75mm min diameter booster to 75mm min diameter sustainer? Possible?

[ColumbiaNX01]

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).

 

[dhbarr]

Sure. Loki m3464 to AT m685 anyone? ( not optimized for anything )

 

[DavidMcCann]

in theory? sure. say...booster with a body tube over it that stops short of the top of the motor. interstage coupler that slides over the top of the booster motor, and the rear of the sustainer motor...

Actual build I couldn't map out for you...but physically it could be done.

 

[Steve Shannon]

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]

 

[ColumbiaNX01]

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]

That sounds interesting. The route I want to go is using either Wildman or Madcow fiberglass tubes. Could you illaberate more about your idea? Do you have any pics? thanks

 

[Igotnothing]

Working on it with EX cases which have no external protuberances. Both in 60mm and 75mm. Was cutting one of the nozzle carriers last night when my saw band failed. I am not particularly good at brazing saw bands so may just get another at HF.

Trick is to design the sustainer to be stable with some inches of motor sticking out the aft end to be the coupler.

Here is a snip of my 60mm version in OR:


For both versions, some of the components are borrowed from other rockets, hence the taper from 66 to 60mm.

 

[JimJarvis50]

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

 

[Steve Shannon]

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

Where's the like button when I need it.

 

[ColumbiaNX01]

theres a lot of stuff to figure out. first thing is to is understand the concept

 

[JimJarvis50]

theres a lot of stuff to figure out. first thing is to is understand the concept

OK, the bottom of the sustainer could look just like the Gecko cable photo I posted not long ago. For a 3" rocket, the motor, without a thrust ring, sticks out maybe 4-5" below the bottom of the air frame. It's the staging coupler, and it sits down into the top of booster air frame. The wires in the photo are for the igniter and the separation charge. I normally put a cap of some type over the based of the motor or the nozzle so that the separation charge is acting within a more restricted volume (i.e., not the core of the sustainer motor).

The sustainer motor sits on top of the faux nose cone that I posted earlier. You can see the slot in the faux nose cone for the wires. The faux nose cone might be mounted perhaps 5" down into the booster air frame. It would sit on perhaps a 1" coupler tube ring, glued about 5" down from the top of the booster airframe. So, if you looked into the top of the booster airframe, you would see the faux nose cone about 5" down. It would be supported by a 1" coupler tube ring, and the booster main parachute is below that. The sustainer just gets get set into the top of the booster tube, with the wires in the slot of the faux nose cone.

I'm always happy to answer specific questions on staging. Just as an FYI, I've flown over 100K three times and I have another flight over 70K. Literally every detail of those four flights is posted in this forum, from the rocket design to electronics to high altitude deployment to safety to pad design, etc. I made those posts in part so that folks wanting to fly similar flights could see at least one way to do it. For those of you that seriously want to do these kinds of flights, spend an afternoon and go back and read my stuff. It's all there. Then, figure out how to do it better.

Jim