compression spring sizing

[meccanicamg]

the formula is as follows:
where:
n=number of springs in parallel
wm=coefficient friction surface
wr= coefficient friction edge
-= spring charge
+= discharge spring

 

[meccanicamg]

in our case n=1 so we will have little impact of friction on the complete package of springs.
f=30kn•1/[1±0,02•(1-1)±0,04]= 28,8kn in release and 31.2kn in charge (to compress it) to reach the arrow stability of about 50mm.