Concurrent optimization of airframe and engine design parameters

Abstract

An integrated system for the multidisciplinary analysis and optimization of airframe and propulsion design parameters is being developed. This system is known as IPAS, the Integrated Propulsion/Airframe Analysis System. The traditional method of analysis is one in which the propulsion system analysis is loosely coupled to the overall mission performance analysis. This results in a time consuming iterative process. First, the engine is designed and analyzed. Then, the results from this analysis are used in a mission analysis to determine the overall aircraft performance. The results from the mission analysis are used as a guide as the engine is redesigned and the entire process repeated. In IPAS, the propulsion system, airframe, and mission are closely coupled. The propulsion system analysis code is directly integrated into the mission analysis code. This allows the propulsion design parameters to be optimized along with the airframe and mission design parameters, significantly reducing the time required to obtain an optimized solution. by an optimizer from the initial guess (represented by an open circle). However, the mission code does not allow for variations in engine design parameters. The engine design is fixed at the time the engine data is produced. In order to determine the optimum combination of aircraft and engine design it is necessary to try many different engine designs. For each engine design the optimum aircraft solution is determined. These optimum solutions are then compared to determine the best overall design choice. This method can be very time consuming. It is shown in Figure 4. This process has been improved by directly coupling the propulsion analysis codes and mission analysis codes with an optimizer. The engineer defines the baseline aircraft and cycle. The optimizer acts as the main program, running the analysis and changing the design parameters to arrive at a solution. This method, called IPAS, is shown in Figure 5. WAS would greatly reduce the time required to reach an optimum solution by performing all the design iterations necessary. The engineer would be free to spend more time analyzing results and developing new configurations. This paper will describe the analysis codes used in IPAS and the methods used to link them. This paper will also give an example of IPAS being applied to a supersonic transport mission. The goal of the analysis is to determine the minimum TOGW aircraft subject to the constraints of noise and TOFL. Intem'ation of Analysis Codes Five analysis codes are directly coupled in HAS. The cycle analysis code used is NEPP, the NASA Engine Performance Program (ref. 1). The mission analysis code used is FLOPS, the FLight OPtimization System (ref. 2). The engine weights are computed using WATE, Weight Analysis of Turbine Engines (ref. 3). The inlet and nozzle performance are calculated using INSTAL (ref. 4). The noise analysis is calculated using FOOTPR (ref. 5). Cycle Anal_ NEPP is an engine simulation code that will perform one dimensional steady state thermodynamic a...

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