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

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