Launch Test 93

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This was my second launch of the fiberglass rocket with the home built altimeter. I've been having some issues with deployment of the main chute while using a very large 80" diameter chute, so for this launch I went back to a 39" chute for both apogee and main deployment. The ground is very soft now, so I'm not too concerned with the landing speed. I also wanted to be able to see what was going on during deployment, so I went with a very light load in the LW-1 motor, .89 pounds of standard KNSU-PG propellant. I was really pushing the lower limit with this motor, as the rocket does still weigh in at ten pounds.

I wasn't even sure I'd launch today, as the forecast was calling for rain. But the rain had held off, and skies were partly cloudy with winds of 12 to 15 mph. This wasn't going to be a very good launch for spectators, so I didn't bother inviting anyone. All I really wanted to do was test the altimeter again, this time at a very low altitude. Software predicted an apogee of 1,216' at 8.9 seconds. So I set my back up timer to 13 seconds in case the altimeter failed.

I drove out the launch site and quickly set up the pad and controller. Once the rocket was on the pad I installed the motor igniter and turned on the timer and the altimeter.

Back at the controller, all clear... 5, 4, 3, 2, 1 and ignition!

Good ignition, although the liftoff was slow due to the light propellant load.

Shortly after clearing the rail the slow moving rocket weather cocks into the wind. Shortly thereafter its flight straightened out some.

I watched as the rocket made what seemed to me a very slow ascent to apogee. The nice part was it was real easy to follow. I counted the flight time, at about 9 seconds the rocket had reached apogee and was starting down, then pop! The altimeter fired the apogee charge, the apogee chute deployed and the rocket started a rather quick descent to the ground. I watched in anticipation of the main chute deployment. Then, about half way to the ground another pop, and the main chute was pulled out of the body tube as the PIRM2 fired and released its retaining pin.

The rocket landed about 250 yards into the wind, as it had weather cocked a lot at launch. At the landing site the rocket was found in perfect condition. So I loaded everything up and headed home to take a look at the data from the altimeter.

Here's the results:

Peak Altitude: 3023 data values = 92.56 kPa = 1,045'

Ground Level: 3139 data values = 95.706 kPa = 0'

Main Deploy: 3076 data values = 93.997 kPa = 602'

While the reported altitude was some 160' less than predicted, it was due to the weather cocking I'm sure. I think I had better use just a tad more propellant next time. A faster moving rocket negates to a large degree the weather cocking effect.

One other change I made this time. I wound the shock cord around the main parachute to help keep the main chute in the body tube. The extra shock cord between the PIRM2 and the main anchor eye bolt is what I used. The shock cord simply "spools off" the bottom of the folded parachute after the PIRM2 releases the key. It seemed to work well, and I'll use the same technique in the next launch.