Bob,

If I might chime in here. Were not the radiators on the Spit simply burried in the wing? If the drawings I've seen are correct the radiator was vertical. The scoop on the bottom of the wing was about twice the boundry layer height and there was a ramp/diffuser in front and back. I'm not an expert so feel free to correct me if I'm wrong.

Bill Jepson

 

 
-----Original Message-----
From: bmears9413@aol.com
To: flyrotary@lancaironline.net
Sent: Thu, 3 May 2007 1:25 PM
Subject: [FlyRotary] Re: Cooling area drag

Hmmm...actually I didnt consider that. Your thinking of having the bottom of the radiator exposed to the outside of the scoop, and just have the air run in the front-down through the rad and out the bottom....right?

Bob Mears

Supermarine Spitfire

 

 
-----Original Message-----
From: jerryhey@earthlink.net
To: flyrotary@lancaironline.net
Sent: Thu, 3 May 2007 3:16 PM
Subject: [FlyRotary] Re: Cooling area drag

Bob,  have  you considered putting the intake above the rad.  You could get rid of the deflectors and the air would follow a simple path down through the rad and out.  Jerry

 

On May 3, 2007, at 4:00 PM, bmears9413@aol.com wrote:

Ed,

Give me some pointers on my cooling system before I get started. You surely will save me some mistakes. My air intake will be below and behind my radiator . I imagined just building some deflectors to "s" the air up to the radiator. Aft of the radiator the air will exit out the back half of the air scoop. the radiator will be laying flat, under the motormount. the oil coolers are under each wing...as it should be in s spitfire.

Thanks,

Bob Mears

Supermarine Spitfire

 

 

 

 

 
-----Original Message-----
From: eanderson@carolina.rr.com
To: flyrotary@lancaironline.net
Sent: Thu, 3 May 2007 11:49 AM
Subject: [FlyRotary] Re: Cooling area drag

Actually, Mark,  I started pulling together what I believed to be the major factors without getting too down in the weeds about rotary cooling, a couple of years ago with the intention of publishing an e book (pamphlet more likely) .  Then I ran into the problem that the seemingly best diffuser (Streamline duct) was simply too long (in its optimum configuration) for most of our needs.  Yes, you can shorten it but then you incur more drag.  So I scratched my head about that for a while until the light bulb came on.

 

After experimenting with a number of duct shapes and reading more, I came to the conclusion that if my understanding about what killed effective cooling was correct then I should be able to achieve my cooling/drag goals with the "Pinched" duct.  But, what I wanted to do and never took the time to do was to go back with Mr. Bernoulli and calculate the air velocity along each segment of the streamline duct and then do the same for my "pinched" duct to see if there was any similarity.   Also, I have not paid much attention to the exiting duct - simply because I don't have room for one.  I tired one back almost 8 years ago and decided the zigs and zags it had to avoid engine/ motormount, etc impeded airflow more than helped it.

 

 

But, alas, just as I was recently about to go to publication, the new "bible" of cooling was published - so how could I possibly compete {:>).  I may still do it as if it passes the gauntlet of folks on this list (or errors if any {:>)) are corrected,as it may be useful to some.

 

Ed

 

 

----- Original Message -----

From: Mark Steitle

To: Rotary motors in aircraft

Sent: Thursday, May 03, 2007 12:34 PM

Subject: [FlyRotary] Re: Cooling area drag

ED,

 

So, tell us, when is your book on cooling going to be available? 

 

Mark

 

On 5/3/07, Ed Anderson < eanderson@carolina.rr.com> wrote:

Less we forget how important drag is in our hobby, I took a formula for calculating drag at different airspeeds and the Hp required to push the given frontal area along at the stated airspeed.

 

This is for two of our traditional GM evaporator cores using their combined frontal area of  180 sq inch or 1.25 sq feet.  This assumes that airspeed shown represents the velocity through the cooling core (which is not really likely to reach speeds above 80 mph if you have any sort of ducting), but that is an assumption on my part since as Bill keeps reminding me I have not instrumented my ducts {:>)

 

Air Speed (MPH)	HP
40	0.533333
60	1.80
80	4.27
120	14.40
140	22.87
160	34.13
180	48.60
200	66.67

 

 

Clearly the faster your cruise speed the more important it is to minimize cooling drag.  Of course the airspeed the core sees should normally not be over 10% of your cruise speed or 30% of your climb speed (According to Horners rule of thumb).  So slowing down your cooling airflow to lessen drag is one reason for paying some attention to your ducting.  However, cooling again depends on many other variables, for instance accepting a high velocity airflow through your core may permit you to use a smaller frontal area  core thereby offsetting to some extent the higher drag.  In fact, space constraints may force you to his configuration regardless.

 

Another factor to consider is trade off between frontal area drag and thermal transfer efficiency.  A large thin radiator is theoretical the most efficient due to that factor.  However, it disturbs a larger segment of air (resulting in higher drag) - not really important in an auto at 60 mph but very important in a Cozy at 200+ MPH.  

 

A thicker core with smaller frontal area disturbs less air and while it has more skin drag that is small compared to the frontal area drag.  Tracy refers to the approach of thicker cores as "... getting the most cooling possible for the smallest column of air disturbed".  So while theoretically the thicker core is less thermodynamic efficient - it turns out with sufficient dynamic pressure available it provides definite benefits in our application.   The average thickness of NASCAR radiators is 3" and up to 7" for the longer high speed tracts.  Since they operate in speed regimes close to what most of us fly - they just might know what they are doing given the $$ they will spend for even a slight speed advantage.

 

Ok, back to creating a company - boy, a lot to learn

 

Ed

 

 

 

  

 

 

Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://members.cox.net/rogersda/rotary/configs.htm #N494BW
http://www.dmack.net/mazda/index.html

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