29mm Aluminum Reloadable Engine


   I was very bored one day and happened to come across some diagrams of reloadable rocket engines, thought the project looked like a good way to spend a few hours, so I decided to give it a try. First I started with some 6061-T6 Aluminum Alloy tubing with a 1.009" ID and a 1.125" OD, and cut it to a length of 7 inches or so (don't have exact measurements with me right now, but I remember it being approximately 7 inches)

6061 Aluminum Tubing 1.009" ID 1.125" OD

     6061 Aluminum alloy is what is typically used in the aerospace industry, since is extremely strong, lightweight, and also very machinable. Out of all the aluminum alloys I have worked with (including home-forged alloys), 6061 is by far my favorite. It machines beautifully. Now that the tube is cut to size it is chucked in the lathe, and the ends are turned down to make them square, smooth, and to get rid of the roughness of the hacksaw cut. From there a boring tool is used to bore a 1/8" wide, and 1/6" deep groove inside of the tube on both sides about 1/4" in from the end of the tube; This will be used to hold some internal retaining rings in place, therefore holding the engine together; so it is an important part of the motor. Wow, I'm terrible at explaining this.... Ill let the picture below better serve you.

Aluminum Tube with internal Snap Ring Groove

    Above you can better see what I was trying to explain. So on the other side of this tube is the same exact thing to hold the aft (rear) retaining ring. Realizing I did not have the proper tools to put in the snap rings I earlier bough from the HomeDepot, I quickly ran to Harbor Freight Tools, my source of cheap Chinese tools, for when I'm too cheap to buy the good stuff. Since this is the only thing I will be using retaining ring pliers for, I figured buying the cheappies couldn't hurt.... oh boy was I was wrong. I should have just bought good old American made ones. These Chinese "retaining ring pliers" are so flimsy they practically bend more than the retaining rings. But after fidgeting with them for a while i was able to test out the retaining ring groove; as seen below.

Aluminum Tube with internal Retaining Ring

After This the nozzle is finally made, which consists of a 1.006 OD X .75" ID aluminum tube with a .75" graphite insert held in place by compression/high temp glue; which is then formed into a nozzle with a 45 degree convergent cone, and a 15 degree divergent cone as seen below.

45 degree convergent cone view.

After that is done the rear bulkhead is constructed, which is just a thick aluminum disc.

Aluminum Rear Rocket Bulkhead

Finally, after the addition of some O-Rings, and some Ammonium Perchlorate Composite Propellant, this sucker is ready to be test fired.

Completed 29mm Reloadable Rocket Engine

I will get a video up of the test fire as soon as possible.