Return-Path: Received: from [65.54.169.54] (HELO hotmail.com) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 855562 for flyrotary@lancaironline.net; Tue, 05 Apr 2005 10:34:39 -0400 Received-SPF: pass receiver=logan.com; client-ip=65.54.169.54; envelope-from=lors01@msn.com Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Tue, 5 Apr 2005 07:33:53 -0700 Message-ID: Received: from 4.174.2.44 by BAY3-DAV24.phx.gbl with DAV; Tue, 05 Apr 2005 14:33:53 +0000 X-Originating-IP: [4.174.2.44] X-Originating-Email: [lors01@msn.com] X-Sender: lors01@msn.com From: "Tracy Crook" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: A lot to learn Date: Tue, 5 Apr 2005 10:33:49 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0119_01C539CA.F44189C0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: MSN 9 X-MimeOLE: Produced By MSN MimeOLE V9.10.0011.1703 Seal-Send-Time: Tue, 5 Apr 2005 10:33:49 -0400 X-OriginalArrivalTime: 05 Apr 2005 14:33:53.0709 (UTC) FILETIME=[7DE40DD0:01C539EC] This is a multi-part message in MIME format. ------=_NextPart_000_0119_01C539CA.F44189C0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable See, I told you this was the most miss-understood detail in water cooled = engines! : ) FWIW, here is my summary of the discussion so far: Ed, you are being way too modest. Yours has been the most coherent real = world analysis so far while still tying it to the theoretical = groundwork. Your brief departure into the irrelevant molecular velocity = (for this discussion), was in response to someone else, not your fault. Jim, excellent point, we must separate the irrelevant and 'things we = can't do anything about' from the discussion about building a actual = honest to god flying machine. Doug's 'rule of thumb' post was based on real physics but left out some = factors that made it not universally applicable. What works for an RV = will not necessarily work for a Pietenpole, even if they had the same = size engine. And while the military must design for "Std air + 40 deg = F" (100 degrees), we have the advantage of not needing to design to that = standard. On those very hot days, I can accept the limitation of using = a lower power setting in climb in order to have other advantages. I'm = not scrambling to intercept MiGs at 40,000 ft. But Doug's point of = using rules of thumb (when accurate and applicable), is very true. Very = few builders have the time or inclination to fully absorb K & W (which = he has done pretty well). Tracy Ok, Jim I agree that the theory part gets out of hand at times (my fault). = Theory only counts if it works in practice {:>). However, I think these = question naturally arise when we start talking about some of this stuff = - the old "how it do that". =20 The only part that really counted was understanding what was = necessary to keep air flow from separating from the walls in a diffuser. = If you eliminate that problem you have done probably 90% of what you = can do to achieve optimum diffuser performance (my opinion of course). = So you can have otherwise adequate core surface and volume, but if you = have a poor duct design with lots of flow separation and eddies then = your system may fail to adequately cool. Ed A Is it possible we're dismissing some important factors getting a = little out of our depth here? Dynamic pressure in the cores and across = the cores would seem to be so highly dependent on surface friction and = core density and passage size as to be impossible to estimate, much less = quantify accurately. If the purpose of the plenum is pressure recovery (converting = dynamic pressure into static pressure) and it's the static pressure drop = that drives the mass of air through the radiator core, why not just = forget about the molecular, boundary layer and core passage size = considerations for the moment since we can't quantify any of that = anyway. As Ed has stated so many times in so many ways, a good = inlet/plenum design does a better job of converting dynamic pressure to = static pressure than a bad one, and he's found out pretty much what he = has to do to make a bad one good. =20 If we measure static pressure at the forward and aft face of the = radiator and we've got the pressure drop across the core. Period. We = know how close we are to Ed's plenum. Then adapt the stuff that Ed has = pioneered for us to make it better An Airspeed indicator I find is = handier and more accurate than a water manometer. The Pitot connection = on the upwind side and the Static connection on the downwind side should = give me upwards of 100, maybe 120 kias drop across the radiator at = cruise. More is better. If I don't have sufficient pressure drop = across the radiator, I probably need to improve my intake and plenum to = get rid of the eddies Ed alludes to. That is what I've got the most = influence over. If I don't get enough pressure recovery, I study Ed's = findings and approach implement them better. =20 I think all this molecular stuff is more appropriate to the ACRE = list where nothing ever really has to fly. This list (to me) is the = guys who actually FLY. A sound qualitative analysis of the issues = involved (which we already have) will lead me to a workable solution. = That is very nice since an acceptably accurate quantitative analysis is = not possible. To that end (to coin a phrase) I don't have to know how = it works or why it works, I only have to know what I have to do to MAKE = it work. And I have been blessed that Ed has found out most of this. Are we PVORT. again? ... Jim S. David Carter wrote: ----- Original Message -----=20 From: To: "Rotary motors in aircraft" = Sent: Monday, April 04, 2005 7:07 AM Subject: [FlyRotary] Re: A lot to learn ! Re: Cooling -Learned a lot Charlie E wrote: At the risk of embarrassing myself with a display of misunderstanding the physics of it all, should your pressure sensors be measuring dynamic pressure or static? Seems like I remember Tracy's measurement pics having foam chunks over the pressure sensors to remove the dynamic component of the pressure measurement. I couldn't remember if your setup has that (& I really don't know if it should, either). Charlie --------------------------------------------- =20 >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html ------=_NextPart_000_0119_01C539CA.F44189C0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
See, I told you this was the most miss-understood detail in water = cooled=20 engines!  : )
 
