This SAE Aerospace Standard (AS) provides the method for presentation of gas turbine engine steady-state and transient performance calculated using computer programs. It also provides for the presentation of parametric gas turbine data including performance, weight, and dimensions computed by computer programs.This standard is intended to facilitate calculations by the program user without unduly restricting the method of calculation used by the program supplier. This standard is applicable to, but not limited to the following program types: data reduction, steady-state, transient, preliminary design, study, specification, status, and parametric programs. This document has been revised to align with the creation of and/or updates to standard documents AS6502, AS755, AS4191, and AS210. Also, supplier/customer model delivery points of discussion were added to improve the efficiency of model delivery. An S-15 document family tree was added to illustrate the relationships of the documents referenced within this document. In addition, other minor changes were also made for clarification purposes.

This SAE Aerospace Standard (AS) provides a method for gas turbine engine performance computer programs to be written using Fortran COMMON blocks. If a "function-call application program interface" (API) is to be used, then ARP4868 and ARP5571 are recommended as alternatives to that described in this document.When it is agreed between the program user and supplier that a particular program shall be supplied in Fortran, this document shall be used in conjunction with AS681 for steady-state and transient programs.This document also describes how to take advantage of the Fortran CHARACTER storage to extend the information interface between the calling program and the engine subroutine. This document has been revised to align with the creation of standard document AS6502 and updates to standard document AS681. Other minor changes were also made for clarification purposes.

Steady state engine performance programs discussed in this Standard will be confined to two basic performance categories: preliminary design or specification. Preliminary design programs may vary in scope, but will be representative of the defined engine performance until the engine is defined by a specification. A specification program will accurately represent the engine described by the specification and will identify the appropriate model specification. Normally, the computer program will be the primary source of performance data.Two additional categories of program are status and data reduction interface programs, which are covered by ARP 1211 and 1210 respectively.

This document provides recommendations for several aspects of air-breathing gas turbine engine performance modeling using object-oriented programming systems. Nomenclature, application program interface, and user interface are addressed with the emphasis on nomenclature. The Numerical Propulsion System Simulation (NPSS) modeling environment is frequently used in this document as an archetype. Many of the recommendations for standards are derived from NPSS standards. NPSS was chosen because it is an available, production system. The practices recommended herein may be applied to other object-oriented systems.While this document applies broadly to any gas turbine engine, the great majority of engine performance computer programs have historically been written for aircraft propulsion systems. Aircraft and propulsion terminology and examples appear throughout. Gas turbine engine manufacturers (suppliers) have long provided their customers with computer programs which simulate engine performance. Application manufacturers and others (customers) use these programs, often called models or simulations, in design studies, mission analysis, life cycle analysis, and performance prediction of their products. These models are used throughout the life of a product, from conceptual design through production, deployment, field use, maintenance, and overhaul. Communication between suppliers and customers is more productive and less error prone if all engine models adhere to common guidelines with respect to presentation of data and interface with other computer programs. No guidelines or reccommended parctices currently exist for Object-Oriented models.

This SAE Aerospace Recommended Paractice (ARP) provides a method for digital computer programs for gas turbine engine performance, steady-state or transient, performance to be written using the FORTRAN 77 language. When it is agreed between the program User and Supplier that a particular program shall be supplied in FORTRAN 77, it is recommended that this ARP be used in conjunction with AS681 for steady-state and transient programs. This ARP also describes how to take advantage of the FORTRAN 77 CHARACTER storage to extend the information interface between the calling program and the engine subroutine. The ARP has the same major section numbers as AS681 to facilitate its use with this document. The information given in each section of this ARP is additional to that given in AS 681.As ARP4191C contains information that was incorporated from AS681. The S15 committee decided to upgrade ARP4191C to AS4191. Therefore as AS4191 supersedes ARP4191C, it (ARP4191C) should be cancelled.