Day 83 Update

I've posted the flight day report from Doonside on our main website here:

http://www.AirCommandRockets.com/day83.htm

It includes a highlights video and photos from the day as well.

I've also updated the flight day report with findings from last night when I was pulling the rockets apart to give them a clean. (see the Update section) It turns out we had some heat distortion issues that we didn't know about on the day. The Polaron VII rocket also flew with a missing o-ring in one of the Tornado couplings!

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Flight testing new splices

Well it's been quite a while since the last update, but rocket development has been continuing although a little slower due to the holiday season coming up. Today we went out to Doonside to test launch the new spliced pairs to see how they behave under flight and landing conditions, as well as sitting in the sun for a while.

The rocket used all 4 spliced pairs previously tested to 140 psi. The rocket was launched a couple of times at 130psi, and the splices held out well without any significant issues. 5 more of these will now be made and fitted to Acceleron V.

I am doing a write up of the whole day along with a few other foam and flour flights we did on the day. I'll post photos and a highlights video in the next few days.

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Keeping neighbours happy

This weekend we were going to do burst pressure tests on a range of bottles, but blowing up bottles in one's back yard isn't something to get your neighbours excited about. We are always looking for ways to lower the noise during these tests. Having the bottle full of water greatly reduces the noise, but a little bit of air can enter the bottle as it expands and so the resultant explosion can still be very loud.

Sound suppression attempt #1:
We filled the bottle with water, and then placed the whole bottle in a small plastic bathtub, filled it full of water, covered the bottle underwater with a towel and held it down with two bricks. ....
Result: Big boom, tub split in half, lawn received a healthy watering.

Sound suppression attempt #2:

So we drove over to dad's house, filled the next bottle with water and suspended it about 1/2m below the water in the concrete in-ground swimming pool.

Result: Quieter boom but what was amazing was the fact you could feel the concrete shake under your feet with the boom! This was a bottle full of water with about 100mL of air in a large pool and it burst at ~160psi. The slow-mo video standing on a tripod on the side of the pool shows the blur as the shockwave hits shortly later followed by tiny ripples on the surface doing interference patterns for about 1-2 seconds. Obviously the shockwave travelled through the water and echoed around the pool. .... WAY COOOL! ... but not the objective. Could the shock wave damage the pool? Unlikely, but we didn't want to take too many more chances.Tiny ripples on the water are the sound waves bouncing around in the pool

Sound suppression attempt #3:
Dad brought out an old SCUBA cylinder with the bottom cut off. This aluminium tank has a wall thickness of about 1cm, and so we place the bottle in it, stuffed old rags in the hole, placed it up against a rock wall, put a bench, lead weights and seat against it to stop the tank from flying in the other direction, wrapped the tank in two layers of foam and burst the bottle ....
Result: A barely audible thud.
Subsequent tests showed that you really only needed the rags in the end of the tank to suppress pretty much all the noise. There was no need for the foam wrap, or weights to hold the tank down.

Putting the bottle in the SCUBA cylinder

Stuffing in rags to suppress the sound.

Tank is under two layers of foam and bench with weights is meant to stop the tank from flying away.

In the end 9 bottles were blown up, and the neighbours didn't complain one bit.
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So far so good ....

During the week we made up four new spliced-pairs of 2L bottles. Each has a capacity of around 3.15L. The splicing and reinforcing technique seems to be working well so far. The Sikaflex is doing its job sealing the splices.

Today they were all pressure tested to 140psi without any leaks, and the bottles and tape showed no stress marks. We are very happy about that. Having a good yield rate means we can produce more of these with less bottles.


Now they will all be assembled into a Polaron type rocket. The initial target launch pressure will be 130psi with a 15mm nozzle. While we are building this rocket we will continue to make up more spliced pairs for the rest of Acceleron. Some of these will also be converted into boosters.


I think I have an approach too now for the pressure switch, so I'll be doing some prototype work on that soon.
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Investigating water behaviour in flight

At Doonside this weekend we flew the Axion rocket again 3 times with a camera on the boom to try and get a better shot of what is happening in the lowest bottle in flight. We used food colouring to enhance the contrast and no foaming agent this time. We also painted the fins a neutral gray to prevent the auto-iris on the camera making everything else too dark.

