Lift Wire Stretching

Stretching a lift wire with a block and tackle system and electric winch

The .080" diameter steel music wire that we use for the lift wire comes tightly coiled and is hard to uncoil and use.  So a first step before turning the wires into lift wires (by terminating the ends with sailing thimbles of the proper size), is to stretch them so they yield slightly and coil back up in a much looser coil.

We did this by hooking up a winch to my old Trooper II SUV at the hitch receiver, attaching a block and tackle setup to that, and then attaching the other end of the block and tackle to one end of the lift wire.  In between was a digital scale so we could measure the force on the wire.

The other end of the lift wire was attached to a large, heavy shipping container.  Then we turned on the winch, and pulled until we reached a value we knew was slightly over yield.  Then we iterated until we found the right amount, and then stretched a bunch of wires that way since we are going to make multiple lift wires (different lengths for the v5 and v6 wings, for instance, plus spares).

Uncoiling the tightly coiled wire prior to stretching

Attaching the wire to the corner of the shipping container

Attachment point at shipping container end

Lift Wire attached to shipping container, other end ready to attach to block-and-tackle setup

Everything hooked up and ready to pull

We stood far away (more than 1 wire length) for safety, and used a camera to read the scale

Looking at a scale reading

Hooking up a phone camera to read and transmit the scale reading

Final setup in place, with phone/camera strapped in to transmit scale reading

Looking at the broadcast scale reading using another phone