Longest burn time commercial or EX amatuer motors?

[Andrew_ASC]

Any type. Any class. Sounding rockets are making these amatuer motors pale in burn time. 20-40s+. So what's the longest burn motors tried? I could care less about matching the thrust curve. I'm thinking any APCP fuel ran that long would melt an aluminum casing or hit a maximum specific impulse barrier allowed.

Pulled up 325 lbf at 1020 psi chamber pressure off an Arcas at 29s.
Warp 9 does 340 lbf at unk pressure out of a I class 38-480 for 0.3s.
The rest blows my mind looking past Arcas specs of burn times today much less thrust specs.
Randomly got curious.

 

[MClark]

Kosdon made a few 42 second I motors. End burn. Thick Phenolic case, burned halfway through. Next step that never happened was to taper case thickness to reduce weight.
At end of burn graphite nozzle was glowing.

M

 

[ksaves2]

Kosdon made a few 42 second I motors. End burn. Thick Phenolic case, burned halfway through. Next step that never happened was to taper case thickness to reduce weight.
At end of burn graphite nozzle was glowing.

M

I was going to shoot off my mouth Mark but I caught the phenolic case so I quess it was one time use eh? Would carbonize the back end of a cardboard rocket to charcol?
I did a one time use 24mm high L/D aluminum case and the nozzle crumbled after the test burn. It burned in <1 sec though. Aft snap ring bowed out and was just about to let go. Kurt

 

[Andrew_ASC]

Do you have any ideas of how long the kosdon casing was?

 

[rstaff3]

Kosdon made a few 42 second I motors. End burn. Thick Phenolic case, burned halfway through. Next step that never happened was to taper case thickness to reduce weight.
At end of burn graphite nozzle was glowing.

M

What the heck would one fly that in? Come in around 15N avg? Or did I botch something?

 

[MClark]

Ksaves, yes to all.
I need to make a correction. The 42 sec burn motor was referred to as H8 (yea, works out to a light I) and there was a I19 with ballpark a 30 second burn.
H8 propellant was cast into standard 29mm casting tube, the I into 38mm. Rough estimate at 0.3"/sec 12.6" would be required for 42 seconds.
We did 20 second burn 4" motors with bates grains and a double secret AN propellant .

 

[MClark]

What the heck would one fly that in? Come in around 15N avg? Or did I botch something?

Used Estes tube and nose cone, tube launched with piston and black powder boost charge. Motor diameter was nonstandard but the I fit nicely into 1.6" tube.

 

[Andrew_ASC]

Roxel Group might manufacture some of that stuff. Whatever your referencing I don't think is normal ANCP or APCP. NATO had some burn test on FOX fuel and its smokeless. HMX explosives additives. Doubled based nitro stuff. Google has patents on rocket motors for 2.75" application (Folding fin aerial rocket???) Crosslinked stuff I never even heard of that doesn't use AP. Then this at Roxel's page for tactical missiles and other military applications.

Never seen pictures of a yellow black spotted rocket fuel before. I don't want to know. LOL.

 

[DavidMcCann]

There is tons of info out there on the ARCAS, some references to the propellant, but I haven't been able to find anything even resembling a formula.

 

[rstaff3]

Used Estes tube and nose cone, tube launched with piston and black powder boost charge. Motor diameter was nonstandard but the I fit nicely into 1.6" tube.

There's some old-school craziness. I like it!

 

[G_T]

At reasonable pressure, say, 500-1000psi, APCP generally burns in the range of 1/8"/sec to 3/4"/sec depending on formulation, roughly speaking. Wired, it can go up to around 2 1/2"/sec. The rest would be obtained by geometry of the grain.

For instance, a propellant which burns at 3/16"/sec in a 6" diameter motor (say, 5 1/4" propellant OD) with a 1.25" core, would burn for approximately 11 seconds.

Our motors aren't large enough diameter to get really long burn times with bates or other cored geometries, without badly degrading the delivered ISP.

For end-burning though, the problem is getting enough thrust to be useful. That requires very fast burning propellant which puts it out of the range of what most amateurs could reliably produce. Then if you've got the thrust, well, in the same size case, you'll end up with roughly the same burn duration. There is only so much oomph you can stick into the case.

Astrobee-D motor, going by memory: 8' long. 6" diameter. Approx 220# loaded, 180# propellant. Burn duration, as a dual-thrust, of 13 seconds. That's well within amateur range of production. I'm probably off in my numbers somewhere but you get the point. Size matters. You get longer burn for sounding rocket motors because the grain(s) are bigger, but the burn rate is the same range as ours.

Gerald

 

[ksaves2]

At reasonable pressure, say, 500-1000psi, APCP generally burns in the range of 1/8"/sec to 3/4"/sec depending on formulation, roughly speaking. Wired, it can go up to around 2 1/2"/sec. The rest would be obtained by geometry of the grain.

For instance, a propellant which burns at 3/16"/sec in a 6" diameter motor (say, 5 1/4" propellant OD) with a 1.25" core, would burn for approximately 11 seconds.

