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ARocket highlights 1998


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>From sedsnm Tue May 26 16:06:09 1998

Date: 26 May 1998 17:19:54 -0500 (added by MTA mail.murraystate.edu)

To: arocket@nmt.edu

From: Terry McCreary

Subject: Comparing propellants?


I'm planning on making many different types of composite propellant and

doing quantitative comparison of performance. My thinking is that for such

a study, the nozzles of the test motors should have no exit cone. That way,

I don't get variation due to differing expansion. I'd like to hear

thoughts, opinions, ranting and raving on this.


P'rfesser


>From sedsnm Tue May 26 20:37:35 1998

Date: Tue, 26 May 1998 21:50:19 -0400

From: Tom Binford

To: arocket@nmt.edu

Subject: Re: Comparing propellants?


Terry McCreary wrote:

>

> I'm planning on making many different types of composite propellant and

> doing quantitative comparison of performance. My thinking is that for such

> a study, the nozzles of the test motors should have no exit cone. That way,

> I don't get variation due to differing expansion. I'd like to hear

> thoughts, opinions, ranting and raving on this.

>

> P'rfesser


I would use a constant expansion ratio - say 4:1.

Tom


From: Terry McCreary

Subject: Re: Comparing propellants?


At 09:50 PM 5/26/98 -0400, Tom wrote:

>

>I would use a constant expansion ratio - say 4:1.

>Tom

>

I thought about that, but constant expansion will give overexpansion at high

chamber pressures, underexpansion at low ones. Pressure and burn rate

measurements should be fine, but thrust and delivered impulse will vary with

expansion.


P'rfesser


>From sedsnm Wed May 27 05:34:56 1998

Date: 27 May 1998 06:49:29 -0500 (added by MTA mail.murraystate.edu)

To: arocket@nmt.edu

From: Terry McCreary

Subject: Re: Comparing propellants?


At 11:11 PM 5/26/98 -0700, you wrote:


>As long as you measure the propellant burn rate and burn rate exponent

>at the chamber pressures you want, it doesn't make a difference.

>

>Anthony

>

I'm looking at comparison of small motors here (29mm) with their inherent

inefficiencies. Also looking at delivered thrust which might be expected to

differ some from calculated thrust. In fact, that's part of the purpose of

the work; i.e., how well do the theoretical parameters (density, burn rate

coefficient, burn rate exponent, expansion) represent delivered performance

in small motors?


If you look at Tripoli and NAR test data, the "delivered impulse" for a

given propellant wanders all over the place. I think Kosdon's fast

propellant has figures between about 180 and 220. Is it TMT testing

procedures? Variation in the propellant itself? Variation in expansion

ratio? Or is such variation normal and expected? That's the purpose of

this study.


P'rfesser


And now a technical question:

When mixing of AP and epoxy, free ammonia is generated - does this also

happend with PBAN ??


Hans Olaf Toft


Date: Tue, 02 Jun 1998 10:59:26 -0700

From: bill

To: Hans Olaf Toft

CC: aRocket

Subject: Re: New aRocket Website


No ammonia evolved when mixing AP with Pban.

BC


To: arocket@nmt.edu

From: Terry McCreary

Subject: Technical question


>And now a technical question:

>When mixing of AP and epoxy, free ammonia is generated - does this also

>happend with PBAN ??

>

>Hans Olaf Toft

>

I wasn't aware that this happened with AP and epoxy; have never noticed it

myself. The AP does react with Tepanol or other bonding agent to liberate

ammonia, though. In any event, AP does not react significantly with PBAN in

my experience.


P'rfesser


Date: Tue, 02 Jun 1998 11:56:12 -0700

From: The Silent Observer

To: arocket mailing list

Subject: Re: New aRocket Website


William Chops Westfield wrote:

>

> When mixing of AP and epoxy, free ammonia is generated - does this also

> happend with PBAN ??

>

> No such odor with PBAN, at least in itty-bitty quantities.

>

> Scary as hell - if you get that ammonia smell when making (pyrotechnic)

> stars, it supposedly means things are about to blow up in your face. (in

> fact, there have been several accident reports of the "I smelled ammonia and

> I tried to carry the bowl outside to dump it, but I didn't make it and spent

> the next several months in the hospital...")

