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Date: Thu, 28 Apr 2011 15:23:05 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Cooling Inlets
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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
>
Perfect timing for me; I need to decide whether to take a loss & sell my 
(RV-7)  James Lyc style cowl & 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


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    On 4/28/2011 8:07 AM, Tracy wrote:
    <blockquote cite="mid:list-4960413@logan.com" type="cite"><font
        color="black"><font size="2"><font face="arial">Finally got
            around to finishing my cooling inlets. (pictures attached)&nbsp;
            Up until now they were simply round pipes sticking out of
            the cowl.&nbsp;&nbsp; The pipes are still there but they have properly
            shaped bellmouths on them.&nbsp;&nbsp; The shape and contours were
            derived from a NASA contractor report (NASA_CR3485) that you
            can find via Google.&nbsp; Lots of math &amp; formulas in it but
            I just copied the best performing inlet picture of the
            contour.&nbsp;&nbsp; Apparently there is an optimum radius for the
            inner and outer lip of the inlet.&nbsp;&nbsp; There was no change to
            the inlet diameters of 5.25" on water cooler and 4.75" on
            oil cooler.<br>
            <br>
            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.&nbsp; <br>
            <br>
            The significant change with the new inlet shape is that they
            appear to capture off-axis air flow&nbsp; (like in climb and
            swirling flow&nbsp; induced by prop at high power)&nbsp; MUCH better
            than the simple pipes. &nbsp;&nbsp; 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. &nbsp;&nbsp; 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).<br>
            <br>
            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.&nbsp; At 130 MPH the pressure would
            almost double when the throttle was advanced to WOT. &nbsp; That
            did not happen nearly as much with the simple pipes.&nbsp;&nbsp; <br>
            <br>
            These inlets ROCK!<br>
            <br>
            Tracy Crook<br>
          </font></font></font><br>
    </blockquote>
    <font color="black"><font size="2"><font face="arial">Perfect timing
          for me; I need to decide whether to take a loss &amp; sell my
          (RV-7)&nbsp; James Lyc style cowl </font></font></font>&amp;
    replace it with James' rotary cowl, or just modify the existing
    cowl.<br>
    <br>
    Some questions:<br>
    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....?<br>
    <br>
    2nd, assuming similar inlet &amp; diffuser efficiencies, could the
    inlet areas mentioned be reduced by roughly 1/3 with reasonable
    expectation of cooling a 2 rotor Renesis?<br>
    <br>
    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 &amp; 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...<br>
    <br>
    Thanks,<br>
    <br>
    Charlie<br>
    <br>
    <br>
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