My Corvair powered Sonex needs a larger spinner to cover the size of the front mounted flywheel/starter setup. With the 13" spinner in the middle of a 54" prop some like to ask, "where's the rest of your prop?" - but in fact it is the same size prop that Sonex recommends for their aircraft with VW and Jabiru engines.The size of the spinner is dictated by the size of the cowling behind it, which is dictated by the size (frontal area) of the engine within it.
If anybody is actually selling that it's just a gimmick. The spin of the nose cone only affects the boundary layer on the nose cone, the potential flow outside of the bounder layer is not strongly affected by the spin, certainly less than by the prop.Have you guys/gals seen the new floater spinners that don't spin with the prop? They just sit there, or turn about 5 rpm.
Here's the flame.1. Contrary to most commonly accepted wisdom, IMHO, the air hitting the prop (front engine) is not actually slowing down or at least very little. Rather, it is hitting the prop at an angle to the free stream as it diverts to go around the cowl. Prop designers deal with this as if it were slowdown, using the leg of the triangle as the slower speed. The bug streaks on my prop are sufficient proof that the angled hit takes place. I'm seeing between 30 and 45 degrees.
OK, flame away.