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7/26/2019 Airbus A380 Wake Test
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1
Presented by
Claude LELAIE
Experimental test pilot
Senior Vice President Product Safety
A380 wake encounters flight tests28th June 2010
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Airbus follow-on methodology : actual wake encounter flight-testing
Encounter test consists of physically flying an aircraft through the wake of
another to measure specific parameters, thus determining the actualseparation to apply.
The follower aircraft flies encounters alternatively behind A380 and a
suitable reference aircraft, with both wake generators flying side by side.
Encounter test principle (1)
Generator
Follower
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Many parameters recorded with focus on the following flight
parameters:
Encounter test principle (2)
Altitude loss
Vertical acceleration
Roll rate
Roll acceleration
Flight mechanic equations show that the roll acceleration isrepresentative of the effect of the encounter on the aircraft.
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Defining encounter technique: how to visualize the wake
In cruise, wake can be visualized within
the contrail.
At lower altitude, visualization requiressmoke generation.
Two solutions envisaged
Generator pods under both wings(tested on A340-300)
Acceptable smoke but limited smoke time
Ranges from 4 to 7 nm
Oil spray system (used on A340-600 andA380, preferred solution)
Excellent smoke visualization
Sufficient production time
Ranges from 4 to 8 nm (representative
distance for 75t Medium follower)
A343 with generator pods
A380 with oil spray system
Cruise test w ith cont rails
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Cruise test techniques (1)
Numerous preparation flights were necessary to tune the flight testtechniques.
First question: normal law or direct law?
Initial tests showed no difference as the motions on all axis were ratherabrupt. Therefore normal law was used.
The question came whether an encounter in normal law with the A318could be compared to the same situation with a B737. The answer is yes
due to the fact that in the worst cases, the roll rate is well above what iscommanded by the A318 flight controls computers.
Few tests with autopilot.
Stick free or not?
No obvious answer to qualify the strength of the vortex. An equalnumber of each have been performed.
For stick free tests, stick was released just prior entering the wake andtaken back when roll motion decreased.
For piloted tests, the pilot tried to minimize the effect of the encounter. Itis NOT a realistic technique for Airline Pilots, but it is a mean to compare2 aircraft.
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Cruise test techniques (2)
Observation of the rate of descent of vortex of both aircraft was an
important issue due to RVSM.
Tests were performed from 5 NM, standard separation for the B747
up to 15 NM, distance approved for the A380 at the time of the tests.
All results were confirmed by Lidar observations.
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Flight test procedure
Comparison flight tests in cruise
Figure referenced to wake generating aircraft
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Cruise: Overview of flight tests performed
Flight tests to develop the flight test techniques:
C1: 11 JAN 2006: A380, A318 for wake encounters
C2: 23 FEB 2006: A380 and A346 side-by-side,A318 for wake encounters
C3: 07 MAR 2006: A380 and A346 side-by-side,
DLR Lidar on-board Falcon,
A346 encounters in trail of A380C4: 09 MAR 2007: A346, DLR Lidar on-board Falcon
Comparison evaluation f light tests:
C5: 23 JUN 2006: A380 and A346, A318 for encounters,
simultaneously DLR Lidar
on-board Falcon
C6: 25 JUN 2006: A380 and B744, A318 for encounters,
simultaneously DLR Lidar
on-board Falcon
Follower aircraft
Generator aircraft
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Example:
A318 11.4 NM behind A380
(FT C5)
Example results (cruise)
Video recording
A318msn1599fl783leg3vtp_082700b.mpg
Video
http://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/A318msn1599fl783leg3vtp_082700b.mpghttp://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/A318msn1599fl783leg3vtp_082700b.mpg7/26/2019 Airbus A380 Wake Test
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Example results (cruise)
A318 stick-free encounters
Example FT C6 (A318 behind A380 side-by-side with B744)
Vertical load factor
Altitude deviation
Roll acceleration
Roll rate
B747-400
A380
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Cruise test results
Rate of descent of vortex of both aircraft is identical. It reach 1000 ft
at a distance between 12 and 15 NM.
In some cases, rough encounters were obtained.
For some parameters, the decrease with distance is rather slow.
Looking at all the parameters, it was found that the A380 and the
B747 are similar.The pilots impression was that no difference could be felt.
All that was confirmed by the results of the on-board Lidar of the
Falcon 20.
