Polaron IV boosters

We have been working on Polaron IV and its launcher in the background while doing the foam experiments. We have further refined plans now on how the boosters will be attached and how they will separate. The photo above shows three newly machined 13mm aluminium nozzles for the boosters.

Each booster is 90mm wide, 2.3L capacity weighs ~150grams dry including recovery system, has a 13mm nozzle and uses a 450mm launch tube.

The simulator predicts that individually each booster should reach about 130m (430') @ 120psi, however, each of the boosters is intended to lift an additional 900 gram weight. This additional weight being a third of the total weight of the main stage fully loaded with water. Under these conditions the predicted altitude of each booster is around 35m (120'). Giving the main stage a release velocity of ~ 25 m/s.

The calculation gets a little trickier because the main stage also fires at the same time when boosters are launched. Though the main stage only uses a 7mm nozzle and foam so that the overall thrust from the main stage will be much smaller compared to the boosters. The consequence of this additional thrust from the main stage means that each booster has less to lift and therefore will be released at a higher altitude and higher velocity. We will do these additional
calculations when we finish building the main stage and know its parameters in detail.

At 120psi, each booster will produce around 90N of thrust at release and about 190N at the end of the launch tube. That is a combined booster thrust of around 570N as the rocket clears the launch pad. Compare that to the Main stage that will produce around 55N thrust with water only and likely around 35N with foam. From static experiments we found that the main stage should thrust for about 6-7 seconds. Rough estimates for main stage altitude are around 230m (750') at the 120psi level. Actual flight though may vary from this figure if the rocket does not go vertically.

The launcher under construction will have two separate air supply lines allowing us to use different pressures in the boosters compared to the main stage. This should allow us to experiment with a wider variety of rocket configurations. Full plans will be published once the design is finalised and the rocket is tested.
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Foam vs. Water-only flight test results

We have updated our main site with the results of the foam vs. water-only test flights.

http://www.AirCommandRockets.com/day49.htm

In the analysis we show that foam flights were about 2-3% lower in altitude than the water only rockets. This was a little dissapointing but also encouraging in other ways and certainly gives us a direction for further research with foam. Since the update We tweaked the simulation's drag coefficient and nozzle loss factor so the simulation matched the highest observed water-only flight altitude. We then added the weight and drag of the attached camera, upped the pressure to 120psi and ran the simulation again. The predicted water-only altitude was 350'. The last camera mission on the day was a foam flight with the camera and the altimeter. The altitude measured was 353'. This would put foam on par with water-only.

The altitudes are too close together to be able to make any definitive conclusions one way or another, and a lot more flights are required.

There are a few reasons we want to pursue foam experiments further:

1. It's a lot of fun.
   
   
2. The residual foam weight issue, described in the update, could point towards a measurable advantage when solved.
   
   
3. These tests were only carried out at low pressures, enough to get the rocket off the ground. As the pressures increase, the take-off and peak velocities will also increase. Due to the difference in velocities between water and foam powered rockets (water = faster & shorter burn, foam = slower & longer burn) the difference in drag will play a more signigficant role since drag is proportional to the square of the velocity. This should favour foam at higher pressures.
   
   
4. Convergent/Divergent (DeLaval) nozzles are yet to be fully analyzed. Although initial tests showed them to be no better at low pressures, higher pressures and nozzle shape optimization are still yet to be tested.
   
   
5. Use of foam may be more optimal for upper stages of a rocket than for the main stage. More simulation is needed.
   
   
6. Efficient generation of foam. From foam thrust measurements we found that foam generated using the Jet Foaming technique produced about 14% less total impulse. We have yet to test alternative ways of generating foam that may be more efficient. A couple of new foam generation ideas are already on the drawing board.
   
   
7. Foam optimisation. So far we have only been using the same ratio of bubble bath to water when mixed, but other combinations will need to be tested.
   
   
8. Different foaming agents. So far we have only tested kids bubble bath to generate foam. There are much better foaming agents available and foam density and viscosity are likely to play key roles in the efficiency.
   
