Required Skills in EX

[RadManCF]

In reading threads about EX, it seems to me that there is much more discussion about propellants than there is about machining EX components. Is propellant chemistry considered to be the hairier/more interesting topic?

 

[Wingarcher]

Given the availability of suitable cases and accessories that provide a solid set of hardware to work from, there is little need to create your own stuff in the "standard" sizes (38mm-4").

The chemistry has a large number of variables that can be explored, so: buy your way into a set of cases and then experiment with the chemicals. Blue flames, green sparks, etc. You have to remember to tune to the case/nozzle combinations you've got, but since most are starting with sensible commercial stuff, that's not too hard. If you start to go EXTREME (Mike Fisher) maybe making up a 5' long case is something you need to do!

N

 

[jderimig]

In reading threads about EX, it seems to me that there is much more discussion about propellants than there is about machining EX components. Is propellant chemistry considered to be the hairier/more interesting topic?

No but anyone can mix propellent (I got pictures to prove it). Precision machining not so much..... Also not that many people doing chemistry either, closer to cooking.

 

[RadManCF]

Given the availability of suitable cases and accessories that provide a solid set of hardware to work from, there is little need to create your own stuff in the "standard" sizes (38mm-4").

The chemistry has a large number of variables that can be explored, so: buy your way into a set of cases and then experiment with the chemicals. Blue flames, green sparks, etc. You have to remember to tune to the case/nozzle combinations you've got, but since most are starting with sensible commercial stuff, that's not too hard. If you start to go EXTREME (Mike Fisher) maybe making up a 5' long case is something you need to do!

N

I thought that might be the case. My interest in EX stems from my interest in machining, and other mechanical work. I know its fraught with difficulty, but maybe liquid fuel would provide more opportunity for this?

 

[jderimig]

I thought that might be the case. My interest in EX stems from my interest in machining, and other mechanical work. I know its fraught with difficulty, but maybe liquid fuel would provide more opportunity for this?

Hybrid N2O motors will feed your interest yet. Lots of degrees of freedom for things like injector designs that are not very sophisticated currently in commercial hybrid motors.

 

[RadManCF]

Hybrid N2O motors will feed your interest yet. Lots of degrees of freedom for things like injector designs that are not very sophisticated currently in commercial hybrid motors.

Any reason to put a turbopump in a hybrid? I really like turbines. I assume this wouldn't be practical for anything meant to fly but I do think it would be interesting to build rockets using pulverized coal, or Bunker C as a fuel, also.

 

[jderimig]

Any reason to put a turbopump in a hybrid? I really like turbines. I assume this wouldn't be practical for anything meant to fly but I do think it would be interesting to build rockets using pulverized coal, or Bunker C as a fuel, also.

Hobby hybrids use N2O which is self pressurizing. Where you want to go is amateur rocketry and is very very difficult and out of the scope of this group.

 

[RadManCF]

Hobby hybrids use N2O which is self pressurizing. Where you want to go is amateur rocketry and is very very difficult and out of the scope of this group.

Kinda what I thought, but like I said, I wouldn't expect a rocket using pulverized coal or Bunker C to fly very well (excessive weight). If I ever build anything like that I'd just test in on the ground just to say I made it work. But thanks for the advice, I'll have to look into hybrids a bit more.

 

[troj]

Something else to consider is partnering with people who like making propellant -- you help out with the hardware design/manufacturing, and they do the guts.

-Kevin

 

[jsdemar]

For larger motors, machining of custom closures and nozzles is required. There are many different designs out there (threaded, snapring, bolted). Here's my 6" P motor hardware and a liftoff photo (2-stage 80Kft).

Propellant mixing is not much more difficult than mixing cookie dough, as long as you understand some basic guidelines and safety. To get the best Isp and grain strength, and to get consistent results, you need a deeper understanding of the chemistry and processing techniques.

