X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao106.cox.net ([68.230.241.40] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTP id 2468417 for flyrotary@lancaironline.net; Mon, 12 Nov 2007 18:20:33 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.40; envelope-from=alventures@cox.net Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao106.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20071112231954.XQPO4787.fed1rmmtao106.cox.net@fed1rmimpo01.cox.net> for ; Mon, 12 Nov 2007 18:19:54 -0500 Received: from BigAl ([72.192.143.193]) by fed1rmimpo01.cox.net with bizsmtp id BzKu1Y0034AaN600000000; Mon, 12 Nov 2007 18:19:54 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Generalizations was Re: Diffuser Configuration Comparison Date: Mon, 12 Nov 2007 15:20:09 -0800 Message-ID: <000001c82582$91c879b0$6401a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C8253F.83A539B0" 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_01C8253F.83A539B0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Ed; =20 I'm sure we are basically in agreement on most of these things regarding coolant system design. Certainly I agree with point number 1; if you haven't done the calcs to determine the amount of the heat load that you need to handle, and determined the mass flow rates needed based on reasonable assumptions of temperature changes; then you haven't begun to design the system. =20 Beyond the basic points we could discuss indefinitely; but I will say = that discussing 'thickness' without stating tube and fin density is like assuming, for example, that all metals have the same density and = strength. Similarly, discussing thickness without some info about diffuser area = ratios is also a bit nebulous. So I learn very little about cooling from = someone telling me that racing radiators are 3.5 - 7" thick. =20 I will repeat my favorite R.O.T. cooling mantra: Every CFM passing = through the cooling system represents drag. Unless I have missed an important = point somewhere, more CFM will always result in more drag. (Tracy) =20 This is true if you assume that you put the air back into the free = stream at a velocity negligibly small compared to the velocity that went in. That = may be true in many cases; but I could have infinite CFM, and with zero = pressure drop, or velocity change, have zero drag. Drag is about the energy (velocity) difference between the air going in and the air going out. =20 Al G =20 1. Mass flow through the core is the most critical element of cooling. = If there is insufficient mass flow then it does not matter how good you = ducting or core is , you will not meet your cooling objective. Your air mass = flow requirement is dependent on your heat rejection needs.=20 =20 2. The maximum duct mass flow possible is a function of free stream kinetic energy available. This means you cooling design point airspeed = is as much (or more) a crucial factor in your design as any other factor.=20 =20 3. Many factors determine what you actually mass flow will be, these include both design, fabrication, installation, environmental and operational factors. A pretty general statement, but valid just the = same. Its the nailing down of the factors in this area that to me represents = the most beneficial (and the most difficult) factors to understand in = detail. =20 4. The maximum flow in the ducts (and through the core) is a function = of the free stream kinetic energy and the pressure loss coefficient of the duct (and core). =20 =20 5. Air Flow separation in the diffuser is the most significant factor = in degrading core effectiveness. Separation reduces cooling by reducing = mass flow, by creating pressure losses, disrupting even velocity = distribution across the core and increasing drag. =20 =20 6. Diffuser's performance depend, in significant part, on the core characteristics. =20 7. It is a balancing and optimization problem of opposing aerodynamic = and thermodynamic attributes. =20 8. If you had enough core and enough air flow - you will cool, but the penalty in drag and weight may be higher than you would like. =20 9. Few of us have the knowledge, understanding, tools, time, $$ or inclination to do it the right the first time , but always time to = re-do-it after the first flight {:>) =20 =20 Besides the generation that appeared to bring this discussion about was = that thicker radiators offer advantages at higher airspeeds. I still stand = by that generalization. =20 note. I did not say that 2 1/2" was too thin or 7" was too thick. But, = I do believe that the Nascar crowd have the resources and inclination to = do the research on radiator size that none of us do have. There speeds are comparable to ours, so again, I personally feel that a core in the = vicinity of 3" thick sets a bench mark that is probably as valid as anything we = could afford to do.=20 =20 Just because my GM cores happen to be 3 1/2" thick has nothing to do = with it {:>) =20 Appreciate you comments, Al. I will try to hold my generalizations to = an ...A'hem ... acceptable minimum {:>) =20 Best Regards =20 Ed =20 =20 =20 Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.dmack.net/mazda/index.html =20 ------=_NextPart_000_0001_01C8253F.83A539B0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Ed;=

