Date: Thu, 11 May 2000 09:11:44 -0700
From: fmoreno4@postoffice.pacbell.net
Subject: Dynacam engine
To: Lancair List <lancair.list@olsusa.com>
Reply-to: fmoreno4@pacbell.net
Message-id: <391ADBC0.8C1AE662@postoffice.pacbell.net>
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Bob Froelich wrote:


  I have not seen any comments on the dynacam engine.  It is proven in
over
  60 years of operation.


The Dynacam was certified many  years ago by satisfying the 150 hour FAA
test of the time, but is (unfortunately) by no
means "proven."  Referring again to Taylor, "The Internal Combustion
Engine in Theory and Practice," Vol. 2 page 579-580
(excerpted), section on "Barrel or Revolver Engines:"

"These are piston engines with cylinders arranged parallel to the main
shaft and acting on it by means of some kind of cam or
"wobble-plate" mechanism.  ... The objective of such designs is to
secure a more compact arrangement than is possible with
the conventional crank-and-rod arrangement.  Many such engines have been
built and tested, abut few have been found
sufficiently rugged to withstand normal piston speeds and mean effective
pressures for any but short periods.  A marine
Diesel engine of this type was put on the market in 1945 but was not a
commercial success....  Such cylinder arrangements
have serious disadvantages with regard to accessibility and mounting
structure, which would make them undesirable for most
services even if a reliable mechanism could be developed  There is no
likelihood of such engines becoming important
competitors to the conventional types."

Taylor is usually moderate and measured in his comments but his opinion
seems clear on this configuration.

I have inspected the DynaCam engines, and I believe the weak point is
the roller that connects the pistons to the wavy cam
that converts piston motion to rotary motion.  The roller has a line
contact on the cam, and so it only takes moderate pressure
(or a little bit of knocking or detonation or excessive clearance) for
the roller to dent the surface of the cam with unfortunate
results.  Oil sleeve bearings as used in our aircraft and in auto
engines (and many other places) are very stiff, very tough, and
very resistant to damage, in comparison.

The engine configurations we have today (radials, in-line, V, flat
opposed) are prevalent because many, many configurations
have been tried and only these few have survived.

Fred Moreno


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