A nozzle is sometimes called the exhaust duct or tail pipe, and is the last component of a jet engine through which the air passes. Up to two parallel nozzles are present on an engine: primary and fan (or secondary). In this chapter, both converging and converging– diverging (CD) nozzle types are discussed, and the two nozzles can be any combination of the two types (i.e., converging and converging–diverging, converging and converging, etc.). Recall that the functions of the nozzles are to convert high-pressure, high-temperature energy (enthalpy) to kinetic energy and to straighten the flow so that it exits in the axial direction. It is from this conversion process that the thrust is derived. Because of the high temperatures that a nozzle experiences, materials used in nozzle construction are usually a nickel-based alloy, titanium alloy, or ceramic composite. In Chapter 2, the nonideal effects of nozzles are discussed. The reader is also encouraged to review Appendix C as many of the fundamentals are covered therein. In this chapter, these effects are covered in more detail along with other design considerations.

As discussed in Chapters 2 and 4, the basic operating principle of a compressor is to impart kinetic energy to the working fluid by the means of some rotating blades and then to convert the increase in energy to an increase in total pressure. Axial flow compressors are covered in Chapter 5. These compressors are used on large engines and gas turbines. However, for small engines – particularly turboshafts and turboprops – centrifugal (or radial) compressors are used.

Two remaining components that affect the overall performance of a turbofan engine are the bypass duct and mixer, as shown in Figure 11.1. Applications have previously been presented in Figures 2.42 and 2.44. These are relatively simple compared with the other components but should be included because they both generate losses in total pressure. Because the length-to-flow-width ratio of the bypass duct is moderate, the duct can incur significant losses. Also, it is desirable to have a uniform temperature gas entering the afterburner or nozzle so that these components operate near peak efficiency. Mixing of two fluid streams at different temperatures is a highly irreversible process, and a mixer consists of 3-D vanes in both the radial and circumferential (annular) directions. Thus, with good mixing of the low-temperature bypassed air and high-temperature primary air, further significant losses can occur. Owing to the temperatures exiting from the turbine, mixers are generally fabricated from a nickel-based alloy. With these losses the thrust and TSFC will both be compromised.

A generalization of the classical theory of flight dynamics is presented that includes quasi-steady aeroelastic effects using residualization approach. This is then used to investigate static stability of the aircraft, which may result in torsional divergence, as well as its controllability, which results in a metric for control effectiveness and potentially control reversal. Several illustrative problems are finally considered: a simplified model for the dynamics of a aircraft with a rigid fuselage, the aeroelastic trim of an aircraft with high-aspect ratio wings, and roll control with aeroelastic effects.

A modelling strategy based on geometrically-nonlinear composite beams and unsteady vortex-lattice aerodynamics is introduce for the computer simulation of very flexible aircraft dynamics. The key challenges of this approach are discussed, including spatial coupling of structural and aerodynamic models and time integration schemes. This is then exemplified using numerical results on several recent prototypes of highly-efficient wings and aircraft. Finally, some of the analysis methods used in aircraft design are reviewed to incorporate the more complex physics associated to increased flexibility.

This chapter first defines the scope for flexible aircraft dynamics. It reviews the historical evolution of airframe designs and of the analysis methods used to support them. It also reviews some basic concepts in dynamics, linear systems, and system identification that are of relevance to the book.

Vortex-lattice solutions for unsteady aerodynamics on lifting surfaces are introduced. They provide a general description for aeroelastic applications with low-speed aircraft undergoing large wing deformations. The basic solution process is first outlined for 2-D problems, using a discrete vortex model for the fluid, and then extended to 3-D models using vortex rings. It is shown how this general solution can then be linearized around an arbitrary reference, and recast in state-space form. A compact form of the linear aerodynamic model is then introduce using methods of model-order reduction, and in particular, balanced realizations are seen to give a computationally-efficiency solution.

This chapter oulines the curretn insutrial methods for experimental modal analysis of air vehicles. Both ground and flight vibration tests are discussed, with a focus on large transport airraft with moderately stiff wings.

Geometrically-nonlinear composite beam solutions are discussed as structural models for airframes with slender subcomponents. As this is intended for aircraft applications, the beam equations of motion are written with respect to a moving reference frame, which is rigidly-attached to a fixed point on the aircraft. Three different solution methods are then discussed, corresponding to a displacement-based formulation, a strain-based formulation, and a hybrid formulation in intrinsic variables. Key issues in numerical solution are discussed, including the parametrization of the finite rotations and linearization around arbitrary equilibrium conditions.