Paul,
I'll snap some photo's of what we've done and drag down some numbers.
For cooling air I am talking about the actual air intakes not the
oil/glycol cooler openings. That is a different set of calcs but
similar. The Rotax is very much air cooled. You hit the nail on the
head that the turbo/muffler is one heck of a heat generator. Therefore
when full turbo is selected the scant 14 inches of air to the front of
the cylinders is not directed where needed and because of exit design
unable to exit freely by draft and/or by force.
The 914 NACA inlet is for induction only, except for what leaks high
pressure air into the lower cowl from the hole made for the filter. The
NACA disturbs me because it leaks high pressure air into the engine
compartment directly below the engine, blocking what air comes in from
the front.
Remember the hole we all made around the front of the cowl. Without
that closed off any pressure coming in the front leaks away.
The radiator we have is actually large enough to do the job, as is the
oil cooler. Our problem is the duct shape and exit. At low speed the
back of our coolers doesn't form enough of a draw to compensate for the
low air speed coming in. We could probably use a cowl flap.
It is a tangled web we weave. And an expensive one.
Enough for now. My turbo oil seal went and now it sucks the oil out of
the engine. Good news is the intake and carbs are really well
lubricated now.
Talk to you soon.
Bud
----- Original Message -----
From: Paul McAllister<mailto:paul.the.aviator@gmail.com>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Tuesday, September 08, 2009 4:14 PM
Subject: Re: Europa-List: Congrats to Jeff,Cooling feedback for Bud
Hi Bud,
I am deep in the middle of doing cooling modifications on my Europa.
I am finding that it has taken me much longer than expected, I think I
started in March and I am still at it.
Rather than get into the details of what I have been doing, I'll leave
that for when we get together at Rough River.
I do have a couple of questions and a request. In your note you state
that the air inlet on the XS is 14 square inches. I come up with the
following:
'Dog box' 4 x 7.125 =
28.5 Sq"s
'Round Inlets' 3" (2 off)
= 14
"914 NACA Engine air inlet' 1.25 x 4 = 5
If I have done my maths correctly the this is a total of 47.5 square
inches. Am I missing something ?
When I compare this to something like a 160hp RV6 then it doesn't seem
right to me.
Would you be prepared to bring some photographs to show what you do on
your exits?
I have a couple of theories on what is happening on my 914. On the
ground I think that the issue is more about thermal gain from the
exhaust & turbo, rather than anything to do with the oil/water radiator
configurations. I decided this from talking to Erich. He told me that
he can taxi around for as long as he wants without over heating when the
top cowl is off. As soon he puts the top on, it over heats in 15
minutes. He lives in Nevada.
In the climb I think the 'Dog box' has stalled air in it due to the
angle of attack and I get over heating. The internal shape is a
miserable. It has all kinds of excuse for an expansion duct. It has
all kinds of bends and sharp shapes in it.
In straight and level, I get over cooling because the radiator inlet
is too big.
I'll bring photographs of what I have been doing to Rough River, its
very radical.
Cheers, Paul
On Wed, Aug 19, 2009 at 6:22 PM, Bud Yerly
<budyerly@msn.com<mailto:budyerly@msn.com>> wrote:
Jeff,
Glad to hear the cooling issues are relieved. Well done and thanks
for passing it on.
For consumption by others and for feedback, I'd like to hear other
fliers comments also.
From my shop experience:
Evans replaced by 60-40 or 50-50 is a 10 degree drop minimum.
(Sorry Mr. Evans)
I Jeff's case, by moving the duct two things probably happened:
For the tri-gear, (those with the wide open area around the nose
gear trunion and with the firewall moved back behind the nose gear to
the added bulkhead), moving the duct down, doesn't cause as much of a
difference. But the bungees/springs/hoses etc. in the back portion of
the nose wheel well can restrict flow, and moving the duct down will
help as it opens the two triangles on either side of the duct adding
significant air exit for the heat. It also moves the hot accelerated
air of the radiators lower in the duct. This heated air streaming out
can cause a potential suction which may help pull air out of the cowl.
