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ZL3AI > APRDIG 21.06.03 20:18l 233 Lines 9426 Bytes #999 (0) @ WW
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Re: Field Day Water Power
From: David VanHorn <dvanhorn@cedar.net>
Date: Tue, 17 Jun 2003 14:01:44 -0500
X-Message-Number: 20
>Normally
>it would suck at the center, then the disk spins it out (and it may not
>even have blades in a debris pump) and then exhaust it. Unless you know
>how the exhaust was extracted from the chamber, you can't say the
>pump would or wouldn't work.
Windmills and Waterwheels have many similar problems.
Not too surprising I guess, since they are both trying to extract energy
from a moving fluid.
This is very similar to what happens when you use helicopter blades for
windmills. You find out that propellers are designed to move air, and
windmill blades are designed to be moved BY air. Significant difference.
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Subject: APRS Power Point Presentation?
From: "David G. Willard" <doc@mitre.org>
Date: Tue, 17 Jun 2003 16:13:13 -0400
X-Message-Number: 21
Does anyone have a PP presentation that I could use for our local radio
club? I sysop the W1ON APRS Gateway in Bedford, MA.
de DoC, W1EO
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Subject: Satellite pass prediction and STK
From: Miller Scott Contr 30SCS/FTI <Scott.Miller@vandenberg.af.mil>
Date: Tue, 17 Jun 2003 20:27:36 -0000
X-Message-Number: 22
Since PCSAT has gone back into its eclipse cycle we haven't heard much
discussion here about satellite pass prediction, but AGI's Satellite Toolkit
5 just recently came out and I thought I'd share it with the list.
STK totally blows away everything else I've seen for satellite modeling.
The basic package is available for free at http://www.stk.com/. The add-ons
for stuff like 3D graphics and interplanetary astrogation aren't, but the
basic package is still very capable. I haven't seen any free packages that
can compute access opportunities between two ground stations through
multiple satellite hops, but STK does it easily. See the screenshot at
http://n1vg.net/pcsat-iss.jpg. In this example, I've got two ground
stations communicating through ISS and PCSAT. Access opportunities are
constrained to times when PCSAT is in full sun, and when the satellites are
at least 18 degrees above the horizon. The tabular report is pretty boring,
but the graphics look cool. It can also do all sorts of RF propagation
modeling, and you can define a horizon mask to have it take into account
obstructions around your station. I find it's easier to just set a minimum
elevation and maybe a maximum range.
Anyway, the point is that STK lets you define very complicated scenarios and
run a wide variety of reports and things against them. And it's not
terribly difficult to use. If anyone's interested, I might put together a
step-by-step tutorial on creating some basic amateur satellite scenarios.
Scott
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Subject: Re: APRS Power Point Presentation?
From: "Wes Johnston" <wes@johnston.net>
Date: Tue, 17 Jun 2003 16:49:33 -0400
X-Message-Number: 23
ftp://ftp.tapr.org/aprssig/presentations/
I'm partial to a few of them ;-)
Wes
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Subject: Re: Field Day Water Power
From: Bob Bruninga <bruninga@usna.edu>
Date: Tue, 17 Jun 2003 17:04:52 -0400 (EDT)
X-Message-Number: 24
>This is very similar to what happens when you use helicopter blades for
>windmills. You find out that propellers are designed to move air, and
>windmill blades are designed to be moved BY air. Significant
>difference.
a comment before we all get kicked off of here...
Hardly any difference at all. A good prop is also a good turbine. It is
almost 100% reversible (under identical design conditions)..
You are comparing a prop (which has a tip-speed ratio of 8 or more) to a
windmill (which has a tip-speed ratio of 1 or less). This is apples and
oranges. The prop was designed for high speed (100 to 300 MPH, high RPM,
and low torque). THe windmil was designed for low speed (7 to 30 MPH,
very low RPM and very high starting torque (remember, they had to pump
water up and down)... Hence totally different designs.
There are many very efficiient wind turbines that use blades that are
identical to props, but they need higher winds, and very low
starting loads. But once a 2 blade wind turbine is up to speed, it
sucks all the available energy out of the wind just like a fat windmill
does at 1/10th the speed. So there is no difference, as long as you
propely engineer the blades to the given conditions.
