What Are Our Motors "Missing"?

Lentamental said:

Just started work on a project at the University of Vermont to launch a 2 stage rocket from a weather balloon,.

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Where are you planning on launching?

The Super Loki burns for 2 seconds and has an average chamber pressure of 1200 PSI (max of 1500 PSI). These pressures are twice what you'll see in the typical HPR or EX motor of that size. It's nearly a full 'O' in a 4" casing. The key is that the casing is 0.083" wall aluminum (the thickness of a 38mm casing!). The case-bonded single grain requires less insulation, giving a higher volume loading. The closures, nozzle, and insulation are engineered to reduce heat transfer into the casing. One-time use, no recovery. 37.5 pounds of propellant out of a total of 51 pounds (including fins and interstage adapter). The booster only went to 6800ft. APCP at about 82% solids (nothing special in formulation, but better processing). It could send an 18 pound dart to almost 250Kft.
See: THE SUPER LOKI DART METEOROLOGICAL ROCKET SYSTEMS

Beyond the Loki-Dart, many of the professional sounding rockets have steel casings and operate at high pressures. This increases the Isp while increasing the mass fraction of the propellant. Again, single case-bonded grain (unlike the Bates grains with thick liners that HPR and most EX motors have). Also, better propellant processing for reliability and density (not necessarily more energetic than typical amateur propellants).

MClark said:

Where are you planning on launching?

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Like most Rockoons, they'll launch inside their computer. Then scrap the idea once the reality of the logistics sinks in.

jsdemar said:

Like most Rockoons, they'll launch inside their computer. Then scrap the idea once the reality of the logistics sinks in.

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Hey, I wanted to hear his dreams.

cjl said:

That's true that many missiles do not use APCP, but most of the non-AP based propellants are actually worse than APCP in performance. Missiles use them mainly for their low smoke output, since that is a rather important factor when you are using a missile in a fight. You don't want a smoke trail leading back to where you are. However, APCP/HTPB propellants are really quite good in efficiency, and only fall behind high energy composite propellants among the current crop of solid fuels (which are used in things like modern ICBMs). As stated above, the biggest factor is the mass ratio. Our motors and rockets in general don't have a very good mass ratio, and even the best probably don't exceed 50-60% (I have an N5800 altitude rocket on the drawing board for example, and even with as much weight shaved off as I dare, it's looking like it'll be about 45-50% propellant mass fraction, which isn't very good compared to many sounding rockets). For comparison, the Arcas had 42 pounds of propellant in a 65 pound rocket, a mass fraction of 65%, and it only had a very slightly larger cross section than my rocket will (since mine is a 4 inch minimum diameter). Having 15% better mass fraction, similar cross sectional area, and a bit more than twice the total impulse does a LOT for performance.

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Some military missiles use double, and triple base propellants, these are more efficient Isp wise, but they have two major problems; one, they contain nitro glycerin, and two, they erode nozzles badly. These propellants are strictly prohibited for use in hobby rocket motors.

Jeremy

jsdemar said:

Like most Rockoons, they'll launch inside their computer. Then scrap the idea once the reality of the logistics sinks in.

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Not entirely incorrect.
I've been doing a bunch of thinking, but by just started, I mean JUST started. Proposed the project to the IEEE last monday, and am taking them all to the CRMRC launch this weekend. With a little luck that will give them the motivation to start really working on the project.
I know rockoons are impractical for scaling up, but they really do work well at this size.

deandome said:

so the bare STEEL airframe would have to weigh less than 10 lbs...a tall order in a cheap, 1959 rocket.

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STEEL is such a naughty word.... Makes me think of a 200lb per foot I-beam...

Yes, in 1959 we had advanced metalurgy that was combining "alloys" of metals. Aerospace steels, i am guessing have quite a high carbon content, and good ammounts of titanium. not so much Iron- like the old building I beam.. missle cases are still made of steel(not that an average person could buy that type of steel...- Back to freds post)

Remember 59, was a good 12 years after the aliens crashed in roswell NM.. and gave us the x-15 and SR-71 :headbang:
(maybe that was an international secret)
haha...

"what makes your rockets go up? FUNDING.. no bucks no Buck Rogers"

Or like the sign said in the speed shop "Speed is just a question of money, how fast do you want to go??"

