VO wrote:
To all,
This I got on our Reflector (Velocity news group).
Question was: Auto Conversions are unreliable and/or unproven?
This is an answer, please comment. Thanks.
Vlad
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If you go with a Mazda, be absolutely sure that the cooling system is the
most reliable and over-built system on board. The Mazda rotaries are very
prone to instant engine failure if coolant loss happens. Most auto engine
conversions will make at least enough power long enough to extend best glide,
opening up a lot more landing options.
This has to do with the fact that Mazda rotary engine exhaust heat is all
gathered in one area of the engine, on the bottom of the housing, exhaust is
ALWAYS happening with very little rest between pulses and rotor housing
sealing is done with O-rings that tend to collapse with age/heat. If a
housing side plate/housing seal ruptures, it is equivalent to loosing 1/2
power output in a normal auto engine conversion. On earlier 13B RX-7, the oil
cooler is mounted over the rubber heater hoses. As the engine ages, cooler
mount O-rings begin leaking and oil soaks the hose. After a while, the hose
ruptures, coolant literally explodes out of the fitting draining the housing
and causing an overheat condition so rapidly that the car cannot be pulled
over to the curb fast enough to save the engine. We get the car in the
service department and all it will do is crank over with no compression and
spout coolant out of the radiator due to water jacket pressurization. A
complete failure. Unless a catstrophic engine failure occurs in an auto
conversion, about the worse you can expect in an auto conversion would be a
blown head gasket 86'ing two holes normally. Now most builders will probably
use Aero-Quip for coolant lines if any are used at all and this shouldn't be
a concern, but helps illustrate how fragile the engine is to this type of
failure.
Late model RX-7's (93-95) had a recall for fuel/cooling systems for fires.
This originated from the fact that Mazda tried to run the cooling system at
19-20 psi which would raise the boiling point of coolant, All they
accomplished was killing the water pump seals and causing coolant leaks on
top of the engine which resulted in engine fires and a huge recall. Yes,
glycol based collant will catch fire if the temp is high enough. So be weary
of people who recommend raising the system pressure without additional
information as to how to eliminate this concern.
This is NOT a blanket condemnation of the rotary engine, meerly a plea to get
the best information available from sources such as Atkins Racing, follow it
implicitly, question and understand whatever is not clear and overbuild in
the cooling system. The Mazda Rotary engine has a huge success in racing and
is becoming better established as an aero engine.
Let's not give Avemco any more reasons to look cross-eyed at Velocity. Build
as best you can.
Dale Alexander
173 RG Gull-wing
DAlexan424@aol.com
Huge exaggerations here and there but more or less true. Pay careful attention to the
cooling system design and plan ahead. Use teflon encapsulated silicone O-rings for
both oil and water seals. Use at least silicone water hose if not AN lines or
aluminum pipe. If in doubt ask on here as someone has tried most everything.
I would say the place that most people still are having trouble with is the
shape and position of the air duct feeding the radiator and oil cooler.
The second mistake is allowing the exhaust pipes to radiate heat to the
radiators or oil coolers. If those heat exchangers can "see" the red hot
exhaust pipes heat will be transferred. As Tracy says; "a breeze on a hot sunny
day will not prevent your getting a sunburn."
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
http://home.earthlink.net/~rotaryeng/ http://www.linux.org