Return-Path: Received: from mail23.syd.optusnet.com.au ([211.29.133.164] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP-TLS id 855193 for flyrotary@lancaironline.net; Tue, 05 Apr 2005 01:48:46 -0400 Received-SPF: none receiver=logan.com; client-ip=211.29.133.164; envelope-from=lendich@optusnet.com.au Received: from george (d211-31-76-250.dsl.nsw.optusnet.com.au [211.31.76.250]) by mail23.syd.optusnet.com.au (8.12.11/8.12.11) with SMTP id j355lqa0013422 for ; Tue, 5 Apr 2005 15:47:54 +1000 Message-ID: <002801c539a3$80c16e60$fa4c1fd3@george> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: A lot to learn Date: Tue, 5 Apr 2005 15:51:23 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0025_01C539F7.517785A0" 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 This is a multi-part message in MIME format. ------=_NextPart_000_0025_01C539F7.517785A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ed, Thanks for that info. I understand what your saying about necking down keeping the pressure = high - very interesting!! A very well thought out observation on your part - I do believe your = right about flow separation causing eddies which blanket the radiator. I appreciate your comments. George (down under) George, you are undoubtedly correct about necking it down causes a = restriction to air flow. Also, there is no doubt in my mind that if you = have the space to implement a full length duct of the correct profile = you will get better results. However, for the Streamline duct that = takes about 14-16" of space to run a proper pressure recovery duct, I = had less than 6". So what to do? My reading indicated that the thing that causes the most severe = disruption to good cooling (assume everything else is adequate) is the = separation of airflow from the interior duct walls. This causes eddies = to form which block/hinder airflow through the part of the core they are = in front of just like a piece of cardboard would. From what I think I understood of the information on diffusers, it is = clear that there is a "dome" of higher pressure air that forms in front = of the core due to conversion of the dynamic component of the airstream = to some pressure increase by the core and/or diffuser. It actually = forms to some extend whether you have a diffuser or not - due to = something I think they refer to as external diffusion. This is simply = the conversion of airstream energy (velocity) into pressure by molecules = of air meeting the resistance of the core and other molecules which slow = down in front of the core. The Streamline diffuser duct describe in K&W chapter 12 makes use of = this higher pressure region to keep the airflow along the duct walls = from separating (or at least separating very late just before the core = which means if an eddy does form, it is much smaller and has less = disruptive effect). But, that is using the 16" to gradually recovery = the dynamic pressure with minimum loss. Which if done correct will give = you around 82% pressure recovery (theoretically) according to K&W - = good if it even approaches that figure in any case. Since I did not have that 16" to play with but only 6" (actually even = less), I was faced with "what to do?" I decided that if I made the = duct wall curve more drastically than the Streamline duct wall due to = the short distance, I was surely looking at airflow separation. But, I = decided that if I made the duct walls "pitch" in even further into the = higher pressure region that would help - but then (as you stated, = George) you start to affect the airflow which causes the higher pressure = dome in front of the core in the first place. What to do? I decided = (rightly or wrongly) that if I increased the velocity of the air by = necking it down, then even if the mass airflow were slightly less than = ideal, that the conversion of the higher velocity air to pressure (the = old 1/2pV^2 component) would compensate by keeping the pressure high and = this in turn keeping my airflow from separating from my radically = curving walls until too late to do much disruption of the airflow = through the core. There were those who claimed that there was no way that would work. = Well, I reduced my inlet area from 48 sq inch to 28 and it works just = fine thank you. Tracy Crook can vouch that I have flown with the small = openings for well over a year and he has never seen steam or smoke = coming from my engine - yet {:>). Seriously, my analysis could be all wet, but so long as the ducts = cool, I'll stick with it. My previous ducts were simply openings which captured air. Photo = attached. This shows the inside of two ducts, the one on the left show = the original duct shape which simply has an inlet opening into a more or = less box. The one on the right shows my first attempt to see if my = theory would work. The opening of the duct on the right is 9 square = inches and it is placed on my left radiator which is my hot radiator = (first one in the series of two). The opening of the duct on left is = original 24 square inches. After successfully flying with this pair. I = was satisfied enough to build two new ducts. The one on the left = radiator is now 18 sq inches inlet and the one on the right 10 sq inches = for a total of 28 sq inches. So a reduction of inlet area from 48 sq = inches to 28 sq inches and it cools just fine as far as I am concerned. = In a hotter climate I would probably enlarge the total area slightly. = But, in any case, it proved (to me at least) that preventing/delaying = airflow separation was the crucial factor. I am certain my ducts are = not as efficient as a full up Streamline duct, but given the space I had = to work with I think my approach has worked well. Hope I answered your question, yes, it appears counterintuitive, but I = had a rationale for doing it. Whether the rational was correct or there = is some other factor I am not even aware of - I certainly don't know. I = didn't even sleep at the Holiday inn last night. Best Regards Ed ----- Original Message -----=20 From: George Lendich=20 To: Rotary motors in aircraft=20 Sent: Monday, April 04, 2005 6:14 PM Subject: [FlyRotary] Re: A lot to learn Ed, I thought necking-down like you have done would cause more of a = restriction and would result in less pressure. I thought that a more direct line of travel from the opening to the = core would give less restriction and more pressure. From what I've been told, this particular design seems to want to = follow the trumpet ( bell) shaped opening style, whereby 1.5 times the = face of the radiator, is required in the length of the duct. I don't = think 6" is enough length. What other styles of duct have you tried which are less successful = than this design. I must say it does look good but seems to fly in the face of other = previous recommendations. George ( down under) -------------------------------------------------------------------------= - >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html -------------------------------------------------------------------------= ----- >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html ------=_NextPart_000_0025_01C539F7.517785A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ed,
Thanks for that info.
I understand what your saying about = necking down=20 keeping the pressure high - very interesting!!
A very well thought out observation on = your part -=20 I do believe your right about flow separation causing eddies which = blanket the=20 radiator.
I appreciate your = comments.
George (down under)
George, you are undoubtedly correct = about necking=20 it down causes a restriction to air flow. Also, there is no doubt = in=20 my mind that if you have the space to implement a full = length duct=20 of the correct profile you will get  better results.  = However, for=20 the Streamline duct that takes about 14-16" of space to run a proper = pressure=20 recovery duct, I had less than  6".  So what to=20 do?
 