>


Fortunately, there are two completely unrelated mechanisms involved

here. In pyrotechnics, the accidents you've heard about involve

aluminum and nitrates in an unacidified mix; the aluminum reacts with

moisture and the nitrate, steals the oxygen, and leaves the nitrogen

bonded to the hydrogens from the water, generating ammonia which evolves

as a gas. This process generates considerable heat, enough to

accelerate the reaction and, if there's enough water present, to

self-ignite the mixture over some time.


With AP and epoxy (or HTPB, if there's moisture present, apparently),

the ammonium ion is being split off the AP and the perchlorate ion

binding to reactive sites on the resin or hardener -- the ammonium then

combines with the hydrogen freed from the reactive site and evolves as

ammonia gas. Other than the effect of foaming in the propellant, this

is a most un-sinister reaction, even though it has very similar symptoms

to the (usually too late) warning of the aluminum-nitrate self-heating

reaction in pyro compositions.


> There doesn't seem to be any heating involved with the epoxy reaction, but

> it still makes be nervous...


If nothing else, it hurts your propellant performance due to reducing

density, though it can give you back something on regression rate if the

resulting porosity is well distributed. Because it's also using up

reactive sites, it may require adjusting the ratio of hardener to resin

-- which way depending on which component the perchlorate is binding to.


--

Thanks for the comments!


The reason for asking is, that PBAN is out of reach for me, while epoxy

is available and basically related to epoxy. What happends when mixing

AP and epoxy is that there is an imidiate generation of ammonia.

Apparently, this goes on for only a short while. When mixing in vacuum,

there is no porocity problems with the final propellant. We normally mix

for 15 min in vacuum.


Hans Olaf Toft


Date: 9 Jun 1998 06:01:12 -0500 (added by MTA mail.murraystate.edu)

To: arocket@nmt.edu

From: Terry McCreary

Subject: Re: Comparing propellants?


At 01:41 PM 6/8/98 -0700, you wrote:

>With a zero expansion ratio nozzle, your C* could actually be lower than for

>a Cf of 1.0. Cf of .71 was obtained with a specific heat ratio of 1.3

>(normal aluminized ap/al/htpb) and a C* of 4330. Vacuum expansion gives a Cf

>of 1.92 with and expansion ratio of 60 for this same propellant.


Do you have a reference for these values? It would be very helpful.


>This means that if you burn some propellant in a motor with no nozzle exit

>at all, the performance you get is not easily converted to performance with

>an expansion section.


The problem with using an expansion section in comparison studies is that

two motors with the same propellant operating at different expansion ratios

will give different delivered impulse. So for comparison I still have to

normalize.


I can either do all studies at no expansion and calculate performance with

expansion, or do the studies with expanding nozzles and deal with resultant

variations in delivered performance. My feeling is that the former approach

should provide better consistency.


I could use nozzle throats that give the same internal pressure for each

propellant. Then constant expansion would be fine. But that will require

preknowledge of the propellant burn characteristics -- which is part of what

I'm trying to find. I could use a nozzle that would expand to atmospheric

for each burn, but that would also require preknowledge of the burn

characteristics. Plus a different nozzle for each burn, and I'm planning a

LOT of burns (about 30-50 for the initial study, and as many as 8-10

studies). That won't be practical.


P'rfesser


Dave/Kristin Hall wrote:


> > > OBGoodPerformance: Last week we tested a solid rocket motor with

> > > a *measured* Isp of 277 sec. Wohoo!

>

> > What were the chamber and exit pressures?

>

> Chamber = 8000 psi

> Exit = very near 0.0 (guage)

>

> > Were any of the ultra exotic

> > chems used? I.E. nitronium perchlorate or boro hydrides.

>

> Nope. The whole point was: You guys are playing all sorts of hard core

> chemistry games trying to squeeze out another 8 seconds of performance

> when we can get an extra 20 just by jacking the pressure...What a waste.


Chaaaaaamber 8000! Yup,well..... I've been wasting time worrying about

chamber wall thickness

too - let's just all go down to some of the historical sites 'bout 3 am and

lift some of those old cannons,

we could use them for these type pressure vessels.


mike hayes


>From sedsnm Fri Jun 19 06:43:24 1998

Date: 19 Jun 1998 07:58:58 -0500 (added by MTA mail.murraystate.edu)

To: arocket@nmt.edu

From: Terry McCreary

Subject: High Isp


Dave/Kristin Hall wrote:

>

> OBGoodPerformance: Last week we tested a solid rocket motor with

> a *measured* Isp of 277 sec. Wohoo!

