Staging mechanism assembly

This week we have been continuing with the staging mechanism of the Acceleron V booster. We've also made the non-return valve that fits inside the long PVC pipe. The valve was adapted from the old Acceleron booster that was mounted in a bottle cap.


More information and photos of the build can be found on the Australian rocketry forum here: http://ausrocketry.com/forum/viewtopic.php?t=1552

It hasn't all been smooth sailing though. After test assembling the base plate in the launcher with the actual booster segments fitted with their nozzles we discovered that the central mechanism couldn't go down far enough to lock into the mechanism. Not wanting to machine up a whole new central nozzle, we decided to put a thick plastic washer underneath it on the base plate, and using somewhat longer screws to hold it all in place was enough to resolve the issue.

The other issue we had was while trying to fit the hose on the end of this central nozzle we found it a little difficult, so we decided to machine down the hose connector a little bit to make it easier. While machining the small thin tube caught on the knife and unceremoniously bent, and was damaged. While trying to straighten it, as suspected it snapped off. Dad came to the rescue and machined off what was left, then proceeded to cut a thread into the mechanism and made a new separate hose connector component that simply screwed into the end. We epoxied it in place and all was good again.

We've also had discussions about how we are going to make the top bracket that holds the boosters together. It's going to involve steam.... but more on that later. :)
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Building continues

We have been continuing with the development of the booster. Here we test assembled some of the components to check for clearances and get an overall idea of how it will go together. The nice thing is that it just fits inside the house. (one inch from the ceiling)

One thing that was very evident is how high the top payload is, and we are going to have to move the flight computer down, or at least extend the Arm button down where it can be reached.


Pictured along with the rocket is a standard sized kid. Simulation says that the booster alone would lob him about 4 meters into the air. :)

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Acceleron V construction

Most of this week has been spent making the base plate for Acceleron V. Here it is partially assembled:
The sustainer air supply and retention mechanism still needs to be machined, which will be done soon.

The bottle splicing is also complete, although the bottles still need reinforcing around their necks. They also all need to be pressure tested. We made a number of spare spliced bottle pairs should any of these leak. We will give all the splices at least 1 week to fully cure.


We used PL for the splicing and Sikaflex for sealing the joints as we had leak issues when making spliced pairs for the Polaron rocket a couple of months back.

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Launch Report update

We've posted an update from the last launch day on our main website here:

http://www.AirCommandRockets.com/day76.htm

There are a number of photos from the day as well as some more design details of the Acceleron V booster build. We are pretty much now focused on getting the Acceleron booster completed. While we are aiming to have it ready for launch at the next NSWRA launch event, it may likely slip until the next one.
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Windy

We only flew a couple of smaller water rockets this weekend at the NSWRA launch day event, mostly due to the high wind conditions. A few of the pyro rocketeers lost their rockets somewhere over the adjoining suburb, so we decided to call it quits a little earlier too.

I'm putting together the launch report at the moment which should be available in the next few days. It also includes a progress update on the Acceleron V booster.

We did launch a couple of small pyro rockets with the boys and safely recovered those. During the week we bought a bigger pyro rocket kit from Suburban Rocketry so we are now building it with the boys in between all the other rocket stuff. I can see we'll probably be building a few of these as they are fun to build, but the cost of motors is pretty high when compared to air and water. :)

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Acceleron V modelling

This weekend we spent a bit of time modeling Acceleron V to scale in 3DS Max in order to figure out the spacial relationships of the new release mechanism and the position of the staging mechanism. We now have a clear idea how to build the base support mechanism and what clearances are needed. The images below include the second stage, although the colour scheme will most likely be different.

The length of the second stage has not been determined yet but will be such that the entire two stage rocket is stable in flight.

The rocket is designed to be launched from our drop away booster launcher.


Detail of the release mechanism and the location of the staging pod. The pod contains one of our flight computers and uses a standard 9mm Gardena release mechanism to release the second stage. Depending on the length of the second stage, the pod can be moved further up the rocket.


Fabrication of the booster segments continues, and we now have a materials list for the release mechanism so we can start construction on that as well. The staging pod is already finished. I'll post actual build pictures next time.

We've also been preparing our rockets for the next NSWRA launch day. There are no major new rocket changes although there are some experiments we want to run in getting more stable descent video as well as flying the whistling nozzle. After the last crash the Axion rocket has been rebuilt.
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Acceleron V Redesign

We've been collecting 2L bottles from friends and family over the last couple of months to make up more spliced pairs for the new Acceleron booster. After we had a few leak problems with the last spliced-pair batch we're now trying the sikaflex glue as a sealant in the joint area but PL premium as the main glue that holds the splice together.

Some of the 2L bottles ready for processingBottles cleaned, trimmed and curled ready for sanding.

All up Acceleron V has three segments in the cluster and each segment uses 3 x 2L spliced pairs giving a total volume of almost 33 liters. Up until now we have been using 10mm nozzles on the Acceleron boosters but with the larger volume and larger weight of water we have decided to go with the larger 13mm nozzles we use with our drop away boosters. Including the second stage, the total liftoff weight is now going to be approaching 16 kilos. Switching to the new nozzles would have also meant that we would have to machine new nozzle seats for the old Acceleron launcher.

Instead we decided to adapt the booster launcher to work with the Acceleron rocket. The old Acceleron rocket uses a speargun release mechanism, so we are replacing this with custom made aluminium gardena nozzle mounted on the baseplate that holds the cluster together. This nozzle will fit into the existing Gardena central release head.

Because this launcher's minimum nozzle spacing does not allow the three segments to be up against each other like in the old Acceleron rocket, we are going to separate the cluster segments further from each other. This will require a new baseplate for the cluster. This again will be made from aluminium and reinforced with fiberglass. By separating the cluster segments we will be able to lower the second stage release mechanism pod further down in between the segments allowing the second stage to also sit lower in the booster. This will help partially solve one of the problems we've been having with the old Acceleron rockets, namely the stability of the second stage on the end of the staging mechanism. The length of the Acceleron booster and the location of the staging mechanism prevented us from making the second stage any longer. If the second stage had been much longer there was the danger of snapping the rocket at the staging mechanism during the boost phase. By lowering the second stage between the segments, we can use the segments themselves as guide rails for the second stage. This will allow us to build a second stage around the length of an Axion or Hyperon rocket.