   
9. The test results from all these experiments and data from other rocketeers may be used to build a foam simulation model for further research.

If all the above issues can be optimised for a particular application, then it still may turn out that foam can have higher performance in particular situations.
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Great Flight Day

We had an excellent flight day on Sunday. The weather was ideal and none of the rockets crashed. We tested the water-only vs foam flights and got altimeter data for all of them. Virtually all the flights were vertical.

I am in the process of doing a full web update but it will take a day or two to collate all the data and get the videos updated.

The update will also cover bottle reinforcing techniques and their results.

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Flight Computers & Misc

Most of this week has been spent working on a new design for the flight computer. As mentioned in the web update a couple of weeks back, we want to make it more automated to enable remote operation. We are building our own IR remote so that we can have full control over its operation. Most of that hardware is now designed and part of the remote's software has been written.

The new flight computer will not have any buttons except for the power switch, instead it will have the IR sensor module. It will also have a small speaker to acknowledge mode changes as well as serving as a recovery aid should the rocket fall in tall grass. The flight computer will also support two servos for staging and recovery as well as the capability to support the Zlog altimeters. The flight computer will be able to start the altimeter recording once the flight computer is armed.

Most of the design for this new hardware is now complete, with about half of the software still to be written.

We have now repaired J4III's body and fins, and are in the process of remounting components in the payload bay in order to protect them better during impact. J4III will now also sport the new shock absorbing nosecone to help provide even more protection should the parachute fail.

We have also made our first jacketed bottle that includes a Robinson coupling. We have pressure tested it to 100psi to check for leaks around the coupling, but will need to burst test it to see how much it can actually hold. If the burst tests are successful we would be aiming for launch pressures of around 180psi. While we believe the bottle burst pressure will be around 220psi+ the Robinson coupling is the biggest unknown.

If the weather holds up this weekend we will try to go back and do the foam and water comparison flights.
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Progress

This week we continued working on the stager mechanism. We finished enough of it to test it staging just in the back yard. We used only air at 20psi a couple of times and at 50psi once. Although it worked it was a little stiff to release and that is something we need to look at. We will probably try softer o-rings first. We still have a major design issue to resolve, but have some ideas. (More on this later)

The camera that wasn't behaving during the last launch day appears to be OK, and the cause looks like a poor battery contact. The contacts must have become more compressed inside the camera. We tried it with another battery that has taller solder blobs on the contacts and that worked fine, even when shaking the camera.

We also had a go at building the first prototype of the shock absorbing nosecone. It basically consists of the top 3/4 of a PET bottle which is filled with soft foam. The sides of the bottle have 8 longitudinal cuts all the way around that allow the bottle to easily split and slide over the existing nosecone. It is lightly taped over the top to enable the tape to separate easily on impact. During a crash the padded nosecone slides down and the foam compresses against the internal nosecone, but also the whole thing acts as an air piston to dampen the shock even more. The prototype weighs 35 grams so not a very significant weight penalty. For record flights, this can be removed and the existing nosecone underneath can just be used.

We have also been on the lookout for new launch sites around Sydney with great help from the local rocketry community. We looked at one location (George Kendall Reserve) that looks pretty good and is only about half hour from home.

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J4IIIb crash and foam flights

This weekend we were going to test performance differences between foam and water-only rockets, but after crashing the rocket on the third flight, we went back to just launching another one for fun. The altimeters are working well for us and I am happy with their performance.

The full update is here:

http://www.AirCommandRockets.com/day48.htm

This update includes a highlights video for the day.
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Polaron IV development & Hybrid Splice

Since the weather has not been favorable this week, we have been doing further development in the workshop. We are currently rebuilding the Polaron rocket and adding three external boosters. With a number of static tests earlier this year we noticed that Polaron was able to produce around 7 seconds of thrust when using foam and a 7mm nozzle. Because of the low peak thrust during take-off we are assiting the rocket with three boosters each with a 13mm nozzle.

