Be careful of what you find on youtube about broad axe hewing. VERY few of them know what they are talking about. If you find anything, other than the historic footage, and it is done by Doug Reed in Pennsylvania or Peter Gott in North Carolina you can take that to the bank.
So back to the question. First, what is the broad axe head pattern, the weight, the geometry of the bit (left bevel, right bevel, double bevel (knife bevel), do you chop right or left handed, and of course the intended use.
Without this information it is hard to recommend a haft pattern. But, some very general info for log hewing would be: 22" + or - haft length for the haft length alone. No offset haft if the head has a knife edge bevel (can be used by either a left or right handed axeman). If the head has a right bevel for a right hand axeman or a left bevel for a left hand axeman you need either a S bent or dog leg bent haft.
Again, watch historic footage if you really want to know about the art of hewing.