All,
I am a new member to the list gathering information for potential
"alternative" engine options for a CozyIV project I am considering. I had
initially been of the mind set that the certificated engines should be the
best designed and constructed for the application but after a year on Mark
Zeitlin's Cozy list and the Canard forums I am now less than impressed by
both the near 50 year technology of the Lycosaurous and "apparent" engine
component failure rates. I have seen a Cozy IV Subaru installation locally
with which I was very impressed but I felt it prudent to learn about the
rotary options as well. Hence, I have been here for a few days and have
been sponging up what I can. If technically viable a 3 rotor 20B, producing
230-250 hp naturally aspirated in the 6-7000 rpm range would seem to be a
"relatively" straight forward option. (I'm not a fan of turbos in cars or
homebuilt aircraft so would tend to look towards a supercharger if NA could
not produce the desired power. I recognize that a supercharger might carry
an unacceptable weight penalty so I'm not ruling out a turbo, I'd just
prefer to avoid one if possible.)
Professionally I am a Marine Systems Engineering officer in the
Canadian Navy (I've been sailing a desk for over 10 years now so those days
of playing with lovely gas turbines are long gone) and have my degree in
metallurgical engineering.
My interest in light aircraft traces it's roots to my youth and air
cadet days but lay dormant and even forgotten for many years. A little over
a year ago the Discovery Wings channel series, a Chopper is Born, A Plane is
Born and From the Ground Up re-awakened me to this hobby and I have since
been on a learning curve. My experience with engines comes of course from
my professional responsibilities but perhaps even more so from my
"mechanicing" of my brothers hobby car during it's restoration and "hot
rodding", a 67 Ford Thunderbird with a 390CID V-8 - indeed not much direct
applicability to the aeroworld but many of the principles are the same.
Anyway, when I viewed AA-Me's water jacket pitting after reading the
attached post I felt I had to offer an opinion. The corrosion presented
looks like much more than "normally expected" water jacket corrosion.
Within the limits of the photography and assuming that the casting has not
been subject to physical abuse, in the water-jacket-pitting_2 photo there
appears to be at least 4 sites of significant material loss at the surface
of the water jacket surface. This raises concerns of poor casting quality
where high energy site inclusions have possibly spalled off or
preferentially corroded. The general corrosion in the jacket runners also
seems to be excessive unless this is a very high hour engine. A failed
radiator cap could account for this if it allowed air to be drawn into the
system during cool down after use. Air drawn in would initially be
entrained in the coolant but upon complete cooling and coolant stagnation
the entrained air would nucleate into bubbles on the jacket surface and
facilitate corrosion. This is why complete expulsion of air from the
cooling system is so critical.
Furthermore I would recommend against the use of a valve stem and
compressed air to check the cooling system pressure integrity and radiator
cap operation. To do this deliberately introduces air into the coolant
which will only exacerbate the cooling jacket corrosion. If you need to
know the cooling system pressure fit a pressure valve and devise some other
way to pressurize the system with liquid only. Early in my career when we
still operated steam turbine plants in our naval ships we took enormous
measures to ensure that the boilers were "pressed full" with de-aerated feed
water when they were shut down to preclude any corrosion in the boiler's
internal surfaces. In that application it was critical not to have pitting
or even the lightest surface corrosion layer because of their effects on
heat transfer rates and hence power output and fuel consumption.
Just a few thoughts for consideration.
Thanks and Cheers
Good Building and Flying
Carl
Carl P. Lindon B.Eng., CD.
Lieutenant (Navy)
DGIIP/DIRAP
Work
e-mail:
lindon.cp@forces.gc.ca
Home
e-mail: carllindon at rogers dot com
The corrosion you see here is very untypical of a rotary and I tend to agree
with Don as to it's electrolysis origin.
The rotary is not in the same ball park as automotive piston engines.
It is also far superior to any aircraft piston engine due alone,
if nothing else, a lack of exhaust valves.
Paul Lamar
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