Return-Path: Received: from [65.54.249.108] (HELO OMC3-S34.phx.gbl) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 853371 for flyrotary@lancaironline.net; Sun, 03 Apr 2005 12:25:41 -0400 Received-SPF: pass receiver=logan.com; client-ip=65.54.249.108; envelope-from=lors01@msn.com Received: from hotmail.com ([65.54.169.55]) by OMC3-S34.phx.gbl with Microsoft SMTPSVC(6.0.3790.211); Sun, 3 Apr 2005 09:24:55 -0700 Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Sun, 3 Apr 2005 09:24:55 -0700 Message-ID: Received: from 4.171.174.121 by BAY3-DAV25.phx.gbl with DAV; Sun, 03 Apr 2005 16:24:55 +0000 X-Originating-IP: [4.171.174.121] X-Originating-Email: [lors01@msn.com] X-Sender: lors01@msn.com From: "Tracy Crook" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Cooling -Learned a lot Date: Sun, 3 Apr 2005 12:24:51 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_006C_01C53848.22997410" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: MSN 9 X-MimeOLE: Produced By MSN MimeOLE V9.10.0011.1703 Seal-Send-Time: Sun, 3 Apr 2005 12:24:51 -0400 X-OriginalArrivalTime: 03 Apr 2005 16:24:55.0906 (UTC) FILETIME=[AC0B2420:01C53869] Return-Path: lors01@msn.com This is a multi-part message in MIME format. ------=_NextPart_000_006C_01C53848.22997410 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Excellent summary Ed, correlates with my experience as well. Only = exception I would take is in the following excerpt: "A good diffuser will reduce airflow velocity through the core which will reduces cooling drag. Pressure = across the core is increased which further enhances cooling." A good diffuser will reduce velocity but the reduction occurs IN the = diffuser, not through the core. As counter-intuitive as it may sound, = the velocity through the core is HIGHER than it would have been without = the diffuser's velocity decrease (and pressure increase). Think about it this way, How could velocity through the core be reduced = by a pressure increase? It isn't. The velocity at this point (through = the core) is increased. This is the single most misunderstood detail in liquid cooled engine = systems. Tracy=20 Subject: [FlyRotary] Cooling -Learned a lot Too right, Jerry My first 40 hours or so were in the marginal cooling zone. {:>). As = other things in this hobby, there are so many variables that interact, that = what may appear simply at first, is almost always a bit more complex. I say(Cooling Axiom 1) if you have enough cooling surface area and air = mass flow then it WILL cool. However, you may incur a high penalty in = cooling drag - which may not be as important for draggy airframes (such as = biplanes) as it is to sleeker airframes. Also a system that adequately cools = an engine producing 150 HP may not cool an engine producing 180 HP. = Picking your cooling design point is important. Optimizing for cruise and = your will be less than optimum for take and climb. Optimize for climb and you = will probably have more cooling drag than required at cruise. Compromise, compromise - cowl flaps are sometimes used to try to have the best of = both worlds. Some folks advocate a thinner, larger surface area core -which is = great for slow moving automobiles stuck in traffic with low dynamic pressure potential, but I think is not the optimum for most aircraft. Once you = trip the airflow and turn it turbulent you have incurred most of the drag penalty. Larger surface area cores disrupt a larger airstream and = incur more drag. Yes, thicker cores produce a bit more drag than the SAME = frontal area thinner cores. But, with a thicker core you can use a core with smaller frontal area. The NASCAR radiator's average 3" thick and on the long tracks where = speeds are higher some even go up to 7" thick. My contention is their = operating environment is more akin to ours than regular automobiles moving at = slower speeds. You know that the NASCAR folks will spend $$ for just a tiny advantage - so clearly they don't use thick cores because it is a disadvantage. But, some folks will continue to point to the large thin radiators designed for environments with much lower dynamic pressure = as being the way to go. Will it cool? sure it will (Cooling axiom 1 = above). Is it the lowest drag option for an aircraft of the RV/TailWind type, = I am convinced it is not. The diffuser makes a considerable amount of difference and can made = the difference between a system that cools adequately and one which does = not. The biggest culprit that lessens cooling effectiveness is turbulent = eddies that form inside the duct due to flow detachment from the walls. = These eddies in effect act to block effective airflow through part of the = core. So keeping the airflow attached to the sides of the diffusers is = crucial for good cooling from two standpoints. A good diffuser will reduce airflow velocity through the core which will reduces cooling drag. Pressure = across the core is increased which further enhances cooling. I have gone from a total of 48 sq inches opening (total) for my two GM = cores and that provided marginal cooling - down to 28 sq inches (total) with adequate cooling with an engine now producing more HP. Experimenting = with the diffuser shape made the difference. The K&W book (Chapter 12) really provided the insight to how and which diffuser shapes provided the better dynamic recovery. The Streamline = duct was shown to be able to provide up to 82% recovery of the dynamic = pressure. Some folks reading the chapter misinterpreted the chart to show only = 42% recovery where there chart was actually only showing the pressure = recovery contribution due to the duct walls and did not include the = contribution due to the core. On the same chart, an equation (which apparently gets = ignored) clearly shows that the TOTAL pressure recovery is 82%. I have taken the Streamline duct as a starting point, but since I do = not have the space to provide the 12-14" for a proper Streamline duct, I = did some "creative" things to try to insure that there was no separation = even though my walls diverge more rapidly than the Streamline duct. Won't = claim mine are as good as a Streamline, but they clearly are much better = than the previous design which basically just captured the air and forced it = through the cores. FWIW Ed Anderson RV-6A N494BW 275 Rotary Hours (Plugs Up) Matthews, NC eanderson@carolina.rr.com ----- Original Message ----- From: "Jerry Hey" = > To: "Rotary motors in aircraft" = > Sent: Sunday, April 03, 2005 9:27 AM Subject: [FlyRotary] Re: phase I flight restrictions was:N19VX flys > It was not long ago that "cooling" was the major issue. Now it = seems > that we have learned enough to make several different configurations > work. I can't lay my finger on what it is we have learned but my > recommendation is to use smaller radiators and EWPs. Jerry > > > >> Homepage: http://www.flyrotary.com/ >> Archive: = http://lancaironline.net/lists/flyrotary/List.html ------=_NextPart_000_006C_01C53848.22997410 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Excellent summary Ed, correlates with my experience as well.  = Only=20 exception I would take is in the following excerpt:
 