A big difference I heard about from a military motor builder was that his motors cost as much as your house.
Mine cost about as much as a mouse (buttons-and-wheel type, not snake-snack type).

deandome said:

1) Could a well heeled, experienced hobbyist create a 1:1 scale model of the Arcas where the airframe/motor liner weighs as much/less than that of the original Arcas? I think the answer is yes, ala the CF/honeycomb/etc. build you mention below. I think they could go much lighter, in fact, than the 15-20 lbs of the old airframe.

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Mark already answered this one (before it was asked), but here's another data point: USC's 2010 project was a 4" airframe (slightly smaller than an Arcas) with a carbon fiber cased O motor. It went to 59,000 feet at Mach 4.2. The motor contained 24 lb of propellant and the airframe weighed 20 lb (all-up, ready to fly). Mucho losses here to drag (M=4.2 is fast), but with a different velocity profile (like Adrian and Lentamental and others have mentioned), something like this could do it.

deandome said:

BTW, I'm not so sure about cjl's statement that a 64 lb arcas had 42 lb of propellant; it had a 10 lb payload, a bunch of insulation, recovery gear, electronics...so the bare STEEL airframe would have to weigh less than 10 lbs...a tall order in a cheap, 1959 rocket.

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ClayD hit this one spot on (hi Clay! ), as did Chris. Steel airframes can be extremely thin (e.g., the ASP IV rocket used a 0.035" wall case).

deandome said:

Would said 1:1 scale, 64 lb total-weight clone hit 32 miles with 42 lbs of one of our current propellants?

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Given an Arcas-style thrust profile, YES, because the physics hasn't changed, and the propellants have only improved. And in case you're still incredulous, here's some RASAero plots for a very conservative Arcas-like vehicle, assuming a propellant Isp of somewhere around 200-210. The volumetric loading of an endburner is 1, BTW.

deandome said:

I don't think so...thus this thread.

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See here's my issue with this thread at this point -- your question has been answered multiple times by people who actually work in the aerospace field (or, in Mark's case, actually built sounding rockets like this for a living), and you are refusing to accept their answers based purely on a hunch that you "don't think" they're being honest or know what they're talking about.

One of those papers in that old lit review I wrote that Mark found eyepop: awkward first year grad school writing, sorry) was written by Merrill King who -- guess what? -- worked at Atlantic Research. And the propellant formulations given in the paper? Yeah, Arcas/Arcon/METROC. One's an AP-based PVC plastisol (totally 1950s technology, no matter what Darryl says :cyclops and one's an AP/HTPB/DOA formula. Both were modified with the addition of silver wire. And that's it. So can we please consider it settled that there's no conspiracy about propellant formulation here?

Jclark said:

Some military missiles use double, and triple base propellants, these are more efficient Isp wise

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:: le sigh :: NC, NG, GAP, and HMX are in the library of the PEP code that everyone has access to. Heats of formation and chemical composition of more exotic things (that didn't exist when the Arcas was built -- CL-20, TAGzT, BTATz, SMX...) are floating around the internet machine -- you can put them in yourself. Optimize a propellant formulation or two and you'll quickly see that DB/CMDB/XLDB formulations aren't really used for Isp...

daveyfire said:

See here's my issue with this thread at this point -- your question has been answered multiple times by people who actually work in the aerospace field (or, in Mark's case, actually built sounding rockets like this for a living), and you are refusing to accept their answers based purely on a hunch that you "don't think" they're being honest or know what they're talking about.

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That's the main thing I've noticed about this thread as well.

Nothing anyone has said here has come close to asserting/proving a hobbyist could hit TWO HUNDRED THOUSAND FEET with a 4.3" diam x 7' long airframe with 42 lbs of ANY of our hobby propellants (and the Arcas probby had more like 30-35 lbs).

We have slow burning propellants...fast burning ones...end burners and even combinations (slow, THEN fast). I THINK one could design a motor that would match the burn time of the Arcas and/or mimic the thrust curve...but if the curves are the same shape, the one with APCP would be well below the Arcas' on the graph. We CANNOT match the thrust AND thrust profile of that propellant, thus we cannot hit 200K with any of our current propellants...in ANY configuration/combination...with the identical airframe, airframe/accessories weight & propellant weight.