The second stage will be pressurised through the central release head allowing it to use a different pressure to the 1st stage. The Acceleron parachute(s) will now be located in the space between the spliced pairs.

With the second stage supported by the segments, it will also mean that the second stage can have a boat tail for better drag efficiency.

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Parachute Detachment Mechanism

In chatting to Mat G. this week, he described how his rocket got stuck in a tree flying one of the computers. I thought that the FC should at least be able to try to help in such a situation. Snagging a parachute on trees is a very common problem, especially when the wind carries the rocket beyond the designated range.

We put together a Parachute Detachment Mechanism prototype (DetMech) that allows the rocket to automatically let go of the parachute cord after a predetermined time.

The full details of the mechanism are available here:

http://www.AirCommandRockets.com/howitworks_3.htm

We want to test fly it next to see how the clamp holds up under high speed deploys. ... yup just another excuse to fly more rockets. :)


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FC V2.0 Development

With the last of V1.6 sold yesterday, we are using the proceeds of the sales on the development of the next version of the FC. The new version is quite different and includes a lot of new functionality some of which is intended for use on pyro rockets.

We are also aiming to reduce the overall footprint and weight of the FC by using surface mount components. Circuit design is about 2/3rds done but the software spec for this version is only about 1/4 complete. The core is still based around the PIC16F628A but will have a few more support chips to offload some of the functionality.

The expected time to completion is likely to be around 6 months as there is a lot of new code to write, but that may be pushed back further depending on time allocation priorities on all other projects currently under way. I'll post progress updates and more details when significant milestones are achieved.

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Flour Rockets

We've had a bit of fun this weekend with the kids launching rockets powered with flour rather than water.

The full write up of the days events is here:
http://www.AirCommandRockets.com/day74.htm

Included are photos and a highlights video.


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Variable Nozzle Testing

This weekend we pulled out the static test stand and continued with more testing. Before the tests we spent a couple of hours making the flexible nozzle membranes and the tools to make them.
Dad machined up the stamp tool that cuts the membrane out of the rubber sheet to the exact size (the brass component), and then the hole punch alignment tool, that allowed us to center the hole punch in exactly the middle.

We ran about 14 tests with different materials and different sized holes. We haven't had a proper look at the data yet, as that will again take a couple of weeks to analyze and write up. One interesting surprise we did get was during one particular test the nozzle made a pretty loud whistling noise. We might fly that one on the next launch day just for fun.

We'll post the full data on the nozzles when the analysis is complete.
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Day 73 - Highlights

We've posted an update on our main website with the highlights from day 73. The update includes photos and a video of the days' events.

http://www.AirCommandRockets.com/day73.htm

.... now it's back to the workshop....
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2 great flights, 2 crashes

We had an overall great day at NSWRA's launch event on Saturday. We got to fly the newly rebuilt Polaron VIb rocket that hadn't flown since May last year. Both flights were almost perfect with very nice vertical flights, and no spin which made for great stable ascent video. Although we had tested the bottles to 130psi, we only launched at 120psi to be on the safe side. During testing earlier in the week, we had 3 out of 4 spliced-pairs leak. So only the bottles that had withstood the full 130psi were used in the rocket. We were very happy with the performance of the rocket, and were glad that the stability improving changes we made had been effective.

While other NSWRA members were drilling holes in the clouds (literally) with their impressive pyro rockets we were busy taking core samples near the launch pad. One was the FTC rocket and the other was Axion II. Full details of the crashes will also go in the update.
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Progress update

We've posted an update on main site that describes some of the things we have been working on lately. At the moment we are trying to get two big rockets (Polaron VIb and Polaron VII) completed by the NSWRA launch event next week, as well as the FTC rocket. Currently they are still in pieces, but should be assembled in the next few days.

The update is here:

http://www.AirCommandRockets.com/day72.htm
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Flight Computer V1.6 Details

We've put up the full details of the latest flight computer on our main website here:

http://www.AirCommandRockets.com/flight_computer_V1_6.htm

There have been a number of changes since version 1.5:

• The altimeter power connector has been removed. The altimeter can still be powered via the second servo connector. If both servos and altimeter are used then the second servo can be connected to the altimeter's pass through connector to connect the second servo motor.
• The PCB is now double sided resulting in less weight and 25% smaller area. The PCB is also only 27mm wide allowing it to be used inside T-8 and T-12 FTC tubing.
• The timing parameters have been changed to represent seconds directly rather than the more confusing offset/multiplier technique used in V1.5. Although the direct setting reduces the range of values possible, they should cover the vast majority of situations as used in the real world. The timing for both D1 and D2 phases can now be set between 0.1 and 99.9 seconds in 0.1 second increments.
• The setting of the two delay parameters in the Normal mode have been removed and the FC now simply requires one press of the ARM button to ARM it. This was done to make it simpler for the rocketeer to use in the field, and prevent accidental timing changes.
• The servo control pulse width range has been extended to allow driving some non-standard servos their full range.

These are now available for purchase. (Includes FREE worldwide delivery!)

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FTC nosecone success

Well nosecone attempt #4 (see below) worked out as planned.


This is the end result of 8 layers of nylon stockings with polyester resin, one thin coat of 5 minute epoxy, thin coat of spray on putty sanded back for a smooth finish and a couple of coats of gloss paint. Ideally the polyester resin will be replaced completely with epoxy. I will update the nosecone build procedure with the next main website update.

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FTC Nosecones

Since we are rebuilding the FTC payload, we've decided to replace the Kinder surprise egg nosecone with a more streamlined one. I machined up the nosecone mold out of a solid piece of plastic and polished it.

The nosecone mold prior to final polishing.

Attempt #1 - Heated the base of a small PET bottle and forced it over the nosecone mold and tried to heat shrink it over the top. Heat gun was too close and the base started crystalizing. The nosecone ended up flying quite nicely into the rubbish bin.

Attempt #2 - Heated the base of another small PET bottle more gently this time. This was only a slightly better result than the previous one. Before long he joined his friend in the bin. It just could not be shrunk down enough to the 30mm diameter.

Attempt #3 - Coated the mold with release agent and impregnated fiberglass matting with resin and then started wrapping it on the mold, but as you can imagine a nosecone isn't easy to round off with flat matting. Before long I had a nice mess on my hands with lots of bubbles, folds, and the rounded front was anything but. After another 5 minutes of trying to correct it, I finally pulled the whole mess off the mold and guess where it went?

