Return-Path: Received: from [24.25.9.102] (HELO ms-smtp-03-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 853620 for flyrotary@lancaironline.net; Sun, 03 Apr 2005 17:15:40 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.102; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-185-127.carolina.res.rr.com [24.74.185.127]) by ms-smtp-03-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id j33LEpY5021407 for ; Sun, 3 Apr 2005 17:14:52 -0400 (EDT) Message-ID: <001b01c53892$34ae5c70$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Cooling -Learned a lot Date: Sun, 3 Apr 2005 17:15:04 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0018_01C53870.AD5EC910" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0018_01C53870.AD5EC910 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable You are absolutely correct, Tracy. I did not make it clear but the diffuser does the velocity reduction and = increases the pressure in front of the core by recovery of (some) = dynamic pressure component of the air flow. This higher pressure in = front of the core then results in an increased pressure differential = across the core. This increase in pressure differential across the = core, as you stated, actually speeds up the air flow through the core = itself. My apologies for being less than careful on that point., Ed A. =20 ----- Original Message -----=20 From: Tracy Crook=20 To: Rotary motors in aircraft=20 Sent: Sunday, April 03, 2005 12:24 PM Subject: [FlyRotary] Re: Cooling -Learned a lot 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_0018_01C53870.AD5EC910 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
You are absolutely correct, Tracy.
 
I did not make it clear but the diffuser does = the velocity=20 reduction and increases the pressure in front of the core by = recovery of=20 (some) dynamic pressure component of the air flow.  This higher = pressure in=20 front of the core then results in an increased pressure differential = across=20  the core.  This increase in pressure differential across the = core, as=20 you stated, actually speeds up the air flow through the core=20 itself.
 
My apologies for being less than careful on that = point.,
 
Ed A. 
----- Original Message -----
From:=20 Tracy = Crook
Sent: Sunday, April 03, 2005 = 12:24=20 PM
Subject: [FlyRotary] Re: = Cooling -Learned=20 a lot

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=20 point (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)=20 if you have enough cooling surface area and air mass
flow then it = WILL=20 cool.    However, you may incur a high penalty in=20 cooling
drag - which may not be as important for draggy airframes = (such=20 as biplanes)
as it is to sleeker airframes.   Also a = system=20 that adequately cools an
engine producing  150 HP may not = cool an=20 engine 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=20 core -which is great for
slow moving automobiles stuck in traffic = with=20 low dynamic pressure
potential, but I think is not the optimum = for most=20 aircraft.  Once you trip
the airflow and turn it turbulent = you have=20 incurred most of the drag
penalty.  Larger surface area = cores=20 disrupt a larger airstream and incur
more drag.  Yes, = thicker cores=20 produce a bit more drag than the SAME frontal
area thinner = cores. =20 But, with a thicker core you can use a core with
smaller frontal=20 area.

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

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

I have gone from a total of 48 sq inches = opening=20 (total) for my two GM cores
and that provided marginal cooling - = down to=20 28 sq inches (total) with
adequate cooling with an engine now = producing=20 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=20 that the TOTAL  pressure recovery is 82%.

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

FWIW

Ed Anderson
RV-6A N494BW = 275=20 Rotary Hours (Plugs 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" was the major issue.  Now it seems
> that we = have=20 learned enough to make several different configurations
>=20 work.   I can't lay my finger on what it is we have = learned but=20 my
> recommendation is to use 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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