What exactly is a "slow burning propellant"?

[AZRxocet]

Nobody debates the FAA rules for class 1 rocketry...regarding flying rockets without a waiver...they are in plain English. I do however find ambiguity in the term "slow burning propellant".
I think we would all agree BP motors qualify as most Estes type kits fly on those without FAA waiver. Now as far as APCP is concerned...I think again it's fine as Blue Thunder, white lightning, blue streak, green Mohave, redline, etc, etc, even metal storm, dark matter, skid marks and the like (although L1 or higher certification is required) are available in motors containing less than 125g of propellant. Then, I seem to be confused about 2 propellants in particular...the speed demons...VMAX & Warp-9. One could easily argue that these are NOT "slow burning", let's face it, they are, for the most part, controlled explosions. Even their names are indications as to how fast they burn.
However, when you consider that a 1/4 A3 black powder motor burns in 0.25 seconds when compared to a CTI H410 VMAX (yes I know it requires a level 1 cert...but it only contains 75.9 g of propellant) burns in 0.41 seconds...one could argue that the VMAX motor "burns slower" than the BP. I think the FAA Code is fine the way it's written...and I sure hope we don't ever need a written determination on it...just wondering what everyone else thinks.

 

[G_T]

Neither Warp-9 nor VMAX are fast as propellants go. Just FYI. Fast for APCP would be certainly > 0.5"/sec. I'd say in the range of 3/4"/sec up to 1.5"/sec and higher.

But it's been a while since I've read the section you are talking about. I don't recall the slow burn stuff. Probably just my memory.

Gerald

 

[Q-Aero]

you can't compare the burning time of a 1/4 A3 of .83g with a Vmax of 80g

 

[grouch]

The Warp 9 end burners are very slow burning.

 

[AZRxocet]

The Warp 9 end burners are very slow burning.

Precisely...there is much more than just the "type" of propellant that affects it's burn rate. Core geometry, spacing, and grain orientation to name a few. So, who's to say if a propellant burns fast or slow? Maybe ALL our hobby and HPR propellants are "Slow burning" compared to other...non commercial...military and government type propellants? Stuff we don't and shouldn't have access to?

 

[Ravenex]

Your confusing burn rate and burn time. Burn rate for a given propellant is affected by pressure and temperature, not geometry. Temperature and pressure fall in a pretty small window in our motors. Burn rate is measured in distance per time. In and end burner the propellant burns from one end to the other consuming propellant at a give inches per second, in a cow burner the motor burns from the inside out at a specific rate. Even warp9 propellant is under 1 in/sec for the pressures found in a hobby motor.

 

[AZRxocet]

Your confusing burn rate and burn time. Burn rate for a given propellant is affected by pressure and temperature, not geometry. Temperature and pressure fall in a pretty small window in our motors. Burn rate is measured in distance per time. In and end burner the propellant burns from one end to the other consuming propellant at a give inches per second, in a cow burner the motor burns from the inside out at a specific rate. Even warp9 propellant is under 1 in/sec for the pressures found in a hobby motor.

So, if I understand correctly, a VMAX motor, if under 125g of propellant, does in fact qualify as a slow burning, class 1 eligible motor not needing a FAA waiver, so long as all the other requirements are met.

 

[crazyed]

Your confusing burn rate and burn time. Burn rate for a given propellant is affected by pressure and temperature, not geometry. Temperature and pressure fall in a pretty small window in our motors. Burn rate is measured in distance per time. In and end burner the propellant burns from one end to the other consuming propellant at a give inches per second, in a cow burner the motor burns from the inside out at a specific rate. Even warp9 propellant is under 1 in/sec for the pressures found in a hobby motor.

This is about what I came up with as I sat having my morning coffee and decided to add a bit to the question. The motors burn rate is determined by how big the nozzle throat is and how fast the chemical burns under a certain pressure. The more pressure the faster it burns and the higher thrust it produces. A delicate balancing done by much experimentation. Black powder is a low explosive and no matter how you pack it it is still a low explosive. Apcp is still apcp and if I have this right, it will be considered slow burning... Even if it Cato's ( an explosion) that can happen regardless of wether or not its fast or slow burning, high or low explosive. It happens due to pressure. But then what is a fast burning chemical... Let's Google it and find out...will be back.

 

[raptor22]

VMax burns fast for APCP, but there are faster burning propellants out there.

I would guess what they had in mind is more along the lines of fast double-base propellants with high explosive components. A good example of a high thrust double-base propellant was used in the Sprint Missile, which likely "contained alternating layers of zirconium "staples" embedded in nitrocellulose powder, followed by gelatinizing with nitroglycerine, thus forming a higher thrust double-base powder" (wikipedia).

Zinc-sulphur micrograins might qualify as well.

 

[UhClem]

Way back when the FAA was revising the Part 101 rules I addressed this very issue in the comment I submitted. I suggested that they change to the version used by the Consumer Product Safety Commission which is "thrust duration not less than 0.050 second".

My comment was not mentioned in the final rule so I must assume that they preferred the unenforceably vague version.