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Ok, Jim
I agree that the theory part gets out of hand at
times (my fault). Theory only counts if it works in practice
{:>). However, I think these question naturally arise when we start
talking about some of this stuff - the old "how it do that".
The only part that really counted was
understanding what was necessary to keep air flow from separating from the walls
in a diffuser. If you eliminate that problem you have done probably 90% of
what you can do to achieve optimum diffuser performance (my opinion of
course). So you can have otherwise adequate core surface and volume, but
if you have a poor duct design with lots of flow separation and eddies then your
system may fail to adequately cool.
Ed A
----- Original Message -----
Sent: Monday, April 04, 2005 12:29
PM
Subject: [FlyRotary] Re: A lot to
learn
Is it possible we're dismissing some important factors getting
a little out of our depth here? Dynamic pressure in the cores and across
the cores would seem to be so highly dependent on surface friction and core
density and passage size as to be impossible to estimate, much less quantify
accurately.
If the purpose of the plenum is pressure recovery
(converting dynamic pressure into static pressure) and it's the static
pressure drop that drives the mass of air through the radiator core, why not
just forget about the molecular, boundary layer and core passage size
considerations for the moment since we can't quantify any of that
anyway. As Ed has stated so many times in so many ways, a good
inlet/plenum design does a better job of converting dynamic pressure to static
pressure than a bad one, and he's found out pretty much what he has to do to
make a bad one good.
If we measure static pressure at the
forward and aft face of the radiator and we've got the pressure drop across
the core. Period. We know how close we are to Ed's plenum.
Then adapt the stuff that Ed has pioneered for us to make it better An
Airspeed indicator I find is handier and more accurate than a water
manometer. The Pitot connection on the upwind side and the Static
connection on the downwind side should give me upwards of 100, maybe 120 kias
drop across the radiator at cruise. More is better. If I don't
have sufficient pressure drop across the radiator, I probably need to improve
my intake and plenum to get rid of the eddies Ed alludes to. That is
what I've got the most influence over. If I don't get enough pressure
recovery, I study Ed's findings and approach implement them better.
I think all this molecular stuff is more appropriate to the ACRE list
where nothing ever really has to fly. This list (to me) is the guys who
actually FLY. A sound qualitative analysis of the issues involved
(which we already have) will lead me to a workable solution. That is
very nice since an acceptably accurate quantitative analysis is not
possible. To that end (to coin a phrase) I don't have to know how it
works or why it works, I only have to know what I have to do to MAKE it
work. And I have been blessed that Ed has found out most of
this.
Are we PVORT. again? ... Jim S.
David Carter
wrote:
----- Original Message -----
From: <jbker@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, April 04, 2005 7:07 AM
Subject: [FlyRotary] Re: A lot to learn ! Re: Cooling -Learned a lot
Charlie E wrote:
At the risk of embarrassing myself with a display of misunderstanding
the physics of it all, should your pressure sensors be measuring dynamic
pressure or static? Seems like I remember Tracy's measurement pics
having foam chunks over the pressure sensors to remove the dynamic
component of the pressure measurement. I couldn't remember if your setup
has that (& I really don't know if it should, either).
Charlie
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