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070224-002 Internal and skin rocket temperatures
Description Measuring the skin and internal temperature of a rocket.
Tested by GK & PK
Date 24th February 2007      3:00pm - 5:00pm
Location Sydney, Australia
Test Procedure Static Fire Test Procedure
References http://www.AirCommandRockets.com/day26.htm
Related 070224_001 - Air and water mixing static fire test

Aim

This experiment was carried out in order to measure the internal air temperature and the skin temperature of a rocket. We wanted to determine to what degree the temperature increase due to air compression would affect the strength of the PET bottles.

Experiment Setup

The 8L  Polaron III  rocket was set up on the launcher and tied down for this experiment. A thermocouple connected to a multimeter with a temperature function was used to read the temperatures. The thermocouple offers a fast response to changing temperatures.

No water was used in these experiments.

When measuring the skin temperature we just placed the sensor onto the bottle, but probably should have been shielded from the environment.

Firing the rocket by hand.
The cool fog inside the rocket after a test firing.
Measuring the inside and outside temperatures of the rocket. The thin wire is the thermocouple.

Results

The ambient temperature was 22 degrees C.

Static Fire Test #3

The rocket was filled to 50 psi and the external skin temperature was measured during filling to be 25 degrees C.

+3 above ambient.

When the air was let out, the thermocouple was placed inside the rocket and the air temperature was measured at 16 degrees C. -6 below ambient.

Water Rocket Static Fire Test #3

Static Fire Test #4

The rocket was filled to 100 psi and the outside skin temperature was measured during filling to be 27 degrees C. Which is  +5C above ambient.

When the air was let out, the thermocouple was placed inside and the air temperature was measured at 8 degrees C. Which is -14C below ambient.

Conclusions / Analysis

  • The temperature measurements indicated that there is unlikely to be much effect on the PET bottle material with the pressures we regularly use unless combined with other sources of heat.

Things to consider

If the bubbles are produced in an efficient manner it may be possible to use that to an advantage with an expanding nozzle. Antigravity Research used detergent to create foam inside the rocket with an expanding nozzle to make the rocket more efficient. When perfected a technique based on the static fire test #1 may be used to generate the same effect without the viscosity penalty of using detergent.

If the temperature of the air inside the rocket drops below freezing at higher launch pressures, it may be likely that the during the air pulse tiny water droplets exiting could be freezing and exiting as ice or snow?



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