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Lynn is obviously more qualified to
have a legit answer, but I suspect that the problem is more
related to the assembly method than the materials. Really long
bolts make it really hard to control stretching. Look at a
Lycoming cylinder attachment, vs a Volkswagen flat 4 cylinder
attachment. The Lyc uses a flange on the base of the cylinder and
short bolts (case through-bolts excepted). And they use the rather
expensive method of threading the head and cylinder for head
attachment. The VW uses long bolts to clamp both head and cylinder
to the crankcase. Even at VW power levels, the long bolts can be
an issue; case fretting, head gasket leaks, etc. And in the
rotary, when the bolts stretch, bending loads get introduced
partially replacing shear loads when the housings try to rotate
past each other.
I suspect that all those issues would go away if the stack could
be assembled with each layer being bolted into the previous one
(offsetting the bolt points), but that would likely require
non-identical components. Unlikely that Mazda would do it, because
the normal method is 'good enough' for intended use, and *much*
cheaper to manufacture.
Charlie
On 8/4/2020 9:44 AM, Kelly Troyer keltro@gmail.com wrote:
Ernest good question...........Need someone smarter
than me for an opinion on that although I would think
by eliminating the differences in expansion rates between
cast iron and aluminum would stop (or minimise ) movement
of the side plates .............
Kelly Troyer
Concerning the stacks moving with heat
cycles: Won't most of that go away when the plates and
housing are made of the same materials?
The thing is that the drag race engine will
never come to full temperature. The senario with a
plane is more like a full power run in a race car
with an hour long straightaway. The rotary eshaft
is super strong and isn’t the problem. The
housings and plate stack likes to move with
repeated thermal cycles. Not saying you can’t make
something that will live, just mentioning
potential problems. You will need to make some
mods to prevent problems.
Bill
Blll , Lynn , Le Roux and
All,
All very valid concerns about
engine twist and bending
moment............To my knowledge
"Mistral" did not use .500 inch (12.7
mm) studs in their 20B engines and to
my knowledge
the "Mistral" side housings were
still cast iron (heavy).............A
purpose built 20B for aircraft in my
opinion should have all alloy housings
and .500 inch studs...........
Think about this hypothetical
situation..............You have an all
alloy 20B boosted to 70 inches map
(about 1500 dyno hp) and tricked out
with all the racing options available
in a
drag race car.............It is
supported from a center housing (as a
stock engine)............Then at about
9000 rpm you drop the
clutch............What kind of bending
and torsional loads do
you think this engine endures
??...........In Rotary racing circles
this happens all the time with amazing
reliability...............Now think
about an all alloy 20B (boosted or NA)
in an aircraft
driving only a propeller (no shock
loads) built to racing standards as a
NA (no boost and approx 350 hp) and
flown between 6000 to 7000 rpm or
boosted to normalize only............
Again the same engine (running
at 6000 to 7000 rpm) boosted just
enough to dyno about 800 hp (piece of
cake for a 20B)...........Of
course this is only my opinion and you
know what
opinions are worth..............I
understand that most of this group are
interested in the 13BREW or RX8
Renesis engines but you have to admit
I have made the forum lively lately
!!..........
As things progress or digress I
will let the forum know until told to
stop............Many thanks to Charlie
for resizing my photos for the group (
I am better with a wrench in my
hands)........
Best Regards,
Kelly Troyer
The
bending loads are carried for the
most part by the upper tension
bolts. The studded engines are
using the tight fitting studs to
manage torsional loads. In high
power street and drag race engines
it was not at all uncommon to fail
an alignment dowel (shear it off)
or break out and alignment hole in
the iron. Very messy as the top
runs have oil pressure. The studs
provide more clamping pressure and
help keep the rotor housings in
the correct shape. The housing
walls tend to move away from the
rotor face during combustion. If
you take apart an old engine you
often find that the rotor housings
have a hint of black death
(similar to black death on the
sides of pistons) on the clamping
surface near the spark plugs. This
is the housing moving on the cast
iron. Early case bolts were necked
down between bolt head and the
threads. Later bolts are
not...........more clamping
pressure. The case bolts used in
high output engines fit snugly in
the holes. So the holes are reamed
with the case bolted up and
torqued. One at a time....so is
costly to have done. It is also a
source of add HP and less wear.
Notice that even later 13-Bs have
the engine mounts on the center
iron so as to reduce engine
twisting. ......Lynn E Hanover
In a message dated 8/3/2020 4:02:49 PM
Eastern Standard Time, flyrotary@lancaironline.net
writes:
Bill : The bending moment and
axial loads you mentioned. Could
it possible be - why some of the
early design allumnium casted
sumps, of the Mistral 3 rotary
engines developed cracks ? as i
remembered that the bed type
mount for the rotary ( pusher
type config.) the thicker sump
and plate, has a lot to do with
these loads and stiffen the
rotars and irons as a solid
unit, as well the bigger
diameter tension bolts and
“dowls”
It was just crossing my mind,
and i have no previous
experience in these loads and
type of mounts as well as the
casted sumps.
The torque loads of the
prop and all ads up.
Included : cut out of the
article Mistral Magic
Could the loads be part of
the sump problem in these type
of mounts? i don’t know.
Cracked
Sump
“I
did have a couple of
teething problems; the
most important one was a
crack in the aluminum-cast
engine sump that I found
during taxi tests. Mistral
reacted in their usual
fashion. After getting
details, they confirmed
they had a crack in the
same area on one of the
sumps they tested. They
designed a reinforced
sump, but never got a
repeat crack on the other
sumps, so none of the new
models were made. I was
offered a temporary
replacement until the new
sumps would be produced to
replace all present sumps.
I decided to wait, and got
my new sump within two
months—and a Mistral
engineer came and
installed it for me.”
Sent from my
iPhone
Le Roux Breytenbach
Charlie, and
everyone rotary,
I can see the
desire to put a rotary
in a similar mount to
a standard aircraft
engine. But I want to
remind everyone that a
Mazda wankel in its
automotive layout
doesn’t work well as
the stack of plates
and housings isn’t
set up to handle the
bending moment. In
Mazda’s racing engines
they added plates to
enable them to hang
the engine from one
end. They still used
cradle mounts. The Lyc
engine shown in the
example has 2
crankcase halves solid
front to rear where
the mounts are. If you
don’t plan to build
the rotary with some
modifications for
axial stiffness and
housing location it
isn’t a good idea to
hang it from one of
the end plates.
Bill Jepson
There
are 8 pics in
this series.
My image
resizer
program got
them down to
around 110-140
KB each, so
they'll need
to come in 8
separate
emails.
--
Kelly Troyer
Dyke Delta_"Eventually"
13B_RD1C_EC2_EM2
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