There are a lot of variables in tower design. Iterative stress analysis is
done to predict where stresses are high. I am not a structural engineer,
but I worked on stress structural analysis software.
When you raise and lower a crank up tower, it changes the area and shape of
the structure. Wind forces on the tower diminish, and the “topple moment”
obviously changes with height, as you have indicated.
The lift cable, and to some extent, the pull down cable, introduces another
failure mode. Upper sections are suspended, many towers the upper sections
are hanging there and there is movement in wind unless the cable is not
slack. Check the pull-down spring, replace it if it is rusty or slack.
So it is complicated. And what about the tornado that comes Sunday while
you’re out and didn’t lower it?
I have seen one tower that uses wind speed to lower the tower, but
auto-lowering worries me.
As you have heard before - talk to the manufacturer. If they’re still
around, they can give specific guidance.
Mickey N4MB
“Ends and beginnings—there are no such things. There are only middles.”
Robert Frost
On Sun, Feb 18, 2024 at 4:02 PM Dave . <ktx85@hotmail.com> wrote:
>
> Wow....
>
> I live in central Iowa.....Originally was planning on a US tower
> Hdx70 tower but it was destroyed in bad weather before I could
> purchase....so this Hy Gain tower became avaliable..I thought I could use
> this for now until I got a 70 replacement...but
>
> Confusion ...
>
> I was looking up a HyGain hg54HD
> IN one factory document I see 16sq ft at 60mph (1990)
>
> In annother factory calculations document I see 25sq ft
>
> I know these calculations are from days of old
>
> And other mfg numbers are ALL over the place
> And let's not forget that many of the antenna mfg windload numbers are
> well...I'm not sure what to call them
>
> Here is the plan
>
> HY-54GD....16sq....supports ?
>
> Concrete base for tower is rated for a HDX70 ( 2 x more Concrete than the
> hy54hd requires)
>
> For comparison
>
> Hdx555 23 Sq. Supports 200lbs
>
> nn4zz tiltplate......1sq. 30lbs
>
> Steppir 4 El 40-6....( 1 trombone)........18.5 Sq. PROJECTED ??? A few
> sites say 12sq......106lbs
>
> 3 .....M2. 2m12 2m yagi. 1.5 Sq each. 8lbs each
>
> 1 wire dipole......
>
> 1 diamond x510HMN..........
>
> Yaesu 2800 rotator...14.33 lbs
>
> 2 inch 1/4 wall 6063 alum mast...4 1/2 foot above the Tilt plate...Tilt
> plate 2 inches above thrust bearing
>
>
> Looks like my wind load with all the above would be 23.5 sq....OOPS...
>
> OBVIOUSLY...I wouldn't leave the tower up in a 60mph wind.( that's asking
> for trouble)
>
> It is 22ft cranked all the way down.....
>
>
> It seems as if you want more than a dipole on top you have to purchase a
> 80,000 tower
>
> Are there numbers SOMEWHERE that are "real" .?
>
> Every mfg seems to have their own calculator..
>
> M2 antennas and nn4zz seem reasonable
>
> It appears all numbers are cover your butt numbers the mfg have come up
> with...
>
> There are so many years and years of politics in between. And
> calculators....
>
>
> And to say hams NEVER overload their towers....well...that would be a
> fairytale
>
>
> Is there some rule of thumb that this might work to say 30-40 mph without
> cranking down?....is there someone with a simular set up that is in use
> that can share some thoughts ?
>
> Sigh
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|