Repairs

All the plastic retaining tubes have been removed from the Polaron V main stage. On inspection one other tube was cracked (other than those that were shredded) . Because of the forces involved we didn't want to take any more chances with plastic, so we replaced them with thin walled brass tubes. Although adding a little more weight, they should be up to the job. We will need to do some tests first though before giving them the all clear. We are giving the PL a week to fully cure. Other than the tube replacement the rest of the rocket and boosters are ready to go.

Acceleron has been mostly repaired with the exception of the staging mechanism. Over the last month or so we have been working on yet another staging mechanism, and with the repairs needing to be done for Acceleron's stager we decided to complete it and put on Acceleron IV. We still have a long way to go with it, and need to do more testing, but so far the development has been going well. I will post full details once it has flown. It is a lot more compact and lighter than what was used on Acceleron previously.

Since we are rebuilding the staging mechanism it was a good opportunity to upgrade the Tachyon sustainer. We are building a completely new sustainer that has ~30% more capacity, more streamlined shape and new parachute deployment based on V1.5 of the flight computer. The fin section now integrates a ring fin with 4 smaller conventional fins. The ring fin struts are made from 6mm carbon fiber tubing and act as supports for the sustainer during the boost phase.

The top part of the pressure chamber consists of a spliced 1.25L pair of bottles Robinson coupled to a special 1.25L bottle. We have a couple of bottles (they don't sell them anymore) that are very streamlined ideal for tail cones of rockets. We Robinson coupled it as opposed to splicing it so that we can use Jet Foaming in this rocket. The nosecone also comes from a slightly different bottle compared to what we normally use. The nosecone has about a 20% longer curved section making it more streamlined.

The sustainer will carry both the altimeter and camera.

22mm Tornado Couplings

I briefly discussed the new tornado couplings in the last update. Since then, I ordered 10 of the 3/4" BSP sockets from Philmac, but at $4 each they are a little pricey. They arrived a few days ago and dad got on the lathe and re-threaded all of them. By the end he was cranking them out every 15 minutes. We have 13 couplings altogether now and want to use them on a number of projects. An upgraded Acceleron booster will need at least 6 of them.

The large bore couplings will enable us to do two things. Use long launch tubes and allow us to experiment with bigger nozzles. The Robinson couplings we have been using were only 8mm and this caused a choking effect when used in combination with a larger nozzle.

Having larger nozzles will allow us to build bigger rockets, as the 9mm nozzles can only provide a certain maximum thrust for a given pressure. To lift heavier rockets we will need to use bigger nozzles.

New Rocket

As the bottles trickle in from friends and family, we have been making up a stockpile of the spliced pairs of bottles, both 1.25L as well as 2L ones. The 2L pairs use 5 bottles each so that is a lot of lemonade that has to be processed. 2 bottles make up the pressure chamber, 1 bottle for the splice sleeve and two bottles are used for the reinforcement rings around the neck of the bottles. We also use the cylindrical sections from the last two bottles to make up the inter-bottle aerodynamic sleeves.

These spliced pairs work well with the new couplings allowing us to assemble various configurations of rockets or boosters.

We have assembled a new rocket to fly this weekend using 3 spliced pairs and 3 of the couplings. The removable fin assembly was taken from Hyperon and the nosecone and deployment system are taken from the Tachyon III sustainer. We pressure tested the rocket to 130 psi without leaks. The rocket has a capacity of ~7.5 liters.

FTC tests

In the background we have been working on some FTC tests. The primary reason for looking at FTC is that we want to use it to make some upper stages of rockets. We bought some T8 6-foot lengths quite a few months ago, but only now are we getting to doing anything with them. The FTC only has an average wall thickness of 0.36mm which is pretty thin.

We made an end-cap out of some PVC we had on hand and the nozzle is based on a 15 mm Gardena nozzle. The one we bought from the local hardware store came with an outside thread. We machined an adaptor with a matching thread that fits snugly inside the FTC. We then epoxied the nozzle inside the adaptor. The seal for the end-cap and nozzle is provided by an o-ring that sits against the FTC. Just behind the o-ring is a groove that allows us to shrink the FTC into it to hold the end-cap and nozzle in place. We copied this technique from Urie's water rockets.

To secure the end-cap and nozzle we wrap a couple of loops of thin fencing wire around the FTC just over the groove. We then apply heat from a heat gun to the FTC while applying tensile stress to the wire. This allows the wire to deform the FTC into the groove. We then let it cool down and twist the wire closed.

For the first test we used a 1 foot length of the FTC and secured the end-cap and nozzle at either end. When we first heated the end of the FTC we kind of forgot, that other parts of the FTC may also get hot and we ended up buckling a part of the FTC past the end cap. Oops. Since it was going to be a pressure test, the slight buckle didn't worry us. On all subsequent heating we filled up the FTC with cold water and that prevented the FTC from shrinking where we didn't want it to shrink.

We then hydrostatically tested the FTC to 190 psi before the FTC split. We were happy that the end-cap and nozzle held and that there were no leaks. One of the nice things about attaching the nozzle and end-cap in this way (without glue) is that we can reuse them for other tests or actual rockets.

We then hydrostatically tested another 1 foot length of FTC, but this time wrapped it with one layer of fiber glass strapping tape. We also added a number of extra wraps of the tape around each end right near the o-rings to help with the seal. As we reached 230 psi the end-cap flew out of the FTC. It looks like the groove in the end-cap was not deep enough and the wire probably loosened where it was twisted.  This allowed the end-cap to slide past the wire.

There was no damage done, and we will reused the same length of FTC in another test, but this time with a deeper groove in the end-cap. We want to see how far we can take the reinforcing. The single layer of tape added 7grams to the 1 foot length of FTC.  I believe Urie's water rockets filled the outside groove where the wire is with Epoxy, and this may be a good way to keep the wire from unraveling.

Our first goal is a launch pressure of 200psi, so I think it is well within the techniques we are using for reinforcement and attachment of the nozzle and end-cap.

Miscellaneous

I bought a new heat gun (Metabo HE2000) a couple of weeks ago. We've been using a blowtorch for shrinking bottles until now, but it was always a bit of a hassle having to light it, and get refills for the gas cylinder. The heat gun has good range of temperature settings and air speeds.

After a couple of months of slow development the new Flight Computer V1.5 software is almost finished. The full write up and user manual will be available on our site shortly.