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Wake Encounter Flight Control Assistance Based on Forward-Looking Measurements > D.Niedermeier > 14.03.2012

Wake Encounter Flight Control Assistance Based on Forward-Looking Measurements D. Niedermeier, C. Horn, J. Ehlers, D. Fischenberg Wetter und Fliegen – Final Colloquium

Munich, March 14th, 2012

2 Wake Encounter Flight Control Assistance Based on Forward-Looking Measurements > D.Niedermeier > 14.03.2012

Motivation

Why Active Wake Impact Alleviation? Avoidance strategies are generally favorable, but Certain conditions (e.g. flight phases) do not allow appropriate evasion!

Development of control strategies that alleviate impact of inevitable encounters

Why Forward-Looking Sensor Based Control? Conventional sensors (e.g. IRS) only react to disturbances already acting on the aircraft Time delays due to sensors and actuators cannot be compensated for Forward-looking sensor: Possibility to generate control command before the aircraft is disturbed

Performance of forward-looking sensor based control is higher (depending on sensor data quality)

3 Wake Encounter Flight Control Assistance Based on Forward-Looking Measurements > D.Niedermeier > 14.03.2012

Control Concept Overview

wake vortex flow

Wake impact alleviation control concept

forward-looking measurement

induced forces and moments

control commands

control allocation

DLC command

aileron command

rudder command

elevator command

vertical force

yawing moment

rolling moment

pitching moment

vert. force allocation

roll and yaw allocation

pitch allocation

measured flow field

aerodynamic interaction model strip

model

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Forward-Looking Measurement Concept


Determination of velocities induced by a flow field in front of the aircraft

Implementation of a sensor model incl. variable characteristics for sensitivity study:

Vertical and horizontal scan angle ranges Number of measurement points Measurement noise Measurement distance Determination of three velocity vector components or line-of-sight component

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Aerodynamic Interaction Model

Modeling of forces and moments acting on a/c due to wake vortex induced velocities Wake vortex induced flow angles (stripwise) considered at:

wing horizontal tail plane vertical tail fin fuselage

Local flow angles local forces global forces and moments Used for wake vortex encounter simulations and for flight control assistance


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Modeling the Wake Vortex Encounter Flight Experiment for Model Validation


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Wake Vortex Encounter Evaluation Wake Parameters and Aerodynamic Interaction Model

measured flight test data

wake vortex model parameter identificaton

aerodynamic interaction simulation

wake model parameters

model accuracy


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Results: Model Output Compared to Flight Test Data

Typical lateral wake fly-through

Do 128 (twin engine turbo prop, MTOW 4 t) behind DLR’s test aircraft VFW 614 ATTAS (twin engine jet, MTOW = 21 t)

Aircraft separation 0.8 nm (tage = 21 s)

Improved strip method version

drag effect

fuselage effect

_______ simulation model output _______ flight test data

Assessment of Wake Vortex Safety


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Control Allocation Concepts: Pilot Assessment

Reference 0: No automatic assistance

Version 1: Compensation of induced moments using elevator, ailerons and rudder

Version 2: Additional compensation of induced vertical force using direct lift control (DLC) capabilities of ATTAS

Pilot Assessment: same WV, different encounter angles from 5° to 30°

DLC additionally improves average ratings, particularly at medium encounter angles of approx.15°


a/c control demands on pilot a/c deviations hazard

1

2

3

4

Pilo

t rat

ing

manualautomatic assistance w/o DLCautomatic assistance with DLC

5 manual ILS approaches 5 assisted ILS approaches w/o DLC 5 assisted ILS approaches with DLC

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Sensor Parameter Sensitivity Study Desktop Simulations

-20 -19 -18 -17-2

-1

0

1

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3

4

5

xg [km]

∆ z g

[m]

-20 -19 -18 -17

-30

-20

-10

0

10

xg [km]

y g [m

]

autopilotWV controllervortex lineref track

25 30 35 40 45 50 55-30

-20

-10

0

10

20

30

t [s]

Φ [d

eg]

25 30 35 40 45 50 55-20

-10

0

10

t [s]A

ilero

n de

flect

ion

[deg

]

Reference Scenario: 9x7 measurement points scanned with 10 Hz 100 m measurement range No measurement error considered Sensor delivers full wind velocity vector Wake vortex impact control works properly if flow disturbance is well known


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Sensor Parameter Sensitivity Study Conclusions


Main Problem: Line-of-sight (LoS) velocity information is not sufficient Information on all three velocity components is more crucial than high accuracy of LoS velocity

Sensor requirements cannot be fulfilled by the current sensor

technology

Wake characterization as sensor post-processing step is required!

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Online onboard wake vortex characterization


Wake vortex characterization from LoS measurements:

Identification of model parameters of an analytical wake vortex model (e.g. Burnham-Hallock) Time histories of several snapshots of the forward-looking sensor are used for identification Variable time frame for identification Initial values from model based wake predictor using MET and ADS-B data or from an autonomous wake vortex approximator (AWA) using the LoS measurements to estimate the initial values In theory, allows to determine the full velocity vector at arbitrary flow field positions

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Online Wake Vortex Characterization: Open Points


Accuracy of initial values coming from wake predictor might be too low depending on encounter situation and atmospheric conditions

Accuracy of initial values coming from autonomous wake vortex approximator might be too low for wake vortices with elevation angle

Online identification might fail for wake vortices with strong curvature

Errors in characterization of wake vortex geometry might lead to adverse effects on a/c reaction (opposite sign in control commands!)

Technology Readiness Level 2-3: Higher number of offline simulations required for feasibility check

NASA Technology Readiness Level Source: www.nasa.gov

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Conclusions

Wake impact alleviation control based on forward-looking measurements can alleviate the wake vortex effects on a/c if good measurement data is available Sensor requirements for forward-looking sensor based flight control are not fulfilled by state-of-the art LiDAR technology Online Onboard wake characterization is required for adequate induced velocity information!


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Outlook

Technology enhancement of forward-looking sensors with focus on application for active control required Development of solutions allowing the application of the online identification algorithm in the operational environment Evaluation of alternative wake characterization methods, e.g. Bayesian methods Development and assessment of alternative control concepts with lower forward-looking sensor requirements, e.g. adaptation of existing feedback control in case of wake vortex encounter Wake Encounter Flight Control Assistance Based on Forward-Looking Measurements > D.Niedermeier > 14.03.2012

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