From: ahahma@polaris.utu.fi (Arno Hahma)
Newsgroups: rec.pyrotechnics
Subject: Re: SOme Rocket Formulas
Message-ID: <1990Dec10.124202.9659@polaris.utu.fi>
Date: 10 Dec 90 12:42:02 GMT

In article <6332@hplabsz.HPL.HP.COM> schediwy@hplabsz.UUCP (Bic Schediwy) writes:
>
>Tell us more. Favorite recipes maybe??
>

Some composites:

Ammonium perchlorate  65 %
Aluminum powder       16 %
HTPB, CTPB,
PBAA or PBAN          17 %
Additives             0,5..0,7 %
(additional
per cent)

The additives are burning rate catalysts (ferric, chromic or cupric oxides and
copper or lead chromate) and polymer stabilizers. The composition will work
just fine without the stabilizers, but it deteriorates, if you store it, say,
more than five, ten years.

Typical parameters for this fuel are:
chamber pressure range        10..140 bar
characteristic velocity       1600 m/s
linear burning rate @70 bar   12 mm/s (this naturally depends strongly on
particle size and catalysts)
pressure exponent n           0,236 (in equation v = ap^n)
Isp @ sea level               2450 Ns/kg


Since the polybutadiene polymers are hard to get (unless you make them
yourself, which is not all that difficult as it may sound), I'll give
some formulas ( no recipes this time ;-) without butadienes:

Ammonium perchlorate   77 %
Polyurethane           23 %
(preferable an
elastomer)
additives             0,3..1,0 %

chamber pressure          10..140 bar
characteristic velocity   1480 m/s
burning rate @70 bar      6 mm/s
pressure exponent         0,05
Isp @sea level            2330 Ns/kg


Potassium perchlorate     75 %
Polyester-styrene         25 %
additives                 0,8..1,2 %

In this case the additives include lampblack in addition to those mentioned
before. The lampblack accelerates the burning by absorbing the radiative
heat from the flame better than the fuel alone.

chamber pressure          25..140 bar
characteristic velocity   1120 m/s
burning rate @70 bar      18 mm/s
pressure exponent         0,74
Isp @ sea level           1750 Ns/kg

This fuel produces a very hot flame (>3500 C). The high temperature and
gaseous potassium chloride make this very erosive to the nozzle. In
practice, only a short burning time with a metal nozzle or graphite nozzle
with a longer burning time are possible to be used. This fuel burns really
quickly, so it is well suited for such fast burning rockets.

Thiokol rubber can also be used instead of polyester-styrene polymer and
it actually works better, since it is elastic, permitting a case bonded
construction. Thiokol also makes the fuel burn even more quickly, about
25..30 mm/s, depending on particle size of the perchlorate.

ArNO
    2

From: ahahma@polaris.utu.fi (Arno Hahma)
Newsgroups: rec.pyrotechnics
Subject: Re: Composite Rocket Motors
Keywords: rockets, motors, solid fuels
Message-ID: <1991Mar20.113708.695@polaris.utu.fi>
Date: 20 Mar 91 11:37:08 GMT

In article <1991Mar18.190909.16819@ims.alaska.edu> fsdes1@acad3.alaska.edu writes:

>Would anyone on the net be able to tell me where I can find a book or other
>information concerning the construction of composite and similar high power

Try George P. Sutton's "Rocket Propulsion Elements", John Wiley & Sons, 1956.
The book is old and does not describe any modern composites, but it is
still quite useful. The book covers liquid and solid propellant engines.

Another book: "Internal Ballistics of Solid Fuel Rockets", sorry, I can't
remember the author(s). This book is a really good one if you are planning
a solid fuel rocket. The book is very technical and involves a lot of
mathematics. There is also a lot about problems involved in the design
of a rocket motor, such as optimizing the working conditions and propellant
composition, chuffing, resonance effects, etc. and how to avoid those problems.
Sutton's book only mentiones these, if you are not familiar with such problems,
his book is of less value. This book is old, too, but that does not matter
actually. You can not find formulas of rocket fuels anyway, and if you can,
they invariably lack something important, such as additives used or the
particle size of the oxidizer.

If you are searching for a formula, you should consult the patent literature
to find its full composition and properties, i.e. the data needed to design
a motor.

>black power engines,but pounding on eight ounces of black powder with a hammer

Use a press rather than a hammer - much more effective and much safer.

>Also, books concerning the design of nozzles for solid fuel engines would be
>handy.  If one is going to cast an engine, a nozzle is a pretty good idea...

Is is well possible to use a nozzleless design. You only need a fuel
with a low minimal burning pressure, a low erosion constant and a low pressure
exponent. A fast burning propellant is advantageous, too. Also, the propellat
must be elastic to permit a case bonded structure.

Both of the books cover this, actually, it is the main problem. It is easy
to solve, once you know the propellant and its properties. You'll  need the
burning equation, i.e. v = a*p^n, of the fuel. I have never seen it given
except in the patent literature.