In cruise, same separation for the A380 than for the
other Heavies has been approved.
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Cruise: applicable separations for all aircraft
Any aircraft
following a
Heavy
747: 5 nm
1,000 ft
1,000 ft
Separation apply to all categories aircraft
ICAO Stateletter Nov 05
A380: 15 nm
+ 10 nm 1,000 ft with precautions
1,000 ft with precautions
ICAO State
letter Oct 061,000 ft
1,000 ft
A380: 5 nm
A h li bl i f H i f
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Approach: applicable separations for Heavy aircraft,
based on Lidar tests
Heavy following a
Heavy 747: 4 nm
ICAO State letter
Nov 05A380: 10 nm
+ 6 nm
ICAO State letter
Oct 06A380: 6 nm
+ 2 nm
Potential reduction pending current Work Groupanalysis of the Airbus wake encounter flight test data
ICAO State Letter
July 08A380: 6 nm
+ 2 nm
Future
A h li bl ti f M di i ft
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Approach: applicable separations for Medium aircraft,
based on Lidar tests
Medium following
a Heavy 747: 5 nm
ICAO State letter
Nov 05A380: 10 nm
+ 5 nm
ICAO State letter
Oct 06A380: 8 nm
+ 3 nm
A380: 7 nmICAO State letter
July 08
+ 2 nm
Potential reduction pending current Work Groupanalysis of the Airbus wake encounter flight test data
Future
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A380 Wake Encounter Safety Assessment
When analyzed with a Lidar, wake encounter hazard can be described
by the measured circulation 5-15.
It is an accepted methodology, but it still rely on a model.The measurement area does not include the important core part of the
vortex.
Li it ti h i Lid d t f ti
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Limitations when using Lidar data for separation
standards
Vortex circulation obtained with Lidar was used to provide an
indication of the severity of a wake encounter.
But, what are the effects of the vortices considering:
Wake velocity profileAircraft weight
Roll inertia, wingspan of the follower?
=> This can only be determined by actual encounter
testing
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Overview of encounter tests during approach
Flight tests to develop the flight test techniques:
L1: 20 NOV 2006: A320 behind A343
L2: 20 DEC 2006: A320 behind A343L3: 21 DEC 2006: A380 behind A343
L4: 18 APR 2007: A320 behind A380
L5: 6 JUN 2007: A300B2 behind A380
L6: 8 JUN 2007: A300B2 behind A380
L7: 11 JUN 2007: A320 behind A346
L8: 13 JUN 2007: A380 behind A380
Comparison evaluation flight tests:
L9: 18 JUL 2007: A320 behind A380 side-to-side with A346
L10: 16 OCT 2007: A300B2 behind A380 side-to-side with A346
L11: 12 DEC 2007: A320 behind A380 side-to-side with A346
Followeraircraft
Generatoraircraft
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Flight test procedure
Comparison flight tests
Figure referenced to wake generating aircraft
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Approach: encounter flight test techniques (1)
Altitude: between 5000 and 12 000 ft (for safety reasons)
Numerous parameters to be consideredWhich flight control law?
It appeared that the encounters were so smooth that the normal law
was hiding most of the attitude variations.
Deviations in pitch (altitude and acceleration) are rather small and are
not a basis for comparison.
Roll direct provides a good assessment of the strength of the vortex
(roll acceleration).
For the A320 the final choice has been alternate law with yaw damper
(normal law in pitch, roll direct plus yaw damper).
Few encounters in normal law and with autopilot.
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Approach: encounter flight test techniques (2)
Which flying technique?
As for cruise, tests have been performed partly stick free, partly piloted.
Best angle to enter in the wake
Computation and models have shown that the worst case is a 10
convergence. It is what has been targeted in average.
If lower, it might be impossible to penetrate the wake.If higher, the upset is too short.
Descent or level flight?
Level flight has been preferred, as it avoid changing the atmospheric
conditions with altitude.
Some tests performed on a 3 descent slope, but no difference identified.
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Approach: encounter flight test techniques (3)
Which follower aircraft?
For the Heavy category, the choice was to get the smallest possible twin (less
inertia in roll) in this category. We choose theA300B2, around 130 t MTOW.
For the Medium, we took a fully instrumentedA320. It is not the worst
aircraft in this category because it is not the smallest, but it must be
considered that the purpose was only to make back to back tests and not to
have an absolute judgement on safety.
