Normally, the afterburners work as a light effect.
The easiest way to change the AB-effect is to replace the concorde effect by the tomcat effect in the [LIGHTS] section in you aircraft.cfg.
That section should look somewhat like this :
(this is from the DSBdesign Tornado GR.4, I dont have that concorde)
[LIGHTS]
//index,type, long, lat, vert, fx_filename
//Types: 1=beacon, 2=strobe, 3=navigation, 4=cockpit, 5=landing
light.6=9, -23, -1.55, -0.3,
fx_dsb_tornado_burner_flamenow if I wanted to change to another AB-effect I would do this :
light.6=9, -23, -1.55, -0.3,
whatever_ab_effect_you_wantand repeat that to all the other AB-lines in the [LIGHTS] section
--------------------------------------------------
Now for the Effects position :
light.6=9,
-23, -1.55, -0.3, whatever_ab_effect_you_want
This number adjusts the position in the length of you aircraft. The smaller the number, the more to the back of your aircraft the effect is positionned.
light.6=9, -23,
-1.55, -0.3, whatever_ab_effect_you_want
If this number is negative, the effect is positionned to the left of the centerline of the aircraft, and if positive to the right. If its zero, its positionned in the middle. The smaller the more to the left and vice versa.
light.6=9, -23, -1.55,
-0.3, whatever_ab_effect_you_want
And this one adjusts the height. The higher the number, the higher the effect. So if the effect is above the aircraft, just lower this number, save the aircraft.cfg and reload the aircraft in FS. Do this untill you're satisfied with the position.
I hope this can help you a bit
(as I read this again, it looks complicated, I'm terrible at explaining things

)