Return-Path: Received: from out009.verizon.net ([206.46.170.131] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2954328 for flyrotary@lancaironline.net; Wed, 28 Jan 2004 22:12:19 -0500 Received: from netzero.net ([4.12.145.173]) by out009.verizon.net (InterMail vM.5.01.06.06 201-253-122-130-106-20030910) with ESMTP id <20040129031218.HBGX11926.out009.verizon.net@netzero.net> for ; Wed, 28 Jan 2004 21:12:18 -0600 Message-ID: <40187A12.1080402@netzero.net> Date: Wed, 28 Jan 2004 22:12:18 -0500 From: Finn Lassen User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax; PROMO) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: Streamline Ducts References: In-Reply-To: Content-Type: multipart/alternative; boundary="------------040304030808030501010204" X-Authentication-Info: Submitted using SMTP AUTH at out009.verizon.net from [4.12.145.173] at Wed, 28 Jan 2004 21:12:18 -0600 This is a multi-part message in MIME format. --------------040304030808030501010204 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit I found that going from a bell shape curve to a straight wedge to my oil cooler the oil temps dropped somewhat. If I understand it correctly, the 7.5 degree max rule is to ensure that the airflow stay attached to the duct walls (no turbulence). According to Bernie Kerr's experiments, that is true for an open duct (e.g. a wind tunnel). However, as soon as you put a restriction in there (a screen or a radiator) that rule no longer holds true and you can have a much steeper angle with the flow still staying attached. He observed this by tufting the walls of a test duct. An experiment anybody could do. Shamelessly copied from http://www.rotaryaviation.com/bernie_kerr.htm (see pictures there): Despite admonitions from some people, that it will not work ( i.e. all the air will try to come out the rear), the air is coming out uniformly or actually a little more at the front. This is a very low velocity test, but I am happy with the results. May try to turn the fan power to the wind tunnel up some with the pulley ratios or a larger hp motor. The other thing that I flight tested was a couple of static pressures in my inlet rings on the 6A. They were located a couple of inches into the the ring, one at the top and one at the bottom. Interesting how close to plenum pressure they both are. This indicates to me that the velocity thru the ring is very low, ie all the diffusing is taking place outside and infront of the ring. The other thing was that the bottom static was higher than the top one indicating that the prop is really swirling the air. I think you really should aim one ring up and the other down to capture the best pressure and flow. Brumwell really hammered me that the prop wash (swirl) is what caused both Ed and Finn to have their large roll excursions taking off behind another plane and that it was not wing vortices. The pics are the tunnel flowing with yarn tell-tells on the radiator at 3 locations along its length. (Written by Bernie Kerr 11/1/02) Finn Ed Anderson wrote: >Hi Ken, > > Good questions and no, I have not attempted to measure the air velocity >throught the ducts. Keep in mind that as long as there is sufficient air >mass flow through the radiator, it WILL cool at 0.1 to 0.4 and higher >ratios of duct velocity to airstream velocity. So adequate cooling is not >necessarily the only criteria for an "optimum" cooling system. > >The only problem is at the higher velocities through the core, you have a >lot more cooling drag. So you can get "good" cooling even with an less than >optimum cooling setup - BUT, you won't get the minimum weight or cooling >drag possible. Air mass flow is the key, if you don't have sufficient then >you will not cool. Low velocity is important as that results in less cooling >drag. > > Since we are basically talking about a constant air density situation at >our speeds, then consider an air mass that flows at 0.1 V through a radiator >of size X and provides adequate cooling. But, radiator of size X is too >large for your installation. If you reduce the size of the radiator then >the airflow at velocity 0.1 simply provides too little air mass flow to >conduct away the heat. BUT, if you increase the velocity through the >smaller radiator thereby increasing airmass flow to the point it carries >away adequate BTU for cooling, then you may find the velocity required >through the duct to be say 0.3. While that WILL increase the cooling drag >over the original size X radiator, at least in this example you will cool >and you have a radiator that fits your constraints. Cooling drag appears to >increase proprotional to area of the core but to the square of the air >velocity throught it. Larger radiators incure more frontal area >resistance - but, since they permit (but you have to make it so via good >ducting) a lower air velocity, the less drag due to the lower velocity more >than offsets the frontal drag of the larger frontal area. > >The worst cooling drag situation would appear to be a large radiator with >HIGH air velocity through the core. There you would have great cooling but >also very high cooling drag. So it would appear that it becomes even more >important to get good ducting and diffuser action (lower velocity) with a >larger frontal area radiator than perhaps with a smaller radiator. Just my >opinion. > > I have not studied the wedge shape duct so can't really comment on it. >But, again I see no reason why it would not cool - so long as there is >adequate air mass flow - it will cool. Whether you get the minimum possible >cooling drag with it, I simply do not know. I would presume it has some >merit - perhaps simplicity of ducting and installation in certain >configurations. Someone else may know of a source on Wedged Ducts >information - if so, I would like to know. > >Ed > > >Ed Anderson >RV-6A N494BW Rotary Powered >Matthews, NC >----- Original Message ----- >From: >To: "Rotary motors in aircraft" >Sent: Wednesday, January 28, 2004 6:01 PM >Subject: [FlyRotary] Streamline Ducts > > > > >>Hi Ed, >>Thanks for sharing your approach and Neal's response. Sometimes we seem >> >> >to forget that what we are trying to do is to convert the speed of the air >to PRESSURE. Your approach seems to be working well. Have you ever >measured the speed of the air moving though the radiator (where slower is >better)? I understand that this type of diffuser should reduce the speed of >the air to somewhere between .1 to .4 of the freestream velocity, so I >wonder how well your modified ducts work (I bet pretty well). Also, do you >know happen to know how well the wedge type duct (for radiators under the >engine) recover pressure? Should the wedge ducts also reduce the speed of >the air to somewhere between .1 to .4 of the freestream velocity or they >inherently less efficient? If anyone else knows the answers to these >questions, please chime in. > > >>Thanks, >>Ken Powell >> >> >> >> >>>> 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 >>> >>> > > > > --------------040304030808030501010204 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit I found that going from a bell shape curve to a straight wedge to my oil cooler the oil temps dropped somewhat.

