Add these into aircraft.cfg:
[smokesystem]
smoke.0 = -18.030, 29.00, 49.00, Opensky_revspray
smoke.1 = -18.030, 29.00, -49.00, Opensky_revspray
Download the effect file by Edward Cox at avsim.... Search after reverser_spray.zip
And get these


Enjoy
Stian