how fast can a B-17 make a 180 degrees turn

[Revi16]

Just some of the many variables are going to be speed, altitude, weight, amount of control deflection (aileron/elevator/rudder), pilot capability, flying formation, not flying formation, etc., etc.. Unfortunately there are too many variables to give an accurate answer.

You also have to factor in that "eye witnesses" usually make the worst eye witness if you know what I mean. (I was washing my 2010 truck in the driveway the other day. The woman who lives across the street from me and can see into my driveway anytime she looks out her window or walks outside commented she liked my new truck. I told her I've had it for three years. Good thing I don't need her as an eye witness.)

You can try looking at these performance reports.
http://www.wwiiaircraftperformance.org/B-17/B-17.html