X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail02.syd.optusnet.com.au ([211.29.132.183] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTPS id 2462254 for flyrotary@lancaironline.net; Thu, 08 Nov 2007 16:56:06 -0500 Received-SPF: none receiver=logan.com; client-ip=211.29.132.183; envelope-from=lendich@optusnet.com.au Received: from george (d211-31-71-103.dsl.nsw.optusnet.com.au [211.31.71.103]) by mail02.syd.optusnet.com.au (8.13.1/8.13.1) with SMTP id lA8LtIHU025914 for ; Fri, 9 Nov 2007 08:55:20 +1100 Message-ID: <001701c82252$11d714b0$67471fd3@george> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Total,duct, Ambient or Velocity???? Date: Fri, 9 Nov 2007 07:55:24 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0014_01C822A5.E25DDE90" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-Antivirus: avast! (VPS 0657-0, 12/12/2006), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_0014_01C822A5.E25DDE90 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ed and Bill, I was just thinking about the vertical side rads ducted to the outside. = I have seen this work very well in smaller planes with smaller engines, = but am unsure how that might translate to larger installations. I think = they work so well because being so close to the air stream being on the = side walls of the cowl, that the slip stream actually creates a suction, = or low pressure area (over the airfoil shaped outlet bump), which = enhances the flow through the rads. This could be something lacking in = some installations. I did ask PL some time ago if the chin scoop was in a high pressure = area, which I think it is, which might make it less effective compared = to side outlets. That's not discounting Ed's comments on inlet pressure, but it may = enhance pressure drop across the core, if we can target low pressure = areas for exits. George (down under) =20 It seems like a cogent discription Ed. I have been studying the = problem for some time. I like your no core example, much cheaper but it = will only fly once. (And for a short time!) The question I have been = pondering is, does it really help us to consider a exit ducting to = direct our exit flows. The data you presented seems to indicate that it = does. The dynamics of the pressure drop across the core contain = compromises related to the efficiency of the heat exchanger, flow of the = water in it and air through it. Many of the designs I see lately pay = very little attention to the exit and re-merging the flow. In = core-in-the-standard-inlet systems such as yours the exit ducting may = not be practical. This is a problem I have see with the Eggenfellner = Sabaru installations as well. At least the rotary can have some exit = area without the cylinders right there in the way! The exit question = tends to favor the chin scoop. The problem is that this has always = proven to be a high drag choice. Currently I'm favoring a verical side = radiator (or radiators) ducted to the outside (cowl) blowing into the = engine area with a diversion duct to turn the air towards the normal = rear bottom exit. Possibly with a cowl flap for climb. These have never = been easy choices. Often we intend an elegant solution, only to be = rebuffed by the need for hoses, wires, and exhaust pipes and other = unimportant stuff like that. ;-)=20 Thanks for all your research, Bill Jepson -----Original Message----- From: Ed Anderson To: Rotary motors in aircraft Sent: Thu, 8 Nov 2007 5:05 am Subject: [FlyRotary] Re: Total,duct, Ambient or Velocity???? Hi Bill, It is my opinion, based on my limited knowledge of the topic, that = dynamic pressure in the duct is the most significant factor. If you = don't have it - you have no flow. If you do have it you will have flow = but you could have significant Major losses - that's why you may need = other types of pressure measurements to figure out the problem. In = fluid flow talk, they appear to refer to loss of energy through wall = friction as a major loss as it is not recoverable (but this is minor at = our speeds) , while trades between dynamic and static in the duct result = in "minor" losses which may or may not really be minor. Here is my understanding, you would like to convert dynamic energy to = static pressure increase in front of the core as that slows down the = velocity reducing drag and tends to give you more even velocity = distribution across the core (assuming little or no separation of flow = from the duct walls). You would like the greatest pressure drop across = the core which results in the highest velocity through the core tubes = generating turbulence for better heat transfer. However, there is a balancing point, more pressure drop generally = means better heat transfer from metal to air, however, it also generally = means less mass flow because of the resistance. Too much pressure drop = =3D too little mass flow and overheating, too little pressure drop =3D = great mass flow but higher duct drag and less heat transfer per unit = time which can also lead to overheating. =20 I like to use this example to emphasize the point. You would get = maximum pressure drop by placing a solid board across the duct - = however, the air flow