Archive for September, 2008

 

2 Bottle Wrocket Hydrostatic Testing

During our Launch day 6 to test the nosecone and parachute deployment we suffered a leak in our H2 rocket which limited launch pressure to 70psi. So we spent this weekend doing hydrostatic testing of the bottles including the robinson coupling where it was leaking.

As is usual with leaks it looks like it was the washers, so we made a new set of 3 washers and fitted them. We stripped the wrocket back to only the pressure bottles. This is the benefit of a modular design, the nosecone and the removable fin assembly just came off (so as not to damage them) and the 2 bottles and nozzle were left to test with.

With the 2 bottles totally full of water it weighs in at around 2.75kg, way to heavy to balance on the launcher. We used our gardena quick release and just connected that straight to the wrocket nozzle in a horizontal position.

2 bottle hydrostatic testing

2 bottle hydrostatic testing

We found that there was a leak in the one way valve coming from a molded join section at around 90psi. I fear the pressure may have been too much for the plastic valve, so we removed it. We will have to look for a brass one to use instead.

We had a few small leaks in the tubing connections which were tightened then we pressurized until around 120psi and left it there for a few minutes. There was a small leak between the cap and the bottle on the robinson coupling, but not enough to stop a launch, I think this was from the bottles swelling in this area. Here is a pic at 120psi

120psi - bottles swelling

120psi - bottles swelling

just on 120psi

just on 120psi

We are happy that we have a pressure body thats ready for launch, we just need to reassemble the rocket and do some timing tests on the nosecone and we are ready to fly. Hopefully with good weather this week we will get a late afternoon mid week launch  :)

Things we learned

  • Dont try to use a launcher for a hydrostatic test … the wrocket is too heavy
  • At 120psi full of water the wrocket is too heavy to go more than 10cm using a manual release.
  • Always check for leaks :)
  • We are probably going to have to look for a new pump soon :)
  • When fully filling a 2 bottle wrocket for hydrostatic testing the water tends to stay in the top bottle instead of making its way into the bottom bottle. The way to get the water into the bottom bottle is to gently squeezing the air out of the bottom bottle. This forces the air into the top bottle and water down into the bottom bottle. Careful not to squeeze too hard so you dont put a crease the bottle

Posted by on September 15th, 2008 2 Comments

Launch Day 6

Launch Day: 6
Date: 08/09/08 Late Afternoon
Location: Montview Oval
Rockets: H2

The weather and Fathers Day hampered testing our new wrocket on the weekend, but an opportunity presented itself for myself and my son Mark to get in two quick test launches this afternoon (Monday) at our local park.

We had rebuilt our two bottle rocket after the crashes from the previous launch day and redesigned the PPNC and were keen to try it out. The weather was closing in when we got there with the wind picking up and the sun starting to get low.

wind pushing the wrocket off course on the launcher

wind pushing the wrocket off course on the launcher

Our goal was to launch at 100psi but at 70psi we heard a leak and decided to launch anyway. The timer had been set for approx 4 seconds so if the chute was going to open it would have been on the way down. Here is the video.

It launched and shuttle cocked into the wind so height wise I think maybe 45m (145ft) at best. The camera work isn’t great and you can see that I assumed it was going to crash when we heard a pop and the chute deployed about 5m above the ground and the rocket glided down to a safe landing.

Here is a still frame from the video showing the rocket before it touches down.

H2 under parachute

H2 under parachute

We were very happy that the deployment worked.

H2 safely on the ground

H2 safely on the ground

We did a quick blow pressure test and could hear a slight leak around the robinson coupling. Quickly removing the faring and tightening the bottle lid we strapped the faring back and prepared for a final launch. By this time the wind was picking up and it was getting cold so we just had time for one more launch.

We again tried for 100psi but our leak was still there at 75psi, so we decided to launch anyway. Here is the result.

You can see from the video that its really snaking around on the way down, I think the door was trying to open but it may have been going too fast.

Here is a nice pic at apogee .. just missed :)

H2 just missing the moon

H2 just missing the moon

It crashed with only minor damage. The sponge under the ping pong ball works well and only the ping pong ball needs to be replaced. There is a small crease in the top of the nosecone but very minor.

H2 damage after crashdown

H2 damage after crashdown

Looking at the nosecone after landing, the chute was out and the door wide open, it was hard to tell what went wrong. I think it maybe didn’t have enough time to open properly or something may have got caught up.