"A good diffuser will reduce = airflow
velocity=20 through the core which will reduces cooling drag.  Pressure = across
the=20 core is increased which further enhances cooling."
 
A good diffuser will reduce velocity but the reduction occurs IN = the=20 diffuser, not through the core.  As counter-intuitive as it may=20 sound,  the velocity through the core is HIGHER than it would have = been=20 without the diffuser's velocity decrease (and pressure increase).
 
Think about it this way,  How could velocity through the core = be=20 reduced by a pressure increase?  It isn't.  The velocity at = this point=20 (through the core) is increased.
 
This is the single most misunderstood detail in liquid cooled = engine=20 systems.
 
Tracy
 
 
Subject: [FlyRotary] Cooling -Learned a lot

Too right, Jerry

My  first 40 hours or so = were in=20 the marginal cooling zone. {:>).  As other
things in this = hobby,=20 there are so many variables that interact, that what
may appear = simply at=20 first, is almost always a bit more complex.  I
say(Cooling = Axiom 1) if=20 you have enough cooling surface area and air mass
flow then it WILL = cool.    However, you may incur a high penalty in=20 cooling
drag - which may not be as important for draggy airframes = (such as=20 biplanes)
as it is to sleeker airframes.   Also a system = that=20 adequately cools an
engine producing  150 HP may not cool an = engine=20 producing 180 HP.  Picking
your cooling design point is=20 important.  Optimizing for cruise and your will
be less than = optimum=20 for take and climb.  Optimize for climb and you will
probably = have=20 more cooling drag than required at cruise.  = Compromise,
compromise -=20 cowl flaps are sometimes used to try to have the best of=20 both
worlds.

