Sprint missile 1/3 scale

[amiles]

My next project is a 9-ft long (1/3-scale), two-stage, tube-launched Sprint missile!

The plan is to use an M6000ST for the booster to get close to 20g acceleration, and then transition to a long-burning L400W for the second stage. The calculated apogee is about 11,500ft.

 

[amiles]

Starting with the second stage motor mount and interstage coupler.

 

[Rschub]

 

[neil_w]

Awesome project. How are you going to stabilize it? Are you just going to rely on the cone?

 

[amiles]

Awesome project. How are you going to stabilize it? Are you just going to rely on the cone?

Just the cone. Plus lots and lots of so much nose weight.

Speaking of which, here is the nosecone on top of the upper stage motor mount and coupler.

 

[yvanthesaxophonist]

This is super sick!

 

[LD124]

Looks awesome! How are you going to constrain it within the launch tube? Some kind of guides that fall away?

 

[amiles]

Looks awesome! How are you going to constrain it within the launch tube? Some kind of guides that fall away?

The plan is to use fall away foam sabots, which is what I've done previously on large tube-launched rockets. You can see an example of them separating and falling away in screenshots from my most recent (and biggest!) launch:

 

[LD124]

The plan is to use fall away foam sabots

Very nice. Foam as in expanded polystyrene or the kind that comes in a spray can?

Those folding fins look interesting, do you have a build thread for that rocket?

 

[amiles]

Very nice. Foam as in expanded polystyrene or the kind that comes in a spray can?

Those folding fins look interesting, do you have a build thread for that rocket?

Two-part expanding poly, which I can then cast in place around the rocket as it sits in a surrogate launch tube.

And yes, here is the build thread for that one, including details on the folding grid fins and the sabots:

https://www.rocketryforum.com/threa...aber-rsd-10-pioneer-irbm.169775/#post-2212637

 

[Johnly]

The plan is to use fall away foam sabots, which is what I've done previously on large tube-launched rockets. You can see an example of them separating and falling away in screenshots from my most recent (and biggest!) launch:

That is stunningly cool.

 

[amiles]

I did the final assembly of the booster motor mount tube and interstage coupler components with the whole thing upside down and mated to the upper stage. This allowed me to ensure three simultaneous points of contact between the two stages: the booster core rests against the aft closure of the upper stage motor, the 7.3" interstage coupler tube in the booster rests against a centering ring in the upper stage, and the two 7.5" airframe sections in the upper and lower portions of the inerstage coupler are in contact.

 

[amiles]

Once the epoxy began to set the booster could be removed and inverted into its natural orientation. Happily, it all worked without accidentally epoxying the two sections together.

 

[amiles]

And here is what it looks like put back together with the nosecone in place.

 

[amiles]

A bunch of "internal fins" - eight for the upper stage and six for the booster - and rings to set the shape. Then lots of cutting notches and holes. The holes serve to reduce weight (especially important for the booster) and allow access and azimuthal flow for the expanding foam.

 

[amiles]

With those parts complete, I can do an initial dry test fit of all the pieces parts...

 

[amiles]

Bwahahahah! It all fits together! The apparent tilt of booster rings is a photographic artifact.

 

[amiles]

Stacked stages at the full nine feet.

 

[terryg]

Where is this going to fly?

 

[amiles]

Where is this going to fly?

MDRA, in eastern Maryland.

 

[WizardOfBoz]

I'm planning on doing my L1 at MDRA. I look forward to seeing this. Very challenging design with all the parts - it looks great!

 

[Rschub]

Please give us some advanced warning for the launch, I would like to make it there for this.

Am I to understand that this will be pour foam/fiberglass skin for the outside shape?

 

[neil_w]

Please give us some advanced warning for the launch,

My brain auto-completed this with “so I have time to get to a bunker”.

Seriously, this looks fantastic, wish I could be there for the flight. Look forward to the video.

 

[pugachu]

A bunch of "internal fins" - eight for the upper stage and six for the booster - and rings to set the shape. Then lots of cutting notches and holes. The holes serve to reduce weight (especially important for the booster) and allow access and azimuthal flow for the expanding foam.

Tose parts look great! Do you have a CNC router, or did you have them made? If you bought them, who's your source?

I like doing oddball stuff, but the cnc router I got off Craigslist has a tiny bed, and needs some TLC before I can use it for rocket parts. (Plus I have to buy CAM software for it)

 

[amiles]

Please give us some advanced warning for the launch, I would like to make it there for this.

Am I to understand that this will be pour foam/fiberglass skin for the outside shape?

Yes, my plan is for a light outer skin for shape, then foam fill, and then carbon fiber sleeves. Or possibly reverse the order of the last two (carbon fiber and then foam fill). And maybe a light fiberglass layer over the CF.

 

[amiles]

Tose parts look great! Do you have a CNC router, or did you have them made? If you bought them, who's your source?

I like doing oddball stuff, but the cnc router I got off Craigslist has a tiny bed, and needs some TLC before I can use it for rocket parts. (Plus I have to buy CAM software for it)

I do not have a CNC router, or anything fancy. These were all cut with a router with circle cutter, a table saw, a jig saw, and hand measurements. That's why I was so pleased when everything actually lined up and fit together.

 

[darrenf]

MDRA, in eastern Maryland.

Red Glare 2025? I was there for your awesome Launch last year. Super cool projects man.

 

[amiles]

Red Glare 2025? I was there for your awesome Launch last year. Super cool projects man.

Red Glare would be great. It will depend on when I can get it ready.

 

[pugachu]

I do not have a CNC router, or anything fancy. These were all cut with a router with circle cutter, a table saw, a jig saw, and hand measurements. That's why I was so pleased when everything actually lined up and fit together.

Wow, I'm impressed!