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My first high-power rocket (scratch built)

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For the past two months my brother-in-law and I have been working on a scratch built high-powered rocket. (By scratch built I mean it was not built from a kit.) It is 100% designed and constructed by us. I did purchase a few pre-fabricated parts: the nosecone, body tubes, the altimeter, and electronics bay.

 

The motor was designed by us, though we initially started by experimenting with some designs on the internet and modified it with trial and error. The rocket fuel is homemade as well. It will have a dual-deployment recovery system (i.e. a drogue chute will deploy at apogee, and a main will deploy at a preset altitude) as well as an onboard video camera. Target altitude for the first flight is about 1.5km; with the ultimate goal being a 3km flight (or higher, as permitted by local law). Most of the rocket is designed and built already, but I chronicled the build with photographs.

 

Edit: I'll be posting the pictures soon.

Edited by blike

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Nozzle:

 

We spent two weekends coming up with a workable motor nozzle design that was both practical to make and able to be made consistently from motor to motor. A well designed nozzle can add to the amount of thrust a rocket engine is able to generate, but for our purposes the small inaccuracies in our convergence/divergence angles from ideal models are insignificant.

 

We made the main divergence nozzle from epoxy which was cast into a waffle cone (yes, a waffle cone). It was sanded down and remove the ridges formed by the cone. The throat mold was also cast from epoxy which was poured into a small tube of wax paper. The throat mold was glued onto the divergence nozzle mold to form our main casting mold.

 

A hole the size of the maximum diameter of our divergence nozzle mold was cut into a PVC endcap. The entire mold is then centered in the hole in the PVC endcap, drenched in WD-40, and concrete is poured over the mold. Two steel washers are then pushed down over the throat mold in order to reinforce the concrete in the high-flow area of the nozzle. A standard golf ball is then pushed down into the concrete to rest on the throat mold, completing the mold. Once the concrete is semi-set, the golfball and epoxy molds are removed, leaving a nice concrete nozzle.

 

Fuel:

The rocket fuel is cast from potassium nitrate (oxidizer), sucrose (fuel), and karo syrup. The ingredients are measured out in specific proportions and dissolved completely in water. The water is then boiled out of the mix, leaving a thick dough-like propellant. The propellant is then cast into three separate inhibitor sleeves which are made from poster paper (see picture). The inhibitor sleeves are necessary to prevent the outside of the grains from igniting prematurely, which would result in the motor pressure exceeding the safety limits of PVC and causing a catastrophic motor failure (likely involving the endcap). A centered "coring rod" is pressed through the middle of each grain to hollow out cores in the grains. These grains are then stacked into a PVC pipe and the nozzle end cap is glued into place.

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Looking good dude. I'm jealous - wish I had somewhere to fly rockets too :D

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We built this device to measure thrust from a standard bicycle pump. The hose and bottom portion was removed and replaced with a pressure gauge. The pump was then filled with water and mounted to a piece of plywood. The motor was then fixed such that it could push against the pump handle. The pressure gauge was filmed during a test fire, and the PSI was plotted against time. Knowing the area of the piston, PSI was converted to pounds of thrust, and ultimately into average and total thrust. Attached is the thrust profile of our second motor (the first went unmeasured). A little disappointing as we are aiming for an "I" class motor (71.93-143.83 lbf·s). For the next motor we will use sorbitol instead of sucrose/karo mix as the fuel, as well as extending the length of the grain by 4 more inches.

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The motor mount was made from a cardboard tube. We took some plywood and cut out three fins. After several simulations we determined that the fin shape isn't that critical, as long as they fall within certain parameters. The centering rings (which center the motor mount in the main body tube) were made from epoxy. These epoxy centering rings were epoxied on the in front of and behind the fins, to add stability. Because the PVC motor didn't fit exactly into the motor mount, several layers of poster paper were glued into a tube, which filled the gap. Fin slots were then cut into the bottom of the main body tube, and everything was epoxied into place.

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Picture of the body tube with motor mount in place:

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We also built a new test stand, as the bicycle pump / PSI gauge stopped functioning properly. The PSI gauge would not reset to zero after the test fires, and eventually started sticking. This test stand uses a scale and has a mount for the camera.

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The launch pad was constructed for about $60 total. Instead of using a launch rod, we used an 8020 aluminum rail system. This is basically a slotted rail, which launch buttons that are attached to the rocket can slide into. The launch rail was bolted into PVC, and a PVC base was constructed. We weren't happy with the stability of the PVC base alone, so we added some steel struts for stabilization. The blast shield is aluminum. I'm curious to see how it holds up under the heat.

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Excellent looking rocket Blike.

Not sure if you've seen this video, but thought I might share it with you and other rocket enthusiasts.

 

it's basically a group of amateur rocket enthusiasts building a space shuttle style machine. it's only a short 10 minute video which cuts out a lot of the detail , more detail of the build and launch is available all over youtube, including video shot by the makers of the rocket.

 

Enjoy

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