Then I emptied the bin ready for more nosecones.

Attempt #4 - I went to the local supermarket and bought a couple of pairs of pantyhose (nylon stockings) and a shoe polishing brush. Okay I did get strange looks at the checkout counter as they were the only things I purchased. Little did they known those stockings will do over 200km/h one day. Instead of the release agent, I stretched the thumb section of a disposable rubber glove over the mold and tied it off. This made sure there were no creases anywhere. I then proceeded to stretch 8 layers of pantyhose over the top of that again tying it off at the bottom. I then simply poured the fiberglass resin all over it and worked it in with a brush and with my gloves. The nosecone is now drying so I will know in the morning if it worked. Otherwise it looks pretty good.

... Oh and the shoe polishing brush I bought earlier I had cut into about 20 strips each with 5 sets of bristles and use them as disposable brushes for the fiberglass. At 10c per strip they can be thrown away after each job.

I'll post results of attempt #4 when it dries and assuming I can get it off the mold.

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FTC rocket upgrade

We've been working on a number of rocket related projects this week. We started redoing the FTC payload bay that includes several improvements. We are replacing the split nosecone made from FTC to one made from Fiberglass. The fiberglass is a lot stiffer, but still lightweight and does not collapse like FTC does when it is cut in half.

Because we used a piece of FTC to form the half-shells, their diameter is also the right size for fitting over the FTC tube. The V1.5 flight computer used is being replaced with the smaller V1.6, and the batteries are being replaced with four AAAAs. The net result is a more compact payload section that is a little lighter than the predecesor. We are also creating smaller fins for the rocket to reduce the overall weight near the tail.

We have also tested an all-Sikaflex splice this week with the glue failing at around 130psi. The glue had given way, as both the sleeve and the bottle that was glued inside the sleeve were undamaged. The glue was left on both surfaces. This means that this glue probably should not be used for pressures above 100psi. We have a number of spliced pairs using this glue already made for the Acceleron rocket, so we will have to replace them with PL splices. We can still use them on other test rockets so we will hang on to them.

Fiberglassing is definitely a messy business but I'm getting used to it a bit more now. Last week I bought a proper respirator with organic gas filters for $45 and its really effective and I can't smell any of the resin when working with the fiberglass.

As we are working on a lot of spliced pairs at the moment, there is quite a bit of sanding to do of the surfaces to be glued. We always used to do it by hand, but we've made it a little easier now by getting a piece of PVC pipe and cutting a pair of long slits in it. We then take two rectangles of sandpaper and put them back to back and place them in the slot. The pipe then goes in the lathe. When it spins the sand paper makes a kind of S-shape and makes it much faster to sand the outside and inside of the bottles. It reduces sanding time by about 1/3 and also is alot easier on the hand strain.

Soldering up the flight computers has also been performed in the background in spare time, and documentation continues to be worked on.

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V1.6 PCBs have arrived

We received the PCBs yesterday from the manufacturer. I was very impressed with their quality, and breathed a sigh of relief when all the components fit. :) We'll definitely be using this manufacturer again. I was keen to see if the layout design would work but unfortunately we had a blackout and so I had to hold off on soldering the first unit until after dinner.

Breathed another sigh of relief when the FC powered up first go. The software is pretty much done, just doing a few more minor tweaks to the servo timing routines and testing it with a range of servo motors.

The version shown above has the assemtech G-switch soldered in and it's set up for 9V operation. With the battery clip the FC weighs in at 18 grams.

Next up we are going to do some flight tests with them, and I'll replace the V1.5 FC in the FTC rocket with one of these to see how it performs under higher G-loads.

The documentation and manual still needs to be completed, but that is also close to being done.

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Fiberglassing

Last weekend we went out to Doonside with some of the NSWRA rocketeers but only equipped with lawn mowers and brush cutters. All the tall grass is now gone from the launch area so it is a lot nicer to move around and set up. Phil also installed permanent launcher bases which will make setting up much easier and there is less gear to bring each launch day.

While we wait for the new flight computer PCBs to arrive (Apparently they have now been shipped) we have been continuing to build the Acceleron V booster. We have mostly been testing and reinforcing the 2L spliced pairs. The booster uses 9 of them. We splice a pair together and then hydro test it up to about 80 psi. If there are no leaks we then add the neck reinforcing rings and wait a few days for them to dry, before testing again to 130psi. This way if the original splice fails at the 80 psi we don't waste time and bottles reinforcing the necks. The neck reinforcements are necessary as at about 110psi stretch marks begin to appear around the neck of the 2L bottles.

We are making a few spare spliced pairs in case any need replacing. The spare ones can later also be used for the new bigger Polaron boosters. A couple of the pairs are all-sikaflex splices so we are keen to see how they hold up.

I have also had my first go at fiberglassing. I wanted a simple project initially to learn the technique and so decided to make a ring fin that should be able to withstand a bit of punishment during tail-first landings under parachute. It was quite easy to do but I can see I need to pay a bit more attention in getting all the bubbles out and work a bit more at getting the resin in all the way through. But overall I was pretty happy with the results. The ring fin is 37 grams, 0.8mm wall thickness and uses 3 layers of fiberglass matting. It is significantly stiffer than a PET ring.

Here is the ring fin after the first rough sanding. I'll spend a bit more time making it smoother before painting it. The ring fin will be attached with CF struts to the main rocket body.

The next few fiberglass projects will likely to be fin strut attachment supports for the pressure chamber, and reinforced balsa fins. When I get a bit more comfortable working with it, I'll have a go at reinforcing some pressure chambers.

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Progress Update

This last week we have been concentrating on getting the FC V1.6 finished. It has taken a little longer to get the PCB designed as we are still learning the Eagle CAD package, but the package is definitely an improvement over what we were using before. We are also using a new PCB manufacturer so some time was spent configuring Eagle's layout tolerance settings specific to their manufacturing process. The boards are currently being made so we hope to have them within a week or so, and then we can start soldering. :) We've also been creating all the documentation that goes with it.

Rocket development otherwise is progressing slowly at the moment as most spare time has gone into building the bigger workshop.

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New Year & Recovery Guide

Recovery Guide

Happy 2009 to all! With the busy time of Christmas over we are now back to more full time rocket development. One of the things we have been working on over the past few months has been a water rocket recovery guide.

