Bo,
I had read Bradley's book, and that must be where I got the 10 degree maximum. But then I searched this forum and found this response from Rex Schimmer to the thread "Bicycle Aerodynamics for those who are interested", back in 2008 in regards to a human powered bicycle called the Varna, which incidentally was clocked at 80 mph!
"Kent,
I think that I have to disagree with you regarding your thinking that the Varna would suffer from unattached air flow above 100 mph. Looking at the pictures the angle that the body converges at is certainly less that the
accepted 11-14 degrees maximum also the bike has a very small surface area which minimizes skin friction which is probably the largest component of drag for the bike. There is no doubt that all of the air flow on the VARNA is attached and probably laminar, due to the low speed, so its pressure drag is only the area of the boundary layer from both sides as they converge at the tail and being pretty short and probably laminar flow the boundary layer is probably pretty thin at the rear of the bike."
I took this bit of information as an excuse to narrow up the rear of my mock-up a couple of inches -- it sure looks a lot better, and of course, looks are important
. Still less than 14 degrees, so time will tell. I'm still trying to figure out how that CanAm 125 went 135 mph on just 22 hp. Methinks it had to have a bit more.
Tom