Hi Earl, sorry, aviation is my profession. LOL.

The above Mig-21 has an exhaust plume. Meaning that Mig is in Military power (MAX power without afterburner.)
This is due to bad combustion at Military power. Most older style jets have that.

When going afterburner (at a HUGE fuel cost), the plume goes away and is replaced by the cleaner burning afterburner flame.

A Mig 21 in full afterburner has some 3-4 minutes of flight time at the lower altitudes. Then he is empty and becomes a glider. No LOL.

Afterburner is rarely used in flight. Mostly for Take Off only. And when you select burner in a MIG 21 in a fight? it is a decision of DO or DIE.

Example; A clean F-16 (no external fuel tanks) has some 7.000 pounds of jet fuel.

Low level, airshow style flying, you have some 6 minutes of afterburner available.
High altitude cruise endurance can go for 3 hrs with the same 7.000 pounds.

Fuel consumption is the single most critical parameter to start or avoid, win or loose, a fight. 

The Mig's are in Military power. That is good to live and fight another day.

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