Is there a simple relationship between draw weight, arrow weight and arrow speed?

E.g. from a 55#, how fast would a 315 grs arrow fly? Or am I oversimplefying things?

On a recurve or stick bow I can see that draw length would have an influence... the farther you draw back the more tension you put on the limbs, hence a faster flight (?)

How does that work with a compound? Is all the "tension build-up" done during the heavy-pull stage, and is the "let-off" stage, and the length of it less or not relevant? In other words, can a 6'5" person get more zing out of the same bow with a longer draw length than a 5'8" person?

Just curious...

Frans

There is no way to calculate arrow speed, it has to be measured, way, way, way to many variables that go into the arrow speed a bow can achieve. There is tremendous varience in the efficiency of bows, all bows, long bows, recurves and compounds.

Simplifying to a 50# bow with 500 gr arrow and looking at stick/string bows, a poor bow would achieve 125 fps, an average bow 150 fps, a good bow 175 fps, and an idealized recurve possibly 200 fps.

Yes, for stick bows, the further you pull back, the faster the arrow goes. This is due to both the higher weight of the bow at the increased pull, and the increased distance over which the bow has to accelerate the arrow.

Most modern compounds have a distict "wall", ie a point at which they can't be pulled back any further. If a compound is set up to pull say 28", then it doesn't matter who pulls the bow, it'll only go back to 28, and only propel the arrow so fast.

Interesting too is that most of the speed advantage on sees in modern compounds, ie 300+ fps, is due to using very light arrows, not due to a tremendous difference in efficiencies. Most traditional archers prefer an arrow of ~10 grs per # of bow weight, thus the 700 gr arrows someone shoots from a 70# recurve are why his bow seems so much slower than a 70# compound shooting a 450 gr arrow! The main advantage of a compound is being able to hold it at much less than full draw weight.

Once you do shoot an arrow through the cronograph you can use this web page to get some basic ideas on ballistics.

http://home.att.net/~sajackson/ke.html

Remember this is theroy, individual results will vary.

For trad bows; brace ht., string thickness, arrow wt., spine, F.O.C., are also factors.

There is a program out there called archers advantage that can calculate speed within 5 fps.