Jerry, is the thrust line 10.7 inches down from the top of the
firewall?


Paul Lamar

There it is.  Tailwinders have been raising the top of the firewall
for
a long time.  This lowers the angle of the windshield and reduces
drag.
  Raise the two corners one inch and raise the center 2.5 inches.
The
top of the firewall is a curve.   Jerry

What is the shape of the curve? If you don't have that tell me how
far

above

the thrust line is the center of the curve and how far above the
thrust

line

is the curve where it reaches the sides of the cowl. I will then
assume
it is an ellipse

Paul Lamar

Jerry,
The Vision designer Steve Rahm is a great admirer of the Tailwind and
I
guess it shows in his design.
The firewall is similar and the thrust line is 10.7  same as the
Tailwind
(strange that). You will notice the TL -ve 4" to the Level Line i.e.
6.7+4 =
10.7"

I asked Steve if I could lower the thrust line as he moved it up a
couple of
inches for another installation and he said SURE a couple f inches
won't
hurt as the lower the thrust line the more it offsets the draggy
fixed gear
(I figure a couple of inches would be the limit however). I have
opted for
another of his suggestion and that is to lower the cowl by 2" for
obvious
reasons, of added advantage. I'm even thinking I could place a flap
on the
rad baffle to release excess pressure, to control airflow through the
rad.

Seeing you have an extra 2 inches to the depth of the firewall ( than
mine),
I figure this would be an option if the cowl is still a problem.

It would seem the thrust line is a bit like the CG where it balances
out the
drag - never realised that before.

Just a suggestion!
However I also like the last suggestion  where the inlet tubes face
forward
on the exhaust side - I'm just not sure how the injectors would be
placed.
George ( down under)

Thanks George,  I think I have it wrong but did Steve Rham design the
One Design aerobatic plane?   After a lot of searching and drawing and
photo taking and mock up making, it turns out that the stock Tailwind
Cowl will fit the project perfectly.  The guys building Tailwinds often
lower the bottom of the cowl and raise the top.  They are looking for
more room and less drag in every case.     It is easy to tie the belly
panels into the bottom of the firewall, so that the lower skin remain
fair, no matter how the firewall was "adjusted."  I now recall the One
Design designer was Dan Rhinn, something like that.  Not important
anyway.  I built one for someone else a few years ago.    Jerry

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