last updated: 20th April 2017 - Day 186 - Light Shadow pyro flights - HPR Level 1 Attempt

Safety First

Search

Site Index

Tutorials

Articles

Rocket Gallery

Labs

Where To Buy

10 Challenges

Links

Blog

Glossary

Contact Us

About


Construction - Basic

Body

Ring Fins

Flat Fins

Nozzle

Nosecone

Construction - Advanced

Robinson Coupling

Splicing Bottles #1

Splicing Bottles AS#5

Reinforcing Bottles

Side Deploy #1

Side Deploy #2

Mk3 Staging Mechanism

Multi-stage Parachutes

Fairings

Construction - Launchers

Gardena Launcher

Clark Cable-tie

Medium Launcher

Cluster Launcher

Launch Abort Valve

Quick Launcher

How It Works

Drop Away Boosters

Katz Stager Mk2.

Katz Stager Mk3.

DetMech

Dark Shadow Deployment

Articles

Recovery Guide

Parachutes

How Much Water?

Flying Higher

Flying Straight

Building a Launcher

Using Scuba Tanks

Nozzles

Video Taping Tips

MD-80 clone

Making Panoramas

Procedures

Burst Testing

Filling

Launching

Recovery

Flight Computer

Servo Timer II

V1.6

V1.5

V1.4

V1.3, V1.3.1, V1.3.2

V1.2

Deploy Timer 1.1

Project Builds

The Shadow

Shadow II

Inverter

Polaron G2

Dark Shadow

L1ght Shadow

Flight Log Updates

#186 - Level 1 HPR

#185 - Liquids in Zero-G

#184 - More Axion G6

#183 - Axion G6

#182 - Casual Flights

#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

#1 to #150 (Updates)

 

FLIGHT LOG

Each flight log entry usually represents a launch or test day, and describes the events that took place.
Click on an image to view a larger image, and click the browser's BACK button to return back to the page.

Day 106 - Measuring bottle stretch thrust

Date:  22nd May 2011
Location:
Workshop, NSW, Australia
Conditions:
pleasant, temp ~20C
Team Members at Event:
Paul K, John K, GK

This week we take a detour from launching rockets and go back to visit an experiment that we've been wanting to do for a while.

Aim

Since a bottle stretches when pressurised, how much energy is stored in the bottle itself? How much of this energy is returned during the thrust phase?

Experiment Setup

Background

In order to measure the stored energy in the bottle walls we decided to completely fill the bottle with water, pressurise it and measure the thrust produced when it is released. Because water is essentially incompressible at these temperatures and pressures all the energy that produces thrust should come from bottle contraction.

In order to get an accurate thrust measurement we needed to eliminate the effects of gravity because the bottle would get lighter as it expelled water. We suspended a 2L bottle horizontally so that it was free to swing along it's axis. We also attached the neck of another bottle to the base of the test bottle so it could be attached to a load cell. Another loop of rope was used to stop the bottle from moving upwards during the thrust phase.

Since the thrust phase was going to be fairly short we used a small 5mm nozzle to stretch the thrust curve out in time as we only sample the load cell at 240Hz. The total impulse is still roughly the same as if we had used a larger nozzle.

Experiment Setup

Even the smallest bubbles in the bottle can give significant errors in the measurements because air is compressible. In order to prevent air entering the bottle during pressurisation we filled the air hose completely with water to fill the void as the bottle expands. We also submerged the entire bottle in a tub of water and fitted the nozzle,  release head and the air hose full of water so that everything was completely free of bubbles. We then placed the bottle on the test stand and suspended the hose vertically so that potentially any remaining bubbles would float to the top of the hose.

From previous experiments we know that a standard 2L bottle increases its volume by 157mL or 7.5% when pressurised to 120psi.

Results

Three horizontal experiments were carried out to measure the thrust produced by bottle stretching alone. One vertical experiment was also carried out  to compare how much thrust a typical 2L bottle produces at the same pressure and same nozzle using the same measuring equipment.

The bottle capacity was 2096mL and was pressurised to 120psi.

First horizontal test setup. Firing horizontally eliminates the effects of gravity on the thrust reading as the bottle loose water.
Attaching the nozzle and release head to the bottle while completely submerged under water to eliminate bubbles.
The bottle is suspended at one end by a string, while the other end is attached to the load cell.
Test #4 was carried out vertically. The support brace around the bottle keeps it aligned but allows it to move freely up and down.
Here it is connected to the air hose and release mechanism. A non return valve is built into the release head. The bottle was filled with 800mL of water.

 

The following graph shows the recorded thrust curves for all three horizontal tests. All 3 thrust curves have a similar shape and timing.

Graph 1 - 3 Horizontal tests

The following graph shows the 3 horizontal thrust curves with the vertical test thrust curve using air and 800mL of water.

Graph 2 - Comparison of normal thrust curve and the bottle stretching thrust curves.

The following graph superimposes the Simulation results from Clifford Heath's simulator thrust curve confirming that the measured results are in close agreement with simulation results.

Graph 3 - Theoretical thrust curve superimposed on the measured results.

The data from the load cell was then further processed in an Excel spreadsheet. The data was first filtered with a 5 point moving average before the total impulse was calculated. The vertical experiment data also had water loss compensation added for the water phase part of the thrust curve.

The following table lists the total impulse for each test run.

Test # Total Impulse Notes
1 3.30 Ns Horizontal, 2L water only
2 3.64 Ns Horizontal, 2L water only
3 3.65 Ns Horizontal, 2L water only
4 31.68 Ns Vertical, 800mL of water

Table 1. - Measured total impulse

In the 3 horizontal experiments no bubbles were observed in the bottle.

Conclusion

This experiment showed what the upper bound is for the thrust produced by stretching alone. It is only an upper bound as in a real rocket the energy is returned over the entire boost period which includes the air pulse. In an ideal rocket with 1/3 the volume filled with water the energy returned during the water phase will span a pressure drop of ~40psi. (Going from 120psi to 80psi during the water phase).  The rest of the energy is returned during the air pulse as the pressure drops from 80psi to atmospheric. But the impulse normally produced during the air pulse is approximately 1/3 of the total impulse.

Taking this into consideration the net thrust produced during a real launch from bottle stretching is likely to be around 1/2 of the thrust measured in this experiment.

<< Previous       Back to top      Next >>



Copyright © 2006-2017 Air Command Water Rockets

Total page hits since 1 Aug 2006:

George Katz - Google Plus