X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao102.cox.net ([68.230.241.44] verified) by logan.com (CommuniGate Pro SMTP 5.2.0) with ESMTP id 2772697 for flyrotary@lancaironline.net; Sat, 01 Mar 2008 12:42:30 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.44; envelope-from=alventures@cox.net Received: from fed1rmimpo03.cox.net ([70.169.32.75]) by fed1rmmtao102.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20080301174151.TSUL17893.fed1rmmtao102.cox.net@fed1rmimpo03.cox.net> for ; Sat, 1 Mar 2008 12:41:51 -0500 Received: from BigAl ([72.192.137.74]) by fed1rmimpo03.cox.net with bizsmtp id vthQ1Y0011cVYgg0000000; Sat, 01 Mar 2008 12:41:24 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: Cooling the 20B Date: Sat, 1 Mar 2008 09:43:46 -0800 Message-ID: <000001c87bc3$cd189a80$6401a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C87B80.BEF7CB80" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C87B80.BEF7CB80 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Bill; your point is valid, but I=92ll take the liberty to add and = clarify. =20 You will need to run between 75% and 100% in your plane most of the = time! The rotary is well up to the task, but you need to concern yourself with = a totally different operation pattern. Radiator wise the rule of thumb is = a minimum of 2ci of radiator per HP for piston engines, Rotaries like = closer to 3 cubic inches per HP. I actually find that with the extra power of the 20B, cruising at about = 50% is just fine. Unless you=92re in a hurry, since speed goes up by the = cube root of power, an extra 25% + dosesn=92t get you that much. I can fly = 200 mph at 9.2 gph, or 210 mph at about 11.0 gph. I tend to think it is not = worth $7 of fuel to gain 3 minutes each hour of flight. The numbers for a = Lancair or Velocity will be different, but you get my drift.=20 =20 But your right, of course; this is quite a different application than racing. The limiting factor on cooling is takeoff and climb. If you get that done, then you=92ll start wondering how to reduce the unnecessary = cooling drag when cruising. Be really careful about fans in your plane. At the higher air speeds we = see a fan can become a real restriction. Also not many fans, (only the = REALLY expensive ones), are designed to be freewheeling in a 200 MPH airstream! = I use an auxiliary fan behind the in-cowl radiator (which is handling = most of the coolant heat load) in my Velocity (rear engine, of course). = It=92s a 4-blade SPAL fan that covers about 65% of the radiator. With the fan on = I can sit and wait for takeoff for long periods of time without concern. = It gets turned off when I get clearance. When I installed the fan, I did = not notice any reduction in the cooling ability in the air, so I conclude = that it does not restrict the airflow. The scoop inlet is about =BC the rad = area, so the air exiting the rad is 50 mph or less. I haven=92t concerned = myself about the fan spinning in flight, and it has operated for about 60 hours = of flying and doesn=92t show noticeable signs of wear. Although I should = perhaps rig the relay to short the fan terminals when turned off. The fan has a secondary function which I think is also important. I = turn it on as I=92m about to shutdown, and leave it running a few minutes after shutdown. It definitely reduces the in-cowl temps while things = (especially the exhaust system) is cooling down. Good for things like the coils and alternator. Radiator wise the rule of thumb is a minimum of 2ci of radiator per HP = for piston engines, Rotaries like closer to 3 cubic inches per HP. Unless I=92m overlooking something; except for a bit lower BSFC (maybe = 10 =96 15%) there is no reason to believe that a rotary takes any more cooling capacity per hp than a piston engine. The split between oil and coolant = heat loads is quite different. The rotary puts close to 1/3 of the waste heat into the oil, whereas a piston engine may be more like 10% or less. So although the combined heat rejection requirement is a bit higher, the coolant side requirement (radiator) of the rotary is actually less; the = oil cooler quite a bit more. As my installation has turned out, the airflow through the oil cooler is less than anticipated, and the effectiveness of the in-cowl rad greater. = I typically see oil temps 20 to 40F higher than coolant =96 so I=92m about = to face some re-plumbing to put in an oil/water heat exchanger. Al ------=_NextPart_000_0001_01C87B80.BEF7CB80 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Bill; your point is valid, but = I’ll take the liberty to add and clarify.

 

You will need to run = between 75% and 100%  in your plane most of the time! The rotary is well up to the = task, but you need to concern yourself with a totally different operation = pattern. Radiator wise the rule of thumb is a minimum of 2ci of radiator per HP = for piston engines, Rotaries like closer to 3 cubic inches per = HP.

I actually find that with the = extra power of the 20B, cruising at about 50% is just fine.=A0 Unless = you’re in a hurry, since speed goes up by the cube root of power, an extra 25% + = dosesn’t get you that much.=A0 I can fly 200 mph at 9.2 gph, or 210 mph at about = 11.0 gph.=A0 I tend to think it is not worth $7 of fuel to gain 3 minutes each hour = of flight.=A0 The numbers for a Lancair or Velocity= will be different, but you get my drift.

 

But your right, of course; this = is quite a different application than racing.=A0 The limiting factor on cooling = is takeoff and climb. If you get that done, then you’ll start wondering how = to reduce the unnecessary cooling drag when cruising.

 Be really careful about fans in your plane. At = the higher air speeds we see a fan can become a real restriction. Also not = many fans, (only the REALLY expensive ones), are designed to be freewheeling = in a 200 MPH airstream!

I use an auxiliary fan behind the = in-cowl radiator (which is handling most of the coolant heat load) in my = Velocity (rear engine, = of course). It’s a 4-blade SPAL fan that covers about 65% of the = radiator. =A0With the fan on I can sit and wait for takeoff for long periods of time = without concern.=A0 It gets turned off when I get clearance.=A0 When I installed = the fan, I did not notice any reduction in the cooling ability in the air, so I = conclude that it does not restrict the airflow. The scoop inlet is about =BC the = rad area, so the air exiting the rad is 50 mph or less. I haven’t concerned = myself about the fan spinning in flight, and it has operated for about 60 hours = of flying and doesn’t show noticeable signs of wear.=A0 Although I = should perhaps rig the relay to short the fan terminals when turned = off.

The fan has a secondary function = which I think is also important.=A0 I turn it on as I’m about to shutdown, = and leave it running a few minutes after shutdown. It definitely reduces the = in-cowl temps while things (especially the exhaust system) is cooling down. = =A0Good for things like the coils and alternator.

Radiator wise the rule of thumb is a minimum of 2ci = of radiator per HP for piston engines, Rotaries like closer to 3 cubic = inches per HP.

Unless I’m overlooking = something; except for a bit lower BSFC (maybe 10 – 15%) there is no reason to = believe that a rotary takes any more cooling capacity per hp than a piston engine. = The split between oil and coolant heat loads is quite different. The rotary puts = close to 1/3 of the waste heat into the oil, whereas a piston engine may be more = like 10% or less. So although the combined heat rejection requirement is a = bit higher, the coolant side requirement (radiator) of the rotary is = actually less; the oil cooler quite a bit more.

As my installation has turned = out, the airflow through the oil cooler is less than anticipated, and the = effectiveness of the in-cowl rad greater.=A0 I typically see oil temps 20 to 40F = higher than coolant – so I’m about to face some re-plumbing to put in an oil/water heat exchanger.

Al

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