X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 50 [XX] Return-Path: Received: from ms-smtp-03.southeast.rr.com ([24.25.9.102] verified) by logan.com (CommuniGate Pro SMTP 5.1.8) with ESMTP id 2023816 for flyrotary@lancaironline.net; Thu, 03 May 2007 12:49:57 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.102; 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-03.southeast.rr.com (8.13.6/8.13.6) with SMTP id l43GmY7a014422 for ; Thu, 3 May 2007 12:48:34 -0400 (EDT) Message-ID: <000901c78da3$11bfb2f0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Cooling area drag Date: Thu, 3 May 2007 12:49:51 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0006_01C78D81.8A536FD0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3028 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0006_01C78D81.8A536FD0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Actually, Mark, I started pulling together what I believed to be the = major factors without getting too down in the weeds about rotary = cooling, a couple of years ago with the intention of publishing an e = book (pamphlet more likely) . Then I ran into the problem that the = seemingly best diffuser (Streamline duct) was simply too long (in its = optimum configuration) for most of our needs. Yes, you can shorten it = but then you incur more drag. So I scratched my head about that for a = while until the light bulb came on. After experimenting with a number of duct shapes and reading more, I = came to the conclusion that if my understanding about what killed = effective cooling was correct then I should be able to achieve my = cooling/drag goals with the "Pinched" duct. But, what I wanted to do = and never took the time to do was to go back with Mr. Bernoulli and = calculate the air velocity along each segment of the streamline duct and = then do the same for my "pinched" duct to see if there was any = similarity. Also, I have not paid much attention to the exiting duct - = simply because I don't have room for one. I tired one back almost 8 = years ago and decided the zigs and zags it had to avoid = engine/motormount, etc impeded airflow more than helped it. But, alas, just as I was recently about to go to publication, the new = "bible" of cooling was published - so how could I possibly compete {:>). = I may still do it as if it passes the gauntlet of folks on this list = (or errors if any {:>)) are corrected,as it may be useful to some. Ed ----- Original Message -----=20 From: Mark Steitle=20 To: Rotary motors in aircraft=20 Sent: Thursday, May 03, 2007 12:34 PM Subject: [FlyRotary] Re: Cooling area drag ED, So, tell us, when is your book on cooling going to be available? =20 Mark =20 On 5/3/07, Ed Anderson wrote:=20 Less we forget how important drag is in our hobby, I took a formula = for calculating drag at different airspeeds and the Hp required to push = the given frontal area along at the stated airspeed.=20 This is for two of our traditional GM evaporator cores using their = combined frontal area of 180 sq inch or 1.25 sq feet. This assumes = that airspeed shown represents the velocity through the cooling core = (which is not really likely to reach speeds above 80 mph if you have any = sort of ducting), but that is an assumption on my part since as Bill = keeps reminding me I have not instrumented my ducts {:>)=20 Air Speed (MPH) HP=20 =20 40 0.533333 =20 60 1.80 =20 80 4.27 =20 120 14.40 =20 140 22.87 =20 160 34.13 =20 180 48.60 =20 200 66.67 =20 Clearly the faster your cruise speed the more important it is to = minimize cooling drag. Of course the airspeed the core sees should = normally not be over 10% of your cruise speed or 30% of your climb speed = (According to Horners rule of thumb). So slowing down your cooling = airflow to lessen drag is one reason for paying some attention to your = ducting. However, cooling again depends on many other variables, for = instance accepting a high velocity airflow through your core may permit = you to use a smaller frontal area core thereby offsetting to some = extent the higher drag. In fact, space constraints may force you to his = configuration regardless.=20 Another factor to consider is trade off between frontal area drag = and thermal transfer efficiency. A large thin radiator is theoretical = the most efficient due to that factor. However, it disturbs a larger = segment of air (resulting in higher drag) - not really important in an = auto at 60 mph but very important in a Cozy at 200+ MPH. =20 A thicker core with smaller frontal area disturbs less air and while = it has more skin drag that is small compared to the frontal area drag. = Tracy refers to the approach of thicker cores as "... getting the most = cooling possible for the smallest column of air disturbed". So while = theoretically the thicker core is less thermodynamic efficient - it = turns out with sufficient dynamic pressure available it provides = definite benefits in our application. The average thickness of NASCAR = radiators is 3" and up to 7" for the longer high speed tracts. Since = they operate in speed regimes close to what most of us fly - they just = might know what they are doing given the $$ they will spend for even a = slight speed advantage.=20 Ok, back to creating a company - boy, a lot to learn Ed =20 Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com=20 http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.dmack.net/mazda/index.html ------=_NextPart_000_0006_01C78D81.8A536FD0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Actually, Mark,  I started pulling together = what I=20 believed to be the major factors without getting too down in the weeds = about=20 rotary cooling, a couple of years ago with the intention of publishing = an e book=20 (pamphlet more likely) .  Then I ran into the problem that the = seemingly=20 best diffuser (Streamline duct) was simply too long (in its optimum=20 configuration) for most of our needs.  Yes, you can shorten it but = then you=20 incur more drag.  So I scratched my head about that for a while = until the=20 light bulb came on.
 
