This project is another attempt to aid in rocket recovery after it has landed. My FRS radio tracking works well, but not at close range. So I wanted an audible rocket locator loud enough to be heard for several hundred feet. The problem is, I wanted it outside of the rocket body, so the sound level wouldn't be limited by the confines of the rocket body tube. It wouldn't be hard to build an amplified alarm, but by the time you buy all the parts, you'd have $15 or $20 invested. And Radio Shack sells a very loud personal alarm for $11, model 49-415A. The nice thing is, the alarm has a plastic pull pin that activates the alarm. So all I needed to do was attach the alarm to my recover line between the parachute and the body tube.
Above is a picture of the completed audible recovery alarm. The alarm is mounted between the body tube and the parachute. The alarm was taped to the recovery line, then the rope looped and taped again to prevent it from sliding on the rope. The pull pin to activate the alarm has a short nylon lanyard on it, so I sewed the lanyard to the rope with some slack in the rope, that way when the parachute deploys, the force of deployment pulls on the lanyard, pulling the plug and activating the alarm. The strain is now all on the rope, with the alarm just there for the ride. To the far left is a custom made protective sleeve for the alarm, OK, it's just an old sock cut in half. It protects the alarm from the deployment charge. The sock is also sewn on the rope with some slack in it, so the sock also pulls off only after the chute opens. I also use cellulose wadding to absorb the deployment charge flame. The picture was taken after it's first flight, and the sock is still clean. So obviously the cellulose wadding is doing its job.
The first test flight using the alarm worked perfectly. The crops are tall enough now that finding a downed rocket could be near impossible, this was my first flight I even dared at this time of the year. There was very little wind, so the rocket only drifted about 400 yards from the launch pad. The rocket used the T-4 motor, with EM-1 and an FRS radio for tracking. The FRS radio was not needed as the rocket landed so close to the pad. I had thought that the FRS radio would pick up the sound of the alarm going off at deployment, but it didn't. The g-switch arming buzzer was all that was heard for the entire flight. Interestingly, the alarm could be heard at deployment without the radio, and the entire decent was audible. Once on the ground, the alarm could be heard from a distance of about 300 feet. It worked so well, I'm sort of kicking myself for not doing it sooner.