last updated: 16th March 2017 - Day 178 & day 181 Acoustic Apogee Detector

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Construction - Basic

Body

Ring Fins

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Nozzle

Nosecone

Construction - Advanced

Robinson Coupling

Splicing Bottles #1

Splicing Bottles AS#5

Reinforcing Bottles

Side Deploy #1

Side Deploy #2

Mk3 Staging Mechanism

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Construction - Launchers

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How It Works

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Katz Stager Mk2.

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Recovery Guide

Parachutes

How Much Water?

Flying Higher

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Building a Launcher

Using Scuba Tanks

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MD-80 clone

Making Panoramas

Procedures

Burst Testing

Filling

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Recovery

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V1.3, V1.3.1, V1.3.2

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Deploy Timer 1.1

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Flight Log Updates

#181 - Acoustic Apogee 2

#180 - Light Shadow

#179 - Stratologger

#178 - Acoustic Apogee 1

#177 - Reefing Chutes

#176 - 10 Years

#175 - NSWRA Events

#174 - Mullaley Launch

#173 - Oobleck Rocket

#172 - Coming Soon

#171 - Measuring Altitude

#170 - How Much Water?

#169 - Windy

#168 - Casual Flights 2

#167 - Casual Flights

#166 - Dark Shadow II

#165 - Liquid Density 2

#164 - Liquid Density 1

#163 - Channel 7 News

#162 - Axion and Polaron

#161 - Fog and Boom

#160 - Chasing Rockets

#159 - Measurement

#158 - Dark Shadow

#157 - Polaron G2

#156 - Foam Flights

#155 - Down The Barrel

#154 - Revisits

#153 - ClearCam

#152 - Mullaley, Axion G2

#151 - Competition Day

#150 - Rocket Salvos

#149 - Glide Fins

#148 - Too Windy

#147 - Descent Rates

#146 - G2 Launcher

#145 - Harness

#144 - Water vs Foam

#143 - Whalan Reserve

#142 - Doonside

#141 - Windy

#1 to #140 (Updates)

 

PROCEDURES
The following procedures describe various things you will need to do when preparing and launching rockets. There are a number of warnings that you should heed if you want to enjoy an extended rocket career.

Determining Maximum Operating Pressure / Burst Testing

 Tests from: 8th October 2006

Setting up for testing bottles.
Burst in progress. The bang scares you into pressing the shutter release.
A little too much air in the bottle does more damage...
...than when there is only water.
Applying some re-enforcement gaffer tape.
Bottle on test stand.
The victims.

  Tests from: 22nd October 2006

A standard 2L Coke bottle.
1.25L bottle re-enforced with Scotch Strapping tape.
An angry looking hose just after burst.
Failure of the re-enforced bottle. Note that the tear is very limited.
Blue Scotch "gaffer" tape on a 2L Coke bottle.
Detail of the base re-enforcing.
Bottle failed at just above the normal burst pressure. This tape is useless for re-enforcing.
Failed shrunk 1.5 L bottle. The neck shattered as well as the nozzle.

Tests from: 15th July 2007

We submerged the bottles under test to contain the noise.
Two 2L Robinson coupled bottles failed at 165psi.
Preparing to test a 2L bottle.
A typical 2 L bottle failure. Splits down the side.
The coupling still retained some of the plastic from the failed bottle.
Stress fractures in the base of a 2L bottle after being subjected to 140psi.
   

 

One of the very first questions you will ask yourself when building your rocket, is "what's the maximum pressure I can put into this thing?" Generally, the more pressure the higher the rocket will go, and so naturally you will want to increase the pressure more and more.

There is a limit, however, and beyond this limit the bottle will rupture. An exploding bottle can be very dangerous, so you should ensure that you never get to this point, ... well kind of...

The Burst Test

You need to perform a burst test on the bottles you will be using for your rocket. Make sure no one goes near the bottle when this test is being performed.

  1. Take an identical bottle to the one you are using for your rocket.
  2. Fill it completely with water so there is no air in it. We use a fairly long piece of garden hose as the air line and also fill it completely with water. This water is pushed into the bottle as it expands during pressurisation. This helps reduce the amount of air in the bottle when it bursts. Less air means smaller boom.
  3. Place the bottle behind a protective barrier.
  4. Connect the bottle up to the pressure supply and slowly start increasing the pressure, continuously taking note of the pressure. (The pressure supply and gauge should be the ones you will be using to launch your rockets.)
  5. When the bottle bursts (you will know when that happens) write down the maximum pressure reached.
  6. Now repeat this test a few more times, recording the pressure at which each bottle burst.

When the burst tests are complete, take the lowest pressure that caused a bottle to burst and take 30% off that value. This will be the Maximum Operating Pressure.

Example:

If your burst pressures were:  160psi, 150psi, and 155psi then the Maximum operating pressure is: 150 x 0.7 = 105 psi.

Never pressurise your rocket above the Maximum Operating Pressure.

You do not want your rocket to rupture on the launch pad ... not only may you injure someone, but you will have to build a new rocket.

Maximum Operating Pressure could be referred to as MOP, which is appropriate because that's exactly what you need if you do this test indoors.

Results

Here is an example of typical burst tests:

Some burst test results for common bottles:

Date Tested: 8th October 2006
Testers: PK and GK.