Our motors aren't large enough diameter to get really long burn times with bates or other cored geometries, without badly degrading the delivered ISP.

For end-burning though, the problem is getting enough thrust to be useful. That requires very fast burning propellant which puts it out of the range of what most amateurs could reliably produce. Then if you've got the thrust, well, in the same size case, you'll end up with roughly the same burn duration. There is only so much oomph you can stick into the case.

Astrobee-D motor, going by memory: 8' long. 6" diameter. Approx 220# loaded, 180# propellant. Burn duration, as a dual-thrust, of 13 seconds. That's well within amateur range of production. I'm probably off in my numbers somewhere but you get the point. Size matters. You get longer burn for sounding rocket motors because the grain(s) are bigger, but the burn rate is the same range as ours.

Gerald

Hi Gerald,
I see Catocene and Ferrocene is available at RCS now. Yeah, my jaw dropped when I saw that and I hear some are working with it now. I think Dr. Frank
had the concept right, single use. I believe the idea of a tapered case like Mark mentions above would be needed to pull this of consistently.
That would be a tough nut to crack economically along with the SU graphite nozzle. An inquisitive experimenter could pull it off I bet but it would be an
investment on a relatively lone burning low powered motor. Kurt

 

[Andrew_ASC]

Yes. I heard use small amounts of CATOcene.

 

[Andrew_ASC]

But a sounding rocket is fundamentally different. If you compare the same fuel APCP type to other, the sounding rocket wins on volumetric efficiency because the airframe is the casing and it's R radius value is always slightly more than negligibly larger than a hobby rocket with a casing restricting radius. Perhaps amatuers could advance to liner bonded carbon fiber or aluminum airframes someday.

 

[Andrew_ASC]

It just has more propellant in the same volume.

 

[markkoelsch]

Aerotech used to make a motor called the i32. If memory serves it was about a twenty second burn.


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[Andrew_ASC]

That would be a tough nut to crack economically along with the SU graphite nozzle. An inquisitive experimenter could pull it off I bet but it would be an investment on a relatively lone burning low powered motor. Kurt

Scale it down to 13-18mm size. And economically it's not so bad to tinker with. It would be small enough that a drill press could make crude nozzles rapidly with less machining. You may be able to find 1" tubing extruded aluminum cheaper to play with than odd ball metric hobby tube sizes. That Catocene is still $70 a bottle.

 

[pyrobob]

Check out John Coker's Nike-Asp here https://www.jcrocket.com/nike-asp.shtml. I was fortunate to see this flight at BALLS 2002, which was righteous. The sustainer is reported to be a Pegasus Fin Motor with a 20+ second burn time.

 

[MClark]

Aerotech used to make a motor called the i32. If memory serves it was about a twenty second burn.


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AT also had a K125 end burn. I did my L2 with one.

M

 

[Steve Shannon]

Wasn’t there a limit imposed on us to stay under 15 seconds, once? I don’t know if that was FAA or who.

 

[MClark]

Wasn&#8217;t there a limit imposed on us to stay under 15 seconds, once? I don&#8217;t know if that was FAA or who.

Yes.
But not at that time.

 

[Steve Shannon]

Yes.
But not at that time.

I really meant my question as trivia, not an effort to catch someone in the act. [emoji4]
Do you remember whose requirement that was and why, Mark? It always seemed odd to me. I thought it was still in place when CTI came out with their 15 second moonburner and changed soon after.

 

[MClark]

I think it was FAA or OCST. Some fed alphabet office.
They were afraid of rockets going into space and pulled 15 seconds out of their butts as the limit.

 

[G_T]

But a sounding rocket is fundamentally different. If you compare the same fuel APCP type to other, the sounding rocket wins on volumetric efficiency because the airframe is the casing and it's R radius value is always slightly more than negligibly larger than a hobby rocket with a casing restricting radius. Perhaps amatuers could advance to liner bonded carbon fiber or aluminum airframes someday.

Check out some BALLS projects.

Liner bonded is no problem at all. Case bonded is more fun. And motor as airframe is pretty standard.

Gerald

 

[G_T]

BTW, 15 seconds is enough to get to space.

I think the burn limit is in NFPA 1127.

Gerald

 

[rstaff3]

I thought the burn time limit was an FAA thing and that went away when they established the current classifications. I could be wrong.

 

[Swissyhawk]

That giant spinning bamboo rocket from Thailand that someone posted here last year had about 45 seconds of thrust.

 

[jsdemar]

I thought the burn time limit was an FAA thing and that went away when they established the current classifications. I could be wrong.

That is correct.

 

[jsdemar]

It just has more propellant in the same volume.

No, it's not that simple. The small sounding rockets typically ran at higher pressures than commercial HPR motors. With the added fwd/aft insulation, monolithic grains, and single-use design, you can get a lot more N-secs in a rocket the same size as a min-diameter HPR.

 

[FredA]

With the added fwd/aft insulation, monolithic grains, and single-use design, you can get a lot more N-secs in a rocket the same size as a min-diameter HPR.

All that has been done by amateurs.
We just can't run the pressure as high in 6061-T6 cases.