John,
You could also try:
"An investigation of the aerodynamics and cooling of horizontally
opposed engine installation"
SJ Miley. SAE 1977.
Which contains velocity ratio investigations for a number of different
nostril shapes, including 'LoPresti' style.
Duncan Mcf.
----- Original Message -----
From: TELEDYNMCS@aol.com
To: europa-list@matronics.com
Sent: Wednesday, October 03, 2007 5:16 PM
Subject: Europa-List: Jab cooling
In a message dated 10/3/2007 3:00:41 AM Eastern Daylight Time,
europa-list@matronics.com writes:
I recall that in 1995 I asked the late Richard Cabrinha why he had
changed
from a chin intake to a pair of Lo-Presti style circular intakes on
his Free
Spirit Mark II, for cooling a Continental IO 360, and he replied
"because
they work!" He told me that if the diameter were too large then
there would
be a reverse flow, spilling air out round the circumference of each
intake.
He refined the size by putting some oil around each rim and doing a
quick
circuit: inspection on landing showed whether the oil film had
spread
inwards or migrated outwards, and he would then the repeat the test
with
different diameters accordingly.
Hi Mike, Graham, and all,
That is essentially what I've done with my string testing, although I
wasn't aware that size had much to do with it (Typical male, huh?) I've
not played with changing the size of the intake at all. It does seem
like 25 square inches of intake should be more than adequate for cooling
this little engine, though.
.
What I've seen in my string tests is an apparent low pressure area
forming on the outboard side of the left intake as viewed from the
cockpit. I've also noticed an apparent high pressure area directly in
front of the inlet when my turbulators are not installed and this high
pressure "bubble" rejects the string as it approaches the intake from
upwind. At one point it turns the string 180 degrees and it blows
towards the fan. Installing turbulators at the lip of the intake helped
considerably. I went from about 50% of the intake "accepting" the
string, to what I'd estimate as about 80% now accepting the string in
the intake. Still not perfect, but I'm still playing with it, too. What
I have seen in terms of engine cooling has been dramatic, though.
I need to dig up the Lo-Presti info and take a look at it. That's
about the fifth time somebody has mentioned that name to me.
An A&P friend of mine stopped by my shop yesterday and I showed him
what I was doing. He's also a glider pilot and amateur aerodynamicist.
We also discussed exit cooling flow. The trigear has a rather large
triangle shaped reinforcing piece on the nosegear leg just below and
outside the line of the cowl. This triangle is flat to the relative
wind, probably worse at climb angles, and I would reckon that it causes
some disturbance right where the cooling air from the cowl is trying to
exit. Whether or not that is interfering with my cooling flow remains to
be determined, but it sure looks like it could use a fairing to split
the flow, hopefully accelerating it and causing a low pressure area in
that region. It stands to reason that cleaning up this area with a
fairing might help create a bit of suction and aid cooling flow, too.
Graham said: I wonder if your turbulator is helping keep the flow
attached over the
whole of the outside of the cowl?
I'm thinking you are correct in your assessment there, Graham. I think
"re-exciting" the flow is indeed causing it to stay attached. FWIW, I've
done some tuft testing on my wings and I seem to have laminar flow at
least as far back as the hinge line of the aileron. The wing tip is much
cleaner than I anticipated, too. There are very few modern sailplanes
that get this level of laminar flow that far back on the wing. Shaw and
Dykins are obviously genius'.
I don't have enough knowledge on the subject to really know one way or
the other how internal duct pressure is related to flow, but my tests
seem to indicate that there is either no relationship, or the
relationship is inverse. If you think about it, restricting the flow
would cause higher pressure, just as it does when you put your finger on
the end of a running garden hose. The pressure increases, but the flow
decreases. That seems to be what is happening here.
Regards,
John Lawton
Whitwell, TN (TN89)
N245E - Flying
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