Sprint ABM Build Thread

[Rschub]

I have been a little obsessed with the Sprint missile recently, I saw a launch video of the full size version about a year ago and it kick started my childhood rocket hobby back to life. So I did the needful and built a LOC Minnie Magg and got certified level one last month. Now for the white whale. I got this.

I have done a fair bit of research and found a drawing I thought I could use, time to fire up the old computer.



Luckily I am a Solidworks nerd, so things proceeded quickly.....




The nosecone will be turned from wood, the nose tip and fin can will be 3D printed, and the body will be hot wired pink foam.

I am not really familiar with whiz bang electronics yet, so here is where it gets interesting.


I am planning on a 6 engine cluster with gap staging to a 3 engine cluster on the sustainer. The center ring will direct ejection gasses to the center tube for rear parachute ejection, and angle the upper tubes towards the upper stage engines. The plan is to use Estes 29mm motors on both stages.

The sustainer will be pinned loosely to bushings in the booster.

One of the things I stressed over was how to launch this thing. Every method of rail launching I came up with was either unworkable or just plain ugly. Then one day I chanced to look at a seldom used view...

...and realized that with a slight deviation from the drawings, my problem was solved.

I think an 8 foot launch tube will allow this pig to get to a respectable velocity before people have to start running. With any luck I'll get a nice smoke ring.

I am using LOC tubing and will be sending out the files for laser cutting the plywood bulkheads shortly. Wish me luck.

 

[0011001100]

I've been wanting to make a Sprint missile for a while. I attempted to draw up one using images online but yours looks really good. Would you be willing to share a drawing/sketch of the profile, including the fins?

 

[Rschub]

Sure thing. This is the image I worked from

This image is tilted about 2 degrees so keep that in mind. This is what I came up with, please don't sell it for coffee money
I think the second stage above the fins is actually a power series nosecone of around n=.65, I have one modeled but the two angle version is easier to make. I am leaning toward just 3D printing the entire nosecone so I might just use it. I had a version with plywood fins, the hatched area in the drawing is what they looked like. Remember, these are old drawings of highly classified at the time missiles. There is a lot of contradictory information out there, this is just what I went with.

 

[0011001100]

That is a much better reference than this image that I had used:

I used one of the online measuring tools and compared it to the known height and base diameter. I also have this .zip folder that I found, but I like your drawing much better.

My plan is to design one that has a base diameter of 400mm and 3d print it out of (still deciding for sure) polycarbonate with carbon fiber. I then may reinforce it with a wrap of carbon fiber or fiberglass or I might just epoxy coat it and sand it smooth. Goal is a 54mm motor mount to fit warp nine motors and eventually a K2050.

 

[Rschub]

I have a ton of pictures, some from this site, and some from the internet. I'll post a few of the more useful ones below.

 

[Rschub]

Oh, the video!

 

[jqavins]

 

[H_Rocket]

It is interesting how the idea of using a W66 Enhanced Radiation Warhead (Neutrron Bomb) as a point defense weapon fell out of vogue.

Oh yeah, blast effects…

 

[Rschub]

This is a build thread.

 

[0011001100]

How is your build coming together? I've gotten around to modeling up mine and have begun making a small scale one to be launched on 18mm motors. Where are you aiming for your CG to be so that it is stable and how much nose weight are you adding?

 

[Rschub]

I just started a new job so this is on the back burner a little. I had contacted a few people about getting some 3D printed parts made for it, so I have made a few modifications to the model.

There is a lot of nose weight needed on my version, due to the 6 pack motor in the first stage, I am revisiting my decision to use black powder motors, cool as it might have been.

With the high base drag and the cone shape, somewhere right around the middle of the fins looks good for the CG, for a one stage rocket.

 

[0011001100]

Understandable. My goal is to eventually print one that is a ~30% scale model. AKA its base diameter will be 400mm to fit on my new printer. But for now I want to make a smaller version or two while the printer is being finished. I did scale my fins up to match better to the actual scale and they should just fit inside the corners of the build plate.

 

[jqavins]

Why is it you wanted BP motors? Is it for the smoke and flame? For simple gap staging? If either of those, you could use composites and BP together, provided you consider a few tricky things. If it's all about some other goal, stop reading now.

Either of the configurations below, for example, might work. Maybe with the addition of a center motor. (I know your spacing between motors is not as I've drawn, but this was easier for a quick sketch.)



