X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 10 [X] Return-Path: Received: from bay0-omc2-s41.bay0.hotmail.com ([65.54.246.177] verified) by logan.com (CommuniGate Pro SMTP 5.1.4) with ESMTP id 1735750 for flyrotary@lancaironline.net; Thu, 04 Jan 2007 13:50:10 -0500 Received-SPF: pass receiver=logan.com; client-ip=65.54.246.177; envelope-from=lors01@msn.com Received: from hotmail.com ([65.54.250.83]) by bay0-omc2-s41.bay0.hotmail.com with Microsoft SMTPSVC(6.0.3790.2668); Thu, 4 Jan 2007 10:49:21 -0800 Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Thu, 4 Jan 2007 10:49:21 -0800 Message-ID: Received: from 4.171.174.58 by BAY115-DAV11.phx.gbl with DAV; Thu, 04 Jan 2007 18:49:20 +0000 X-Originating-IP: [4.171.174.58] X-Originating-Email: [lors01@msn.com] X-Sender: lors01@msn.com From: "Tracy Crook" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Ideal cooling Date: Thu, 4 Jan 2007 13:49:13 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0057_01C73007.1E958C10" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: MSN 9 X-MimeOLE: Produced By MSN MimeOLE V9.50.0034.2000 Seal-Send-Time: Thu, 4 Jan 2007 13:49:13 -0500 X-OriginalArrivalTime: 04 Jan 2007 18:49:21.0915 (UTC) FILETIME=[0C2CECB0:01C73031] Return-Path: lors01@msn.com This is a multi-part message in MIME format. ------=_NextPart_000_0057_01C73007.1E958C10 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Monty wrote: Now for the optimum part: The absolute best possible performance would be a system that used = just enough air Mdot to heat the cooling air to the same temperature as = the water radiator exit temp ( water going back to the engine from the = radiator). This condition is impossible to achieve in practice. So you = try to get as close as you can. How close you get is called the heat = exchanger effectiveness. The closer the air and water exit temps are, = the better the effectiveness. Monty: I'll respectfully disagree on this part. It may apply if you have = unlimited dynamic pressure to work with, because it doesn't consider = radiator thickness and air-side pressure drop. We don't have this case Al=20 Have to vote for Monty's position on this one. His statement (I = assume intentionally) did not specifically get into radiator thickness, = dynamic pressure, etc because he was trying to get down to the basic = principal involved. In this he is correct (IMO). All these other = factors are just that, factors. They do not change the basic principal. = Limited dynamic pressure only means that the radiator has to be = designed to work with what is available. The goal remains the same. Dynamic pressure data was available from the EM2 data log that I = posted but I had to eliminate it and many others for the sake of = readability. In this case, dynamic pressure on the left rad inlet was = slightly higher than the full amount available at the current airspeed = (I am assuming this is due to the benefit of prop blast into the inlet). = Note: Dynamic pressure is not a standard feature of the EM2, mine is a = custom job. You can use the TAS readout for this function though. You = just have to reverse the calculation from pressure to airspeed or get a = conversion chart. Really finding the discussion on the EM2 data interesting. As is = obvious, interpretation of the data is as important as the data itself. = And Rusty was right, having this capability is a two edged sword, you = can spend unlimited time analyzing data and trying to optimize various = things. Identifying the "low hanging fruit" is absolutely key if you = are to do anything other that tweak on the airplane. When Paul Lamar = came here and we did a bunch of in-flight pressure measurements, a lot = of important things came to light but we disagreed completely on what = they meant and how to address them. (discussion on 'Cooling Study' on = my website describes that effort). Paul has done a lot to perpetuate the idea that my cooling system is = "marginal at best". I still can't figure out where he gets this from. = You do not fly an aircraft for 12 years and 1600+ hours in Florida, fly = it to the desert southwest over 10,000+ foot mountains and win air races = with a "marginal" cooling system. Much has been made of the 'spray bar' = cooling system I used when racing. Anyone familiar with air racing = knows this is common practice. It is not necessary for normal operation = and if you installed a cooling system that you could race without the = spraybar, your top speed and MPG would suffer significantly. I wish = those who have criticized the spraybar setup would enter a race like the = Sun 100 and show me how to do it right! Monty is also correct about the need for studying steady state = conditions. You need to do that and the transient stuff to get the = whole picture. I posted a transient snapshot because it illustrated a = few points I was interested in and the fact that a bunch of straight = lines on a graph are much less visually interesting. Tracy ------=_NextPart_000_0057_01C73007.1E958C10 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Monty wrote:

Now for the optimum=20 part:

 

The absolute best = possible=20 performance would be a system that used just enough = air Mdot to=20 heat the cooling air to the same temperature as = the water=20 radiator exit temp ( water going back to the engine from the = radiator). This=20 condition is impossible to achieve in practice. So you try to get as = close as=20 you can. How close you get is called the heat exchanger effectiveness. = The=20 closer the air and water exit temps are, the better the=20 effectiveness.

 

Monty:

I=92ll = respectfully=20 disagree on this part.  It may apply if you have unlimited = dynamic=20 pressure to work with, because it doesn=92t consider radiator = thickness and=20 air-side pressure drop.  We don=92t have this = case

 

Al=20

 

Have to = vote for=20 Monty's position on this one.  His statement (I assume=20 intentionally) did not specifically get into radiator thickness, = dynamic=20 pressure, etc because he was trying to get down to the basic principal = involved.  In this he is correct (IMO).  All these other = factors are=20 just that, factors.  They do not change the basic = principal. =20 Limited dynamic pressure only means that the radiator has to be = designed to=20 work with what is available.  The goal remains the=20 same.

 

Dynamic = pressure=20 data was available from the EM2 data log that I posted but I had to = eliminate=20 it and many others for the sake of readability.  In this case, = dynamic=20 pressure on the left rad inlet was slightly higher than = the full=20 amount available at the current airspeed (I am assuming this is = due to=20 the benefit of prop blast into the inlet).  = Note:  Dynamic=20 pressure is not a standard feature of the EM2, mine is a custom=20 job.  You can use the TAS readout for this function though.  = You=20 just have to reverse the calculation from pressure to airspeed or get = a=20 conversion chart.

 

Really = finding the=20 discussion on the EM2 data interesting.  As is obvious, = interpretation of=20 the data is as important as the data itself.  And Rusty was = right, having=20 this capability is a two edged sword, you can spend unlimited time = analyzing=20 data and trying to optimize various things.  Identifying =  the "low=20 hanging fruit"  is absolutely key if you are to do anything other = that=20 tweak on the airplane.  When Paul Lamar came here and we did a = bunch of=20 in-flight pressure measurements, a lot of important things came to = light but=20 we disagreed completely on what they meant and how to address = them. =20 (discussion on 'Cooling Study' on my website describes that=20 effort).

 

Paul has = done a lot=20 to perpetuate the idea that my cooling system is "marginal at = best".  I=20 still can't figure out where he gets this from.  You do not fly = an=20 aircraft for 12 years and 1600+ hours in Florida, fly it to the desert = southwest over 10,000+ foot mountains and win air races with a = "marginal"=20 cooling system.  Much has been made of the 'spray bar' cooling = system I=20 used when racing.  Anyone familiar with air racing knows this is = common=20 practice.  It is not necessary for normal operation and if you = installed=20 a cooling system that you could race without the spraybar, your top = speed and=20 MPG would suffer significantly.  I wish those who have criticized = the=20 spraybar setup would enter a race like the Sun 100 and show = me how=20 to do it right!

 

Monty is = also=20 correct about the need for studying steady state conditions.  You = need to=20 do that and the transient stuff to get the whole picture.  I = posted a=20 transient snapshot because it illustrated a few points I was = interested in and=20 the fact that a bunch of straight lines on a graph are much less = visually=20 interesting.

 

Tracy

 

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