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CC: Amateur Rocketry List

Subject: Re: Big solid grains-release of core


If a long mandrel were coated with a hydrocarbon based mold release, part of that

hydrocarbon would remain on the surface of the core when the mandrel was pulled

out. This would create a slightly tacky, oily, fuel rich surface on the grain

core. This can be a problem for quick, chuffless ignitions.


But what if this slightly oily core was dusted with an oxidizer after the mandrel

was pulled? (90 micron AP or KP.)

This could bring the fuel rich surface of the core closer to an acceptable

fuel/oxygen balance... Thus making it easier to ignite. (Or, at least that is

the objective)


I have tried this idea only once before in a O sized tapered core motor, but it

chuffed once at ignition anyways. I believe I may have dusted the core with too

much AP. I put roughly 4-5 oz. of the oxidizer down the length of the core with

the intent to roll it around a few times and then dump out the excess. But after

rolling it a few times, it was all gone, there was no excess AP left to dump out.

It adsorbed all of it and still required more to obtain a uniform coating. I

didn't like the idea of non-uniformity in the core, so I added more.


I probably went too far in favor of the oxygen but I can try the dusting content

and procedure differently next time.


What do you think?


Anthony Colette


Henry Spencer wrote:


> > Anybody ever try PVA (polyvinyl alcohol) film? or paint-on? Some guys who

> > make thin fiberglass-epoxy tubes over mandrels coat the mandrel with PVA. A

> > release sheet supported film is available from (??) for use as a release on

> > molds for fiberglass lay-ups... Is pva flammable?

>

> Almost anything organic, short of Teflon, is flammable. The question is

> whether it's flammable *enough* to make a good igniter. For that I

> suspect you'd want something with some built-in oxidizer.

>

> Henry Spencer

> henry@spsystems.net

> (henry@zoo.toronto.edu)


Date: Sun, 02 Aug 1998 13:36:40 -0700

From: bill

To: bbs

Subject: [Fwd: Big solid grains-release of core]


This is a multi-part message in MIME format.

--------------5E92A726B5E274DA3BB63C0F


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Date: Sun, 02 Aug 1998 13:35:43 -0700

From: bill

To: rockitman@sprintmail.com

Subject: Re: Big solid grains-release of core


The latest issue of HPR has an article by Chuck Piper, formerly of the RRI. They

routinely dusted their cores with perchlorate, worked great, your re-invention is

practical and a good idea! they actually added oil and dumped it out as I recall,

before adding the perchlorate)

BC


X-Originating-IP: [204.203.208.82]

From: "Brian Garlock"

To: arocket@nmt.edu

Subject: Re: Anybody know the whole story?

Date: Sun, 09 Aug 1998 21:48:43 MST


AP's days are

>numbered, as more and more people become envrionmentally "aware."

>

>Chris Valade

>


Chris is right. There is a new solid oxidizer better than AP.

Ammonium Dinitramide (ADN) Check out:

http://www-mpl.sri.com/h[projects]pyu3883.html


Brian Garlock

"To the moon, Alice, to the moon!"


Date: 10 Aug 1998 09:58:39 -0500 (added by MTA mail.murraystate.edu)

To: arocket@nmt.edu

From: Terry McCreary

Subject: New oxidizers


> AP's days are

>>numbered, as more and more people become envrionmentally "aware."

>>

>>Chris Valade

>>

>

> Chris is right. There is a new solid oxidizer better than AP.

>Ammonium Dinitramide (ADN) Check out:

>http://www-mpl.sri.com/h[projects]pyu3883.html

>

> Brian Garlock


ADN and other new oxidizers do have some drawbacks. According to Journal of

Pyrotechnics #6 (article by Jeroen Louwers) it is apparently fairly

sensitive to impact; 3-6 Nm vs. 15 for AP, 7.5 for RDX and 7.4 for HMX. It

also has a low melting point (93C) and is hygroscopic. And its density is

closer to that of AN than of AP.


Louwers focuses on his work with hydrazinium nitroformate, HNF. Though it

is incompatible with HTPB, it provides very high impulse with GAP binder.


Both are quite expensive. Particle size control and burn rate control

appear to be problems.


I'm reminded of nitronium perchlorate, which was a subject of research for

about 20 years before it was finally determined to be less than useful in

solid propellant. Hopefully these new oxidizers will do better, but I'd bet

that we'll see AP for quite a few years to come.