>

> Chamber = 8000 psi

> Exit = very near 0.0 (guage)

>

> Nope. The whole point was: You guys are playing all sorts of hard core

> chemistry games trying to squeeze out another 8 seconds of performance

> when we can get an extra 20 just by jacking the pressure...What a waste.


True, you can get substantial improvement in performance by increasing

pressure, but in practical terms a 6" dia aluminum-cased motor would need a

wall thickness of about 1 1/4" (probably more) to handle that pressure.

That's about 25 lb per foot of casing. And that's a lot of weight. Yes,

you can use composite construction but that simply makes the weight penalty

somewhat less.


Playing with the chemistry gives improvement that can be realized at any

pressure.


P'rfesser


>From sedsnm Fri Jun 19 09:25:45 1998

From: Dave/Kristin Hall

Subject: Re: High Isp

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

Date: Fri, 19 Jun 1998 08:22:59 -0700 (PDT)

Cc: arocket@nmt.edu (RocketGeeks)


> True, you can get substantial improvement in performance by increasing

> pressure, but in practical terms a 6" dia aluminum-cased motor would need a

> wall thickness of about 1 1/4" (probably more) to handle that pressure.

> That's about 25 lb per foot of casing. And that's a lot of weight. Yes,

> you can use composite construction but that simply makes the weight penalty

> somewhat less.


Uhmm.... Actually, the case in question weighs less than the normal steel

cases we use around here. Yes, it's thicker, and thus, there is some loss

in available volume for propellent, but the weight reduction and

increased Isp more than make up for the loss. We've checked the

numbers against a "conventional" motor using a CL-20 based propellent

and the high pressure boys (as opposed to the chemistry boys) are winning.


>From sedsnm Fri Jun 19 09:44:10 1998

Date: 19 Jun 1998 10:59:40 -0500 (added by MTA mail.murraystate.edu)

To: Dave/Kristin Hall

From: Terry McCreary

Subject: Re: High Isp

Cc: arocket@nmt.edu


At 08:22 AM 6/19/98 -0700, you wrote:


>Uhmm.... Actually, the case in question weighs less than the normal steel

>cases we use around here. Yes, it's thicker, and thus, there is some loss

>in available volume for propellent, but the weight reduction and

>increased Isp more than make up for the loss. We've checked the

>numbers against a "conventional" motor using a CL-20 based propellent

>and the high pressure boys (as opposed to the chemistry boys) are winning.


I guess I want to compare apples to apples...


It sounds like part of the advantage is the case material (an advanced

composite, presumeably)? If the case in question is reduced in thickness

(with concurrent decrease in weight and increase in propellant volume) so

that it is appropriate for, say 800 psi instead of 8000 psi, does the

high-pressure motor still beat the lower-pressure one in terms of total

impulse? i.e., using same case material for both.


A tenfold reduction in pressure corresponds to about tenfold reduction in

wall thickness. Whether that's significant depends on the actual thickness,

though. About how thick is the casing for this high-pressure motor?


BTW, if the answer to any question asked is "I could tell you, but then I'd

have to kill you", please assume I don't want to know that badly... :-)


Idle curiosity,

P'rfesser


>From sedsnm Tue Jun 23 04:07:34 1998

From: Arno Hahma

Subject: Re: propellant characterization...

To: spiegl@cig.mot.com (Mark Spiegl)

Cc: arocket@nmt.edu


>standard core geometry with 2 ends inhibited was burned. Burn_rate vs

>pressure was estimated, yielding literally hundreds of datapoints. Your


If you are using a tubular grain with linearly increasing burning

surface as a function of burn ratio, you don't even have to estimate

anything. Such a test rocket motor can be used to fully characterize a

propellant in the pressure range the motor delivers. Just remember to

account for the dead volume of the motor in the equations.


The motor with two different burning surfaces (a smaller one changing

stepwise into a larger) gives only two measurement points. However, if

you let the motor "scan" from one surface to another linearly, you can

get as many datapoints as your measurement system bandwidth allows.


>Where do you get these numbers (k, M, T, etc), is the simulated output

>from a thermodynamic program like AFAL or Propep good enough, or must

>these values be empirically determine as well?


Yes, they are good enough.The point is you need to know propellant

characteristics pretty accurately, before you can even build a test

rocket motor to check the parameters out. The theoretical calculations

make far less error to the nozzle diameter than inaccurate

determination or estimation of burn rate data anyway. That is why a

strand burner is a major benefit, you only need one test firing with a

motor to check the data.


