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Thanks Charlie,
I'll definitely use your leaf blower test.
Looks like I hate the idea of making ducts. I'd really like to use
as much as the existing cowling as possible.
The thing that makes the most sense (at the moment) is a 12" wide
x 17" (plus tanks) long, 2.5" thick radiator slanted with bottom
at front and top at rear (cleanest exit air flow down and out).
The easiest to duct for the incoming air is probably top at front
and bottom at rear. With a 12" or wider radiator I might be able
to use existing cowl bottom as bottom of the duct, use straight
sides and just have to shape the top of the duct to proper wedge.
Extending the scoop (maybe 10"W x 3"H) almost out to the prop (27"
to rear) may allow for almost straight sides?
Someone who loathes fiberglass less would probably chop off the
entire O-360 air/filter inlet from the bottom of the cowling and
make something more well designed.
Finn
On 9/6/2019 2:19 PM, Charlie England ceengland7@gmail.com wrote:
I've never
experimented with minimal angles off perpendicular; those may
not matter much. But at some point, you end up with a 'wedge'
diffuser, and then the shape of the wedge becomes important.
Finn, look at K&W chapter 12; section 12-2 deals with
'oblique flow'. BTW, figure 12-12 in that chapter doesn't seem
to jive with real world experiments. Tracy found, and warned
me about, the need to pinch the aft end of a wedge
significantly to avoid the vast majority of the flow happening
in the aft third of the core. It's impressive how much pinch
is needed to keep flow even across the core.
Charlie
Rich. I said ???if the airflow is there???. The
question I was answering was about the angle of the heat
exchanger. We do need to be sure we don???t trap air inside,
and of course that there is actual airflow through. Many
of our rotary installs would be helped by using manometers
to check if the area behind the radiators are lower
pressure. Motorcycles are another ???special case??? since
most require the air to turn 90 degrees to exit the
fairing. The only really excellent design on bikes was the
Britten. I raced motorcycles in the past and the only
different configuration I saw was the Honda RC 51. ( if I
have the right number) with both radiators in the cheek
position in the fairing.
Bill Jepson
Not totally true as I learned from
overheating my norton rotary dragonfly. It makes sense
that air flows from high pressure to low. But. Many
times oh has a mind of its own counterintuitively. For
example as the air exit the exchanger if it is not
allowed to exit straight or gently deflected,
independent of the delta the air will stagnate and not
go where you expect. Pay as much attention to the exit
as you do with the entry
Yrmv
Answer is nothing; provided
the airflow is there. Also there needs to be
a vent or tap to get all the air out of the
inside.
Bill Jepson??
Finn
asks-
"BTW, what happens when you lay down (at a
20 degree) angle a radiator that is
designed to be upright?"
I always wondered about that myself. The
stock FD (3rd gen) radiator has to be at
about a 45 degree angle (?) to the
incoming airstream. And it has 2
"supplemental" staged electric fans (no
pump fan), one is always on if the AC is
on, the fans have different blades and
different speeds controlled by ECU and
temp sensor. I suppose the fins are canted
or perhaps they are best tilted to airflow
to create turbulence and help remove some
heat..........don't know much about
radiator design............
MW
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