Download - Mae 331 Lecture 23
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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!$wind j#( )
=
!" j#( )!"wind j#( )
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SideslipandRoll AngleFrequencyResponse toVortical Wind
=
!" j#( )!p
wind j#( )
=
!" j#( )!pwind j#( )
MacRuer, Ashkenas, and Graham, 1973
! Sideslip angle resonance at Dutch roll natural frequency
! Roll angle is integral of vortical wind input
Sideslipand Roll AngleFrequency Response to Side Wind
MacRuer, Ashkenas, and Graham, 1973
! Sideslip and roll angle resonance at Dutch rollnatural frequency
!" j#( )!"wind j#( )
=
!" j#( )!$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
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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
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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
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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
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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
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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
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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# $R( ) s
2+ 2%&
ns+&
n
2( )DR
! Wind inputs thatresonate with modes ofmotion are especiallyhazardous
Natural frequency : !n ,rad/s
Natural Period : Tn =2"
!n
, sec
Natural Wavelength : Ln = VN Tp ,m
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Nonlinear-Inverse-Dynamic Control
! Nonlinear systemwith additive control:
! Output vector:
! Differentiate output until control appears ineach element of the derivative output:
! Inverting control law:
!x t( ) = f x t( )!" #$ +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
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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"
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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