Some folks advocate a thinner, larger surface = area core=20 -which is great for
slow moving automobiles stuck in traffic with = low=20 dynamic pressure
potential, but I think is not the optimum for most = aircraft.  Once you trip
the airflow and turn it turbulent you = have=20 incurred most of the drag
penalty.  Larger surface area cores = disrupt=20 a larger airstream and incur
more drag.  Yes, thicker cores = produce a=20 bit more drag than the SAME frontal
area thinner cores.  But, = with a=20 thicker core you can use a core with
smaller frontal = area.

 =20 The NASCAR radiator's average 3" thick and on the long tracks where=20 speeds
are higher some even go up to 7" thick.  My contention = is their=20 operating
environment is more akin to ours than regular automobiles = moving=20 at slower
speeds.  You know that the NASCAR folks will spend = $$ for=20 just a tiny
advantage - so clearly they don't use thick cores = because it is=20 a
disadvantage. But, some folks will continue to point to the large = thin
radiators designed for environments with much lower dynamic = pressure=20 as
being the way to go.  Will it cool? sure it will (Cooling = axiom 1=20 above).
Is it the lowest drag option for an aircraft of the = RV/TailWind=20 type, I am
convinced it is not.

The diffuser makes a = considerable=20 amount of difference and can made the
difference between a system = that=20 cools adequately and one which does not.
The biggest culprit that = lessens=20 cooling effectiveness is turbulent eddies
that form inside the duct = due to=20 flow detachment from the walls.  These
eddies in effect act to = block=20 effective airflow through part of the core.
So keeping the airflow = attached=20 to the sides of the diffusers is crucial for
good cooling from two=20 standpoints. A good diffuser will reduce airflow
velocity through = the core=20 which will reduces cooling drag.  Pressure across
the core is=20 increased which further enhances cooling.

I have gone from a = total of=20 48 sq inches opening (total) for my two GM cores
and that provided = marginal=20 cooling - down to 28 sq inches (total) with
adequate cooling with = an engine=20 now producing more HP.  Experimenting with
the diffuser shape = made the=20 difference.

The K&W book (Chapter 12) really provided the = insight=20 to how and which
diffuser shapes provided the better dynamic=20 recovery.  The Streamline duct
was shown to be able to provide = up to=20 82% recovery of the dynamic pressure.
Some folks reading the = chapter=20 misinterpreted the chart to show only 42%
recovery where there = chart was=20 actually only showing the pressure recovery
contribution due to the = duct=20 walls and did not include the contribution due
to the core.  = On the=20 same chart, an equation (which apparently gets ignored)
clearly = shows that=20 the TOTAL  pressure recovery is 82%.

I have taken the = Streamline=20 duct as a starting point, but since I do not
have the space to = provide the=20 12-14" for a proper Streamline duct, I did
some "creative" things = to try to=20 insure that there was no separation even
though my walls diverge = more=20 rapidly than the Streamline duct.  Won't claim
mine are as = good as a=20 Streamline, but they clearly are much better than the
previous = design which=20 basically just captured the air and forced it through
the=20 cores.

FWIW

Ed Anderson
RV-6A N494BW 275 Rotary Hours = (Plugs=20 Up)
Matthews, NC
eanderson@carolina.rr.com

-----=20 Original Message -----
From: "Jerry Hey" <jerryhey@earthlink.net>
= To:=20 "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent:=20 Sunday, April 03, 2005 9:27 AM
Subject: [FlyRotary] Re: phase I = flight=20 restrictions was:N19VX flys


> It was not long ago that = "cooling"=20 was the major issue.  Now it seems
> that we have learned = enough to=20 make several different configurations
> work.   I = can't lay my=20 finger on what it is we have learned but my
> recommendation is = to use=20 smaller radiators and EWPs.  =20 Jerry
>
>
>




>> =20 Homepage:  http://www.flyrotary.com/
>&= gt; =20 Archive:   http://lancai= ronline.net/lists/flyrotary/List.html
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