But thanks to your false assertion that someone here HAS demonstrated that possibility...and my refuting it...I just found a detailed description what you just stated about the silver wires. Simply put, Arcas' propellant was indeed fundamentally different & more 'potent' than ours : https://www.tdkpropulsion.com/wp-content/uploads/2010/06/WireLitReview.pdf

In the United States, the concept of increasing propellant burn rates with embedded metal wires was first explored by Rumbel, et al. at Atlantic Research Corporation in 1955 [2]. ARC used this technology in several sounding rockets, beginning in 1958 [6]. The most successful of these vehicles, ARCAS, remained in use until 1991 [7]. These sounding rockets were designed using PVC plastisol propellant [8], and the inclusion of axially embedded wires in the propellant grain produced a burning rate enhancement of nearly 400%. This allowed the vehicles to use an endburning grain geometry, resulting in gentle vehicle acceleration and burn times between 17.5 and 29.2 seconds – ideal for fragile electronic payloads
[6].

Wire enhancement of burning rate also proved popular for missile development. The endburning configuration pioneered by ARC produced not only longer action times, but also higher mass fractions, allowing the developed missiles to be smaller. As such, wire-enhanced motors were fielded extensively in the Redeye and Stinger missile programs [9].

3. Theory of Operation
The seminal model of the combustion process of a propellant with embedded metal wires was developed by Caveny and Glick in 1967 [5]. It was the first model to account for both transient and steady-state burning rates of propellants with embedded wires, and thus can be used to model either chopped wire distributed throughout the propellant, or stranded wire embedded as a single piece in the grain. [see the PDF for the whole, 11 page treatise]

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There were a lot of interesting things said here but I ended up answering my own question by finding out a) Arcas propellant (and those used in other small military/research rockets) is indeed much more 'energetic', pound-for-pound, than what we use, and b) what the differences are that make 'a' true.

I guess the next question is, 'why don't any of our motors use metal wires like this?' Maybe it only works in the PVC base stuff, not APCP? Maybe they explain it in the paper I link to...but I need to go get another degree before I can digest it's finer points.

deandome said:

Nothing anyone has said here has come close to asserting/proving a hobbyist could hit TWO HUNDRED THOUSAND FEET with a 4.3" diam x 7' long airframe with 42 lbs of our propellant (and the Arcas probby had more like 30-35 lbs).

But thanks to your false assertion that someone here HAS demonstrated that possibility...and my refuting it...I just found a detailed description what was in the Arcas' propellant. Seems like it was indeed fundamentally different, both in it's 'PVC plastisol' base compound & then...moreso...by the then-revolutionary utilization of metal fibers inside the grain (someone here did hint at this earlier in the thread) : https://www.tdkpropulsion.com/wp-content/uploads/2010/06/WireLitReview.pdf



There were a lot of interesting things said here but I ended up answering my own question by finding out a) Arcas propellant (and those used in other small military/research rockets) is indeed much more 'energetic', pound-for-pound, than what we use, and b) what the differences are that make 'a' true.

I guess the next question is, 'why don't any of our motors use metal wires like this?' Maybe it only works in the PVC base stuff, not APCP? Maybe they explain it in the paper I link to...but I need to go get another degree before I can digest it's finer points.

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Adding wires doesn't make it "pound for pound more energetic". That parameter is the specific impulse, Isp. The wires increase the burn rate so that the end-burning configuration can produce enough thrust. Like an F10, but bigger. I'd love to see an end-burning 4" P, even if it takes embedded wires to increase the burn rate fast enough to get enough thrust.

Jclark said:

Some military missiles use double, and triple base propellants, these are more efficient Isp wise, but they have two major problems; one, they contain nitro glycerin, and two, they erode nozzles badly. These propellants are strictly prohibited for use in hobby rocket motors.

Jeremy

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Those actually tend to be worse in terms of Isp than a good APCP. A double base propellant consisting of nitrocellulose and nitroguanadine has a maximum theoretical Isp of about 247 seconds for example (at 10MPa Pc), while a 20% aluminum APCP can exceed 270 seconds at the same chamber pressure. The main benefit of double base propellants is a relatively small plume and low smoke output.

deandome said:

I guess the next question is, 'why don't any of our motors use metal wires like this?' Maybe it only works in the PVC base stuff, not APCP? Maybe they explain it in the paper I link to...but I need to go get another degree before I can digest it's finer points.

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Maybe you should go get another degree, because I do believe daveyfire is going for his PhD in this specific discipline.

Chill out.

deandome said:

We have slow burning propellants...fast burning ones...end burners and even combinations (slow, THEN fast). I THINK one could design a motor that would match the burn time of the Arcas and/or mimic the thrust curve...but if the curves are the same shape, the one with APCP would be well below the Arcas' on the graph.

