Composite propelent questions

[ScrapDaddy]

Just wondering why all of the warp-9 propelent kits are capped.

Oh and here is a side question what is the maximum average thrust for each motor class? Like is a A1000000000 be possible sopposing a burn time of .001 seconds?

Another question, what is the fastest burning grain configuration? (C slot, bates, d slot etc) I.e. Which one exposes the most surface area?

 

[cjl]

Warp 9 are plugged (I imagine that is what you meant) because at burnout, they tend to have extremely sharp dropoffs in pressure, which can extinguish the delay grain. Because of this possibility, they would not reliably eject, which is why they are plugged.

As for the fastest burning grain configuration, out of the standard configurations, a star grain or finocyl would expose the most propellant, giving the greatest thrust and shortest burn.

 

[ben_ullman]

Warp 9 are plugged (I imagine that is what you meant) because at burnout, they tend to have extremely sharp dropoffs in pressure, which can extinguish the delay grain. Because of this possibility, they would not reliably eject, which is why they are plugged.

As for the fastest burning grain configuration, out of the standard configurations, a star grain or finocyl would expose the most propellant, giving the greatest thrust and shortest burn.

What is a star or finocyl grain?

could you please explain why a pressure drop would extinguish propellant? :confused2:

Ben

 

[green dragon]

Star core ( or finocyl ) should be easily found by a google search.

I;ve seen old progressive burn composites extinguish the delay at burnout, sue to a sudden pressure drop, so that part is very true.

as for fast burn grainwise ( regardless of prop formula ) .. depends what you condider 'standard' .. a multi perforated grain would burn rather fast, and the old all-surface burn ( suspended rod and tube ) were real quick, half the burntime of coreburner/ bates grains.

hmm.. I should make some of those up

 

[Jeroen_at_CTI]

could you please explain why a pressure drop would extinguish propellant?

Try a google search for "depressurization extinguishment".

In summary:

The thermal profile beneath the propellant surface gets thinner at higher burn rates (higher pressures). At lower pressures the burn rate is lower and the thermal profile (preheated solid propellant zone) is much thicker, because there is more time to preheat the propellant by conduction from the burning surface.

When the pressure drops, the propellant thermal profile depth is too thin all of a sudden for the steady burn rate at the at the lower pressure. Hence it extinguishes.

Depending on chamber volume, geometry, propellant type etc, re-ignition may occur because of heat capacity of the propellant combustion products and radiation.

Some other propellants - such as double base propellants - extinguish because they can not sustain combustion at low pressures, because the flame length is too long at low pressures (heat release to far away from the burning surface). This can create interesting extinguish - re-ignition effects, L* instability.

Jeroen

 

[MarkII]

The Space Shuttle SRBs have a variable core geometry to provide different levels of thrust over the course of the burn. At the upper end of the core is a star/finocyl grain geometry. This shape promotes instant ignition and an initial high level of thrust, which is important to get the entire assembly moving from a standing start so that it can get up into the air and clear of the pad promptly while minimizing any lateral movement.

Mark K.

 

[The EGE]

There's a minimum allowable burn time for motors, something like 0.05 or 0.1 seconds. No motor - not even a W9 core-burner - has that short of a burn time, but it's the minimum that separates rocket motors from explosive devices.

1 billion newtons is a ridiculous amount of thrust. The most powerful single motors in the world are the Shuttle SRBs (Solid Rocket Boosters) at 12,500,000 N each at sea level. Total thrust of the Shuttle at liftoff is about 66,000,000 Newtons - one sixteenth of your theoretical motor.

BTW, a 0.001 second A would be an A1250 to an A2500. And it wouldn't be a rocket motor, it'd be effectively a miniature shaped charge!

 

[ScrapDaddy]

There's a minimum allowable burn time for motors, something like 0.05 or 0.1 seconds. No motor - not even a W9 core-burner - has that short of a burn time, but it's the minimum that separates rocket motors from explosive devices.

1 billion newtons is a ridiculous amount of thrust. The most powerful single motors in the world are the Shuttle SRBs (Solid Rocket Boosters) at 12,500,000 N each at sea level. Total thrust of the Shuttle at liftoff is about 66,000,000 Newtons - one sixteenth of your theoretical motor.

BTW, a 0.001 second A would be an A1250 to an A2500. And it wouldn't be a rocket motor, it'd be effectively a miniature shaped charge!

Well I guess we both love math then but one quick calculation for you, Warp-9 burns 1in^3 every second, at that rate what is the highest impulse possible using a star grain configuration in an 18mm motor?

