Foam and CD Nozzle Thrust Data

We have finished processing the thrust data from a couple of weeks ago that compares Convergent-Divergent (CD) nozzles to straight trough nozzles. We did 12 tests in all comparing 7mm and 9mm CD nozzles to 7mm and 9mm straight through nozzles.

The update is here:

http://www.aircommandrockets.com/day32.htm

The tests were done in exactly the same fashion as the last set of static tests when comparing foam and water thrust.

The results were interesting, although not unexpected. The update also includes the data in a spreadsheet format if others want to use it for further analysis.
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Simultaneous Launches and foam flights

In order to get back into flying we decided to have a go at launching multiple rockets simultaneously. Other than being lots of fun, one of the biggest problems was knowing which rocket you should be watching and the other things like nosecones falling off.


We then also flew a number of flights using the Jet foaming technique and 7 mm nozzles. The slow take-offs are quite a contrast to fully open nozzles using only water.

The update is here: http://www.aircommandrockets.com/day33.htm
The update also includes pictures and a video of the day's highlights.

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CD Nozzle Tests

We tested two CD nozzles this weekend. There were 12 tests in all:

• 3 tests with 7 mm straight through nozzle
• 3 tests with 7 mm CD nozzle
• 3 tests with 9 mm straight through
• 3 tests with 9 mm CD nozzle

Since it takes a bit of work to translate the video frames (around 6000 in total) into a spreadsheet it will take some time to do that. Once we have the data in a usable format we will publish it again.


We went through almost a liter of bubble bath solution, but collected the water during the tests so it just didn't go onto the lawn.

We think this will be it with the static tests for a while, as we are keen to get back to real flying.
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Convergent Divergent Nozzles

In order to see if a water rocket can benefit from CD nozzles (de Laval nozzle) while using foam we have built a couple to hopefully test this weekend.


One is a 9mm nozzle (aluminium above) and the other a 7mm (black plastic). The divergent part is conical in shape and has a slope of 4 degrees from the centerline. This value was obtained by reviewing the video and seeing at what angle the spray emerges. The actual angle of the spray varies over time from quite wide to quite narrow near the end as the pressure drops.

The average angle was about 4.7 degrees during the middle of the burn. We chose a value of 4 degrees because our thinking was that if it was more than 4.7, there would be nothing touching the sides during the middle of the burn and hence ineffective. That is just a guess and not based on any scientific or mathematical calculations.

We just want to test to see if there is a noticeable effect when a CD nozzle is used with foam compared to a straight through nozzle. If there is a difference, further tests will be performed to see how the shape can be optimised.

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Thrust Data for Water-only and Foam rockets

Well it has taken a while but we finally managed to get some good thrust data for a water-only water rocket and compare it to a water rocket using foam generated by our Jet Foaming technique.

http://www.aircommandrockets.com/day31.htm

The update includes the thrust data curves for 6 firings in total (3 water and 3 foam), as well as an analysis of the results. There is a video that shows how we measure the thrust.


The write up is a bit lengthy but we wanted to make sure that as much data was available for others if they wanted to process the data further or use it in their designs.

Feedback is always welcome.
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Thrust Measurements for Water and Foam

We finally managed to get some good thrust data for water and for foam today. We ran three identical tests for water and three for foam so that we could see how reproducible the results are and how much the two differ. The only thing that differed was the addition of bubble bath to the mix, and use of our Jet Foaming technique to generate the foam. All rocket, pressure, water volume, and other parameters were as close to identical as possible in all the tests.

We were quite happy with the data and were quite surprised by the results. The data will be published on our website as soon as we are done processing the raw data, and had a chance to properly analyse it.

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Thrust Measurement Rig - First Trials

We finished building the water rocket thrust measuring rig today, and did four firings to test it out. The first two tests did not use any dampening on the lever arm and as a result it was virtually impossible to see the scale needle as it flew around so much.

