> > > > > Tailwind engine mounts have no offset in theory.  In fact, most of

 > > > > them are built in space without a fixture of any kind and you can
 > > > > imagine that many of them must warped out of alignment, one way or
 > > > > the other. Difficult to see once the engine is installed.
Yet first
 > > > > flight reports usually say that the airplane flies normally.   I
 > > > > personally have flown in three TWs that had motor mounts built
 > > > > without a fixture and all three felt about the same to me and had no
 > > > > trim issues.  Also, it is quite possible to kick an engine mount one
 > > > > way or the other with spacers at the firewall . I saw a
Cassutt racer
 > > > > with 3/4" spacers on one side, none on the other.  Apparently helped
 > > > > turning left.   The Tailwind does off set the leading edge of the
 > > > > vert. stab 1/2".  I moved this to the opposite side for the rotary.
 > > > > Jerry
 >
 >
 > > Jerry,
 > >
 > >   Your experience seems to fit with Tracy's (no offset
required). However,
 > > this doesnt resolve the issue for most builders in attempting
to use Paul's
 > > proposed front housing/mount since I beleive most kit
manufacturers provide
 > > mounts with thrust offset that goes the wrong way (as Vans
does). On an RV,
 > > shimming the mount at the firewall would be a bad option as that would
 > > cause a misalignment of the landing gear. Arent Tailwind gear
sockets also
 > > integral to the engine mount? Probably could add shims at the
engine end of
 > > the mount which would probably work if the mount were a conical design
 > > rather than Dynafocal.
 > >
 > > Mike Wills

 >I am not following you Mike. Why is what we are doing any different
 >that what Tracy did using the stock dynafocal mount that came
 >with the RV4? What would you like us to do different other than use
 >the conical mount?
 >
 >Paul Lamar

 Paul,

   Tracy didnt use a stock RV4 Dynafocal mount. He cut it up and then
 rewelded the Dynafocal cups to the firewall/landing gear structure that was
 left of the original mount. The result is a much modified mount with no
 offset to which he attached a submount (also with no offset).

   Jerry indicates that the typical Tailwind mount is also built
with no offset.

   This is not true of Vans mounts and I'd bet most other kit manufacturers
 also provide mounts with an offset that goes the wrong way for a 13B with a
 2.17 PSRU. I wouldnt know if all manufacturers use the same amount of
 thrust offset.

   The new front cover will need to be manufactured in a way that removes
 this wrong way offset to at least get us back to zero offset. I take back
 what I said previously about shims being a reasonable solution on the RV.
 Simply adding shims at the isolator will remove the thrust angle. But the

 > prop hub will no longer be centered on the firewall or in the cowl as
 > viewed from the top. Vans mounts are designed with both a thrust angle and
 > an offset to center the prop hub. If you remove just the angle(with shims)

 and leave the offset, then the prop is no longer centered.

   Am I more clear now? If not I'll try to remember to bring in a drawing of
 the stock RV-4 conical mount to illistrate the problem.

   Of course you could ignore all of this, build the airplane with thrust
 offset the wrong way, and add a huge trim tab or vertical stab offset.  :-)

 Mike Wills

Or use a 2.85:1 gear box.

Paul Lamar

Mike,  The point I was trying to make is that small deviations of the
engine thrust line don't cause a noticable effect.  All kinds of
aerodynamic  forces at play that have a larger effect.   The Tailwind
is   fast and fuel efficient with the engine pointed straight down
the road.   I suspect that off setting the engine from the thrust
line creates as much inefficiency as it does benefit.  This is
strickly an opinion.   I have no way of really knowing.   I was
talking to a Cassutt builder some months back who told me that the
Cassutt  guys are  now installing their engines straight ahead and
they are no longer off setting the Vert Stab.  either.    We need a
wind tunnel.  Given a choice,  I would rather bend a trim tab at the
other end of the airplane.      Jerry

 
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