Shell Altitude vs. Mortar Length

Ron Dixon

Introduction: During the mid 1980’s, I was the President and General Manager of San Diego Fireworks, Inc. At many of our Pyrotechnic Safety and Training Seminars, I was asked about the correlation between mortar length and altitude attained by aerial shells. Further, I have overheard many theories relating to a “vacuum” created within a mortar, if that mortar is longer than some optimum length. Others have made statements indicating that exceptionally long mortars would project shells well beyond “normal” altitudes for given sizes of shells. Upon reaching saturation of these various theories, our staff decided to perform some basic tests to see if any of these theories had merit. Prior to making the determination to conduct this field test, we had the opportunity to view videotape produced by a Japanese firm. This videotape showed shells being fired from a thickwalled glass mortar. Our observations indicated that there was a considerable amount of gas generated by the lift charge and that the vast majority of this gas was produced well after the shell had left the open end of the mortar during launch. Although our methods were not purely scientific, in that we did not use precise measurement recognized in the industry as acceptable and would be able to determine if the theories were in fact accurate or erroneous. We were not looking for precise data, but data sufficient to determine if these theories warranted further investigation.


Ref: JPyro, Issue 11, 2000, pp70-72
(J11_70)


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