For anyone who wants to play with propep, here's some data:


ADN N4H4O4 density=0.06507 lb/in^3, dH formation = -282 cal/g

HNF N5H4O6C density=0.06725, dH formation = -94


P'rfesser


Date: 11 Aug 1998 09:30:35 -0500 (added by MTA mail.murraystate.edu)

To: arocket@nmt.edu

From: Terry McCreary

Subject: Re: Propep Questions


>For a better example: if you make a basic

>formulation consisting of an oxidiser and a basic fuel say Hydrocarbon

>based. If you add Aluminium/Aluminum/AL or perhaps another metal to it

>Propep will increase the impulse(well from the testing I've done anyway).


You are correct; Al will increase the impulse both theoretically and in

practice...up to a point.


If you do a "multiple run" of propep on the propellant, varying the aluminum

content, you'll find the maximum calculated impulse and the optimum amount

of aluminum to add. For an AP propellant that maximum is around 20%,

depending on the other components.


Problem is, the aluminum is assumed to burn completely in the combustion

chamber for calculation purposes. In small motors that doesn't happen;

still-burning aluminum is ejected and provides a beautiful white exhaust

flame. So in practice, the benefit of added aluminum quickly reaches a

point of diminishing returns.


My understanding is that this limit is reached somewhere between 10-15% Al

in small (29, 38mm) AP motors. The combustion temp in an AN motor will be a

bit lower, and the mechanisms for the chemical reactions are definitely

different from AP motors. I'd hypothesize (well, just a SWAG) that the

"limit" of Al in AN motors might be even lower.


Summary: aluminum helps. Too much aluminum hurts. "Too much" in practice

is less than "too much" by calculation.


Incidentally, this general subject is under study and (hopefully) will be

reported in a future issue of Journal of Pyrotechnics.


P'rfesser


From: Arno Hahma

Subject: Re: Aluminium combustion (was: Propep questions)

To: terry.mccreary@murraystate.edu (Terry McCreary)

Cc: arocket@nmt.edu


>chamber for calculation purposes. In small motors that doesn't happen;

>still-burning aluminum is ejected and provides a beautiful white exhaust


Aluminium particles require several to several tens of milliseconds to

burn depending on the pressure and environment they are burning in (for

particles with about 1000 m^2/kg initial surface area). It is no wonder

they are ejected out of small motors, where the particles do not spend

that long a time.


>different from AP motors. I'd hypothesize (well, just a SWAG) that the

>"limit" of Al in AN motors might be even lower.


I think you should leave the Al out of AN motors, it is pretty useless

there, unless it is extremely fine dust. That, in turn, makes the fuel

hazardous to mix and use. In addition, Al + a nitrate is not a good

idea anyway, since Al tends to reduce nitrates into ammonia. That

consumes both materials, changes the fuel ballistics and reduces

safety.


In addition, AN is unlikely to ignite the Al anyway. You need about

2200 K temperature to ignite Al and the base fuel has to be able to

supply that without the Al. Otherwise the combustion will not be stable

and the Al is likely to be extinguished, at least in small motors. If

the Al is coated with some organic material, that helps ignition, it

may burn at lower temperatures. Many so called pyro aluminiums are,

they contain carbon on their surface and mixed into them, which makes

them much more flammable than pure Al powder. That also makes them more

hazardous to use.


>Incidentally, this general subject is under study and (hopefully) will be

>reported in a future issue of Journal of Pyrotechnics.


It will be reported elsewhere as well ;-).


>P'rfesser


ArNO

2


Date: 11 Aug 1998 11:28:25 -0500 (added by MTA mail.murraystate.edu)

To: arocket@nmt.edu

From: Terry McCreary

Subject: Re: Aluminium combustion (was: Propep questions)


>Aluminium particles require several to several tens of milliseconds to

>burn depending on the pressure and environment they are burning in (for

>particles with about 1000 m^2/kg initial surface area). It is no wonder

>they are ejected out of small motors, where the particles do not spend

>that long a time.