Clustering the two types is notoriously difficult, but not impossible. I think it should be OK if you take the following steps:

• Make sure the composite motors are one of the easier to light compositions (or use CTI motors with their pyrodex slugs, but that means having two or three matching cases).
• Make sure that the rocket's pad weight and the BP motors' thrust are such that if the composites don't light the rocket won't move, i.e. that the rocket weighs more than the BP motors' combined thrust.
• Put some sort of sabot around the sustainer so that if the composites fail to light but the BPs stage to sustainer BPs, the sustainer alone can shoot on out of the tube and not burn the booster up.
• Make sure that the BP motors have longer burns than the composites, so staging does not occur while the composites are still burning.

 

[Rschub]

Why is it you wanted BP motors? Is it for the smoke and flame? For simple gap staging? If either of those, you could use composites and BP together, provided you consider a few tricky things. If it's all about some other goal, stop reading now.

Either of the configurations below, for example, might work. Maybe with the addition of a center motor. (I know your spacing between motors is not as I've drawn, but this was easier for a quick sketch.)
View attachment 536859View attachment 536861


Clustering the two types is notoriously difficult, but not impossible. I think it should be OK if you take the following steps:

• Make sure the composite motors are one of the easier to light compositions (or use CTI motors with their pyrodex slugs, but that means having two or three matching cases).
• Make sure that the rocket's pad weight and the BP motors' thrust are such that if the composites don't light the rocket won't move, i.e. that the rocket weighs more than the BP motors' combined thrust.
• Put some sort of sabot around the sustainer so that if the composites fail to light but the BPs stage to sustainer BPs, the sustainer alone can shoot on out of the tube and not burn the booster up.
• Make sure that the BP motors have longer burns than the composites, so staging does not occur while the composites are still burning.

Joe
You are right, the 6 pack was mainly for the sound and fury, I like the ideas you have above about mixing motor types. I made both motor mounts removable so I could experiment with different loadouts. Even though I started with the most complex loadout for design purposes, I think the best course of action is to fly it first as a single stage to check the basic stability then slowly work up to the multi stage, multi motor configurations. I also came up with a rail launch configuration I think I can live with, so I don't have to lug around a giant 3 piece launch tube.

 

[Grog6]

I casted one out of Boron Nitride slip I had from an old experiment, and apparently didn't fire it hot enough; it turned back into powder at about mach 4, lol.

 

[Hobie1dog]

I'm looking forward to the completion of this one.

 

[Bill S]

Any progress on this build?

 

[Rschub]

Hi, sorry about the delay.
I have decided to redesign some sections to more fully take advantage of 3d printing. I purchased a 3d printer and will be assembling and trying it out soon.
I have redone the lower stage to take advantage of gas dynamic stabilization, as there was some question about the stability of just the cone. The new model really has almost a ring fin on the bottom as shown.



There is a type of 8020 rail that is 1" wide, but only 1/2" thick, it will fit through one of the holes and work with standard rail buttons mounted on the internal body tube, which I can live with.

Most of the exterior will be 3d printed ASA, the printer I have should be capable of printing that material.
I am still making the interchangeable motor mounts, to allow single and multi stage flights as well as the original cluster concept, the first flight will be single stage however.
So, that's the status right now.

P.S. I have another project that has distracted me a bit from this one, that might show up in another thread over the weekend.

 

[Rschub]

Now I am rethinking my cluster plan, mostly due to this post

@jqavins and @BABAR

View attachment 548944

 

[charrington]

Wow! Ive been wanting to do a sprint for awhile now and the 'ring' fin design is absolutely brilliant. Please keep us updated! Do you plan on releasing the cad files in the future as open source or paid?

Also, for the launch rail issue. Have you looked into fly away rail guides? I was thinking something along the lines of additive aerospace's set but make it so that it fits around the sprint and then has an extended forward guide compared to the rear (Kind of like what you see in the picture of it posted above where it is attached to the white arm).

 

[Rschub]

I did look at fly away guides, they would be big and clunky. I was not confident that I could make them work.

 

[amiles]

Any progress on this? I too have long been interested in this one, and am planning to build a large (one-third scale) two-stage version as my next project. Design is more or less complete, and I've just put together this small model for stability flight testing.

 

[Rschub]

I have been distracted by other rocket projects and recently had some medical issues. I have realized that there are some things I will need more experience with before proceeding. As far as progress, I have continued to refine the CAD model as I gain more knowledge. I keep finding solutions here on the forums for the various problems I envision. I have a 3D printer that I can print the external parts with once the design is frozen.
I am not sure of the scale, but mine is 59ish inches tall.
I have a few rockets in the pile that have jumped ahead of this one, but who knows? I would like to fly it at LDRS.