Engine Thermodynamic Cycle and Mission Analyses
have been performed to identify the most important technologies to pursue in order to achieve given mission requirements. Comparative aircraft propulsion system studies identified the most promising engine configurations and thermodynamic cycles for supersonic and subsonic missions.

Cycle analyses, flowpath definition methodologies, and weight estimation procedures are used to characterize advanced propulsion concepts while subsequent mission analysis generate merit criteria such as takeoff gross weight and direct operating cost. This involves installing conceptual propulsion systems on hypothetical airframes and "flying" the resulting aircraft on a representative mission profile. Such an overall simulation captures the multi-variable tradeoffs inherent in nearly all advanced technology assessments. Typically, aircraft takeoff gross weight is minimized subject to many mission-related constraints, such as maximum runway length, minimum landing approach speed, and allowable noise limits. It is also frequently necessary to perform sensitivity studies to identify the most important variables and determine their vulnerability to technology shortfalls and/or ground rule changes. The knowledge acquired through such studies helps guide the conceptual/preliminary designs and ultimately identifies the most beneficial technologies as being worthy of pursuit.

The depth of our analyses can be varied from relatively simple and rapid studies that capture only the first-order effects, to more comprehensive analyses that include higher-order effects. The process usually begins with the generation of a engine performance model using an engine cycle analysis code such as NPSS. This is accompanied by a flowpath definition and weight estimate such as generated by the NASA WATE code. An installation code (INSTAL) estimates the nacelle weight and drag. All of this propulsion information is then fed into a mission analysis code (FLOPS) to perform the mission simulation. In addition to using these codes to conduct system studies, N&R engineers have also participated in the development of these and similar codes.