I got to thinking and I thought of some neat graphical and gameplay features.
Contrails of all planes at high altitudes
Dark exauhst from the Arado's engines (someone already brought this up)
Visible heat waves behind Ar 234's engines
Jet wash

The ability to damage individual instraments and the radio
Puffs of smoke and audio changes with slightly/moderatly damaged engines
The ability to ignite the fuel stream of an aircraft if they're leaking (BOOM)
Engine fires
Canopy obscured by oil and fuel

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Lt. Col. Aaron "txace-" Giles of the 457th BG
"Fait Accompli"
In arena: semperfi