The recovery guide is intended for rocketeers wanting to add a recovery system to their water rocket. The guide covers the multitude of approaches rocketeers have taken over the years, discusses some common misconceptions and provides links to various websites covering all aspects of recovery.

The current iteration of the guide is here:

http://www.AirCommandRockets.com/recovery_guide.htm

This guide will continue to evolve as more systems are documented and as more links are explored. If you have a recovery system you'd like to share that is not on the list please let us know either through the guide's form, email, or comments on this blog, and we'll classify it and add the references to the relevant sections of the guide.

Plans for Air Command in 2009

Some of the things we are planning for the first half of this year:

• Continue work on the recovery guide.
• Release V1.6 of the flight computer. The new version has a PCB around 25% smaller than V1.5 and is designed to fit in regular rockets as well as T8 FTC. It is also simpler to set up and use. A small quantity of these will be available for sale. We are aiming to release by end of January.
• 33L Acceleron V development. We have a lot of pressure testing and reinforcing to do on this rocket and we may need to upgrade the Acceleron launcher for bigger nozzles. We're looking forward to the flights of this one. :)
• Polaron VI rebuild with larger boosters.
• Baryon III multi-stage flights - Actually trying to get the second stage separated properly this time. :)
• Continue with the static testing. We have a number designs we would like to evaluate.
• Fiberglassing body tubes for stronger and higher pressure rockets.

We look forward to seeing everyone's progress this year.
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FTC flights update

We've updated the main website with the FTC flights report from last Sunday. Included is a short video of the highlights from the day.

http://www.AirCommandRockets.com/day71.htm

In putting together the pictures and video for the update we noticed that in both of the last two higher pressure flights the rocket was bending quite a bit on take off. This probably explains the lower than expected altitude. The rocket is very flexible and under the acceleration loading it just bends. This is likely to be inducing fairly large drag.
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T8 FTC rocket flights

We had perfect launch weather this weekend, but since it wasn't a NSWRA launch day, we went back to our old launch site to test fly the FTC rocket and check out all its systems.

We had to launch at a lower pressure in order to keep the rocket in the park. We launched the FTC rocket 4 times and also launched a number of other rockets on the day. There were no crashes on the day so we were happy.

We are putting together another update for our main website with more pictures and a video of highlights from the day. This should be available in the next few days, but it may be after Christmas depending on how we go for time.
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Still Here

In the lead up to Christmas we've had to curtail rocket development as we are busy with family and work related obligations. Development is still continuing in the background although not enough for an entire update. I am waiting until the start of the holidays to have more time for development. We will also be extending the workshop under the house to have more room for building and storing larger rockets.

Since the NSWRA picnic was also canceled due to bad weather we haven't had a chance to launch our FTC rocket yet. We will try to launch it on a weekend at the local park at a lower pressure to check out all systems. If all goes well, we will launch it at full pressure at the next NSWRA launch day.

We hope everyone has a great Christmas and a safe new year!

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Software

We've been spending quite a bit of time this week writing and testing the FC V1.6 software. We are making it a little more user friendly to set up and operate in the field. The delay, offset and multiplier parameters were more difficult to set because you really needed to have the manual with you. Although you loose the precision of V1.5 the new settings allow you to set the time directly, so you can quite easily set it in the field. The settings allowed, however, should cover pretty much most flight profiles.

This also has meant that we've needed to update the operator manual which will be published when the FC is finished.

Last weekend was supposed to be a launch day but the wet weather cancelled those plans. :( NSWRA is meeting again this weekend so we will try to make it, but at this stage I'm not sure since family commitments were scheduled around last launch day and can't be moved. In any case NSWRA is meeting again the following week for a launch/picnic day, so we should be able to make it to that. We have four rockets itching to get off the pad, so they'll need to wait a bit longer.

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Open Day, G-switch, Acceleron V

We've update our main website with the latest development progress on a number of fronts.

http://www.AirCommandRockets.com/day70.htm

I've spent most of last night doing final work on the FTC rocket to get everything well secured. The rocket has also had another pressure test to 180 psi without any visible issues. Phil had a good suggestion to re-string the nosecone so that the parachute is attached to the nosecone and the nosecone is attached to the rocket. In this way more tangles can be avoided. I've also been a bit concerned at the forced on the top of the rocket where the parachute is attached. The main worry is that a high speed deploy could separate the payload section from the rest of the rocket. I've now threaded another kevlar line through the full length of the payload bay that is attached firmly to the pressure chamber end cap and the other end is looped through the main parachute line. Should the parachute rip off the payload bay, it should all remain connected to the rocket.

We are hoping for nice weather this weekend so we can go flying.
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Open Day Preparation

We've been flat out this week trying to get things ready for the open day this Saturday. The main project has been a rebuild of the Acceleron booster. This is our biggest booster to date at ~33L capacity. Acceleron III was 24L and Acceleron IV was 18L because it used 1.25L bottles.

The new booster has three 2L bottle spliced pairs tornado coupled together per segment. There are three segments in total. At 130psi the pyro rocket equivalent is an H310. (~250Ns total impulse)

We have simplified the pod at the top of the booster. The deploy mechanism is the same as the previous versions of Acceleron based on a FC, pressure switch and servo, but the parachute is no longer located in the pod. This meant that the pod could be smaller and lighter. The parachute now resides between the bottle necks of one segment so there is no extra drag. The parachute will be deployed using the piano hinge technique we have been using recently. This should mean the parachute opens sooner. Too many times before the parachute deployed late.

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Batteries and FC V1.6 progress

Batteries
I'm always on the look out for small yet moderately powerful batteries to power the on board electronics. It's always a compromise between cost, weight, voltage and current capacity. I've been using the Lithium CR123As in pairs to give me 6V but the amount of current they supply is much more than I need and hence are unnecessarily large. 9V batteries are pretty good in price, voltage and current but are comparatively heavy ~45 grams. A stack of button cells generally cannot supply enough current to drive servo motors.

When cost isn't an issue and you are after minimal weight and maximum power density then I expect some of the tiny Li-po batteries are the way to go. But they do need a charger, are expensive and not readily available.

