X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ms-smtp-04.southeast.rr.com ([24.25.9.103] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2247978 for flyrotary@lancaironline.net; Tue, 07 Aug 2007 11:18:57 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.103; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-103-061.carolina.res.rr.com [24.74.103.61]) by ms-smtp-04.southeast.rr.com (8.13.6/8.13.6) with SMTP id l77FI7IC015570 for ; Tue, 7 Aug 2007 11:18:08 -0400 (EDT) Message-ID: <001b01c7d906$49f78d60$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: RV -7A Cooling Update 8/6/07 Date: Tue, 7 Aug 2007 11:19:03 -0400 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="utf-8"; reply-type=original Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 X-Virus-Scanned: Symantec AntiVirus Scan Engine Marc, I think our terminology can get confusing when applied to technical areas. You are correct - in the sense of turbulent vs laminar flow, turbulent flow (which we all most certainly have) basically causes more molecules of air (or any medium) to contact the hot metal (than laminar) and therefore transfer more heat. This is turbulence on the "micro" level. However, when the airflow becomes chaotic and forms large eddies and swirls, this disturbance, at the "macro" scale, of air flow overwhelms any benefit that may come from having more air molecules in contact with the metal because of its adverse effect on pressure recovery, drag and cooling.. So micro turbulence is good, macro turbulence is bad - or at least that is the way it appears to me. Ed ----- Original Message ----- From: To: "Rotary motors in aircraft" Sent: Tuesday, August 07, 2007 9:19 AM Subject: [FlyRotary] Re: RV -7A Cooling Update 8/6/07 > It was my impression that the "turbulence" was necessary to cool the water > flowing thru the tubes (this is IN the radiator, not in the ductwork!). If > the air slid on past very little cooling happens. Am I all wet here? > Marc Wiese > > > ---- Dennis Haverlah wrote: >> >> >> I've been busy with Family vacation, dealing with the exceptional wet >> weather in >> central Texas and my tennis playing but finally I have some more >> thoughts on radiators and cooling. My cooling is marginal for Texas in >> the summer. I want to climb at 120 kts and 26 + inches MP on a 100 deg >> F day without exceeding 215 on water and oil. >> >> I have the Griffin radiator (core 19 X 13 X 2.5 inches) and stock RX-7 >> '89 oil cooler as shown on pictures I have previously posted. The >> radiators are mounted under the engine at about a 30 deg. angle. My >> latest test flight with OAT of 92 deg F on the ground was encouraging. >> I had temp. probes on the outlet side of the oil and water radiators >> to measure the temp. of the heated air. The temp. probes had an upper >> limit of 160 deg. F. The air exiting the water radiator exceeded the >> 160 Deg. limit soon after take-off. I estimate the air temperature >> rise through the water radiator was at least 80-90 deg. Cooling water >> temp. never exceeded 210 deg. F. >> >> The air exiting the oil radiator was at 135 - 140 deg. F. (A delta T of >> about 40 - 45 deg F.) Oil temperature rose to 213 deg. F. max and at >> cruse 24 in. MP, 160 mph at 5500 feet the oil temp. decreased to 210 deg. >> F. >> >> >> I'm close to ideal cooling but I've been surprised how little effect my >> air >> flow modifications have have had on overall oil and water cooling. After >> studying K&W Chapter 12 some more I've decided I mounted my cooling >> radiators >> incorrectly!! As mentioned above, the radiators are below the engine at >> about >> a 30 Deg angle (alpha = 60 deg.) to the incoming air stream. The tanks >> are >> orientated fore and aft. This positions the fins across the air stream. >> >> Ch. 12.2 of K & W Fig. 12.6 shows a radiator block at an oblique angle >> (alpha) >> to the incoming air. The tubes are at the angle alpha to the flow. In >> the >> K & W analysis the tubes are slightly aerodynamic in shape they turn the >> flow >> as it enters the radiator fins. In the radiators I am using the tubes >> are >> separated about 1/2 inch. My fins are separated by about 0.080 inch. >> Because >> I mounted my radiator with the tanks fore and aft, the fins are at the >> angle >> alpha to the flow and the fins turn the air. The fins are very sharp thin >> metal >> and I believe air flow separation and turbulence is occurring at the >> leading >> edge of each fin. Because the fins are very close together the flow is >> restricted >> through the entire radiator surface. I believe the separated, turbulent >> flow at >> the leading edge of the fins limits the amount of air flowing through the >> radiator regardless of how "good" the diffusers are ahead of the >> radiators. >> >> If I have to do it over, I will defiantly mount my radiators with the >> tanks on the left >> and right side of the incoming air so that the tubes turn the air through >> alpha - not >> the fins!! >> >> Any comments - Am I out to lunch on this one? >> >> PS. The end of the first paragraph in Ch. 12.2. states "We shall >> consider first the >> simple case of parallel inflow at an angle alpha to the tubes, as shown >> in Fig. 12.6" >> I have not found a consideration in Chapter 12 of the case of the fins >> being at >> an angle alpha. >> >> Dennis Haverlah >> > > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html