X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from qw-out-2122.google.com ([74.125.92.24] verified) by logan.com (CommuniGate Pro SMTP 5.3c4) with ESMTP id 4031390 for flyrotary@lancaironline.net; Sat, 19 Dec 2009 20:47:19 -0500 Received-SPF: pass receiver=logan.com; client-ip=74.125.92.24; envelope-from=rwstracy@gmail.com Received: by qw-out-2122.google.com with SMTP id 9so908480qwb.25 for ; Sat, 19 Dec 2009 17:46:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to :content-type; bh=GnRYr12fKWaOJfCJ0mgjiPjKPbO1cnsi+Htk1hV22PQ=; b=OJhw2LcHDqBRIEmkfQhfbns4FDiWAKFTzLCJaDTAflXw5ddWRoc42/MvWmijTFGV0t S6XizOn1lED1KmKrLlFY/+ZzeXI6zqg+2B/3k7vInwnAcd4KBFsTNdiJP8y0RM7ls+FT OlfnwMzPkdD2KnF4XRO7A5e8OQXhMK6iictAI= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:content-type; b=ZhIp2OiS/KI6IZM/PIsGW5Q4xSLyGD4LRnTlFQk5BN9T3HfsHAt26VYML2lbeONfNJ S6kcio+2leLs/ZD6+c2xlT7hhc7O6Brj16BBTmVLVDGBEzQ3Ul2VvM5FoO1aB5/7o1nU xIXJOFYLBNJilfWcxrfgOMXs1getiKFfn9B+4= MIME-Version: 1.0 Sender: rwstracy@gmail.com Received: by 10.224.22.132 with SMTP id n4mr3161980qab.176.1261273601495; Sat, 19 Dec 2009 17:46:41 -0800 (PST) In-Reply-To: References: Date: Sat, 19 Dec 2009 20:46:41 -0500 X-Google-Sender-Auth: 40e18fdd14357b26 Message-ID: <1b4b137c0912191746h7b766656xae8acceda67f2054@mail.gmail.com> Subject: Re: [FlyRotary] Re: Oil Cooling From: Tracy Crook To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=00c09f99e1e5fb5388047b1f2459 --00c09f99e1e5fb5388047b1f2459 Content-Type: text/plain; charset=ISO-8859-1 In retrospect it does seem obvious but I had never thought about matching the airflow characteristics of the water and oil heat exchangers before. I should know by tomorrow if this is just wishful thinking. Those heat exchanger volume figures you mentioned are at best just a rule of thumb but still useful. Other details can make a world of difference. For example, my RV-4 has had the same cooling components since day one but cooling on that first flight looked hopeless. Now it is fine on even the hottest days. Heat exchanger size isn't everything. My 20B has significantly less than 1.5 times the core volume of my 13B installation. I'm hoping that better diffusers and other details will make up for the relatively smaller heat exchangers. I can't think of any reason why the 20B would need more than 1.5 times the 13Bs cooling requirement if all other factors are the same. That's a big if of course. Tracy On Sat, Dec 19, 2009 at 7:15 PM, George Lendich wrote: > 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) > > Just an update on my RV-8 / 20B oil cooling experiments. > > 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. > > Tracy > --00c09f99e1e5fb5388047b1f2459 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable In retrospect it does seem obvious but I had never thought about matching t= he airflow characteristics of the water and oil heat exchangers before.=A0 = I should know by tomorrow if this is just wishful thinking.

Those h= eat exchanger volume figures you mentioned are at best just a rule of thumb= but still useful.=A0 Other details can make a world of difference.=A0 For = example, my RV-4 has had the same cooling components since day one but cool= ing on that first flight looked hopeless.=A0 Now it is fine on even the hot= test days.=A0 Heat exchanger size isn't everything.

My 20B has significantly less than 1.5 times the core volume of my 13B = installation.=A0 I'm hoping that better diffusers and other details wil= l make up for the relatively smaller heat exchangers.

I can't th= ink of any reason why the 20B would need more than 1.5 times the 13Bs cooli= ng requirement if all other factors are the same.=A0 That's a big if of= course.=A0

Tracy


On Sat, Dec 19, 2009 at 7:1= 5 PM, George Lendich <lendich@aanet.com.au> wrote:
Tracy,
All that makes perfect sense and leads= me to a=20 question which has more curiosity value than anything else. What actual siz= e did=20 you settle on for the 20B. I'm curious to know if the 20B requires more= cooling=20 than=A01.5 times a 13B.
=A0
Calculating the ( rule of thumb) radia= tor size of=20 approx=A0600 cu" for 200hp, giv= ing 3 cu" per=20 HP,=A0the=A0size of the Mazda oil cooler then gives a .8 per cu" per h= p. I=20 wondering if this holds true for the 20B and indeed the single=20 rotor.
George ( down under)=A0

Just an update on my RV-8 /= 20B=A0=20 oil cooling experiments.=A0

On the theory that airflow patterns=20 inside the cowl were blocking airflow through oil cooler, I installed a par= tial=20 exit duct behind the radiator directing the airflow downward toward the cow= l=20 outlet.=A0 It looked very restrictive but flight tests showed almost no=20 affect on water cooling (which is OK)=A0 but a significant improvement in o= il=20 cooling.=A0=A0 I further restricted the airflow through the rad by putting= =20 some roof ridge vent material inside the inlet diffuser.=A0 This gave a tin= y=20 increase in water temp but a further improvement in oil cooling.=A0=A0=20 Long story short,=A0 after several more tests it became apparent that back= =20 pressure under the cowl was having a major effect on the oil=20 cooling.=A0=A0 I have no idea why my instrument did not read the pressure= =20 correctly.=A0 It works fine on the bench and is properly referenced to the= =20 static system in the plane.=A0=A0 The temptation is to keep changing the=20 cooling outlet scheme until the internal cowl back pressure is low enough t= o get=20 the cooling good enough.=A0 My belief is that this would lead to a very hig= h=20 drag solution.=A0 You may remember the experiment I did by flying with the= =20 cowl removed.=A0 The cooling was never a problem then (except perhaps too= =20 much cooling) but the drag was enormous.=A0 The fuel burn was 60% higher at= =20 the test airspeed of 130 mph.

The conclusion I eventually came to wa= s=20 that the rad (because of it's relatively low air flow resistance) is ho= gging the=20 airflow capability of the cowl cooling outlet.=A0 (cowl flap did not have= =20 enough effect to fix the problem). =A0 Keep in mind that the oil cooler is = a=20 thick AC evaporator core that is very restrictive.=A0=A0 The current=20 experiment is to replace it with a much less restrictive (to airflow) oil= =20 cooler.=A0 I found the largest cooler that would fit in the same location a= s=20 the AC core and I'm using the same diffuser as before (slightly modifie= d to fit=20 the larger face of the new cooler).=A0 This cooler is only 2" thick an= d core=20 volume is 30% less than the AC core.=A0 It is slightly larger in volume tha= n=20 an RX-7 cooler.=A0 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 degr= ee=20 day) so I'm hoping that this smaller cooler will be enough.=A0 Should b= e=20 ready to flight test it this week.

I should point out another sympto= m.=20 Power setting (and therefore airspeed) had very little effect on the=20 cooling=A0 (i.e., it didn't get much hotter at high power as long as ai= rspeed=20 went up as well.=A0=A0 Things got hot fast in climb however.=A0 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= .=A0=20 If the cooler is simply too small, more airflow will not help much.=A0=20

Tracy

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