ColumbiaNX01
Red blooded white American male
I have a question for you guys. Is a 75mm minimum diameter booster to a 75mm minimum diameter sustainer possible? I have seen 75mm minimum diameter booster to 54mm sustainer (75mm airframe).
Absolutely it can be done. From bottom to top: high thrust booster motor in zipperless construction booster, then the booster chute, AV-bay, then transition coupler fitting over either the bottom three inches of the sustainer motor (thrust ring removed from snap ring case or turned down on AT or CTI case if you want to keep the entire airframe the same) or a custom built outside coupler that fits on OD of booster and sustainer BT. Remainder of rocket is standard minimum diameter construction. If you line the inside of the transition coupler with phenolic you could use the booster electronics to light the sustainer shortly after booster burnout the sustainer motor will separate the stages. Second channel in booster deploys booster chute at booster apogee (include a tracker). That way you don't have to mess around with head end ignition or conductors on the outside of the sustainer BT to ignite the sustainer motor, but it doesn't easily allow you to optimize interstage coast for maximum altitude.
[emoji1010] Steve Shannon [emoji1010]
Trick is to design the sustainer to be stable with some inches of motor sticking out the aft end to be the coupler.
Yep, using the motor as a coupler is part of the answer. I have some rockets where the motor has no thrust ring, but I also have motors with thrust rings, and then I roll the airframe using another airframe as the mandrel, rather than a coupler tube. It just depends on what motor hardware you have or that you can get.
Another part of the puzzle is figuring out what the motor sits on. I don't really care to have the lower airframe pushing on the upper airframe. So, I have a piece of coupler ring sitting down inside the top of the booster. Then, a bulkhead-like faux cone sits on top of that ring, and that's the thrust point. The faux cone also protects the chute (if you're using a conventional dual-deploy setup). A picture of a well-worn faux cone is attached, which I actually plan to use one more time. For the way I do it (with the thin Gecko/Taperwire for the electronics), there needs to be a gap for the wires at the point where the motor sits. Other problems that need to be solved include:
- Need to design the faux cone so that it came come out of the airframe without binding. This can be a design challenge.
- Need to be able to get the chute past the coupler ring in the tube (it's a small restriction in the diameter of the tube, but it matters).
- Must be designed to accommodate the nozzle and space for a separation charge (and still not bind in the airframe).
- Must still pull the chute out, like a nose cone (I use lead weights to make the faux cone heavier).
If using the Gecko wires that I use, it is not good to have the sustainer turn against the booster. In the pic, I used some prongs that fit into the bottom of the CTI threaded closure. Those have been removed, and now I key the airframes instead.
There are a lot of different ways to do this, but this is one example of how I do it.
Jim
theres a lot of stuff to figure out. first thing is to is understand the concept
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