Thanks Ed. I went out to the garage and looked at my chin scoop radiator.

It fails to conform to the shape reccomended in the article. :(

But it does cool well in ground testing so far. I leaned heavily toward pressure recovery from the supposed bow wake effect, and can't verify if I get any diffuser effect because of the slope of the cooler core. I know this is not optimal, but I wanted greater core area and less core depth so air would pass thru the core with a lower differential pressure.

Here is a link to my EAA Capter's site, direct to my pictures:  http://gallery.eaa326.org/members/semery/

Constructive comments are always welcome.

I did try to keep external drag to a minimum, and have an Inlet area of about 52 In Sq, over a Core face area of 306 In Sq.

for a intlet / core ratio 17 % which seems small for the core.

The Horse Power target is 200, so the 1.8 cubic inch core volume to HP = 360 cubic inches. My core is 2" thick for 612 cubic inches. So I theoretically only require 59% of my existing core volume. 180 square inches of 2 inch thick core.

My inlet opening = 29% of that, so I'm close to optimum on inlet opening area. As I continue to test, and eventually fly, I could change to a smaller cooler, which could set it more 'normal' to the air flow, while also moving it aft allowing a longer diffuser.

The side mounted oil cooler was not a matter of choices. The Mazda cooler comes in one size, so does the cowl cheek opening. I just measured my diffuser inlet, 24.8 In Sq. The cooler face: 87.75 In Sq. Ratio = 28%. I think that's pretty good considering the airflow must turn 90 degrees to pass thru the core, then get sucked out thru surface louvers on the cowl side.
Here's hoping for the best, and trying again if it doesn't work.

-----Original Message-----
From: Thomas Mann <tmann@n200lz.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, Dec 21, 2009 6:01 pm
Subject: [FlyRotary] Re: Mereidth effect: [FlyRotary] Re: Air Flow Question

Thanks for the links Ed.

It looks like I have some reading to do!

 

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Monday, December 21, 2009 7:19 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Mereidth effect: [FlyRotary] Re: Air Flow Question

 

 

Thomas, Here is probably the best, most understandable (without a lot of math) on the cooling challenge that I have come across.   You might want to check it out.   Here is one of the statements you will find in this short article

 

It has been shown that the diffuser efficiency is key in the reduction of the overall radiator drag. It is the most critical part, and unfortunately the most frequently botched by homebuilders.

 

http://contrails.free.fr/engine_aerodyn_radia_en.php

 

Also note his comment about how to control airflow once your intake is 30-50% of your core area – may surprise you.

 

 

http://contrails.free.fr/tunnel_en.php

 

 

Here is a summary by Meredith on the effect.  There is still some debate about whether the P-51 cooling system actually resulted in a net thrust – but, most agree whether it did produce significant thrust or not the cooling drag was probably close to an optimum minimum. 

 

http://contrails.free.fr/refroid_meredith_en.php

 

You are right, there is always trade offs.  You can certainly put an oil cooler in front of your radiator – in effect you are just making a thick radiator as far as airflow is concerned.  Obviously you will have hotter air flow through the part of your radiator behind the oil cooler so its cooling effectiveness will be reduced.  Also, you may find that a lot of the air in their common duct may want to go through the other part of the radiator core – due to its less air resistance.

Placing them side by side (or top bottom) is another approach.  However, it is my opinion that unless your oil cooler and radiator core have similar air flow characteristics or great care is taken in designing your ducts to each, that air will take the route of least resistance.  So one  core could end up “bleeding’” cooling air from the other.  Similarly, the exit pressure of one (generally the one with the least air resistance) will be higher than the one with less resistance. So this can cause airflow problems under the cowl as well.

Its my opinion that keeping  your oil and coolant cores separate (if possible and there are always space constraints in our vehicles) and also keeping their air flow separate is generally the best course of action to get the best cooling.  But, compromises are frequently necessary, in which case you simply have to try and figure out the possible interaction and effects.

 

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 Thomas Mann
Sent: Monday, December 21, 2009 6:17 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Air Flow Question

 

“Stick with this group, we’ve all been there and have conquered the cooling beast – well, at least tamed it a bit.

 

Ed”

 

 

That is the plan Ed.

I’m trying to figure out how much radiator I can fit into my configuration. I’m running the numbers and drafting it out in AutoCAD.

 

I’m hoping that I can cash in on the Meredith Effect in my design. I’m planning on an adjustable exhaust opening much like the P-51s had. I’m not sure if I need it or not but it’s easier to not use it vs. add it later.

 

Question: If I use a separate oil cooler, can I place it in front of the radiator?

I’ve seen some installations like this but it seems to me that there is a cost involved.

 

T Mann

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