Here was the setup I used:
A5 receiver halves (newer style) w/ polished internals and both ports plugged
stock powertube w/ packing tape over RT/Cyclone hole
Orange Howitzer front bolt
Maddmann blue spring
AKA 2-Liter Plus Dual w/ HP spring and 7/8" extension cap
Lapco ION barrel adapter
12" Freak front
ION threaded Freak back
HPA on remote line
Metadyne folding stock
Gold cup oil
F1 shooting chrony
I performed this simple test by shooting with the FVA flushed with the inside of the powertube as my control and adjusted the FVA 1 full revolution at a time. I was quite proud of this experiment as it finally put my recent study of Calculus to use through integration. So for you naysayers of Calculus saying there will never be a use for it, here's a practical example for you. BTW, if I messed up at any point in my math, please let me know as I want to make sure it is correct.
Here's the data I obtained:
As you can see, the velocity drop off obtained is exponential and non-linear. In other words, it's rate of change increases for every turn instead of it being constant.
For those interested in where the Calculus aspect comes into play, it involves where the FVA screw meets the curvature of the powertube. To find the cross-sectional area is takes up, although very small, involves integration.
Here is the formula for the powertube.
And here is the integration to find the cross-sectional area of the FVA screw in the powertube.
The area marked a1 is the cross-sectional area that the FVA screw takes up when the contact area with the PT is wider than or equal to the width of the FVA screw itself. The striped area is the cross-sectional area of the FVA screw fully exposed when its width is maximized.
In the equation sheet, Area1 is equal to a1 or smaller. Area2 is cross-sectional area of the screw when it is exposed beyond the when the sides are the only contact points to the PT. Area3 refers to the cross-sectional area of the FVA screw when it crosses the X-axis.
As you can see from the data, after a certain point, the cross-sectional area the FVA takes up is pretty linear and does not take up an exponential area of the total powertube area for gas to flow through.
I've talked with Cockerpunk slightly regarding flow rates but both volumetric and mass flow rates don't appear to have a correlation to the performance shown. I don't know much about gases and their behaviors, so if anyone is able to help show a relationship between the velocities and cross-sectional area of the FVA in the PT, it would help out a ton. I'd really like to be able to illustrate the relationship.
In more practical terms (and based on other tests I've conducted), the FVA is almost 4 times as effective at adjusting the velocity than drive springs or hammer weights. It must be noted, though, that adjusting the FVA creates a balancing act of ball velocity and Cyclone performance and should be taken into consideration.
This post has been edited by Lord Odin: 29 June 2009 - 09:44 PM