8/11/2019 Mae 331 Lecture 23

1/11

Atmospheric Hazards to FlightRobert Stengel,Aircraft Flight Dynamics, MAE 331, 2012

! Microbursts

! Wind Rotors

! Wake Vortices

! Clear AirTurbulence

Copyright 2012 by Robert Stengel. Al l rights reserved. For educationa l use only.http://www.princeton.edu/~stengel/MAE331.html

http://www.princeton.edu/~stengel/FlightDynamics.html

Frames of Reference

! Inertial Frames! Earth-Relative

!

Wind-Relative (Constant Wind)

! Non-Inertial Frames! Body-Relative

! Wind-Relative (Varying Wind)

Earth-Relative VelocityWind Velocity

Air-Relative Velocity

Angle of Attack,

Flight Path Angle,

Pitch Angle, #

Pitch Angleand Normal VelocityFrequency Response to Axial Wind

!!"# j$( )

"Vwind j$( )

!VN!" j#( )!Vwind j#( )

MacRuer, Ashkenas, and Graham, 1973

! Pitch angle resonance at phugoidnatural frequency

! Normal velocity (~ angle of attack) resonance at phugoidandshort periodnatural frequencies

Pitch AngleandNormal VelocityFrequency Response toVertical Wind

MacRuer, Ashkenas, and Graham, 1973

! Pitch angle resonance at phugoidand short periodnatural frequencies

!

Normal velocity (~ angle of attack) resonance at short periodnatural frequency

!

!" j#( )VN!$wind j#( )

=

!" j#( )!"wind j#( )

8/11/2019 Mae 331 Lecture 23

2/11

SideslipandRoll AngleFrequencyResponse toVortical Wind

=

!" j#( )!p

wind j#( )

=

!" j#( )!pwind j#( )

MacRuer, Ashkenas, and Graham, 1973

! Sideslip angle resonance at Dutch roll natural frequency

! Roll angle is integral of vortical wind input

Sideslipand Roll AngleFrequency Response to Side Wind

MacRuer, Ashkenas, and Graham, 1973

! Sideslip and roll angle resonance at Dutch rollnatural frequency

!" j#( )!"wind j#( )

=

!" j#( )!$wind j#( )

Microbursts

1/2-3-km-wide

Jet

impinges on surface

High-speed outflow

from jet core

Ring vortexforms inoutlow

Outflow strong enough toknock down trees

The Insidious Nature ofMicroburst Encounter

! The wavelength of the phugoid mode and the disturbanceinput are comparable

DELTA 191 (Lockheed L-1011)

http://www.youtube.com/watch?v=BxxxevZ0IbQ&NR=1

HeadwindDowndraft

Tailwind

Landing Approach

8/11/2019 Mae 331 Lecture 23

3/11

Importance of Proper Responseto Microburst Encounter

! Stormy evening July 2, 1994

! USAir Flight 1016, Douglas DC-9, Charlotte

!

Windshear alert issued as 1016 began descent along glideslope

! DC-9 encountered61-kt windshear, executedmissed approach

! Plane continued to descend, striking trees and telephone polesbefore impact

! Go-around procedure was begun correctly -- aircraft's nose rotatedup -- but power was not advanced

! That, together with increasing tailwind, caused the aircraft to stall

! Crew lowered nose to eliminate stall, but descent rate increased,causing ground impact

Optimal Flight PathThrough Worst JAWSProfile

! Graduate research ofMark Psiaki

! Joint Aviation Weather Study (JAWS)

measurements of microbursts(ColoradoHigh Plains, 1983)

! Negligible deviation from intended pathusing available controllability

! Aircraft has sufficient performancemargins to stay on the flight path

Downdraft

Headwind

Airspeed

Angle of Attack

Pitch Angle

Throttle Setting

Optimal and 15 PitchAngle Recovery during

Microburst Encounter

! Graduate Research ofSandeep Mulgund

! Airspeed vs. Time! Altitude vs. Time

! Angle of Attack vs. Time

Encounteringoutflow

Rapid arrest ofdescent

!

FAA Windshear Training Aid, 1987,addresses properoperating procedures for suspected windshear

Wind Rotors

8/11/2019 Mae 331 Lecture 23

4/11

Aircraft Encounters with

a Wind Rotor

Radius, ft

TangentialVelocity,

ft/s

! Tangential velocity vs. radius forLamb-OseenVortex

Geometry and Flight Condition of JetTransport Encounters with Wind Rotor

! Graduate researchofDarin Spilman

!

Flight Condition

! True Airspeed = 160 kt

! Altitude = 1000 ft AGL

! Flight Path Angle = -3

! Weight = 76,000 lb! Flaps = 30

! Open-Loop Control

! Wind Rotor! Maximum Tangential

Velocity = 125 ft/s

! Core Radius = 200 ft

a) co-axial, ! = 0

! !

35

35

vortex

vortex

wind

!

