Return-Path: Received: from access.aic-fl.com ([204.49.76.2] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 853857 for flyrotary@lancaironline.net; Sun, 03 Apr 2005 22:51:37 -0400 Received-SPF: none receiver=logan.com; client-ip=204.49.76.2; envelope-from=unicorn@gdsys.net Received: from b9k4u9 (unverified [204.49.76.88]) by access.aic-fl.com (Rockliffe SMTPRA 4.5.6) with SMTP id for ; Sun, 3 Apr 2005 21:50:26 -0500 Message-ID: <003f01c538d2$1f9010f0$584c31cc@b9k4u9> From: "Richard Sohn" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Cooling -Learned a lot Date: Sun, 3 Apr 2005 21:52:31 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_003A_01C53897.6FD367F0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_003A_01C53897.6FD367F0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Let me add one more item to the diffuser function. When you have narrow = spaced fins on your radiator and the air velocity is high, the = turbulence on the surface of the radiator can block any flow of air = through the radiator. I ran into that problem when I first placed the = heater cores on my SOOB in the same way the Rotaxes place the radiator = on a 582. It did not work at all. I could not even fly the airplane. I = have 35% more fin area on the heater core than the Rotax rad. Than I = realized that the fin spacing on the Rotax is double from what it is on = the heater core. Subsequently, I build a diffuser with the result of = being able to fly the airplane. After a couple of changes, every thing = is working just fine.=20 Richard Sohn N-2071U ----- Original Message -----=20 From: Ed Anderson=20 To: Rotary motors in aircraft=20 Sent: Sunday, April 03, 2005 2:15 PM Subject: [FlyRotary] Re: Cooling -Learned a lot 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_003A_01C53897.6FD367F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Let me add one more item to the diffuser = function. When=20 you have narrow spaced fins on your radiator and the air velocity is = high, the=20 turbulence on the surface of the radiator can block any flow of air = through the=20 radiator. I ran into that problem when I first placed the heater cores = on my=20 SOOB in the same way the Rotaxes place the radiator on a 582. It did not = work at=20 all. I could not even fly the airplane. I have 35% more fin area on the = heater=20 core than the Rotax rad. Than I realized that the fin spacing on = the Rotax=20 is double from what it is on the heater core. Subsequently, I build a = diffuser=20 with the result of being able to fly the airplane. After a couple of = changes,=20 every thing is working just fine.
 
Richard Sohn
N-2071U
 
----- Original Message -----
From:=20 Ed=20 Anderson
Sent: Sunday, April 03, 2005 = 2:15=20 PM
Subject: [FlyRotary] Re: = Cooling -Learned=20 a lot

You are absolutely correct, = Tracy.
 
I did not make it clear but the diffuser does = the=20 velocity reduction and increases the pressure in front of the = core by=20 recovery of (some) dynamic pressure component of the air flow.  = This=20 higher pressure in front of the core then results in an increased = pressure=20 differential across  the core.  This increase in pressure=20 differential across the core, as you stated, actually speeds up the = air=20 flow through the core itself.
 
My apologies for being less than careful on = that=20 point.,
 
Ed A. 
----- Original Message -----
From:=20 Tracy = Crook
To: Rotary motors in = aircraft=20
Sent: Sunday, April 03, 2005 = 12:24=20 PM
Subject: [FlyRotary] Re: = Cooling=20 -Learned 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=20 across
the core is increased which further enhances=20 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 = 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=20 in the marginal cooling zone. {:>).  As other
things in = this=20 hobby, there are so many variables that interact, that what
may = appear=20 simply at first, is almost always a bit more complex. =20 I
say(Cooling Axiom 1) if you have enough cooling surface area = and air=20 mass
flow then it WILL cool.    However, you may = incur a=20 high penalty in cooling
drag - which may not be as important = for draggy=20 airframes (such as biplanes)
as it is to sleeker = airframes.  =20 Also a system that adequately cools an
engine producing  = 150 HP=20 may not cool an engine producing 180 HP.  Picking
your = cooling=20 design point is important.  Optimizing for cruise and your = will
be=20 less than optimum for take and climb.  Optimize for climb and = you=20 will
probably have more cooling drag than required at = cruise. =20 Compromise,
compromise - cowl flaps are sometimes used to try = to have=20 the best of both
worlds.

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

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

The=20 diffuser makes a considerable amount of difference and can made=20 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=20 of the diffusers is crucial for
good cooling from two = standpoints. A=20 good diffuser will reduce airflow
velocity through the core = which will=20 reduces cooling drag.  Pressure across
the core is = increased which=20 further enhances cooling.

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

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

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

FWIW

Ed=20 Anderson
RV-6A N494BW 275 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=20 "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=20 EWPs.  =20 Jerry
>
>
>




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