As I previously mentioned, the actual pressures are frequently only a

couple of bar off the calculated, but that depends on the propellant,

of course. Some, like AP propellants, are not that good, but some

others behave very much the same in the strand burner as they do in an

actual motor.


>And, realistically, do you calculate pressure/KN from above or is it


Yes, I do. I calculate them from the burn rate data and theoretical

thermodynamic data, at first.


>measured from a small BEM. (just trying to understand the steps in your


Next, I check the data with a test motor, if the propellant has not

been fired in a motor previously. If it has, I simply make a

correction, since I already know, how much differently the propellant

behaves in a motor and into which direction.


> |U| Mark C. Spiegl


>From sedsnm Tue Jun 23 15:45:43 1998

23 Jun 1998 15:45:12 -0600

X400-MTS-Identifier: [/c=US/admd= /prmd=USDOE/; 04B07359021E8851-mtaSNL]

Conversion: Allowed

Original-Encoded-Information-Types: IA5-Text

Disclose-Recipients: Prohibited

Alternate-Recipient: Allowed

X400-Originator: maberna@sandia.gov

X400-Recipients: non-disclosure;

<"04B07359021E8851*/c=US/admd= /prmd=USDOE/o=SNL/ou=ccmail/s=maberna/"@MHS>

Date: 23 Jun 1998 15:45:12 -0600

From: Michael A Bernard

To: VRGNJ@aol.com (IPM Return requested),

mhaze@txdirect.net (IPM Return requested),

ssstolt@seanet.com (IPM Return requested)

cc: arocket@nmt.edu (IPM Return requested)

Subject: Re[2]: Getting Started


The idea is that an aluminum case will "probably" rupture or open in a

longitudinal split when the motor over presurizes. Whereas a steel casing will

"probably" fragment into lots and lots of sharp flying shards. In reality either

could happen to either one. Most snap ring or screw type closures are, and

should be, designed to let loose way before the casing itself goes.


Mike Bernard


From: Larry79054@aol.com

Date: Fri, 26 Jun 1998 03:17:48 EDT

To: arocket@nmt.edu

Subject: Re: Case rupture


John,

May I mention that, for several years now, the RRS has been using a type

of steel tubing for zinc-sulfur rockets called D.O.M. (Drawn Over Mandrel).

This is made from strip steel stock that is rolled up into a cylindrical shape

and then automatically resistance-welded edge-to-edge to form the cylinder.

This cylinder is then passed over a plug (or, as it's sometimes called, a

"turnip" because it sort of resembles one) which smooths out the inside seam

so it is not lumpy, etc., and produces a surface on the seam which is smooth

and seems to be a contiguous part of the wall. The outside seam is smoothed,

too, apparently, because when you look at the tubing, it is often quite

difficult to even see a seam inside or outside at all! The resultant tubing

is rated at least as strong as seamless tubing, has 1/2 the cost, and does not

have the very slight helical twist that seamless usually has down its length

(this seems to be a natural by-product of the extrusion process, not a flaw,

per se.)

Our experience has been nothing but positive and no rockets have

exploded as a result of the type of manufacturing process used. Remember,

zinc-sulfur engines don't have any insulation, so they get extremely hot in

operation. I have fired and "impact recovered" seamless tubing as many as

eight times before a permanent bend was produced in the tubing (although

noticeable bending in two planes was observed after the fifth or sixth

flight), but I don't have personal experience with D.O.M. in that way. I know

others have fired, and impacted, D.O.M. tubing at least twice, so I suspect it

would hold up just as well as seamless. Of course, there's tubing out there

that has seams and nowhere near the quality or strength of the tubing I've

described, so caution is advised. But, don't discard the idea out-of-hand.

Larry Teebken


Date: Fri, 26 Jun 1998 00:38:50 -0700

From: bill

To: Larry79054@aol.com

CC: arocket@nmt.edu

Subject: Re: Case rupture


Standard Conduit (yes EMT) has been used also for micrograin motors since 1949.

Probably hundreds if not thousands of firings. Surprisingly strong, that electric

resistance weld. Motors up to the 3" size which is 3.5 " OD. Richard Nakka has

made KNO3/Sugar rockets from the same material. The micrograin motors do get hot

enough to flow the zinc plating on the tubing!

Bill Colburn


Date: Sun, 02 Aug 1998 12:09:07 -0700

From: Anthony Colette

To: Henry Spencer
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