I came across this video a few weeks back, and finally had a go at pulling apart a 9V battery this week.

http://au.youtube.com/watch?v=tr5ZB1eFhwc

Judging by the YouTube video comments a number of issues need to be looked out for:
- Only go for Energizer or Duracell alkaline batteries
- Don't short anything out while doing so.
- Wear gloves should you spill some acid

I only need 6V to power all the electronics so 4 of the cells are all I need. It also means that getting two 9V batteries I can make up three 6V battery packs. At only a few dollars per battery pack it means they are very affordable, and available everywhere. After removing the casing, connectors, and two cells the weight of the battery drops from 45 grams to 25 grams. In comparison a AAA 6V battery pack weighs ~44 grams, and AA battery pack weighs ~90 grams.

I just soldered wires to the contacts to make up the connections. I have started doing this ever since we found that some battery holders under G forces can easily loose contact. They powered the flight computer and servos just fine.

The small form factor means that they can be rearranged to fit the available space.

Flight Computer V1.6

I've ordered all the parts now for the next iteration of the flight computer. This will be a slightly larger run of 20 compared to the 10 made for V1.5. I am waiting for all the components to arrive first in order to verify their dimensions before finalising the PCB. I'm also investigating a small and cheap G-switch option to trigger it rather than the commercial G-switch costing around $9. The PCB will be designed so both variants can be used.

The updated software is also almost finished. We had a request come in from a water rocket team (Oberon WR) who built version 1.5 of the FC but their servo was only turning only around 90 degrees even though the full range of movement was 180 degrees. We tested this with one of our cheap 180 degree servos and sure enough the full range was around 90 degrees. I checked the PWM signal on the CRO and the standard range of ~1ms to ~2ms was correct coming out of the FC. I updated the code to give a range between 0.5ms and 2.5ms and that gave the full range of the servo movement. If I have sent you a copy of the V1.5 code, I can send you the update if you have this issue. Other servos worked fine with the 1-2ms timing.

It seems that some servo manufacturers don't adhere to the standard 1-2ms for full range. This change will also be rolled into V1.6. It may end up as another configurable parameter: 1-2ms for full range or 0.5 - 2.5ms for full range.

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FTC Parachute Deployment Mechanism

We've posted an update on our main website with details of how the T-8 FTC parachute deployment mechanism works.

http://www.AirCommandRockets.com/day69.htm



Included in the update are photos and a short video of how the mechanism works. We are hoping to test fly it at the next opportunity.

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Sewing on fins

We decided to sew the fins to the FTC rocket. Hopefully this will provide additional strength for the expected G forces. Okay so it's not your ordinary needle and thread but the idea is the same. The wire threads through the split sleeve and through the fin. The wire does not go through the pressure chamber.


PL premium still provides the majority of the strength, but the wire is there to ensure the fin does not come off should the glue fail while the rocket stretches during pressurisation. The wire also keeps the fin in place while the glue dries.

Once the initial glue dries the wire is trimmed and the twisted part is folded down and a more glue is used to create a fillet on either side of the fin. We are trying a technique to minimise the amount of bubbling from the PL, as PL is not very nice for smooth fillets. After we form the smooth fillet with the PL we place scotch tape over the fillet to minimise the amount of atmospheric moisture entering the glue. Hopefully this will slow down the cure rate and won't produce the big bubbles we normally get. Will have to check tomorrow to see how it went.

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NSWRA Open Day

NSWRA is having an open day this month on the 22nd November at Toongabbie East Primary School. We will have a water rocket stand there along with the pyro guys. If you are interested in any form of rocketry why not come along? See the flyer below for details:
We are going to be busy over the next few weeks to get the rockets ready for the open day. We want to bring the Polaron rocket with the drop away boosters, the new bigger Acceleron booster, and the new FTC rocket with us. We'll also bring along some of the other smaller rockets.

We have had a bit of a break from water rocket development this last month due to other family commitments, but are now back and should be updating the main site and blog more frequently.

I've also been continuing work on the next iteration of the flight computer (V1.6). The software has had a bit of a revamp to make it easier for the rocketeer. I'm also in the process of laying out a new smaller double sided PCB for it. We've located a local PCB manufacturer with very reasonable rates for the boards so we will likely have around 20 of them made, most of which will go up for sale assembled as was with V1.5. I've switched from using an old version of Protel for the schematic and PCB layout to Eagle which is much more advanced and certainly has some very neat features. Luckily the PCB manufacturer can take the Eagle files directly which greatly simplifies the process.
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FTC Payload

I've been quite busy this last week with non-rocket related things but have continued the steady progress on the FTC payload section in my spare time.

All the components are now fitted inside the payload section, but more work is still needed to secure things a bit better for the expected G forces of around 70G. The entire payload section shown above currently weighs 118 grams and includes the complete deployment system with servo motor, parachute, flight computer, altimeter and batteries. The flight computer is V1.5 on a 25mm wide PCB to fit into the T-8 tube.

The complete deployment system is only made from items found around the house. The full details will be given in the next main website update along with a video of how it works.

We will be picking up some kevlar line for the parachute on Saturday which should make things a little lighter and stronger.

It's been fun trying to fit everything into such a small space. For deploying the same size parachute as we have been using on our smaller rockets the entire deployment system is about 25% lighter than our existing ones and has a lot less drag.

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FTC rocket update

Over the past couple of days we have been putting a bit of effort into getting the FTC rocket ready for its first flight. I did a test to see if the fins can be glued directly to the reinforced FTC body, but PL premium does not hold well to the the glass strapping tape. They will have to be attached a different way.

The parachute ejection system is not complete yet, but is working quite well. We can use a fairly large parachute in it.

I've started soldering together V1.5 of the flight computer in a format that fits into a T8 tube. There will be one small RC servo motor for deployment. The payload section will also include one of the altimeters. Other than that, the pressure chamber is finished.

Pictures will be posted when more of it is assembled.
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Thrust Data Available

We have spent all week collating the data from the thrust tests. Our main website has now been updated with the results here:

http://www.AirCommandRockets.com/day68.htm

There were some interesting results and we want to do further follow up experiments, as well as some new ones.


It's a bit of a long write up so feel free to skip the boring sections.
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17 Tests in 3.5 hours

Today was a good day for testing. We went through quite a bit of air out of the scuba tanks, but the tests went relatively quickly and we got through most of what we wanted to get done.


We are in the process of analyzing the results at the moment and putting together a video of the tests as well. It will take a few days to write up the results.