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You keep asserting it, and it continues to be wrong. The Arcas had a specific impulse of around 240 seconds, which is completely doable with APCP. Several hobby propellants do indeed come fairly close, and with a more optimized nozzle and higher chamber pressure than most hobby motors use, it wouldn't be difficult at all.

deandome said:

We CANNOT match the thrust AND thrust profile of that propellant, thus we cannot hit 200K with any of our current propellants...in ANY configuration/combination...with the identical airframe, airframe/accessories weight & propellant weight.

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Sure we can. It would be somewhat challenging, as the burn rate would need to be astronomical by hobby propellant standards, but it isn't undoable. A catalyzed propellant with possibly some wires for increased burn rate would be able to hit similar numbers without any impossible technologies required.

deandome said:

But thanks to your false assertion that someone here HAS demonstrated that possibility...and my refuting it...I just found a detailed description what you just stated about the silver wires. Simply put, Arcas' propellant was indeed fundamentally different & more 'potent' than ours : https://www.tdkpropulsion.com/wp-content/uploads/2010/06/WireLitReview.pdf

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The wires increase the burn rate. That is all. They do not increase the energy content at all.

(What's entertaining about you quoting that specific paper is that its author is here on the thread. Daveyfire wrote that paper )

deandome said:

There were a lot of interesting things said here but I ended up answering my own question by finding out a) Arcas propellant (and those used in other small military/research rockets) is indeed much more 'energetic', pound-for-pound, than what we use, and b) what the differences are that make 'a' true.

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Nope. It has a specific impulse of 240ish. That's about the same as a really good hobby propellant, pound for pound.

deandome said:

I guess the next question is, 'why don't any of our motors use metal wires like this?' Maybe it only works in the PVC base stuff, not APCP? Maybe they explain it in the paper I link to...but I need to go get another degree before I can digest it's finer points.

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Because we don't need to. As I stated above, the metal wires only increase the burn rate, and no hobbyist has so far demonstrated a significant need or desire for anything faster than warp 9 or vmax. Wires also add to the manufacturing difficulty, so you don't want to use them unless they are necessary (and we don't need a higher burn rate at the moment).

patelldp said:

Maybe you should go get another degree, because I do believe daveyfire is going for his PhD in this specific discipline.

Chill out.

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Yep. David lives and breathes this stuff. One of the very few people I have ever known, maybe the only person I have ever known :wink:, that took a Father and Son hobby and is making it into a career. Livin' the dream.

Now I know being an 'expert' doesn't mean one is always right... but it does mean you might want to think two or three times before betting against his information.

Your mileage (or altitude) may vary. I wish I understood everything in this thread, but like Fred said, I am not an aerospace engineer. I just put little tubes of propellent into wood and paper thingies and most of the time I get them back to do it over again.


BTW: Daveyfire is a really nice guy as well and it always seemed to me to take a lot before he throws up his hands in 'mild' disgust. :wink:

I get that better now...but the ISP of this PVC stuff has to be a LOT higher, too...it's not all the burn time at good thrust. If just adding a few wires to ACPC would give us those kind of altitudes in small rockets, people (EXP) and/or mfgs would be offering it.

Adrian A said:

Adding wires doesn't make it "pound for pound more energetic". That parameter is the specific impulse, Isp. The wires increase the burn rate so that the end-burning configuration can produce enough thrust. Like an F10, but bigger. I'd love to see an end-burning 4" P, even if it takes embedded wires to increase the burn rate fast enough to get enough thrust.

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deandome said:

I get that better now...but the ISP of this PVC stuff has to be a LOT higher, too...it's not all the burn time at good thrust. If just adding a few wires to ACPC would give us those kind of altitudes in small rockets, people (EXP) and/or mfgs would be offering it.

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Sigh.

They have all stated the ISP is 240 for the ARCAS propellant. Please note that CTI has obtained north of an ISP of 220 with a mass producible propellant. Couple that with casing optimization (READ SINGLE USE), single use boosters with no recovery (AGAINST TRA AND NAR REGULATIONS), and very good manufacturing of the propellant, there is no difference between the ARCAS and what we are doing now.

If someone cared to go through the pain and suffering of adding wires, they would. In the Example of Derrick Deville, he didn't need to, rather than fuss with that he just made a bigger motor to go 100k feet plus.

