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(This document supersedes and cancels AIR 12) 'Ground resonance' is a term which originated in the early days of autogiro development in this country. It is a somewhat ambiguous term as the conditions it describes usually occur at the ground but do not have any association with the common expression 'ground effect'. However, the troubles usually associated with 'ground resonance' do occur when the ship is on or near the ground.

It is recommended that all helicopter engine development programs include an evaluation of engine starting requirements. The evaluation should include starting requirement effects on helicopter weight, cost, and mission effectiveness. The evaluation should be appropriate to the engine stage of development.

This SAE Aerospace Information Report (AIR) outlines a recommended procedure for evaluation of the vibration environment to which the gas turbine engine powerplant is subjected in the helicopter installation. This analysis of engine vibration is normally demonstrated on a one-time basis upon initial certification, or after a major modification, of an engine/helicopter configuration. This AIR deals with linear vibration as measured on the basic case structure of the engine and not, for example, torsional vibration in drive shafting or vibration of a component within the engine such as a compressor or turbine airfoil. In summary, this AIR discusses the engine manufacturer’s "Installation Test Code" aspects of engine vibration and proposes an appropriate measurement method.

This SAE Aerospace Information Report (AIR) defines the helicopter bleed air requirements which may be obtained through compressor extraction and is intended as a guide to engine designers.

This SAE Aerospace Information Report (AIR) defines the helicopter bleed air requirements which may be obtained through compressor extraction and is intended as a guide to engine designers.

This SAE Aerospace Recommended Practice (ARP) identifies and defines methods of compliance with power available and inlet distortion requirements for rotorcraft with inlet barrier filter (IBF) installations. The material developed herein is intended to provide industry-recommended methods of compliance with civil airworthiness regulations. It is intended to serve as a basis for new or revised FAA advisory material describing acceptable methods for determining power assurance, establishing power available, and for substantiating acceptable engine inlet distortion for IBF installations. The ARP does not address other types of inlet protection systems such as inertial separator, electrostatic precipitators, or foreign object debris (FOD) screens.

This SAE Aerospace Recommended Practice (ARP) identifies and defines a method of measuring those factors affecting installed power available for helicopter power plants. These factors are installation losses, accessory power extraction, and operation effects. Accurate determination of these factors is vital in the calculation of helicopter performance as described in the flight manual. It is intended that the methods herein prescribe and define each factor as well as an approach to measuring said factor. Only standard installations of turboshaft engines in helicopters are considered. Special arrangements leading to high installation losses, such as the fitting of an infrared suppressor may require individual techniques for the determination and definition of engine installation losses.

This SAE Aerospace Recommended Practice (ARP) identifies and defines a method of measuring those factors affecting installed power available for helicopter powerplants. These factors are installation losses, accessory power extraction, and operational effects. Accurate determination of these factors is vital in the calculation of helicopter performance as described in the RFM. It is intended that the methods presented herein prescribe and define each factor as well as an approach to measuring said factor. Only basic installations of turboshaft engines in helicopters are considered. Although the methods described may apply in principle to other configurations that lead to more complex installation losses, such as an inlet particle separator, inlet barrier filter (with or without a bypass system), or infrared suppressor, specialized or individual techniques may be required in these cases for the determination and definition of engine installation losses.

This SAE Aerospace Recommended Practice (ARP) provides a guide for the preparation of a Helicopter Engine/Airframe Interface Document and Checklist. This document and checklist is intended to provide complete relevant information on the characteristics, performance, and engine interfaces. Of most importance is the identification of the data and the location of data to assure that the engine manufacturer and the airframe manufacturer supply information that can be easily located by either manufacturer.

This Aerospace Recommended Practice (ARP) defines the measurement parameters that may be used by a pilot or operator to monitor the thermodynamic health of a turboshaft engine in a helicopter and the measurement system accuracies desired.

This SAE Aerospace Recommended Practice (ARP) defines the measurement parameters that may be used by a pilot or operator to monitor the thermodynamic health of a turboshaft engine in a helicopter and the measurement system accuracies desired.

A general method for the preliminary design of a single, straight-sided, low subsonic ejector is presented. The method is based on the information presented in References 1, 2, 3, and 4, and utilizes analytical and empirical data for the sizing of the ejector mixing duct diameter and flow length. The low subsonic restriction applies because compressibility effects were not included in the development of the basic design equations. The equations are restricted to applications where Mach numbers within the ejector primary or secondary flow paths are equal to or less than 0.3.