X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fmailhost03.isp.att.net ([207.115.11.53] verified) by logan.com (CommuniGate Pro SMTP 5.2.0) with ESMTP id 2773626 for flyrotary@lancaironline.net; Sun, 02 Mar 2008 10:45:36 -0500 Received-SPF: pass receiver=logan.com; client-ip=207.115.11.53; envelope-from=bbradburry@bellsouth.net Received: from arptk8ng400 (adsl-146-123-159.mco.bellsouth.net[72.146.123.159]) by isp.att.net (frfwmhc03) with SMTP id <20080302154455H0300i0otfe>; Sun, 2 Mar 2008 15:44:56 +0000 X-Originating-IP: [72.146.123.159] From: "Bill Bradburry" To: "'Rotary motors in aircraft'" References: In-Reply-To: Subject: RE: [FlyRotary] Cooling the 20B Date: Sun, 2 Mar 2008 10:44:57 -0500 Message-ID: <57537D4F66BB4C62848526322CCC2699@ARPTK8NG400> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_003C_01C87C52.75B1FAE0" X-Mailer: Microsoft Office Outlook 11 Thread-Index: Ach7w6D/PvJwIvacSOugu68vUA/v5QAuJB9A X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6000.16545 This is a multi-part message in MIME format. ------=_NextPart_000_003C_01C87C52.75B1FAE0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Al, do you recall the CFMs of your fan? And/or dimensions? =20 Bill B=20 =20 _____ =20 From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen Sent: Saturday, March 01, 2008 12:44 PM To: Rotary motors in aircraft Subject: [FlyRotary] Cooling the 20B 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_003C_01C87C52.75B1FAE0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Al, do you recall the CFMs of your fan?=A0 And/or = dimensions?

 

Bill B 

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Saturday, March 01, = 2008 12:44 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] = Cooling the 20B

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.  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.  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.

 

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’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.  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’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.  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’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.  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’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.  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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