(Same affect as using the exhaust venturi.)
I once did this with a cowl flap which lowered a reshaped upper
metal duct ramp and and the cowl ramp bottom together and went from 12
minutes to overheat on the ground to 30 minutes to 240 F. It was
capable of max continuous climb with the flap open. I now just reshape
the fixed ramp dimensions for simplicity.
Finally, I have found that moving the air intakes up to near the
seam and putting a plenum over the engine or perhaps adding a duct like
Jeff did, forces air over the cylinders. This helps on climb out in
super hot conditions, but not much affect in cruise.
Tips for those who prefer a stock install:
Sealing the front and sides of the metal duct tight to the
fiberglass cowl opening is really important. A leak in this area can
cause a high pressure bubble of air in the cowl under the cylinders and
literally trap heat under the engine and reduce the effectiveness of the
inlet air intakes. It also reduces the pressure differential across the
radiator/oil cooler which is essential to the heat transfer for cooling.
The hole for the nose gear leg adds turbulence and pressure to the
back side of the radiator exit. Consider a piece of silicone cowl seal
slit to make cowl installation easy and close this hole up.
Open up the inlets fully. Don't leave a lip as it just restricts
the flow into the cowl.
Mostly, you can lower temps 20 degrees just doing the following:
Begin by closing off the area between the sides of the oil cooler
and duct.
Always lower the oil cooler as far as you can if you have a 912S or
914 (2-2.5 inches is possible but change the elbow out for a straight
fitting).
I just found this leak. The area between the oil cooler and
radiator is nearly a 1/2 inch and you'd be surprised how much potential
cooling air goes under the radiator, up and over the oil cooler then out
through the space above the oil cooler. This high pressure air degrades
the radiator effectiveness as the air passes up the back of the radiator
and out. Assembling the oil cooler as close to the radiator as
possible, or by adding sheet metal/sealing material to reduce this exit
air gap is a help. (Don't let any seal rub the cooler though.)
Finally, the seal under the oil cooler must be tight between the oil
cooler and the fiberglass ramp and continue up the sides of the oil
cooler.
From NACA documentation, I found it interesting that 70% of the air
hitting against a radiator will build pressure and force itself out
around the radiator in either free air or in a loose duct rather than go
through the core. So keep it tight.
Also somewhere I found the statement that in a tightly cowled inline
engine, for efficient cooling drag ratios, the ratio of air outlet to
inlet should be as close to 1-1 when in cruise as possible, and 4 to one
with the cowl flaps open, in climb. I can't find that reference right
now. However, in the Europa, with the cowl inlet air hole area of 14 or
so square inches, we need a minimum of 56 inches of exit air, just for
the cowl air. But in a mono wheel, ours is two triangles either side of
the duct and fiberglass ramp of about 15 to 20 inches, and if you are
lucky, 13 square inches between the firewall and upper metal duct for a
total of 33 inches of cowl exit air max. As you can see, this makes the
air exit of the cowl nearly 1 or 2 to 1. This is OK for cruise, but a
disaster for cooling in high power climbs at low speed, especially if
turbo equipped. This 4-1 ratio works in my experience. To cool well in
summer I try to get 100 square inches of exit air (Tri-gear) out of the
cowl (Mono with fixed duct 60 square inches, cowl flap added 90). That
is just for the cowl air, and does not include the duct exit for the
radiator. That is a lot of glass and metal work, and seems to be worth
it.
I would like the time to reshape my duct in my demonstrator to see
the affect of each of the above. My demonstrator just passed
airworthiness, and will fly soon, (N12AY, Classic, tri-gear, 914, fixed
pitch for data reasons (LSA experimenting) then Airmaster). I am
obligated to do a stock installation with just sealing the duct as above
and taking data. It's not rocket science, it just takes time.
Feedback?
Again, Good Job Jeff!
See you at Rough River.
Bud Yerly
Custom Flight Creations
Europa Dealer
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