Each flight log entry usually represents a launch or test day, and describes the events that took place.
Click on an image to view a larger image, and click the browser's BACK button to return back to the page.

Team Members at Event: GK and PK

Development

We continue to develop our multistage rocket, but we had to have a chuckle today, as it is just turning out to be much more complicated than what we initially anticipated. When we did a full component count today, we found that there are close to 300 individual components for the booster alone. (not counting all the pieces of tape) 

We are going to pursue with our approach, but in the future we will simplify the design. In any case it will be fun to see when it finally gets off the ground. There is just something to be said about the simplicity of a crushing sleeve mechanism.

Tachyon

We finished the Tachyon sustainer this week. That means we now have final flight hardware that we can mate to the booster. There are a number of new functional and construction techniques used on this rocket that we haven't tried before:

• Nosecone shape - The tip of the nosecone is round, and is simply made by gluing half a ping-pong ball to the hole left after removing the bottle throat.  The curvature fits well to make a clean aerodynamic shape
• Sideways opening hinged door - The parachute hatch door hinge is parallel to the rocket axis. The door itself provides a clean aerodynamic cover.
• Soft sponge for chute ejection - We are trying a simple approach for providing the force to eject a parachute. No need for rubber bands, pistons, springs and the like. This is a single component solution that is inexpensive, lightweight and can be reused, should the rocket crash.
• Simple pin pulling mechanism - The pin that opens the door is attached to a piece of thread, and the other is tied directly to the RC servo horn.
• RC micro-servo actuator - We decided to go with this slightly heavier option, but it comes in a nice neat package, it is easily mountable, powerful, and the position can be set directly by the flight computer. These cost us $6.50 delivered.
• Removable fin assembly - The fin assembly is now made so that it can be attached to the lowest bottle without any tape, glue or rubber bands. This allows us to swap the fin assembly on the rocket in the field, should it become damaged during landing.
• 5 mm nozzle - The nozzle is newly machined to conform to the standard 9mm Gardena mechanism, but the internal hole is only 5mm. This allows us to use a 7mm or 9mm nozzle for testing the sustainer by itself, and the 5mm one for boosted flight.

Tachyon uses V1.3.1 of the flight computer to deploy the single 42 cm parachute. We are using a 9V battery to power it, so that we get plenty of current capacity while we are doing tests. If we ever end up going for any records, we can replace the battery with a much lighter one to gain those few feet. The 9V battery just makes it much more convenient, because they are cheap, and available everywhere.

The deployment mechanism is also now removable from the nosecone. This allows us much easier access in assembling all the components. All the components are mounted on cardboard bulkheads. The entire deploy mechanism is held in place with a piece of curled bottle which provides enough support for the G forces that the rocket is likely to encounter. Mounting the payload section this way allowed us to produce a much more streamlined nosecone and payload section.

The Acceleron III pod bulkheads are made from corrugated plastic used to make signs.

Removable fin assembly

We first tried gluing the fins directly to the PET bottle with PL Premium, but we found that the plastic we chose for the fins did not stick to PL Premium at all even with careful cleaning and sanding. The glue held great to the bottle though. Instead of choosing a different fin material ( we liked it's rigid yet non-brittle properties ) we decided to make a self contained fin assembly that could be removed.

The fin material itself came from the cover of a folder bought at OfficeWorks. The plastic is translucent, quite rigid, but not brittle. You can cut it with scissors.

To each fin are attached four L-brackets made from a 2L juice PET bottle plastic. This plastic is much thicker than regular PET bottle plastic. These L-brackets are attached with aluminium pop rivets to the fins instead of glue. The pop rivets are hammered flat on both sides to make them more aerodynamic. These L-brackets are then simply taped with glass-fibre reinforcing tape to two PET plastic rings that fit the profile of the bottle.

The upper ring is made from a larger bottle and heat shrunk to fit exactly the profile of the rocket body. The lower tapered ring is simply a section of another bottle, and because of its conical shape it does not need to be shrunk.

The reason the fin arrangement does not need to be taped to the rocket body is because of the little lip that exists at the base of the curved section of the bottle. (refer to diagram). When you are putting the assembly on, you have to distort the bottle (collapse it inward) in order to slide the tight fitting upper ring over the lip. Once over the lip the bottle can spring back to its original shape. The tapered lower ring prevents the fin assembly from moving up the bottle, and the lip prevents it from moving back. It is impossible to remove the assembly without distorting the bottle again. This way you can swap the fin assembly in less than a minute should you need to.

Testing

We assembled the staging mechanism release trigger and tested it under pressure. At first it turned out that the rubber bands just weren't providing enough pulling force when pressurised (you were right Trevor). When there was no pressure the coupling released just fine. We added a few more rubber bands and it worked a treat.

For the tests we were only pulling on the release mechanism with a string. The next step is to have the servo release the trigger. But for that we need to complete V1.4 of the flight computer. The actual cable going to the servo is made out of Tiger Tail - a strong and very thin steel cable coated with nylon. It is used for making necklaces.

We have also had a number of requests for details of the Acceleron launcher, so we have included a cross section detail showing the the nozzle seat and how air is supplied to the booster.

A couple of days ago was our first vertical launch anniversary. We would like to thank all the people in the water rocket community for contributing their ideas to make this a really enjoyable hobby.