The thermodynamics, grain geometry, and nozzle diameter are all related. These are determined mostly experimentally and through motor simulation ( https://burnsim.com ).

So, motor design, formulation, processing, safety, and motor burn simulation are all interrelated. Skipping something along the way makes for a bad day. Getting it all working together is a lot of fun.

 

[rockets4kids]

You read more about propellants than machining because (1) most people who go EX already own hardware (pretty much a requirement for L2) and (2) far less of an investment is required to manufacture propellant than hardware.

 

[ClayD]

everyone is pointing to all the special machining being limited to the *larger motors*

this is not true, there are many things that can be special purpouse made on the small scale that is not commercialy used, but an amature who wants something :special: can make.

TFish on here has some neat pics of modifications he has done that others dont do on small cases.


lesson, its all as hard as you make it....

And Jderimig, last i cooked something it wasnt toxic, nor could it cause a flash fire....

 

[ClayD]

You read more about propellants than machining because (1) most people who go EX already own hardware (pretty much a requirement for L2) and (2) far less of an investment is required to manufacture propellant than hardware.

Not true either... The lathe i use costs less than the mixer and first batch of chems i bought.

 

[RadManCF]

Not true either... The lathe i use costs less than the mixer and first batch of chems i bought.

That gets to some of the reasons I'm interested in pulverized coal and fuel oil as propellants- they're dirt cheap.

 

[jderimig]

And Jderimig, last i cooked something it wasnt toxic, nor could it cause a flash fire....

Not all cooks could make that claim that unfortunately.

 

[RadManCF]

And Jderimig, last i cooked something it wasnt toxic, nor could it cause a flash fire....

Flour could easily cause a flash fire. It's just like coal dust.

 

[rockets4kids]

Not true either... The lathe i use costs less than the mixer and first batch of chems i bought.

I'll bet you've got a cheap lathe (or got a really good deal) and an expensive mixer.

 

[ClayD]

I had no idea flour would start a fire... dont you put that or bakingsoda on grease fires...???

@rockets4kids... actually spent more on chems
i also got cheap lathe and mixer... (the lathe is still good quality for what what spent...)

 

[bobkrech]

That gets to some of the reasons I'm interested in pulverized coal and fuel oil as propellants- they're dirt cheap.

Coal is not a good propellant. It will not burn out in the combustion times available in a rocket.

Kerosene is number 1 fueld oil. Liquid oxygen/kerosene is the highest performance low cost liquid propulsion system. The Russian RD-172 is the highest thrust rocket motor ever flown. SpaceX uses 9 LOX/Kerosene motors in the Falcon 9 booster. Cryogenic motors are not hobby rocket motors, and never will be, as thehazards are orders of magnitude higher than solids or hybrids, as failures always result in a massive explosion and fire.

Bob

 

[RadManCF]

Coal is not a good propellant. It will not burn out in the combustion times available in a rocket.

In the case of lump coal, I agree, but what about pulverized coal? I worked in a coal fired power plant back in college, and have first hand knowledge of the difficulties involved with lump coal (starting the fire is a PITA, and if the coal gets wet, life gets really difficult). From what I know of pulverized coal, its much easier to deal with. It can be transported pneumatically through pipes, and can be ignited with a natural gas pilot flame. Reading about mine explosions involving coal dust leads me to believe that pulverized coal has potential for use a propellant. My thinking for a pulverized coal rocket would be a hybrid design, using the nitrous oxide in place of compressed air for moving the coal. I probably wouldn't start with coal either, but with flour (easier to obtain, lower energy content).

Kerosene is number 1 fueld oil. Liquid oxygen/kerosene is the highest performance low cost liquid propulsion system. The Russian RD-172 is the highest thrust rocket motor ever flown. SpaceX uses 9 LOX/Kerosene motors in the Falcon 9 booster.

I'm actually curious about how the heavier fuel oils would perform. Due to their greater weight, and the need for heating in order to flow, I wouldn't expect an engine using #6 fuel oil as the propellant to actually leave the ground, I'd just like to see how much thrust would be produced. Again, I'd use nitrous as the oxidizer.

