The RX8 core is a good core to use as are Chrysler Doge pick up
cores. Large frontal area with thin cores. The Dodge core is 20" by
30" and is very very effective in a cross counter flow configuration
on the TTC engine. Two cores back to back.
Let's take the Dodge in a non cross flow config.
20 by 30 is 900 square inches.
We have learned more about this subject since Neil Ungar started
flying and on the time to climb engine. Neil complained about over
cooling. It appears we can reduce the intake area of the wedge
diffuser to 15%, of the frontal area of the core, from the 20%
recommended previously.
In other words 15% of 600 square inches is 90 square inches. The
core is 20 inches wide so the height of the 4.5 inches high and 20
inches wide.
Both Neil and the TTC rads are directly in the prop blast so if
that is not the case then you may note higher water temp when
taxiing.
Here is the dodge core on top with the diffuser underneath. Yet
another 3D :-) It is far enough forward to give room for the intake
manifold behind it. This leaves room underneath for and oil cooler.
The exhaust out the back of the cabin may help to attach more air to
the aft sides of the cabin. This is a problem that was addressed by
vortex generators previously (or in addition).
Paul Lamar
Excellent recommendations, thank you! I was thinking of having the
radiators on the top/back (low pressure) of the upper cowling with a
long K&L duct. Your version may be easier. I will play with some
radiator models on the actual engine. The smaller the rad size the
easier it will be to fit. 20x30 will be a challenge.
In this model, it seems that two 20x30x1 counterflow radiators
would give a total volume of 1200ci? Is it correct that we need
about 600ci for water cooling and 200ci for oil? If so, I assume
that using cross counterflow rads would each need to be about 1/2 the
Dodge size as long as I have 600ci?
My RX8 has twin oil coolers about 8x10x2. The single RX7 oil cooler
is about the same volume. The latter should fit up front if the
water cooler intake is a little higher.
Has anyone used 3D printing to create their engine cowling?
Scott Gettings
Those volume numbers depend on the thickness of the core. Thinner
core less cubic inches are required as thin cores are far more
efficient for a given volume. Dodge were leading the way with other
manufactures catching on.
This is a cross counter flow rad for a Tango
14" by 24" They are Dodge Neon cores.
Some what more compact at higher cost to make. You also need a
skilled tig welder.
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Scott,
We should change the standard to square inches of frontal area
because all the recent cores are around 5/8 to 3/4 inch thick
including the RX8. Rad core frontal area is more correlated to
cooling than volume.
600 square inches frontal area for 250 HP single core. 2 x 300 square
inches for cross counter flow. Two Neon rads are about that. Maybe a
bit more so they should handle a mild turbo charge.
BTW have you considered a 8" prop extension to help the air stick to
the cabin sides? You can lesson the angel at which they go back. If
you go back at 7 degrees and then cut it off flat that will implement
the Kamm effect. Same as the recent Priuses.
Paul Lamar
The original Seahawker glass goose came with vortex generators on the
sides of the center pylon. The sides of the pylon quickly exceed 7
degrees about mid wing. Other builders have had success using turning
vanes. I did some early airflow testing and found that after mid-wing
we quickly get disruption of air flow out to 3 to 5 inches away from
the pylon.
A six-inch prop extension is standard, but I don't think we have any
data on the optimal prop location with the current pylon design, nor how
the Kamm effect might be engineered into this design. Is this
something that could be modeled?
Scott Gettings.
Piece of cake. :-)
I'll try a vertical mounting of the cross counter flow while I am at it.
The TTC resumes next week.
Paul Lamar
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