do i need a catalyst ?

[pyro5ive]

hi ! what is the difference between 70/30 whistle mix with a catalyst and without a catalyst ? Thanks.

[DavidF]

Without the catalyst, the whistle will have less power and may not burn properly. Adding a % or two of fine charcoal or powdered perlite will make it burn better, but won't do much for the power.

[NeighborJ]

Aside from the fact that a catalyst makes whistle burn faster, it will also change its sound and make it burn smoother. Whistle rockets will often chuff and cough without a cat especially with a fuel rich mix like 70:30, this makes poor use of its thrust. A hot mix seems to work much better without a cat (76:23:1).

 

I like using sali whistle inserts without a cat because they need about 1/2 the fuel to whistle the same time but the sound is still different.

[DavidF]

NeighborJ, is the 76-23-1 a typo? What's the '1', if not the catalyst? Phlegmatizer? Just curious.

 

Also, what about the volume of the sound? Aren't the non-catalyzed sali whistles anemic-sounding? I have a leftover bunch of 76-23 sali whistle with no catalyst, and I forget why I even made it. I never thought of using it for inserts. I've tried 70-30-1 benz whistle and 76-23-1 RIO whistle side by side as simple pressed columns in tubes and the sali whistle seemed 3 times as loud. I figured the loudness was directly related to the burn speed.

[NeighborJ]

Yeah David I realized what I did with the "1" after I reread it... 76:23sali:+3mineral oil is what I use for inserts. The sali without the cat is plenty loud, infact it only really differs with a raspy sound and a rare hiccup.

The Benzo whistle has been a whole different animal and seems to need a cat or something with any ratio.

[lloyd]

The standard US military whistle is perc/salicylate/red gum. No catalyst. It's PLENTY loud, and is perfectly reliable as to burn time.

 

Since I've made tens of thousands of whistles with that particular mixture, I'm not afraid to express an opinion about it.

 

Lloyd

[DavidF]

Not that I doubt you Lloyd- I don't- but could you humor me a bit so I can understand this better? I have a vague understanding that whistles make the sound from the burning of surface layers and the rarefaction of the gases in the empty part of the tube, which causes oscillations that make the sound. I probably didn't express that very well. But the volume of the whistle, at least in my mind, is a separate issue. Obviously the volume without catalyst is good, as you and NeighborJ both say. But how can that be?

 

If a whistle burns for half the time, wouldn't it be twice as loud? OK, not necessarily twice, but 'more'? To me, more burning (per unit of time) equates to more whistle sound. I am basing my assumption on nothing more than the example I gave above. The sali whistle burned way louder and was way faster. I assumed one thing was because of the other. My additional assumption was that faster burning sali whistle would be louder than slower burning sali whistle.

 

It's interesting that the military would choose to use sali whistle.

 

In the whistle inserts I've made (always catalyzed), the Ti I put in never makes much of a tail. I bet the tails would be better with the slower uncatalyzed whistle, but maybe they wouldn't scoot around as much?

[lloyd]

"If a whistle burns for half the time, wouldn't it be twice as loud? OK, not necessarily twice, but 'more'?"

--------------

Not necessarily. The noise volume relates to the gas volume release per unit of time during the flame and smoulder phases as compared to one-another, not to the gross burn rate. If the gas release were extremely high during flame, and extremely small during smoulder, you'd expect a very high-amplitude note (loud!).

 

But one can easily imagine a case where the gas-release volume changes between the phases would be imperceptibly small. In that case the volume would be miniscule, even though the average of the two burn rates might be high.

 

I would be more prone to suspect a change in frequency, rather than a change of volume. Since I didn't compare any of these many whistles to those with a suppressant, I cannot speak to what frequency the note would have been with one.

 

(These many, many whistles were part of a military contract. They don't give you a choice of what formula to use.)

 

LLoyd

[NeighborJ]

Lloyd the formula which you are referring to is it the 69:28:3 formula listed as military whistle? I'm curious how these were made, dry powder pressed? Granulated dried then pressed? Pressed damp?

 

I've tried unsuccessfully to use Phenolic resin and then bake to cure but they all turned out to be salutes. I put the project on hold until I had more free time or some good info to build upon.

[lloyd]

That's the 'standard' formula for most US military whistles; yes.

 

In 'normal practice', it's water-moistened, granulated, dried in a heated drying area, then pressed. Our project was to press it dry from conditioned, freshly-mixed powdered ingredients, without the added time-consuming and space-occupying steps of granulating and drying.

 

We had good results with the process. They worked reliably over time and over many lots, and all within 'spec' for burn time and 'audible signal'.

 

Lloyd

[NeighborJ]

Thanks Lloyd I suspect that anything at all which burns steady will smooth out a whistle fuel. The red gum is likely what makes that mix work. I've even used hexamine, charcoal and BP with good results in place of RIO or Cu Oxy. It's the phlegmatizers which seem to hurt the steady burn.

[lloyd]

Yeah. The military is really 'big' on reliability. They'll sometimes sacrifice performance for consistency. In this case, it gives both.

 

That formula has been the standard since the 1940s, and there's a reason for it: It works... every time!

 

FWIW, inconsistencies in compression between increments will make a lot of difference in the 'evenness' of the burn. It's best to make the individual increments end up less than one i.d. tall, when fully-compressed. Too-tall increments will immediately show their presence by fluctuations in the burn rate and the sound.

 

Lloyd

[Maserface]

Lloyd,

I find the military's approach to be quite interesting, and would like to know more. Can you share any of the mil-spec numbers(?) that outline their process, or their materials?

[lloyd]

They're all old, released military specs, available on line. Here's one that details one entire simulator that contains the 'standard' whistle timing/warning element:

 

pyrotechnics.emilspec.com/MIL-DTL-10058/page26.html

The whistle spec is drawing 7549227. (didn't look for a source for that, but it's out there, for free).

It's 'nothing special'; just the 69/28/3 formula cited above. The drawing does give fill and compression spec's, though; so it's of some value.

Lloyd

[drtoivowillmann]

Copper powder and almost all copper salts are suitable catalists for whistling mix.

Iron oxide is only good with clorates: better not!!!

 

Yours truly: Toivo

[NeighborJ]

I finally got a chance to try the military whistle formula without any catalysts. It is VERY loud and shrill. This clip shows a 2oz insert with 1" of comp pressed into it without any phlegmatizers. The red gum seems to make it burn fast and the individually milled chems also help to create a smooth burn.

 

I had concerns about how solid the grain would be but they were put to rest when I felt how hard it was, even when pressing it on my drill press and without a tube support.

 

The only concern I have with this formula is safety. Is it safe to press these without a phlegmatizer? The military does it that way so why did we ever start to look for other ways.

Edited April 22, 2017 by NeighborJ

[lloyd]

I don't know if you pre-granulated it, or not. I have pressed it in both that and the 'raw' powdered form. It really seems insensitive to pressing forces.

 

I can't tell you how it would respond to ramming, because I've never rammed it. But I've pressed a few dozens granulated, and many thousands from raw powder, and never a mishap.

 

(Just for the record -- "It hasn't blown up yet" is no guarantee. But my feeling is that it is not particularly sensitive.)

Lloyd

[Scorpion812]

Alot of things work better with a catalyst