APU Sound Model Tutorial

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APU Sound Model Tutorial
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Overview

• KC-135R APU
• Sound Recording/Analysis
• V Modeling

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KC-135R APU

• KC-135R Has Two APUs
• Units are Located in Open Aft Cabin Area
• Sound Level is Significant in Cockpit

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Notes on Recording

• Need Calibrated SPL Microphone
• Record at Source for Model Details
• Record in Cockpit for FAA Level D Certification
• Record Digitally
• (24 Bit) Mono
• Associate with Instrumentation if Possible

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Sound Analysis Tools

• Adobe Audition
• Adobe Systems Incorporated
• Edit in Frequency Domain

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Sound Spectrograph
Time
Freq
Brighter Colors Are Greater Amplitudes
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APU Sound Components

• Intake/Exhaust Door Open/Close
• Start Motor
• Turbine and Noise Spectra
• Bleed Air Valve Open

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APU Sound Components
Start Motor
Turbine
Bleed Air Valve Open
Door Open
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Enlarged Start Section
Start Motor
Turbine Spool
Door Open
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Starter Motor
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Turbine
Turbine Discrete Blade Passing Frequency (DBPF
NTSB term)
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Turbine Removed
Removed Turbine DBPF
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Model Inputs

• Intake/Exhaust Door Open/Close, Start Motor,
  Bleed Air Valve
• Discrete Events
• Turbine
• Model Based on RPM From Host

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V APU Model
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Summary

• Very high fidelity model
• V and FXDirect enabling technologies
• That was just an APU
• Modular design eases re-use