Wagtail update

Given the long time between updates it's probably time for a wagtail update:

The improved Wagtail design is nearly complete.

Figure 1. Image of the design concept for the Wagtail Mk II

Features include:

• Finocyl grain, mainly to increase the burn time from 3.5 seconds to 7 seconds and thereby lower the g forces.
• Single grain rather than 2-segment grain. Only one main joint - where the nozzle attaches, rather than the three joints in the earlier design.
• Head-end pyrogen ignition rather than nozzle-mounted pyrotechnic igniter to reduce the risk of disastrous nozzle blockages.
• Motor propellant mass fraction increased from 69% to over 75%, including casing, nozzle, fins, igniter and payload adaptor.
• The manufacturing technique has been designed to greatly simplify manufacture and minimise cost whilst producing a precision, high performance rocket motor. The tooling will be precision turned with integral datums (data? Anyway, features) on which parts are precisely aligned to minimise trajectory dispersion.
• The nozzle is submerged (in the propellant grain) and rather like the waxwing sea-level nozzles, mainly for ease of design and manufacture
• It can be scaled up easily to an 8-inch motor that is similar to a Sparrow motor. Our mixing and casting rig is designed for motors up to 8-inches and over 2 metres long with about 60 kg of propellant (four Zuni grains).
  

The propellant mixer has been commissioned:

• It has been changed from electric to hydraulic power with remote control and closed circuit camera for operator safety.
• The bowl is detachable so the propellant slurry can be taken to the casting rig.
• A hot water system has been installed to heat the jacketed mixing bowl so we can mix better propellants.
• The venting mechanism has been tested with compressed air to simulate a fire in the mixer. The lid of the bowl is normally held on by vacuum but is hinged so that it can lift up in the event of positive gauge pressure in the bowl, so the mixer can't burst.

The casting rig has been completed.

Casting is done under vacuum and the rig is water-heated to cure the propellant.

A hydraulic core extractor is being designed. Like the mixer it will be remotely operated and monitored by cctv so the operators are safe.

The next task is to thoroughly test the pyrogen igniter system. It will probably have two electric matches igniting a 1 gm B-KNO3 pellet igniting about 40 gm of Wagtail fuel, burning for less than half a second in a mini rocket motor. It can be easily customised to suit Ausroc 2.5 ignition, perhaps with a burn time of several seconds.

Comments, suggestions and questions are welcome.

Philip Teakle