|
|
Neat looking installation. Seeing the
turbo, I think you were wise to go to a larger core than the 1.8 ratio would
indicate. That is the trouble with a “rule of Thumb” –
it may not apply if your installation is different than that for with the rule
was derived – or depending on your design point selection.
Theory is a starting point – as pointed
out by several, deviation from the “perfect” system almost always
happens in the “real world”. Finding a similar (successful )
installation to copy is not a bad approach.
Air up near the prop end of the cowl is
turbulent to say the least – for that reason it is likely that not using
a more “optimum inlet” to keep out the boundary layer, may
not have that much (if any) adverse affect. The main thing is to get
sufficient air mass flow through the core, if you do that it will cool
(assuming the core is adequate).
Looking forward to hearing how the system
performs in the air. The most frustrating thing I encountered back many
years ago was what seemed to work and cool well on the ground – didn’t
in the air and vice versa. But, finally got it sorted out.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of shipchief@aol.com
Sent: Tuesday, December 22, 2009
9:49 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Mereidth
effect: [FlyRotary] Re: Air Flow Question
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.
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
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.
Also note his comment about how to control
airflow once your intake is 30-50% of your core area – may surprise you.
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.
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.
Rv-6A N494BW Rotary
Powered
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.
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.
__________ Information from ESET NOD32 Antivirus, version of virus signature
database 3267 (20080714) __________
The message was checked by ESET NOD32 Antivirus.
http://www.eset.com
|
|