I'm actually surprised to see you say that...I've always considered the heavy fighters a cakewalk, but granted, I've been careful to always send a corsair against them, and that makes for a very easy fight.
Just start by going to a point to the left of them so they turn to intercept you there, and then shortly before reaching their weapons range, turn the other way and head right - they'll get a few missiles off as they try to turn back again to keep you in their firing cone, but the corsair is fast enough that you don't even need to roll to evade them. As soon as you're out of their firing cone, which happens very quickly, you just circle around them and close in and slaughter them all.
The same tactic should work with a condor too although you may need to use afterburners and it might not have enough ammo/missiles to take them all out, but yes, Foxtrots will fail.
The only times I fail to take out a squadron of heavy fighters with a corsair is when it started with limited ammo from a previous engagement.