It might be an easier approach to construct
a strand burner to measure the pressure exponent and the constant
yourself - in fact, this is the way I chose. You also have the advantage to
be able to develop fuels of your own - this is not possible if you just
scan some libraries to find formulas. Even though you would find a fully
decribed process, you'd have to be able to exactly reproduce the conditions
. The most important parameters are the particle size of the
oxidizer, the catalysts and their amounts. The former affects the burning
equation constant, and the latter both the constant and the exponent of
pressure. If you make a mixture of your own, both of these criteria stay
constant, at least within a single lot of chemicals you are using.

It is really fun to develop rockets and even more fun to shoot them. Or what
would you think about an 60 Ns engine, that weighs about 40 grams and
costs 10 cents? Or an 1200 Ns engine,  800 grams weight, mass ratio 2,5 and
cost 2 dollars? BTW, what size would the latter one on the model rocket
scale,  a K, L or what?

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From: ahahma@polaris.utu.fi (Arno Hahma)
Newsgroups: rec.pyrotechnics
Subject: Re: Composite Rocket Motors
Message-ID: <1991Mar21.154341.13501@polaris.utu.fi>
Date: 21 Mar 91 15:43:41 GMT

In article <40383@cup.portal.com> dbell@cup.portal.com (David J Bell) writes:

>>cost 2 dollars? BTW, what size would the latter one on the model rocket
>>scale,  a K, L or what?

> How about some instructions?

If I tell you the bigger motor uses an external burning propellant grain,
you might understand, it is not possible to explain the construction here.
Building a motor requires some tools, but it is really easy, once you have
them. There are only three parts in the motor - I'll let you guess what they
are ;-).

ArNO
    2

From: ahahma@polaris.utu.fi (Arno Hahma)
Newsgroups: rec.pyrotechnics
Subject: Re: Composite Rocket Motors
Message-ID: <1991Mar22.163033.20937@polaris.utu.fi>
Date: 22 Mar 91 16:30:33 GMT

In article <1991Mar22.171138.3214@waikato.ac.nz> chem2149@waikato.ac.nz writes:

>I am experimenting with KClO4 propellants with only a few sucessful
>formulations.  I realise that the pressure exponent for KClO4 propellants is
>generally high but the main problem that I encounter is the high combustion
>pressure limit.  Most motors chug and explode, some continue into the air
>chugging away and never reach a stable combustion mode (a novelty I suppose).

The minimal combustion pressure is around 40..50 bar. It is better to make the
rocket operate at a much higher pressure to prevent chuffing, if (when)
the nozzle is eroded. Thus, you'll need a strong casing even if you are
using a case bonded type with an internal burning grain.

>problems and have sucessfully built KClO4 type propellant motors.  I would like
>to know the formulations, rough idea of particle size of KClO4, inital and
>final burning to nozzle area ratios, density, burning rate (quote pressure)
>etc.

It is difficult to give any accurate values, since I have not measured all
the necessary data ( i.e. I have no sieve analysis of the perchlorate).
The burning speed is about 17 mm/s at 70 bar for a polyester-KClO4-fuel
(25:75) and the pressure exponent about 0,83 - very high.

The ignition is the key how to prevent the fuel from chuffing. The nozzle
has to be strongly plugged, for example a 2 mm aluminum plate glued with
epoxy resin in the diverging section of the nozzle. The igniter charge
has to be calculated to raise the pressure slightly above the calculated
operating pressure. Also, the igniter must not burn too fast, but maintain
a flame for a while to give the propellant time to ignite. Black
powder is good for this, so is the aluminum-KClO4-binder-mixture, pelletized
with a press (important!).

In my opinion, potassium perchlorate fuels are about the most difficult to
use. They have a very high burning temperature and pressure exponent as
drawbacks. On the other hand, they burn very fast and are quite dense, the
polyester-perchlorate has a density 1,85 g/ccm.

Anyway, why bother using KP, as you can reach as much specific impulse even
with ammonium nitrate fuels? They burn cool, about 1300 C or even less -
ordinary steel will do for the nozzle.

>     I plan to use 3/4" to 1 1/2" internal diameter motor sizes using cardboar
>tubes and clay nozzles.  The KClO4 oxidiser is mainly for the white smoke trai
>and white flame (depending on binder).  I dont want any formulations which use
>Al powder due to nozzle erosion problems at these temperatures.

If you find a cardboard tube (of THAT size), that can stand 100 bar or more and
some clay strong enough to stay in the tube, then it works. I wonder, how you
manage to do that.

>good mates-cost nothing) using a NH4ClO4/Al/Binder 65/20/15 propellant (400g).
>     The previous rocket to push the barrier lost its three fins at 400m.

What did you use as a binder? Polybutadiene or polyurethane? And how were
you able to mix the fuel with so little resin - I guess the grain was
external burning?

>was due to air flow (approx 0.9 MACH) over the thin Al fins (recovered one)

I have been able to reach supersonic velocities even with 40 gram engines cast
in plastic shotgun shells - that should be no problem at all.

>which had a very impressive wobble due to the speed (a new version of speed
>wobbles).  The video camera picked up the sound 500m away easily.

Must have been nice to see! Did the rocket continue straight, or did it
lose its stability entirely?
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