which indicates the CG travel to ensure that the aircraft remains in balance within horizontal and vertical limits. Loading starts at the OEM point; if the passengers boarding first opt to sit in the aft end, then the CG can move beyond the airborne aft limit, but it must remain within the ground limit. Therefore, initial forward cargo-loading should precede passenger boarding; an early filling of the forward tank fuel is also desirable.

8.6 Aircraft Component Groups

The recognized groups of aircraft components are listed in exhaustive detail in the ATA’s publication. This section presents consolidated, generalized groups (for both civil and military aircraft) suitable for studies in the conceptual design phase. Both aircraft classes have similar nomenclature; the difference in military aircraft is

described in Section 8.6.2. Each group includes subgroups of the system at the next level. Care must be taken that items are not duplicated – accurate bookkeeping is essential. For example, although the passenger seats are installed in the fuselage, for bookkeeping purposes, the fuselage shell and seats are counted separately.

8.6.1 Civil Aircraft

Structure group (MSTR = MFU + MW + MHT + MVT MN + MPY + MUC + MMISC)

(8.6)

Fuselage group (MFU)

Wing group (MW): includes all structural items (e.g., flaps and winglets)

H-tail group (MHT)

V-tail group (MVT)

Nacelle group (MN and MPY) (nacelle and pylon)

Undercarriage group (MUC)

Miscellaneous (MMISC) (e.g., delta wing)

The basic structure of the aircraft – the fuselage shell (seats are listed separately under the Furnishing group) is as follows:

Dry-equipped engine (ME)

Thrust reverser (MTR)

Engine control system (MEC)

Fuel system (MFS)

Engine oil system (MOI)

The power plant group comes as a package, with all items dedicated to the power plant installation. These are mostly bought-out items supplied by specialists:

Systems group (MSYS = MECS + MFC + MHP + MELEC + MINS + MAV ) (8.8)

Environmental control system (MECS)

Flight-control system (MFC)

Hydraulic and pneumatic system (MHP) (sometimes grouped with other systems)

Electrical system (MELEC)

Instrument system (MINS)

Avionics system (MAV)

The systems group includes a variety of equipment, all vendor-supplied, bought-out items:

Seat, galleys, and other furnishings (MSEAT)

Oxygen system (MOX)

Paint (MPN)

Most of the weight is in the fuselage, yet the furnishings are itemized under different headings. Paint can be quite heavy. A well-painted B737 with airline livery can use as much as 75 kg of paint:

Contingencies (MCONT)

This is a margin to allow unspecific weight growth (MCONT).

The MEM is the total of the previous twenty-two items. This is the weight of the complete aircraft as it comes off the production line to be come airborne for the first time.

Add the following items to the MEM to obtain the OEM:

Crew: flight and cabin crews (MCREW)

Consumables: food, water, and so forth (MCON)

The OEM is when the aircraft is ready for operation.

Add the payload and requisite fuel to obtain the MRM. At the takeoff point at the edge of the runway, the MRM becomes the MTOM = (MRM – taxi fuel):

Payload (MPL) (passengers at 90 kg per passenger, including baggage)

Fuel (MFUEL) (for the design range, which may not fill all tanks)

MTOM: The aircraft at the end of the runway is ready for takeoff. The civilaircraft MTOM is the total weight of all component groups, as shown in Equation 8.10.

The MTOM = M(x) dx = Mi, where the subscript i stands for each component group listed previously.

For civil aircraft, the MTOM is equal to

(MFU ) + (MW) + (MHT ) + (MVT ) + (MN) + (MPY ) + (MUC) + (MMISC)

+(ME) + (MTR) + (MEC) + (MFS) + (MOI ) + (MECS) + (MFC) + (MHP)

+(MELEC) + (MINS) + (MAV ) + (MSEAT ) + (MOX ) + (MPN ) + (MCONT )

8.6.2 Military Aircraft (Combat Category)

This extended section of the book can be found on the Web site www.cambridge

.org/Kundu and lists generic military aircraft-component mass as required in the conceptual design stage. The list covers aircraft components in the following groups.

Structure Group Power Plant Group Systems Group Furnishing

Manufacture’s Empty Mass Operators Empty Mass Maximum Takeoff Mass Maximum Ramp Mass