If I understand it correctly, the 7.5 degree max rule is to ensure that the airflow stay attached to the duct walls (no turbulence). According to Bernie Kerr's experiments, that is true for an open duct (e.g. a wind tunnel). However, as soon as you put a restriction in there (a screen or a radiator) that rule no longer holds true and you can have a much steeper angle with the flow still staying attached. He observed this by tufting the walls of a test duct. An experiment anybody could do.

Shamelessly copied from http://www.rotaryaviation.com/bernie_kerr.htm (see pictures there):

Despite admonitions from some people, that it will not work ( i.e. all the air will try to come out the rear), the air is coming out uniformly or actually a little more at the front. This is a very low velocity test, but I am happy with the results. May try to turn the fan power to the wind tunnel up some with the pulley ratios or a larger hp motor.
 
The other thing that I flight tested was a couple of static pressures in my inlet rings on the 6A. They were located a couple of inches into the the ring, one at the top and one at the bottom. Interesting how close to plenum pressure they both are. This indicates to me that the velocity thru the ring is very low, ie all the diffusing is taking place outside and infront of the ring. The other thing was that the bottom static was higher than the top one indicating that the prop is really swirling the air. I think you really should aim one ring up and the other down to capture the best pressure and flow. Brumwell really hammered me that the prop wash (swirl) is what caused both Ed and Finn to  have their large roll excursions taking off behind another plane and that it was not wing vortices.
 
The pics are the tunnel flowing with yarn tell-tells on the radiator at 3 locations along its length. (Written by Bernie Kerr 11/1/02)

Finn

Ed Anderson wrote:
Hi Ken,

    Good questions and no, I have not attempted to measure the air velocity
throught the ducts.  Keep in mind that as long as there is sufficient air
mass flow through the radiator,  it  WILL cool at 0.1 to 0.4 and higher
ratios of duct velocity to airstream velocity.  So adequate cooling is not
necessarily the only criteria for an "optimum" cooling system.

The only problem is at the higher velocities through the core,  you have a
lot more cooling drag.  So you can get "good" cooling even with an less than
optimum cooling setup - BUT, you won't get the minimum weight or cooling
drag possible.   Air mass flow is the key, if you don't have sufficient then
you will not cool. Low velocity is important as that results in less cooling
drag.

  Since we are basically talking about a constant air density situation at
our speeds, then consider an air mass that flows at 0.1 V through a radiator
of size X and provides adequate cooling.  But, radiator of size X is too
large for your installation.  If you reduce the size of the radiator then
the airflow at velocity 0.1 simply provides too little air mass flow to
conduct away the heat.  BUT, if you increase the velocity through the
smaller radiator thereby increasing airmass flow to the point it carries
away adequate BTU for cooling, then you may find the velocity required
through the duct to be say 0.3.  While that WILL increase the cooling drag
over the original size X radiator, at least in this example you will cool
and you have a radiator that fits your constraints.  Cooling drag appears to
increase proprotional to area of the core but to the square of the air
velocity throught it.   Larger radiators incure more frontal area
resistance - but, since they permit (but you have to make it so via good
ducting) a lower air velocity, the less drag due to the lower velocity more
than offsets the frontal drag of the larger frontal area.

The worst cooling drag situation would appear to be a large radiator with
HIGH air velocity through the core. There you would have great cooling but
also very high cooling drag.   So it would appear that it becomes even more
important to get good ducting and diffuser action (lower velocity) with a
larger frontal area radiator than perhaps with a smaller radiator.  Just my
opinion.

    I have not studied the wedge shape duct so can't really comment on it.
But, again I see no reason why it would not cool - so long as there is
adequate air mass flow - it will cool.  Whether you get the minimum possible
cooling drag with it, I simply do not know.  I would presume it has some
merit - perhaps simplicity of ducting and installation in certain
configurations.  Someone else may know of a source on Wedged Ducts
information - if so, I would like to know.

Ed


Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message ----- 
From: <kenpowell@comcast.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, January 28, 2004 6:01 PM
Subject: [FlyRotary] Streamline Ducts


  
Hi Ed,
Thanks for sharing your approach and Neal's response.  Sometimes we seem
    
to forget that what we are trying to do is to convert the speed of the air
to PRESSURE.  Your approach seems to be working well.  Have you ever
measured the speed of the air moving though the radiator (where slower is
better)?  I understand that this type of diffuser should reduce the speed of
the air to somewhere between .1 to .4 of the freestream velocity, so I
wonder how well your modified ducts work (I bet pretty well).  Also, do you
know happen to know how well the wedge type duct (for radiators under the
engine) recover pressure?  Should the wedge ducts also reduce the speed of
the air to somewhere between .1 to .4 of the freestream velocity or they
inherently less efficient?  If anyone else knows the answers to these
questions, please chime in.
  
Thanks,
Ken Powell


    
 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
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