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.

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 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

Lidar performance simulations Lidar CNR simulation (β = 3.10-7 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 points @ 18 m CLRC 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

On board installation Real time display Line of sight n° range (m) More than 5000 vortices were measured during 12 flight hours. CLRC 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

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 2018 Okinawa 18th-21st June

WV Doppler Lidar for formation fligth

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 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 time(s) CNR (dB) 32 30 28 26 24 22 20 Velocity (m/s) 6 4 2 -2 -4 -6 -8 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 time(s) CNR (dB) Velocity CNR Hard target Output optic reflection 32 30 28 26 24 22 20 CLRC 2018 Okinawa 18th-21st June