Some of the tests included:

• Robinson coupling choking and blow through effect,
• Jet foaming techinque with and without foam,
• Reduced mixing chamber for jet foaming,
• Some tests were done with a 9mm nozzle and some with a 7mm nozzle,
• Foaming agent concentration difference
  
• We tested 2L of carbonated drink in the rocket,

After we analyze these we will have a better idea about what things we want to redesign and test further. The next set of tests will include the variable nozzle with different holes and with and without foam.

FTC Rocket

We have also done some more work on our FTC rocket. We have the fins cut out now, but more importantly come up with the way we want to do parachute deployment in a T-8 FTC tube where there isn't a whole lot of room. The best part is that all the components are common items that can be found around the house.

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Software

After importing a lot of thrust data from the test stand into Excel it quickly became obvious that the data still needed a lot of processing before it was useful. While it is easy to do in Excel, it is quite tedious, as the data has to be trimmed, aligned in time, averaged, calibration scaling applied, total impulse calculated and then graphed. This was taking perhaps 10 minutes per data set so I decided to extend the functionality of the WDQ to CSV exporter application I wrote a few weeks ago.


The application now can do all of the above tasks. With a few mouse clicks I can get total impulse, average thrust, thrust duration etc. This allows us to quickly review the data during testing and alter our tests based on the observed data. This should help in the design process as we make changes to the design we can get instant feedback on the design.

The full software functionality will be covered in the day68 update with the calibrated test results.

We are hoping to do a full set of tests this long weekend.
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Calibrated Testing

This weekend we performed a number of calibrated tests on the test stand. We first measured the load cell's linear response by suspending successively heavier weights on the load cell, and then flipping the test stand over and applying the same weights again so that force was applied in the other direction. The load cell responded very well.

The first test was an attempt to measure the power loss due to the blow through effect in a rocket with Robinson couplings. The test results from the three identical firings were very good as the thrust curves were in very close agreement with each other. That gives us confidence on the repeatability of the experiments.

When we were testing the rocket without the couplings we had a small problem where the thrust curve just exceeded the gain setting and as a result the top of the curve was clipped. We will re-run this again but with a lower gain setting. We try to keep the gain as high as possible in order to get maximum resolution.

Full details of the tests and data analysis will be put on the main site in due time. We will rerun the non-coupling tests before publishing the results.

There were a couple of minor issues we had to resolve with the test stand initially such as the little locking tabs in the gardena release mechanism flying out during release. But once fixed the tests were quite quick.

Because we had the test stand and equipment setup on Saturday we didn't go launching any water rocket with NSWRA, although I went over with the kids to watch other people's pyro rockets. It was nice for a change not to have to go and spend a couple of hours setting and packing up, and I got to enjoy other people's rockets and actually had time to talk to them. I've put together a highlights video from the day up to about lunch time here:

http://au.youtube.com/watch?v=4PPcZH3pK0Q


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Test Stand Details

We've put the details of the test stand on our main website here:

http://www.AirCommandRockets.com/day67.htm

It includes a couple of thrust curves.

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Test Stand First Firing

We ran our first couple of thrust tests on the new test stand. The tests were uncalibrated as we wanted to see what the overall performance was and if the gain on the amplifier is set correctly for the range of thrusts we will start testing with. Overall everything went really well and I am looking forward to doing the actual tests.

There are still a number of small modifications we need to do like automating the release of the nozzle and adding a non-return valve to it. We also still need to try PK's suggestion with a couple of resistors to eliminate noise a bit more.

I'm hoping we will get to do some calibrated firings this weekend with exactly measured pressure and water volume. We will suspend known weights from the setup so we can get reference values to measure the actual thrust.

Overall setup. The stand is normally firmly attached to one of the house pilons, and the table is well away from the splashing water.


The large spike at the start of the thrust curve is mainly due to me pulling the release head off the nozzle by hand. This should be smaller when automated where it falls away freely.



Full details of the test stand and first tests should be published on our website early next week.
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Test stand work

It's been a fairly quiet week as we have had a number of non-rocket related engagements. This weekend I continued work on the test stand. The test stand now has the basic frame and the load cell and load cell amplifier attached. The load cell to rocket coupling is also almost finished. We still need to support the rocket under test to stop it moving from side to side, but that will be done over the next day or so. We are quite keen to try the test stand and we will likely do a few test runs this week.

My mum has also started helping out in preparing the bottles and sleeves for splicing. This has drastically reduced the amount of time it takes to splice bottles together. I was able to do 4 splices in less than an hour.

I'm also in the process of writing up the full details of the test stand, but those will only be published after we have fired the rockets a few times so we can also report on the repeatability and accuracy of the setup.

If people have suggestions for tests they would like to see results for please let us know in the comments section below.

Some of the thrust tests we have planned are:
(each test is likely to be run 3-5 times to eliminate variance in water and pressure levels)

• 9mm nozzle with water only
• 7 mm nozzle with water only
• 5 mm nozzle with water only
  
• 9mm nozzle with Jet foaming
• 7mm nozzle with Jet foaming
• 5mm nozzle with Jet foaming
  
• 9mm CD nozzle
• 7mm CD nozzle
• 15mm nozzle with water only
• A look at the chocking effect of Robinson coupled bottles vs full bore tornado couplings.
• Variable nozzle performance with water
• Variable nozzle performance with foam
• Different foam generating techniques
• Comparison of different foaming agents
• Comparison of foaming agent concentration
• Test differences in the convergent section of the nozzle
  

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Multi-stage rocket

We flew our new two stage rocket with drop away boosters last Saturday. While things didn't go exactly according to plan, we still learned a lot from the two flights.

The full update is available here along with photos and video:

http://www.AirCommandRockets.com/day66.htm


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Improved Sensitivity and New Rocket

This week I spent a day rewiring the load cell and amplifier after one of the guys (PK) on the Australian Rocketry forum made some good suggestions about how to reduce the signal noise. I placed the load cell amp close to the load cell and enclosed the whole thing in a metal box. I also used coax cable to run the long lead to the DataQ logger. The noise level dropped off dramatically. It is now down to around 0.02V over the -9V to 9V range.


On the 70Kg load cell that allowed me to resolve down to ~5 grams = a sheet of A4 paper. (Yes I actually put a folded sheet of paper on it). This means we can get thrust measurement accuracy down to about 0.05 Newtons. This hopefully should be good enough to observe the subtle changes to components under test.

