[TowerTalk] Antenna surface area
Bill Hider
n3rr@erols.com
Sun, 10 Jun 2001 03:16:01 +0100
Hummm, I did not see that in his posting.
You are just verifying my posting, since, as you say, we must take Gene's
calculation and multiply by 0.6 to obtain wind area.
That makes sense to me, since Gene said that his calculation resulted in a
higher number than the mfrgs said.
0.6 is the multiple for the approximation of the integral I proposed in my
posting.
Bill, N3RR
----- Original Message -----
From: Michael Tope <W4EF@dellroy.com>
To: Bill Hider <n3rr@erols.com>; EUGENE SMAR <SPELUNK.SUENO@prodigy.net>;
<towertalk@contesting.com>; Stu Greene <wa2moe@doitnow.com>
Sent: Sunday, June 10, 2001 3:31 AM
Subject: Re: [TowerTalk] Antenna surface area
> Bill,
>
> Gene specifically said that he was calculating projected area without any
shape
> factors. The projected surface area at right angles to a cylindrical tube
is simply
> diameter x length. The effective area is computed by including the drag
coefficient
> of the object. For a cylinder, the drag coefficient is around 0.6. Thus
the effective
> area of an antenna with round members is about 40% smaller than the
projected
> area (a round tube of length, L and diameter D, is more aerodynamic than a
flat
> plate length L and width, D).
>
> 73 de Mike, W4EF....................
>
>
> ----- Original Message -----
> From: "Bill Hider" <n3rr@erols.com>
> To: "EUGENE SMAR" <SPELUNK.SUENO@prodigy.net>; <towertalk@contesting.com>;
"Stu Greene" <wa2moe@doitnow.com>
> Sent: Saturday, June 09, 2001 6:13 PM
> Subject: Re: [TowerTalk] Antenna surface area
>
>
> > The formula Gene proposed is not exactly correct, nor does he precisely
> > state what to do with the taper.
> >
> > Regarding the formula, Gene's thinking is: If you think of the wind as
> > hitting the tube broadside (at 90 Deg to the tube), the exposed surface
area
> > as seen by the wind looks like a rectangle whose length is the length of
the
> > tube and whose height is the full OUTSIDE diameter of the tube. Hence,
L x
> > Dia. Unfortunately, it is not that simple.
> >
> > The tube is a cylinder as seen by the wind, hence the angle that the
wind
> > *hits* the tube, even if it is perpendicular to the tube, hits at 0 Deg
on
> > the centerline and then the angle increases to 90 Deg as the wind hits
the
> > tube away from the centerline (above and below the centerline of the
tube
> > for a horizontal element). This assumes the wind-front is wider than
the
> > outside diameter of the tube, which is probably a very good assumption.
So,
> > the surface area exposed to the wind by the tube is not simply L x Dia.
> > It's the exposed tube length times the integral from 0 to Dia of the
surface
> > area of each tube (Pi x Dia), where Dia is the Outside diameter of the
tube.
> > Gene, this is why the manufacturer's wind area is less than what you
> > calculated, and theirs is correct. [If anyone has trouble picturing
this,
> > let me know and I'll try to explain it in more detail.]
> >
> > But, I question the correctness of adding all of these calculations up
and
> > saying that's the *wind area*. It certainly is the 1/2 of the *surface
> > area* if it's done this way, but the wind cannot be simultaneously
hitting
> > the elements at 90 Deg and the boom at 90 Deg, so it should take that
into
> > account by specifying the *larger* of both calculations, but not the sum
of
> > both.
> >
> > Regarding the taper: each tube should be calculated separately for the
> > *exposed* length of the tube *only*. Remember, some tubes are *inside*
> > other tubes, causing the taper.
> >
> > Bill, N3RR
> >
> >
> > ----- Original Message -----
> > From: Stu Greene <wa2moe@doitnow.com>
> > To: EUGENE SMAR <SPELUNK.SUENO@prodigy.net>; <towertalk@contesting.com>
> > Sent: Sunday, June 10, 2001 2:42 AM
> > Subject: Re: [TowerTalk] Antenna surface area
> >
> >
> > > At 09:06 PM 6/9/01 -0400, you wrote:
> > >
> > > > Area = L X diameter for the exposed surface of each piece of
aluminum,
> > > > simple as that.
> > >
> > >
> > >
> > > Shouldn't the calculation be L X (Diameter X pi) ? Or length times
> > > circumference?
> > >
> > > And this doesn't reflect tapering of the elements.
> > >
> > >
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> > > -----
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> > >
> >
> >
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>
>
> List Sponsor: Are you thinking about installing a tower this summer? Call
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> for information on our fabulous Trylon Titan self-supporting towers - up
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> 96-feet for less than $2000! at 888-833-3104 <A
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>
> -----
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>
>
List Sponsor: Are you thinking about installing a tower this summer? Call us
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