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Date: Tue, 13 Sep 2011 20:03:36 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: K & W Konfusion
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That sounds familiar; I think I found an old thread in the flyrotary 
archives about that. Seems like one of the sources was a race car page.

Tracy, can you share what duct formulas you used to create your wedge 
diffuser on the -8? Do you consider it 'good enough' compared to a 
straight streamline diffuser & a thicker, smaller frontal area radiator? 
(Please temper your answer with the knowledge that most of us won't be 
flying at O2 altitudes. :-) )

I did stumble upon an article & companion spreadsheet that I'm sure I 
saw in the past (it was in EAA Sport Aviation), but I have no actual 
memory of it. The article appeared in the JAN 2004 issue. Title is 'Cold 
Water' by Neil Willford & David Lednicer. The spreadsheet is on the EAA 
website under members only ( you must log in ). Then under member 
resources, click on the Sport Aviation archives, and find the Jan 2004 
issue. The spreadsheet is much tougher to find. It's at
> http://www.eaa.org/sportaviationmag/moreinfo.asp
but I can't find any link to that page from any other page on the EAA 
site (I got the link by emailing their help desk guy). Anyway, scroll 
down to Jan 2004 to find the cooling spreadsheet.

It supposedly uses K&W as a source for the formulas, etc. I haven't had 
time to re-read the article, & I've only plugged in a couple of 
variables, so I can't tell yet whether it will be truly useful.

