12 replies to this topic

[Draco_Americanus]

Can black iron oxide be subsituted for red iron oxide of the same mesh size? My thinking is rust is rust, but is the reactivity different?

[Mumbles]

Reactivity will be slightly different, but still work fairly well I would imagine. Probably no noticeable difference.

[pyrotrev]

Chromium oxide, dichromates, copper oxychloride and copper chromite also work as catalysts to speed up the decomposition of perchlorates.

[Wyvern]

I dont know if this has been asked before but what makes whistle mix actually whistle, is it because when it burns it oscilates somehow Creating a audiablr frequency?

[BrightStar]

I dont know if this has been asked before but what makes whistle mix actually whistle, is it because when it burns it oscilates somehow Creating a audiablr frequency?

Whistle in itself doesn't oscillate - it just burns at a rate proportional to gas pressure. When you pack it into a tube, the column of air above it forms a resonator (rather like an organ pipe) and the pressure sensitive whistle comp will drive the oscillation of the air. This explains why the pitch is determined by the length of the air space and why the frequency descends throughout the burn. A wider tube will produce a louder noise.

It's an interesting balancing act to achieve this behaviour. Consider r = burn rate, a = proportional constant, P = gas pressure, n = pressure exponent such that r = a (P ^ n). If n < 1, eg approx n = 0.15 for black powder, the mixture in an open tube will just burn, n > 1 the mixture may detonate, n =1 (approx) it will whistle...

Slightly offtopic, but I tried using granulated whistle in an experimental squib yesterday. 1/4" by 2" card tube three quarters filled, e-match, glued endplugs. It worked well - not too much light or smoke output and a really loud bang. Could be useful for small scale SFX...

Edited by BrightStar, 16 May 2007 - 11:51 PM.

[Wyvern]

Ahh right i see now, just made up a batch of Whistle myself and made a small 1/2" ID rocket, absolutely love the stuff

[Draco_Americanus]

I cant wait till i can try this stuff in a larger rocket, I have been useing it as propelent for the magnum bottle rockets and they are too small to get the whistle.
For a nice spark trail is +1% Titanium(or other metal flake) a proper amount?

[Yugen-biki]

I have found that adding red iron oxide to my 1lb whistle rockets will give a smother burning rate and less CATOs. But it is not at all needed to make good whistle rockets.

[Wyvern]

At the moment i have only been making 1/2" ID rockets but i dont have any rocket tooling but i have had an excellent success rate using BP rocket tooling just without making a clay nozzle, i am assuming the chaces of a cato would increase the larger the core so ill wait till i get some proper tooling for any larger rockets than i am making at the moment

[Mumbles]

I think normal whistle rockets have a core about 1/2 the length of that of BP, and slightly thicker. 1/2 ID of the tube, instead of 1/3 ID.

With something like a 4oz I don't think it would be a big deal, but you're right. Larger rockets probably wouldn't respond to favorably.

Edited by Mumbles, 25 May 2007 - 06:34 PM.

[Richard H]

Whistle in itself doesn't oscillate - it just burns at a rate proportional to gas pressure. When you pack it into a tube, the column of air above it forms a resonator (rather like an organ pipe) and the pressure sensitive whistle comp will drive the oscillation of the air. This explains why the pitch is determined by the length of the air space and why the frequency descends throughout the burn. A wider tube will produce a louder noise.

The literature available (See Oztap, Hardt, JPyro et al) does suggest that the whistle effect is partly caused by vibrational burning of substances of an aromatic nature, particularly benzoates and salicylates of the earth metals. Indeed Oztap makes it clear that a tube is not even required to achieve the effect. In one test a small quantity of granulated composition was placed on a flat surface, and a sharp 'thunder whistle' resulted.

It is believed that the high frequency decrepitations of these fuels as they are oxidised are responible for the consequent audible effect. Granted, the tube and other factors like geometry of the composition grain have significant bearing upon the overall effect.

[cplmac]

I agree with you there Rich, and Picrate can whistle too. You CAN get whistle fuel to whistle or at least chirp without any confinement whatsoever or without pressing. You just require a more powerful oxidizer. This is a video of a batch of chlorate whistle I made being tested unconfined about 2 grams of loose grains being lit on the ground.

Unconfined chlorate whistle grains

The whistle or in this case the chirp was clearly not the result of the tube, although without question the tube does tune the sound.

[Wyvern]

Fired a 1lb Perc/Benzoate whistle rocket up today, bit disappointed with the noise but hey.
i think i need a proper press rather than a vice to press these so they will make a better sound.

Edited by Wyvern, 07 July 2007 - 11:19 PM.