There are a couple different contrail effects out there. Here are some effects you can replicate in any plane you wish. You have to adjust wingtip position for each type aircraft by adjustting the x, y, z, entries in the effects.xml file. x= adjustment from wingtip to fuselage, y= up/down, z= fore/aft. You can replace "wtv_p51_l" with the model you are adding this to, i.e. "wtv_p38_l". Wingtip contrails are also a good reference point for adding nav lights.
.xpd file
<Effect Type="Track" EffectName="wtv_p51_l" Location="emitter_r_vapor" MinVel="230" MaxVel="900"/>
<Effect Type="Track" EffectName="wtv_p51_r" Location="emitter_l_vapor" MinVel="230" MaxVel="900"/>
.xml file
<wtv_p51_r ClassName="TrackEffect" FlatTrack="0" Lifetime="0" InitialDelay="0" ParticleLifetime="0.15" FadeInTime="0.02" FadeOutTime="0.12" PosX="5.6" PosY="-0.1" PosZ="-0.4" CountSegments="5" SegmentLength="4" Width="0.1" WidthGrow="1.2" InitialAlpha=".00" InitialColor="250 250 255" Alpha=".55" Color="250 250 255" FinalAlpha=".00" FinalColor="250 250 255" BlendMode="QuadSprite" Texture="tr_smoke_6.dds" ZBias=".03"/>
<wtv_p51_l ClassName="TrackEffect" FlatTrack="0" Lifetime="0" InitialDelay="0" ParticleLifetime="0.15" FadeInTime="0.02" FadeOutTime="0.12" PosX="-5.6" PosY="-0.1" PosZ="-0.4" CountSegments="5" SegmentLength="4" Width="0.1" WidthGrow="1.2" InitialAlpha=".00" InitialColor="250 250 255" Alpha=".55" Color="250 250 255" FinalAlpha=".00" FinalColor="250 250 255" BlendMode="QuadSprite" Texture="tr_smoke_6.dds" ZBias=".03"/>