Minor addendum: I'm looking at an old book, "Solid Propellant Rocket

Research" edited by Martin Summerfield. On p. 290 is a table of data from

metal combustion in plastisol propellant. For propellant that is 1% by

weight 5 um aluminum, ignition of the aluminum occurs at the propellant

surface. When increased to 10% by weight, ignition of the metal occurs both

at the surface and downstream; i.e., some metal does not ignite immediately

(they don't give downstream distance, which would be very useful here).

This ignition lag undoubtedly contributes to the lack of increase in

performance at high levels of aluminum.


P'rfesser


From: Arno Hahma

Subject: Re: Aluminium combustion (was: Propep questions)

To: terry.mccreary@murraystate.edu (Terry McCreary)

Cc: arocket@nmt.edu


>metal combustion in plastisol propellant. For propellant that is 1% by

>weight 5 um aluminum, ignition of the aluminum occurs at the propellant

>surface. When increased to 10% by weight, ignition of the metal occurs both

>at the surface and downstream; i.e., some metal does not ignite immediately


Sure, more energy is needed to heat the Al up to its ignition point.

The more Al you add the more it cools the flame close to the propellant

surface. Consequently, the metal ignites further out of the surface

than at low percentages, i.e. ignition lag is increased.


>This ignition lag undoubtedly contributes to the lack of increase in

>performance at high levels of aluminum.


Yes it does. The ignition lag is a few times as long as the time of

combustion, as a rule of thumb.


>P'rfesser


ArNO

2


From: Arno Hahma

Subject: Re: Aluminium combustion (was: Propep questions)

To: rrgp@pnet.net (bill)

Cc: arocket@nmt.edu


>Precombustion agglomeration is another pronounced problem with aluminum,

>particularly in highly loaded Hybrid fuel grains. Partial burns done by NASA


You're quite right! That property is one of the reasons it is hard if

not impossible to predict the Al combustion efficiency or rate. You

always have to do testing and when the !"#§"#§ metal does not burn, you

try to guess what the h*"#" to do next to make it burn. Fortunately,

there are ways to prevent the Al from agglomerating and that of course

makes it burn much faster. But, it doesn't remove the problem of not

being able to say exactly in advance, how fast or slow the metal is

going to burn.


>of the grain. Combustion efficiency was down. This is where the use of mag/al

>came from, the anaylsis of these reports and some test firings withs high

>loadings of 50/50 Mg/Al.


While Mg/Al (magnalium) ignites well, it burns somewhat slower than

pure Al and usually strongly regressively. Apparently, the evaporating

Mg cools the particles and slows down their regression rate, as Al2O3

can accumulate on the surface (not hot enough to get rid of it). Pure

Al of the same specific surface area shows about twice the regression

rate of magnalium. Pure Mg burns about as quickly as pure Al and in a

much more predictable way.


>BC


ArNO

2


From: VRGNJ@aol.com

Date: Wed, 12 Aug 1998 09:36:38 EDT

To: arocket@nmt.edu

Subject: Multiple fuel slugs


Has anyone had any experience with solid fuel rocket motors using multiple

precast fuel slugs of different compositions within the same motor casing

Specifically, what I am concerned about is the practical problems that would

be incurred and anyting unusual that may be necessary if one uses very fine

grain fuel slugs of a very fast burn nature near the base, and slower burning

courser fuel slugs of a slightly different composition at the top of the

stack.

There are several objectives, including lengthening the total thrust

duration.


From: Arno Hahma

Subject: Re: Multiple fuel slugs

To: VRGNJ@aol.com

Cc: arocket@nmt.edu


> Has anyone had any experience with solid fuel rocket motors using multiple

>precast fuel slugs of different compositions within the same motor casing


Yes, it works fine. You just need to calculate the pressure profile so,

that the case does not burst and that the remaining, slower grain does

not extinguish from the pressure drop.


>grain fuel slugs of a very fast burn nature near the base, and slower burning

>courser fuel slugs of a slightly different composition at the top of the


Don't do that, put them the other way around. When the rocket

accelerates and the fast grains burn out, the slower grains at the top

slam down towards the nozzle. That causes problems, at least the rocket

gets a real good kick ;-). That is, the center of gravity suddenly

moves and that is not good news for keeping the rocket in the same

direction it is supposed to be going at. If the grain cracks from the

impact, it can get blown out of or plug the nozzle and burn, shall we

say, "stepwise" ;-).


