A preliminary design method has been developed for determining weight and dimensions of aircraft gas turbine engines. The method, using hand calculations, permits assessment of engine technology levels, comparisons of thermodynamic cycles or mechanical arrangements. A two-spool conventional turbofan is exemplified. The method can be applied to any number of spools and for virtually any component arrangement, and for non-conventional engines as well. The primary output is the engine weight including accessories and nozzles, but not the inlet, nacelle or other installation features. Engine dimensions are also determined as required for a complete propulsion installation or external drag analysis.
Rotating components comprise the major portion of total engine weight. To achieve a desired accuracy of +-5% to 10%, these components are weighed on a stage-by-stage basis. Spool speeds are established by blade-pull stresses or aerodynamic speed limitations. Blade weights are calculated based on flow areas, and disc volume is determined as a function of the centrifugal force of the blades. Blade weights, disc weights, and other components are estimated by correlations of these components from a large data base of manufacturers’ existing production engines and proposed future engines.
A typical two-spool turbofan is included as a sample case in the appendix. This sample problem shows the step-by-step weight calculation procedure, and also illustrates the recommended engine design procedure that must be used when the weight method is applied to an engine that has not already been designed.