On 5/14/2010 1:13 AM, knormoyle@surfnetusa.com wrote:<snip>
> And don't forget some safety factor. Also, it's easy to overestimate how
> strong a wall attachment
>
Not very! Not very strong that is.
> to a house is. (plus you have to worry about leaks/wood damage)
>
> Separate analysis would be questions like: are you going to bend the tower or
> base attach? You can
>
Done wrong a 40-50' tower with antenna can wreck a whole wall.
> imagine that at some very low angle the answer is yes (probably not for you).
> You can get that by
> figuring out the horizontal component of the cable forces on the tower.
>
>
And those forces are different at every point for every foot you raise
the tower. Attached at the same distance from the tower base as the
height on the house the maximum load will be the initial load which will
less and less.
OTOH if you attach to the top of the tower the initial load will be
quite large for the initial lift with a major portion being a pull
toward the tower base and a very heavy side load on the two legs of the
tower base.
Using trig you could easily calculate the loads for different attach
points (house, tower, and winch) at the initial lift and at 30 and 60
degrees for the tower angle or you could do it for every 10 if you
wished, but the angle for horizontal, or 90 degrees, 30 and 60 would be
the easiest. HOWEVER you have to remember that when lifting like this
the tower angle referenced to the ground or vertical is not the same as
the angles as seen by the lifting cable which is (or are) the important
angles.
Drawing it out to scale on graph paper and figure the angles and
distances would probably be the easiest and quickest, plus it's a good
math refresher. <:-)) Just don't confuse your sine and cosines. <:-))
BTW, I put up a temporary 30' tower that is back guyed, used 2:1
mechanical advantage with 3 working pulleys and am able to raise 40' of
25G by myself. That's without anything on the 25G, but it's a whale of
a lot easier with two people.
I'll have to take some photos and put them up on my page.
www.rogerhalstead.com (mytowerproject)
73 and good luck,
Roger (K8RI)
> -kevin
> ad6z
> ------- Original Message -------
> > From : Alfred Frugoli[mailto:ke1fo@arrl.net]
> Sent : 5/13/2010 12:10:18 PM
> To : towertalk@contesting.com
> Cc :
> Subject : RE: [TowerTalk] Calculating load when raising tower
>
> Hello Everyone,
>
> Is there a simple equation for figuring out the forces that would be
> experienced in tilting up a tower? I'm buliding a raising fixture, and want
> to make sure that pulleys and the winch can handle the associated loads.
> The tower is a 30 foot tower, and will be raised by a cable attached near
> the top of the tower, that will run through a pulley 15 feet above ground
> about 30 feet away from the tower (on an appropriately reinforced point on
> the house), then back to a pulley near the top of the tower then to a winch
> mounted at an appropriate height at the tower base. The tower is a 30 foot
> aluminum tower with a rotor, 5 foot aluminum mast, and a small tribander
> just above the top of the tower.
>
> A 2nd question is would it be better to have the cable routed in a different
> way, or attach at a lower point on the tower (level with the raising point
> at ~15 feet)?
>
> 73 de Al, KE1FO
>
> K3 #3055
> K3 #4094
> -----
> Check out my Amateur Radio Contesting blog at ke1fo.wordpress.com.
> _______________________________________________
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