Our pilot thankfully survived the landing .. although in the inverted (crash) position, he will fly another day :)

Assume the brace position

Assume the brace position

Things we learned

  • The new nosecone design appears to work, which is good.
  • The speed flap and the single elastic to the timer I think will be more reliable, needs more testing
  • We will need to pressure test the robinson coupling better when we make changes.

Posted by on September 9th, 2008 Comments Off

H2

Stats:
Name:                       H2 – (Happy V2)
Build Date:                8/09/2008
Capacity:                   2.5L – 2 x 1.25L
Nozzle Size:               9mm
Fill Volume:               ~ 700ml
Launch Pressure:       100 psi
Dry Weight:               265 grams
Recovery:                  Nosecone with Tomy timer + 60cm (24″) ripstop nylon parachute
Status:                      ACTIVE (3 flights)

Notes:
This rocket is a rebuild of H1, new upper pressure bottle and nosecone fitted. It has 2 x 1.25L bottles connected with a robinson coupling, a nosecone with a tomy timer,  60xm (24″) parachute and a removable fin assembly with trapezoid shaped fins.

This is our first piloted rocket

Flights:
Rocket deployment system was successful on first launch.
Second flight was a deployment failure although minor damage.
Third flight parachute deployed at apogee

Highest Altitude:
Rocket has made 3 flights up to approx 260ft

Pics:
H2

H2

Posted by on September 8th, 2008 4 Comments

Nosecone Mk II

After our recent parachute deploy failure it was back to the drawing board for the ping pong nose cone (PPNC)  and side parachute deploy. Having built the first version there were a number of things I wanted to fix. These were

  • The placement on the nosecone of the timer
  • Want to use a single rubber band to not wind past the timer – this reduces the chance of being caught up on the timer itself.
  • The size of the door probably needs to be a little smaller and lower (dont want it near the pointier point of the nosecone, this makes the door not close properly
  • The vertical height of the nosecone support structure may be too high based on our parachute size.

The PPNC shell and support structure were largely based on our original design

Timer Placement
This is probably the most important thing for the new nosecone. We think the root cause of the parachute deploy failure was that the elastic band when it wrapped around the nosecone got caught up on the timer itself and wouldn’t allow the door to open. Nosecone Mk II has the timer located just before the door hinges. This gives the elastic band enough space to be stretched but not too much that it will wrap back past itself or the door. Hard to explain , so here is a pic.
Door hinge and timer location

Door hinge and timer location

The door has 2 wire hinges. The door is made out of the same diameter bottle, just put on backwards, so that the natural curve of the bottle will fling the door open by itself. The parachute deployment plate is just visible on the right with its two elastic bands that eject the parachute. The timer is to the left mounted on the side of the nosecone support structure. A hole is drilled in the side of the bottle to allow the handle of the timer to extend beyond the rockets diameter.

The little green guy is our fearless pilot. The tape is on the inside to ensure the nosecone structure doesn’t snag on the hinges when it is removed.

Nosecone Door

Nosecone Door

Above you can see the door in the open position, notice how it curves the opposite way when open, also the one elastic band on the door which is enough to keep it closed and connects to the timer.

We added an extra section at the top of the nosecone support structure, this was to keep the top of the door below the curve in the nosecone (although it doubles as a pilots cockpit), this will help keep the door closed properly as it will sit flatter against the side of the nosecone. The size also fits our parachute better, not too loose, not too tight.

New Timer

This nosecone had a proper Tomy timer, sent to me by Trevor in Cairns (thanks again). These are available from Toy stores. I will have to find them here in sydney. This is what the packaging looks like. They are about $3 each.

Tomy Timer Packaging - Front

Tomy Timer Packaging - Front

Tomy Tomer Packaging - Back

Tomy Timer Packaging - Back

The timer is much better than the previous fish swimmer in nosecone Mk I, as it has a built in regulator. This means that when you cut the wheels off you don’t need to put any weight back on it to stop it from just unwinding quickly.
Here is the timer ready to go into the nosecone. The wheel you can see on the front was cut off.
Tomy Timer ready for installation to nosecone
Tomy Timer ready for installation to nosecone
Ready to Fly
Here is the final configuration, parachute is packed, elastic band is connected to the timer (far left), the speed flap (launch detect) is attached and the nosecone is attached to the top of the pressure bottles.
Ready to Fly

Ready to Fly

Also our fearless pilot is strapped in and readyfor launch

Posted by on September 8th, 2008 Comments Off