My  reading  indicated = that the=20 thing that causes the most severe disruption to good cooling (assume=20 everything else is adequate) is the separation of airflow from the = interior=20 duct walls.  This causes eddies to form which block/hinder = airflow=20 through the part of the core they are in front of just like a piece of = cardboard would.
 
From what I think I understood of the = information=20 on diffusers, it is clear that there is a "dome" of higher pressure = air that=20 forms in front of the core due to conversion of the dynamic component = of the=20 airstream to some pressure increase by the core and/or diffuser.  = It=20 actually forms to some extend whether you have a diffuser or not - due = to=20 something I think they refer to as external diffusion.  This is = simply=20 the conversion of airstream energy (velocity) into pressure by = molecules of=20 air meeting the resistance of the core and other molecules which slow = down in=20 front of the core.
 
The Streamline diffuser duct describe = in K&W=20 chapter 12 makes use of this higher pressure region to keep the = airflow along=20 the duct walls from separating (or at least separating very late just = before=20 the core which means if an eddy does form, it is much smaller and has = less=20 disruptive effect).   But, that is using the 16" to = gradually=20 recovery the dynamic pressure with minimum loss.  Which if done = correct=20 will give you around 82% pressure recovery (theoretically) according = to=20 K&W -  good if it even approaches that figure in any=20 case.
 
Since I did not have that 16" to play = with but=20 only 6" (actually even less), I was faced with "what to do?"   I = decided=20 that if I made the duct wall curve more drastically than the = Streamline duct=20 wall due to the short distance, I was surely looking at airflow=20 separation. But, I decided that if I made the duct walls "pitch" = in even=20 further into the higher pressure region that would help - but then (as = you=20 stated, George) you start to affect the airflow which causes the = higher=20 pressure dome in front of the core in the first place.    = What to=20 do?  I decided (rightly or wrongly) that if I increased the = velocity of=20 the air by necking it down, then even if the mass airflow were = slightly less=20 than ideal,  that the conversion of the higher velocity air to = pressure=20 (the old 1/2pV^2 component) would compensate by keeping the = pressure high=20 and this in turn keeping my airflow from separating from my radically = curving=20 walls until too late to do much disruption of the airflow through the=20 core.
 
There were those who claimed that = there was no=20 way that would work.  Well, I reduced my inlet area from 48 sq = inch to 28=20 and it works just fine thank you.  Tracy Crook can vouch that I = have=20 flown with the small openings for well over a year and he has never = seen steam=20 or smoke coming from my engine - yet {:>).
 
Seriously, my analysis could be all = wet, but so=20 long as the ducts cool, I'll stick with it.
 
My previous ducts were simply = openings which=20 captured air.  Photo attached.  This shows the inside of two = ducts,=20 the one on the left show the original duct shape which simply has = an=20 inlet opening into a more or less box.  The one on the right = shows my=20 first attempt to see if my theory would work.  The opening of the = duct on=20 the right is 9 square inches and it is placed on my left radiator = which is my=20 hot radiator (first one in the series of two).  The opening of = the duct=20 on left is original 24 square inches.  After successfully flying = with=20 this pair.  I was satisfied enough to build two new ducts.  = The one=20 on the left radiator is now 18 sq inches inlet and the one on the = right 10 sq=20 inches for a total of 28 sq inches.  So a reduction of inlet area = from 48=20 sq inches to 28 sq inches and it cools just fine as far as I am=20 concerned.  In a hotter climate I would probably enlarge the = total area=20 slightly.  But, in any case, it proved (to me at least) that=20 preventing/delaying  airflow  separation was the crucial=20 factor.  I am certain my ducts are not as efficient as a full up=20 Streamline duct, but given the space I had to work with I think my = approach=20 has worked well.
 
Hope I answered your question, yes, = it appears=20 counterintuitive, but I had a rationale for doing it.  Whether = the=20 rational was correct or there is some other factor I am not even aware = of - I=20 certainly don't know.  I didn't even sleep at the Holiday inn = last=20 night.
 
Best Regards
 
Ed
----- Original Message -----
From:=20 George Lendich
To: Rotary motors in = aircraft=20
Sent: Monday, April 04, 2005 = 6:14=20 PM
Subject: [FlyRotary] Re: A = lot to=20 learn

Ed,
I thought necking-down like you = have done would=20 cause more of a restriction and would result in less = pressure.
I thought that a more direct line = of travel=20 from the opening to the core would give less restriction and more=20 pressure.
 
From what I've been told, this = particular=20 design seems to want to follow the trumpet ( bell) shaped opening=20 style, whereby 1.5 times the face of the radiator, is required = in the=20 length of the duct. I don't think 6" is enough length.
 
What other styles of duct have you = tried which=20 are less successful than this design.
 
I must say it does look good but = seems to fly=20 in the face of other = previous recommendations.
George ( down under)
 

>>  Homepage: =20 http://www.flyrotary.com/
>>  Archive:  =20 = http://lancaironline.net/lists/flyrotary/List.html

>>  Homepage: =20 http://www.flyrotary.com/
>>  Archive:  =20 = http://lancaironline.net/lists/flyrotary/List.html
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