Capacity Burst Pressure
(psi)
Notes
1.25 L 190 This was a standard 1.25L bottle with the label and cap ring removed. This bottle had a significant amount of air in it and as a result got quite shredded.
1.25 L 185 Same bottle as above but this time there was no air in it. This one only split along the side.
1.5 L 175 A standard 1.5L bottle with label and cap ring removed. There was no air in this one and it split along the side.
1.25 L 195 We used 3 bands of gaffer (duck) tape on the widest part of this one. During filling the hose sprung a leak and it went only up to 180psi. Refilling it a second time it was already pre stressed and failed at 195 on the neck part of the bottle.

Date Tested: 22nd October 2006
Testers: PK and GK.

Capacity Burst Pressure
(psi)
Notes
2 L 168 This was a standard 2L "shaped" Coke bottle had the label still attached. It is likely that the label provided a little re-enforcement.
1.25 L 250 A standard 1.25L bottle re-enforced with 1 layer of Scotch 3M strapping tape. The bottle showed very good shape retention at high pressures.
2 L 190 The same Coke bottle as above but this time it was re-enforced with a single layer of blue Scotch "Gaffer" tape. This tape is quite flexible and provided very little re-enforcing strength. In the video it is quite obvious that bottle stretched significantly before bursting. This tape is useless for re-enforcement.
1.5 L

Heat Shrunk to 1 L

170? This was test to see if shrinking a bottle using hot air would make it stronger because of the smaller diameter and hence slightly thicker walls. Nope! The bottle stretched quite asymmetrically and burst at regular pressure. This bottle also failed unlike the others. The bottle failed at the neck and shattered the nozzle. Ooops, that was a good nozzle. When bottles stretch it is very common for little stretched "V"s to form right at the base of the neck. The bottle probably failed at one of these and the crack propagated all the way to the top shattering the nozzle around it.

Date Tested: 15th July 2007
Testers: PK and GK.
Notes: These tests were carried out under water about 40-50cm below the waterline.

Capacity Burst Pressure
(psi)
Notes
2 L 165 This is a standard straight walled 2L bottle. The wall has a small ridge in the middle of it. Typically contains Pepsi. The bottle burst on the side.
2 L and 2.25L
coupled
165 A 2L bottle as above and a 2.25L bottle were coupled base to base using our standard 8mm Robinson coupling with three thick hard rubber washers. It appears the bottle burst again on its side and the crack propagated to the coupling hole. From there the cracks fanned out from the hole. There was significant damage all around the coupling. The 2.25L bottle was stretched but otherwise undamaged.
2L - A standard 2L bottle again but this time without the central ridge on the flat section. We pressurised this bottle to 140psi. We stopped the pressurisation and held it for 40 seconds. During this time the bottle continued expanding and air having entered it it started floating to the surface. We aborted the test and let the pressure out. The bottle was stretched considerably. Normally the bottle has a 2280ml capacity, but after stretching it held 2360ml unpressurised.
2L 150 Same bottle as above. We pressurised it to 130psi and held it at that pressure for 3 minutes. No visible continued inflation could be seen. Then we slowly increased the pressure and the bottle failed at 150psi.

 

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Filling and Pressurising
 
SCUBA tanks and compressors work well as air supply.
A funnel makes it easier to pour the water in.

Filling the rocket

To fill the rocket with water, remove the nozzle, and simply pour the water in. Using a funnel can make it easier, and putting marks on the bottle at various levels allows you to easily fill it to the right level for a particular flight profile.

Placing the rocket on the launcher

  1. Place your finger over the nozzle and turn the rocket upside down.
  2. Thread the rocket into the launcher, and pull back the hose quick release.
  3. Align the nozzle with the quick release hose fitting
  4. Quickly remove your finger and drop the nozzle into the fitting
  5. Snap the fitting in place.

The amount of water lost is negligible.

Pressurising

Before pressurising the rocket clear the area of kids or anyone who could accidentally launch it. Leaving a big loop in the string is good idea.

On your first attempt you should only pressurise the rocket to around 30 psi. This will help you determine which way the rocket is going to go as well as familiarise yourself with the whole launch procedure. The rocket can still reach pretty high altitudes at this pressure.

Increase the pressure on successive launches to see the difference in altitude. Remember DO NOT exceed your maximum operating pressure. (See determining maximum operating pressure)

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Launching
 

Countdown and Launch

Warning

Make sure all people in the launch area are aware that a rocket will be launched and may fall on or fly directly at them!

When pressurisation is finished, check the surrounding area again and make sure everyone is aware that a rocket launch is imminent. Check with people wanting to take pictures of the launch that they are ready, batteries are charged up, lens covers removed, film in camera, camera is out of the camera bag etc.

You may also have someone time the flight with a stop watch to help you record your rocket's flight performance.

In a clear loud voice count down to zero and on zero pull the string firmly until the rocket is released.

Now shout and cheer and yell “Wow look at it go, …. look how high it is …it is a bit windy up there … the rocket is coming back …. LOOK OUT!!! … the wind shield was dirty anyway ….”

Rockets can land anywhere. With the same rocket, off the same launch pad on successive lift offs there were more than a 100 meters between the locations where they landed for us even though they both mostly went straight up.

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Recovery
 
After touchdown, inspect the rocket for any damage. Damage is very common after a hard landing especially without a parachute. Make sure that the main bottle does not have any kinks or scratches that may cause it to burst at a lower pressure.

Also inspect that the fins and nosecone are still securely attached. If something is loose usually a bit of tape can fix it.

Don't try to launch a rocket with loosely attached components. A rocket launch puts quite a lot of stress on the component joints, and if a fin should fall off during take off, the rocket may have a less predictable path.

It is fascinating to see peoples reaction to an out of control rocket flying parallel to the ground.

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