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MathWorks Aerospace

& Defense Conference 2006

Hardware-In-the-Loop Simulation of an Aircraft Brake System

Alan Johnson, Andrew N. Hall, Gary McKaySystem Design and IntegrationCessna Aircraft Company

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Outline

• Antiskid Background

• Motivation

• HIL: Hardware; Software

• Antiskid Control

• HIL Tests

• Concluding Remarks

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Cessna makes jets, too.

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Why antiskid?

• Better performance

• Even tire wear

• Directional stability

• Safety

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accumulator

pump brake metering valve

antiskid valve

antiskid control box

pedals

brake

wheel speed transducer

Antiskid Brake System

reservoir

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Experimental Flight Data

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Motivation: • Product improvement

• Smooth ride

• Engineering curiosity

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• Flight test – expensive

• Analytical – slow simulation

• Hybrid – HIL: real-time; cost?

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HIL Simulation

• Already had:

– MATLAB

– Simulink

– Real-Time Workshop

• PIII leftovers

• Compatible A/D – D/A card

• xPC Target

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HIL: Hydraulic components

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HIL: Computer interface

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reservoir

accumulator

pump brake metering valve

antiskid valve

antiskid control box

pedals

brake

VCO Simulink

airplane

Simulink

airplane

HIL Block Diagram

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Simulink airplane model

aero 3 DoFbrake and landing gear

FD = μFz

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brake torquewheel-tire inertia

Wheel-tire equation of motion:

τ = I α

tire-road force

slip velocity

A/D

D/A

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0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

slip ratio

mu

NASA TN D-1376, Figure 78

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0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

slip ratio

mu

NASA TN D-1376, Figure 78

50 knots

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0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

slip ratio

mu

NASA TN D-1376, Figure 78

50 knots

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Some Assumptions and Limitations

• Tire μ, Brake μ

• 3 DoF

• Trailing link gear model

• Ground effect aero

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Antiskid Control Background

• Control logic (black box)

– Input: Wheel speed

– Output: Control current

• Antiskid valve

– Input: Commanded pressure; control current

– Output: Brake pressure

brake metering valve

antiskid controlwheel speed sensor

brakes

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Pressure vs. Control Current

Change control in two ways:

• Electrically

• Hydraulically

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HIL Usefulness

• Cost-effective

• Time-saver

• Multi-purpose