Brief Intro Aircraft Antiskid

HYDRO-AIRE DIVISIONCRANE®

A BRIEFINTRODUCTIONTO AIRCRAFT

ANTISKIDby

Gregg Butterfield

Crane Company, Hydro-Aire Division

Prepared as a Presentation for the1993 ADIUS Conference

(Applied Dynamics International Users Society)


Aircraft Antiskid vs Automobile Antilock

These days everybody is familiar with automotive antilock brakes. But there areconsiderable differences between antilock braking for automobiles and antiskidbraking for aircraft.

6 Aircraft tires are designed for intermittent usage at much higher loadsthan automobile tires. (See figure next page.)

6 During an aircraft stop the load may range from nearly nothing atbrake application, when many aircraft are still nearly airborn, togreater than static loads due to spoiler deployment and thrust vectoring.

6 The energies absorbed by aircraft brakes are orders of magnitudehigher than the energies absorbed by automobile brakes.

Speed Energy/BrakeBoeing 747 200 ft/sec (120 knots) 2 x 107 ft-lbsNissan 200 SX 88 ft/sec (60 mph) 1 x 105 ft-lbs

6 In aircraft antiskid braking, cornering is generally not a consideration.

Learjet - LR-55Boeing 747-300

F-18A

Cessna 650, Citation III

Beech BE-90, King Air

Boeing 707

Lockheed C-5A, Galaxy

SAAB 340

Nissan 200 SXHonda Civic

0

50

100

150

200

250

300

Load/Footprint Area(lb/sq in)

Comparison of Aircraft and AutomobileTire Load Over Footprint Area



Some of the Aircraft SimulatedSince the Installation of the AD100

(Summer 1990 - 1993)

6 Space Shuttle

6 A-12

6 C-17

6 SAAB 2000

6 Jetstream 41

6 MD-80

6 Piaggio P-180

6 Boeing 777

6 F-22

6 F-18

6 Cessna 560

6 Cessna X

6 TU-204

6 Learjet Model 45

6 CL-604

6 Global Express (upcoming)

6 EMB-145 (upcoming)

6 C-130J (upcoming)

6 Gulfstream V (upcoming)

These simulations range from the very simple to the very complex and detailed.

BASIC ANTISKID CONTROL LOOP

rotors to the wheel

stators to the gear

Brake


brakepressure

line

AntiskidValve

valve currentMain WheelControl Card

wheel speed signal

Wheel SpeedTransducer

Ground Speed

What Is A Skid?

time

velo

city skid

skid

skid

Antiskid attempts to keep the wheel right at the vergeof skidding, because that is where the coefficient offriction is highest and braking will be most efficient.

slipvelocity

ground speed

wheel speed

Wheel Speed

Runway

Direction of Motion

Brake Torque

Drag Force

Skids

Slip Velocity

Coe

ffici

ent o

f Fric

tion

m

peak

Slip Velocity = Ground Speed – Wheel SpeedDrag Force = Coefficient of Friction x Weight on the WheelAntiskid attempts to keep the wheel at the peak of the mu-slip curve.

NOTICETHIS DOCUMENT CONTAINS PROPRIETARY INFORMATION WHICH IS THE PROPERTY OFHYDRO-AIRE DIVISION, CRANE CO. AND SHALL NOT BE COPIED OR REPRODUCED, INWHOLE OR IN PART, OR THE CONTENTS DIVULGED OR USED FOR MANUFACTURE,WITHOUT THE SPECIFIC PERMISSION OF HYDRO-AIRE DIVISION, CRANE CO. RECIPIENT, BYTHE ACCEPTANCE, USE OR RETENTION OF THIS DOCUMENT, ACKNOWLEDGES ANDAGREES TO THE FOREGOING TO MAINTAIN THE CONTENTS IN CONFIDENCE.


braked attorque Tb

vw

stretched rubber

rel

axed

rub

ber

driven at

linearvelocity

vf

Transforming thepulley system so that

it looks like a tire.

vf

vg

relaxed rubber

vw

rr

the

tire

Since the rubber is stretchedover the bottom pulley andrelaxed over the top pulleyvf is greater than vw .

Tire/Dual Pulley Analogy

belt belt

Even when there is no actual slip ( vf = vg ) the speed obtained by measuringrotational velocity at the axle ( ωw I rr = vw ) is less than the ground speed, vg ,resulting in apparent slip.

stretched rubber


real slip

Slip Velocity

Coe

ffici

ent o

f Fric

tion

µ

appa

rent

slip

Apparent Slip/Real Slip

Although the tire is not actually slipping on the front side of the mu-slipcurve as far as antiskid is concerned it might as well be.


TTOOPPSSEECCRREETT

Antiskid Control Loop Block Diagram


VAXStation 3100

MacintoshQuadra 900

LN05R

Anti-Skid

ControlCard

I/O CabinetAD 100

Airplane, Gear, Brake, and Tire Models

Q-bus

fromDAC wheel

speedcurrent

to antiskid servo

brake

pressurexdcr

Hydraulic Simulator

pressure

BMVreturn

returnA/SValve

brakepressureto ADC

VAXServer 3300

Ethernet

Voltage Controled OscillatorSimulates the output of awheel speed transducer

VCO

solenoidvalve

supply pressuretriggerfromDAC

switch &power supply

Ethernet

VAXStation 3100

DEClaser 2100

Ethernet

MacintoshQuadra 900

Ethernet

ANTISKID SIMULATION - HARDWARE IN THE LOOP

x

the number ofwheels



Hydraulic Simulator

6 Aircraft line lengths, diameters, and total degrees of bend areduplicated as closely as possible. Where there is flex hose the actualaircraft part is used whenever possible.

6 Actual aircraft valves are used. These may include:

° Antiskid valve° Brake metering valve° Autobrake valve° Shutoff valves° Check valves° Pressure regulator

6 Actual brakes from the particular aircraft are used wheneverpossible.

6 Other hardware may include:

° Hydraulic fuses° Swivel joints° Etc.

3 The intent is to duplicate the aircraft brake 3hydraulic system as closely as possible.


Components of Antiskid Simulation

6 Aircraft Model

° Forward Motion° Vertical Motion° Pitch

Vertical gear/tire stiffness and damping are generally included inthis part of the model.

6 Gear Model

Gear models range from the very simple:

° Fore-aft motion relative to aircraft.° Damped mass-spring.

To the very complex:

° Fore-aft motion° Lateral motion° Yaw° Tire shimmy° Shimmy damper° Etc.


Components of Antiskid Simulation

continued

6 Brake Torque

° Simple table driven model. Brake torque is a function ofbrake pressure and aircraft velocity or wheel speed.

° More complex table driven model. Brake torque is afunction of brake pressure, aircraft velocity, and wheelspeed. Additional dynamics may be applied to bothpressure and torque.

° Energy/temperature driven model.

6 Wheel Model

The wheel is acted on by brake torque and the drag force betweenthe tire and the runway.

Brief Intro Aircraft Antiskid

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