Investigations in Model Rocketry

BLAST OFF!

• My name is Natasha Honcharik and I am a Sophomore at Wachusett Regional High School.

• I started my research in rocketry in September of 2011.

• My experiments were performed at home and in sports fields at my school.

PURPOSE:

• The purpose of this experiment is to find out what factors in a model rocket engine’s design affect the maximum altitude of the rocket and the temperature of the engine’s flame.

BACKGROUND INFORMATION:

• Engines are designated with a letter and a number. The letter indicates impulse, or total change in momentum, and the number indicates average thrust in newtons. “A” engines have a 2.5 newton-second impulse and “B” engines have a 5.0 newton-second impulse.

• Thrust * burn time = total impulse

• Factors affecting engine performance:o Type/Amount of propellanto Nozzle sizeo Burn patterns

Burn PatternsSolid fuel only burns on the surface, called the flame front.

Burn patterns are the way the flame front changes.

A larger flame front at one point in time means more fuel burning at once and more thrust.

The flame front (shown in yellow) starts as a cone shape corresponding with the initial peak in these example thrust curves.

BACKGROUND INFORMATION:

HYPOTHESIS:

• If a rocket engine with a greater total impulse is used then the rocket’s apogee (highest point reached) will be higher.

• If a rocket engine with the same total impulse but a greater average thrust is used then the flame will have a higher average temperature.

This was justified because impulse is equal to change in momentum. A greater momentum would mean the rocket would reach a greater velocity and thus a greater altitude.

This was justified because a higher thrust is caused by a larger flame front where more fuel is burning at once. Because more fuel was burning at once, it was hypothesized that the temperature from the flame would be hotter.

PROCEDURE (EXPERIMENT # 1):

• Independent variable: type of engine

• Dependent variable: altitude reached

• The rocket was remotely launched and recovered ten times with each of four engine types (A6, A8, B4, and B6) and altitude data was recorded by an electronic altimeter inside the rocket.

PROCEDURE (EXPERIMENT # 2):• Independent variable: type of engine used

• Dependent variable: average flame temperature

• The engines were placed upside down in this apparatus and ignited remotely. The average temperature was measured with a temperature probe.

• Average burn time was measured with a video camera and multiplied by the average thrust given by the manufacturer to calculate total impulses.

Cylindrical hole

Ignition wire

Cement slabs

Temperature probe

PROCEDURE (EXTENSION):• Independent variable: engine type

• Dependent variable: thrust produced

• The same apparatus was used with a force plate replacing the bottom concrete slab.

RESULTS (ALTITUDE):This is a box and whisker graph of the altitude data recorded. Student t-tests were performed and there was found to be a statistically significant difference between each group. A8 engines reached the lowest altitude, followed by A6, B4, and B6.

RESULTS (TEMPERATURE):This is a box and whisker graph of the temperature data recorded. Student t-tests were performed and there was found to be a statistically significant difference between each group except between A6 and B6 engines which were also the lowest in temperature overall.

(note: temperature is relative because the probe could not be placed directly in the flame without damage, so radiant heat was measured.)

RESULTS (extension):

This is an example graph of one of the B4 engine’s thrust curves. Note the initial spike and then leveling off. This includes only the propellant phase of the engine.

This curve was averaged and multiplied by burn times to calculate impulses which were found to be close to but less than the given impulses. These were then used to roughly predict altitudes without air resistance.

RESULTS (EXTENSION- PREDICTED ALTITUDE):

In these graphs of impulse and propellant mass vs. altitude, the blue represents the actual average altitude of each engine type. The red is the predicted altitude without air resistance using thrust and burn time data from the National Association of Rocketry, and the green is the same calculated altitude using my measured data. Altitude increases linearly with impulse and propellant mass, while the altitude without air resistance increases exponentially because calculations for air resistance involve velocity squared.

CONCLUSIONS:• An engine with a higher impulse does yield a higher altitude.

• However engines with the same impulse ranking do not always reach the same altitudes because the rankings are maximums, not exact values.

• Temperature was not related to thrust as hypothesized. While both thrust and temperature are affected by burn patterns and propellant formula, thrust is also affected by nozzle design, causing it to differ.

CONCLUSIONS:

• Quest brand engines (A6 and B6) were more efficient than Estes brand (A8 and B4).

• They reached a higher altitude with approximately the same amount of propellant.

• Quest engines also had an overall lower temperature. This shows that they more efficiently converted their fuel’s chemical energy into thrust rather than thermal energy.

• This may be due to Quest’s greater attention to nozzle design. Quest engines were found to not only have smaller nozzles, but they also had different nozzle sizes for different engines whereas Estes brand engines all had the same size nozzle. Quest is a smaller, lesser known brand, so Estes mass production might lead to less attention to individual detail and less efficiency.

ACKNOWLEDGEMENTS:

• Thank you to my parents who bought me lots of rocket engines and supervised my experiments.

• Thanks to Dr. Neil Ault for being my adviser at science seminar.

• Thank you to my physics teacher Mrs. Carol Sullivan for helping me every step of the way and being the best teacher ever.

• Also thanks to my school, Wachusett, for lending equipment and facilities.

THANK YOU!!