The effect is added by adding two "[Extra.#]" entries to the aircraft's DP file:
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[EXTRA.0]
location=6.00,0.27,0.55
effect=fx_contrail_grn
[EXTRA.1]
location=-6.00,0.27,0.55
effect=fx_contrail_red
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...and here are the FX effect files:
fx_contrail_grn.fx
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[Library Effect]
Lifetime=5
Version=1.00
[Emitter.0]
Lifetime=0.00, 0.00
Delay=0.30, 0.32
Bounce=0.00
No Interpolate=1
Rate=1.00, 1.01
X Emitter Velocity=0.00, 0.00
Y Emitter Velocity=0.00, 0.00
Z Emitter Velocity=0.00, 0.00
Drag=0.00, 0.01
X Particle Velocity=0.00, 0.00
Y Particle Velocity=0.00, 0.00
Z Particle Velocity=0.00, 0.00
X Offset=0.00, 0.00
Y Offset=0.00, 0.00
Z Offset=0.00, 0.00
[Particle.0]
Lifetime=20.00, 20.00
Type=21
X Scale=1.40, 1.60
Y Scale=1.40, 1.60
Z Scale=0.00, 0.00
X Scale Rate=0.25, 0.30
Y Scale Rate=0.25, 0.30
Z Scale Rate=0.00, 0.00
Drag=-2.60, -1.79
Color Rate=0.10, 0.20
Fade In=0.01, 0.01
Fade Out=0.30, 0.30
Rotation=-20.00, 20.00
Face=0, 0, 0
[ParticleAttributes.0]
Blend Mode=1
Texture=fx_smoke.bmp
Bounce=0.00
Color Start=0, 244, 0, 120
Color End=0, 249, 0, 255
Jitter Distance=1.00
Jitter Time=5.00
TempK=109.00
TempRate=0.01
uv1=0.00, 0.00
uv2=1.00, 1.00
X Scale Goal=1.00
Y Scale Goal=1.00
Z Scale Goal=0.00
Extrude Length=20.00
Extrude Pitch Max=15.00
Extrude Heading Max=15.00
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fx_contrail_grn.fx
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[Library Effect]
Lifetime=5
Version=1.00
[Emitter.0]
Lifetime=0.00, 0.00
Delay=0.30, 0.32
Bounce=0.00
No Interpolate=1
Rate=1.00, 1.01
X Emitter Velocity=0.00, 0.00
Y Emitter Velocity=0.00, 0.00
Z Emitter Velocity=0.00, 0.00
Drag=0.00, 0.01
X Particle Velocity=0.00, 0.00
Y Particle Velocity=0.00, 0.00
Z Particle Velocity=0.00, 0.00
X Offset=0.00, 0.00
Y Offset=0.00, 0.00
Z Offset=0.00, 0.00
[Particle.0]
Lifetime=20.00, 20.00
Type=21
X Scale=1.40, 1.60
Y Scale=1.40, 1.60
Z Scale=0.00, 0.00
X Scale Rate=0.25, 0.30
Y Scale Rate=0.25, 0.30
Z Scale Rate=0.00, 0.00
Drag=-2.60, -1.79
Color Rate=0.10, 0.20
Fade In=0.01, 0.01
Fade Out=0.30, 0.30
Rotation=-20.00, 20.00
Face=0, 0, 0
[ParticleAttributes.0]
Blend Mode=1
Texture=fx_smoke.bmp
Bounce=0.00
Color Start=244, 0, 0, 120
Color End=249, 0, 0, 255
Jitter Distance=1.00
Jitter Time=5.00
TempK=109.00
TempRate=0.01
uv1=0.00, 0.00
uv2=1.00, 1.00
X Scale Goal=1.00
Y Scale Goal=1.00
Z Scale Goal=0.00
Extrude Length=20.00
Extrude Pitch Max=15.00
Extrude Heading Max=15.00
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