1. 1 The Design Process 1.1 Introduction
2. Apersistent problem is that of the often overlapping nomenclature of aerodynamicsandpropulsion.Becausethesefieldsgrewmoreorlessindependently,the samesymbolsarefrequentlyusedtorepresentdifferentvariables.Facedwiththis profusion of symbology, the option of graceful surrender was elected, and the traditional conventions of each, as appropriate, are used. The Table of Symbols encompasses all of the aerodynamic and propulsion nomenclature necessary for thistextbook,theformerapplyingtoChapters1-3andthelattertoChapters4-10, respectively.Ourexperiencehasshownthatinmostcasesreaderswithappropriate backgrounds will have little difficulty interpreting the symbology and, with practice,recognitionwillbecomeautomatic. 1.6 Charting the Course
3. The constant ratio of specific heats used in the preceding equations must be judiciously chosen in order to represent the behavior of the gases involved realistically. Because of the temperature and composition changes that take place duringthecombustionofhydrocarbonfuels,thevalueofγ withintheenginecan be considerably different from that of atmospheric air (γ = 1.4) Two commonly occurringapproximationsareγ = 1.33inthetemperaturerangeof2500-3000◦R andγ = 1.30inthetemperaturerange3000-3500◦R.ThecomputationalcapabilitiesofAEDsys(seeSec.1.10.1)mayalsobeusedinavarietyofwaystodetermine themostappropriatevalueofγ tobe usedinanyspecific situation. 1.10 Looking Ahead