Appendix 1
6. AIRFRAME CONSIDERATIONS.
a. Instrumentation Accuracy.
(1) The accuracy of any power assurance check is strongly dependent on the air data and engine parameters. SAE ARP 1217 (May 1979) provides guidance on the desired measurement accuracy for parameters used for engine health and diagnostic monitoring. The parameters to be considered with their respective functions include:
Pressure Altitude Air data basis for Flight Speed establishing power Free Air Temperature plant inlet pressure (stagnation) and temperature Torque Direct measurement of Power Turbine Speed power output.
Gas Generator Speed(s) Measured Gas Temperature Fuel Flow Primary thermodynamic and limiting parameters Secondary trend monitoring and potential limiting parameter
(2) The overall power check accuracy can be assessed on a suitable statistical basis using equations that link the measured parameters and inserting system accuracy distributions for each value. This approach will provide an overall assessment of power check accuracy and will highlight major contributors to error. The accuracy assessment at each parameter should include the following elements:
Sensor error Indicator error System error Reading error
(3) This assessment might show that while conventional instrument displays of air data are acceptable, servo driven digital displays are desired for engine parameters.
Further, displays that provide a "snapshot" of engine readings at a given moment may be useful in avoiding variation in power level during the finite period needed to manually read and log the set of parameters.
b. Installation Loss Definition.
(1) Installation loss definition is an extremely important aspect of any form of rotorcraft engine performance. Engines are certificated and sold with uninstalled performance guarantees and estimates as to the power output capabilities. Installation of the engine in the rotorcraft imposes power output penalties that must be accounted Page A1-6
Appendix 1 for in any sort of power assurance check procedure. Normal practice dictates that the engine manufacturer provides a computer program that accurately predicts the engine power output capability throughout the approved flight envelope. This computer program has the capability to correct the power output for the losses incurred by the rotorcraft installation.
(2) Losses that can reduce engine power available are as follows:
(1) Air intake total pressure loss (II) Air intake total temperature rise
(iii) Exhaust back pressure
(iv) Accessory power extraction
(v) Compressor bleed air extraction
(vi) Off-optimum power turbine output speed effects
(3) The above items and methods of dealing with them are clearly defined in SAE Aerospace Recommended Practice (ARP) 1702. Typically, these losses will not be a fixed percentage but will vary with engine operating conditions and environment.
(4) Any calculations involving power assurance data should use the approved engine performance program, and the rotorcraft losses should be input on a discrete basis so that the interaction between losses and their independent variability is properly considered. This approach is clearly defined in ARP 1702. Accurate consideration of the losses should produce a Power Assurance Check that will preclude premature removal of acceptable engines or continued operation of inadequate power plants.
7. ROTORCRAFT FLIGHT MANUAL RFM).
a. The Power Assurance Check data for the installed engine (engine data adjusted for inlet losses, exhaust losses, bleed extraction, power extraction, and off-optimum output shaft speed operation) should be presented in the RFM in an easily useable format. The data format may consist of charts of engine torque (at constant power turbine shaft speed) versus allowable values of gas generator speed and gas path temperature covering the range of ambient conditions for takeoff operations.
Associated limitations for the rotorcraft transmission and the engine should be noted.
b. The RFM should also:
(1) Include succinct statements of the reason for the Power Assurance Check and what must be done if the Power Assurance Check results are not acceptable.
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Appendix 1
(2) Clearly state that Power Assurance Check either is a pre-takeoff or in-flight procedure, as required by operations, specifications and/or other approval authority documents.
(3) Be kept simple, easy to use, and identify equipment operation limitations and requirements.
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7/30/97/ FUEL
FUEL FLOW
CONTROL
TRANSMITTER
FUEL PUMP FIGURE АРХ1-1 BY-PASS
TEE NEEDLE VALVE
FUEL PRESSURE
TRANSMITTER * U.S. GOVERNMENT PRINTING OFFICE: 1997 - 430 - 037 / 80092 FUEL FUEL NOZZLE
PRESSURE GAGE
COCKPIT FUEL AIRCRAFT
FLOW GAGE FUEL TANK Appendix 1 AC 27-1A Page A1-9 INSTALLED ENGINE FUEL FLOW CAPACITY CHECK