If the faster propellant is on the top, there are no problems of it

burning out. One only has to take care there is enough room for the gas

flow to pass the lower grain. Also, the lower grain will burn

erosively, if the gas velocity over it gets too large. That is not

really a problem, if you know how much the erosion is accelerating the

combustion. However, the erosive burn rate is rather difficult to

estimate or measure, so I would build a rocket in a way, that avoids

erosion as well as possible.


ArNO

2


Date: Wed, 12 Aug 1998 07:41:44 -0700

From: bill

To: bbs

Subject: Re: Multiple fuel slugs


I would stay with the original suggested arrangement: making the assumption that

the liners (of cartridge cast grains) would support the upper grains. That would

be ideal from an erosiveness standpoint.Another advantage of the arrangement Arno

suggested is ignitability, but it should not be a problem either way.

Speaking of falling down, we just had a 5.4 quake here in quakeville; seemed about

3 - 4 seconds of rolling quake.

BC


Date: Sun, 27 Sep 1998 20:43:08 -0400

From: Tom Binford

To: arocket@nmt.edu

Subject: Burn Testing


This is a multi-part message in MIME format.


I just completed a series of burn tests of several propellant

formulations.

Comments welcome. The attached file is a list of firings, propellant

formulations,

and results.


Tom


Burn Test Results


Motor configuration

RMS 38/240 casing. Nozzles all have .438" exit, throat bored to desired size.

2 grains, each 1.25" OD, .414" ID, 1.82" long. All motors had active delay.

Web thickness .418, max off center .050" (Calculations assume on center.)


Propellants:

All are HTPB based, designation is AP%-metal%. z indicates zinc, otherwise aluminum.

Amounts given are %, may not add to 100 due to formula modifications.

55-30z 80-0 68-10 65-20 40-40z 75-0

AP, 200u 55 80 51 65 40 75

AP, 90u -- -- 17 -- -- --

Zinc dust 30 -- -- -- 40 --

Al, -400 mesh -- -- 10 20 -- --

HTPB, R45M 8 11 12 8 11 14

Dioctyl Adipate 4.5 6.5 6.5 4.5 6.5 8.5

Isonate 143 1.5 2 2 1.5 2 2

Tepanol .5 .5 .5 .5 .5 .5

Polydimethylsiloxane trace in all, kills surface tension and allows bubbles to break. (<.1)

Theoritical density .075 .056 .059 .0645 .076 .0555

Actual (hand mix) .069 .0518 .0535 .059 .073 .051

ProPep Isp (500 PSI) 160 217 229 243 120 200

Flame none yel/wh white white none none

Smoke black none white white black thin black

40-40z used for delay, 75-0 too smokey, development discontinued.

68-10 is what is used in my moonburners.


All motors were burned nozzle up. Burns were videotaped for burn time and exhaust

characteristics.

Burn time is from first full thrust to flame out (paling of smoke on zinc comps).


Results:

Burn Propellant Kn Duration Rate ("/sec)

1-4 40-40z and 75-0 No further work on these.

5 55-30z 302 2.033 .206

6 55-30z 339 1.933 .216

7 80-0 105 3.7 .113 Chuffs

8 80-0 198 2.033 .206

9 80-0 268 1.7 .246

10 65-20 105 3.367 .124 Very hot, lots of nozzle erosion

11 65-20 198 2.267 .184 ditto

12 55-30z 198 2.267 .184

13 55-30z 105 2.8 .149

14 68-10 105 4.4 .095 Severe, repeated chuffing

15 68-10 198 3.033 .138

16 68-10 302 2.733 .153


Using the equations r=k*Pc^n and Pc=(k*Kn*(Dp-Dg)/Cd)^(1/(1-n))

where r=burn rate, "/sec, Pc=chamber pressure, Kn=propellant area/nozzle throat area,

Dp=density of propellant, lb/cu in, Dg=density of gas, Cd=discharge coefficent.

K is a rate constant, n is the burn rate exponent.

(Equations from Sutton, 6th Ed and "Solid Propellant Rockets" by Alfred J. Zaehringer.)


With the objective of being able to determine burn rate as a function of Kn, I substituted

for Pc, yielding r=k((k*Kn*Dp)^(1/(1-n)))^n. I assumed the density of the gas to be

insignificant in relation to the propellant density, and the discharge coefficent to be 1

(dependant on propellant type and nozzle configuration, NOT actually 1).