Cryogenic motors are not hobby rocket motors, and never will be, as thehazards are orders of magnitude higher than solids or hybrids, as failures always result in a massive explosion and fire.

Bob

Don't worry, I'm not interested in dealing with cryogenics. It's a can of worms I really don't want to open. Hybrids seem like they'd provide plenty of opportunity for tinkering, which is the root of my interest in EX. I guess I should ask, how far can I go with EX in Tripoli? I know liquid fuel wouldn't be allowed, but could I do work with hybrids?

 

[RadManCF]

I had no idea flour would start a fire... dont you put that or bakingsoda on grease fires...???

I'd never heard of putting flour on a fire, but baking soda definitely works. I'm a Millwright by trade, and recently spent two weeks at a General Mills oat mill. They were especially worried about the possibility of flour or grain dust exploding. As part of the hot work permit procedure, a fire watch was required for I think about three hours after all cutting, welding, or grinding had ceased.

 

[bobkrech]

I'd never heard of putting flour on a fire, but baking soda definitely works. I'm a Millwright by trade, and recently spent two weeks at a General Mills oat mill. They were especially worried about the possibility of flour or grain dust exploding. As part of the hot work permit procedure, a fire watch was required for I think about three hours after all cutting, welding, or grinding had ceased.

Baking soda does not burn or explode. Baking soda puts fires out. When you heat it it makes carbon dioxide.

Bob

 

[bobkrech]

In the case of lump coal, I agree, but what about pulverized coal? I worked in a coal fired power plant back in college, and have first hand knowledge of the difficulties involved with lump coal (starting the fire is a PITA, and if the coal gets wet, life gets really difficult). From what I know of pulverized coal, its much easier to deal with. It can be transported pneumatically through pipes, and can be ignited with a natural gas pilot flame. Reading about mine explosions involving coal dust leads me to believe that pulverized coal has potential for use a propellant. My thinking for a pulverized coal rocket would be a hybrid design, using the nitrous oxide in place of compressed air for moving the coal. I probably wouldn't start with coal either, but with flour (easier to obtain, lower energy content).

I've been in the propulsion business professionally for more than 4 decades. Please listen and learn.

Rocket propellants burn quickly when used properly. They explode when used incorrectly. It's all in the chemical kinetics. Your welcome to try what you propose, but you can't outrun the supersonic blast wave that will be generated when you attempt to ignite it.

I'm actually curious about how the heavier fuel oils would perform. Due to their greater weight, and the need for heating in order to flow, I wouldn't expect an engine using #6 fuel oil as the propellant to actually leave the ground, I'd just like to see how much thrust would be produced. Again, I'd use nitrous as the oxidizer.

Again it's all in the chemical kinetics. The burn rate of heavy hydrocarbons is slower than light hydrocarbons. In a liquid motor, you don't have enough residence time to burn them out and ignition may be problematic. Any delayed ignition results in a detonation.

Solid parafin wax has been used in hybrids successfully with nitrous oxide, but nitrous combustion is slow compared to LOX. Alpha Hybrids makes hybrid parafin/nitrous hybrids.

Don't worry, I'm not interested in dealing with cryogenics. It's a can of worms I really don't want to open. Hybrids seem like they'd provide plenty of opportunity for tinkering, which is the root of my interest in EX. I guess I should ask, how far can I go with EX in Tripoli? I know liquid fuel wouldn't be allowed, but could I do work with hybrids?

It's not a can of worms. The best hybrids use LOX, but it's not for hobby use.

I don't want to discourage your enthusiasm but you need a TRA L2 high power certification before you can do EX under TRA rules. At that point, you are likely to know a lot more about rocket motors than you do at present. And that's a good thing, because if you try to do what you are proposing in the manner that you are proposing to do it, you won't live long enough to get your L2 certification. If you're really interested in learning about propulsion I strongly suggest you obtain a copy of Sutton's Rocket Propulsion Elements to get a basic understanding of how rocket motors and rocket propellants function.

