I saw within the last week or so a post with the answer you're looking for, but for the life of me, I can't find it. I searched some but without luck. I think it was for fast torpedoes and 90AOB though.
One thing that you can try is to build you hitman's Kriegsmarine Whizwheel. It gives you the ability to figure out lead angle for various torpedo speeds, target speeds, and AOB's. If you don't want to build it, I believe there used to be or still is a flash player version that you can use on your computer. I have it at work and play around with it some.
I built one to use during the game, but I use it for other things mostly. There are a ton of other uses for it-intercept courses, target speeds through bearing observations, etc.
The TDC should figure out lead angle for you. The whizwheel does the same thing as the TDC but you do the solution yourself and a lot slower.
Link below:
http://www.subsim.com/radioroom/show...t=kriegsmarine