Working back, the derived k and n DO NOT give valid chamber pressures, they DO reasonably

predict burn times at other Kn ratios.


Propellant Burns used k n

80-0 7,8 .143 .47

55-30z 5,12 .142 .26

65-20 10,11 .137 .38

68-10 15,16 .127 .22


The next series of tests will use 3 grain motors (RMS 38/360) on my test stand

to collect thrust data. This will give a much better chamber pressure determination.

I will also get actual impulse figures.


Date: Mon, 28 Sep 1998 01:05:24 -0400

From: Tom Binford

To: Kory Hamzeh

CC: arocket@nmt.edu

Subject: Re: Propellant Degassing and Coring


Kory Hamzeh wrote:

>

> Hi All,

>

> I have a few more questions for any one who is willing to share some of

> their knowledhe with me:

>

> 1. I plan, for the first time, to drill out a core in my AP/MG propellant

> grains. I've never drilled out AP motors before. What are some safety

> precautions, drilling speeds, techniques, that I should be aware of?

>

I usually drill cores by hand (turn the drill bit by hand). For larger

cores, I use a drill press at the lowest RPM (about 150). Use a heavy

feed and pull the drill out often. The object is to keep the chips from

wrapping around the drill or packing in the flutes and generating heat.

If the drill gets warm at all to the touch, wait for it to cool before

continuing.


> 2. Can I degass my propellant right after I casted it (but before its

> cured, of course)? Most people I've talked to degass before they cast.

>

For small motors, I don't degas at all. I get approx 90% of theoretical

density.

For large grains, I mix under vacuum. I tried degassing a mixed batch

and it just swelled up but was too thick for the bubbles to surface. It

went back down when the vacuum was released and I gained no improvement

in density. If your propellant is relatively fluid, it will work much

better.


> 3. What are some relatively inexpensive sources for degassing chambers? I

> know Chris K used oak, but it looks like it would be a mess to build and

> coat the entire enterior and all of the joints and seems with RTV. I've

> purchased everything that I need except for the chamber itself.

>

I've used Mason jars with a hose barb soldered into the lid. Good to

about 1 Kg of propellant.


> Any help would be greatly appreciated.

>

> Thanks,

> Kory


You're welcome - Tom


Date: 28 Sep 1998 12:44:23 -0500 (added by MTA mail.murraystate.edu)

To: arocket@nmt.edu

From: Terry McCreary

Subject: Re: Propellant Degassing and Coring


>1. I plan, for the first time, to drill out a core in my AP/MG propellant

>grains. I've never drilled out AP motors before. What are some safety

>precautions, drilling speeds, techniques, that I should be aware of?


Slow speed. Caution. Clean up dust and scraps, don't allow them to

accumulate. If the formulation doesn't have Tepanol (HX878) you may get a

lot of AP bits coming loose.


For reference: In the 2nd ed of Gordon Campbell's propellant making book he

describes the use of a router for cutting moonburners and the like!

Non-metallized propellant though. He claims never to have had an accident

with it.


I've heard unconfirmed reports of people drilling titanium-containing

compositions. At high speeds. This is a Very Bad idea.


>2. Can I degass my propellant right after I casted it (but before its

>cured, of course)? Most people I've talked to degass before they cast.


In a good vacuum, the propellant will foam to 2-5 times its initial volume,

depending on solids loading. I would suggest degassing before casting. For

first trials, Campbell recommends substituting fine salt or some such in

place of AP, for a check on degassing and packing technique. Cut up the

grain afterward, see how it looks. Weigh several identical grains to check

for large bubbles.


>3. What are some relatively inexpensive sources for degassing chambers? I

>know Chris K used oak, but it looks like it would be a mess to build and

>coat the entire enterior and all of the joints and seems with RTV. I've

>purchased everything that I need except for the chamber itself.


I've seen a short piece of 8" PVC used, with 1" plexiglas top and bottom. A

good pressure cooker might do a decent job.


I'll bet I could coat the inside of an 18" cubical box with about two tubes

of RTV, in about half an hour, using a body putty spreader or just a piece

of stiff cardboard.


P'rfesser


Date: Mon, 28 Sep 1998 19:55:58 +0200

From: Hans Olaf Toft
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