Original URL: http://www.theregister.co.uk/2010/09/03/release_mechanism_update/

Vulture 1 Mk 2 release mech prepped for testing

Coming soon: Hypobaric chamber - The Revisiting

By Lester Haines

Posted in SPB, 3rd September 2010 12:20 GMT

The Paper Aircraft Released Into Space (PARIS) team is preparing to turn down the pressure with a second visit to QinetiQ's hypobaric chamber.

You'll recall that our first attempt to put together a pressure-operated release mechanism for the Vulture 1 aircraft didn't quite run on rails.

Undaunted, we stuck with our plan to have an entirely mechanical release system. Some of you have asked why we don't just rig something electronic, run off a GPS system, which will let the plane go at the required altitude.

Well, we don't trust electronics much, and it's not nearly as much fun as pottering about in the shed with oxygen tubes and rubber bungs - vital components of the Mk 2 release mechanism:

A graphic of our Mk 2 release mechanism

You can get more details on how this top-class piece of British engineering works - and how we put it together - in our previous piece, which concluded with it fully assembled:

The release mechanism fully assembled

Of course, you're wondering exactly how, as the oxygen tube inside the outer casing expands, it will release the Vulture 1.

First up, we tidied up the end components of the plunger rod, with a couple of washers, a nut and a steel spacer, all epoxied into place. This snap shows those components at their start position relative to the PVC tube end cap, with the oxygen tube fully compressed:

The plunger rod assembly where it emerges from the PVC tube

Next up, we welded a steel "release rod" to a bracket which is fitted tightly onto the plunger rod with a wing nut. The wing nut allows the release rod to be removed, which is vital for the pre-flight suspension of Vulture 1. Note the plastic guide channel for the release rod, which is a bit of off-the-shelf electrical box conduit:

The plunger rod attached to the release rod by a bracket

At the longitudinal midpoint of the release mechanism, inside the plastic guide conduit, is the spot at which Vulture 1 will hang from the release rod by a wire passing through the floor of the main payload box. The wire is simply looped loosely around the rod, and when the end of the rod passes through the loop at the required expansion of the oxygen tube, the aircraft will drop away (yes, we have calculated the expansion and correct rod travel distance, thanks...).

The release point in the release rod guide channel

Well, we now present the finished set-up, with a 500g test weight suspended underneath:

The complete set-up, showing the rod start position, the position of the Vulture 1 suspension loop and the test weight

To clarify, the unattached end of the release rod starts at position A, travels in the direction of the blue arrow until it reaches the Vulture 1 suspension loop (B), and away we go...

You're probably wondering now if the force of the expanding air inside the oxygen tube will be sufficient to overcome the friction in the system.

Bear in mind that all moving surfaces will be lubed with a special low-temperature grease, but a quick blast without any lubrication at all showed it didn't require much bike pump energy to operate the system:

So, we're back off to QinetiQ on 13 September to test the Mk 2 to 20,000 metres at an ascent rate of around 300 metres a minute, which is how fast we expect PARIS to soar heavenwards. This will tell us if the mechanism works at slow rates of air expansion, something which did for the Mk 1 (more here, if you missed the link above).

Expect our report on a further bout of world-class boffinry in a couple of weeks... ®

Additional PARIS resources