 

[ben_ullman]

Well I guess we both love math then but one quick calculation for you, Warp-9 burns 1in^3 every second, at that rate what is the highest impulse possible using a star grain configuration in an 18mm motor?

making a star grain in 18mm is going to be one heck of a challenge.

Ben

 

[ScrapDaddy]

making a star grain in 18mm is going to be one heck of a challenge.

Ben

I just want to know a hypothetical situation, I never said I would do it but man that would be so cool! :wave:

 

[daveyfire]

The thermal profile beneath the propellant surface gets thinner at higher burn rates (higher pressures). At lower pressures the burn rate is lower and the thermal profile (preheated solid propellant zone) is much thicker, because there is more time to preheat the propellant by conduction from the burning surface.

When the pressure drops, the propellant thermal profile depth is too thin all of a sudden for the steady burn rate at the at the lower pressure. Hence it extinguishes.

To add to Jeroen's excellent explanation, here's a figure I gathered from a propellant text by Natan Libis, illustrating the variation in thermal wave thickness as a function of pressure (exaggerated for clarity). Essentially, if the pressure drops faster than the thermal wave equilibrates, the propellant extinguishes. Think of two different types of CATOs -- ones that go "fwoosh-thump" tend to leave burning propellant, as they happen slow enough so that the thermal profile can keep up, while ones that go "bang" usually extinguish the propellant.

 

[ben_ullman]

To add to Jeroen's excellent explanation, here's a figure I gathered from a propellant text by Natan Libis, illustrating the variation in thermal wave thickness as a function of pressure (exaggerated for clarity). Essentially, if the pressure drops faster than the thermal wave equilibrates, the propellant extinguishes. Think of two different types of CATOs -- ones that go "fwoosh-thump" tend to leave burning propellant, as they happen slow enough so that the thermal profile can keep up, while ones that go "bang" usually extinguish the propellant.

thats a nice graphic. I more or less had the idea I just wanted to ask some questions of my own

Ben

P.S. getting all this scrap?

 

[ScrapDaddy]

Sorta I got the idea..... I think if the propelent burns to fast the air on the sides of the propelent escape quickly with the propelent, and creating a vacum chamber...... I think I am wrong though....

I'm getting that or the fact that the propelent the prpelent is sucking all the heat and mositer out of the air

 

[cjl]

What is a star or finocyl grain?

Star grain: https://www.nifo.dk/astro/stargrain/star_grain_burn.gif
Finocyl: https://www.nakka-rocketry.net/rnx/pfc1.jpg

 

[ben_ullman]

Star grain: https://www.nifo.dk/astro/stargrain/star_grain_burn.gif
Finocyl: https://www.nakka-rocketry.net/rnx/pfc1.jpg

Im aware but thanks!

Ben

 

[MarkII]

Star grain: https://www.nifo.dk/astro/stargrain/star_grain_burn.gif
Finocyl: https://www.nakka-rocketry.net/rnx/pfc1.jpg

Both styles create very large surface areas that can be ignited all at once. When a great deal of surface area is burned, a great deal of thrust is the result.

Mark K.

 

[JDcluster]

:y:Ben better do some homework before he comes out of retirement.....

There are no certified delays for any of the Warp 9 loads. They had trouble with them when they did light. Warp 9's would make some pretty interesting SU motors....


JD

What is a star or finocyl grain?

could you please explain why a pressure drop would extinguish propellant? :confused2:

Ben

 

[MattieShoes]

There's a minimum allowable burn time for motors, something like 0.05 or 0.1 seconds. No motor - not even a W9 core-burner - has that short of a burn time, but it's the minimum that separates rocket motors from explosive devices.

1 billion newtons is a ridiculous amount of thrust. The most powerful single motors in the world are the Shuttle SRBs (Solid Rocket Boosters) at 12,500,000 N each at sea level. Total thrust of the Shuttle at liftoff is about 66,000,000 Newtons - one sixteenth of your theoretical motor.

BTW, a 0.001 second A would be an A1250 to an A2500. And it wouldn't be a rocket motor, it'd be effectively a miniature shaped charge!

Incidentally, does anybody know what the total impulse of the shuttle SSRBs are? Would they have a letter, or do we run out before we get there?

 

[MarkII]

Incidentally, does anybody know what the total impulse of the shuttle SSRBs are? Would they have a letter, or do we run out before we get there?

