Jump to content


Member Since 02 Jul 2006
Offline Last Active Jun 12 2007 03:47 AM

Posts I've Made

In Topic: Rocket/Missile Formulas and Construction

06 June 2007 - 06:09 PM

You're lucky. Much as I've tried, I just can't get those visco rockets to work.

Skipping back a bit to these visco rockets...

These things are really cool to me, being easily thrown together.

I found that about any visco fuse will actually work, they all just produce different thrust characteristics. You will need to try using 6 strips of fuse to start at about 1" each, then try 7, 8, 5 etc. I use slightly thicker fuse.

First of all, the tutorial in the link on page 1 states that you should make these nice little twisted nozzles and tie them with string. I've found this idea really to be useless and inconsistent. Paper burns away rapidly and loses strength. So does what I recommend but at a much more consistent rate from rocket to rocket.

So what do I say? Use the hot glue gun you already have out to make the nozzles. You simply make sure the main fuse is centered in the bunch. Squirt hot glue all around it, about 1/3" in length. Hold the fuse perfectly centered as the glue hardens.

The hole from the fuse burning through the glue initially gives a nice small hole for higher pressure. The glue erodes quickly but the motor also burns out quickly.

If you make them consistent with strong rolled paper cases, they have some oomph! Easily enough to lift a few more grams.

One other thing, these have a tendency to spit out the nozzles with a pop once you push their limits. Soak Ca glue into the paper ends, so that the paper becomes a solid plastic-like material bonded to the nozzle and plug. This way the nozzle is not bonded to one layer of inside paper, rather the whole roll.

In Topic: Idea about rocket fuel

06 June 2007 - 06:55 AM

Personally, if I was someone seeking a simple high Isp propellant with minimal problem areas, ammonium perchlorate is a good place to start. The problem with AN as stated, is mainly its hygroscopicness. Paraffin at lowered levels as in propellent would not infact seal the propellant of its hygroscopicness completely, though I can imagine it would help a bit. I am unfamiliar with something like paraffin working well as a binder for AN.

The amounts of fuel in AN propellants are generally so high that it makes them insensitive to detonation in a rocket motor, so the propellant actually being an explosive you would not have to worry about.

The AN is more stable and takes more heat to get it going. It requires better ignition over AP propellant. Some AN mixtures yield a brittle grain structure, and thus case design must be accounted for. If your grains are tight and seal to the liner of the motor, they will act as the case. I.E. a load bearing structure. The core will be forced to expand under pressure, and cracking may occur. This will CATO a motor. Therefore, the grains are to slightly free float in the motor, so the pressure may flow around them and equalize. This permits the case to expand, while the grains remain the same size.

AP motors using R45 (HTPB) or PBAN have much more elasticity. They become a rubber-like material. They are much more forgiving in that aspect.

And not to mention, who can resist those flames from APCP?!? A 1% CuO is sufficient for very pretty violet/blues. Brass will also work and not act as a catalyst for those colors. A bright purple is possible with brass and strontium nitrate. >7% Al will give nice bright white flames like the space shuttle. There are just tons of known formulas for AP propellent out there, so there is much to play with.

Selwyndog, not to contradict your info, but where are you deriving these "exhaust gas velocities" from?

2200m/s is over 7200 feet/sec. Nowhere in a conventional design rocket motor do gas velocities reach near 7200fps, unless when possibly viewed on a molecular level near the reaction zone.

Gas velocities are mainly subsonic internally through the core, unless a nozzle throat exceedingly larger than the core diameter is used. They converge into the throat and are accelerated to supersonic velocities out of the throat while passing through the divergence portion of the nozzle.

If you reached gas velocities well into the supersonic range internally, your cores would instantly CATO due to an extremely high rate of core erosion.

In Topic: Flare formulas

26 October 2006 - 05:47 PM

The majority of strontium nitrate flare comps use approx 50/50 strontium nitrate and magnesium, perhaps with +10% PVC. One aluminium based forumla I did find was 'Red Wingtip Flare' in Davis COPAE used for signalling between aircraft in WWI. The formula is:

Strontium nitrate - 24 parts
Flake aluminium - 6 parts
Sulfur - 6 parts

It was bound with shellac and pressed into 4.25" long by 1.625" id cases and would burn for 1 minute at 12,000 to 15,000 candlepower.

I haven't tried this myself - would be interested if you can make it work.

Excellent, thanks.

I don't have sulfur here currently, so I may just try SN/Al bound and pressed.

Now these are obviously red flares, is there a flare composition which is much brighter in general, like a white?

In Topic: Ultimate water-proof fuse?

06 August 2006 - 05:09 PM

Why not use this http://www.frogfot.c...ro.html#silicfu KMnO4 fuse and pass it thru heat shrink tubing (something like PIC fuse)?
Heat shrink tubing needs about 100C to shrink, is it going to set the fuse off?
Ooops! Sorry my mistake :blink: , they do NOT burn underwater!
But heatshrink tubing seems a good idea. :rolleyes:

Just use the PTFE. I promise you, you will not ever think of trying another idea again for underwater fuse. It is just so simple and cheap, there's no reason not to use it.

In Topic: Ultimate water-proof fuse?

30 July 2006 - 03:54 AM

Is this tape you mention the same as commonly available PTFE thread tape?

I ask because PTFE is extremely non-flamable, and I wondered if it would retard the burning of the fuse.

Yes that's what is is. I said silicone because I believe they are merely the same.

PTFE will not slow the burn rate, because it is not the PTFE which is burning as a fuel. The fuse doesn't "know" it's there, it simply gets burned through.

That PIC fuse looks to the eye like it would create quickmatch, as the plastic separates from the propellant easily (although I'm sure it burns perfectly).

But honestly, now that I've tried this, I'd much rather buy visco and wrap it with tape as opposed to buying PIC, the stuff works wonders. The added structural strength you can choose to add yourself by how many wraps you do is a plus too.

You can increase the burnrate up to about 60% by very thick tape wrapping, I tried this with the 2.2mm stuff. Bigger diameters would burn even faster if wrapped well. As I said a light wrapping has no influence on burnrate.