Things are lining up for me this year to have another go at a 38mm 3-stage rocket at BALLS.
I have my motors, the complete second stage, and back half of the sustainer. I need to make a new nosecone and chute cannon for the sustainer, and the booster stage. I'm simulating different motor options.
One goal is to stay within K total impulse for the K multi-stage record. For that, I would use:
AT I1299 booster. 46 Gs and 150 feet/second out of the tower to minimize weathercocking.
CTI J530 second stage. Get all the impulse you can in this size.
CTI J420 sustainer. If the ignition delays are long enough, the peak speed will be about Mach 2.69 at 21,000 feet.
The total impulse would be 2546 Ns, just under the max 2560 for the K impulse class.
RASAero2 has the max altitude at about 57,000 feet. This would be a substantial improvement over the current K complex record of 24,242.
If that flight is successful and survives, I'm tempted to try an all-out 38mm max altitude attempt. For that I would use a longer first stage so that I could fly:
CTI J530 booster
CTI J530 2nd stage
CTI J420 sustainer.
RASAero predicts north of 80,000 feet for that configuration, but the sustainer would reach just under Mach 3 at about 30,000 feet, and I'm a little worried about my nosecone and fins surviving that. I have had a nosecone implode flying a single stage J530 in a light MD rocket, and once I had the tip-to-tip layer peel off when flying with a J570. On a 2-stage flight in Argonia in 2019 I was flying with a relatively heavy and draggy nosecone, and the top speed was just under 2000 feet/sec at 13,000 feet with no issues. 3000 feet/sec at 30,000 feet is probably a lot worse.
For the airstart logic, I'll be flying prototypes of the Blue Raven altimeter, which has tilt sensing. My plan is to use the onboard measured tilt as the main ignition criteria. This is different than the usual method of using altitude or time for the ignition criteria, and then inhibiting the ignition if the tilt is too high. From what I have seen so far, the optimum ignition delays for max altitude result in tilt at ignition around 12-18 degrees, all of which lead to tolerable horizontal recovery distances for the Black Rock Desert. The airstart ignition logic would be along the lines of:
If altitude > 2000 feet and speed < 800 feet/sec and tilt > 14 deg and tilt < 30 degrees then ignite the sustainer. The second stage ignition would be similar but with tighter angles. The idea here is to ignite at a known tilt, while the velocity and altitude at ignition will depend on how straight the boost is. The minimum tilt would correspond to optimum altitude, and the maximum tilt would correspond to staying within the recovery area. If the rocket is going off at a moderately bad angle from the start, then when it slows down enough to meet the velocity criteria, it could be within the acceptable tilt window for ignition already, so I need to pick a velocity that will result in survivable top speed for the sustainer. For a really bad initial angle, the ignition would be inhibited altogether because the tilt would already be more than the max allowable by the time it slows down below the velocity threshold.
I have my motors, the complete second stage, and back half of the sustainer. I need to make a new nosecone and chute cannon for the sustainer, and the booster stage. I'm simulating different motor options.
One goal is to stay within K total impulse for the K multi-stage record. For that, I would use:
AT I1299 booster. 46 Gs and 150 feet/second out of the tower to minimize weathercocking.
CTI J530 second stage. Get all the impulse you can in this size.
CTI J420 sustainer. If the ignition delays are long enough, the peak speed will be about Mach 2.69 at 21,000 feet.
The total impulse would be 2546 Ns, just under the max 2560 for the K impulse class.
RASAero2 has the max altitude at about 57,000 feet. This would be a substantial improvement over the current K complex record of 24,242.
If that flight is successful and survives, I'm tempted to try an all-out 38mm max altitude attempt. For that I would use a longer first stage so that I could fly:
CTI J530 booster
CTI J530 2nd stage
CTI J420 sustainer.
RASAero predicts north of 80,000 feet for that configuration, but the sustainer would reach just under Mach 3 at about 30,000 feet, and I'm a little worried about my nosecone and fins surviving that. I have had a nosecone implode flying a single stage J530 in a light MD rocket, and once I had the tip-to-tip layer peel off when flying with a J570. On a 2-stage flight in Argonia in 2019 I was flying with a relatively heavy and draggy nosecone, and the top speed was just under 2000 feet/sec at 13,000 feet with no issues. 3000 feet/sec at 30,000 feet is probably a lot worse.
For the airstart logic, I'll be flying prototypes of the Blue Raven altimeter, which has tilt sensing. My plan is to use the onboard measured tilt as the main ignition criteria. This is different than the usual method of using altitude or time for the ignition criteria, and then inhibiting the ignition if the tilt is too high. From what I have seen so far, the optimum ignition delays for max altitude result in tilt at ignition around 12-18 degrees, all of which lead to tolerable horizontal recovery distances for the Black Rock Desert. The airstart ignition logic would be along the lines of:
If altitude > 2000 feet and speed < 800 feet/sec and tilt > 14 deg and tilt < 30 degrees then ignite the sustainer. The second stage ignition would be similar but with tighter angles. The idea here is to ignite at a known tilt, while the velocity and altitude at ignition will depend on how straight the boost is. The minimum tilt would correspond to optimum altitude, and the maximum tilt would correspond to staying within the recovery area. If the rocket is going off at a moderately bad angle from the start, then when it slows down enough to meet the velocity criteria, it could be within the acceptable tilt window for ignition already, so I need to pick a velocity that will result in survivable top speed for the sustainer. For a really bad initial angle, the ignition would be inhibited altogether because the tilt would already be more than the max allowable by the time it slows down below the velocity threshold.
Last edited:
