# Index for “Design for Customer”

The definition of design for customer relates to the merit of the design by establish­ing a value index. The suggested definition is as follows:

(DOC*/DOC) x (Unit Cost*/Unit Cost)
(t/10t * + 0.9)

Kn is inversely proportional to the DOC and aircraft unit cost; that is, a lower DOC gives a higher Kn; a value of more than 1 is better. The unit cost includes the engine and aircraft size and the DOC includes the design merits, passenger number, and range capability. Typically, an aircraft with more passengers has a lower DOC, driv­ing the value to more than 1, but it is evaluated with respect to price and delivery time.

17.9.1 Worked-Out Example

From the worked-out example of the Bizjet, the following values are obtained. Because derivative aircraft values are obtained through simplified assumptions, they must be worked out in better detail. The linear relationship is used to work out the following example to provide a general idea.

Standard Parameters of the Baseline Aircraft

Unit cost* in millions of U. S. dollars = \$8 million; MTOM = 9,400 kg.

DOC* in U. S. dollars per seat/nm = \$0.352 per nautical mile per passenger (ten passengers).

Delivery time t* in years (from the placement of order) = 1 year.

Baseline aircraft = \$0.8 million/passenger and \$0.000851/kg MTOW.

Parameters of the Extended Variant Aircraft

Unit cost in millions of U. S. dollars = \$9 million; MTOM = 10,800 kg.

DOC in U. S. dollars per seat/nm = \$0.2875 per nautical mile per passenger (fourteen passengers).

Delivery time t in years (from the placement of order) = 1 year.

Large variant aircraft = \$0.6428 million /passenger and \$0.000833/kg MTOW.

K (DOC* /DOC) (0.352/0.2875)

nJarger = (.UnitCost/UnitCost*) x (t/10t* + 0.9) = (9/8) x (1/10 + 0.9)

= 1.224/(1.125 x 1) = 1.088 (a better value)

Parameters of the Shortened Variant Aircraft

Unit cost in millions of U. S. dollars = \$6 million; MTOM = 7,600 kg.

DOC in U. S. dollars per seat/nm = \$0.482 per nautical mile per passenger (six passengers).

Delivery time t in years (from the placement of order) = 1 year.

 _____________ (DOC* /DOC)_________________ (UnitCost/UnitCost*) x (t/10t* + 0.9)

Small variant aircraft = \$1 million/passenger and \$0.00079 kg MTOW.

= 0.7303/(0.75 x 1) = 0.974 (a lower value)

In general, a smaller derivative aircraft is penalized because it is heavier than it would be if it were a baseline design. The wing area is larger than what is required. The smaller variant is competitive aircraft, and there are aircraft in this class with similar DOC. Several new all-composite, four-passenger lighter jet aircraft have appeared recently and are selling at less than \$5 million with better DOC. These new aircraft are yet to be proven in operational usage, and it will be some time before all-composite aircraft overtake conventional construction. The example of a six-passenger, smaller variant is a robust, all-metal aircraft with a larger cabin vol­ume and high-end amenities suited to corporate demand. In a mixed fleet of three sizes, the total package offers benefits that are difficult to match. When an airline operates a mixed fleet of variants along with its baseline aircraft, the spare-parts

600 a.

MTOM kg)

stock, training, and maintenance costs can be shared. Private ownership in this class is increasing and there is room for both types.

However, modifications to the smaller variant can improve the index Knsmaller. If re-engined with a smaller turbofan (i. e., the Williams type) and re-engineered with lighter and less expensive equipment, the aircraft price could be decreased to about \$5 million, making it even more attractive; however, it loses some component com­monality and incurs additional development costs. If the wing tips can be shortened at practically no extra cost, then the weight can be decreased to less than 7,000 kg, and the index can reach a value of more than 1.

Design for customer can help manufacturers establish the aircraft price for a family of variants, giving each type a comparative value for the customer. Typically, the smaller variant should be priced lower with a smaller profit; other aircraft prices are adjusted, with the baseline aircraft price unchanged. That is, the price of the larger aircraft can be increased to compensate the family price structure. The goal of the baseline size is maximum sales. In the example, the price of the smaller variant is \$6 million, resulting in a small profit. The baseline aircraft aims for the most sales to maximize profit.

In general, route traffic load continues to increase; consequently, sales of the larger variant also increase and also the associated profits for the manufacturer, making up for the relatively smaller profit from the smaller variants. When a new market emerges for a larger traffic load, manufacturers seize the opportunity for a new baseline design.

The aircraft price per passenger and unit mass are explained herein. There is a sharp increase in per-passenger price with a smaller payload, as shown in Fig­ure 17.2. In the figure, the dashed lines represent generic data; it is a magnified ver­sion of Figure 16.2. The solid lines represent the Bizjet family. The smaller aircraft price is slightly depressed to suit the market.