I recently got back into model rocketry after a six year break and I have to say that being older now, I can appreciate the hobby more than when I was a little kid.
First of all, when I first got into the hobby, Ididn't have the skills, or knowledge, to build and design my own models, so I stuck to the kits. However, recently, I have been designing and flying my own designs and have been pretty satisfied with the results.
Now for the part about the two rockets:
One of the things that I have been doing is trying to make a single-stage high altitude low-power rocket. To analyze the results I build at least three of the exact same type (this is to rule out any anomalies that can occur in faulty construction on one rocket). Well after nine rockets and three design modifications, I launched my latest two rockets with spectacular results, both good and bad.
The two rockets that launched were identical except for the weight, which was a 10 gram difference. The rocket design was as follows, an 11 inch body tube length, 24 millimeter ID, 3 clipped delta fins, standard Estes noce cone, streamer recovery, and powered by a single Ests D12-5. The two weights were 75 and 85 grams. After I did the calculations, I figured that the 75 gram rocket would reach a maximum altitude of just over 2000 feet and a maximum velocity of 405 miles per hour. The 85 gram rocket would reach about 1800 feet and 370 mph.
I launched the 75 gram rocket first and it was a perfect flight(well almost perfect but close enough); the take-off went fine(a very slight wobble, but that could be because I made the fins out of an old oatmeal box), quick acceleration to 400 mph and after the coast, perfect ejection and recovery and no damage to the fins at all on landing. I was feeling quite good about my design and since I had an exact copy ready to launch, I decided to launch it as well. This was the bad flight and I think I know exactly what went wrong. The 85 gram rocket launched fine(with a slight wobble, but that was to be expected) until about 1.3 seconds after launch. At that time, I noticed that the slight wobble suddenly turned into quick spirals. The whole thing took about half a second, and after the quick spirals, the entire rocked "disassembled" in mid-flight. There were about fifteen large pieces that I could see after the rocket "disassembled" (I choose not to say explode because from my analysis, there was no unexpected explosion).
Here is what I believe went wrong:
The most important fact is that I used hot glue to secure the fins to the rocket (because I am lazy and don't like to wait) and to make the fillets. the second important fact is that with the body tube ID (24 millimeters) I just friction fit the D12-5 into the tube and glued it in place. These were the two things led to its destruction. I believe that in the 1.3 seconds after launch, the engine transferred enough heat through the body tube (home rolled from computer paper) to heat the hot glue enough to melt it. At 1.3 seconds, the rocket was treveling its fastest (370 mph) and I believe that one fin fell off at this speed. With one fin gone, it would have produced the quick spiral, and that spiral lasted less than half a second. With the rocket missing one fin and spinning, I found that a second fin detached from the body tube, but not from melted glue, but from aerodynamic forces ripping it off (due to the fact that when I recovered the body tube the paper was ripped and sheared off where that fin was attached). After the second fin detached, the angle off attack of the rocket kept increasing, and as it was flying at 370 mph, with a high angle of attack, the aerodynamic forces bent and crumpled the body tube right above the end of the engine casing. At this point, the nose cone was forced out of the rocket by the wind resistance, and the streamer deployed but the shock cord seperated from the body tube and the streamer seperated from the nose cone. At this point, the "rocket" was just one fin, a severely bent body tube, and the engine. All of this happened very quickly, and the ejection charge in the engine still haden't deployed. Well five seconds after the "explosive deconstruction" the ejection charge deployed, but since the body tube was bent right above the motor casing (the body tube had about the shape of an "L") as the ejection charge went off, the hot gasses did not follow the bend in the tube but just blew a large hole through the body tube and the embers burned about one third of the entire body tube. This was the quick death of my second of the two rockets. The only piecs that I got back were the noce cone and mangled body tube.
So now you see the Tale of Two Rockets, both of identical design and quite different results. I guess the moral of the story is that when scratch building rockets, don't use hot glue in close proximity to the motor.
If anybody else has stories of rocket failures I would like to hear them and what you think went wrong.