FWIW, here is my summary of the discussion so far:
 
Ed, you are being way too modest.  Yours has been the most = coherent=20 real world analysis so far while still tying it to the theoretical=20 groundwork.  Your brief departure into the irrelevant=20 molecular velocity (for this discussion), was in response to = someone=20 else, not your fault.
 
Jim, excellent point, we must separate the irrelevant and 'things = we can't=20 do anything about' from the discussion about building a actual honest to = god=20 flying machine.
 
Doug's 'rule of thumb' post was based on real physics but left out = some=20 factors that made it not universally applicable.  What works for an = RV will=20 not necessarily work for a Pietenpole, even if they had the same size=20 engine.  And while the military must design for "Std air + 40 deg = F" (100=20 degrees), we have the advantage of not needing to design to that = standard. =20 On those very hot days, I can accept the limitation of using a lower = power=20 setting in climb in order to have other advantages.  I'm not = scrambling to=20 intercept MiGs at 40,000 ft.  But Doug's point of using rules of = thumb=20 (when accurate and applicable), is very true.  Very few builders = have the=20 time or inclination to fully absorb K & W (which he has done pretty=20 well).
 
Tracy
Ok, Jim
 
I agree that the theory part gets out = of hand at=20 times (my fault).  Theory only counts if it works in practice=20 {:>).  However, I think these question naturally arise when we = start=20 talking about some of this stuff - the old "how it do that". =20
 
The only part  that really = counted was=20 understanding what was necessary to keep air flow from separating from = the=20 walls in a diffuser.  If you eliminate that problem you have done = probably 90% of what you can do to achieve optimum diffuser = performance (my=20 opinion of course).  So you can have otherwise adequate core = surface and=20 volume, but if you have a poor duct design with lots of flow = separation and=20 eddies then your system may fail to adequately cool.
 
Ed A
 

Is it possible we're dismissing some important = factors=20 getting a little out of our depth here?  Dynamic pressure in = the cores=20 and across the cores would seem to be so highly dependent on surface = friction and core density and passage size as to be impossible to = estimate,=20 much less quantify accurately.

If the purpose of the plenum = is=20 pressure recovery (converting dynamic pressure into static pressure) = and=20 it's the static pressure drop that drives the mass of air through = the=20 radiator core, why not just forget about the molecular, boundary = layer and=20 core passage size considerations for the moment since we can't = quantify any=20 of that anyway.  As Ed has stated so many times in so many = ways, a good=20 inlet/plenum design does a better job of converting dynamic pressure = to=20 static pressure than a bad one, and he's found out pretty much what = he has=20 to do to make a bad one good. 

If we measure static = pressure at=20 the forward and aft face of the radiator and we've got the pressure = drop=20 across the core.  Period.  We know how close we are to = Ed's=20 plenum.  Then adapt the stuff that Ed has pioneered for us to = make it=20 better  An Airspeed indicator I find is handier and more = accurate than=20 a water manometer.  The Pitot connection on the upwind side and = the=20 Static connection on the downwind side should give me upwards of = 100, maybe=20 120 kias drop across the radiator at cruise.  More is = better.  If=20 I don't have sufficient pressure drop across the radiator, I = probably need=20 to improve my intake and plenum to get rid of the eddies Ed alludes=20 to.  That is what I've got the most influence over.  If I = don't=20 get enough pressure recovery, I study Ed's findings and approach = implement=20 them better. 

I think all this molecular stuff is more=20 appropriate to the ACRE list where nothing ever really has to = fly. =20 This list (to me) is the guys who actually FLY.  A sound=20 qualitative analysis of the issues involved (which we already = have)=20 will lead me to a workable solution.  That is very nice since = an=20 acceptably accurate quantitative analysis is not = possible.  To=20 that end (to coin a phrase) I don't have to know how it works or why = it=20 works, I only have to know what I have to do to MAKE it work.  = And I=20 have been blessed that Ed has found out most of this.

Are we = PVORT.=20 again? ... Jim S.


David Carter wrote:
----- Original Message -----=20
From: <jbker@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.n=
et>
Sent: Monday, April 04, 2005 7:07 AM
Subject: [FlyRotary] Re: A lot to learn ! Re: Cooling -Learned a lot


  
Charlie E wrote:

At the risk of embarrassing myself with a display of misunderstanding
the physics of it all, should your pressure sensors be measuring dynamic
pressure or static? Seems like I remember Tracy's measurement pics
having foam chunks over the pressure sensors to remove the dynamic
component of the pressure measurement. I couldn't remember if your setup
has that (& I really don't know if it should, either).

Charlie
---------------------------------------------

    
  

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