would be nil and cooling likewise. On the other = hand, if you remove all obstructions in the duct (including the core) , = the pressure drop would be nil, the airflow would be maximum but = cooling would still be nil. The only significant difference is the no = core approach is cheaper and causes less drag {:>) In any case, all the literature I have read seems to indicate that the = difference in pressure between the inlet and out let of the duct is a = (if not THE) key factor. That dynamic pressure is the only thing = (assuming no fans/blowers) that will move significant air through the = duct. Since this dynamic pressure is referenced to the dynamic pressure = available in the freestream flow as that is what it starts out as, I = personally think referencing dynamic pressure measurements to ambient = air is what we are mainly interested. This is rather than referencing = it to the duct static pressure as shown in the diagram. But, you have = to remember this is all from the guy who has not done any duct = instrumentation. But, my reason for focusing on dynamic pressure is that you can = infer a lot from your duct dynamic pressure readings about what is going = on in the duct. If your dynamic pressure is down, then your static = pressure is up and vice versa. If you have dynamic pressure then you = have flow while static pressure does not necessarily tell you that. =20 However, it all really depends on what you are trying to figure out on = what measurements you take. It would appear if you know how to interpret what you are measuring = then all provide some useful information. That's about the extent of my limited knowledge. Ed ----- Original Message -----=20 From: WRJJRS@aol.com=20 To: Rotary motors in aircraft=20 Sent: Thursday, November 08, 2007 12:28 AM Subject: [FlyRotary] Re: Total,duct, Ambient or Velocity???? Ed, The slide is a good way to explain the various references. I am = still confused as to what will give you the "best" data. The static in = duct pressure compared to the total, or to the velocity? It probably = doesn't matter if you use the same method all the time. Bill Jepson -------------------------------------------------------------------------= --- See what's new at AOL.com and Make AOL Your Homepage. -------------------------------------------------------------------------= ----- Email and AIM finally together. You've gotta check out free AOL Mail! -------------------------------------------------------------------------= ----- No virus found in this incoming message. Checked by AVG Free Edition.=20 Version: 7.5.503 / Virus Database: 269.15.24/1115 - Release Date: = 7/11/2007 9:21 AM ------=_NextPart_000_0014_01C822A5.E25DDE90 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ed and Bill,
I was just thinking about the vertical = side rads=20 ducted to the outside. I have seen this work very well in smaller = planes=20 with smaller engines, but am unsure how that might translate to larger=20 installations. I think they work so well because being so close to the = air=20 stream being on the side walls of the cowl, that the slip stream = actually=20 creates a suction, or low pressure area (over the airfoil shaped outlet = bump),=20 which enhances the flow through the rads. This could be = something=20 lacking in some installations.
I did ask PL some time ago if the chin = scoop was in=20 a high pressure area, which I think it is, which might make it less = effective=20 compared to side outlets.
That's not discounting Ed's = comments on=20 inlet pressure, but it may enhance pressure drop across the core, if we = can=20 target low pressure areas for exits.
George (down under)  
It seems like a cogent discription Ed. I have been studying the = problem=20 for some time. I like your no core example, much cheaper but it will = only fly=20 once. (And for a short time!) The question I have been pondering is, = does it=20 really help us to consider a exit ducting to direct our exit flows. = The data=20 you presented seems to indicate that it does. The dynamics of the = pressure=20 drop across the core contain compromises related to the efficiency of = the heat=20 exchanger, flow of the water in it and air through it. Many of the = designs I=20 see lately pay very little attention to the exit and re-merging the = flow. In=20 core-in-the-standard-inlet systems such as yours the exit ducting may = not be=20 practical. This is a problem I have see with the Eggenfellner Sabaru=20 installations as well. At least the rotary can have some exit area = without the=20 cylinders right there in the way! The exit question tends to favor the = chin=20 scoop. The problem is that this has always proven to be a high drag = choice.=20 Currently I'm favoring a verical side radiator (or radiators) ducted = to the=20 outside (cowl) blowing into the engine area with a diversion duct to = turn the=20 air towards the normal rear bottom exit. Possibly with a cowl flap for = climb.=20 These have never been easy choices. Often we intend an elegant = solution, only=20 to be rebuffed by the need for hoses, wires, and exhaust pipes and = other=20 unimportant stuff like that. ;-) 
Thanks for all your=20 research,
Bill Jepson

