Some may recall my premature opening test with the Micro 400 Suppressor from a couple months ago where calculating the rate of spin was mentioned. Well, since I'm still stuck at home I've finally got some time.DuckHunt wrote: ↑Thu Mar 19, 2020 6:13 pmGlad to see I wasn't the only one to notice that. It somewhat suprised me because we're only talking about 3.5" of travel and it certainly rotated. And this was from a Proflight arrow that has way less spin than most of us shoot on custom arrows. It might take more distance between the paper to calculate the actual spin. Then shot distance might matter. How far does it travel before reaching maximum rotation speed? You, well anyone else, could test that alone for days.
I contemplated exactly how I could capture the angle of change between the two pieces of paper in the test setup above. Then it hit me that I was making it harder than it really was. Simply place both pieces of paper with the sides aligned perfectly with the top board and I'll be able to measure the angle relative to the side of the paper on each piece. Calculate the difference between the two and wallah, your rate of spin, albeit over only 3.5" of travel.
Since arrow speed shouldn't be a factor, I chose my Micro 335 as the test platform because its way easier to dig arrows out of the target. Then I grabbed a cheap Chinese-made 2-blade Rage clone and removed the band and started with it fully deployed. Using a 2-blade will make it easier to keep track of the rotating blade. I fired shots with the three different arrow/fletching combinations that I have and measured the results.
First Arrow: A stock 18" Diablo
Raw Data: 7° change in 3.5"
Twist Rate: ~1:180"
I'm an engineer so you might want to double check my math. Another way to think of it is 4 revolutions in 20 yards. Of course it would be somewhat less than 4 rotations, because it will take some distance to achieve maximum spin rate.
Second Arrow: A stock 16.5" ProFlight
Raw Data: 9.1° change in 3.5"
Twist Rate: ~1:138"
5.2 revs in 20 yards
Final Arrow: A 16.5" Spynal Tap fletched helical with 2" Blazers using E-Z Fletch Bolt
Raw Data: 32.5° change in 3.5"
Twist Rate: ~1:38.8"
18.5 revs in 20 yards
The helical Blazers certainly crank up the spin. Of course the increased accuracy comes at the expense of a few FPS of speed. I guess it comes down to a personal preference if you're chasing speed or accuracy. Personally I'm happy with the accuracy of the helical Blazers.
Why don't arrow manufactures advertise the spin rate of their arrows? Depending on how they fletch them, it should be easy to calculate. Then customers can select the solution that suits their needs. Having that info up front when buying a fletching jig would be handy as well.