Yeah 3 minute rule is cool, but requires too much fiddling with the plot to be worthwhile.. but I just thought of a cool way to do it with sheer numbers without touching it. Thanks for the tip!
Use 3 minute rule to find closing speed, subtract ownship speed inside the line of sight and divide resultant by cos(AoB) to calculate speed.
Its not exact, but its close (since we cannot compute instantaniously).
Sooo...
Speed of Contact = (Difference in range in 3 minutes / 100 +/- cos(OSAoB)OSspeed) / cos(AoB)
or for quick solutions
Speed of Contact = (Difference in range for 1 minute / 33 +/- cos(OSAoB)OSspeed) / cos (AoB)
Sound right?