The plenums were fabricated using three layers of RAF BID and EZ
Poxy. No Gemini space suit was donned for protection during fabrication.
They were step-cured at 50 degree F increments. Otherwise I’m
guessing that they would deform while taxiing in after the first
flight. Several hundred hours on the previous set showed no effects
upper plenum shape was molded by placing a 2 inch thick layer of
foam over the top of the cylinders, rounded on the corners, and
covered with gray tape. The glass is formed around the push rod
tubes and just lays onto the flat areas around the valve covers.
the NACA internal inlet/tunnel area was glassed on to the spar and
then the snout from the plenum was layered over that to make a movement
joint. In the picture to the right you can see the forward element
of the right tunnel that is glassed to the top of the spar.
probably best to carry the plenum shape over the top of the engine
area so cool air is blown on the case for better oil cooling.
my plenums enclose only the cylinder heads. The necks, or finned
barrels, each have their own two-layer epoxy/BID wraps that clamp
around them. There are one-inch slots on top and bottom for an air
ramps coming from the main plenum. On the bottom of each barrel
there is a one inch slot and a specific ramp leading into the lower
plenum. The air ramps can be seen on some of the engine shots in
Canards and the lower right. The air ramps and the barrel wraps
are held in place on the barrels with safety wire. The upper plenums
are easily removed, removing the pins and lifting straight up.
the lower plenums included placing flat half-inch thick foam pieces
around the top and bottom and outside of the exhausts, covered with
gray tape. The augmentation area around the aft exhaust tubes are
metal, pivoting, three-inch heat ducts from Home Depot. They are
wrapped with fiberfrax. To protect the cowls, on three sides of
the exhausts a layer of fiberfrax is trapped with thin aluminum
shields riveted inside the plenums.
glass under the cylinders was shaped to fit against the inside of
the cylinder heads. There is a (fairly complex) triangular wall
enclosing that open lower triangular area between the heads. The
lower spark plug and sender wires, and the valve cover oil drain
tubes pass through this triangular wall. This allows the lower plenums
to be simply removed without dealing with the wires.
are any number of ways the plenums can fit to the engine. While
mine have a lot of detail around the cylinder heads, the plenums
could probably be mated more easily against the engine case. With
the fore and aft attaching pins in place the plenums can move up
and down on the cylinders a little. For normal engine movement,
there is an overlapping lip segment in the tunnels between the engine
and the spar. Again see the eleventh picture in the Featured Canards.
the plenums off you can see the internal cylinder-head wraps between
the cylinders. I tried to enhance the top air flow between the fore
and aft cylinders a little and included airfoil flow guides.
For those that have installed stock engine baffling with good results,
good on ya. The 0-235 was initially installed with the LongEZ baffling
that came on it, slightly trimmed, using updraft armpit inlets.
Cooling was unacceptable. And I needed something
to keep me off the streets and out of trouble anyway. The first
plenums were fabricated fairly quickly and provided good cooling
from the start. In reaching for that ethereal extra five knots it
is pleasing to have reduced the frontal area by losing the eighteen
square inch armpit scoops, and to have significantly streamlined
the cowls. The dd NACA inlets fit in the existing frontal area and
worked great. The quickcowl attachment was also more easily accomplished
in conjunction with the cooling enhancements, since I was doing
No over-rationalization there, I’m sure.
EZs with plenums
In our intense summer heat we have seen a significant operational improvement
with the plenums here. Dave Perry in our hangar, aka Dancin’ Dave,
will be glad to give a report, in boisterous ringing Russian accent if
you let him. He routinely idles outside our hanger running his engine
for extended periods making sure everyone sees his strobe lights and new
pin stripes, with no CHT problems at all. This is a big change. He has
short exhausts and does incorporate exhaust augmentation. It will also
suck a string into the NACA inlet idling on the ground.
Dave’s oil cooler exits out the top of the firewall. Since his cowl
is not pressurized he uses two cooling tubes from the NACA inlets to feed
the oil cooler. It works well but also reaches the upper comfort zone
in hot weather.
may tell you of creating an exquisite pair of plenums that are so beautiful
that they must be seen to be believed. We spoke on the phone several times
discussing how to fabricate them. They didn’t work. Then we spoke
on the phone several times trying to figure out how to make them work.
