1. On-board wake vortex tracking with an 1
On-board wake vortex tracking with an 1.5µm fibered Coherent Doppler LIDAR for aircrafts in formation flight
Dolfi-Bouteyre Agnès, Goular Didier, Augère Beatrice, Planchat Christophe, Fleury Didier, Lombard Laurent, David Tomline Michel, Valla Matthieu, Besson Claudine.

2. Aircraft Formation Flight: Saving Energy Like Birds Do
Birds V formation  drag reduction
Increase flight distance
For commercial aircraft : Wake vortex persistence  distant formation flight
Drag reduction  tracking error in wake vortex position
Software + lead aircraft position + wind  wake vortex position
Wake vortex positioning with a Lidar can help flight test pilot .
When birds fly in formation , they are able to fligth much further without getting tired .
In the same way, formation fligth can be used by aircraft to reduce fuel burn .
In formation flight, the plane behind put its wing over the wake vortex created by the plane located ahead which reduce the drag and increase its flight range.
Close formation flight, as bird or military aircraft , is not possible for commercial aircraft due to collision hazards.
But because of the persistance of wake vortex of large commercial aircraft , formation flight for distances between 10 to 40 wingspans can still be beneficial.
This require accurate monitoring of the position of the wake vortex generated by the plane located ahead.
Software that gives extra situation awarness of where lead aircraft is, what is the wind that is experincing .that help to predict the wake postion
CLRC Okinawa 18th-21st June

3. Lidar specifications Seeded wake vortex position measurement
from 30 to 200 m
precision > 2m
Reduction of blind zone length  short pulse laser
10ns rise/fall time AOM 150 ns long at -30 dB pulses
A LIDAR was designed to determine the wake vortex position at a distance of 30 m to 200 m from the LIDAR
This require to use a short laser pulse to reduce the blind zone length and start measuring the wind field at ~20 m from the LIDAR.
In Fibered Coherent Doppler LIDARs developed at ONERA, laser sources are based on “Master Oscillator Power Fiber Amplifier” (MOPFA). The pulses are generated by a Fiber Coupled Acousto-Optique Modulator (AOM).
CLRC Okinawa 18th-21st June

4. Lidar performance simulations
Lidar CNR simulation (β = m-1.sr-1)
40 mm
A 40 mm diam. optic was chosen to have an about flat CNR* over the detection distance (20 m to 220 m).
Simulation show a less than 5dB variation of the CNR
over the detection distance.
mm optics less than 5dB variation of the CNR over the detection distance.
First measurements 18 m
CLRC Okinawa 18th-21st June

5. Lidar performance simulations
Lidar performance simulation with a velocity ramp
(β =1e-7 m-1.sr-1)
CNR<-20 dB V
Short pulse  poor velocity accuracy ( 0.5 to 2 m/s)
but enough to detect and localize large aircraft WV
CLRC Okinawa 18th-21st June

6. Lidar integration and ground tests
Day averaged measured CNR
Simulation
(β = 10 e-7 m-1.sr-1)
(β = 1.5 e-7 m-1.sr-1)
laser
telescope
scanner
The overall CNR curve translation measured between days was due to the variation of β ( from 1.5E-7 to 10E-7 m-1.sr-1)
CLRC Okinawa 18th-21st June

7. Lidar test with representative vibrations
Objective : Measurement of CNR with representative aircraft vibrations
Bended target
D = 18 m
Lidar
qscan
Wtarget
Shaker
Hard target Lidar measurements were performed during shaking .
We used a rotating bended target in order to measure various velocity during the scan .
The LIDAR performance was tested on a rotating target bended to obtain a velocity component along the LIDAR axis.
CLRC Okinawa 18th-21st June

8. Lidar test with representative vibrations
There were a less difusive part in the center of the rotating target .
Negligible sensibility to vibration was observed because of the all fibered design.
CLRC Okinawa 18th-21st June

9. On board installation Real time display
Line of sight n°
range (m)
More than 5000 vortices were measured during 12 flight hours.
CLRC Okinawa 18th-21st June

10. Post processing
Short pulse  average velocity on each range gate is close to wake vortex velocity profile.
Wake vortex detection and localization based on average velocity map and gradient detection.
simulations
Input
X=Xcore
X=Xcore + 6m
30 m detection
CLRC Okinawa 18th-21st June

11. Wake vortex core localisation accuracy
Vortex 1 & 2 positions
Vortex wind field projected on lidar axis
Lidar spectrum with noise
Signal processing
Deduced Vortex 1 & 2 positions
2000 times
Simulated vortex positions
further vortex
Closer vortex
Correction of the bias for closer vortex is under process to further improve the localization accuracy to 1 m.
CLRC Okinawa 18th-21st June

12. Seeding quality
Simulations show that seeding vortices resulted in β between 1e-7 m-1.sr-1 and 2,5e-6 m-1.sr-1
Without seeding, contrails can be another option to observe the vortex
CLRC Okinawa 18th-21st June

13. very short range detection capability real time display of wind maps
Conclusions
An onboard fibered LIDAR sensor for wake vortex tracking for aircrafts flying in formation flight has been developed with
very short range detection capability
real time display of wind maps
localization accuracy <= 2m
Ongoing new developments
Real time localisation display
Increase of the scanning angle
Reduced localisation error <=1m
CLRC Okinawa 18th-21st June

14. WV Doppler Lidar for formation fligth

15. Lidar test with representative vibrations
Objective : Measurement of CNR with representative aircraft vibrations
Lidar
Vibrating
Pot
Wtarget
qscan
D=17m Z
With vibration: 0.2g
Frequency chirp : 4.5Hz-5Hz
Without vibration
Velocity (m/s) 6 4 2 -2 -4 -6 -8
time(s)
CNR (dB) 32 30 28 26 24 22 20
Velocity (m/s) 6 4 2 -2 -4 -6 -8
time(s)
CNR (dB)
Velocity
CNR
Hard target
Output optic reflection 32 30 28 26 24 22 20
CLRC Okinawa 18th-21st June