-----Original Message-----
From: Ed = Anderson <eanderson@carolina.rr.com>
To: Rotary motors in = aircraft=20 <flyrotary@lancaironline.net>
Sent: Thu, 8 Nov 2007 5:05=20 am
Subject: [FlyRotary] Re: Total,duct, Ambient or=20 Velocity????

Hi Bill,
 
It is my opinion, based on my limited = knowledge of the=20 topic, that dynamic pressure in the duct is the most significant = factor. =20 If you don't have it - you have no flow.  If you do have it you = will have=20 flow but you could have significant Major losses - that's why you = may=20 need other types of pressure measurements to figure out the = problem.  In=20 fluid flow talk, they appear to refer to loss of energy through  = wall=20 friction as a major loss as it is not recoverable (but this is minor = at our=20 speeds) , while trades between dynamic and static in the duct result = in=20 "minor" losses which may or may not really be minor.
 
Here is my understanding, you would like to = convert dynamic=20 energy to static pressure increase in front of the core as that slows = down the=20 velocity reducing drag and tends to give you more even velocity = distribution=20 across the core (assuming little or no separation of flow from the = duct=20 walls).  You would like the greatest pressure drop across the = core which=20 results in the highest velocity through the core tubes generating = turbulence for better heat transfer.
 
  However, there is a balancing point, more = pressure=20 drop generally means better heat transfer from metal to air, however, = it also=20 generally means less mass flow because of the resistance.  Too = much=20 pressure drop =3D too little mass flow and overheating, too little = pressure drop=20 =3D great mass flow but higher duct drag and less heat transfer per = unit time=20 which can also lead to overheating. 
 
I like to use this example  to emphasize the=20 point.  You would get maximum pressure drop by placing a solid = board=20 across the duct - however, the air flow would be nil and cooling=20 likewise.  On the other hand, if you remove all obstructions in = the duct=20 (including the core) , the pressure drop would be nil,  the = airflow would=20 be maximum but cooling would still be nil.  The only significant=20  difference is the  no core approach is cheaper and = causes less=20 drag {:>)
 
In any case, all the literature I have read seems = to=20 indicate that the difference in pressure between the inlet and out let = of the=20 duct is a (if not THE) key factor.  That dynamic pressure is the = only=20 thing (assuming no fans/blowers) that will move significant air = through the=20 duct.  Since this dynamic pressure is referenced to the dynamic = pressure=20 available in the freestream flow as that is what it starts out as, I=20 personally think referencing dynamic pressure measurements to ambient = air is=20 what we are mainly interested.  This is  rather than = referencing it=20 to the duct static pressure as shown in the diagram. =20 But, you have to remember this is all from  the guy who has not = done any=20 duct instrumentation.
 
But, my reason for focusing on dynamic = pressure  is=20 that  you can infer a lot from your duct dynamic pressure = readings about=20 what is going on in the duct.  If your dynamic pressure is down, = then=20 your static pressure is up and vice versa. If you have dynamic = pressure then=20 you have flow while static pressure does not necessarily tell you = that. =20
 
However, it all really depends on what you are = trying to=20 figure out on what measurements you take.
It would appear if you know how to interpret what = you are=20 measuring then all provide some useful information.
 
That's about the extent of my limited=20 knowledge.
 
Ed
 
 
----- Original Message -----
From:=20 WRJJRS@aol.com=20
To: Rotary motors in = aircraft=20
Sent: Thursday, November 08, = 2007 12:28=20 AM
Subject: [FlyRotary] Re: = Total,duct,=20 Ambient or Velocity????

Ed, The slide is a good way to explain the various references. = I am=20 still confused as to what will give you the "best" data. The static = in duct=20 pressure compared to the total, or to the velocity?  It = probably=20 doesn't matter if you use the same method all the time.
Bill Jepson
 



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