I was just curious if anybody knew how much draw length affects arrow speed from a r/d longbow or recurve. If you had two equal bows with the same weight arrows and such but one archer pulled 50# at his 25” draw length and the other archer had a 30” draw length how much weight would the second archer need to pull at his 30”dL to achieve the same speed?

A general rule of thumb I’ve seen for compounds is that 1” difference in dl is equal to about 10fps and 1 lb of weight is equal to about 2fps so therefore 1”of dl is the equivalent to about 5# of weight. So a guy shooting a 50# bow with a 25” dl would get the same speed as a guy shooting 40# with a 27” dl. How much different is it for traditional bows?

IIRC the average for trad is about 3# per inch of draw over/under 28".

Draw lengths usually determine limb length as well (have optimal working range).
It aint just finger pinch.

FWIW my old Hoyt Huntmaster was a 58" bow and hit the wall at 29".

I wonder what the draw length is for adult American males?

Try this http://backcountrybowhunting.com/calculator/