No Dampner in this photo

We then put a disk in a bucket of water on a long lightweight dowel mounted near the scale to act as dampner. This was suggested by Clifford Heath a while back and a similar technique was used by Antigravity Reaseach when they did their thrust measurement. The needle motion was much more steady. Thanks also to Jim Fackert for suggesting the camera pointed at the scale to take readings. We should also thank Gordon M, Richard W, David L, Trevor, Brian and others for useful suggestions on how to set up the thrust measurement rig.

Dampner Added to lever arm

We have plotted the initial thrust curves of an 8L rocket with a 7mm nozzle using only water and then again using foam and the difference in curve shape was quite substantial. We will not publish these initial results just yet, as we would like to confirm the data by repeating the experiment a number of times and then averaging the results. Full data will be published once we obtain it. Hopefully in the next few days.

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Acceleron II Flights

We test flew the Acceleron II booster (18.75 L capacity) three times this weekend with very good results. The encouraging results in the booster's almost always vertical launches means that we are ready to progress to the next stage of development - staging mechanism and the sustainer.

Full details can be found here:

http://www.aircommandrockets.com/day30.htm

We also took some measurements of the speed of the booster just after the start of the air pulse and had a close look at the sound the rocket generates in order to extract accurate timing of events during launch.

The twin parachutes also worked well to bring the booster to a safe landing each time.

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Tips for producing water rocket videos

We have updated our site with some useful tips in helping to produce videos relating to water rockets. The update can be found here:

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


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Acceleron II Details

We have updated our main site with detail photos and diagrams of the Acceleron II cluster booster.

http://home.people.net.au/~aircommand/day29.htm

The booster is now finished awaiting launch when the weather improves.

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Acceleron II Development

We continue to further develop our Acceleron II booster. We have now added another 6 L of capacity, which makes it almost 19L in total. The nozzles are now 10 mm which is almost 30% more nozzle area.

The top bottle is still the same dummy payload that carries about 600mL of water for ballast that represents the weight of the second stage. That means as it stands the booster lofts about a 750gm sustainer (including water).

The dry weight is now ~1.3 Kg (including the empty dummy payload) which is a bit on the heavy side, but simulations predict an altitude beyond 100m. The booster will, however, only need to travel around 12m before it releases the sustainer at roughly 50m/s = 180 km/h = 112 mph. The simulation is based on 120psi which is what we currently use on this booster. 15-20 more psi is easily achieved, and gain us a few more m/s.

Simulations also show that this Booster / Sustainer combination should be able to achieve altitudes beyond 200 meters (650 feet) with the 120psi - 130psi range.

In this photo the booster still does not have the parachutes fitted. We hope to have it finished this weekend and take it on a test flight weather allowing. Full details of the rocket will be posted on the website once we had a chance to fly it.
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Continuing Development

This week we have continued development and design work for the thrust measurement rig, and have manufactured a number of parts for it. We have also bought an analog kitchen scale that will be used to measure the thrust.

More research has been done into nozzle design, and we now have a plan for what designs we will test.

More work has also been done on Acceleron II including bottle reinforcement. More details will be posted in the next web update. There were no launches this week due to other commitments.
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Jet Foaming Test Flights

This weekend we had a chance to fly a couple of rockets using the Jet Foaming technique.

The results of those flights including video and photos are here:
www.aircommandrockets.com/day28.htm

We definitely need to do more testing on the foam, as it seems to be giving the rocket a bit more performance, but we won't know for sure until we can build a thrust measuring device and performs some static fire tests again.

Feedback and suggestions are always welcome.
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Foam generation tests and Baffle tests

We have updated our website with the latest static fire tests showing in detail how the water behaves inside a water rocket when a baffle is fitted to the lowest Robinson coupling.

The update also shows the Jet Foaming technique we developed to generate foam inside the rocket to provide a different thrust profile to the normal water/air mix.

We intend to develop CD nozzles to help improve the rocket efficiency.

