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Posted for "Mike Hutchins" <mhutchins@attglobal.net>:
Thanks Scott for posting the pictures.
Here are some additional comments related to Scott’s pictures in the order
they occurred. All cylinders are referenced bases on the TCM cylinder
ordering, i.e. pilot side front to back = 6-4-2 and copilot side front to
back = 5-3-1. All of the comments apply only to the cylinder head; it is not
necessary to provide additional cooling to the barrel.
Photo 1. Polar plot of CHT taken at several positions on the head. The BLUE
trace is cylinder #6. For all of the traces, the exhaust port corresponds to
the 8:30 position and the intake port is at the 4:30 position. Note that the
exhaust port area is the hottest area for all of the heads, except #6. Also
note that the top of #6, at the 10:30 position is substantially cooler than
the rest of the cylinders. This is related to the blast effect of air as it
enters the cowling with baffles that leave most of the head exposed to the
incoming air.
Photo 2. Important details – the baffle has walls on both sides of the fins
to sandwich the fins in between to prevent the escape of cooling air out the
sides. The small step-off in the bottom portion of the baffle provides
adequate exit area for the cooling air. This step-off is necessary to
prevent choking off the air flow, thus reducing the cooling obtained. George
told me that the pushrod tube can substantially block the air flow;
therefore the step-off is a necessary detail. Alternatively, you can forego
the step-off and leave the medial half of the cooling fins exposed
(corresponding to the medial most bend in the baffle shown) with nearly the
same cooling efficiency.
Photo 3. The “curved wing” Scott refers to would be mounted on the shelf
just above the oil cooler and would extend forward of the slanted surface of
the oil cooler so it can “catch” some of the upward deflected air stream.
The “curved wing” would extend rearward to the cylinder head cooling fins
and would curve downward to deflect the air down the forward face of the
cylinder head cooling fins. Recall the polar plot of cylinder #6 and
consider this mod only if #6 is running hot and/or the front baffle covers
most of the forward facing fins of #6.
Photo 4. Essentially, George created a separate air compartment under the
cowl just for the intercooler air.
Photos 3 & 4. Think about radiant heat from the exhaust system. It can be a
more significant contributor to cylinder head heating than you realize. The
exhaust system is running red-orange hot during cruise conditions and can
radiate A LOT of heat into the head. George told us that IR radiation
increases with the 4th power of temperature (my guess is on the Kelvin
scale). To block the IR heat path into the head, fabricate a small heat
shield for each of the exhaust runners under the head. The heat shield can
be mounted to the exhaust pipe with hose clamps and should allow a small ¼”
– ½” airspace between the exhaust pipe and the heat shield. If the heat
shield spans a slip joint, make sure there is adequate flexibility in the
stand off legs to allow movement of the slip joint. The portion of the
exhaust pipe stub or down-tube exiting the exhaust port can also radiate a
lot of heat into the flat surfaces of the fins just behind the exhaust
stack. This area can also benefit from a heat shield. The insulating wraps
for exhaust systems were NOT recommended for this application because of the
very high temperatures involved. The stainless steel beneath the insulating
wrap can readily reach its phase-transition temperature and disintegrate.
Now you are really having a bad day!
Photo 5. The “baffle work” Grayhawk mentions is a bypass channel that gets
the air around the flat spot and down to the lower cooling fins on the
intake side of the head. I think it was Carl Cadwell that recently posted an
elegant fix to this problem for the #2 cylinder. This is also the reason why
you DO NOT want to place any material between the heads in this area.
Photo #6. Make sure the hole is wide enough to get air past the full width
of the flat spot in your cylinder head. There seems to be a fair amount of
variability in the dimensions of this flat spot from engine-to-engine so you
should not rely on dimensions from another installation. Similarly, be sure
to extend the opening down far enough to expose enough fin area for adequate
airflow through the hole and into the fins. Lastly, the “roof” or “awning”
referred to in association with this opening in the baffle is suggested to
redirect the airflow. The airflow in the area of this forward facing baffle
is from bottom-to-top as the incoming air is redirected from its
front-to-back direction into a bottom-to-top direction before it once again
resumes its forward-to-back path. The “roof” is therefore placed above the
hole and extends forward, perpendicular to the baffle and parallel to the
horizon. The purpose is to create a high pressure area under the “roof” that
will encourage air to flow through the hole and thus through the exhaust
port-side cooling fins under the head.
Thanks again Scott for providing some of the more critical pictures from the
seminar.
I hope this helps some of you who were unable to attend. The “Devil is in
the Details” was an often quoted remark, as was the impact of that red-hot
exhaust system just inches away from the bottom of the heads.
Best Regards,
Mike
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