Thanks for your time.
First of all, when I first got into the hobby, Ididn't have the skills, or knowledge, to build and design my own models, so I stuck to the kits. However, recently, I have been designing and flying my own designs and have been pretty satisfied with the results.
Now for the part about the two rockets:
One of the things that I have been doing is trying to make a single-stage high altitude low-power rocket. To analyze the results I build at least three of the exact same type (this is to rule out any anomalies that can occur in faulty construction on one rocket). Well after nine rockets and three design modifications, I launched my latest two rockets with spectacular results, both good and bad.
The two rockets that launched were identical except for the weight, which was a 10 gram difference. The rocket design was as follows, an 11 inch body tube length, 24 millimeter ID, 3 clipped delta fins, standard Estes noce cone, streamer recovery, and powered by a single Ests D12-5. The two weights were 75 and 85 grams. After I did the calculations, I figured that the 75 gram rocket would reach a maximum altitude of just over 2000 feet and a maximum velocity of 405 miles per hour. The 85 gram rocket would reach about 1800 feet and 370 mph.
I launched the 75 gram rocket first and it was a perfect flight(well almost perfect but close enough); the take-off went fine(a very slight wobble, but that could be because I made the fins out of an old oatmeal box), quick acceleration to 400 mph and after the coast, perfect ejection and recovery and no damage to the fins at all on landing. I was feeling quite good about my design and since I had an exact copy ready to launch, I decided to launch it as well. This was the bad flight and I think I know exactly what went wrong. The 85 gram rocket launched fine(with a slight wobble, but that was to be expected) until about 1.3 seconds after launch. At that time, I noticed that the slight wobble suddenly turned into quick spirals. The whole thing took about half a second, and after the quick spirals, the entire rocked "disassembled" in mid-flight. There were about fifteen large pieces that I could see after the rocket "disassembled" (I choose not to say explode because from my analysis, there was no unexpected explosion).
Here is what I believe went wrong:
The most important fact is that I used hot glue to secure the fins to the rocket (because I am lazy and don't like to wait) and to make the fillets. the second important fact is that with the body tube ID (24 millimeters) I just friction fit the D12-5 into the tube and glued it in place. These were the two things led to its destruction. I believe that in the 1.3 seconds after launch, the engine transferred enough heat through the body tube (home rolled from computer paper) to heat the hot glue enough to melt it. At 1.3 seconds, the rocket was treveling its fastest (370 mph) and I believe that one fin fell off at this speed. With one fin gone, it would have produced the quick spiral, and that spiral lasted less than half a second. With the rocket missing one fin and spinning, I found that a second fin detached from the body tube, but not from melted glue, but from aerodynamic forces ripping it off (due to the fact that when I recovered the body tube the paper was ripped and sheared off where that fin was attached). After the second fin detached, the angle off attack of the rocket kept increasing, and as it was flying at 370 mph, with a high angle of attack, the aerodynamic forces bent and crumpled the body tube right above the end of the engine casing. At this point, the nose cone was forced out of the rocket by the wind resistance, and the streamer deployed but the shock cord seperated from the body tube and the streamer seperated from the nose cone. At this point, the "rocket" was just one fin, a severely bent body tube, and the engine. All of this happened very quickly, and the ejection charge in the engine still haden't deployed. Well five seconds after the "explosive deconstruction" the ejection charge deployed, but since the body tube was bent right above the motor casing (the body tube had about the shape of an "L") as the ejection charge went off, the hot gasses did not follow the bend in the tube but just blew a large hole through the body tube and the embers burned about one third of the entire body tube. This was the quick death of my second of the two rockets. The only piecs that I got back were the noce cone and mangled body tube.
So now you see the Tale of Two Rockets, both of identical design and quite different results. I guess the moral of the story is that when scratch building rockets, don't use hot glue in close proximity to the motor.
If anybody else has stories of rocket failures I would like to hear them and what you think went wrong.
Thanks for your time.