 

I’m sure we are basically = in agreement on most of these things regarding coolant system design. =  Certainly I agree with point number 1; if you haven’t done the calcs to = determine the amount of the heat load that you need to handle, and determined the = mass flow rates needed based on reasonable assumptions of temperature = changes; then you haven’t begun to design the system.

 

Beyond the basic points we could = discuss indefinitely; but I will say that discussing ‘thickness’ = without stating tube and fin density is like assuming, for example, that all = metals have the same density and strength.  Similarly, discussing = thickness without some info about diffuser area ratios is also a bit nebulous.  So = I learn very little about cooling from someone telling me that racing = radiators are 3.5 – 7” thick.

 

I will repeat my favorite = R.O.T. cooling mantra:  Every CFM passing through the cooling system = represents drag.  Unless I have missed an important point somewhere, more CFM = will always result in more drag. (Tracy)

 

This is true if you assume that = you put the air back into the free stream at a velocity negligibly small = compared to the velocity that went in.  That may be true in many cases; but I = could have infinite CFM, and with zero pressure drop, or velocity change, have = zero drag.  Drag is about the energy (velocity) difference between the = air going in and the air going out.

 

Al G

 

1.  Mass flow through = the core  is the most critical element of cooling.  If there is = insufficient mass flow then it does not matter how good you ducting or core is , you = will not meet your cooling objective.  Your air mass flow requirement is dependent on your heat rejection needs.

 

2.  The maximum duct =  mass flow possible is a function of free stream kinetic energy = available. This means you cooling design  point airspeed is as much (or more) =  a crucial factor in your design as any other = factor. 

 

3.  Many factors = determine what you actually mass flow  will be, these include both design, = fabrication, installation, environmental and operational  factors.  A = pretty general statement, but valid just the same.  Its the nailing down = of the factors in this area that to me represents the most beneficial (and the = most difficult) factors to understand in detail.

 

4.  The maximum flow = in the ducts (and through the core) is a function of the free stream kinetic = energy and the  pressure loss coefficient of the duct (and core).  =

 

5.  Air Flow = separation in the diffuser is the most significant factor in degrading core = effectiveness.  Separation reduces cooling by reducing mass flow,  by creating pressure losses, disrupting even velocity distribution across the core = and increasing drag. 

 

6.  Diffuser's = performance depend, in significant part, on the core = characteristics.

 

7.  It is a balancing = and optimization problem of opposing  aerodynamic and = thermodynamic attributes.

 

8.  If you had enough = core and enough air flow - you will cool, but the penalty in drag and weight may = be higher than you would like.

 

9.  Few of us have the knowledge, understanding, tools, time, $$ or inclination to do it the = right the first time , but always time to re-do-it after the first flight = {:>)

 

 

Besides the generation that = appeared to bring this discussion about was that thicker radiators offer = advantages at higher airspeeds.  I still stand by that = generalization.

 

note. I did not say that 2 = 1/2"  was too thin or 7" was too thick.  But, I do believe = that the Nascar crowd have the resources and inclination to do the research on = radiator size that none of us do have.  There speeds are comparable to ours, = so again, I personally feel that a core in the vicinity of 3" thick = sets a bench mark that is probably as valid as anything we could afford to = do. 

 

 Just because my GM = cores happen to be 3 1/2" thick has nothing to do with it = {:>)

 

Appreciate you comments, = Al.  I will try to hold my generalizations to an ...A'hem ... acceptable = minimum {:>)

 

Best = Regards

 

Ed

 

 

 

 

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