The full launch report is available here: http://home. people.net. au/~aircommand/ day82.htm


Acceleron V

Since a few people have now asked about when Acceleron V is going to fly again, I might as well do an update. We are in the process of getting Acceleron V back in the air. There were a couple of issues that we really wanted to solve before trying again. The number one priority is getting the spliced pairs reliable enough to be able to launch with them and not worrying about being very close to the burst limit. The last explosion showed that the spliced pairs just weren't there yet. Even though they were tested to 130psi, they were obviously close to that pressure. Although we could fly the rocket at lower pressure, the rocket's flight envelope was really not designed for anything lower than 110psi. Ideally the rocket needs 130-140psi.

The need for stronger spliced pairs is the reason we have been doing the splice tests recently. If further tests with the new splice technique continue to go well, we are hoping to replace the existing spliced pairs with the new ones on the rocket. We have 4 new spliced pairs curing at the moment and we will hydro test them to 140psi. We will then make a Polaron style rocket and test fly them at 130psi. If the spliced pairs perform well in real life situations then we will make up more to replace those on Acceleron V.

The other issue is the pressure switch. We want to have a reliable pressure switch to detect burnout. The pressure switch we used on the first flight just wasn't reliable enough, and the old pressure switch (TDD) leaks a little. When these issues are resolved, then we will try to put Acceleron V up again.

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Splice test #3 - Sikaflex - Success

We did a successful burst test on the Sikaflex asymmetric splice with a PL attached sleeve. (splice #5) The bottle ends were also reinforced with a jacket made from another PET bottle and held down with glass strapping tape. We learned a couple of things from this test:

The Sikaflex works great as a sealant and the width of the sleeve was more than sufficient to hold the splice together.

The final burst pressure was 190 psi! This is a better result than was expected. The actual failure was due to the strapping tape breaking, weakening the bottle reinforcing and then ultimately bursting the bottle. The sleeve still held though. The normal burst pressure of these bottles is about 165 psi.


This is a photo of the splice under test. The needle on top of the bottle was added to see how much bottle distorts close to the sleeve.

I'll make up three of these splices next and see how reproduceable the results are. I won't be testing them to destruction but pushing them to 140 psi, for an operational pressure of 130psi in actual rockets. If the results can be replicated, it would give us a nice safety margin.

I do have good slow motion video of the bottle's distortion and ultimate burst. I'll post the video with the next main website update, as I am busy the next couple of nights getting ready for this weekend's launch event.
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Splice test #2 - Epoxy

After letting the epoxy splice sit for a week we pressure tested the spliced-pair to destruction today. At around 120 psi a small leak developed. We kept increasing the pressure until the splice failed at ~150psi.

This time it was the PET bottle that failed rather than the splice. It fairly cleanly tore itself off from around the edge of the sleeve. The epoxy glue though separated cleanly from the bottle that flew off. This means that the epoxy did not do as good a job of holding onto the PET, even though the 1cm x 1cm tests showed promising results.

The sleeve was glued on with PL premium.

We are now waiting for the sikaflex and PL to cure on the next splice test.

The reinforcing shells worked well and the bottles did not show any signs of stress in the neck area. We have taken them off again, and will use them on the next splice test.

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Bits and pieces

We've updated the main website with some of the things we've been working on over the last month or so:

http://home.people.net.au/~aircommand/day81.htm

The update includes discussion of the splice variants we are currently testing as well as details of my involvement in the rocket challenge on Channel 7's 'Beauty and the Geek - Australia'.

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Splice test 1

I tested the splice yesterday, but it sprung a leak at 130 psi, which was disappointing, but not unexpected for the first attempt. It was only 4 days since I did the splice so it may not have been quite long enough for a full cure of the splice. Except for the leak the splice held well though, and there were no stress marks on the bottles. All up the reinforced double-walled spliced pair was 3.15L and weighed 139 grams.

The reinforcing shells used on both ends of the rocket can be easily removed and reused for the next test since they are not glued, saving a couple of bottles there. They protected the inner bottles well during the test.

