Longest burn time commercial or EX amatuer motors?

[wclaybaugh2]

The current version of the RRS standard propellant static tested at 9.1 second burn on the first static test and a planned 7.2 seconds for an upcoming test at nearly double the pressure.

Core burning grain but a propellant designed for a slower burn rate.

When I last looked at end burning grains I concluded it would take about 6 in/sec burn rates to duplicate the performance of a typical core burning grain in the same package (same diameter and similar length motor). Back then it appeared that APCP was unlikely to get much past 3 in/sec without moving to an energetic binder; it also looked like 6 in/sec was pretty close to the place where deflagration becomes detonation....

Bill

 

[3stoogesrocketry]

I've made a few 20+ sec. burn disposable 98mm sparky moonburner motors.

One of the best flight videos I've seen. Any basic info about the motor?

 

[DeeRoc29]

AT 98mm fiberglass casing, standard AT liner, moonburning grain of my sparky formula cast in a phenolic casting tube, nozzle and custom forward closure epoxied in place. 3 have worked great. One catoed at ignition a few years ago due to poor surface prep before epoxy.

 

[DabCat]

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 .

I19 you say? Sounds like a fun motor...

 

[prfesser]

The current version of the RRS standard propellant static tested at 9.1 second burn on the first static test and a planned 7.2 seconds for an upcoming test at nearly double the pressure.

Core burning grain but a propellant designed for a slower burn rate.

When I last looked at end burning grains I concluded it would take about 6 in/sec burn rates to duplicate the performance of a typical core burning grain in the same package (same diameter and similar length motor). Back then it appeared that APCP was unlikely to get much past 3 in/sec without moving to an energetic binder; it also looked like 6 in/sec was pretty close to the place where deflagration becomes detonation....

Bill

Even getting past 1"/second with APCP apparently isn't easy. The affidavits submitted to BATFE during the lawsuit included references to about 300 propellants from the peer-reviewed literature. Not sure I recall any that were even 1"/second. Not sure I'd want to attempt a propellant that burns at 1"/second.

 

[kjhambrick]

Longest Burn - Lowest Thrust...

https://https://www.youtube.com/watch?v=mQkX_-zzBEc

Wow !

This video was too good to not fix the llnk: Ill fated launch of Linda Newman's 7.5" Upscale of Der Red Max. Sorry for your loss, Linda, but that was pretty spectacular!

Thanks @RocketflierVB !

-- kjh

 

[wclaybaugh2]

Even getting past 1"/second with APCP apparently isn't easy. The affidavits submitted to BATFE during the lawsuit included references to about 300 propellants from the peer-reviewed literature. Not sure I recall any that were even 1"/second. Not sure I'd want to attempt a propellant that burns at 1"/second.

Terry:

That sounds right.

Energetic binders--for amateur noodling I'd personally consider NC because I use that for gas generators but the rest are far too dangerous for my taste--appear to be the standard trick. But the real issue seems to be that the burn rates required to get to combinations of thrust and burn time that make sense for sounding rockets are so high that one is approaching supersonic burning....

Bill

 

[jsdemar]

Even getting past 1"/second with APCP apparently isn't easy. The affidavits submitted to BATFE during the lawsuit included references to about 300 propellants from the peer-reviewed literature. Not sure I recall any that were even 1"/second. Not sure I'd want to attempt a propellant that burns at 1"/second.

The fastest I've made is about 0.75"/sec with ferrocene and CuO, 90u AP and fines.
Here's the test firing from 2003. A 38mm with 100 pounds thrust!
http://thrustgear.com/oldtests/DSCN0582.MOV
http://thrustgear.com/oldtests/WB238H323.gif

 

[Spacedog49Krell]

The fastest burning propellant I've tested in a nozzled motor was DBCP at ~1"/sec.

 

[Neutronium95]

When I last looked at end burning grains I concluded it would take about 6 in/sec burn rates to duplicate the performance of a typical core burning grain in the same package (same diameter and similar length motor). Back then it appeared that APCP was unlikely to get much past 3 in/sec without moving to an energetic binder; it also looked like 6 in/sec was pretty close to the place where deflagration becomes detonation....

What do you mean by duplicate the performance? Match the thrust they can prpduce or something else? For me the appeal of endburners is that they ebable very long burn times with a very low average thrust.

Just as a random example, it looks like the Warp 9 propellant in the Aerotech I49 burns at about .72in/s. I van certainly see the desire for a faster burn rate in order to get reasonable amounts of thrust from higher L motors, but 6in/s is ridiculous.

 

[wclaybaugh2]

What do you mean by duplicate the performance? Match the thrust they can prpduce or something else? For me the appeal of endburners is that they ebable very long burn times with a very low average thrust.

Just as a random example, it looks like the Warp 9 propellant in the Aerotech I49 burns at about .72in/s. I van certainly see the desire for a faster burn rate in order to get reasonable amounts of thrust from higher L motors, but 6in/s is ridiculous.

