On 10/18/2014 9:11 AM, TexasRF--- via TowerTalk wrote:
Hi Rick, I have used the falling derrick system on towers up to 60ft. I am
not familiar with the tipping point phenomenon so you might elaborate on
that a bit.
73,
Gerald K5GW
For example, on Field Day I use 30 feet of 11 inch aluminum tower as
a falling derrick to erect 40 feet of same kind of tower with a 2
element SteppIR on top plus low band wires. An "armstrong" winch
is used. As the tower nears vertical, there will be an angle
of perfect balance where the weight of the falling derrick exactly
balances the weight of the tower. If I were to keep pulling on
the falling derrick, I would exceed the tipping point and the derrick
would come crashing down, while jerking up the tower. Of course, thanks
to Murphy, an unplanned experiment has been done to see what would
happen in this case. Luckily, everything survived the rather violent
action, but I would not want to do a large tower this way. Instead, I
have to transition from pulling the derrick down to restraining the
tower to let it down easy. This is tricky to do with one person, which
is required as I am in category 1B, 1 operator. With two people
(dueling armstrong winches), you can do a gradual handoff of control.
For a bigger tower, using motor winches, I'm not sure how to elegantly
hand off control from one winch to the other. During lowering of the
tower, there is a similar tipping point. How are you dealing with this?
73
Rick N6RK
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|