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