The letter system of motor classification is only used for hobby rocket motors, so it peaks out at O. But it can be hypothetically extended to Z and beyond. After Z-class, the next levels would be AA, AB, AC, etc. Each one of the Space Shuttle Rocket Boosters has a total impulse of 1,300 MNs (meganewton-seconds), or 1,300,000,000 Newton-seconds. That would hypothetically make each one about a 97% AD. (For comparison, each of the F1 engines in the first stage of the Saturn V was a hypothetical AC. But there were 5 of them in that stage - 5 x AC.)

The SSRBs are the largest reloadable motors* ever created. :jaw: Each one is loaded with about 504,000 kg (1,111,130 lbs.)† of APCP‡. They have a burn time of 123.7 seconds, a maximum thrust of 14.77 MN and an average thrust of 11.52 MN. Each one has a specific impulse of 268.0 seconds in a vacuum. The SSRBs are NOT certified by either NAR or TRA! :roll:

Mark K.

* Each one uses a 3710/1300000000 motor case. :y:

† Therefore, you must pay a HAZMAT charge to ship them in the US.

‡ And to my eyes anyway, the burning SSRB propellant sort of resembles AT's White Lightning in appearance.

 

[MarkII]

So, using the NAR naming conventions, each SSRB motor would be called an

AD1152000000-72

Mark K.
​

 

[RoyAtl]

So, using the NAR naming conventions, each SSRB motor would be called an

AD1152000000-72

Mark K.
​

I'm assuming you mean it's 72 seconds between burnout/sep and the drogue chutes coming out?

 

[MarkII]

I'm assuming you mean it's 72 seconds between burnout/sep and the drogue chutes coming out?

I was thinking of that interval as being analogous to the delay in model rocket motors, but your post reminded me that the SSRBs use electronic deployment, of course, so the corrected hypothetical designation would be

AD1152000000-P :headbang:
​

Thanks for catching that error, Roy. (My error-checking ability at 4:00 am this morning was somewhat attenuated. ) As we all learned some time ago, the SSRBs do use bifurcated grains. But even with that structure, they would still be subject to hazmat charges. That issue is somewhat mitigated by the fact that you wouldn't need to have an LEUP. :w:

Mark K.

P. S. I'd love to see a thrust curve of the SSRB compared to, say, a Pro150 O.

 

[shreadvector]

They are not "bifurcated".

Look up that word.

Bi means two. Like Bicycle or Bifocals (which are different from Tricycles and trifocals).

A grain cut in two is bifurcated. A grain in many parts is segmented.

The SS-SRBs are segmented.

When I worked there, the rail cars said "EXPLOSIVE A" on them.

I was thinking of that interval as being analogous to the delay in model rocket motors, but your post reminded me that the SSRBs use electronic deployment, of course, so the corrected hypothetical designation would be

AD1152000000-P :headbang:​

Thanks for catching that error, Roy. (My error-checking ability at 4:00 am this morning was somewhat attenuated. ) As we all learned some time ago, the SSRBs do use bifurcated grains. But even with that structure, they would still be subject to hazmat charges. That issue is somewhat mitigated by the fact that you wouldn't need to have an LEUP. :w:

Mark K.

P. S. I'd love to see a thrust curve of the SSRB compared to, say, a Pro150 O.

 

[daveyfire]

When I worked there, the rail cars said "EXPLOSIVE A" on them.

Yea... ATK is very careful about labeling for shipment. When we order raw AP from them -- even larger crystal sizes -- it ships as 1.1A.

 

[MarkII]

They are not "bifurcated".

Look up that word.

Bi means two. Like Bicycle or Bifocals (which are different from Tricycles and trifocals).

A grain cut in two is bifurcated. A grain in many parts is segmented.

The SS-SRBs are segmented.

When I worked there, the rail cars said "EXPLOSIVE A" on them.

You are correct. My bad. I was making a lame attempt at humor, but I guess the joke was on me.

Mark K.

 

[Incongruent]

Theoretically, you could have an A motor with 1000000000 newtons of thrust, if you have an unbreakabke case, nozzle, and forward bulkhead. And fill it with a really high explosive. But you would be accelerating the gas to an incredibly high speed, and at some point (someone do the math) the gas exiting through the nozzle would pass light speed, so...

Thete's also the physical impossibility of constructing a case that strength, unless it were really thick and in the middle of a neutron star or something to prevent splitting, and the gas exiting would expand into an explosion... etc.

What would a black hole be with the jets of plasma that sometimes shoot out of them?

Maybe Rocksim or Openrocket a design with as small a burn time as possible and as high thrust as possible?