After experimenting with a number of duct shapes = and=20 reading more, I came to the conclusion that if my understanding about = what=20 killed effective cooling was correct then I should be able to achieve my = cooling/drag goals with the "Pinched" duct.  But, what I wanted to = do and=20 never took the time to do was to go back with Mr. Bernoulli and = calculate the=20 air velocity along each segment of the streamline duct and then do the = same for=20 my "pinched" duct to see if there was any similarity.   Also, = I have=20 not paid much attention to the exiting duct - simply because I don't = have room=20 for one.  I tired one back almost 8 years ago and decided the zigs = and zags=20 it had to avoid engine/motormount, etc impeded airflow more than helped=20 it.
 
 
But, alas, just as I was recently about to go to = publication, the new "bible" of cooling was published - so how could I = possibly=20 compete {:>).  I may still do it as if it passes the gauntlet of = folks=20 on this list (or errors if any {:>)) are corrected,as it may be = useful to=20 some.
 
Ed
 
 
----- Original Message -----
From:=20 Mark = Steitle=20
Sent: Thursday, May 03, 2007 = 12:34=20 PM
Subject: [FlyRotary] Re: = Cooling area=20 drag

ED,
 
So, tell us, when is your book on cooling going to be = available? =20
 
Mark

 
On 5/3/07, Ed=20 Anderson <eanderson@carolina.rr.com&g= t;=20 wrote:=20
Less we forget how important drag is in our = hobby, I=20 took a formula for calculating drag at different airspeeds and the = Hp=20 required to push the given frontal area along at the stated = airspeed.=20
 
This is for two of our traditional GM = evaporator cores=20 using their combined frontal area of  180 sq inch or 1.25 sq=20 feet.  This assumes that airspeed shown represents the = velocity=20 through the cooling core (which is not really likely to reach speeds = above=20 80 mph if you have any sort of ducting), but that is an assumption = on my=20 part since as Bill keeps reminding me I have not instrumented my = ducts=20 {:>)
 

Air Speed (MPH)

         =20 HP

40

0.533333

60

1.80

80

4.27

120

14.40

140

22.87

160

34.13

180

48.60

200

66.67

 
 
Clearly the faster your cruise speed the = more=20 important it is to minimize cooling drag.  Of course the = airspeed the=20 core sees should normally not be over 10% of your cruise speed or = 30% of=20 your climb speed (According to Horners rule of thumb).  So = slowing down=20 your cooling airflow to lessen drag is one reason for paying some = attention=20 to your ducting.  However, cooling again depends on many other=20 variables, for instance accepting a high velocity airflow through = your core=20 may permit you to use a smaller frontal area  core thereby = offsetting=20 to some extent the higher drag.  In fact, space constraints may = force=20 you to his configuration regardless.
 
Another factor to consider is trade off = between=20 frontal area drag and thermal transfer efficiency.  A large = thin=20 radiator is theoretical the most efficient due to that factor.  = However, it disturbs a larger segment of air (resulting in higher = drag) -=20 not really important in an auto at 60 mph but very important in a = Cozy at=20 200+ MPH.  
 
A thicker core with smaller frontal = area disturbs=20 less air and while it has more skin drag that is small compared to = the=20 frontal area drag.  Tracy refers to the approach of thicker = cores as=20 "... getting the most cooling possible for the smallest column = of air=20 disturbed".  So while theoretically the thicker core is less=20 thermodynamic efficient - it turns out with sufficient dynamic = pressure=20 available it provides definite benefits in our = application.   The=20 average thickness of NASCAR radiators is 3" and up to 7" for the = longer high=20 speed tracts.  Since they operate in speed regimes close to = what most=20 of us fly - they just might know what they are doing given the $$ = they will=20 spend for even a slight speed advantage.
 
Ok, back to creating a company - boy, a lot = to=20 learn
 
Ed
 
 
 
  
 
 
Ed Anderson
Rv-6A N494BW Rotary=20 Powered
Matthews, NC
eanderson@carolina.rr.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW=
http://www.dmack.net/mazda/index.html

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