Maybe this will help.
You can see the flat sides of the blades in this tail shot due to them being offset. The offset blade angles cause rotation because as they travel through a medium (bone, meat, foam target, whatever) there is a transverse force put against the outside flat area of the blades much like the propeller on an airplane or blades of a fan. The result of his force is rotation along the axis of the insert. That part of their design is very easy to understand because we see that happen all the time in our natural environment. Somewhere on YouTube there is even a video of someone hitting these heads with compressed air while the arrow shaft is on rollers showing you how it makes the arrows spin.
The single bevel acts in two ways, friction and pressure. I can explain both of those below separately.
Friction:
If you look at the bevel area of the single bevel broadhead only, it forms a right triangle. A traditional double bevel forms an isosceles triangle (two equal sides with a short base equal to the blade width). Side “3” of that right triangle is the cut of the bevel itself where the blade was ground into an edge. It is the hypotenuse and thus will always will be the longest side of that right triangle which means it also will have the largest surface area. As that head pushes through the meat and the meat pushes back into all sides of that head, there will be more friction and pressure put on side “3” than any other side just because it’s larger. This pushes into and against side “3” more than side “2” causing a tiny bit of rotation.
Pressure from how the meat is cut:
In addition to this, the meat along that side is cut asymmetrically. It is cut in line with the flat sides then forced to push and squish over the bevel because the leading edge of that bevel is on the far outside corner of the flats. This causes even more pressure to be exerted along side “3” as the meat is forced over the bevel but un-resisted along side “2” due to where the meat is cut in relation to the bevel. As a result, you get an even higher assymetrical pressure differential across the bevel itself (side “3”) which causes clockwise rotation.
Add it all up:
1) The arrow has clockwise rotation from flight due to fletching and air acting on the head before it enters game.
2) Once entering game, the head causes additional or at least helps to maintain clockwise rotation from offset blade angles.
3) The single bevel design causes additional clockwise rotation from increased friction and pressure due to an asymmetrical bevel.
4) The pressure differential caused from the relation of where the meat/bone/whatever is cut in comparison to the single bevel design causes additional rotation to be gained or maintained inside the target.
End result:
Momentum of the arrow isn't lost to stopping the rotation from the fletching. Wound channels are more destructive as the blade rotates and cuts more blood vessels. Shots through fibrous material (BONE) are easier as the rotation exploits the natural weaknesses between the fibers causing them to split along a weak spot rather than have to be cut along a strong spot (think about drilling wood with a wood spade bit vs simply punching through the wood with that spade - the rotation splits the fibers of the wood apart and makes it easier to penetrate).
Topic: Medicine Bear/Badger broadheads (Read 377 times)