We also tested a hybrid splice technique for joining bottles.

The full update including pictures are here:

http://www.AirCommandRockets.com/day47.htm

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Glue test results

The glue test results are now available here:

http://www.AirCommandRockets.com/day46.htm

We tested one splice that held at least 170 psi. This glue although not as nice to work with as PL is definitely a viable alternative if you can't get your hands on PL here in Australia. It has good bonding strength to PET.

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Glue Tests

This weekend we did some tests with the VISE polyurethane glue that Damo of Damo's Water Rockets found here locally in Australia. PL premium is not sold here and shipping costs can be quite high from the US. The VISE glue seems to have good adhesion properties to PET but its viscosity is much higher compared to PL which makes it more difficult to work with when splicing bottles.

We did tests to change the viscosity of the glue and also glued two splices. One with the regular vise glue and one with the thicker mixture. We will publish the findings in the next update of the main web page.

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Zero-G experiments

We had a chance to fly an experiment several times this weekend that we have wanted to do for quite a while. The purpose of the experiment was to demonstrate what forces act on internal components of a water rocket in flight. Gravity based parachute deployment systems appear to work on the ground, but are unreliable in flight.

The experiment shows what happens to a handfull of loose M&Ms inside the rocket during take-off and susequent zero-G (freefall) conditions. The M&Ms were inspired by Mike Melvill's handfull of M&Ms inside of SpaceShipOne.

The update includes lots of photos,videos and an explanation of the experiment.

It can be found here:

http://www.AirCommandRockets.com/day45.htm

The update also includes our first altimeter flights and some interesting results about foam.

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Development and repairs

We spent this weekend in the workshop repairing J4 II after its explosion last week. We basically replaced all the bottles with new ones, as some of them had been in use for 6 months or more. All the brass couplings were replaced with new Aluminium ones, reducing the rocket weight further.

We also taped all the inter-bottle rings to the rocket with a wide flexible tape, similar to electrical tape. This made the rocket much more solid.

We also reconfigured Hyperon III into a 3 bottle configuration as it will fly a long payload section when the weather clears up. Hopefully next weekend.

We also finally ordered a couple of altimeters last week, so I am hoping they will arrive this week. If they arrive in time, we should be able to fly them on the next launch opportunity.

We've also been working on a new simple and compact electrical pressure switch which we hope to test in the next few days. The prototype only weighs 10 grams but it should be possible to reduce that down further. The purpose of the switch is to serve the same role as the TDD, but without the exposed external moving parts. We use a TDD to detect when the pressure drops inside the rocket (at burnout) to activate the staging mechanism.


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Flight computer V1.3.2 test flights

We had a chance to fly a couple of rockets this weekend. It was mostly about testing a new flight computer and doing some foam flights just for fun. We got some good onboard video as well.

http://home.people.net.au/~aircommand/day44.htm

... oh and got a good wakeup call on water rocket safety ...
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Hyperon Flights at Damo's space port

We had an excellent weekend launching rockets with Damien Hart from Damo's Water Rockets. It was good to finally meet him and his family in person. The weather was well behaved and so were the rockets. (Well mostly)

We took turns in launching rockets, and as a grand finale we combined Damo's booster with our sustainer for a two stage flight.

The full details of the flight day are available here:

http://www.AirCommandRockets.com/day43.htm

and Damo's great write up of the day is here.

We'll have to do that again.
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Deployment systems

This weekend I spent time making the deployment systems around the two new flight computers. These will be fitted to 90mm rockets. One of them will be fitted to J4II instead of the NOAA deployment system we have been using. The other will be a spare for one of the three rockets (Tachyon II, J4 II and Hyperon). The new flight computers are now using the CR123A lithium batteries.

