# 3 stage with strap on boosters

### Help Support The Rocketry Forum:

#### jmartyg

##### Well-Known Member
Goofing around with Rocketsim demo, I thought about something like attached. I've only used this program for about an hour, so this is really rough.

The intent is:
The 3 strap-ons each have one fin and are ignited at the same time as the d12 booster.They would each be rigged to be in place with the booster, but as the booster comes off, it allows them to separate from the main airframe. The booster separation would occur during the delay time of the strap-ons and they each would come down with streamers.

I have no idea how to sim this either, maybe i should have done it as a 2 stage and the strap-ons part of that rather than the 3rd...

some notes:
-I didn't add much for recovery
-I didn't look into adding the nose cones for the strap-ons, but they would be nessled under the transition.
-I didn't get to the fins for the sustainer yet. I want them to be almost invisible between the strap-ons though.

Thoughts? Is it worth pursuing?

View attachment trouble.rkt

Last edited:

##### Well-Known Member
This is an interesting idea which is definitely worth developing!

As I understand it, the strap-on boosters are to be held on by the D12 booster - when it falls off, so do the strap-ons. All four boosters therefore detach from the sustainer at the same time.

The file indicates that you will be using B6-4's for the strap-ons. I'd recommend B6-2's - you want them to deploy their streamers before they hit the ground.

Given the reverse transition half way up the body, I suspect you'll need bigger fins than would be "almost invisible between the strap-ons" for the sustainer to be stable.

It's worth noting that although the B6-0 has no official ejection charge, when it burns through its propellant it produces enough forward pressure to eject a nose cone and streamer - my own parallel-staged models rely on this. If you can devise a way to lock the strap-ons to the rest of the rocket and separate by blowing their noses using this forward pressure, you can have them separate before the D12 booster.

#### jmartyg

##### Well-Known Member
Thanks for the info. Good eye on the B6-4. I figured I should build around that as I can adjust for a B6-0, B6-2, B6-4 and B6-6 if needed.

Here is how i'm thinking on attaching them. The attached image is an exaggeration - the end result would have the tubes almost touching one another. The blue is the strap on, and the black is the sustainer and booster. The blue chunk in the middle would be half a piece of body tube to keep it aligned.

This way, I think, that if any strap on engine fails to ignight, then it would still go along. If the main booster doesn't, and detaches, then there is still enough to keep the strap on from shifting position.

#### jmartyg

##### Well-Known Member
Attached is the latest revision. I put it to 2 stages to try and sim it better.
Added mass for the invisible nose cones, on the real nose cone, and added fins for the sustainer. I still have to refine the shape and size.

Also, looks like im having issues mounting fins onto the BT-80 tube in the booster today, but it seems to be ok with the smallerones in the sims, so I dont know if its a big issue or not.

About 275 feet single stage and 1600 with the boosters.

#### Jimmy Wilson

##### New Member
Thanks for the info. Good eye on the B6-4. I figured I should build around that as I can adjust for a B6-0, B6-2, B6-4 and B6-6 if needed.

Here is how i'm thinking on attaching them. The attached image is an exaggeration - the end result would have the tubes almost touching one another. The blue is the strap on, and the black is the sustainer and booster. The blue chunk in the middle would be half a piece of body tube to keep it aligned.

This way, I think, that if any strap on engine fails to ignight, then it would still go along. If the main booster doesn't, and detaches, then there is still enough to keep the strap on from shifting position.

View attachment 63447
I was looking through the posts and found yours. Did you ever build this? I had the same thoughts and built one many years ago. My booster had four fins that aligned with the upper stage, and the strap on booster with a single fin. The rocket was quite long, as I didn't have the software available then as is now. I did that to offset the mass on the aft end of the rocket. I staged a "D-0" in the main booster to a "C6-7" upper stage. If my feeble memory serves me well I used "C6-3" for the strap on booster because they had a similar burn time as the D engine. I used small parachutes for the strap on boosters and the main booster just tumble recovered. Our rangemaster went over the design and flight principles with me, and his only requirement was to use a "restraint" system comprised of sewing thread that secured the rocket to the launch pad in case the main booster didn't ignite and the rocket lay over and "land shark." The thread restraints were tied under the main booster and would burn through allowing the rocket to launch properly if all three engines ignited as planned. Much to my delight everything worked as I designed it. For the strap on boosters I used basswood to make the mounts. The design was very close to yours. There was a single strip of basswood on the upper stage and booster, and a "sandwiched" pair of strips with a spacer between them for the main rocket frame's strips to slide into. The strips on the main rocket were cut at an angle and the strap on were cut at the opposite angle to capture them with the booster holding it all together as in your design. Thanks for your time, and your patience for this long winded read.
regards
Jimmy

#### Joshua Smith

##### kernelsmith
TRF Supporter
We need an online .rkt viewer. A website or app that will just show a basic view and basic info like length, weight, location of centers. Sometimes I wish I knew JavaScript!!!

#### GlenP

##### Well-Known Member
See this thread on a Soyuz scratch with four strap on parallel-staged boosters for some ideas and inspiration. Posted by @wrad