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Hi Dennis,
Sorry to hear you experiment did not work as hoped
for. Unfortunately, I don't have any information on size of turning
vanes. 1st your radiator core and oil cooler core are plenty large
enough for 160 HP - that's the good news, so it would appear to be strictly a
matter of air flow.
As you discovered, what would appear to make logical sense
by putting the turning vane in for diverting air to your engine intake - did not
turn out as expected. It frequently happens that way. It took me 5
different attempt to finally get my oil temps where they should be. I even
ended up with a 5" dia duct at one point which made it flyable (bearly), but it
wasn't until I moved my oil cooler up under the nose that the problem was
licked.
I would first recommend you remove the diverter you put in
- unless it clearly showed a marked improvement in engine performance. You
may not be helping either - on the other hand if your engine performance
did indeed show a meaningful improvement then that would mean more power and
more heat to get rid of - the two go hand in hand. But. unless you picked a
couple hundred rpm static, I would remove it - for the moment at
least.
I have a small opening (10x2") that serves for my oil
cooler and my engine inlet. I made no effort to put a vane to divert flow
to the engine for two reasons.
First, if your duct is doing the job it will be
slowing down the air and converting is kinetic energy it into pressure -
that should provide plenty of air for your engine - it does for mine with a
smaller volume duct.
Second (and probably most importantly) , you are very
likely creating a major air flow separation/disturbance/eddie with your flow
separator particularly in a climb attitude. This will have a major adverse
impact on your cooling and is likely the principle reason your cooling
deteriorated - airflow separation.
If you have K&W turn to page 279. There
you will see several configurations of cores and ducts coming into them at
various angles from straight on (figure A) to an almost 20 deg angle (figure
D). If you took figure B and reversed the inlet and outlet, it would
appear that would be close to your configuration.
You should be able to get adequate cooling with you
radiator at the angle it is without turning vanes. The only turning vanes
related to cooling I can recall seeing in K&W are those fabricated as part
of the core (see figure 12.8) but there may be some mention of
using turning vanes up stream else where - I do not recall.
I could not tell what type of profile your duct follows
from the inlet opening to your core. But, if it looks anything like figure
12-10 in K&W then you do need to correct the shape as that shape
or any similar to it creates air flow separation = cooling killer.
In fact the paragraph under it tells you what the
objective is - you need to keep your duct walls nearly parallel (perhaps
slightly converging) until just before your core and then flare (like a trumpet)
the duct to meet the core.
My total inlet area is 52 square inches - my outlet is
quite a bit bigger (does not mean its better - just bigger). So I agree, your 50
inches should provide enough air.
My believe is that you are getting flow turbulence which
is compromising your cooling core capability to reject heat.
Keep working at it, I would remove the divider as I
believe it is hurting cooling much more than it is helping engine power. I
would strive to get a smooth duct from the inlet (without any jogs or sharp
edges) to the core. You would naturally have to blend the round intake
area to the rectangular core area and keep the cross section as constant as you
can and approx the size of your inlet until within six
-nine or so inches of the core and then rapidly flare it to a
bell/trumpet shape. That would help keep the boundary layer flow high
until you are ready to flare the duct to get your pressure
recovery.
That's about all I can think to suggest at this
time. You'll get there, it will just take a bit of messing with it. With
few exceptions, cooling always seems to be the biggest challenge. We
pretty much have a tractor configuration that we have proven works - which is
the one similar to what I, Bill Eslick, Tracy and others fly with using the
standard cowl openings, but, I believe that you are going to be one of the first
on this list that works out what is needed using the James Cowl. You'll
get it whipped, disappointing as it is to find your installation is not
"perfect", it will not take you long to whip it into shape.
Best Regards and good luck
Ed
----- Original Message -----
Sent: Sunday, May 27, 2007 2:11 PM
Subject: [FlyRotary] James Cowl - RV-7a - Renesis -
Cooling
>I had very marginal
cooling on my first and second flight - RV 7A, James
> cowl, Griffin
Scirocco aluminum double pass water radiator with a Mazda
> 1989? RX-7
oil cooler. Water radiator fin size - 22LX13WX2.5T inches.
> Oil -
19LX4.5WX 2T inches. The radiators are mounted side-by-side
>
under the engine and are at about 25 - 30 degree to the inlet air flow.
>
(The air must turn 60-65 deg to flow through the radiators) See
photos
> 1 and 2. After my first 2 flights, I constructed a
divider/duct to
> provide a duct for the engine combustion air to make
the sharp turn 90
> deg. up after the inlet to get to the filter.
The bottom of this duct
> was also supposed to provide a duct wall for
the air going to the
> radiators. See photo 3. Two flights
demonstrated this really hurt -
> not helped - my cooling.
Now I can barely take off and fly the pattern
> before getting up to 210
- 215 on oil and water. The divider duct took
> out about 8-10 sq.
in. of inlet area but removed the engine combustion
> air requirement
form the remaining inlet air going in the larger inlet.
>
> My
inlet is about 50 sq. in. and the outlet is about 67 sq. in. This
>
cowl was used successfully on the Power Sport a/c so I believe the inlet
> and outlet are at least big enough for 160 + hp. When I first
posted
> pictures of the radiator installation someone suggested I may
need
> turning vanes to improve flow to the radiators. I am now
ready to try
> the turning vanes below the radiators.
>
>
Does anyone have info. I can use to design the turning vanes? The K&W
> document on page 273 mentions guide vanes but does not go into
detail.
> I am thinking of 2 inch wide vanes long enough to go from
the left to
> right side of the radiators and spaced 4 inches apart
with the top of
> the vanes about 3/4 inch below the radiator
fins.
> Comments or -- Any other ideas?
>
> Dennis
H.
>
>
>
>
> --
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