Return-Path: Received: from mtiwmhc11.worldnet.att.net ([204.127.131.115] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 853306 for flyrotary@lancaironline.net; Sun, 03 Apr 2005 10:22:33 -0400 Received-SPF: none receiver=logan.com; client-ip=204.127.131.115; envelope-from=keltro@att.net Received: from 204.127.135.41 ([204.127.135.41]) by worldnet.att.net (mtiwmhc11) with SMTP id <20050403142141111000dbq7e>; Sun, 3 Apr 2005 14:21:46 +0000 Received: from [209.247.222.98] by 204.127.135.41; Sun, 03 Apr 2005 14:21:42 +0000 From: keltro@att.net (Kelly Troyer) To: "Rotary motors in aircraft" Subject: Re: [FlyRotary] Cooling -Learned a lot Date: Sun, 03 Apr 2005 14:21:42 +0000 Message-Id: <040320051421.17377.424FFBF5000DEA93000043E12158766720019D9B040A05@att.net> X-Mailer: AT&T Message Center Version 1 (Feb 14 2005) X-Authenticated-Sender: a2VsdHJvQGF0dC5uZXQ= MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="NextPart_Webmail_9m3u9jl4l_17377_1112538102_0" --NextPart_Webmail_9m3u9jl4l_17377_1112538102_0 Content-Type: text/plain Content-Transfer-Encoding: 8bit So spoken by a man who has been there !! Great report Ed !! -- Kelly Troyer Dyke Delta/13B/RD1C/EC2 -------------- Original message from "Ed Anderson" : -------------- > 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" > > > > 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 --NextPart_Webmail_9m3u9jl4l_17377_1112538102_0 Content-Type: text/html Content-Transfer-Encoding: 8bit
So spoken by a man who has been there !! Great report Ed !!
--
Kelly Troyer
Dyke Delta/13B/RD1C/EC2
-------------- Original message from "Ed Anderson" <eanderson@carolina.rr.com>: --------------


> 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"
>
>
> > 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
--NextPart_Webmail_9m3u9jl4l_17377_1112538102_0--