Archive for September, 2008

 

Launch Day 8

Launch Day: 8
Date: 23/09/08 Afternoon
Location: Montview Oval
Rockets: H2

Today was another test day. After our last adventure with the parachute deploying and nearly loosing the wrocket, we decided to try a late main parachute deploy to see how it would hold up to opening whilst returning to earth quite fast.

We launched H2 at 100psi and had the timer set for approx 6.4-6.8 seconds (2 winds). There was a bit of wind about so we angled the launcher into the wind. The simulators told us a flight time of about 8.8 seconds which is what he had verified on other flights. In hindsight the 6.4 seconds was a little too late and H2 crashed down without a deploy. We ran the video through virtualdub our video editing s/w frame by frame and we only ended up with a flight time of 7.1 seconds.  This didnt leave enough time to deploy the chute. The smaller flight time than anticipated was probably due to the wind.

Here is the video .. roll the video tape .. I mean stream the bits !

H2 did sustain a bit of damage and the mounting of the tomy timer came off the nosecone structure which meant we didnt get a chance to test with the chute again. So seeing as the nosecone shell was a write off anyway we put it back on the stand and launched twice more at 110psi, which is our highest launch pressure to date.

I will go ahead and build the dual chute deploy system with a drogue chute and the main chute. This will need a new nosecone design and extension as well as a second tomy timer. I have ordered 5 today that should arrive before the weekend. so it looks like no launches this weekend but a lot of building.

Things we learned

  • Predicting the exact deploy time for a late deployment is quite hard, there is not much margin for error. A better system (I think) will be a dual deploy with a drogue at apogee and a main chute later.

Posted by on September 23rd, 2008 2 Comments

Launch Day 7

Launch Day: 7
Date: 20/09/08 Afternoon
Location: Berry Oval
Rockets: H2

Hottest Day of the year today 33 degrees C, so blue sky’s were not a problem, but as the afternoon grew longer the wind started to pickup. We were fairly keen to get a launch in today to test the parachute deployment. We tried a few of the bigger parks, but cricket and baseball are into full swing and the big parks were in use.

We ended up at Berry oval which is always empty in the afternoon, but its a little small. We have flown H2 here before and its always landed in the park so we decided to go for a launch.

We setup as usual, put H2 on the launch pad, setup the timer for 1 wind and waited for the wind to die down a little. We pressurized to 100psi waited another 2 minutes or so until the tops of the trees were still then launched. Here is the video

As you can see, the side deploy nosecone worked really well. Although its not really visible in the video I can clearly remember seeing the rolled up parachute falling alongside the rocket briefly before it opened and the main section of the rocket fell underneath the parachute.

Our jubilation was quickly overshadowed as it started to become obvious the  wind up high was really blowing harder than on the ground or the tops of the trees. The parachute and wrocket drifted out of the park, over the road and into thick bushland.

The search was on … from previous golfing experience I knew to improve the chances of finding it we would have to pick a landmark on the line where we last lost sight of it, which in this case was a tree sticking up higher than the rest .. and we aimed for that, although how far in it landed we weren’t sure.

We scaled a wire fence and headed in through thick bush, always looking up to see if we could see H2 stuck in the tree tops , stamping our feet to scare way any snakes and using sticks to brush spider webs out of the way. (When you have 16 of the worlds top 20 most poisonous snakes and the worlds most deadly spider this is good practice).  It was hard at this stage to even spot the large tree were were aiming for, after a few minutes the trees opened up, the ground was more open and we scaled a hill where the tree we were aiming for was. We looked around from this vantage point and couldnt see the bright yellow chute.

We went past the big tree and the ground sloped down to a fence, again through thick bush to the expressway that we could hear below. It was at this stage that I though we would be building a new wrocket when Mark called out he could see it.

It was hanging in trees about 4m up. There were lots of thin dead trees so getting a long pole wasnt a problem, so after a bit of shaking H2 was back with us … with no apparent damage. The search for the wrocket had been more of an adventure than launching it :)

Here is a picture we took from Google Earth showing where it was launched and where we recovered it (click pic for a larger view).

H2 Flight Path

H2 Flight Path

As you can see Goggle Earth estimated the landing spot at 195m from the launch site, about half of that through thick bush. You can also see how close to going on the expressway it was. Here is a pic from Google Streetview of where it landed, there is a 2m fence between where we were and the edge of the cliff (not visible in the pic) so we were not in any danger of going over the cliff. H2 landed a few meters back from the fence, the treeline you can see is pretty much the fence line.