Even a Helocopter with a failed engine will auto-rotate its unpowered
blades to act like a turbine to slow its descent and cushion its
inevitable crash...
For a given speed of water, and a given pressure, and a given RPM, a
bladed "thingy" should work about the same whether it is driving the
water, or the water is driving it...
Bob
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Subject: Re: Field Day Water Power
From: "Mike Yetsko" <myetsko@insydesw.com>
Date: Tue, 17 Jun 2003 17:15:55 -0400
X-Message-Number: 25
>acomment before we all get kicked off of here...
>
>Hardly any difference at all. A good prop is also a good turbine. It is
>almost 100% reversible (under identical design conditions)..
I don't think this is true... I've been told most props for air vehicles
are airfoils, and depend almost as much for the surface effect as they do
for angle of attack.
And look at propellers for boats. 30 degrees? Water rushing 'at' a
prop would just create incredible turbulance in that case. Heck, some
props don't even work well when run backwards, let alone trying to
get the energy transfer to work in the other direction!
Mike
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Subject: Re: Field Day Water Power
From: Bob Bruninga <bruninga@usna.edu>
Date: Tue, 17 Jun 2003 17:34:14 -0400 (EDT)
X-Message-Number: 26
On Tue, 17 Jun 2003, Mike Yetsko wrote:
>>>Agood prop is also a good turbine. It is almost 100% reversible
>
>I don't think this is true... I've been told most props for air vehicles
>are airfoils..
So are good wind turbine blades.
>And look at propellers for boats. Water rushing 'at' a
>prop would just create incredible turbulance in that case.
No, not at all, If you disconnect the piston motor that has incredible
torque requirements to turn it over, and instead, let the shaft run free
and connect it to an alternator, then it would spin perfectly well. Look
at the blades on water turbines intended to be towed behind a boat to spin
a generator, THeir blades are identical to a prop..
>Heck, some props don't even work well when run backwards, let alone
>trying to get the energy transfer to work in the other direction!
I'm not talking about running a prop backwards, I am talking about running
the FLOW backwards. The propeller goes the same direction with respect to
the forces involved whether it is pump or a turbine. I agree, you dont
"turn" them backwards, just reverse the flow. Sorry if I confused
everyone by saying "run the pump backwards". What I meant was, run the
flow backwards... to make it work like a turbine...
BOb
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Subject: Re: Field Day Water Power
From: Jim Sanford <wb4gcs@amsat.org>
Date: Tue, 17 Jun 2003 18:00:51 -0400
X-Message-Number: 27
Bob:
I partially agree.
>Hardly any difference at all. A good prop is also a good turbine. It is
>almost 100% reversible (under identical design conditions)..
>
>You are comparing a prop (which has a tip-speed ratio of 8 or more) to a
>windmill (which has a tip-speed ratio of 1 or less). This is apples and
>oranges. The prop was designed for high speed (100 to 300 MPH, high RPM,
>and low torque). THe windmil was designed for low speed (7 to 30 MPH,
>very low RPM and very high starting torque (remember, they had to pump
>water up and down)... Hence totally different designs.
Agree
>There are many very efficiient wind turbines that use blades that are
>identical to props, but they need higher winds, and very low
>starting loads. But once a 2 blade wind turbine is up to speed, it
>sucks all the available energy out of the wind just like a fat windmill
>does at 1/10th the speed. So there is no difference, as long as you
>propely engineer the blades to the given conditions.
>
>Even a Helocopter with a failed engine will auto-rotate its unpowered
>blades to act like a turbine to slow its descent and cushion its
>inevitable crash...
THis is the key to the design difference, rotational speed. BTW, I've
BEEN in an autorotating helicopter. It works as advertised, but don't
EVER want to do THAT again! Mine was a trainng event, but I know a lot
of folks who've walked away from near-fatals due to that effect.
>For a given speed of water, and a given pressure, and a given RPM, a
>bladed "thingy" should work about the same whether it is driving the
>water, or the water is driving it...
This is where I disagree, Bob. Look at the difference between a turbine
(steam or gas) and a centrifugal pump. Yes, a pump can probably be made
to work as a water turbine, but I think a proper design will work MUCH
better.
Very 73,
Jim
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