Return-Path: Sender: "Marvin Kaye" To: lml@lancaironline.net Date: Thu, 21 Oct 2004 09:18:02 -0400 Message-ID: X-Original-Return-Path: Received: from imo-m15.mx.aol.com ([64.12.138.205] verified) by logan.com (CommuniGate Pro SMTP 4.2.5) with ESMTP id 481458 for lml@lancaironline.net; Thu, 21 Oct 2004 09:11:47 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.138.205; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-m15.mx.aol.com (mail_out_v37_r3.8.) id q.191.310fffda (4214) for ; Thu, 21 Oct 2004 09:11:13 -0400 (EDT) From: Sky2high@aol.com X-Original-Message-ID: <191.310fffda.2ea90f6d@aol.com> X-Original-Date: Thu, 21 Oct 2004 09:11:09 EDT Subject: Re: [LML] Re: Keeping Ada Cooling Cool - Plenums X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1098364269" X-Mailer: 9.0 for Windows sub 5000 -------------------------------1098364269 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Chris, I saw your plenum setup when we were both at ADA and I was impressed - especially with the preliminary data you had collected. Most importantly, I liked the gentle sloped and long (about 10"?) diffusers into the "chamber" in front of the cylinders and one other feature that is very important. Your cowl rework matches the only really successful plenums I have seen - that is, the cooling air inlets are built into the lower cowling so that the inlets can be efficiently connected to the plenum (See Lee Behel's Legacy if you get a chance), thus the removal of the plenum top is easy for access to the engine and the top cowl is "merely" for fuselage aerodynamics. On our Lancairs, pressurizing the upper cowling at 180 Kts IAS tends to puff it out and this may alter the airflow over the cowl, including early separation - the plenum may eliminate this as a drag issue. Nice work! Scott Krueger AKA Grayhawk N92EX IO320 Aurora, IL (KARR) Some Assembly Required Using Common Hand Tools and some heavy breathing. In a message dated 10/21/2004 1:21:33 AM Central Standard Time, Christopher.Zavatson@udlp.com writes: I actually did consider using the cowl as the plenum top. There were two issues. The first was how to transition the top of the diffusers to the cowl without creating a step that would cause flow separation given sealing and engine movement considerations. The second issue was controlling leakage in a conventional baffle system. NASA did a study pertaining to the cooling of horizontally opposed aircraft engines that produced some very enlightening data. They took an Aztec engine installation and found 55% of the air entering the inlets was being lost to leakage. 38% was attributed to the flexible baffle seals and the rest was traced down to various sheet metal to engine interfaces. A hardtop plenum and RTV got things sealed up. Accepting a method of sealing that is so inherently lossy is not an issue if you have an oversized cooling system. I was going in the opposite direction by reducing inlet and exit areas. System efficiency was now of greater importance and so I did not want to go down the path of accepting a sealing method that has been shown to have a very high leak potential. Do leaks really have an impact? If you are already losing half your cooling air, you could probably drill a few more holes in the baffling and not see a difference in cooling. On my first flight with the plenum, I actually had a leak. One of the SCAT ducts was not pushed up onto the diffuser quite far enough. There was no visible gap, but the internal spiral wire was not entirely up on the diffuser so there was a short section of unsupported silicone creating the seal. You could just barely squeeze a finger between the diffuser and the SCAT duct in that area. On that first flight, the cylinder closest to that leak ran 20 degrees hotter. Do leaks really make a difference? In this case it did. While a conventional baffle systems will work ( I used one for 6 years), it is, IMHO, much easier to achieve a well sealed and efficient system with an enclosed upper plenum. The benefits of this efficiency become more apparent, the faster we want to fly. -------------------------------1098364269 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Chris,
 
I saw your plenum setup when we were both at ADA and I was impressed -=20 especially with the preliminary data you had collected.  Most important= ly,=20 I liked the gentle sloped and long (about 10"?) diffusers into the "chamber"= in=20 front of the cylinders and one other feature that is very important.  Y= our=20 cowl rework matches the only really successful plenums I have seen - that is= ,=20 the cooling air inlets are built into the lower cowling so that the inlets c= an=20 be efficiently connected to the plenum (See Lee Behel's Legacy if you get a=20 chance), thus the removal of the plenum top is easy for access to the engine= and=20 the top cowl is "merely" for fuselage aerodynamics.  On our=20 Lancairs, pressurizing the upper cowling at 180 Kts IAS tends to puff i= t=20 out and this may alter the airflow over the cowl, including early separation= -=20 the plenum may eliminate this as a drag issue.
 
Nice work!
 
Scott Krueger=20 AKA Grayhawk
N92EX IO320 Aurora, IL (KARR)

Some Assembly Required=20
Using Common Hand Tools
and some heavy breathing.
 
 
In a message dated 10/21/2004 1:21:33 AM Central Standard Time,=20 Christopher.Zavatson@udlp.com writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>I=20 actually did consider using the cowl as the plenum top.  There=20 were
two issues.  The first was how to transition the top of the=20 diffusers to
the cowl without creating a step that would cause flow&nbs= p;=20 separation given
sealing and engine movement considerations. 
= The=20 second issue was controlling leakage in a conventional baffle
system.&n= bsp;=20 NASA did a study pertaining to the cooling of horizontally
opposed airc= raft=20 engines that produced some very enlightening data.
They took an Aztec=20 engine installation and found 55% of the air entering
the inlets was be= ing=20 lost to leakage.  38% was attributed to the
flexible baffle seals=20= and=20 the rest was traced down to various sheet
metal to engine interfaces.&n= bsp;=20 A hardtop plenum and RTV got things sealed
up.  Accepting a method= of=20 sealing that is so inherently lossy is not an
issue if you have an=20 oversized cooling system.  I was going in the
opposite direction b= y=20 reducing inlet and exit areas.    System
efficiency was now o= f=20 greater importance and so I did not want to go
down the path of accepti= ng a=20 sealing method that has been shown to have
a very high leak=20 potential.  Do leaks really have an impact?  If you are
alrea= dy=20 losing half your cooling air, you could probably drill a few
more holes= in=20 the baffling and not see a difference in cooling.  On my
first fli= ght=20 with the plenum, I actually had a leak.  One of the SCAT
ducts was= not=20 pushed up onto the diffuser quite far enough.  There was
no visibl= e=20 gap, but the internal spiral wire was not entirely up on the
diffuser s= o=20 there was a short section of unsupported silicone creating
the seal.&nb= sp;=20 You could just barely squeeze a finger between the diffuser
and the SCA= T=20 duct in that area.  On that first flight, the cylinder
closest to=20= that=20 leak ran 20 degrees hotter.     Do leaks really make=20 a
difference?  In this case it did. 
While a conventional= =20 baffle systems will work ( I used one for 6
years), it is, IMHO, much=20 easier to achieve a well sealed and efficient
system with an enclosed u= pper=20 plenum.  The benefits of this efficiency
become more apparent, the= =20 faster we want to fly.

 
 
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