Not really sure where to put this post, but it's a scratch built rocket, so I'll post here.
This morning on my way to work I stopped and launched a rocket that I've launched many times before, usually on 24/40 reloads, and sometimes D12s for small fields. It is a scratch built, three-fins-and-a-nose cone, dual deploy rocket in BT-55. Very simple and straightforward.
Today's motor was a D15 (blue thunder) reload, a motor that I've used before multiple times and I launched from a 3/16" rod. Almost right off the pad, seemingly while the rocket was still under thrust, it went side ways and both ejection charges fired. It floated down from about 100 feet.
I'm not expecting to know exactly "what happened", but I have data from the flight, and I'm always interested in seeing what I can learn from it. The data/simulating/testing aspect of rocketry is what gets me the most excited.
Here are plots of the altitude derived from barometric pressure, and the filtered velocity calculated from it. The red lines are from a very normal launch previously, and the blue is from today's launch.
The burn time of the D15 is 1.2 seconds, according to thrustcurve. So it seems it went sideways while under thrust.
I only have altimeter vent holes on one side of the body tube. I think that what happened is that the vent holes were on the low pressure side of the rocket as it got sideways, and that resulted in a false altitude over 300 feet. It certainly didn't go that high.
What I don't understand, is why the rocket went sideways to begin with. The margin of stability is more than 2 calibers, but maybe it suffered a bad case of "long rocket syndrome".
According to the altimeter, both ejection charges fired at 2.15 seconds, after it got sideways and stalled out. So it wasn't a case of premature deployment. The fact that the rocket got sideways was the initial cause.
I probably should add a minimum of one vent hole on the other side of the rocket, but I'm not sure why the rocket got so sideways to begin with.
The only thing I did differently this morning was hold the igniter in place with a short piece of wire insulation, because I didn't have the red cap that one normally uses. It didn't hold the igniter very firmly, so I wonder if it got ejected from the motor before it had built up full pressure. But usually Blue Thunder lights so fast...
So what do you think?
This morning on my way to work I stopped and launched a rocket that I've launched many times before, usually on 24/40 reloads, and sometimes D12s for small fields. It is a scratch built, three-fins-and-a-nose cone, dual deploy rocket in BT-55. Very simple and straightforward.
Today's motor was a D15 (blue thunder) reload, a motor that I've used before multiple times and I launched from a 3/16" rod. Almost right off the pad, seemingly while the rocket was still under thrust, it went side ways and both ejection charges fired. It floated down from about 100 feet.
I'm not expecting to know exactly "what happened", but I have data from the flight, and I'm always interested in seeing what I can learn from it. The data/simulating/testing aspect of rocketry is what gets me the most excited.
Here are plots of the altitude derived from barometric pressure, and the filtered velocity calculated from it. The red lines are from a very normal launch previously, and the blue is from today's launch.
The burn time of the D15 is 1.2 seconds, according to thrustcurve. So it seems it went sideways while under thrust.
I only have altimeter vent holes on one side of the body tube. I think that what happened is that the vent holes were on the low pressure side of the rocket as it got sideways, and that resulted in a false altitude over 300 feet. It certainly didn't go that high.
What I don't understand, is why the rocket went sideways to begin with. The margin of stability is more than 2 calibers, but maybe it suffered a bad case of "long rocket syndrome".
According to the altimeter, both ejection charges fired at 2.15 seconds, after it got sideways and stalled out. So it wasn't a case of premature deployment. The fact that the rocket got sideways was the initial cause.
I probably should add a minimum of one vent hole on the other side of the rocket, but I'm not sure why the rocket got so sideways to begin with.
The only thing I did differently this morning was hold the igniter in place with a short piece of wire insulation, because I didn't have the red cap that one normally uses. It didn't hold the igniter very firmly, so I wonder if it got ejected from the motor before it had built up full pressure. But usually Blue Thunder lights so fast...
So what do you think?