The update is here: www.aircommandrockets.com/day27.htm

We have now test flown the rocket with very good results. The video and update will be posted on the website soon.
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Updated Day 25 Flight Log

Today we updated flight log 25 with a couple of pictures from our under water tests from 2 meters. There is also underwater video showing what happens to the rocket under water.

Otherwise construction of the two new flight computers is continuing, and Polaron III is ready to be tested with the new coupling baffle. Just need to get some nice weather now.
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Coupling baffle and Burst Test

Yesterday a new aluminium coupling nut was made that incorporates a baffle to direct the air sideways onto the walls of the bottle. This should help eliminate the blow-through seen in the static fire tests. This will be tested this week to see what effect it has on performance. The holes are 6mm in diameter, with a total of 4.

We also performed some pressure tests on a reinforced bottle based on the reinforcing technique described by Richard Wayman here:

http://wrockets.trib-design.com/index.php?project=RICHARD&page=hp

We didn't quite get up to the burst pressure of the 1.25L bottle, because we had an issue with the hose failing to hold onto the rocket. We went up to 220psi, before it flew off the test stand. We are making a new attachment that will prevent the bottle from flying off. But all the signs were encouraging for a significant improvement in strength.

We ended up using hot water instead of the heat gun to shrink the outer bottle which worked quite well and pretty evenly.

We also finally have a new proper domain name: http://www.AirCommandRockets.com

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Progress update

Last night, I continued soldering up the new flight computers (FC) for Acceleron and J4 II. It's still will be a couple of days before they are both finished and tested. A preliminary weigh-in of the entire FC including battery and motor & gearbox was 37 grams. This may increase slightly.

We are trying to beat the version 1.2 weight. On Polaron III the entire parachute deployment system including nosecone, but not parachute weighs 133 grams. With V 1.3 we are hoping for under 100 grams.

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Static Fire Tests and Development

This week we carried out some static fire tests on the 8L rocket to see what was happening with the nozzle spray. The full details of the tests are here:

http://home.people.net.au/~aircommand/day26.htm


We were quite surprised at what goes on inside the bottle when there is some water in the upper bottle. We're working on a solution to the problem.

We're also continuing the development of the Acceleron rocket. With newly manufactured couplings the rocket can be fitted with another three 2L bottles. (Each booster segment capacity will be increased by 2L). We have also created new nozzles that have a 10mm hole rather than the 8mm hole as before. The O-rings are now on each nozzle and not in the launcher. This was done because after every launch the o-rings were flushed out of their groove and had to be reseated. Because of the new nozzles, we have also needed to make the corresponding launcher seats.

Yesterday we received a shipment of the PIC microcontrollers we use for the flight computers. At AUD$2.48 each they are as cheap as chips! We now have all the parts build two new V1.3 flight computers. They will be smaller and lighter than the V1.2 prototype that currently flies on Polaron III. The two new FC's will be fitted to Acceleron and J4II. Polaron III will continue using V1.2 for the time being.

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Flight Day 25 - Polaron III, Underwater.

We had a successful launch day this weekend. We flew Polaron III, J4 II and Acceleron. All three rockets performed very well and we obtained some nice in-flight video. We also performed more underwater launches from a greater depth.

The full details of the flight day are now available very on our website.

http://home.people.net.au/~aircommand/day25.htm
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Polaron III payload attached

Last night I attached the payload section to the rest of the rocket. I also added a horizontal cardboard tube into the payload section. This tube will hold a second parachute that is pulled free when the deployed parachute opens.

A second parachute was added as this a fairly big rocket and one small chute would not have been enough.

The entire rocket including camera, flight computer and parachutes weighs 689 grams empty. It stands at 1520 mm long, with 110mm diameter.

The water fill capacity will be just over 1900 ml, so basically almost the entire lower bottle.

At the first launch pressure of 120 psi, the simulator predicts around the 125 meter mark, with slightly higher pressure and no camera predictions are around the 150 meter mark.

Hopefully the weather will be good this weekend for a launch.
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