Visual effects are often done in the lights section of aircraft.cfg
You could copy some from an existing model e.g. F-15 model
f-15upfw.zip below,
install the appropriate effects, and adjust the position of the burners to suit, with a bit of trial and error
[lights]
//Types: 1=beacon, 2=strobe, 3=navigation
yadayada....
light.11= 6, -22.7, -2.2, -0.3, fx_F14_Burn1 ,
light.12= 6, -22.7, -2.2, -0.3, fx_F14_Burn2 , // Eng1 Afterburner Burn2
light.13= 6, -25.0, -2.2, -0.3, fx_F14_Burnerflame , // Eng1 Afterburner Flame
light.14= 7, -22.7, 2.2, -0.3, fx_F14_Burn1 , // Eng2 Afterburner Burn1
light.15= 7, -22.7, 2.2, -0.3, fx_F14_Burn2 , // Eng2 Afterburner Burn2
light.16= 7, -25.0, 2.2, -0.3, fx_F14_Burnerflame , // Eng2 Afterburner Flame
light.17= 6, -22.0, -2.2, 0.0, fx_F14_Blueflame , // Eng1 Blueflame,
light.18= 7, -22.0, 2.2, 0.0, fx_F14_Blueflame , // Eng2 Blueflame,