More Bottle Rockets - Staged BP to Whistle

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Date: 2005-10-15


My first attempt at staging bottle rockets, especially with different types of motor in each stage.

The first stage was a BP based rocket essentially identical to the propellant proving motor except without the flash report. No special effort was made to reduce its coast/delay section length.

The second stage was a Salicylate Whistle motor, of the same geometry as the BP motor, charged on the same tooling, just without a clay nozzle. The top of the whistle grain was capped off with a thin clay bulkhead.

A short stick of thin blackmatch was used to passfire in the interstage space, it was pushed up into the core of the whistle rocket. A short length of plastic drinking straw was used to couple the stages, being an almost perfect friction fit to the ID of the tubes used. The tube being the only mechanical coupling between the stages, acceleration being trusted to keep the motors together and the relatively strong shape of the tube to bear any lateral aerodynamic shear forces.

Each stage had its own independent stabilizer stick, hot-melt glued in place. The first stage was fused with blackmatch. The stick for the first stage was placed in the launch tube, with the second stage stick laying freely alongside the tube.


Worked great.

The delay on the first section was perhaps a bit long, letting the rocket become almost horizontal before the second stage fired. The lower performance of this batch of BP propellant made the motor struggle a little off the pad. There was much more aerodynamic noise and the end-burning part of the flight could also be heard where normally the rocket is simply too high to hear this.

It still worked well, considering the BP motor was lifting more than its own weight in payload (Whistle is more dense than BP).

The whistle stage was nice and loud, but offered little visual effect compared to the nice spark tail of the BP motor. Next time I will add some metal to the end-burning part of the whistle grain.

Analysis of the recorded sound track suggests the core-burning time of the BP motor is about 350 ms, the end-burning phase about 2 s more. The whistle motor core-burns for about 200 ms and then end burns for about 1.5 s. The whole performance is complete in just over 4.1 seconds. There appears to be little thrust in the end-burning phase of either motor. Note the effects of doppler shift on the spectral trace of the whistle motor, comparison with a static test trace could provide much information about the relative velocity and acceleration of the whistle stage.


title type size
Test Video video/x-msvideo 1.905 Mbytes
Pre-Test Picture image/jpeg 32.874 kbytes
Audio Spectrogram image/jpeg 67.445 kbytes