Sounding rockets have fairly specific combinations of thrust and burn time for optimal (highest altitude) performance.

For a six inch diameter upper stage with about 60% propellant fraction, that wants to be around 1500 lbf. and about 8 seconds, for one example. Lower thrust and longer burns just result in a powered gravity turn. Higher thrust and shorter burns waste energy on drag and also lower altitude.

Six in/sec is the burn rate required to get the needed thrust on a 6” diameter end burning motor.

Bill

 

[Neutronium95]

Sounding rockets have fairly specific combinations of thrust and burn time for optimal (highest altitude) performance.

For a six inch diameter upper stage with about 60% propellant fraction, that wants to be around 1500 lbf. and about 8 seconds, for one example. Lower thrust and longer burns just result in a powered gravity turn. Higher thrust and shorter burns waste energy on drag and also lower altitude.

Six in/sec is the burn rate required to get the needed thrust on a 6” diameter end burning motor.

Bill

Getting an 8 second burn time out of a 6" motor should be easily doable with normal propellants in a core burning geometry. That just sounds like a terrible application to try to shoehorn an endburner into.

I'm mostly interested in them as options for longburn motors in much smaller diameters, a size range where a 1 in/s burn rate seems to be more than sufficient, judging by the performance of the Aerotech endburning motors.

 

[MClark]

I did a Bates grain 6” P, 1000 lbs for 14 seconds. Also shorter versions.
Nothing exotic required.

 

[MClark]

P Motor I had NOTHING to do with airframe, just made the motor. Unstable due to CG/CP.

 

[wclaybaugh2]

Getting an 8 second burn time out of a 6" motor should be easily doable with normal propellants in a core burning geometry. That just sounds like a terrible application to try to shoehorn an endburner into.

That is certainly correct.. Switching to end burning would be to increase propellant fraction and resulting performance or, possibly, to avoid the coning caused by moon burner grains.

One could also presumably use end burning at more conventional burn rates and active guidance to avoid the gravity turn. But that adds complexity and the associated cost and unreliability.

Bill

 

[wclaybaugh2]

The fastest I've made is about 0.75"/sec with ferrocene and CuO, 90u AP and fines.
Here's the test firing from 2003. A 38mm with 100 pounds thrust!
http://thrustgear.com/oldtests/DSCN0582.MOV
http://thrustgear.com/oldtests/WB238H323.gif

I’m aware of a professional “quadruple base” mix that would do near 3 in./sec. And silver wires will get APCP up to that range.

And—just kidding here—micrograin appears to be up around 100 in/sec….

Bill

 

[Spacedog49Krell]

I’m aware of a professional “quadruple base” mix that would do near 3 in./sec. And silver wires will get APCP up to that range.

And—just kidding here—micrograin appears to be up around 100 in/sec….

Bill

Micrograin burning 100in/sec would be on a cool day. I've measured micrograin burn-rates on hot days (107°F) at 128 in/sec. Another interested data point I found in my micrograin tests, since we are discussing end-burners, micrograin is a quasi-end-burning propellant.

 

[jsdemar]

Re: ZnS and micrograin…Why bother with an extremely dangerous composition that has an ISP of 60 at best? And it’s not that cheap compared to other non-APCP options.

 

[wclaybaugh2]

Re: ZnS and micrograin…Why bother with an extremely dangerous composition that has an ISP of 60 at best? And it’s not that cheap compared to other non-APCP options.

John:

Agreed. Nasty stuff to mix, process, and breathe.

Kinda doubt it gets as high as 60 seconds, too, I always found it to be around 35 seconds in flight, apparently in some part because a good bit of powder-packed motors ends up getting swept out the nozzle before burning.

Bill

 

[wclaybaugh2]

Micrograin burning 100in/sec would be on a cool day. I've measured micrograin burn-rates on hot days (107°F) at 128 in/sec. Another interested data point I found in my micrograin tests, since we are discussing end-burners, micrograin is a quasi-end-burning propellant.

I’m aware of evidence that it burns up the side of the “grain” as well as from the end.

Bill

 

[FredA]

I never did understand the fascination with micro-grain.
Dangerous and worthless....what a combo.
Guess it's all in the flash.

 

[Spacedog49Krell]

I’m aware of evidence that it burns up the side of the “grain” as well as from the end.

Bill

The flame temperature is too low along the chamber walls to maintain a high propagation rate. I found the residue along the walls to be mainly zinc and not ZnS. To match the pressure curves, the flame front appears to be propagating through the crystalline interstitial gaps in the central core of the propellant. This matches my research on interstitial gas propagation for the semiconductor industry.

 

[wclaybaugh2]

I never did understand the fascination with micro-grain.
Dangerous and worthless....what a combo.
Guess it's all in the flash.

I want to be sensitive about hijacking a discussion—which may have already occurred in the transition from burn time to burn rate—but Fred’s post leaves me wondering when APCP became an amateur propellant?

