This SAE Aerospace Recommended Practice (ARP) specifies a set of functions and their expected behavior that constitute an Application Programming Interface (API) for gas turbine engine customer programs. The main body of this document contains a description of each of the API function calls and of the data that passes through these functions. Implementations of this API in specific programming languages are contained in separate appendices. These appendices include language specific details and the definitions for each function as required for the given language.AS681 is the parent document of ARP4868. All of AS681 applies to customer engine programs written to conform to this document.

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 Practice (ARP) provides guidance for the presentation of gas turbine engine transient performance models with the capacity to be implemented as digital computer programs operating in real time and is intended to complement ARP1257 and AS681.Such models will be used in those applications where a transient program must interface with physical systems. These applications are characterized by the requirement for real time transient response.These models require attention to unique characteristics that are beyond the scope of ARP1257. This document is intended to facilitate the development of mathematical models and the coordination of their requirements with the user. It will not unduly restrict the modeling methodology used by the supplier.The objective of this document is to define a recommended practice for the delivery of mathematical models intended for real time use. Models used in this application may also be contained in deliverable computer programs covered by ARP1257.

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.

This SAE Aerospace Recommended Practice (ARP) describes a class of digital computer programs for use by organizations other than the engine supplier for reduction of engine test data relating to the interface of the engine in the airframe or test facility. This ARP also is intended as a guide for the preparation of such computer programs.ARP1210 was reviewed and found to be out of date. The vast majority of ARP1210 was deemed completely unnecessary as already being redundant to or in some cases now in conflict with its parent document AS681 ("Gas Turbine Engine Performance Presentation for Computer Programs"), and some of the material was deemed no longer valid. The superseding documents are AS681 and AIR5509 ("Using Engine Test Data to Model Engine Performance").

This SAE Aerospace Recommended Practice (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 AS681.