Bob

 

[RadManCF]

I've been in the propulsion business professionally for more than 4 decades. Please listen and learn.

Rocket propellants burn quickly when used properly. They explode when used incorrectly. It's all in the chemical kinetics. Your welcome to try what you propose, but you can't outrun the supersonic blast wave that will be generated when you attempt to ignite it.

I gues I should have asked this sooner: Has anyone ever attempted to use a powdered solid fuel that was delivered to the combustion chamber by pneumatic mean? I also want to say that I do appreciate the danger involved with pulverized coal, my primary job at the plant where I worked was wiping it up.

Again it's all in the chemical kinetics. The burn rate of heavy hydrocarbons is slower than light hydrocarbons. In a liquid motor, you don't have enough residence time to burn them out and ignition may be problematic. Any delayed ignition results in a detonation.

Solid parafin wax has been used in hybrids successfully with nitrous oxide, but nitrous combustion is slow compared to LOX. Alpha Hybrids makes hybrid parafin/nitrous hybrids.

Thanks, I've wondered about why a more expensive oil with a lower heat content would be chosen over a cheaper oil with a higher heat content, and figured that the higher viscosity was the primary reason. The plant I worked in used oil as a backup fuel source, and had been built with #6 fuel oil in mind. At some point, the plant was converted to use #2 oil, as it is much easier to handle.

It's not a can of worms. The best hybrids use LOX, but it's not for hobby use.

I don't want to discourage your enthusiasm but you need a TRA L2 high power certification before you can do EX under TRA rules. At that point, you are likely to know a lot more about rocket motors than you do at present. And that's a good thing, because if you try to do what you are proposing in the manner that you are proposing to do it, you won't live long enough to get your L2 certification. If you're really interested in learning about propulsion I strongly suggest you obtain a copy of Sutton's Rocket Propulsion Elements to get a basic understanding of how rocket motors and rocket propellants function.

Bob

Thanks for the advice. I knew about TRAs L2 requirement to participate in EX, but was unsure about the limits placed on their activities. I've seriously considered joining RRS at some point as well. I'll definitely look into the Sutton book. A bit about my background, I minored in physics in college, and just started an apprenticeship as a Millwright. I'm particularly interested in turbine work. I've figured that many of the skills I will acquire as a millwright would be transferable to EX.
In reading about various types of machinery over the years, I've noticed that the same type of component often gets used for many, wildly different applications. One example, I was reading about gas burners, and later was reading about gas chlorination for swimming pools. The device for injecting chlorine into the water was a carbon copy of one of the gas burner designs I had read about. Just a venturi tube with air or water flowing through it, dragging along the gas or chlorine. Paint sprayers and oil burners are another example. In both cases, atomization of the fluid is required. Air atomization and pressure atomization is used in both applications. Knowing this, I can't help but think of a liquid fuel rocket engine as being conceptually very similar to an oil burner, or a paint sprayer, the biggest difference being the De Laval nozzle. I don't actually plan on doing that, I just wonder how correct that perception is.
Again, thanks for the advice.

 

[Handeman]

I knew about TRAs L2 requirement to participate in EX, but was unsure about the limits placed on their activities.

They don't place any limits or restrictions on your activities, except at a sanctioned launch.

The NAR ban on EX and the Tripoli requirements concerning EX apply ONLY to sanctioned launches. Neither organization has any rules about EX activities that do not occur at a launch that they are sanctioning. They have no rules of any kind about how you build, what type motors you make, or anything else, if the activities don't occur at a sanctioned launch.

What local, state, or federal laws apply is a whole different question.

With that said, it is a VERY good idea to follow those Tripoli rules for EX just for the safety benefits. If you get a L2 before you jump into EX, you will have learned a lot more about HP rockets, motors and how they work. It could significantly change the way you approach EX and will probably make it much safer.

