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Ed Anderson wrote:
Hi Mike,
Paul tends to contribute most any problem only to the "Plugs Up" orientation
even though others with the engine "right side" up have had similar problems with
cooling. My only problem with water temp with the plugs up orientation was early
on when I failed to "burp" the engine and get all the air pockets out which
resulted in a high temp situation during a ground up before I noticed the coolant
temp gauge pegged. After that incident, upon a complete drain and refill, I run the
engine for 2-3 minutes and then add coolant, run it again, add coolant if
necessary until you have all the air out. I need to do this only after a complete
drain and refill. My coolant temp normally runs between 180-190F, it might get up
to 200F on a hot day max power climb out. So the coolant system in my installation
was not the real bug-a-boo.
Paul has two major areas (as best I recall) that he believes of great concern,
one is, as you mentioned, concerning cooling and the other has to do with the
lubrication system.
Paul does have a point about any lowering of coolant level (coolant leak) would
diminish the amount of coolant at the high point of the block which in the case of
the Plugs up is the hottest point (around the plugs) first. While the regularly
orientation engine would still be bathed in coolant on that hot area - at least
until the coolant level dropped below that point. Of course a severe coolant leak
will soon put both the Plugs up and regular orientation engine in the overheat mode
quickly. That is one reason I use stainless steel braided coolant lines and a
coolant pressure gauge to 1. reduce the probability of a leak and 2. to detect one
immediately should it occur.
Paul's other concern as I recall was about the flow back of cooling oil from the
central rotor housing (dumped there by the two rotors) back down to the oil sump.
If you look at some of the cut-a-ways of the Central housing courtesy of Paul , it
appears that with the regular engine orientation that the oil has essentially a
vertical path (assisted by gravity) from the central housing to the oil sump. In
the Plugs up orientation, the rotation makes the angle for the oil flow to be more
like 45 degrees (not certain on that number it could be less), so that the oil
would not have a vertical drop. There is no arguing that the 45 degree path is not
as conducive to oil flow as is the 90 deg drop. However, the opening into the oil
sump is approx 2 square inches (as best as I recall) and appears to handle the oil
flow just fine at the 45 degree angle for engine producing around 6000 rpm. Now,
the oil flow increases as the engine rpm goes up, so while the situation may be
adequate for 6000 rpm ( the evidence is that it is), an engine turning 8000 or
10,000 rpm with the resulting increase in oil flow to the sump, could possibly
exceed the capability of the oil drain back on the Plugs Up installation. However,
since that rpm range is unlikely for an aircraft application and the oil drain
back is adequate for the 6000 rpm range, I am not concerned.
However, I did have a fit with the oil cooling. I initially used an Earl's oil
cooler set back in the engine compartment. First, I vastly underestimated the
amount air flow required to carry away the heat. I started out with a 3 " dia air
duct and ended up with a 5" dia air duct which along with Paul Lamar's suggestion
of putting a snorkel inlet for the airflow finally got the oil temp down to where I
could fly most days. However, on a 90+F day the oil temp would still get higher
than I liked especially at max power settings.
Jim Mosur, who also has a Plugs Up 13B in his RV-6, was having similar oil
cooling problems and ended up putting a regular Rx-7 Oil cooler up front and made a
2 x 11" duct for airflow. He stated that it dropped his oil temp approx 30F down
to the 180F range. So always eager to adopt a proven idea, I did the same and my
oil temp dropped from as high as 220F on a hot day take off to 180F-190F. Also, I
noticed that once the oil cooler was doing a better job of rejecting engine heat,
the coolant temperature dropped also by approx 5-10F.
So, I consider the cooling problem solved (at least for engine producing 180 hp
or less) for the plugs up orientation. Paul may have a valid point about the Plugs
Up orientation as far as long term durability, however, there is no evidence one
way or the other at this point. But, there is nothing to indicate that the plugs
up orientation leads to any sort of catastrophic type failure. One individual has
over 800 hours on a Plugs Up installation and Jim Mosur has over 200 hours. If
there were oil starvation at any point, the damage would be done long before those
number of hours running time.
I am impressed with your analysis of the problem, but not having had any
experience (and way too long out of school), I honestly could not meaningfully
critique it. But, we certainly appreciate your viewpoint and would like to hear
more as its developed.
Best Regards
Ed Anderson
The 800 hours cited above was proven to be wrong.
The real hours for Andy Venable's Christavia proved
to be about 450 as I recall. There is always an exception
to the rule. Andy has what amounts to a dry sump system with
an entirely separate large container for the oil sump.
There is no need to tempt fate and put an engine
in plugs up. In the early days, before electronic ignition and
distributors sticking up, I would say maybe yes but now the engine
can be made lower when it is right side up. This is because of
the plugs themselves. The Mazda engineers designed the engine the way
they did for very good reasons. It is not wise to second
guess their decision on this.
Paul Lamar
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