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- Dec 29, 2011
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I've gone through simulations of too many motors for too long. Motors up through O, the largest I've made, have worked as designed within quite narrow specs. Burn time within 0.1 second of predicted. Flights coming in usually within 1 to 2 percent of predicted altitude. The only exception is when I pushed the case pressure too close to the limit and had a nozzle ejection at MEOP in the burn, which was designed essentially very close to the case limits in a 75mm. I didn't account for the extra force on the nozzle retention due to acceleration and was out of my best nozzle washers. I think the inferior one I used was not quite full diameter, warped the snap rings, and that was the end of that. Had I not been tired when assembling that motor, I'd have not used that washer. Lesson learned; move on. (PS - that motor was 1 success 1 fail)
I've modeled some motors in the larger O through baby Q range - triple taper monolithic core case bonded and not quite erosive - that I think I can probably make. There are some engineering challanges but I think I have ways of dealing with them. These are narrow motors for their total impulse, and do not have particularly long burns. They however do have pretty high mass fractions. This leads to survivability problems. Min diameter rockets based on these motors, in sizes from 88mm on up, all end up quite fast, in the M5 range +/- a hair at burnout per RasAero.
Making one of these for launch at BALLS in the next couple years is tempting. Though I have some of my own ideas that I think could work, I'd rather hear what people have done that has proven to work. This is a tougher problem than getting a second stage to survive these conditions as atmospheric pressure will be much greater.
This is still in the thought experiment stage. I'm not interested in discussing the motors further at this time, and certainly not in the open forums. The overall rocket concept is four smallish fins and a nosecone, with the fins attached to the motor tube.
I think I can handle the attachment, and getting the motor to survive the burn - at least in static test. But there will be considerable external heating and aero forces on the fins and nosecone, and even on the outside of the motor case. If aluminum gets too warm it loses most of its strength. Composites can peel apart.
I have experience and equipment for machining. I have experience making high quality composite parts. I have no experience with M5 rockets.
What has worked? What might work? What doesn't work? $$unobtainium$$ materials are not applicable. These motors were designed to be inexpensive for the total impulse and I'd like to keep it that way as much as possible. If possible solutions are too pricy or too unlikely to work, I'll drop the project.
Thanks,
Gerald
I've modeled some motors in the larger O through baby Q range - triple taper monolithic core case bonded and not quite erosive - that I think I can probably make. There are some engineering challanges but I think I have ways of dealing with them. These are narrow motors for their total impulse, and do not have particularly long burns. They however do have pretty high mass fractions. This leads to survivability problems. Min diameter rockets based on these motors, in sizes from 88mm on up, all end up quite fast, in the M5 range +/- a hair at burnout per RasAero.
Making one of these for launch at BALLS in the next couple years is tempting. Though I have some of my own ideas that I think could work, I'd rather hear what people have done that has proven to work. This is a tougher problem than getting a second stage to survive these conditions as atmospheric pressure will be much greater.
This is still in the thought experiment stage. I'm not interested in discussing the motors further at this time, and certainly not in the open forums. The overall rocket concept is four smallish fins and a nosecone, with the fins attached to the motor tube.
I think I can handle the attachment, and getting the motor to survive the burn - at least in static test. But there will be considerable external heating and aero forces on the fins and nosecone, and even on the outside of the motor case. If aluminum gets too warm it loses most of its strength. Composites can peel apart.
I have experience and equipment for machining. I have experience making high quality composite parts. I have no experience with M5 rockets.
What has worked? What might work? What doesn't work? $$unobtainium$$ materials are not applicable. These motors were designed to be inexpensive for the total impulse and I'd like to keep it that way as much as possible. If possible solutions are too pricy or too unlikely to work, I'll drop the project.
Thanks,
Gerald
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