Ed K. modified my stock oil cooler which I had retrieved from a
wreck. He cut off the stock tanks which included the thermostat
and
replaced them with the tanks you see. It no longer matters
which way
the oil flows through the cooler. While he was at it, he
cleaned the
core which was found to be full of debris. Finally he
pressured tested
the unit. I have placed it in front of the firewall. Air
will be ducted from the right nostril. For those who are
interested, Ed
can build a NEW oil cooler using cores that are identical to
the stock
Mazda. He can shorten up the cooler a bit and make it wider as
well,
which should make it easier to fit under the cowl. Jerry
That seems to be a pretty good place for an oil cooler. That is
where
Chuck Dunlap mounted his. Use a smooth interior surface duct
to feed air to a wedge shaped diffuser on top of the oil cooler.
Chuck used rolled up sheet aluminum.
Paul Lamar
Probably not a big deal (much structural margin), but that
mounting method
imparts bending loads (buckling?) on members that are already
heavily
loaded in compression. Welding anything to the tube at mid
span seems
like it would add a discontinuity which would make it more
likely to fail.
Especially since the mounts are essentially cantalevered from near
mid-span.
Matt-
Good point Matt. Also you might set up a vibration mode in the
tube that
might lead to fatique at the joints.
Paul Lamar
I thought about that but in this case the loads will be very small
and the convenience great. In addition to the oil cooler
(which is
rubber shock mounted) I have also mounted the coils on a bracket
welded to the engine mount. Although I have not done it yet, I
expect use the motor mount to support the radiator (and louvers) as
well. This probably shows the limits of my imagination but I can
not think of a better way to do it. I like the heavy structure of
the
engine mount. I do not like attaching the oil cooler, radiator, or
coils to the engine because of vibration. At one point, a couple of
years ago I experimented with attaching the oil cooler to the sheet
metal firewall, but that came with it's own set of compromises.
As a
matter of practice, in homebuilts, it is not unusual to see brackets
for whatever, welded to the engine mount. Of course that does not
make it "right." I am not worried about it. Jerry
Tropical storm Ophelia is bearing down upon us here in
Wilmington. So
far, not too bad, winds gusting to 38 mph. KILM is still VFR,
though.
When we lose power, I'll be out of the loop for awhile.
I agree with Matt. Welds on truss members compromises them to an
unknown degree; especially with respect to compression. Then
adding an
external moment makes it worse. If you must attach to the truss
members, I would suggest designing a structure that is attached using
clamps such as these. Use the ones with high temp. silicone rubber.
Build a substructure that clamps to the truss members near the truss
joints and it will have less effect on the structural integrity
of the
mount.
Aubrey
You show two short cantilevered arms in your picture. If you were to
run a slightly thinner support all the way across, connecting the two
mount struts, you might possibly be better off.
What you need to be concerned about is buckling. You can easily
stand on an empty pop can, but if you just tap the side, it crushes
easily under your weight. A cantilevered support on the mount strut
is a
lot like tapping on the side of the pop can you are standing on. It is
likely to put just the right amount of kink in the strut to cause
it to
buckle under load. You won't know it is a problem until you pull back
hard on the stick and the engine suddenly hinges under the fuselage.
If you instead connect the two struts with a single oil cooler
support, it would reduce the amount of twist you are putting on each
strut, and could actually help stabilize the center.
This is all conjecture unless you do the structural analysis or
test
load the mount with the same simulated g load on the oil cooler
support.
Bill Dube'
Thanks for your comments Bill. The trusses in my shop were designed
to carry a heavy snow load pressing down. They were not designed to
carry the heavy weight of all the stuff I have stored on the lower
beams. In this case the truss structure while present is not
helping. What I am counting on is the strength and stiffness of
wood. Likewise my engine mount is made of 7/8 in. .049 4130 which I
have been using almost daily for many years. It can handle the
tiny weight of the oil cooler without measurable compromise. That is
just me talking but I am willing to bet my life on it. However, it
is quite possible to add a doubler to the tube opposite the bracket
or to add a gusset or as you said, I could connect the two brackets
together. Reinforcement is likely.
BTW, except for the original tack welds, I will TIG braze the
brackets so that the truss member is not deeply heat penetrated.
Thanks again. You engineers keep us uneducated hammer and tong guys
from going off the deep end. At least you try. Jerry
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