I tried to utilize the web to figure the optimum size ratio for an ancient Roman torsion spring, (e.g. it’s length vs. it’s diameter).   The varying opinions quickly got me disoriented.  It was all a bit of a muddle.

So I’ve decided to use a “cut the chatter” kind of strategy and act from what I know already.  Because Firefly’s springs have proven themselves highly successful over the years, especially with the short limb rotations we are currently exploring, I will use that same spring ratio on Phoenix.  That is:  6.6 times as long as they are wide in diameter.  6.6 to 1, if you will.

Firefly has not had her springs adjusted in the last 4 years and has always shot a very consistent 316 fps, plus or minus 10 fps.  Her power is enough to shoot a 520 gram bolt 800 yards.  I believe that if there are gains to be made in performance they will be found somewhere other than the spring ratio.  “The spring ratio is not to be monkeyed with!”,  says my executive function.  A voice that demands obedience from the other functions that keep this project puttering along.

Developing Firefly’s torsion springs was not an easy process.  When gains are hard-won, one tends to be less flippant in considering potential “improvements”.  Counting one’s blessings can make a lot of sense.

Here is a preview of one of Phoenix’s washers, shown in cross section.

3washers

 

The new washers will be 2  3/4″ inches long.  This will make Phoenix’s springs about 16 1/2 ” long, and with their 2 1/2″ diameter, they will be 6.6 times longer than they are wide.

And so, in a gesture of mathematically precise conservatism, Phoenix’s spring ratio will be exactly the same as her older sibling, because, well … why not?  That’s how pleased I am with the performance generated by Firefly’s spring ratio.  No changes needed for Phoenix in this area.

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