Multistaging

Digit · Postby **Digit** » Sat Mar 19, 2016 11:45 am

Howdy fellow thrust nuts

The next phase of my clubs voluntary beginners program involves two builds, the second one of which is scratch building a multi stage rocket. I have a little project in mind but I don't want to tumble recover the booster. Is it possible to parachute recover both stages? If so what is involved and can anyone give me a bit of mentoring?

My biggest concerns are how to ignite the sustainer stage and how not to melt the sh*t out of the booster 'chute in the process.

Cheers!

Kryten · Postby **Kryten** » Sat Mar 19, 2016 11:55 am

For small rockets the booster stage is usually tumble recovery

Lister · Postby **Lister** » Sat Mar 19, 2016 12:52 pm

The problem with small 2stage rockets is that you usually ignite the sustainer off the booster motor.. so you use a D12-0 for the booster and when that burns through it ignites the sustainer motor and you jettisons the booster. So having the small booster section with a parachute is rather difficult and you dont really have much space to put a parachute.

Have a screen shot of your design?

SpaceManMat · Postby **SpaceManMat** » Sat Mar 19, 2016 4:22 pm

Not just a space issue either, you need some way of deploying the recovery device. Usually the ejection charge would do this, but there isn't one in the booster motor. I would expect a small steamer would be easier than a chute, for deployment you would have to use inertia / aero drag. I've not heard of anyone that has done this in LPR.

Lister · Postby **Lister** » Sat Mar 19, 2016 5:39 pm

You could possibly attach a thin cotton thread to a chute for the booster that would pull out from the top of the booster as the sustainer kicks in.. but you would need a heat shield or a good nomex deployment bag to protect your chute from the sustainer motor.

Digit · Postby **Digit** » Sat Mar 19, 2016 5:50 pm

Thanks for the replies all, I think I'll k.i.s.s. for now and start with a conventional black powder & tumble setup. I'll revisit this idea once I've progressed to L1.

camacd · Postby **camacd** » Sun Mar 20, 2016 7:49 pm

Hi Digit.

I went through this exact thought process a few months ago, and settled on a D booster, which direct ignites a C sustainer, and it worked beautifully. I have flown it 3 or 4 times and its gone really well each time.

If you want to pinch my design, I can send you through the open rocket file.

Cam

OverTheTop · Postby **OverTheTop** » Sun Mar 20, 2016 8:43 pm

settled on a D booster, which direct ignites a C sustainer, and it worked beautifully.

Very cool idea!

Digit · Postby **Digit** » Sun Mar 20, 2016 9:25 pm

That sounds really interesting Cam. A few things I'm trying to nut out is motor retention in sustainer and holding the two parts of the rocket together. I've found a good how-to over at apogee's site. Reading through it.

Digit · Postby **Digit** » Mon Mar 21, 2016 11:42 am

Ok the Apogee pages were a great help but I have a few more questions while I'm playing with open rocket designs. Is it good practice to have a launch lug on the booster assembly? (This would give me 3 lugs if I want two on sustainer to be usable as a stand alone rocket).

And maybe a silly question, does a minimum length booster stage actually need to have fins on it?

Cheers.

camacd · Postby **camacd** » Mon Mar 21, 2016 1:23 pm

Hi Digit,

See photos. The key to my design was the neat fit of a C motor into a spent Estes D casing. I cleaned out a spent D motor and cut it to a suitable length, and glued it into the booster motor mount to act as a motor stop, and also to confine the ejection gasses from the booster.

I filed a small slot in the top of the casing, to allow for the sustainer motor retaining hook.

Beyond that, its just ensuring the geometry is right so that the sustainer sits nicely into the spent casing when the two airframes are joined together. I had it sitting about 5mm into the casing.

The booster tumble recovered nicely, and landed each time within about 50m of the launch pad, so it was easy to find.

Digit · Postby **Digit** » Mon Mar 21, 2016 9:23 pm

Wow that is one awesome setup.

Changing motor diameters like that is pretty neat. Can anyone help me with OR, I've designed my rocket and am trying to workout how to see booster stage decent. i.e. it actually tumbles instead of becoming a lawn dart.

Cheers.

camacd · Postby **camacd** » Mon Mar 21, 2016 9:37 pm

OR file for mine attached.

If you plot sim 17 (I did lots of iterations) it shows the point at which the booster starts to tumble. I dunno how I made it do that

ogivemeahome · Postby **ogivemeahome** » Tue Mar 29, 2016 6:44 pm

Digit wrote:Can anyone help me with OR, I've designed my rocket and am trying to workout how to see booster stage decent. i.e. it actually tumbles instead of becoming a lawn dart.

Cheers.

I did this (probably the hard way) by doing a "save as" and deleting all but the booster from the design. Instead of a motor, I inserted a mass to give the same overall mass and Cg as a booster with a spent case. As long as the Cg and Cp are close (a margin of near zero calibres), then it should be unstable enough to tumble. Make a note of any changes and do the same for the original file.