Tie Rod¶
The tie rod is the internal threaded rod that draws the Slocum hull sections together and holds the glider closed. It is mounted to the bottom of the aft electronics tray and runs forward through each section, threading into a tie rod receiver in the forward section (or in an add-on module). Tightening the rod is what pulls the mating hulls over their O-ring seals and squares them up.
Source
Paraphrased from the Slocum G3 Glider Maintenance Manual (Rev. A), the UG2 community Slack, and the Teledyne Webb Research user forum. This is a condensed field reference — always defer to the official Teledyne documentation for your specific glider.
How it works¶
You reach the tie rod through the vacuum seal port on the aft endcap. With the PEEK vacuum seal plug removed, a hex bit driven by a 15 inch-pound torque T-handle engages the rod end:
| Action | Tool | Bit |
|---|---|---|
| Main aft tie rod | 15 in-lb torque T-handle + 24" extension | 3/16" hex |
| Add-on / energy-bay tie rod extension | 15 in-lb torque T-handle | 5/32" hex |
- Opening: unscrew the tie rod until tension releases, then separate the sections with the hull separator tool. The rod must be fully disengaged from its receiver before the sections will come apart.
- Closing: route the rod through the payload bay tie rod guide tube, bring the sections together, then screw the rod into the forward section (or add-on module) receiver and tighten to 15 inch-pounds. The sections should draw together smoothly, tight and square, with index marks aligned and O-rings unpinched.
Protect the seal and threads
Take care not to damage the sealing surface or cross the threads with the side of the tool assembly. Keep payload-bay and battery cabling clear of the guide tube so it does not impede the rod as it is inserted.
Why 15 inch-pounds — the glider is built to 'burp'
The 15 in-lb figure is used as a safety limit. It intentionally under-tensions the hull so that, if internal pressure ever builds up — most importantly during a battery thermal-runaway event — the glider will "burp": momentarily flex and vent at a hull seam instead of failing explosively. In an old TWR demonstration a glider was pressurized with air and physically bent and burped at a seam, relieving the pressure. Over-tightening past 15 in-lb defeats this relief path. (The behavior was characterized on single-seal G1/G2 hulls; the G3 double-seal hull has not been formally re-tested for the pressure at which it burps.)
Servicing the tie rod assembly¶
If the tie rod assembly itself is removed (glider already disassembled):
- It is held to the bottom of the aft electronics tray by six screws.
- On reinstallation, apply a drop of Loctite 243 (blue) to each of the six screws before fitting them to the tray standoffs.
Length varies — especially on add-on bays¶
Tie rods are not all the same length, and this is the most common field frustration when closing G3 gliders.
Hand-push short sections together first
Operators report that tie rods on stack-on / add-on bays (for example an AD2CP bay) vary noticeably bay-to-bay, and some are very short. With a short rod, the threads will not catch until the hulls are already most of the way home. Manually push the hull fully over the O-ring seals — by hand, as far as it will go — before trying to draw it in with the tie rod. Many G3 sections have to be seated almost completely by hand before the rod will catch, unlike the G2 where the rod could pull the sections together from the start.
This friction is compounded by the G3's double O-ring seal and dried-out O-ring grease; see assembly and O-ring lubrication notes for related tips.
G2 vs. G3¶
When the second O-ring was added, the G3 carbon-fiber hulls grew 0.5 inches longer than the G2's and the internal tie rod was lengthened to match. As a result, G2 hulls will not fit on a G3 glider (and vice versa).