Static fire test
Before getting into anything like the construction and launch of a rocket, or even the initial development of a sensor package I wanted to get a feel for how the blackpowder engines behave. Taking a page from the book of real life rocket engine development I wanted to do a ‘static fire’, where the engine is fired whilst held down so that it may be studied. The problem with doing this for these prefab engines is that their burn times are on the order of (fractions of) seconds which makes observing them a hurried affair.
I own a cheap point-and-shoot camera which has limited high-speed functionality (120fps @ 320x240 or even 240fps @ 160x120). It’s also waterproof which I figure is almost the same as rocket/fire proof.
I taped the smallest engine I had (1/2A rated, 0.33s burn time and 1.25N thrust). Those numbers mean that it will burn for a third of a second and during that time will provide approximately 123 grams of thrust. To securely fasten this monster I used duct-tape and a broom, as seen here.
Inserted into the bottom of the engine is the electrical igniter, which contains a small pyrotechnic to set off the black powder upon ignition. Clipped on to that are two small crocodile clips which lead to my ignition switch.
See here the results of the static fire test:
Despite the bad quality of the camera in high speed mode the discreet events involved in engine ignition are distinctly visible:
A - Lighting of the ignitor charge (first puff of smoke)
B - Ignition of the propellant
C – Further burning of the propellant and formation of clearly defined exhaust plume
D – Generation of thrust (evident by the fact that the broom flies away)
E – (off screen) Ignition of the parachute expelling charge
The thrust proved greater than anticipated and the jumping broomstick was quite the surprise, as was the smoke generation, but otherwise the test was a resounding success.