I'm very happy with the setup now. All we have to do is build the stand. The stand is a little more complex because it is going to be put on a pivot to allow us to flip it upside down and fill the rocket with water. I'll have to wait with this until next week as we have to get our rockets ready for the August 30th launch day.

Big thanks also goes to Tarp, astro and patch and others who helped me get the right parts and steer me in the right direction.

New Rocket - 2 Stage with drop away boosters

We have decided to combine a couple of our existing rockets to make up a bigger rocket to launch on Saturday. We are taking the two stage rocket launched last time and adding another 2L bottle to the bottom of it. This actually came from Polaron VI launched a couple of months ago and includes the booster retention tubes. We will attempt to launch the rocket using the Gluon II boosters.

This will be our most complex rocket to date, and because of that I am not sure how successful we'll be in getting it off the ground. But it will sure be fun to try. A brief outline of the rocket configuration:

Sustainer: (Tachyon V) 3.35L capacity using 1300mL of water + foam, 9mm nozzle. It is fitted with our V1.5 flight computer for deployment, has a FlycamOne2, a z-Log altimeter and a single parachute.

Main Stage: (Baryon III) 9.2L capacity using about 3 L of water + foam, with a 9mm nozzle. The sustainer is released by the Mk2 stager, and the single parachute is deployed upon release of the second stage using the piano hinge principle.

Boosters: (Gluon II) Attached to the mains stage are three boosters, each with a 3.35L capacity using about 1.25L of water each. Each has a 13mm nozzle and is equipped with a piano hinge parachute deploy mechanism that releases the parachute as soon as the booster separates from the main stage.

I haven't measured it but it stands about 2.5m tall. Will post details of rocket and if a flight is successful with the next update.

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Test stand update

On Friday I received the the load-cell so I was keen to get it hooked up since now I had all the components. It took most of Saturday to get everything designed and soldered up, and today I powered it up and ran some tests.

The current setup with the load cell amplifier, batteries and data logger housed in the box.

I was able to easily measure loads as low as 20 grams on the 70Kg load-cell. Initially I had some issues with noise being picked up by the wiring, and was able to reduce that about 10 fold with appropriate shielding and grounding things. Later, on the Australian rocketry forum one of the guys suggested how to even further improve the noise margin with cabling and locating the amplifier close to the load cell in a metal box. So the next step is to try that. Luckily I have all the necessary components, but will buy a new diecast aluminium box tomorrow and fit the amplifier in that.

The more accurate the setup is, the more accurately we can determine what effects design changes have on the rocket. With the above setup we can resolve ~0.2Newtons of thrust over the typical test range of about 30N to 150N. That range applies for our typical rockets with pressures of around 120psi with nozzles under 10mm. The same setup will also be used for full bore tests of up to around 600N.

I'm pretty happy with the sensitivity of the setup as is and would be great for most of the tests, but hopefully with the improved cabling and shielding we should be able to achieve higher resolution. I'll post an update when we test that.

I mounted the load cell for the time being to a big chunk of steel which will be eventually mounted on the test stand.
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New test stand work

We have been working on a side project for the past couple of weeks. We are keen to build a new thrust measuring test stand for testing design changes, but doing it the old way of recording a kitchen scale on video and then manually transferring the data into a spreadsheet just wasn't going to cut it for accuracy, and especially for making multiple runs.

We are doing it properly this time with an electronic data logger and a load cell hooked up to the laptop. The main problem with trying to do it the proper way is the higher cost involved as the equipment typically isn't your regular mass produced consumer electronics. The guys on the Australian Rocketry forum were a great help in recommending which equipment to use, things to look out for, and generally how to set it up. The data-logger we chose was from DATAQ. They have a number of different loggers with different capabilities at a very reasonable prices. I was very impressed with the delivery time from the time that I ordered. I placed my order just before lunch time on Thursday with the Australian distributor, and the package from Melbourne was waiting for me on Friday when I got home from work.

The load cells also tend to be quite expensive - easily upwards of $150-200+. We had been researching a lot of different companies and finally found a new 70kg load cell from a Chinese manufacturer whose cost and delivery were far cheaper than local distributors. It is still likely to be about 10 days before it arrives. I don't know what the quality is like yet, but I believe it should be great for our purposes.

The data-logger and load cell aren't enough though, and we also need a load cell amplifier as the datalogger only reads in the -10V to 10V range. The load cell only produces miliVolts over the entire deflection range which is too low for the datalogger to get enough resolution. The amplifier basically converts these small voltage changes to a voltage range usable by the logger. It also provides the necessary excitation voltage for the load cell. Again you can buy these off-the-shelf but you will pay upwards of $100+. Being on a limited budget, we decided to build our own load cell amplifier instead, which is based on an instrument amplifier IC. The circuit is relatively straight forward and these IC's are designed for exactly this task. The IC has been ordered and is on its way from the US.

I'll publish the full details of the entire setup and suppliers when it's calibrated and working properly.

The data logger came with free "lite" software for capturing and viewing the data. However, being free there are some limitations in terms of exporting the data and maximum allowed sample rate. The max sample rate is 240Hz which is more than ample for us. The full software with higher allowed sample rates is another $200. You can also buy a $99 software add-on that lets you save the captured data into Excel friendly format. (doh)

The free software, however, does record the data into their own proprietary binary file format. I recorded a number of waveforms today, and looked at the data in a hex editor. I noticed that it was not encrypted, so it was relatively easy to reverse-engineer its format and write a small program that allows me convert their format into a text .csv file format that is directly readable by Excel. (saved $99 there :) )

The entire thrust measuring test stand + software should cost us under $300 when finished.

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Baryon II and Variable Nozzle

We have finished doing the flight log update for the last launch day at Doonside. The primary goal for us was to test the Mk2 staging mechanism with a bigger booster and sustainer.


Details of the new booster and sustainer are also included in the update.

http://www.AirCommandRockets.com/day65.htm

We have also been working on a technique to expel extra foam from the rocket in flight and came across a way to make a simple variable diameter nozzle. The details of the concept and a video of how it works is included in the above update.


There is lots of testing that needs to be done on the nozzle, and different materials to try so it looks like we might need to set up our old test stand again.

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Thermal Testing

We have finished writing up results of the initial thermal tests. We will be adding to this post as we do further testing over the coming months.

http://www.AirCommandRockets.com/day64.htm

I am in the process of completing the flight log update from Doonside last week. Hopefull that will get finished in the next few days.

