"kevin lane" <n3773@comcast.net> wrote:
  > > > I am fabricating the bed mount plate for my 20B in an rv-8.  my
understanding, from Tracy's advice, is to offset the engine about 1 1/2
degrees to the right if I use his 2.85 drive.  as I see it there is a
centerline of the fuselage and a centerline of the engine/redrive.  if I
mount them such that they are 1 1/2 degrees out of parallel, then those
centerlines will intersect.  my question is where? ...snip...   < < < I'm not an RV builder, but I did have the same decision to make when I was fabricating the mount for the 13B in my Lancair LNC2.  I temporarily installed the cowling to the fuselage and found that in its normal position the centerline of the fuselage aligned perfectly with the centerline of the cowl.  I also noticed that there was a tilt to the flat face that would mate up with the spinner, so I assumed that the c/l of the prop should match the c/l of the fuselage, consequently when I built the mount all the offset was at the rear of the engine.  The center of the prop hub is aligned with the c/l of the fuselage.  From an aerodynamic standpoint, I don't know that it makes much difference where the offset comes from, except that if you keep the firewall end of the engine centered on the firewall, the c/l of the prop will be offset to the left or right, as required.  This would impact how the cowling fits up to the fuselage and give you a convex surface on one side and a concave surface on the other where the cowling meets the fuse (when viewed from above or below).  Personally, I'd prefer to keep the lines of the fuselage nice and smooth and symmetrical so aligned the prop hub's and fuselage's c/l's.  What happens under the cowling has little impact on the final external appearance, ergo, I build in the offset back where it would be invisible.  Just my 2c.

  <Marv>

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