Your question is incomplete in that I cannot figure out what information you would like to get about these long radius bends, what fluids you are carrying, what materials you are used to working with and what materials you'd like to work with.
What do you know already? What are you trying to do: Figure out flow restrictions or flow loss? Figure out to how make them? Figure out how long a blank you need?
One good reason for such bends is a air-powered messenger service between cash registers and a central office. But you might not be interested that application. 8<)
I often find that people just want to know what is implied by a designation of "10D radius bends". If that is all you are after, then it only means that the radius of the bend at the centerline of the pipe is ten times the nominal pipe diameter. So, for 8 inch pipe a 10D radius bend would have an 80 inch bend radius at the centerline, the bend radius at the inside would be less by half of 8.625 inches and the outside would be bigger by the same amount.
If you are looking for something else, you'll need to expand your question like racookpe1978 suggested.
Having had a whole lot of 4" and 6" 5D and 8D bends made in error (by the pipe bending co.) based on the OD, it is important to clearly specify NOMINAL diameter.
It's what we all (should) know but .....
In the witch hunt that followed, to my surprise and disappointment, I only found one specification that clearly said a 5D bend is 5x nominal, and that was US Military code. I could not find it it any B31 or similar.
