Monday, 4 June 2018

OBT, Opensource Boat Tail Rocket project

 



Over the last week I've designed, simulated and then scratch built this little rocket with a boat tail. The boat tail is the small section below the fins which tapers to the minimum diameter of the motor mount. I wanted to learn about boat tails and make one as they are useful for a couple of reasons. There primary function is to smooth out the airflow and they create a lot less turbulence than a typical square ended rocket (there's a great PDF on boat tails here). The second reason being that boat tails are often used when coupling a smaller rocket to a larger booster for example in boosted dart type projects or other multistage designs. This OBT (Open Boat Tail) rocket has a decent payload section and should be a useful addition to my rocket collection as I need to do some flying of the new nanoalt altimeter from the flame trench with other commercial altimeters to see how it compares.

The OBT is made with some 3d printed components and I have CNC routed the fins out of 2mm balsa but that could easily be achieved with a craft knife! It uses classic estes tubing BT50 for the body and BT20 for the motor mount tube. All the supporting software I have used is opensource as indeed this design is so feel free to check out the repository. If you make one I would love to see it!

All measurements can be got by opening the openrocket file (.ork) and you can see the general placement of the parts..its a crude simulation really and could be dialled in a little more. Its worth noting the 3d printed parts are over ridden in the simulation with their actual mass and depending on your approach your components weight may differ. There is a pdf of rough instructions on the repository with some pictures (repeated here) that show the general assembly. All the STL files for the parts (centring ring, boat tail, nosecone etc) are provided, but they are scaled and tweaked for my printer and the shrinkage of my current PLA filament.. so they may need tweaking.  I've generated these models in OpenSCAD and therefore if you download OpenSCAD (again free and opensource) you can tweak the dimensions to suit your printer. (hit me up if you need help on how to do that).

So here it is... all the files are on this repo



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