ORIGINAL: gregow
Thanks for the replies. Here is a couple images, the forst is one of the better fixed blade heads and the second is the one I refered to as non-planing. This might help.
It looks like they're betting the removal of "side area" would reduce the "planing". Planing seems to be nothing more than what vertical fin/rudders do. The only way to get rid of that is to remove them.
da rock, yes several manufactures have played with rotational stability in the broadhead, but in the end all those efforts allow the front of the arrow to ''steer'' itself better which is not what you want. A neutral broadhead is the best.
I'm not suggesting an attempt to create rotational stability with the arrowhead's shape, I'm suggesting shaping the sucker to reduce it's side area and that area's interaction with the air. As each flat blade of of the arrowhead is rotated the air it encounters works on the blade almost exactly as air works on a propeller blade. There will be an AOA (angle of attack) created that would be a source of lift and drag. The idea is to shape the arrowhead blades to reduce that AOA. Rotational stability has nothing to do with the idea.
soarrich, your idea sounds interesting, I was thinking about an asymetrical diamond shape cross section, with a 30 - 40 degree leading edge and a longer, lower angle trailing edge. The cross section of the non-planing head in the photo is a triangle, it does not plane but it is also fragile. How to beef it up and not change the aerodynamics? Maybe add a half round to the back side of the triangle, that would increase it's strength, but how would that new shape effect flight?
The planform shape of each blade really isn't going to matter much at the terribly low Reynolds numbers they're seeing. There really aren't much "aerodynamics" in play there. The shapes aren't going to matter much. For examples why, look at the discussions about the electric foamys designed for 3D flight, where the model operates most of the time at very slow airspeeds. They use flat foam sheets with square leading and trailing edges. Nothing really "aerodynamic" there at all.
It appears that what happens to an arrow in the planing envelope isn't something that could be very aerodynamic. The design feature that matters most with the 3D foamies is area and location. You can't change location.
But truth is, experimentation is fun. So try something "aerodynamic" and let us know how it works.