manufacturing tolerance allocations. The difference is minor: The maximum deviation is on the order of less than ±0.2%. An older aircraft would degrade in performance: During operation, the aircraft surface would become deformed, dented, warped, and/or contaminated, increasing viscous drag, and so forth. Manufacturers consider actual problems of operational use by maintaining a record of performance of all aircraft produced. Manufacturers’ comments cover average aircraft degradation only up to a point. In other words, like any product, a brand new aircraft generally would perform slightly better than what is indicated in the pilot’s manual – and this margin serves the operators well.

If a new design fails to reach the predicted value, who is at fault: Is the shortcoming originating in the aircraft or the engine design or from both? Is it a bad aircraft or a bad engine (if a new engine design is incorporated)? Over time, the aerospace industry has successfully approached these issues. As mentioned previously, some aerospace stories could be more exciting than fiction; readers may examine some old design cases. Today, engine and aircraft designers work cooperatively to identify the nature of and then repair shortfalls. In general, it is convenient for the shaping of external nacelle mould lines to be the responsibility of airframe designers and the internal shaping (i.e., intake duct and exhaust duct) to be that of engine designers.

The compressibility effect of the airflow influences the shaping of an aircraft. Airflow below Mach 0.3 is nearly incompressible – in a regime, all aircraft are propeller-driven (i.e., piston engine). From Mach 0.3 to Mach 0.6, the compressibility effect gradually builds up; however, turboprops are still effective up to Mach 0.5. Above Mach 0.6, the aircraft component geometry caters to compressibility effects. Jet propulsion with reactionary thrust becomes more suitable above Mach 0.6. Therefore, the aircraft component configuration is divided into two classes: one for flying below Mach 0.5 and one for flying above Mach 0.6. A carefully designed turboprop can operate at up to Mach 0.6, with the latest technology pushing toward Mach 0.7. Lifting-surface geometries are those that are affected by compressibility. The fuselage being cylindrical (i.e., axi-symmetric) makes is easier to address the compressibility effect.

4.12 Military Aircraft: Detailed Classification, Evolutionary Pattern,

and Mission Profile

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

.org/Kundu and gives introductory comments on typical military aircraft classification; military aircraft role, statistics, and design considerations; and some relatively newer requirements (evolutionary patterns), and so forth. Figure 4.30 shows

(a) Lockheed F104, Starfighter; (b) McDonnell F4, Phantom; (c) Grumman F14, Tomcat; (d) Northrop F117; and (e) Lockheed F22.

Figure 4.30. Chronology of fighter aircraft design evolution (USA)

4.13 Military Aircraft Mission

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

.org/Kundu and describes military aircraft multiroles, indicating that the same class

of military aircraft can have a wide variety of payload ranges. Figure 4.31 shows weapon configurations for (a) air interdiction, (b) close air support, (c) air defense, and (d) maritime attack.

Figure 4.31. Typical multirole missions

4.14 Military Aircraft Statistics (Sizing Parameters – Regression Analysis)

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

.org/Kundu and gives the statistics of military aircraft as discussed in the following subsections.

4.14.1 Military Aircraft Maximum Take-off Mass (MTOM) versus Payload

In this subsection, at www.cambridge.org/Kundu, Figure 4.32 shows typical statistics of military aircraft payload – range.

Figure 4.32. Military aircraft payload – range (no drop tank or refueling)

4.14.2 Military MTOM versus OEM

In this subsection, at www.cambridge.org/Kundu, Figure 4.33 gives the relation between MTOM and OEM, as well as the operational empty mass fraction (ratio of OEM to MTOM).

Figure 4.33. MTOM versus OEM

4.14.3 Military MTOM versus Fuel Load Mf

In this subsection, at www.cambridge.org/Kundu, Figure 4.34 gives the relationship between internal fuel load and fuel fraction versus MTOM.

Figure 4.34. MTOM versus fuel load

4.14.4 MTOM versus Wing Area (Military)

In this subsection, at www.cambridge.org/Kundu, Figure 3.35 shows wing area, SW, and wing-loading MTOM/SW versus MTOM.

Figure 4.35. MTOM versus wing area

4.14.5 MTOM versus Engine Thrust (Military)

In this subsection, at www.cambridge.org/Kundu, Figure 4.36 presents the relationship between total TSLS and the two types of aircraft mass (e.g., MTOM and TTOM).

Figure 4.36. Aircraft weight versus total take-off thrust