He had a strong resistance to changing them, because they looked so good.
that if he wanted to admire them and show them off so much that he should
just put them on his mantle. Later I saw him at Oshkosh flying with dd
inlets. He said that he was flying good with a new set of plenums with
the detail I had suggested. I inquired about the first set and he said
they are at home on his mantle. Good for him. I can understand that, kinda
like having your cake and eating it too. Congrats to him for pushing though
and getting it working.
try this at home!
Since converting to dd plenums several years and 500 hours ago there
has been an intent to get the CHTs to come up just a little by reducing
the size of the NACA inlets over the spar, expecting this would
indicate that the cooling drag had been minimized and optimized.
The intake area with the 0-235 had been reduced several times, from
the old male gorilla 2x9 inlets with eighteen-square-inches per
side (see Featured Canards), down to the female NACA 1x6s with six
inches per side.
was no CHT temp bump up on the 0-235. Now the 0-290 temps appear
about the same, even with the smaller 1x5 square inch NACA inlets
per side. The testing at cruise is not complete. The only firm conclusion
so far is that a 60% reduction in cooling inlet size does not yet
result in 300 knots.
Depends on cowling internal resistance.
At Burt’s birthday last summer I walked the ramp and found 7 downdraft
installations out of the 102 EZs. Talking with two owners that used exhaust
augmentation indicated that their plane worked well. I expect that several
do not use augmentation but still get the cylinders to cool somehow. I
am not familiar with how to make dd cooling work without exhaust augmentation.
Neither do I know how some updraft, per plans EZs cool with so much intestinal
ductage. So, augmentation use and cowl stagnation skews the inlet size
that triggered my interest in developing low pressure aft of the cylinders
was seeing a fellow at a fly-in taxi in with a very hot engine. He got
out complaining about the high CHTs.
A bystander suggested that his two 9x9 inch armpit inlets were too large.
The pilot told the bystander that he was crazy and that he was going to
make them even bigger. The crazy bystander was Gary Hertzler.
If you’re really good you can demonstrate oil flow evidence corroborating
that if the inlet is too large and if there is enough internal stagnation,
an air bubble can form in the inlet and the airflow will take the easier
path, around the inlet. Ram air pressure can be stymied.
So I decided
to aim early at internal simplicity and augmentation. Does anyone need
help in getting a good mental image of how the exhaust augmentation works?
is good cooling?
To me, good cylinder cooling means normal temps at full throttle. The
first downdraft plenums were installed with significant attention to detail
and successfully ran wide open at 2000 feet over the hot ranchland with
excellent cooling from day one.
In our 100
degree temperatures, good CHTs to me with the 0-235 meant a little over
400 degrees after liftoff to 2000 ft. Staying wide open at 2000 feet at
around 200 mph they were about 390. When the power was pulled back a little
they went to 350 or lower.
mph climbs to 10K the 0-235 CHTs started around 400, gradually reducing
during the climb, to 340-350 by reaching 10K. During cruise they further
reduced to 320-340. Some cruise temps were even lower.
I did some
instrument error testing, putting all four CHT washer senders on the top
and bottom of two cylinders. The top dd cooler-side temps were about 60
degrees lower than the hot / bottom side temps. Some of the digging I
did recommended that downdraft installations (spam cans) should have the
washer type senders on the top while bayonet senders should be in the
bottom fitting provided for them. These readings are from washer senders
on the lower side, with a little fudge factor to the good.
testing thus far includes installing the senders on different cylinders
for further comparison. A bayonet sender has been installed on a couple
of cylinders and the readings are the same as the bottom washer senders.
It may sound improbable, but, it is fully within the realm of possibility
–no further comment for now- that this can be screwed up. Proper
cylinder head and barrel (neck) airflow could be missed or dismissed or
just totally overlooked. The fins could be completely blocked with RTV
globs-with updraft or downdraft cooling. Or the space between the cylinder
necks could be left open, with the air going through that wide open space
rather than the fins. I don’t know what to say about these omissions,
other than another set of eyes might be beneficial.
has a beautiful stock Glastar. His experience is useful when comparing
EZ temps with the best of other types. For some time I have been envious
of his stock cooling setup with good cylinder and oil temps. However he
recently mentioned that like the rest of us, this summer his temps are
higher than desired and even borderline.
now. All of these cooling and cowling tweaks fit well into my overall
interest to simplify the internal cowl airflow and finesse the outer shape.
This is the easy stuff. Later, some oil cooling torture.