I suggest we just let this troll continue on his own and disregard further comments.

cjl said:

Because we don't need to. As I stated above, the metal wires only increase the burn rate, and no hobbyist has so far demonstrated a significant need or desire for anything faster than warp 9 or vmax. Wires also add to the manufacturing difficulty, so you don't want to use them unless they are necessary (and we don't need a higher burn rate at the moment).

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I'm FINALLY getting it, but I have to wave a flag at this. Why the Arcas works...as I NOW see it...is that it is a LOOONG burn, but at a higher thrust than we can get with our end burners...so when it gets to 30K feet or so, it's still burning for another 20 sec or so (guess), and because the air is thinner, burning at this altitude gives you a LOT more 'effeciency'. We could (maybe) match that burn time, but the thrust would be a lot lower, so after 10 sec, it's much lower, so the energy is being wasted fighting drag. The total impulses are the same, but the Arcas using a lot more of it in thin air.

The wires do that, I guess...I see them as either making slow-burn propellants give higher thrust, or slowing down fast-burning ones/high thrust ones (Warp 9) if that makes any sense.. But bottom line, a lot of 'us' want to go as far as we can with a particular size/weight (rocket and/or motor).

So if we COULD match this kind of long burn/high(er) thrust performance, we WOULD. People would pay TRIPLE the price for an "Arcas-type" motor that would increase their altitudes 4-10x over all the other motors in the same total impulse class.

Apparently, we can't do that...even the mad scientist EXP guys...or else SOMEONE would have had a 65 lb rocket hitting 200K' by now (or a 30 lb rocket hitting 100K, etc). So you experts can keep saying "yes we could do it", but you're kinda neglecting to finish that statement. It should read "yes, we could do that IN THEORY...but nobody seems to know how to get APCP to burn long & hard like that low/1959-tech Arcas motor does, or even get in that ballpark, even though hobbyists have access to lighter/stronger airframes, motor casings & nozzles".

aren't the shuttle boosters stranded..

I think there has been some exer's who have made stranded propellant.

(i didnt think it increased the burn rate, but the burn surface area..)
Propogating thermal energy into the propellant.

Dont forget, your delivered and theoretical ISP are different......
a propellant ISP may have a 240ISP, but in a bad motor design only deliver 175.

I think the fact it was done in 1959 means it could be done again. Reproducing and Arcas, isnt really REsearch.

Clay

Adrian A said:

I'd love to see an end-burning 4" P, even if it takes embedded wires to increase the burn rate fast enough to get enough thrust.

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ME TOO!! ARC got it to work in their 4.5" design with an asbestos-EPDM liner; the 6" ARCON kept burning through, so they had to scrap it. 4" with, say, calendared Kevlar-EPDM would probably work if we got the burning rate up high enough.

deandome said:

We CANNOT match the thrust AND thrust profile of that propellant

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Nono, we can. I still don't understand where you're getting this idea from that our technology is outmoded compared to 1950s sounding rockets.

deandome said:

But thanks to your false assertion that someone here HAS demonstrated that possibility...and my refuting it...I just found a detailed description what you just stated about the silver wires. Simply put, Arcas' propellant was indeed fundamentally different & more 'potent' than ours : https://www.tdkpropulsion.com/wp-content/uploads/2010/06/WireLitReview.pdf

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(I hope you see the irony in your "refutation" of my "false assertion" by citing something that I wrote for a class and then posted to my blog )

deandome said:

There were a lot of interesting things said here but I ended up answering my own question by finding out a) Arcas propellant (and those used in other small military/research rockets) is indeed much more 'energetic', pound-for-pound, than what we use, and b) what the differences are that make 'a' true.

Click to expand...

So the difference is... silver wires? Here, I screencapped the formulation table out of King's paper and attached it. I scrubbed out the ones and decimals of the percentages (since this is the Prop forum, not the Rx one), but any prophead worth their salt could optimize these formulations for specific impulse (your "pound-for-pound" measure), with or without silver wire, and see that they're identical to (or underperform, in many cases) our hobby-grade propellants. 50's technology, woo.

Perhaps doing the calculations would help you -- in case you're not aware, there's a free program called PEP that's in wide distribution (e.g. https://www.lekstutis.com/Artie/PEP/) that you can download and run various rocket propellant formulations through to see what the specific impulse will be. Go download it and put in the Arcas formulation (or something close to it), add some silver, and see what the Isp is. Run a standard AP composite next. See what the difference is. You'll probably be surprised at the lack of difference. (It might even take some bold and italic formatting.)

deandome said:

I guess the next question is, 'why don't any of our motors use metal wires like this?' Maybe it only works in the PVC base stuff, not APCP? Maybe they explain it in the paper I link to...but I need to go get another degree before I can digest it's finer points.