H2 landing location

H2 landing location

We put the numbers into Cliffords water rocket simulator and came up with ~ 80m (260 feet), which wouldn’t be too far off the money.  Here is a pic after recovery, you can see how thick the bush was here.

Mark with H2 after recovery

Mark with H2 after recovery

Things we learned

  • Make sure you have a big area to launch in when there is wind around. In this instance I think we may have outgrown Berry Oval
  • Looking at the treetops is not always a good indication of how fast the wind is blowing further up
  • We may need to look at a 2 chute deployment system with a smaller drogue chute deploying then the main chute later or possibly just deploying the main chute further past apogee
  • The parachute deploy and PPNC seems to work well, we will continue to test before we fly a camera and an altimeter but we are heading in the right direction
  • The robinson coupling worked perfectly, no leaks and the wrocket sat on the launch pad at full pressure for at least 2minutes without loosing any noticable pressure
  • The wrocket flew very straight, again I was able to see it backside from apogee for the first few metres before the chute deployed

Posted by on September 20th, 2008 Comments Off

H2 Reassembly and Nosecone testing

The weather is predicted to be fine this weekend so we are looking forward to launch day 7. Our Modular H2 rocket was put back together after the hydrostatic test. We have used the Robinson coupling that didn’t have the slow leak at 125psi so all should be well from the propulsion part of the wrocket.

We made a new launch release flap out of corrugated cardboard. After many tests the old one wasn’t holding its shape well. A new one fixed that. These weighs in at 1 gram.

Here is a pic of H2 put back together.

H2 ready for launch day

H2 ready for launch day


Nosecone Testing and Calibration

As with our last timer we have tested the number of turns on the new tomy timer to find out how many turns equate to what number of seconds. We want to get the deploy near or just before apogee.  The results were

Number of Turns .     Seconds
1.0 3.2s
1.5 4.4s

These timings are fine for H2 up to a 120psi launch which is what we will test up too.

Here is a video of the new nosecone and side deploy in action. The video is 1 turn of the timer, you can see the parachute get kicked out the side. For the video the wrocket is sitting unpressurized on the launcher.

Posted by on September 20th, 2008 Comments Off

3 Bottle Wrocket Hydrostatic Testing

We decided to add another “robinson coupled” bottle to H2 to make a 3 bottle wrocket and hydrostatic test it.  We were interested to see how this coupling would go and whether we would see the drip leaks we encountered on the 2 bottle hydrostatic test.

Adding the third bottle used the same technique as joining the first two bottles, which was surprisingly fast when you know what you are doing (well have done it more than once…. :) ). I also created an additional fairing for the third bottle using the “low tech” hotplate technique.

Additional Safety Precautions

I decided that even though we are not burst testing these bottles, there is still significant energy inside the bottles at 125psi, so I will be using my safety goggles on these hydrostatic tests.

Safety Goggles

Safety Goggles

Hydrostatic Test

I took Georges advise and filled the hose leading to the pump with water, but it only filled back to the 10mm section and wouldn’t take anymore (air locked possibly). Evidently this turned out to be not enough as it stated out fine and no air was being pumped into the bottle,  but as the pressure rose the air just went around the water in the hose and got in. I will have to find a way around this problem for future tests.

You can see here the amount of air that made its way into the first bottle

air in first bottle - 3 bottle test

air in first bottle - 3 bottle test

The test itself went well. The bottles held pressure well, all the way up to the maximum on the pump gauge, which was 125psi. The first to second bottle still had the drip leak (about 3 drips every 2 seconds) but the second to third showed no leaks. This pressure was held for about 3 minutes.

125psi - hydrostatic test

125psi - hydrostatic test

here is a pic of the bottles at 125psi (you may need to click on the pic for the full size to see detail)

3 bottles at 125psi

3 bottles at 125psi

Just out of interest I weighted the 3 bottle assembly, including the 3 x 1.25L bottles, 2 x robinson couplings, 2 x fairings and nozzel. It weighs in at 193grams

Final Thoughts

Our next launch is to test the parachute deployment, so we will probably go back to 2 bottles – most likey take off the first one with the dripping connection. Once we have the parachute system working properly we will add the third again and go for some height :)

Posted by on September 18th, 2008 Comments Off