In a message dated 98-10-09 09:55:36 EDT, k5ed@dzn.com writes:
> I wrote:
>
> >> Antenna area (sq ft) load (#) (@ 80mph
> using 25#/sq ft)
> >> TH7 9.4 235
> >> Disc1 (40m 1 el) 2.7 68
> >> 214FM (2m 14el) 1.7 43
> >> WARC 2/2 (12/17m yagi) 3.1 78
> >> mast .1/ft
2.5/ft
>
> As you can see Steve, I did multiply by the wind pressure (25 psf).
Hi, Ed --
QSL - sorry. Let me run the numbers again with your specs.
>
> My distribution again was:
>
> > Antenna area (sq ft) Hgt above tower(ft) bending moment
> (ft#)
> > TH7 9.4 .5
> 118
> > WARC 2/2 3.1 5 390
> > Disc1 2.7 10
> 270
> > 214FM 1.7 12
> 516
> > mast 1.2 6 (avg)
> 180
>
> Note that bending moment is calculated from areaXwind pressureXHgt above
> tower. So I did allow for load distribution up the mast.
>
> The load WILL be supported. Try the MARC program (I don't have it) with
the
> antenna distribution I posted and let me know the results. Placing the
high
> area antennas close to the tower makes a big difference.
>
Okay, while the windspeed used went up (from 70 to 80 MPH), the mast
height was shortened from 16 to 12 feet. The bending moment changed slightly
from 25,992 in-lbs to 25,754 in-lbs. The recommended mast (50K psi yield and
1/4" wall) remains the same. Same conclusion vis-a-vis the aluminum mast. BTW,
the MARC Program is based on the Dave Leeson, W6NL, ex-W6QHS, calculations in
his book, "Physical Design of Yagi Antennas", so we're using the same
technique.
Cheers, Steve K7LXC
http://www.championradio.com
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