As I recall the article, they were measuring the angle from a line perpendicular to the duct centerline; to the face of the core.

 

There’s a whole ‘nuther factor to consider when shaping the duct and placing a radiator at an angle; and that is the flow distribution through the core.  For maximum effectiveness, you want the distribution to be at least fairly uniform so ever part of the core is doing an effective job. Based on flow measurements that I have done, any time you’re expecting the air to turn, it’s a good idea to do some flow tests to see if you need to add turning vanes.

 

When I designed the scoop for my main radiator, I chose to try and follow a K&W profile, but it had to turn nearly 90^o and be a bit shortened (Photo 1). Then I rigged a flow test, and found the flow velocity was much higher through the far end of the rad than the forward end.  I then did some trial and error placement of a couple turning vanes (photo 2) until the flow was very uniform. Doing flow tests on the rads and oil cooler was also allowed measure the pressure drops.

 

Flow testing isn’t so tough – you just need a big centrifugal blower, some ducting, a small hand-held anemometer, and a water monometer. And then you have to be inclined to want to do such a thingJ.

 

Al

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of George Lendich
Sent: Saturday, January 16, 2010 7:56 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Inclined Radiators was : [FlyRotary] Re: Scoops

 

Tracy, Ed &Al,

I don't know if we are all talking about the same thing so to clarify in my own mind,  I would like to say my opinion on these notes I have, suggest to me that the 55 degrees, is from the direction of the air flow i.e. 55 degrees from the horizon or X axis. That would be only 35 degrees from the Y axis or  vertical. So 35 degrees inclined vertical isn't too bad - in a bell shaped duct. However I could be wrong and the original reference could have been 55 degrees inclined from vertical, which also sounds plausible, seeing their talking inclined, one might think inclined from vertical.  Al what's your thoughts on this.

 

However I believe Tracy, you are saying 80 degrees from vertical and  I believe he must be referring to a wedge shaped duct, as I don't think you could fabricate a bell shaped duct to cope with that degree to the duct walls.

 

This brings me to the question on what angle is desirable in a wedge shaped duct, if your unable to fit in a bell shaped duct or should I merely be considering the size of the inlet opening. I believe I remember in wedge shaped ducts they should be as high or as wide as the Rad, considering the placement of rad i.e. under engine or side of cowl with appropriate depth of the inlet opening.

Comments please.

George ( down under)  

 

Well the basic idea has validity because I carried it to an extream.  My rad is inclined about 80 degrees to the 5" duct so flow axis is almost perpendicular to the duct.  A 5" rad would never cool that 20B so inclining it radically was the only answer in my configuration.  Water cooling has never been my problem.  Oil cooling is working pretty good with the new oil cooler.  It was the "30 row oil cooler" from CXracing if anyone is curious.

Tracy

On Sat, Jan 16, 2010 at 4:18 PM, George Lendich <lendich@aanet.com.au> wrote:

Ed,

I would like to see that again, as I believe would others,  like Al and Thomas. I'm hoping someone tries it in an aircraft to test the theory.

TIA

George ( down under)

I recall an article on some experiments done on inclined radiators in race cars.

 

Basically the figures that George mentioned were quoted in the source.  However (big however) what may not have been clearly pointed out was that the major part of the reason cooling effectiveness (not efficiency) increased was that inclining the heat exchanger permitted you to install ever larger area cores in the same size duct.  So the increase in cooling effectiveness by inclination was in large part due to the larger size radiator permitted by inclined placement in the duct.

 

For example take a duct that is 24” wide (X) and 12” high (Y) at zero degree inclination.  If you incline the radiator by 30 deg and then increase its height to again fill the duct,. you can get an approx 15% increase in the frontal size of the radiator (in the same 24x12 duct).  At 60 deg you could gain approx 100% increase in frontal size by again increasing the height of the core to fill the duct.  . Naturally that aids in getting rid of the heat.  They also point out the larger core adds weight until you reach a point where the adverse effect of the heavier radiator core offset its benefit (this was all addressing their use in race cars).

 

The source indicated that up to 30Deg the drag increases and heat transfer goes down due to uneven air flow distribution and disturbances – apparently above that angle this adverse effect decreases and of course you have the much larger frontal area..

 

At least that is what I recall.  If anyone is interested I’ll see if I can find the article in my files

 

Ed

Ed Anderson

Rv-6A N494BW Rotary Powered

Matthews, NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.rotaryaviation.com/Rotorhead%20Truth.htm

---

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Friday, January 15, 2010 1:13 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Scoops

 

 

Thomas,

Nice research.

I found my notes on inclined radiators, they state

1. 0-20/30* will decrease cooling and increase drag.

2. Over 30* things improve.

3. At approx 55* cooling effectiveness is 30% greater than non-inclined rads

and drag is less by 20%.

 

George; do you have the source for that info? It may be a good idea to verify this information.  I don’t recall the specifics; but what I do recall is that the conclusion was configuration dependant, and should not be taken as generally applicable.  Sorry, but I don’t remember what the factors were; maybe something about the configuration of the core.

Or maybe my memory just isn’t right.  Worth checking.

All

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