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----- Original Message -----
From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, January 18, 2004 3:09 PM
Subject: [FlyRotary] Re: Cooling Article - SportAviation Mag
> Ed Anderson wrote:
> > Excellent article in EAA Sport Aviation Mag I received today, on liquid
cooling. In reading it, much seemed familar and sure enough one of the two
references is Kuchemann and Weber. They also point out that the Streamline
Duct is a more practical alternative to the 7 Deg optimum duct for aviation
use as well as other useful information. Well worth reading.
> >
> >
> > Ed Anderson
> > RV-6A N494BW Rotary Powered
> > Matthews, NC
>
> Ed, the definition of solidity of the radiator has me turned around. He
> uses low solidity to mean all closed up. Just seems counter-intuitive
> to me. Can you help me make sense of it?
>
> --
> http://www.ernest.isa-geek.org/
> "Ignorance is mankinds normal state,
> alleviated by information and experience."
> Veeduber
>
I agree, Ernest. Their use of the term "Solidarity" seems just the
opposite of what I would think. But, it is the same definition used in K&W.
Solidarity is ratio of Open space area of the core (where air can flow) to
the total frontal area of the core. So as the Solidarity ratio goes higher
it means there is more open area whereas you would think that "more
Solidarity" would mean less open area.. Why they didn't call it "Openness"
ratio I don't know.
Lower solidarity means less open space and more fins whereas Higher
solidarity means more opens space and perhaps less fins or obstructions to
air flow. Again its that age old compromise, more fins means more heat
dissipating surface, but more fins will also slow down the mass flow so that
finding the optimum balance between enough fins to dissipate the heat better
but not too many that if adversely affects cooling by slowing down the mass
flow too much. K&W makes this point several times - there is an optimum
pressure drop/heat transfer value which balances amount of heat transferred
to the air flow and continuing adequate mass flow. However, it is not
exactly easy to determine and you need to know a lot more info about the
core to really figure it out.
But, in any case, I thought the article was good. Although some things
stated in it needs to be interpreted carefully. They make a point about
large radiator always winning out. However, that depends on many things.
If the air flow velocity is as high in a larger radiator as in say a smaller
radiator then the larger radiator will have more cooling drag. The larger
radiator can also contribute to external drag is you have to modify you
cowling such that it offers more air resistance. And as they mentioned, it
can be a problem to find the space for a large radiator.
The author mentioned the desirability of having your air velocity through
your core as 1/10 of your cruise airspeed (also mentioned in K& W) as ideal.
Its only ideal, of course, if it provides adequate cooling. If it does then
you have cooling with minimal cooling drag. The assumption is that your
diffuser is very efficient and drops the cruise airspeed down to no more
than 1/10 of that value as it goes through the cooler. The slower velocity
means less cooling drag. Recall that the airmass flow stays constant in the
cooling system, if the velocity decreases its because the diffuser volume
has increased so that the product p*Velocity*Area remains constant.
On the other hand, while more air velocity through a smaller radiator will
create more cooling drag, its will also provide more mass flow and more
cooling effect. So in some (many?) cases, the compromise might well be to
go for a smaller radiator for ease of placement, less external drag and
accept the penalty of increased cooling drag.
At least that's the way I see it. By the way I using K&W equations, it
turns out to cool a 160 HP rotary at 120 MPH (climb) TAS you need two cores
of 95 square inches each at 3.1 inch thick. At cruise at say 170 MPH TAS
even with 160 HP you only need cores of 65 square inches for each core (if
using two). So the two cores are adequate for full power climb, but provide
excess cooling capacity at cruise.
Enough, back to my variable intake manifold. Coming along nicely at this
point, hooking up the motor tomorrow to drive the jack screw and run the
tubes in and out.
Best Regards
Ed Anderson
Ed Anderson
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