Having recently performed the 1cm x 1cm shear tests on the Araldite super strength epoxy, I've made a new splice using this glue last night, and it looks like it has a much better seal. It does not bubble up like the PL. I used very gentle heat from the heat gun to make it flow better into the corners once the splice was assembled. Tonight I'll add the extra outer sleeve and glue it on with PL.

If the epoxy fails, next I'll try the sikaflex on the inner splice for a better seal, and then again use PL for the outer sleeve.

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New Splices

We have been using the same symmetrical splice technique on our 2L bottles for a couple of years now, but I have never quite been happy with it. We have had quite a few failures along the way, and the no-leak yield hasn't been as high as we would like. This meant a lot of wasted bottles and wasted time. The other issue has been the relatively low pressures the spliced pairs could hold. 130psi has been the limit we could practically push them to.

We used to use 2.25L bottles as the sleeve since they fit well over the 2L bottles and no shrinking was required. But recently we have found that some of the 2.25L bottles don't fit as well as they used to so it has been difficult to use them as well. To try to stop the leaks we have been using a different glue to do the sealing in the joint and PL to hold the splice together but this made the process more complex and we still ended up with leaks although less often.

So we are currently trialing a different technique that will hopefully yield better results. The technique is not new but a combination of several different techniques used together. We are using just PL glue for this splice and only the one type of bottle. I'll post the full technique on the main site, but here is a quick run down:

We first heat shrink about 2-3 cm of one of the bottles using hot water so that it fits inside another bottle of the same type. Then curl the edge on a pan. This has the effect of giving a tight seal where the heat shrink section ends and meets the other bottle since they are the same diameter at this point. We sand and glue these sections together. We then make up a sleeve about 4 cm wide made out of the same type of bottle. Because the diameter is the same we simply cut the sleeve to turn it into a strip. We then use another section of sleeve about 4 x 4cm and glue half of it to the sleeve strip to cover the gap. We let the glue dry for a couple of days. Then we glue the sleeve strip over the splice to provide further strength to the splice.

The drawback is that inserting one bottle into the other means that the volume is smaller, but not by too much.

We have had to previously reinforce the necks of the bottles with rings made from other bottles, but it only strengthened the necks not the rest of the bottle. This time we are going to use Richard Wayman's bottle-on-bottle technique to not only strengthen the neck but a significant portion of the rest of the bottle.

Hopefully this technique will yield better sealing results and will be able to take higher pressures.

The glue is curing at the moment so tests will be carried out at the next opportunity.

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It's been a while since the last update because there has only been little rocket related development in the last two weeks.

Crestwood Fair and other stuff

Last Sunday I spent the whole day helping to man NSW rocketry association's stall at the Crestwood fair. David and Neville did a great job of organizing the stall and getting all the display materials together. We had all sorts of rockets on display, and I even brought along a couple of water rockets including the Acceleron V to sit in the corner. It was a fun day talking with people about rockets. Quite a few interested people stopped by for a chat. We gave out close to 50 fliers on the day, so we'll see how many people turn up to the next launch at Doonside.


Over the last two weeks there were also several birthday parties, accountants to see, kid's school concerts, and kids cricket games which meant a lot of time away from the rocket workshop. Now that the dust is settling down, we'll be back to more regular development. Dad is also back from Europe so we'll have more time to spent on developing the next set of rockets.

Work has also been continuing on the website extension. There is just a lot of typing to do, and it's taking a lot longer than I originally expected. There are around 70 pages on there so far.

New workshop
We had a long weekend this week, but instead of rockets I decided to concentrate my efforts on making significant progress on the new workshop under the house. The current workshop is just getting too small. Dad and I spent all three days putting up the internal walls, which I'm happy about, because those are done now and the ceiling is next. We had the electricians come in earlier in the week to put in all the power points and lighting, and we'll need them to come back to finish everything off after we have painted. There is probably 3 weeks or so more work on it, because we need to put in new doors, do the little trim bits to finish it off, and then fit it out with benches and shelving.

Coming up
Last week we've also made a booster for Paul's pyro rocket, so we are hoping to fly it this upcoming weekend if the weather improves. It will be our very first two stage pyro rocket launch.