35

Typical Flight Paths inWind Rotor Encounter

! from Spilman

-50

0

50

100

150

200

250

![

deg

]

0 5 10 15 20 25 30Time [sec]

"i= 0

"i= 60

-60

-50

-40

-30

-20

-10

0

![

deg]

10

20

0 5 10 15 20Time[sec]

25 30

"i= 0

"i= 60

-300

-200

-100

0

100

200

300

- 40 0 - 30 0

h

[ft]

-200 -100 0 100 200 300y [ft]

400

rotor coreradius

flightpath

initialentry point

-500

0

500

1000

1500

0 5

h[

ft]

10 15 20 25 30

!i= 0

!i= 60

Time [sec]

ground

Linear-Quadratic/Proportional-Integral Filter (LQ/PIF) Regulator

8/11/2019 Mae 331 Lecture 23

5/11

LQ/PIF Regulation ofWind Rotor Encounter

! from Spilman

-50

0

50

100

150

200

!

[deg]

0 2 4 6 8 10

Time [sec]

LQR-PIF controlno control input

0

200

400

600

800

1000

1200

h(AGL)[ft]

0 2 4 6 8 10

LQR-PIF control

Time [sec]

no control input

Wake Vortices

C-5A Wing Tip Vortex Flight Test

http://www.dfrc.nasa.gov/gallery/movie/C-5A/480x/EM-0085-01.mov

L-1011 Wing Tip Vortex Flight Testhttp://www.dfrc.nasa.gov/gallery/movie/L-1011/480x/EM-0085-01.mov

Models of Single and DualWake Vortices

TangentialVelocity,

ft/s

Radius, ft

Wake Vortex

Wind Rotor

Tangential

Velocity,ft/s

Radius, ft

Wake Vortex Descent andDownwash

8/11/2019 Mae 331 Lecture 23

6/11

Wake Vortex Descent andEffect of Crosswind

! from FAA Wake Turbulence Training Aid, 1995

Magnitude and Decay ofB-757 Wake Vortex

! fromRichard Page et al, FAA Technical Center

NTSB Simulation of US Air 427and FAA Wake Vortex Flight Test

! B-737 behind B-727 in FAA flight test

! Control actions subsequent to wake vortexencounter may be problematical

! US427 rudder known to be hard-over from DFDR

Causes ofClear Air Turbulence

! from Bedard

8/11/2019 Mae 331 Lecture 23

7/11

DC-10 Encounter with Vortex-Induced Clear Air Turbulence

! from Parks, Bach, Wingrove, and Mehta

DC-8 and B-52H Encounterswith Clear Air Turbulence

!

DC-8: One engine and 12 ft ofwing missingafter CAT encounterover Rockies

! B-52 specially instrumented forair turbulence research aftersome operational B-52s were lost

! Vertical tail lostafter a severe andsustained burst (+5 sec) of clearair turbulence violently buffetedthe aircraft

! The Boeing test crew flew aircraftto Blytheville AFB, Arkansas andlanded safely

Conclusions

! Critical role of decision-making, alerting, and

intelligence

! Reliance on human factors and counter-intuitive strategies

! Need to review certification procedures

! Opportunity to reduce hazard through flightcontrol system design! Disturbance rejection

! Failure Accommodation

! Importance of Eternal vigilance

SupplementalMaterial

8/11/2019 Mae 331 Lecture 23

8/11

Alternative Reference Framesfor Translational Dynamics

! Earth-relative velocity in earth-fixed polar coordinates:

vE =

VE

!

"

#

$

%%%

&

'

(((

vE =

VE

!E

"E

#

$

%%%

&

'

(((

! Earth-relative velocity inaircraft-fixed polar coordinates(zero wind):

! Body-frame air-mass-relativevelocity:

! Airspeed, sideslip angle,angleof attack

vA=

u!uw

( )

v!vw

( )

w!ww( )

"

#

$$$$

%

&

''''

=

uA

vA

wA

"

#

$$$

%

&

'''

VA

!A

"A

#

$

%%%

&

'

(((=

uA

2+ v

A

2+ w

A

2

sin)1

vA/ V

A( )

tan)1

wA/ V

A( )

#

$

%%%%

&

'

((((

!rI =H

B

Iv

B

!vB =

1

mFB v

A( )+H

I

BgI! "

BvB

!= L

B

I

B

!

B = I

B

"1M

B v

A( )" "BIBB#$ %&

! Rate of change ofTranslational Position

! Rate of change of AngularPosition

! Rate of change ofTranslational Velocity

! Rate of change ofAngular Velocity

Rigid-Body Equations of Motion

! Aerodynamic forces and moments depend on air-relative velocityvector, not the earth-relative velocity vector

Angle ofAttack,

FlightPath Angle,

PitchAngle,#

Wind Shear Distributions Exert Momentson Aircraft Through Damping Derivatives

! 3-dimensional wind

fieldchanges inspace and time

wE x,t

( )=

wx x,y,z,t( )

wy x,y,z, t

( )w

z x,y,z,t( )

!

