On May 29, 12:50*pm, "Bob Murray" wrote:
"Veeduber" wrote in message

...



To All:

For those of us who own a lathe and milling machine, somewhere in our
past there is probably a tiny steam engine. *Indeed, there's probably
more than than one. *A company in England provides the basic castings
as a kit. *As the machinist, you are expected to provide all else,
from the machine to do the work to the KNOWLEDGE needed to operate the
machine.

Producing such an engine, from the basic one-cylinder model to larger
engines of remarkable complexity, serves as silent testimony as to our
abilities.

It strikes me as little more than a step along the way to produce a
FULL SIZE engine such as the Pobjoy. *The crankshaft calls for a
professional piece of goods, probably obtainable from a Chinese
manufacturer, but the cylinders, being identical, call for much less
in the way of skills and tooling. *With cast-iron cylinder barrels and
cast aluminum heads, the bulk of the engine can be produced on the
tooling found in the shops of literally thousands of amateur
machinists found in every country around the world.

While the copyright to the engine is presently held by the same
company that produces the Rotax, there are enough example of the
Pobjoy in aviation museums that it would be a relatively minor chore
to produce a set of drawings. Indeed, knowing the engine's bore &
stroke even a good PHOTOGRAPH gives a wealth of data leading to a
usable drawing. *So long as those drawings contained significant
differences from the original there should be no question as to
violation of those rights. *Such differences could be calling out
parts and bearings NOT used in the original Pobjoy.

With suitable drawings in hand we could produce the required molds
needed to produce the required castings. *The drawings will also tell
us what gears and bearings are required, allowing us to order them
from suppliers who deal in such components. *The drawings will also
show what type of valve guides are needed and even the valves, springs
and rocker-arms. *With a bore of 75mm and a stroke of 87, we can
determine what EXISTING pistons my be used as well as the size of the
carburetor that is required.

The 'Experiment- Amateur-built' licensing category exists to promote
aeronautical education in America. *Learning how radial engines work
and even building one yourself is no more difficult, in my opinion,
than building your own airframe.

-Robert S. Hoover


There is also the Lawrance 5-cyl. radial, about 35 HP from 75 cubic inches,
and a crankcase just under 9" in diameter.

As far as crankshafts, most radials used built-up cranks which can be
machined fairly easily. *In the size of engine under discussion, the parts
that need to be ground can be finished on any commercial tool & cutter
grinder, and then assembled.

BTW, 75 cubic inches works out to 250cc per cylinder - how many 250 singles,
500 twins, and 1000-1200 fours are out there that could donate pistons,
pins, & rings; valves, springs & keepers, etc.?

Another Bob

Seem to me that the most modern motorcycle cylinders would be the
best. Metallurgy is still advancing rapidly and there are a lot of
innovations in recent bikes. Some even use "diamond-like coatings" on
high wear parts like cams and followers.

Recall that the Merlin and Allison V-12's of WWII used dual overhead
cams and 4 valves per cylinder which is the norm for motorcycles
today.

I worked up a CAD drawing of a radial using 5 banks of 4-cylinder
500cc motorcycle cylinder blocks. (7 banks didn't leave enough room
for intake and exhaust plumbing between the blocks.) The result is an
amazingly small 20 cylinder liquid cooled radial engine.

20 cylinders is enough that you could stop worrying about 2-plugs per
cylinder. If you fouled a couple, you probably wouldn't notice.

Looking through race parts catalogs turned up automatic transmission
planetary gear sets that are rated for 1500hp but are only 6" in
diameter and weigh about 15 pounds. The gear ratios are just right
for a PSRU. If they stand up to the hammering from a drag racer,
handling a couple of hundred HP should be a breeze.

To build this engine would require making a case, crank and rods with
the planetary in a nose case with thrust bearings. (Of course a lot
of other fiddly bits would need to be made as well.) However, the
heads, cylinders and pistons are the hard part and they are available
cheap.