Project
216 Ejection ballast test

Test Analysis

• I got this idea while reading STL's launch report on their "Oddball Excursion" final flight in which they used a small amount of water on top of the ejection charge to prevent damage to the parachute assembly. One of the main reasons I haven't used nosecone weight to balance my rockets is because I don't want that weight falling back down ballisticly if something goes wrong. When I read their flight report it occurred to me that water would be a great ballast for the rocket. I could be ejected at apogee without thought about where it would fall and it would cool the ejection charge.

Construction

• 16" of 2" PVC holds 2.5 lbs. of water. The total assembly weighs 3.67 lbs. There is a 4" time delay fuse on the bottom of a 1/2" PVC union which has a .002 piece of brass shim stock in it. When the fuse burns up to the union, it ruptures the shim stock disc and blows out the water in a fraction of a second. The water is held in the PVC pipe by a test cap, preventing it from leaving the pipe when the engines cut out and the rocket starts to coast.

Pros

• Great source of nose weight.
• No problem with ejecting the water at apogee.
• Water will cool the ejection charge and prevent damage to the parachute assembly.

Cons

• 4" of delay fuse was too long, 27 seconds. Delay needs to be 20 seconds max. This can be accomplished by trimming the delay fuse to 3".

Pictures

Video

• Video of the test.

Drawings

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