Data acquisition:
Time histories of all flight mechanical parameters.
Videos.Pilots assessments.
E t t t lt
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Stick-free encounters:
A300B2 4.3 NM behind A380 (#67)
A320 4.6 NM behind A380 (#49)
Encounter test results
Video recordings and Vimosac3Danimations
67.mp2
A320_SBS2_Enc49_sf_380.avi
Video
sf_380_300_V1238_no67_track.avi
A320_SBS2_ap_sf_49_vimo_2.avi
Vimosac3D
http://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/67.mp2http://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/A320_SBS2_Enc49_sf_380.avihttp://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/sf_380_300_V1238_no67_track.avihttp://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/A320_SBS2_ap_sf_49_vimo_2.avihttp://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/A320_SBS2_ap_sf_49_vimo_2.avihttp://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/sf_380_300_V1238_no67_track.avihttp://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/A320_SBS2_Enc49_sf_380.avihttp://../Local%20Settings/Temporary%20Internet%20Files/Content.Outlook/4PHEEK6H/67.mp27/26/2019 Airbus A380 Wake Test
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Comments on the videos
The videos are coming from tests behind A340-600 or A380,
and it is not possible to make the differences between those
aircraft.
As the A320 is flown in roll direct, in order to facilitate themeasurements, the roll motion is amplified. When in normal
law, flight by wire is fully active and the roll angle becomes
very small.
E t t t lt
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Encounter test results
A300B2 stick-free encounters
Example FT L10 (A300B2 behind A380 side-by-side with A346)
Vertical load factor
Altitude deviation
Roll acceleration
Roll rate
A340-600
A380
E t t t lt
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Encounter test results
A320 stick-free encounters
Example FTs L9 and L11 (A320 behind A380 side-by-side with A346)
Altitude deviation
Roll accelerationVertical load factor
Roll rate
A340-600
A380
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Approach: A380 as follower
The large roll inertia and roll control capability of the A380implies a very low sensitivity to wake induced effects.
This has been demonstrated by Airbus flight tests, with theA380 performing encounters in the wake of another A380 at
a distance in trail below 1 nm whilst being fully controllable.
The Working Group and Steering Group have
recommended to apply Minimum Radar Separations toA380 as follower (ICAO State Letter from July 2008 forapproach and take-off).
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Conclusions for approach
The Working Group is presently assessing all these results with various
methodologies, including a new one proposed by Airbus. It is the DWIM:
Direct Wake Impact Methodology.
Some more flight tests are planned by the end of the year with Authoritieson board. The analysis on these flights and the preparation of a Safety
Assessment Report will probably not allow to conclude before Autumn 2011.
For the time being, all separations are based on Lidar validations.
Comparison: circulation (Lidar) / roll accelerations
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Comparison: circulation (Lidar) / roll accelerations
(encounters) in approach
LIDAR is NOT the right tool to measure the effect of a
wake vortex on a follower aircraft
Lidar measured circulation of A380
wake is stronger
The rol l acceleration which represents the effect on the
fol lower aircraft is identical behind A380 and A340-600
A340-600
A380
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Lidar / encounters: conservative or not ?
If we use Lidar to compute the A380 separation in comparison with the
B747, it is obviously conservative versus encounters and therefore safe.
If we imagine that the A380 is the old aircraft and the B747 the new
one, using the Lidar data would lead to a decrease of B747 separationcompared to A380. Therefore, we could have stronger encounters
behind a B747 than behind the A380.
Lidar is not conservative. In some cases it could lead
to a reduction of safety margins.
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RECAT Consequences for the A380
RECAT is necessary to optimize the traffic flow and safety.
If RECAT is using Lidar and models to validate separations, there is astrong disadvantage for the A380 as shown on the Lidar curves.
However, we have demonstrated, thanks to the encounters, that the
Lidar is NOT the right tool for the assessment of the consequences of an
encounter.
Based on the results of our tests, the A380 and the B747 has to be put in
the same category.
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Conclusions
More than 300 flight hours have been performed to study the effect of
wake wortex.
More than 1000 encounters have been done, in cruise and in approach.
This experience is unique.
It has allowed to show that A380 and B747 vortex have the same effect onfollower aircraft in cruise and in approach.
All these tests have also demonstrated that the circulation obtained by
Lidar measurements is not always the optimum tool to qualify the effect ofa vortex. Validation of separations must also take into account results of
encounter campaigns.