I also spent time this weekend building and testing a circuit that is going to form the core of a data acquisition system for our rockets. It is again based on the PIC16F628A microcontroller we have been using for the flight computers, but this one will be dedicated for collecting in-flight data. The part of the circuit that I tested was the RS-232 communications between the PIC and my PC through RS232. This way we will able to download the collected data from the unit. Eventually this RS232 interface could also be connected to a telemetry stream back to a base station. Each of these data acquisition units will record one or two channels based on the sample frequency required. It is planned that any number of these small units will be able to be placed on the rocket to gather as many channels of data as required.

I am also hoping to use one of these acquisition modules in our static thrust measuring rig for when we test new rockets.

Hopefully on Sunday we will get to fly more rockets again.
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Quiet week

We've had a quiet week this week, with dad in Europe and I've been busy fixing gutters and do ing paving, there wasn't a lot of time for rockets this week.

I did pressure test the two untested spliced pairs of bottles up to 115psi, and they both held well. We are reluctant to push them too far so that we don't have to rebuild them.

I also pressure tested the Hyperon rocket again to 130psi. And again it held up well to the pressure. I had disassembled a part of it during the week and needed to make sure it still sealed well.

I have finally received the CR123A Lithium batteries I bought on eBay this week. At $1.38 including delivery is pretty inexpensive. I tested them with the new flight computers and they work well. I was surprised that they are relatively light for their size. Since I don't have a battery holder for them, nor could I find one at the local electronics store, I have resorted to simply taping the contacts on with electrical tape. I realise this is less than desirable, but it seems to be holding well, so we will go with it for now.

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Hyperon Standard Platform

We have updated the main site with our latest water rocket developments.
The update is available here:

http://www.AirCommandRockets.com/day42.htm

The update includes more details about a standardised rocket platform we are developing for doing a number of experiments.

A video is included that shows how we make our Robinson couplings.

Analysis and developments

This week we have been doing a bit of analysis of the Acceleron IIIb flights we captured on video. We noted a few things:

1. It looks as if the stage separation was taking place a little later than we would have liked. The booster was already slowing down when the release happened. This can be seen at the top of the flight path as the booster starts pitching over. Since the release sequence is initiated by the pressure switch, we will need to make the pressure switch activate at slightly higher pressure. We can adjust the tension on the spring of the TDD, or alternatively add slightly less water to that segment with the pressure switch. Less water means that the segment will stop producing thrust slightly sooner compared to the other two segments that are still accelerating the rocket.

2. We now have a better idea of the time it takes to get to apogee and hence can set the parachute deploy delay for the sustainer appropriately. The parachute deployed about 2.5 seconds after passing through apogee.

3. The parachute deploy delay for the booster will be shortened as even the minimum setting allowed by the software on the day wasn't quite enough.

4. After release the booster looks like it falls more like a back-gliding rocket. It actually saved us a whole lot of work after the first launch since the parachute deployed so late. This is actually a favourable feature because if the parachute fails the rocket should land at a lower rate than if it hit nose first.

We have also been continuing with the next iteration of the flight computer. We are trying to reduce its weight and foot print to make the whole deployment system smaller and lighter.



The new flight computer uses a more compact and lighter launch detect switch. It works in two dimensions allowing you to mount the PCB in different orientations. The deploy servo is directly mounted to the PCB and the battery is directly below the PCB giving a more compact design. The full details of the flight computer will be posted once it has been tested.







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2 Stage successful flights

The full details of the 2 stage rocket are now available here:

http://www.AirCommandRockets.com/day41.htm

There are lots of photos and a video as well showing the day's highlights. The in-flight video turned out quite well.

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Acceleron IIIb flies!

We had a fantastic day of launching the big 2 stage rocket today. We flew it three times in total before we packed up. Both first and second stages behaved well and we got some great inflight video looking back from the sustainer.

The weather was great too with very little wind and mild temperatures.

I will post full details, photos and videos shortly.

(click image to enlarge)
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Acceleron IIIb details available

We have updated the main website with details of the Acceleron IIIb booster, the Tachyon II sustainer as well as the Flight computer used by the booster. The update also includes the burst test results.

The update can be found here:

http://www.AirCommandRockets.com/day40.htm

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