As I am sure you know, the forces grow quite high on the pull point as
included angle of the strap approaches 0 degrees. Numbers for you to think
about are: If the included angle is 60 degrees, the force on the strap is
1.15 times the force if it was a direct vertical pull. At 30 degrees, the
force is 2 times vertical pull and at 5 degrees the force is 11.47 times a
straight vertical pull.
Steve
K9SL
On Thu, Feb 2, 2012 at 8:02 AM, Gary Schafer <garyschafer@comcast.net>wrote:
> A friend of mine did this with a small (30') tower on field day. When the
> tower got down low it pulled the Jeep that it was attached to and slid the
> wheels.
> The tower swung out off center and crashed down. There is tremendous force
> on the cable when the tower is near the ground.
>
> You also need side guys on the tower when raising/lowering like that.
> The falling derrick is a must.
>
> 73
> Gary K4FMX
>
> > -----Original Message-----
> > From: towertalk-bounces@contesting.com [mailto:towertalk-
> > bounces@contesting.com] On Behalf Of Wilson Lamb
> > Sent: Thursday, February 02, 2012 10:49 AM
> > To: towertalk-request@contesting.com
> > Subject: [TowerTalk] Question about lowering a Fold-Over tower
> >
> >
> > Dick,
> > Please don't do this until you can get some onsite help. You're looking
> > for
> > trouble!
> >
> > As that tower gets near horizontal, the compression/buckling load from
> > the
> > cable will be LARGE, easily enough to pull out a brace, if that's where
> > you
> > hook on. Who knows if your hinge hardware can take the load? It might
> > be
> > enough to spin the tires of your car, if on grass.
> >
> > Worse yet, if you get the least lateral displacement you will get the
> > cable
> > off to the side of the hinge/tower plane and you will then have the top
> > of
> > the tower trying to go sideways because of the cable pull being off
> > axis!
> > You can tear your hinge apart and wreck your beam in a heartbeat!
> >
> > The falling derick advice is right on, BUT you have to be sure the base
> > of
> > the derick is wide enough to provide the lateral stability you need to
> > prevent the off center situation above. AND you have to secure the
> > cable to
> > the top of the derick so the derick can't slip on the cable and drop the
> > tower as it gets low! 20' of Rohn 25, guyed to the sides, would make a
> > good
> > derick.
> >
> > There may be other problems, but this should be enough to convince you
> > to
> > wait for some local guidance.
> >
> > Good luck,
> > Wilson
> > W4BOH
> >
> >
> >
> >
> > Hi Guys,
> > I'm going to lower a 90' Heights aluminum fold over tower with my car
> > tomorrow evening. I've done this before without destroying the tower
> > so
> > hopefully I can have another successful lowering!
> >
> > My question is what is the best height on the tower to attach my Nylon
> > Strap for lowering the tower?
> >
> > A few thoughts:
> >
> > 1) The 90' tower folds over at ground level and has a 36" wide base.
> >
> > 2) In the past, I attached my nylon strap around the tower at aprx. the
> > 35' level and then attach a 1/4" steel cable to the nylon strap and
> > raise
> > and
> > lower the tower with my car.
> >
> > 3) I keep the top of the tower 13' off of the ground so there's room to
> > attach my 24' boom Yagi to the top of the tower. Keeping the top of
> > the
> > tower 13' off of the ground makes it easier to lower and raise the
> > tower
> > with a
> > vehicle than if the top of tower was on or near the ground. That said,
> > with the top of the tower 13' off of the ground it's still quite touchy
> > raising and lower the tower as only as a small movement in the vehicle
> > makes a
> > big change in the tower.
> >
> > So I'm looking for the best strap height to lower the tower and the
> > best
> > strap height for raising the tower. After using the 35' height
> > before... I
> > don't think that one height is the ideal height for raising and
> > lowering
> > the tower. Since it's easy to locate the nylon strap anywhere on the
> > tower
> > I'm looking for the best height for lowering and best height for
> > raising.
> >
> > All thoughts appreciated!
> >
> > Thanks-
> >
> > Dick- K9OM
> >
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
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>
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