Micrograin was a sufficient solution when there was nothing else available (pre 1970?). If one was a teen in the ‘60’s in Southern (or Northern) California than the RRS, PRS, and RRI were the only amateur rocket builders one could find and all used S/Zn (to write the oxidizer first, in accord w/ convention) because it had been invented by their common founder, George James.

So when did APCP become amateur?

If this belongs in a separate discussion I’d be delighted if someone who understands how to make the segue would make that happen, with my thanks.

Bill

 

[VernK]

Lower thrust and longer burns just result in a powered gravity turn.

Agreed. Do you (or anyone else) know of a simulator that will properly simulate the gravity turn effect? I would like to asses the risk a planned two stage project with a long burn sustainer will suffer from this problem.

 

[wclaybaugh2]

Agreed. Do you (or anyone else) know of a simulator that will properly simulate the gravity turn effect? I would like to asses the risk a planned two stage project with a long burn sustainer will suffer from this problem.Vern:

Vern:

RASAero would be my choice. Open Rocket will work as well but with less accurate aero.

I’d be happy to run sim’s in both for you, if you’d like.

Bill

 

[jsdemar]

Other than the gravity turn with an endburner, there are also dynamic stability challenges as the CG moves forward. It becomes a "mass on the end of a stick", over-stable, with over-correcting fin motion.

 

[wclaybaugh2]

The flame temperature is too low along the chamber walls to maintain a high propagation rate. I found the residue along the walls to be mainly zinc and not ZnS. To match the pressure curves, the flame front appears to be propagating through the crystalline interstitial gaps in the central core of the propellant. This matches my research on interstitial gas propagation for the semiconductor industry.

How did you measure flame temperature on the inside wall?

A fellow named John Novak—who was a researcher at then TRWonderful—once brought out to the MTA (this is very early 1970’s) a film-based recording infrared camera that imaged a then standard RRS Beta rocket bolted to the then test stand. It showed that the bulkhead end started heating one frame after ignition. (Possibly relevant that the bulkhead was down, not up and less powdered propellant may have been blowing out the nozzle compared to in-flight.)

I don’t recall the frame rate but I do recall that it made a great almighty racket that I had previously only heard from thousand plus frames / second film cameras.

Bill

 

[wclaybaugh2]

Other than the gravity turn with an endburner, there are also dynamic stability challenges as the CG moves forward. It becomes a "mass on the end of a stick", over-stable, with over-correcting fin motion.

John:

A very good point.

This can be delt w/ in part via a sufficiently energetic boost combined w/ a high spin rate on the sustainer. But certainly an issue that needs some care.

But note that *all* sustainers are “masses on a stick” because of the presence of a payload.

Bill

 

[jsdemar]

John:

A very good point.

This can be delt w/ in part via a sufficiently energetic boost combined w/ a high spin rate on the sustainer. But certainly an issue that needs some care.

But note that *all* sustainers are “masses on a stick” because of the presence of a payload.

Bill

For the amateur Karman seekers, there isn't much of a payload... altimeter, camera, and recovery gear. Without the sophistication of a de-spinning mechanism, most people don't want to impart spin stabilization. They want the video proof as well as the GPS data. Personally, I'd prefer spinning it well above the roll resonance, and let the GPS get lock again while tumbling at apogee. But, there's still a good chance of a non-symmetrical radial mass distribution ruining the spin stability. So many trade-offs to consider.

 

[Spacedog49Krell]

How did you measure flame temperature on the inside wall?

A fellow named John Novak—who was a researcher at then TRWonderful—once brought out to the MTA (this is very early 1970’s) a film-based recording infrared camera that imaged a then standard RRS Beta rocket bolted to the then test stand. It showed that the bulkhead end started heating one frame after ignition. (Possibly relevant that the bulkhead was down, not up and less powdered propellant may have been blowing out the nozzle compared to in-flight.)

I don’t recall the frame rate but I do recall that it made a great almighty racket that I had previously only heard from thousand plus frames / second film cameras.

Bill

The wall temperature is a calculation from the residual byproducts measured.

I have not flown a pressure transducer fitted micrograin, but I have a thrust to pressure conversion formula that matches data from two groups in Europe that have directly measured pressures of 1800 psi. The ignition pressure pulse can be measured in 70 - 90ms after ignition at the bulkhead. The flame front lags behind the pressure front. I'm recording the highest thrust between 175 - 300 ms after ignition. After peak thrust, the rest is ZnS sublimation blowdown.

Replacing some of the zinc with aluminum does increase the Isp to 55-60 seconds.

The ability to measure micrograin parameters makes measuring APCP propellant characteristics a cake walk. 500 to 1000Hz resolution of flight performance parameters allows even the measurement of slag and unburned particles passing through the nozzle of current commercial motors.

The increasing cost of zinc dust will be the demise of micrograin.