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Mk2 Stager with bigger booster and sustainer

This weekend we flew the Mk2. Stager with a bigger booster and a bigger sustainer to see how it performs under greater loads and higher pressure. The Baryon II booster has a 7.2L capacity, 15mm nozzle and launches with 2.8L of water. The 3.35L Tachyon V sustainer uses a 9mm nozzle and 1300ml of water/foam mix. We flew both at 120psi.


It was a good flight, but the high wind conditions on the day caused the rocket to fly in an arc rather than straight up and as a result did not reach the expected altitude. Staging happened as expected and both parachutes on the booster and sustainer opened as expected.


We are currently putting together a flight log update, although it will be perhaps a week before it is posted, as we are also in the process of completing the write-up of the thermal experiments we did last week. There wasn't enough time to post the thermal results last week as most of our spare time was taken up building the new booster and sustainer. Sometimes you have to find the balance between sitting at the computer typing and actually building hardware.

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Testing, testing and more testing

With the NSWRA launch day being postponed this weekend due to unfavorable weather conditions, we spent more time in the workshop testing all sorts of things and building a new two stage rocket that will use the Mk2 Stager.

First we pressure tested the new 3.35L sustainer to 120psi. It is using a new bottle we have not used before so we were curious to see how well it would hold up. Then we pressure tested the reinforced FTC to 180 psi. 180 psi will be the first launch pressure of this rocket. This is the actual FTC pressure vessel we will be using for our first FTC flights. The nozzle and end-cap are already attached and the entire length of the FTC has a single wrap of glass strapping tape.

After some recent great discussions on the Yahoo water rocket forum, about thermal properties of bottles, we spent some time doing thermal tests on how warm the air gets inside a rocket during pressurisation. This is important as high temperatures can weaken a bottle. The glass transition temperature for PET depends on a number of factors but can be as low as 69 degrees C.
Wikipedia lists this temperature as 75C.

"The glass transition temperature, Tg, is the temperature at which an amorphous solid, such as glass or a polymer, becomes brittle on cooling, or soft on heating. "

We are in the process of collating the information and we will try to publish it sometime this week.

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Repairs and painting

After the CATO of the reinforced rocket (Tachyon IV) at Doonside, I have rebuilt a new reinforced bottle and pressure tested the entire rocket last night to 170psi. There were no visible stress marks on it so should be good to go for this Saturday.

I am also replacing the fin section on this rocket with 3mm plywood fins directly glued to the bottle. I coated the fins with 5 minute epoxy to add a little strength and water proofing. They will be sanded and painted tonight.

At the last Doonside launch event a couple of the members suggested trying vinyl paint for the rockets. I bought some white vinyl and plastic spray paint at SuperCheap Autos, but at $15 a can that is not all that cheap. I tried the paint on a PET bottle a couple of days ago. I lightly sanded half of the bottle with very fine sand paper and left the other part untouched. After a few goes I realised that you have to spray in multiple thin coats to get good coverage without runs. The paint dried within minutes.

The paint is a little flexible so bending and squeezing the bottle had no effect on it flaking off, like we have had with other paints. The paint on the unsanded side, however, did come off very easily when scratched with a finger nail. It was a different matter on the sanded side though. The paint held very well even when scratched. I'm keen to see how well it holds up in the sun with heat and UV.

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Mk2. Staging Mechanism Details

We have posted the launch report on our website from the latest Mk2 Stager test flights. We have also included the full details of how the staging mechanism works.

The launch report is available here:

http://www.AirCommandRockets.com/day63.htm

The stager details are available here:

http://www.AirCommandRockets.com/howitworks_2.htm


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Mk2. Stager Test flights

On Sunday afternoon we finally made it to the local park to test fly the Mk2 Stager, with a small booster and sustainer.

It was a good day of test flights. The first launch was good with good staging. We had a failure on the second launch with no release, but no damage was done to the staging mechanism. We made a couple of minor adjustments and then the final two flights of the day went well again. We had to leave the oval after flight #4 as it was getting too dark to shoot good video.

From simulations and the observed flight times which were relatively close to the simulated predictions the sustainer reached over the 100m (330') mark. Not bad for a little 600ml bottle with 200ml of water at 110psi.

This is a couple of frames taken from ground video of the staging taking place. The sustainer arced over a little probably because its stability is marginal mostly due to its short length. Seen here staging is happening around the 10-15m mark.

We will post the full results of the test launches in the next few days with photos and video. Soon after that we will also do the full write up of the mechanism itself.

The next test flights of stager will likely be on a medium sized booster and a bigger sustainer. We haven't settled on the configuration yet as we were waiting to see how these tests would go. The bigger booster and sustainer will have to be flown at Doonside.

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Drop Away Boosters Explained

This week we've updated the main site with the theory and an explanation of how the drop away boosters work on the Polaron rocket.

http://www.AirCommandRockets.com/howitworks_1.htm



Other than that only small amount of work has been done on actual hardware due to other commitments. The weather looks a little windy for this weekend, but hopefully it will settle down on launch day.
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Booster and sustainer work for stager test

The booster is now complete for the flight test of the Mk2 stager. The sustainer needs a little more tape, and a coat of paint on the fins and it too is ready to go.



The booster is only a 2.1L spliced pair, and the sustainer is only 600mL. We built both of them small so we could test the stager at the local park. For this test we weren't all too concerned with aerodynamic efficiency. The booster uses the same parachute deployment technique that the drop away boosters use on the Polaron rocket. The parachute is behind a flap held by a wire. The other end of the wire is attached to the sustainer and as soon as the sustainer is released, it pulls the wire and deploys the parachute on the booster.

The sustainer does not have a recovery system. It just has a soft nosecone to protect it (somewhat) on landing.

We don't expect this combination to go very high, and we still need to run simulations to see what to expect. If the weather is good this weekend we will launch it.

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15mm Nozzles

We had a good weekend launching rockets despite a couple of CATOs. We launched the Axion rocket with a 15mm nozzle and a long launch tube which gives the rocket a nice kick on take-off.

The full update is available here:

http://www.AirCommandRockets.com/day62.htm

The update also includes a video of some static fire tests of the Mk2 stager we have been working on. We are keen to fly it as soon as we finish the little booster and sustainer. We will be able to test it locally without having to wait until the next launch day at Doonside.

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