X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.3c4) with ESMTP id 4031264 for flyrotary@lancaironline.net; Sat, 19 Dec 2009 19:16:13 -0500 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (mail.aanet.com.au [203.24.100.34]) by poplet2.per.eftel.com (Postfix) with ESMTP id 1CE6E17382E for ; Sun, 20 Dec 2009 08:15:34 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id 93866BEC00B for ; Sun, 20 Dec 2009 08:15:29 +0800 (WST) Message-ID: <1D37FA6BCC8D46E9BDCE224223B76AC8@ownerf1fc517b8> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Oil Cooling Date: Sun, 20 Dec 2009 10:15:29 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0026_01CA815D.5AF94E30" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5843 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 091219-1, 12/19/2009), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_0026_01CA815D.5AF94E30 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Tracy, All that makes perfect sense and leads me to a question which has more = curiosity value than anything else. What actual size did you settle on = for the 20B. I'm curious to know if the 20B requires more cooling than = 1.5 times a 13B. Calculating the ( rule of thumb) radiator size of approx 600 cu" for = 200hp, giving 3 cu" per HP, the size of the Mazda oil cooler then gives = a .8 per cu" per hp. I wondering if this holds true for the 20B and = indeed the single rotor. George ( down under)=20 Just an update on my RV-8 / 20B oil cooling experiments. =20 On the theory that airflow patterns inside the cowl were blocking = airflow through oil cooler, I installed a partial exit duct behind the = radiator directing the airflow downward toward the cowl outlet. It = looked very restrictive but flight tests showed almost no affect on = water cooling (which is OK) but a significant improvement in oil = cooling. I further restricted the airflow through the rad by putting = some roof ridge vent material inside the inlet diffuser. This gave a = tiny increase in water temp but a further improvement in oil cooling. = Long story short, after several more tests it became apparent that back = pressure under the cowl was having a major effect on the oil cooling. = I have no idea why my instrument did not read the pressure correctly. = It works fine on the bench and is properly referenced to the static = system in the plane. The temptation is to keep changing the cooling = outlet scheme until the internal cowl back pressure is low enough to get = the cooling good enough. My belief is that this would lead to a very = high drag solution. You may remember the experiment I did by flying = with the cowl removed. The cooling was never a problem then (except = perhaps too much cooling) but the drag was enormous. The fuel burn was = 60% higher at the test airspeed of 130 mph. The conclusion I eventually came to was that the rad (because of it's = relatively low air flow resistance) is hogging the airflow capability of = the cowl cooling outlet. (cowl flap did not have enough effect to fix = the problem). Keep in mind that the oil cooler is a thick AC = evaporator core that is very restrictive. The current experiment is to = replace it with a much less restrictive (to airflow) oil cooler. I = found the largest cooler that would fit in the same location as the AC = core and I'm using the same diffuser as before (slightly modified to fit = the larger face of the new cooler). This cooler is only 2" thick and = core volume is 30% less than the AC core. It is slightly larger in = volume than an RX-7 cooler. Without any back pressure (flying with cowl = off), the AC core had way more than enough cooling capacity (146 F oil = temp on a 93 degree day) so I'm hoping that this smaller cooler will be = enough. Should be ready to flight test it this week. I should point out another symptom. Power setting (and therefore = airspeed) had very little effect on the cooling (i.e., it didn't get = much hotter at high power as long as airspeed went up as well. Things = got hot fast in climb however. This also indicated to me that cooling = was limited by airflow through the system rather than by the oil = cooler's ability to transfer the heat to the air. If the cooler is = simply too small, more airflow will not help much. =20 Tracy ------=_NextPart_000_0026_01CA815D.5AF94E30 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Tracy,
All that makes perfect sense and leads = me to a=20 question which has more curiosity value than anything else. What actual = size did=20 you settle on for the 20B. I'm curious to know if the 20B requires more = cooling=20 than 1.5 times a 13B.
 
Calculating the ( rule of thumb) = radiator size of=20 approx 600 cu" for 200hp, giving = 3 cu" per=20 HP, the size of the Mazda oil cooler then gives a .8 per cu" = per hp. I=20 wondering if this holds true for the 20B and indeed the single=20 rotor.
George ( down under) 

Just an update on my RV-8 / = 20B =20 oil cooling experiments. 

On the theory that airflow = patterns=20 inside the cowl were blocking airflow through oil cooler, I installed a = partial=20 exit duct behind the radiator directing the airflow downward toward the = cowl=20 outlet.  It looked very restrictive but flight tests showed almost = no=20 affect on water cooling (which is OK)  but a significant = improvement in oil=20 cooling.   I further restricted the airflow through the rad by = putting=20 some roof ridge vent material inside the inlet diffuser.  This gave = a tiny=20 increase in water temp but a further improvement in oil = cooling.  =20 Long story short,  after several more tests it became apparent that = back=20 pressure under the cowl was having a major effect on the oil=20 cooling.   I have no idea why my instrument did not read the = pressure=20 correctly.  It works fine on the bench and is properly referenced = to the=20 static system in the plane.   The temptation is to keep = changing the=20 cooling outlet scheme until the internal cowl back pressure is low = enough to get=20 the cooling good enough.  My belief is that this would lead to a = very high=20 drag solution.  You may remember the experiment I did by flying = with the=20 cowl removed.  The cooling was never a problem then (except perhaps = too=20 much cooling) but the drag was enormous.  The fuel burn was 60% = higher at=20 the test airspeed of 130 mph.

The conclusion I eventually came to = was=20 that the rad (because of it's relatively low air flow resistance) is = hogging the=20 airflow capability of the cowl cooling outlet.  (cowl flap did not = have=20 enough effect to fix the problem).   Keep in mind that the oil = cooler is a=20 thick AC evaporator core that is very restrictive.   The = current=20 experiment is to replace it with a much less restrictive (to airflow) = oil=20 cooler.  I found the largest cooler that would fit in the same = location as=20 the AC core and I'm using the same diffuser as before (slightly modified = to fit=20 the larger face of the new cooler).  This cooler is only 2" thick = and core=20 volume is 30% less than the AC core.  It is slightly larger in = volume than=20 an RX-7 cooler.  Without any back pressure (flying with cowl off), = the AC=20 core had way more than enough cooling capacity (146 F oil temp on a 93 = degree=20 day) so I'm hoping that this smaller cooler will be enough.  Should = be=20 ready to flight test it this week.

I should point out another = symptom.=20 Power setting (and therefore airspeed) had very little effect on the=20 cooling  (i.e., it didn't get much hotter at high power as long as = airspeed=20 went up as well.   Things got hot fast in climb however.  = This=20 also indicated to me that cooling was limited by airflow through the = system=20 rather than by the oil cooler's ability to transfer the heat to the = air. =20 If the cooler is simply too small, more airflow will not help = much. =20

Tracy
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