- Joined
- Dec 29, 2011
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I think I first found out about galvanic corrosion issue between carbon and aluminum 25 or 30 years ago. Easton Aluminum manufacturs very high quality carbon over aluminum arrows. The earlier ones were pretty nice, but, only good for one season before they'd be failing. Some later ones had this somewhat red coating on the aluminum, under the carbon. That got me curious... Later arrows were good pretty nearly indefinitely.
Just for the heck of it, I attached a crude quick and dirty Burnsim of something like one of the little 88mm motors. I did double taper here not triple taper, and this isn't really optimized all that well. Burnsim doesn't handle some details quite correctly, but that is a subject for the research forum perhaps, rather than here. Sawtooth is just an artifact of using a fairly coarse step simulating the tapers. The motor is not extreme, except in being fairly long. It just has a decent mass fraction. Case bonded propellant so no traditional liner and no casting tubes. Liner would be cast in place, with thickness profile dependent on expected liner erosion. The propellant is the case insulation for most of the length and much of the case, so liner mass is reduced and propellant volume is increased. Overall this is really a pretty mild motor. I could push it a lot harder but no point to doing it unless I know how to make the rocket survive! I just think it would be cool to hit M5 in single stage and have it survive.
Larger motors get hairier. The sims on a 5" full P / baby Q are absurd. The mass fraction goes up as the motor gets larger. Drag is relatively low during the boost since nozzle exit is essentially full diameter. If it could survive it would be insane.
Cleaning and prepping the inside of an aluminum motor tube with some sort of surface treatment is practically a prerequisite for this sort of motor. Otherwise a cast in place liner will peel out easily, greatly increasing the chance of a CATO towards the end of a burn.
I figure these are single use. If aluminum, I'd expect the motor tube to have lost temper by the time it cools off. Too much heating on the outside plus the usual heating on the inside. Being single use is part of the reason I want to make it as cheaply as makes engineering sense.
I want to avoid solving the problems by just throwing mass at them. Yes, I could likely make a heavy nosecone, thicken the case wall, and use heavy solid fins. It would survive (well, perhaps, after all it is a rocket. What could go wrong???). It would also lack the performance. I wish I could solve the problems by adding a booster. But then it would go too high.
What I am considering doing is another round of propellant development to reduce the burn rate while increasing the density ISP a bit more. Slowing the burn would help by increasing the altitude for any given speed. External heating would be reduced a little. Internal heating would be increased a fair bit, necessitating additional insulation. That would add mass and slightly reduce available volume for propellant, which would be compensated for by increasing the density ISP of the propellant. Trying that approach would likely add some months to the development process. It might not even work.
Gerald
Just for the heck of it, I attached a crude quick and dirty Burnsim of something like one of the little 88mm motors. I did double taper here not triple taper, and this isn't really optimized all that well. Burnsim doesn't handle some details quite correctly, but that is a subject for the research forum perhaps, rather than here. Sawtooth is just an artifact of using a fairly coarse step simulating the tapers. The motor is not extreme, except in being fairly long. It just has a decent mass fraction. Case bonded propellant so no traditional liner and no casting tubes. Liner would be cast in place, with thickness profile dependent on expected liner erosion. The propellant is the case insulation for most of the length and much of the case, so liner mass is reduced and propellant volume is increased. Overall this is really a pretty mild motor. I could push it a lot harder but no point to doing it unless I know how to make the rocket survive! I just think it would be cool to hit M5 in single stage and have it survive.
Larger motors get hairier. The sims on a 5" full P / baby Q are absurd. The mass fraction goes up as the motor gets larger. Drag is relatively low during the boost since nozzle exit is essentially full diameter. If it could survive it would be insane.
Cleaning and prepping the inside of an aluminum motor tube with some sort of surface treatment is practically a prerequisite for this sort of motor. Otherwise a cast in place liner will peel out easily, greatly increasing the chance of a CATO towards the end of a burn.
I figure these are single use. If aluminum, I'd expect the motor tube to have lost temper by the time it cools off. Too much heating on the outside plus the usual heating on the inside. Being single use is part of the reason I want to make it as cheaply as makes engineering sense.
I want to avoid solving the problems by just throwing mass at them. Yes, I could likely make a heavy nosecone, thicken the case wall, and use heavy solid fins. It would survive (well, perhaps, after all it is a rocket. What could go wrong???). It would also lack the performance. I wish I could solve the problems by adding a booster. But then it would go too high.
What I am considering doing is another round of propellant development to reduce the burn rate while increasing the density ISP a bit more. Slowing the burn would help by increasing the altitude for any given speed. External heating would be reduced a little. Internal heating would be increased a fair bit, necessitating additional insulation. That would add mass and slightly reduce available volume for propellant, which would be compensated for by increasing the density ISP of the propellant. Trying that approach would likely add some months to the development process. It might not even work.
Gerald
