Variants in the Family of Aircraft Design

The family concept of aircraft design is discussed in previous chapters and high­lighted again at the beginning of this chapter. Maintaining large component com­monality (genes) in a family is a definite way to reduce design and manufactur­ing costs – in other words, “design one and get two or more almost free.” This

Short van ant

(4 to 6 passengers)

……………… JtL………………….. J 41.71 ft (1271 m)

Baseline aircraft

(8 to 10 passengers)


49.54 ft (15.1 m)

Long vanant

(12 to 14 passengers)

‘ d

58.2 ft (17.74 m)

Figure 11.4 Variant designs in the family of civil aircraft encompasses a much larger market area and, hence, increased sales to generate resources for the manufacturer and nation. The amortization is distributed over larger numbers, thereby reducing aircraft costs.

Today, all manufacturers produce a family of derivative variants. The Airbus 320 series has 4 variants and more than 3,000 have been sold. The Boeing 737 fam­ily has 6 variants, offered for nearly 4 decades, and nearly 6,000 have been sold. It is obvious that in three decades, aircraft manufacturers have continuously updated later designs with newer technologies. The latest version of the Boeing 737-900 has vastly improved technology compared to the late 1960s 737-100 model. The latest design has a different wing; the resources generated by large sales volumes encour­age investing in upgrades – in this case, a significant investment was made in a new wing, advanced cockpit/systems, and better avionics, which has resulted in continu­ing strong sales in a fiercely competitive market.

The variant concept is market and role driven, keeping pace with technology advancements. Of course, derivatives in the family are not the optimum size (more so in civil aircraft design), but they are a satisfactory size that meets the demands. The unit-cost reduction, as a result of component commonalities, must compromise with the nonoptimum situation of a slight increase in fuel burn. Readers are referred to Figure 16.6, which highlights the aircraft unit-cost contribution to DOC as more than three to four times the cost of fuel, depending on payload-range capability.

The worked-out examples in the next section offer an idea of three variants in the family of aircraft.

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