We are bringing a couple of water rockets with us as well of course. We will fly the rocket with the camera mounted on the boom again to see if we can get a clearer view of the water behaviour in the rocket during flight. Acceleron V is currently slated to fly at the end of the month's NSWRA launch.
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A different perspective

We had a good flight day on Sunday at Doonside. Although the wind was fairly strong we managed to get 3 flights in.



The first flight was that of a modified rocket giving us a different perspective of the rocket. We were using the technique to investigate what happens inside the lowest bottle during flight. We mounted the camera on a long boom sticking out the side and looking back at the rocket and nozzle.

The full writeup with pictures and video of the flight is here:
http://www.AirCommandRockets.com/day80.htm

I want to fly this one again, but actually remember to put the food colouring in it this time for better contrast enhancement. The fins also need to be painted a darker colour to work better with the camera's auto-iris.
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Lots of progress, little time to write about it

Here is a quick update as there has been lots of stuff happening in the background but have had little time to do proper write ups on the main website.

Flight Computers
Flight computers V1.7 and 2.0 are coming along well. We are developing two different ones at the same time with different capabilities. V1.7 is aimed at providing a very simple, inexpensive and small solution to parachute deployment. Focus is on least number of components in a lightweight package coupled with a single 3.7g servo and a small 6V battery.

V2.0 is a more advanced version offering expanded functionality over V1.6, with extension modules that are also suitable for pyro rockets. V2.0 also offers a much more flexible programing model capable of sequencing complex operations.

One of the main design criteria for these flight computers is that they can be fully configured in the field without any special external equipment like keypads, displays or a laptop. Both are now using surface mount devices for smaller footprints.

Website Extension
A lot of writeup time has been spent doing work on the website extension. This is mostly why there has been fewer updates on the main site. Currently the plan is to go live with the extension at the end of September. Some of the recent write ups will be available with the extension.

Rocket development
Acceleron V is currently resting until dad gets back from Europe. I've gone and given it a bit of a service clean such as the non-return valve that was showing signs of corrosion, and generally made sure that everything was in order. We need to take two cars full of equipment to the launch site and it takes both of us to set it up and launch it, so it will wait until he gets back.

The new rocket I want to fly this weekend (Sunday) is also close to ready. I'm using the Acceleron launcher, (without boosters) as it already has provisions for the 2 meter guide rail, as the rocket design does not allow us to use our regular launcher.

Other projects
I've also been helping out with prototyping work for a paid rocket project which I can't post about yet, but it has been quite interesting and something different. This has also taken up quite a bit of my time over the last two weeks.

On top of that I am finally working again on the new bigger workshop under the house. I'm hoping the electrician will be able to come in this week for a quote for all the wiring, and then we can put up the wall panels and then it should start looking like a real workshop. :)

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How to make a nozzle tutorial

This weekend we've put together a couple of short video tutorials on how to make a 9mm Gardena nozzle. One of the issues that people have been reporting is that they are unable to get a hold of the older bottle caps with removable seals. The video covers an alternate source of caps that are suitable for making the nozzles:

http://www.youtube.com/watch?v=hiixdmrSEbA

The second video shows how to resolve an issue with some launchers as not all Gardena (and clones) quick connect fittings are created equal. The problem reported by quite a few people is that the nozzle does not lock all the way down into the launcher. The nozzle appears to be locked in position but releases itself as pressure builds. The solution is fairly simple:

http://www.youtube.com/watch?v=y56A9_sIelU


We did not attend the launch at Doonside this week because the weather predictions indicated strong wind and rain. When I woke up in the morning I saw that it was pouring, and decided to skip the hour long drive to the launch site. A number of people attended the launch but said the weather was less than ideal.

The good news is that NSWRA now has permission to launch 2 times a month at Doonside. So the wait time for doing bigger test flights is reduced.
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Acceleron Photos from 4th July

A big thanks goes to Andrew from NSWRA for shooting the following photos of the Acceleron V booster in flight. We didn't get any still photos of the launch on the day as we were busy shooting video. (click on the images for a higher res version)

In the first one you can see the turbulent flow from the red and blue nozzles, whereas the green nozzle has very nice laminar flow (seen further down the plume).

