Well, somewhere in between a micro-stinger and something that could be called just plain stinger.
A test of the new 50 mm long, 9.5 mm ID tubes from skylighter. Made in pretty much the same way as my 8 mm ID micro stingers. 1.8 mm spin and lift vent holes, RP propellant, thin blackmatch fusing. I did attempt to proof the spin vent with some waterglass.
Too heavy.
Or at least too little lift thrust output. The lift/core was about 30-35 mm deep into propellant grain, somewhat longer than in a micro-stinger, but the extra mass of the thicker, longer, kraft tubes and extra propellant must have been too much.
The launch wire was twisted up badly by its thrashing before it actually managed to leave the ground. It did hover for a moment before its propellant was expended.
The spectrogram is interesting. There is a rapid 130 ms rise to around 650 Hz (39 kRPM), then an almost linear fall to 600 Hz over 400 ms, followed by a much steeper fall for 300 ms before burn-out. There is also modulation sidebands (about 80-90 Hz each side of fundamental, also seen in the harmonics) indicative of precession, probably the violent thrashing that bent up the heated steel wire. The modulation frequency rises rapidly at the peak of the fundamental, but drops as the device spins down.
It is almost as if the gas pressure was not shared equally with each hole. That makes some sense, the clay nozzle was narrowed with the launch pin, and the spin vent was widening all the time, so it probably got the lion's share of the gas.
I might try again with straight meal as the propellant, and perhaps a 2.5 mm or larger core, the extra surface area might work, inspite of the larger nozzle. I can also try extending the core the entire length of the grain, but I risk drilling out the bulkhead if I do not set the depth stop correctly.
| title | type | size |
|---|---|---|
| Test Video | video/x-msvideo | 580.864 kbytes |
| Pre-Test Picture | image/jpeg | 54.445 kbytes |
| Post-Mortem Picture | image/jpeg | 43.285 kbytes |
| Spectrogram | image/gif | 119.274 kbytes |