X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.121] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTP id 2468548 for flyrotary@lancaironline.net; Mon, 12 Nov 2007 20:06:53 -0500 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.121; envelope-from=eanderson@carolina.rr.com Received: from edward2 ([24.74.103.61]) by cdptpa-omta04.mail.rr.com with SMTP id <20071113010615.BBEA5837.cdptpa-omta04.mail.rr.com@edward2> for ; Tue, 13 Nov 2007 01:06:15 +0000 Message-ID: <000701c82591$b06c43b0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Generalizations was Re: Diffuser Configuration Comparison Date: Mon, 12 Nov 2007 20:08:23 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0004_01C82567.C73B9890" 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 This is a multi-part message in MIME format. ------=_NextPart_000_0004_01C82567.C73B9890 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I agree, Al. =20 I must admit that I have a tendency to try and generalize concepts - at = least in part because it may have taken me a while to grasp them and I = hope to help others understand the basics. However, there is no doubt = we are on the same sheet of music. I certainly appreciate you pointing = out anytime you feel I have made a perhaps misleading "over = generalizations". I am the first to admit my knowledge is very limited in this area. = Every once in a while I find something that appears to turn on the = "light bulb" and I am guilty of rushing to share it with others. But, I will be the first to say that there is much of it I do not fully = understand and anytime you (or anyone else) feels that I have = misunderstood/misinterpreted or mischaracterize something, I want to be = the first to be informed. I think I'll wait for my next little nugget, I finally found a study = that actually addressed the effects of core thickness and its effect on = cooling and drag. But, I'm going to try out some calculations using the = information and see if I can get them to make sense , before I share = (what I think I've found). Ed ----- Original Message -----=20 From: Al Gietzen=20 To: Rotary motors in aircraft=20 Sent: Monday, November 12, 2007 6:20 PM Subject: [FlyRotary] Re: Generalizations was Re: Diffuser = Configuration Comparison 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.=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 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). =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 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.=20 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 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 ------=_NextPart_000_0004_01C82567.C73B9890 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
I agree, Al. 
 
I must admit that I have a tendency to try and = generalize=20 concepts - at least in part because it may have taken me a while to = grasp them=20 and I hope to help others understand the basics.  However, there is = no=20 doubt we are on the same sheet of music.  I certainly appreciate = you=20 pointing out anytime you feel I have made a perhaps misleading "over=20 generalizations".
 
I am the first to admit my knowledge is very = limited in=20 this area.  Every once in a while I find something that appears to = turn on=20 the "light bulb" and I am guilty of rushing to share it with=20 others.
 
But, I will be the first to say that there is = much of it I=20 do not fully understand and anytime you (or anyone else) feels that I = have=20 misunderstood/misinterpreted or mischaracterize something, I want to be = the=20 first to be informed.
 
I think I'll wait for my next little nugget, I = finally=20 found a study that actually addressed the effects of core thickness and = its=20 effect on cooling and drag.  But, I'm going to try out some = calculations=20 using the information and see if I can get them to make sense , before I = share=20 (what I think I've found).
 
Ed
 
 
 
----- Original Message -----
From:=20 Al = Gietzen=20
Sent: Monday, November 12, 2007 = 6:20=20 PM
Subject: [FlyRotary] Re: = Generalizations=20 was Re: Diffuser Configuration Comparison

Ed;

 

I=92m = sure we are=20 basically in agreement on most of these things regarding coolant = system=20 design.  Certainly I agree with point number 1; if you haven=92t = done the=20 calcs to determine the amount of the heat load that you need to = handle, and=20 determined the mass flow rates needed based on reasonable assumptions = of=20 temperature changes; then you haven=92t begun to design the=20 system.

 

Beyond = the basic=20 points we could discuss indefinitely; but I will say that discussing=20 =91thickness=92 without stating tube and fin density is like assuming, = for=20 example, that all metals have the same density = and=20 strength.  Similarly, discussing thickness without some=20 info about = diffuser=20 area ratios is also a bit nebulous.  So I learn very little about = cooling=20 from someone telling me that racing radiators are 3.5 =96 7=94=20 thick.

 

I will repeat my = favorite R.O.T.=20 cooling mantra:  Every CFM passing through the cooling system = represents=20 drag.  Unless I have missed an important point somewhere, more = CFM will=20 always result in more drag. (Tracy)

 

This is = true if you=20 assume that you put the air back into the free stream at a velocity = negligibly=20 small compared to the velocity that went in.  That may be true in = many=20 cases; but I could have infinite CFM, and with zero pressure drop, or = velocity=20 change, have zero drag.  Drag is about the energy (velocity) = difference=20 between the air going in and the air going out.

 

Al=20 G

 

1.  Mass flow = through the=20 core  is the most critical element of cooling.  If there is=20 insufficient mass flow then it does not matter how good you ducting or = core is=20 , you will not meet your cooling objective.  Your air mass flow=20 requirement is dependent on your heat rejection needs.=20

 

2.  The maximum = duct=20  mass flow possible is a function of free stream kinetic energy=20 available. This means you cooling design  point = airspeed is as=20 much (or more)  a crucial factor in your design as any other=20 factor. 

 

3.  Many factors = determine=20 what you actually mass flow  will be, these include both design,=20 fabrication, installation, environmental and operational =  factors. =20 A pretty general statement, but valid just the same.  Its the = nailing=20 down of the factors in this area that to me represents the most = beneficial=20 (and the most difficult) factors to understand in=20 detail.

 

4.  The maximum = flow in the=20 ducts (and through the core) is a function of the free stream kinetic = energy=20 and the  pressure loss coefficient of the duct (and core). =20

 

5.  Air Flow = separation in=20 the diffuser is the most significant factor in degrading core=20 effectiveness.  Separation reduces cooling by reducing mass = flow,=20  by creating pressure losses, disrupting even velocity = distribution=20 across the core and increasing drag. 

 

6.  Diffuser's = performance=20 depend, in significant part, on the core=20 characteristics.

 

7.  It is a = balancing and=20 optimization problem of opposing  aerodynamic and = thermodynamic=20 attributes.

 

8.  If you had = enough core=20 and enough air flow - you will cool, but the penalty in drag and = weight may be=20 higher than you would like.

 

9.  Few of us have = the=20 knowledge, understanding, tools, time, $$ or inclination to do it the = right=20 the first time , but always time to re-do-it after the first flight=20 {:>)

 

 

Besides the generation = that=20 appeared to bring this discussion about was that thicker radiators = offer=20 advantages at higher airspeeds.  I still stand by that=20 generalization.

 

note. I did not say that = 2 1/2"=20  was too thin or 7" was too thick.  But, I do believe that = the=20 Nascar crowd have the resources and inclination to do the research on = radiator=20 size that none of us do have.  There speeds are comparable to = ours, so=20 again, I personally feel that a core in the vicinity of 3" thick sets = a bench=20 mark that is probably as valid as anything we could afford to=20 do. 

 

 Just because my GM = cores=20 happen to be 3 1/2" thick has nothing to do with it=20 {:>)

 

Appreciate you comments, = Al. =20 I will try to hold my generalizations to an ...A'hem ... acceptable = minimum=20 {:>)

 

Best=20 Regards

 

Ed

 

 

 

Ed Anderson
Rv-6A = N494BW Rotary=20 Powered
Matthews, NC
eanderson@carolina.rr.comhttp://www.andersonee.com
http:/= /members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda= /index.html

 

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