The second photo is my favorite one with the air pulse starting and the sun reflecting from the sustainer.

The last one shows the rocket shortly after staging occurred. The black fins of the sustainer are about to clear the nose of the booster.


I'll post some of the other photos of the flight in next main page update.

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Development continues

It's been a while since the last update so I thought I'd post about what we've been up to. In the last few weeks I've been catching up mostly on non-rocket related matters, but development has been progressing.

Acceleron Vc
The rocket is now mostly repaired. The broken ring brace was easily repaired with a bit of epoxy glue, and a new coat of paint. New separator rings have also been made and are currently having the servo and camera fitted. The only thing that needs to be done is for the whole rocket to be pressure tested again and re-assembled.

We are also making up a whole bunch of new spliced pairs of 2L bottles (we are processing about 40 bottles) to have spare ones ready in case some of the original pairs fail during testing. These will also be used for the Polaron rockets and new bigger boosters.

New rocket
We have also been building a new smaller rocket (not named yet) to try to better understand how foam and foam generation behaves during flight. This rocket was built small so that we can fly it at our local park. I'll post full details in the next main website update.

I've also been working on an extension to our website that hopefully will go live in the next month or two because there is still lots of information to enter and format.
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Day 79 Flight day report

We've updated our main website with the latest launch day report here:

http://www.AirCommandRockets.com/day79.htm

Included are pictures from the day and a couple of videos. We also discuss the new mini video camera we bought to replace the broken FCO2, and additional thermal testing we did on black Tornado couplings.

Photo: David Kelleher

I'm still putting together the pyro rocket highlights video which will be ready in the next day or so.

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Acceleron Vb CATO

We just had a fun weekend at Doonside. The weather was perfect for launching and so we set up Acceleron Vb with all the modifications for the next test flight. About 10 seconds from launch the booster exploded on the pad. It was quite an impressive boom to say the least. One of the spliced bottles came apart. Although quite a few pieces came off, surprisingly there was little damage caused to the booster and sustainer. Repairs are already under way to get it ready again for the next flight.

We got good high speed footage of the explosion (over the years we have learned to keep the camera rolling while pressurising). Photos and video will be posted on the main website soon.

Other than that we ended up flying Axion V three times with foam and all the flights went really well with good onboard video and altimeter data. We were a little dissapointed that Acceleron V did not get to fly (as a cohesive unit :) ) this time, but at least the repair bill will be under $5.
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Modifications Update

During the week we've continued to make the necessary modifications to the Acceleron V rocket.

The new nozzles are now finished and internally polished for better efficiency. The new nozzle seats and fill tubes are completed also. The new pressure switch is about half completed. Depending on how tests go with it this week we may need to use the old Acceleron pressure switch as a back up.

We still need to do pressure tests on the sustainer (today) as it has many new bottles. We will also do additional pressure tests on the new nozzle seats and nozzles.

We made a new fin alignment jig last week that is fully adjustable allowing fins of any dimension to be aligned with the rocket axis while they are glued in place. As a result the sustainer now has 3 new larger fins well aligned. The surface area of the fins is about 3x larger than the previous set.

We are now doing the final preparation for the next launch day coming up this week. The weather outlook for the next few days looks good, so we are hoping that will extend into the weekend.

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Acceleron V first flight

We've updated our main website with details of Acceleron V's first test flight here:

http://www.AirCommandRockets.com/day78.htm

The update includes photos and a video of the flight.


Although the flight didn't quite go according to plan, there were a lot of positives we got out of it, and obtained some valuable data about the rocket's performance. Reviewing the altimeter and video data we think we know what happened. We now have a plan for what changes we will need to make by the second test flight in a few weeks time. Luckily they are only minor changes.

Complex rockets take time to sort through the various issues as there are many things that can go wrong. Without flights like these we don't learn what works and what doesn't. Overall we consider the flight mostly a success.

I've also uploaded a highlights video of the pyro rockets from the launch day here:

http://www.youtube.com/watch?v=JBEqzpBVFV0

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