Charlie


On 09/13/2011 03:46 PM, Ed Anderson wrote:
> Sorry, Charlie,
>
> Here is something I came across a long time ago - no idea how valid it 
> is, but it is related to inclined radiators.  It seems to imply that 
> anything inclined between 0 and 30 deg is bad but beyond 30 less than 
> 55 deg is better.  I suspect one reason has to do with the fact that 
> declined that way gives you the room to put in a larger core and 
> therefore get more cooling or at least offset any adverse effect on 
> airflow cooling.  But, that's just speculation on my part.
>
> I'll check on my volume of Hoerner's Tome on aeroynamics and cooling 
> and see if I can find anything in it that might help
>
>
> Ed
>
> --------------------------------------------------
> From: "Charlie England" <ceengland@bellsouth.net>
> Sent: Tuesday, September 13, 2011 3:23 PM
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Subject: [FlyRotary] Re: K & W Konfusion
>
>> Hi Ed,
>>
>> 1st, I'm afraid you have unwarranted excess confidence in my 
>> knowledge. :-)
>>
>> Thanks for the expansion (pardon the pun...) on what K&W is trying to 
>> say. I'm beginning to get a little bit of a handle on what's actually 
>> happening, & I'm hoping to be able to get a reasonable estimate of 
>> the performance differences between a straight duct & small face, 
>> thick rad & a wedge with larger face, thin rad (like Tracy's -8 & 
>> some others now flying). I'm also really interested in the potential 
>> drag reductions from exit ducts for higher speed planes like most of 
>> us are flying or building.
>>
>> Charlie
>>
>> On 09/11/2011 05:59 PM, Ed Anderson wrote:
>>>
>>> One, additional thing might be worth porting out is that with the 
>>> vector quantity Vb = Vi +Vt with Vt the component tangential to the 
>>> face of the core - as you might imagine, you don't get a lot of 
>>> cooling contribution due to Vt, as theoretically it doesn't 
>>> contribute (much) to the flow through the core (at least that is how 
>>> I read it).  Therefore the condition where vb = vi with vt = 0 
>>> probably means maximum cooling effect from the air flow which (one 
>>> reason) is why straight in flowing ducts (where Vb = Vi) cool better 
>>> than one with twists and turns.
>>>
>>> Ed
>>> --------------------------------------------------
>>> From: "Ed Anderson" <eanderson@carolina.rr.com>
>>> Sent: Sunday, September 11, 2011 6:08 PM
>>> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>>> Subject: [FlyRotary] Re: K & W Konfusion
>>>
>>>> Hi Charlie,
>>>>
>>>> Having pulled my hair out over some things in Chapter 12 of K& W,  
>>>> I can empathize.  Let me see if I can help you with this particular 
>>>> question.
>>>>
>>>> As you know, Vb is a vector quantify having both magnitude and 
>>>> direction and here is composed of two vector quantities:  Vi - 
>>>> (vector  in line or incident with the core)  and Vt (vector 
>>>> tangential to the face of the core). In this case ( a special case 
>>>> of the straight duct) Vt = 0.  No, the first chapter does NOT spell 
>>>> this out, so you did not miss it, but when you examine figure 12.6  
>>>> you will see it.
>>>>
>>>> In your first reference the Vt value = 0 (they do not point this 
>>>> out) and Vb is therefore equal solely to Vi (or the vector  
>>>> parallel to the duct, straight into the core).  So here Vb = Vi 
>>>> because Vt = 0, straight duct condition only.
>>>>
>>>> Now in figure 12.6 the incoming oblique air flow does have two 
>>>> components (Vi and Vt) relative to the orientation of the block - 
>>>> Vt is not zero here and of course neither is Vi.  So Vb = Vi + Vt.  
>>>> If you have a good copy and look carefully you can see that at the 
>>>> bottom of the vector triangle it shows Vb as the vector sum of Vi 
>>>> and Vt- and Vb is pointed in the direction of the airflow through 
>>>> the core (or parallel to the holes through the core or 
>>>> perpendicular to the core face).
>>>>
>>>>  If you look at figure 12-7, the same vector combination is there 
>>>> and a bit easier to see.   So in effec,t your first reference to Vb 
>>>> in chapter 12 is a special case of the overall vector components of 
>>>> the airflow (Vi and Vt) except in that case Vt = 0 and Vb = Vi.
>>>>
>>>> So it is probably more correct to say that Vb is the vector sum of 
>>>> the incident and tangential vectors of airflow  or Vb is the vector 
>>>> expression of the airflow through the core.
>>>>
>>>> What is missing in figure 12.6 is the showing the vector sum of Vb 
>>>> AFTER it exits the core.    If they did, what you would probably 
>>>> see is Vt much smaller or zero and Vb = Vi (since the duct is 
>>>> straight after the core). So if the vector sum on the one side of 
>>>> the core is Vb then it will also be Vb on the opposite side of the 
>>>> core - however the values of the vector components vi and vt will 
>>>> be different (if not a straight duct) - but their sum will remain 
>>>> the same - vb.
>>>>
>>>> At least that is the way I read it - and no, I've never found and 
>>>> K&W for dummies - if you do please let me know.
>>>>
>>>>
>>>> Dummy Ed
>>>>
>>>> Edward L. Anderson
>>>> Anderson Electronic Enterprises LLC
>>>> 305 Reefton Road
>>>> Weddington, NC 28104
>>>> http://www.andersonee.com
>>>> http://www.eicommander.com
>>>>
>>>>
>>>> --------------------------------------------------
>>>> From: "Charlie England" <ceengland@bellsouth.net>
>>>> Sent: Sunday, September 11, 2011 3:13 PM
>>>> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>>>> Subject: [FlyRotary] K & W Konfusion
>>>>
>>>>> Anyone else having problems interpreting K & W's chapter 12 on 
>>>>> cooling?
>>>>>
>>>>> I confess to only having available (downloaded) chapters  on 
>>>>> inlets & cooling, but their use of terms is a bit hair-pulling for 
>>>>> me. For instance, VsubB is defined on the 1st page of the chapter 
>>>>> as 'velocity of the air ahead of the block' & diagrammed that way 
>>>>> in fig 12-1, then it's apparently diagrammed as the velocity 
>>>>> *leaving* the cooling block in fig 12-6. And quite a few of the 
>>>>> terms don't seem to be defined at all (this may be due to my 
>>>>> failure to take a physics course in college, & the 30+ year 
>>>>> interval since my one semester of Calculus...).
>>>>>
>>>>> If there's a 'K&W for Dummies' book, please recommend a source...
>>>>>
>>>>> Charlie