Thanks, I am aware of the Flap40 +100 approximation. Ours says;
Recommended holding speeds can be approximated by using the following
guidance until more accurate speeds are obtained from the QRH:
• flaps up manoeuvring speed approximates minimum fuel burn speed and
may be used at low altitudes
• above FL250, use VREF 40 + 100kt to provide adequate buffet margin.
I am interested that you refer to a flat drag curve. Have you ever seen one for the NG? I haven't and would really like to get my hands on one.
So the best I've got now is that Vref40 +100 is close to min drag, and ci 0 = MRC. Thats ok I guess but I would like a more definate way of determining min drag (max endurance).
Cheers.