3.23.12 Cabin Height, Hcab

This is the internal cabin height from the floor, as shown in Figure 3.50.

3.23.13 Cabin Width, Wcab

This is a the internal cabin width, as shown in Figure 3.50.

3.23.14 Pilot Cockpit/Flight Deck

This is a term used for the enclosed space for the flight crew in the front fuselage. Chapter 15 describes the flight deck in more detail.

A military aircraft fuselage is very different because it does not have passengers to carry and is more densely packed. Various types of fuselage cross-sections are shown in Figure 4.7 (see Web site). Their associated fineness ratios and other statistical data on fuselage parameters are provided in Section 4.7.

3.24 Undercarriage

Chapter 7 is devoted entirely to a discussion of undercarriage design.

3.25 Nacelle and Intake

A nacelle is the structural housing for an aircraft engine. In civil aircraft, nacelles are invariably externally pod-mounted, either slung under or mounted over the wing or attached to the fuselage (see Figure 4.28). The front part of the nacelle is the intake and the aft end is the nozzle. Military aircraft engines are invariably buried in the fuselage; the front is called the intake in the absence of a nacelle. Chapter 10 discusses the nacelle in detail.

In addition to housing the engine, the main purpose of the nacelle is to facilitate the internal airflow reaching the engine face (or the fan of gas turbines) with minimum distortion over a wide range of aircraft speeds and attitudes. For subsonic turbofans, the intake acts as a diffuser with an acoustic lining to abate noise generation. The inhaled air-mass flow demanded by an engine varies considerably: At idle, just enough is required to sustain combustion, whereas at maximum thrust, the demand is many times higher. A rigid intake must be sized such that during critical operations (i.e., takeoff, climb, and cruise), the engine does not suffer and generates adequate thrust. Supersonic intakes are even more complex and are designed to minimize loss resulting from shock waves.

3.26 Speed Brakes and Dive Brakes

Speed brakes and dive brakes have the same definition. They are mounted specifically on the fuselage for military aircraft and as spoilers on the wings for civil aircraft (Figure 3.51). However, there are civil aircraft that use this type of device mounted on the fuselage.

Speed brakes are specifically designed to reduce speed rapidly, typically on approach and in military combat maneuvers.

Figure 3.51. Speed brakes and dive brakes

Speed and dive brakes are primarily drag-producing devices positioned in those areas that will create the smallest change in moments (i.e., kept symmetrical to the aircraft axis with the least moment arm from the CG). Figure 3.51 shows fuselagemounted devices.

The Boeing F22 does not have a separate dive brake. It uses the two rudders of the canted V-tail deflected in opposite directions along with spoilers and flaps deflected upward and downward, respectively.