2.9 Comparison between Civil and Military Aircraft Design Requirements

This section compares the civil and military aircraft design classes, as shown in Table 2.2.

Once the configuration is finalized, the governing equations for sizing, engine matching, and performance analysis are the same for all categories (although drag estimation presents some difficulty for complex configurations, especially supersonic designs). The crux of a military aircraft design is systems integration for survivability, maneuver control (i.e., FBW), target acquisition, weapons management, navigation (i.e., unknown terrain), and communication strategies (e.g., identification of friend or foe). Military aircraft design is very different compared to civil aircraft design. A major aspect of combat aircraft design is the systems architecture for threat analysis and survivability – without these in the combat aircraft design of the Eurofighter Typhoon or the F22 Raptor class, any coursework exercise is meaningless. Military certification standards are more elaborate and time consuming. These crucial issues are not within the scope of this book – only a few specialist books are available that address systems architecture for threat analysis and survivability – and

some of those are obviously confidential. However, seminars on these topics are offered to those who are well versed in aircraft design.

The simpler case of an AJT in subsonic operation provides an idea of military aircraft design, although the author would not apply the certification regulations as extensively as in the civil aircraft examples for reasons discussed previously. It is possible that the CAS version of the AJT could become supersonic in a shallow dive.

2.10 Airworthiness Requirements

From the days of barnstorming and stunt-flying in the 1910s, it became obvious that commercial interests had the potential to short-circuit safety considerations. Government agencies quickly stepped in to safeguard people’s security and safety without deliberately harming commercial interests. Safety standards were developed through multilateral discussions, which continue even today. Western countries developed and published thorough and systematic rules – these are in the public domain (see relevant Web sites). In civil applications, they are FAR for the United States [8] and CS (EASA) for Europe. They are quite similar and may eventually merge into one agency. The author’s preference is to work with the established FAR; pertinent FARs are cited when used in the text and examples. FAR documentation for certification has branched out into many specialist categories, as shown in Table 2.3.

Table 2.4 provides definitions for general, normal, and transport categories of aviation.

Table 2.4. Aircraft categories

MTOW = maximum takeoff weight

PAX = passengers

In military applications, the standards are Milspecs (U.S.) and Defense Standard 970 (previously AvP 970) (U.K.); they are different in some places.

Since 2004, in the United States, new sets of airworthiness requirements came into force for light-aircraft (LA) designs and have eased certification procedures and litigation laws, rejuvenating the industry in the sector. Europe also has a similar approach but its regulations differ to an extent. Small/light aircraft and microlight types have different certification standards not discussed in this book.

2.11 Coursework Procedures

The coursework task is to conduct a mock market study. The instructor divides the class into groups of four or five students who will work as a team (see the Road Map of the Book, which gives the typical allotted time). However, how the class is conducted is at the instructor’s discretion.

Step 1: The instructor decides which class of aircraft will be used for the design project. Students will have input but the instructor ultimately explains why a certain aircraft is chosen. Designing a conventional civil or a military trainer aircraft is appropriate for undergraduate introductory work. In this book, a Bizjet and an AJT aircraft design are used.

Step 2: The instructor discusses each suggestion, discarding the impractical and coalescing the feasible. The instructor will add anything that is missing, with explanations.

Step 3: Each team must submit a scaled, three-view sketch of the proposed design. There will be differences in the various configurations. CAD is recommended.

Step 4: The instructor discusses each configuration, tailoring the shape, with explanation, to a workable shape. Each team works on its revised configuration; preferably, the class will work with just one design.