From: Tracy <rwstracy@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Fri, April 29, 2011 9:49:00
AM
Subject: [FlyRotary] Re:
Cooling Inlets
Some questions:
Prior reading seemed to indicate
that the oil cooler did ~1/3 of the cooling, implying a 2/1 ratio on air
requirements. This setup seems to have a significantly higher percentage
allocated to oil. Is this a byproduct of heat exchanger differences, or the less
efficient heat transfer ability of oil, or....?
2nd, assuming similar
inlet & diffuser efficiencies, could the inlet areas mentioned be reduced by
roughly 1/3 with reasonable expectation of cooling a 2 rotor Renesis?
On
the subject of exit area: Does either heat exchanger have an exit duct? The RV
guys with really fast Lyc powered planes all have some variation of exit ducting
to smoothly re-accelerate and redirect exit air parallel to & at or above
the slipstream. Even the stock RV-8 has a rounded lip at the bottom of the
firewall (which the really fast guys say is much too small a radius...). And
there's always the near-mythical P-51
system...
Thanks,
Charlie
The inlets were originally closer to
the 2 - 1 area ratio but many experiments (mostly failures) ended up with the
current sizes. I just don't have it in me to go back and un-do them
all. Also wish I had tried these inlets with my original oil cooler which
had about 1/3 more core volume and much thicker. Might have been
able to do the oil cooling with less CFM airflow. But, I don't think
there is much penalty for having more than enough (but properly faired) inlet
area and throttling the airflow with a cowl flap.
Yes, I do think both
inlets could be scaled down in area for a 2 rotor.
Neither of my heat
exchangers have exit ducts. Just not enough room to do this in their
current locations.
Tracy
On Thu, Apr 28, 2011 at 4:23 PM, Charlie England
<ceengland@bellsouth.net>
wrote:
On 4/28/2011 8:07 AM, Tracy wrote:
Finally got around to finishing my cooling inlets. (pictures
attached) Up until now they were simply round pipes sticking out of
the cowl. The pipes are still there but they have properly
shaped bellmouths on them. The shape and contours were derived
from a NASA contractor report (NASA_CR3485) that you can find via
Google. Lots of math & formulas in it but I just copied the best
performing inlet picture of the contour. Apparently there is an
optimum radius for the inner and outer lip of the inlet. There
was no change to the inlet diameters of 5.25" on water cooler and 4.75" on
oil cooler.
The simple pipes performed adequately in level flight at
moderate cruise settings even on hot days but oil temps would quickly hit
redline at high power level flight and in climb.
The
significant change with the new inlet shape is that they appear to capture
off-axis air flow (like in climb and swirling flow induced by
prop at high power) MUCH better than the simple pipes.
First flight test was on a 94 deg. F day and I could not get the oil temp
above 200 degrees in a max power climb. They may have gone
higher if the air temperature remained constant but at 3500 fpm the rapidly
decreasing OAT kept the temps well under redline (210 deg F).
I have
an air pressure instrument reading the pressure in front of the oil cooler
and was amazed at the pressure recovered from the prop wash. At 130
MPH the pressure would almost double when the throttle was advanced to WOT.
That did not happen nearly as much with the simple pipes.
These inlets ROCK!
Tracy
Crook
& replace it with James' rotary cowl, or just modify
the existing cowl.
Some questions:
Prior reading seemed to indicate
that the oil cooler did ~1/3 of the cooling, implying a 2/1 ratio on air
requirements. This setup seems to have a significantly higher percentage
allocated to oil. Is this a byproduct of heat exchanger differences, or the
less efficient heat transfer ability of oil, or....?
2nd, assuming
similar inlet & diffuser efficiencies, could the inlet areas mentioned be
reduced by roughly 1/3 with reasonable expectation of cooling a 2 rotor
Renesis?
On the subject of exit area: Does either heat exchanger have
an exit duct? The RV guys with really fast Lyc powered planes all have some
variation of exit ducting to smoothly re-accelerate and redirect exit air
parallel to & at or above the slipstream. Even the stock RV-8 has a
rounded lip at the bottom of the firewall (which the really fast guys say is
much too small a radius...). And there's always the near-mythical P-51
system...
Thanks,
Charlie