X-Mozilla-Keys:
Bill Freeman wrote:
Bill Freeman wrote:
*** SNIP ***
. . . stand up to detonation better.
. . . . . . The sky would be
the limit for HP if this problem could be solved.
Paul Lamar
Paul,
AHEM . . . I must respectfully submit ---
Well, DUH! For *any* spark ignition engine!!
Just keeping ya honest. ;-)
Bill
Not neccessarily so Bill. One of the structural subtleties of the
rotary is most of the various loads go through the one piece rotor.
The main thing the e-shaft sees is output forces. In a piston engine
the compression force must go through the piston pin, rod, crankshaft
back up through another rod, piston pin and into another piston.
Or in the case of a single cylinder piston engine it relies on the
inertia of the flywheel to supply these forces.
This and a few other features make the rotary nye on to cannon proof
when it comes to high pressures. Francesco Iannetti told me you can
boost
it to 55 psi (70 psi absolute) before the side housings lift off the
rotor
housings and the water O ring seals start to leak combustion gases into
the cooling system. Try that with your average car piston engine.
You would be in blast zone of shrapnel bomb.
Paul Lamar
If you are saying that the rotaries that we have today (Mazda)
are grossly overdesigned for their normal loads, well OK. But
the primary cause there is engineering safety factors intended to
cover up a lot of ignorance. Since we have been racing and
blowing up std piston engines for over 100 years, we engineers
have a darned good idea what it takes to break one. So, if
you are trying to design a cost effective and *light* (read CAFE
mileage std) motor, you do *not* overdesign it. And, FEA
permits us to cut the margins much finer than we used to be
able to do safely. So, std car motors don't have the strength
and cooling margins to survive at much beyond the normal
highway loads. However, with a lot of boost, detonation is
the primary assassin, assuming that you are in the general ballpark
of the rated hp. Overheating is often a serious issue, too.
I am not saying that but I think you are right. The Mazda is over
designed. If it was re-designed for lightest possible weight then
that would result in even a better stock power to weight ratio than
it already enjoys. Do you agree?
I submit that if Mazda had had enough experience (50-75 more years)
*and* FEA when they designed the 12A, 13B, et al. those engines
would be significantly less robust, altho some of the robustness
is inherent in the design.
You hit my main point on the head here.
I still think the strongest argument for
the rotary is the 'non-installed parts' especially *very expensive*
ones like exhaust valves. All these missing pieces cost and weigh
less, and will never break or wear out.
The primary dificulty at this time is that no one is really making
a purpose built rotary in the 150 +/- 50 hp range that most
light AC need. So, here we are backend engineering a too-
heavy-to-start-with motor into a fairly-decent-but-probably
still-a-bit-too-heavy power plant.
Perhaps but we are already equalling the power to weight
ratio of the best aircraft engines in this HP range. With a little
more boost we will easily exceed those aircraft engine power to
weight ratios.
Not altogether a bad thing, but let's keep in mind what it is
that we're about. I was working on my O-470 again and am
repeatedly reminded that the way to make a light engine is to
use a lot of very light pieces. Some of the parts are nearly
astoundingly light. We should seek to emulate this where ever
practical.
Bill
There is one other factor I failed to mention and that is
it is not possible to use cast iron pistons in a piston
engine and get a decent power to weight ratio. RPM's will
be too limited and HP is RPM times torque. Half the RPM
half the power.
Cast iron is hard to melt. Cast iron rotors are no problem
for the rotary.
Paul Lamar
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