The requirements for low weight in combination with operation at high tangential velocities (and, in the case of the turbine, at high temperatures) impose severe constraints on the design of turbomachinery, which are in turn reflected in structural characteristics unique to aircraft engines. Even a casual perusal of the cross-sectional drawings in figures 1.15-1.20 shows that an engine is composed of closely related components of rather complex shape. The reasons for these shapes and relationships must be understood at least qualitatively if one is to appreciate the compromises required in engine design, and it is such qualitative understanding that we aim for here. Techniques are available for much more precise treatment of all these matters, some in the literature and some as part of the fund of proprietary information held by each engine manufacturer, but neither the space nor the author's understanding is sufficient for a quantitative treatment here.

Many of the unique features of engine structures stem from the requirements of high-speed turbomachinery, so the structural characteristics dictated by these requirements will be discussed first. The high operating temperatures and the resulting thermal stresses produce a second set of characteristics. Finally, the need to support the rotating components of an aircraft engine in the proper spatial relationships against the thrust, pressure, and inertial loads requires specialized static structural members or frames.