Since it is not practical to bolt the device on to the front cover
for structural reasons two things are different.

First: The front end housing is replaced with an aluminum part
that accepts the stock front cover (with minor modifications)
and the stock water pump. This reduces the engine weight by
about 30 pounds.

Two: The engine is moved back somewhat
as the front cover and the water pump are inside the dynafocal
mount. These points are apparently being missed when considering
the CG location. The weight of the motor mount brackets, whatever
are not being used, also must be considered. If it is an alloy  plate
under the engine and it is 14.5 by 15 by 1/2 that is 10 pounds
right there. Less what ever holes you can put in it. If you
NC mill it down the cost will be several hundred dollars.
If you use the un-milled motor plate/motor mount idea you
will add about three pounds further forward. I digress.

This sketch is roughly how it should be done but I cannot guaranty it
will be done this way or even at all. What is shown in this
sketch is the use of low cost barry rubber bushing instead
of a dynafocal type mount or a conical mount. The conical
mount would vary only in detail from what is shown here.

Paul Lamar

If it is of any help in your calculations - On my Thorp T-18 I had to move
the prop forward 4.2 inches to achieve the correct CG within the middle of
the envelope.  This was on my second engine mount.  On the first engine
mount I calculated the need to move the engine/prop forward ~3", this was
adequate but toward the rear of the envelope. Although all amatuer built
planes are slightly different, my weight and balance was done by an A&P with
aircraft scales.  John Thorp designed the T-18 to utilize the Lyc 0-290G and
a 4" prop extension, however many iterations have been done, up to Lyc
IO-360s with CS props (read- nose heavy, battery behind baggage area,
ballast in tail).

So in my opinion there would be adequate clearance for the dynafocal
adaptor/mount.  I have read with interest the discussion of the dynafocal
mount/adaptor and believe it to be a good idea.  Since I brought up the
issue of the engine offset designed into some aircraft it has been
interesting to learn that some designs do not incorporate any offset, and
some have eliminated the offset with supposedly no effect.  Knowing that
some popular aircraft "designers" (and I use the term very loosely) do not
have the qualifications to design aircraft, I will conclude that educated
designers know the importance of offset.  Having said that, I recall having
heard that a design is a series of compromises.  I will concur with a
comment from the RV group that the engine is not merely turned but actually
offset to keep the center of the engine on centerline or there abouts which
would make building a universal adaptor quite a project.  Did someone say
2.85:1 for conformity?

It has been my conclusion that building an engine mount (two actually) and
cowls is just part of the package - just like laying out, marking, drilling
(twice), deburring, counter-sinking/dimbling, and riveting every connection
in my airplane - time consuming, rewarding, and not impossible.
Terry Adams

 
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