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Well, yeah, I (since I'm "they") tried to explain it -- and that's one of the relatively non-math-y points of the paper -- but basically, processing propellants with silver wire is like processing a 50/50 blend of cat hair and sand in rubber cement. It's just awful. I have some silver wire I could send you if you want to try it. Here's me with a bag of the stuff:

The propulsion world has since moved on to modifying burning rate with various chemical additives to provide speed without the processing issue.

The main things preventing long burns like this from taking ahold in the hobby market, as I can see it, are the insulation issue, and the long burn time. Ported geometry motors (e.g., BATES) have propellant to insulate the case during the entire burn time. End burners expose the aft end of the case to the entire mass flow of the propellant -- after 30 seconds, you're asking for trouble without some serious insulation and thermal management (NFPA 1125 200 C external case temperature requirement, remember). Also, low thrust/long burn motors tend to only work well in small, light, Arcas-like rockets, thus making them a niche market that manufacturers probably won't want to cater towards, just due to the fact that certifying and producing a motor takes some opportunity capital.

BTW, dude, chill man. It's a thread on a hobby forum, this is me relaxing (instead of studying). No bold needed.

(and with that I will stop feeding the troll.)

gdjsky01 said:

BTW: Daveyfire is a really nice guy as well and it always seemed to me to take a lot before he throws up his hands in 'mild' disgust.

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Thanks man! Looking forward to being back at Lucerne sometime soon

Not to mention that they are also classified as 1.1 HE.



JD

Jclark said:

Some military missiles use double, and triple base propellants, these are more efficient Isp wise, but they have two major problems; one, they contain nitro glycerin, and two, they erode nozzles badly. These propellants are strictly prohibited for use in hobby rocket motors.

Jeremy

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I have been involved with making literally tons of PVC propellant for auto airbags. Those grains we made on a compounder extruder and had thin webs and lots of perfs. We tried to make not using the extruder solid grains and standard looking single pref grains of reasonable size (2" or so) and they tend to get cracks. The thermal expansion is bad and by the time the grain is heated to the center to cure (It is thermosetting) the outside is overcooked. We did develop a technique to make good grains but it was a pain in the but and not worth it. I believe it was used by ARC because it was what they had at the time.

PVC is not the answer

The wires are a pain to do, very labor intensive. I know an old guy that was involved in a different system that gave the wires a try and it was abandoned for easier but more scary methods of increasing burn rate. The wires he used were silver and a fixture to string them in the case is needed. A BIG problem with the wires is getting the propellant to bond; a disbond allows the flame to flash along the wire and boom.

Wires are not the answer.

The guys going real high likely feel it is easy, more cost effective and will have a greater success to just make the rocket bigger. In commercial motors no one would pay the price for not just the labor and materials to make a wired motor but also the development costs prorated on the few motors that would be sold.
The only practical application for the very fast burn would be end burn grains. In a core burn motor the Warp and the like already tear up rockets and are a novelty motor, faster would not sell more motors.

Mark

daveyfire said:

...this is me relaxing (instead of studying).

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David, thanks for taking the time for posting this stuff and sharing your insight and expertise. I've learned a lot from this thread.

deandome said:

The wires do that, I guess...I see them as either making slow-burn propellants give higher thrust, or slowing down fast-burning ones (Warp 9) if that makes any sense..

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The wires make every propellant faster, even the fast ones. What is different on the ARCAS, is that it is using an end burning configuration.
Lets compare the AT H999 and the I49.
https://www.thrustcurve.org/motorsearch.jsp?id=156
https://www.thrustcurve.org/motorsearch.jsp?id=719

Thats the same propellant, but in a different configuration (BATES vs. end burning). Now lets assume we are building a much longer motor, based on the design of the I49. If the motor becomes pretty long it might become an K, but it will be an K49. Playing this further, the thrust stays still the same but the rocket becomes heavier until the point is reached were it doesn't make any sense at all. A M49 would hardly be able to lift its own weight. Now if you embed wires into the propellant, you can increase the burn rate about 4 fold, changing our imaginary M49 into an 38mm M196 (its still an M). This would probably be a great motor for high altitude shots, assuming it would get an assisted kick out of the launcher, like the ARCAS does.