"

#

###

$

%

&

&&&E

! Gradient of windproduces differentrelative airspeedsover the surface ofan aircraft

! Wind gradientexpressed in bodyaxes !Clshear "Clpwing

#w

#y$Clpfin

#v

#x

!Cmshear "Cmqwing,body ,stab

#w

#x

!Cnshear "Cnrfin,body

#v

#x

WB = H

E

BW

EH

B

E

WE =

!wx !x !wx !y !wx !z

!wy !x !wy !y !wy !z

!wz !x !w

z !y !w

z !z

"

#

$$$$

%

&

''''

Aircraft Modes of Motion

! Longitudinal Motions

! Lateral-Directional Motions

"Lon

(s) = s2+ 2#$

ns+$

n

2( )Ph

s2+ 2#$

ns+$

n

2( )SP

"LD

(s) = s# $S( ) s# $R( ) s

2+ 2%&

ns+&

n

2( )DR

! Wind inputs thatresonate with modes ofmotion are especiallyhazardous

Natural frequency : !n ,rad/s

Natural Period : Tn =2"

!n

, sec

Natural Wavelength : Ln = VN Tp ,m

8/11/2019 Mae 331 Lecture 23

9/11

Nonlinear-Inverse-Dynamic Control

! Nonlinear systemwith additive control:

! Output vector:

! Differentiate output until control appears ineach element of the derivative output:

! Inverting control law:

!x t( ) = f x t( )!" #$ +G x t( )!" #$u t( )

y t( ) =h x t( )!" #$

yd( )

t( ) = f* x t( )!" #$ +G * x t( )!" #$u t( ) !v t( )

u t( ) =G * x t( )!" #$ vcommand% f* x t( )!" #$!" #$

Landing Abort using Nonlinear-Inverse-Dynamic Control

! from Mulgund

400

500

600

700

800

900

1 103

-7500 -5000 -2500 0 2500 5000 7500

Umax= 60 ft/sec

Umax

= 70 ft/sec

Umax

= 80 ft/sec

Umax

= 90 ft/sec

Umax

= 100 ft/sec

Umax

= 110 ft/sec

Altitude(ft)

Range (ft)

100

150

200

250

300

350

-7500 -5000 -2500 0 2500 5000 7500

Umax

= 60 ft/sec

Umax

= 70 ft/sec

Umax

= 80 ft/sec

Umax

= 90 ft/sec

Umax

= 100 ft/sec

Umax

= 110 ft/sec

Airspeed(ft/sec)

Range (ft)

-5

0

5

10

15

-7500 -5000 -2500 0 2500 5000 7500

Umax

= 60 ft/sec

Umax

= 70 ft/sec

Umax

= 80 ft/sec

Umax

= 90 ft/sec

Umax

= 100 ft/sec

Umax

= 110 ft/sec

Alpha

(deg)

Range (ft)

Angle of Attack Limit

Wind Shear Safety Advisor

! Graduate research ofAlexander Stratton

!

LISP-based expert system

ON-BOARD DATA

Reactive sensorsWeather radarForward-lookingLightning sensorsFuture products

AIRCRAFT

SYSTEMS

CREW

Interface

ADVISORYSYSTEMLOGIC

GROUND-BASEDDATA

LLWASTDWRPIREPSForecastsWeather dataFuture products

Estimating the Probability ofHazardous Microburst Encounter

! Bayesian Belief Network! Infer probability of hazardous

encounter from

pilot/control towerreports

measurements

location

time of day

GeographicalLocation

Surface Humidity

Time of Day

ConvectiveWeather

Probability ofMicroburst Wind Shear

Lightning

LightningDetection

Mod/HeavyTurbulence

TurbulenceDetection

Precipitation

WeatherRadar

PilotReport

Low-LevelWind Shear Advisory

SystemAirborne

Forward-LookingDoppler Radar

Reactive Wind ShearAlert System Terminal Doppler

Weather Radar

8/11/2019 Mae 331 Lecture 23

10/11

NTSB Simulation of American 587

! Flight simulation obtained from digital flight data recorder (DFDR)tape

Digital Flight Data RecorderData for American 587

American 587 (Airbus A-300-600)Encounter with B-747 Wake

! PIO and/oraggressive use ofrudder seen aspossible cause

! Aviation Daily, 5/22/02! Boeing Issues Detailed

Guidance On RudderUse For Roll Control

Aircraftas Wake VortexGeneratorsand Receivers

! Vorticity, , generated by lift in 1-gflight

! =KgeneratorW

"VNb

! Rolling acceleration response to vortexaligned with the aircraft's longitudinal axis

Kgenerator !4

!

Kreceiver

!

CL!

2"VNb

!p =

Kreceiver1

2!VN

2Sb

Ixx"

8/11/2019 Mae 331 Lecture 23

11/11

Rolling Response vs. Vortex-Generating Strength for 125 Aircraft

! Undergraduate summer project ofJames Nichols

0.0001

0.001

0.01

0.1

1 10 100

RollingResponse

Vortex Generating Strength