Civil Aircraft Mission (Payload-Range)
The payload-range capability constitutes the two most important parameters to represent commercial transport aircraft. It is the basic aircraft specification and requirement as a result of market studies for new aircraft designs.
Figure 4.4 shows the payload-range capabilities for several subsonic-transport aircraft (i. e., turbofans and turboprops). The figure captures more than fifty different types of current designs. The trend shows that the range increases with payload increases, reflecting the market demand for the ability to fly longer distances. Long – range aircraft will have fewer sorties and will need to carry more passengers at one time. The classic debate on the A380 versus the B787 passenger capacity is captured within the envelope shown between the two straight lines in Figure 4.4. It is interesting that there are almost no products carrying a high passenger load for shorter ranges (i. e., < 2,000 nm). At the other extreme, the high-subsonic, long-distance executive jets, the Bombardier Global Express and Gulfstream V, are already on the market (not shown in Figure 4.4) carrying executives and a small number of passengers very long ranges (> 6,500 nm) at a considerably higher cost per passenger. It is obvious that because of considerably lower speeds, turboprop-powered
aircraft cater to the shorter-range market sector – they provide better fuel economy than turbofans. The author considers that the future may show potential markets in the less affluent areas. Major countries with substantial population centers could fly more passengers within their borders, such as in China, India, Indonesia, Russia, and the United States.
The points in Figure 4.4 include the following aircraft: Lear 31A, Lear 45, Lear 60, Cessna 525A, Cess 650, Cess 500, Cess 550, Cess 560, Cess 560XL, ERJ 135ER, ERJ 140, ERJ 145ER, CRJ 100, CRJ 700, ERJ 170, DC-9-10, CRJ 900, ERJ 190, 737-100, 717-200, A318-100, A319-100, A320-100, Tu204, A321-100, 757-200, A310-200, 767-200, A330-200, L1011, A340-200, A300-600, A300-100, DC-10-10, MD11, 777-200, 747-100, A380, Short 330 and 360, ATR 42 and 72, Jetstream 31, Saab 340A, Dash 7 and 8, Jetstream 41, EMB 120, EMB 120ER, Dornier 328-100, and Q400.
Commercial aircraft operation is singularly dependent on revenue earned from fare-paying passengers and cargo. In the operating sector, load factor is defined as the ratio of occupied seats to available seats. Typically, for aircraft of medium sizes and larger, operational costs break even at approximately one-third full capacity (this varies among airlines; fuel costs at 2000 level with regular fares) – that is, a load factor of about 0.33. Of course, the empty seats could be filled with reduced fares, thereby contributing to the revenue earned.
It is appropriate here to introduce the definition of the dictating parameter, seat – mile cost, which represents the unit of the aircraft DOC that determines airfare to meet operational costs and sustain profits. DOC is the total cost of operation for the mission sector (operational economics are discussed in detail in Chapter 16). The U. S. dollar is the international standard for aircraft cost estimation.
seat-mile cost = DOC———————– = (cents/seat/nm) (4.1)
number of passengers x range in nm
The higher the denominator in Equation 4.1, the lower is the seat-mile cost (i. e., DOC). The seat-mile cost is the aircraft operating cost per passenger per nm of the mission sector. Therefore, the longer an aircraft flies and/or the more it carries, the lower the seat-mile cost becomes. Until the 1960s, passenger fares were fixed under government regulation. Since the 1970s, the fare structure has been deregulated – an airline can determine its own airfare and vary as the market demands.
A careful market study could fine-tune an already overcrowded marketplace for a mission profile that offers economic gains with better designs. Section 2.6 addresses the market study so that readers understand its importance.