 

[RadManCF]

They don't place any limits or restrictions on your activities, except at a sanctioned launch.

The NAR ban on EX and the Tripoli requirements concerning EX apply ONLY to sanctioned launches. Neither organization has any rules about EX activities that do not occur at a launch that they are sanctioning. They have no rules of any kind about how you build, what type motors you make, or anything else, if the activities don't occur at a sanctioned launch.

What local, state, or federal laws apply is a whole different question.

With that said, it is a VERY good idea to follow those Tripoli rules for EX just for the safety benefits. If you get a L2 before you jump into EX, you will have learned a lot more about HP rockets, motors and how they work. It could significantly change the way you approach EX and will probably make it much safer.

I definitely plan on getting my L2 before getting into EX. As I've said before, I'm interested in EX because I'd like to explore the mechanical aspects of rocket engines. Would that make me unusual among the EX crowd?

 

[ClayD]

They don't place any limits or restrictions on your activities, except at a sanctioned launch.

The NAR ban on EX and the Tripoli requirements concerning EX apply ONLY to sanctioned launches. Neither organization has any rules about EX activities that do not occur at a launch that they are sanctioning. They have no rules of any kind about how you build, what type motors you make, or anything else, if the activities don't occur at a sanctioned launch.

What local, state, or federal laws apply is a whole different question.

With that said, it is a VERY good idea to follow those Tripoli rules for EX just for the safety benefits. If you get a L2 before you jump into EX, you will have learned a lot more about HP rockets, motors and how they work. It could significantly change the way you approach EX and will probably make it much safer.

Actualy he got it right, they require L2 to participate in TRA research.
I dont know why your bogging the muck with this sanctioned stuf...

TRA also has a code that restricts what fuel is used(or MOTOR TYPE). So a TRA L2, isnt going to be of any use if you want to fly LOX. you need to find another amature group to be apart of, or have your own facility or arangements for flights and testing...

 

[THarrison]

I've been in the propulsion business professionally for more than 4 decades. Please listen and learn.

Wow. Condescend much?
:eyeroll::eyeroll::eyeroll:

 

[Handeman]

Actualy he got it right, they require L2 to participate in TRA research.
I dont know why your bogging the muck with this sanctioned stuf...

Because TRA rules don't require L2 to participate in research, the rules only apply at a launch. You can do all the EX motors you want as a TRA L0, you just can't fly them at a TRA launch.

 

[ClayD]

Because TRA rules don't require L2 to participate in research, the rules only apply at a launch. You can do all the EX motors you want as a TRA L0, you just can't fly them at a TRA launch.

TRA rules require you to be L2 to "participate" in research activity. IF you look at the scope of thier influence it does not cover the hobby manufacture of motors in process, but does have manufacturing restrictions as to what you can make and "participate" with in thier launches. So inpart you and I agree. However, The sanctioned launch comments alleude to you implying there are non-sanctioned launches occurring. IMO, this is malarky, and if it's occuring, its probably occuring to break the rules and likewise should loose thier TRA prefectureship. Hence "Bogging up the convo with the sanctioned stuff", sanctioned or not doesnt come to play.

TRA uses the Research Safety code to broaden and enlighten the amature motor makers in its ranks. I know of NO TRA'EXer who would use the Research Safety Code to say that a L0 or even NON-Member should not be allowed to explore the world of EX motors. Ever been to a Mix PARTY, usually have a good amount of non-L2 Tra people there. I even have heard of some TRA members mentoring youths who cannot be L1, in motor making.

TRA is the best association imo if you want to "START" making motors. There are indeed other associations, but my guess are not as diverse, or as regionaly occupied as TRA is.


YES, TRA clearly doesnt regulate what each of us does off field... no one here claims that it does... I could make a pulse jet rocket at home, and TRA would never care until i showed up with it at a launch.