Parachute Recovery System

Posted on Feb 6, 2014

Before I began building amateur rockets, I built and flew model rockets, starting in the summer of 1971. Looking for a greater challenge, the following year I decided to begin building my own rockets, entirely from scratch. Although my first rocket was a simple one, not equipped with a parachute, I was soon working on my second, and larger rocket,

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which I wanted to recover by parachute. It seemed natural, therefore, to base the parachute recovery system for this rocket on a concept that was similar to that used for model rockets, specifically, the concept of using an "ejection charge" with a time delay, to deploy the parachute. Unlike model rockets, however, I used an ejection charge that was entirely separate from the engine, a self-contained unit containing a small charge that was electrically ignited. Instead of a time delay, I utilized a pendulum switch, similar to the method I read about in the book "The Amateur Scientist", which was based on the naive notion that, as the rocket would "turn over" at the peak of the trajectory, the pendulum would fall over, closing the switch contacts. Needless to say, if the parachute did successfully eject during these early flights, it did so almost immediately after engine burnout. Thinking that the pendulum was simply too sensitive to angle, I tried a mercury switch, which needless to say, led to the same futile results. It wasn`t until I began to understand the concept of free-body motion and the consequences of aerodynamic drag, that I realized that such a method is doomed to failure. Any such inertial type of switch will close immediately after burnout, as the rocket begins to decelerate at a rate greater than that due to gravity alone, as a consequence of drag. The pendulum, mercury, or any other inertial mass, however,...

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