However, don't hold your breath that AT will produce such a motor. When somebody, I believe Adrian, inquired about an full I, Gary indicated that they might have to use a thicker liner. Thats the impressive thing on the ARCAS motor, it burns for 30s with only a relative thin layer of insulation between the chamber and the casing.

Reinhard

mikec said:

David, thanks for taking the time for posting this stuff and sharing your insight and expertise. I've learned a lot from this thread.

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seconded.

it does beg the question, especially of EXers, why has nobody really done a dart attempt at 200k+ AGL.

it's about finding the most efficient way to get there with the amount of thrust you have available. like anything else, you can't go too fast too low, or you'll use all your thrust ripping through the atmosphere...

very cool stuff, and thread. i wish there were more topics on tailoring rocket design to achieve utmost efficiency. i imagine even basic commercial F and G motors could be attaining much more altitude with some tweaking in the airframe design.

the boosted dart design itself is an attempt at creating a more efficient vehicle. most of the mass is contained in the booster, which disconnects from the dart, which has been optimized for efficiency itself.

i would be interested in reading more about boosted dart design, as well as optimizing airframes for efficiency based on available thrust, as well as a specific thrust profile. if anyone has any pertinent links or references, dont hesitate to post up.

thanks.

Reinhard said:

The wires make every propellant faster, even the fast ones. What is different on the ARCAS, is that it is using an end burning configuration.
Lets compare the AT H999 and the I49.
https://www.thrustcurve.org/motorsearch.jsp?id=156
https://www.thrustcurve.org/motorsearch.jsp?id=719

Thats the same propellant, but in a different configuration (BATES vs. end burning). Now lets assume we are building a much longer motor, based on the design of the I49. If the motor becomes pretty long it might become an K, but it will be an K49. Playing this further, the thrust stays still the same but the rocket becomes heavier until the point is reached were it doesn't make any sense at all. A M49 would hardly be able to lift its own weight.

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That's if you kept it at 38mm. I think as you increase the end area you'd increase the thrust proportionally. So a 4" endburning M (or N or L or K) might be about a []350. An M350 would be cool, but not many people could either provide the light weight and tower necessary to get it going fast enough at liftoff, or better yet, the kick-butt booster you'd need to get it going really straight.

Reinhard said:

Now if you embed wires into the propellant, you can increase the burn rate about 4 fold, changing our imaginary M49 into an 38mm M196 (its still an M). This would probably be a great motor for high altitude shots, assuming it would get an assisted kick out of the launcher, like the ARCAS does.

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As I think about the ARCAS, the breach loading launcher is probably the biggest show-stopper about getting similar performance from a single-stage hobby motor. But put a small Vmax or Warp-9 booster stage under it to get it some speed out of the tower, and now you're talking.

Reinhard said:

However, don't hold your breath that AT will produce such a motor. When somebody, I believe Adrian, inquired about an full I, Gary indicated that they might have to use a thicker liner. Thats the impressive thing on the ARCAS motor, it burns for 30s with only a relative thin layer of insulation between the chamber and the casing.

Reinhard

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Wow, good memory. I did ask about it when those came out, and said that from an altitude record designer's perspective, it would be worth losing some propellant volume fraction to a thicker liner in order to get the full I impulse. Gary replied that he'd think about it, and that was the end of that as far as I know.

About 10 years ago, I worked on an endburner design for tiny high-performance motors. It was more difficult than making a P motor. With an endburrner, all the things that optimize burnrate and Isp also cause thermal problems and casing failure. Mitigating those problems reduces volume loading and mass fraction. You can chase your own tail until the motor can't lift itself. I ended up with a thin CF casing, ablative liner, and a highly-catalyzed propellent with milled AP.
https://thrustgear.com/micro/
Here is the same propellant (toned down a little) in a 38mm Bates grain configuration (1400 psi, Isp=227, 0.5sec burn plus tail):
https://thrustgear.com/oldtests/DSCN0582.MOV
https://thrustgear.com/oldtests/WB238H323.gif

If I were to cast a similar propellant into a thin steel casing with a good ablative liner, it would perform like an Arcas. It would require a lot of engineering and test (which equals $$$$). But, as others have pointed out, just make a bigger motor.

( Deandome is an ancient troll-like creature. If you look up "troll" in the dictionary, do you know what you'll find? No, not a picture of Deandome! Look for him under 'I', somewhere between idiosyncratic and idle. )