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This is my 'favorite' picture of the fired grain. Lots going on in here In this picture the injector is on the left and the nozzzle on the right.

I used a turbulator insted of a a pre combusion section. The idea of the turbulator is to have some burning and have the flow from the simple nozzle become spread and turbulant. There is regression in this area, but less than 'down stream'

Far left, you can see the krytox line on the bore where the fitting sealed to the bore of the grain, no evidence of any blow by

Preheater ring - (the area to the right of the bore and before the swirls) this started out as one ofthe thinner sections, looks likethere was minimal regression in this area - that is what i was planning on

RTV Bond - I put a bond in using red RTV, I wanted to see about sealing grains or other features together, there is a stright and a taper. Looks like it worked well. The missing RTV in the gaps, pulled out whan I was cutting the sample.

Turbulator - The grain includes a molded in place turbulator section that runs from the preheater ring down. I added a 'neck down' feature in the grain as part of the turbulator, where the swirls fair into the minor diameter and then flare back out inti the spiral pattern. The neck is at approximately from 3.5 - 4 " (seethe ruler below the part)

It is really interesting to look at the three zones, turbulator (1.25 - 3.5) neck (3.5-4), combustion chamber (4.0 plus)
Observations
  • the burned surface looks very different on each side of the neck in the turbulator section the nylon is 'glassy and black' on the combustion chamber side it is pocked and has the grey - brown color. Obvious difference between the two zones.
  • The neck has obvious erosion lies that start at the end of the turbulator groves, transit the neck at a more axial angle, then reconnect with the groves in the combustion chamber
  • scalloping in the combustion chamber, it is pretty obvious from the texture that there was a lot of turbulence coming out of the neck section, thats a good thing.
  • The color change is really interesting. To the left of the neck the O/F ratio would be high, and lower to the right, im not sure what is really going on but it is obvious that there is a transition right at the neck.

1737650770569.png
 
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This is my 'favorite' picture of the fired grain. Lots going on in here In this picture the injector is on the left and the nozzzle on the right.

I used a turbulator insted of a a pre combusion section. The idea of the turbulator is to have some burning and have the flow from the simple nozzle become spread and turbulant. There is regression in this area, but less than 'down stream'

Far left, you can see the krytox line on the bore where the fitting sealed to the bore of the grain, no evidence of any blow by

Preheater ring - (the area to the right of the bore and before the swirls) this started out as one ofthe thinner sections, looks likethere was minimal regression in this area - that is what i was planning on

RTV Bond - I put a bond in using red RTV, I wanted to see about sealing grains or other features together, there is a stright and a taper. Looks like it worked well. The missing RTV in the gaps, pulled out whan I was cutting the sample.

Turbulator - The grain includes a molded in place turbulator section that runs from the preheater ring down. I added a 'neck down' feature in the grain as part of the turbulator, where the swirls fair into the minor diameter and then flare back out inti the spiral pattern. The neck is at approximately from 3.5 - 4 " (seethe ruler below the part)

It is really interesting to look at the three zones, turbulator (1.25 - 3.5) neck (3.5-4), combustion chamber (4.0 plus)
Observations
  • the burned surface looks very different on each side of the neck in the turbulato section the nylon is 'glassy and black' on the combusiton chamber side it is pocked and has the grey - brown color. Obvious difference betwee nthe two zones.
  • The neck has obvious erosion lies that start at the end ofthe turbulator groves, transit the neck at a more axial angle, then recoonect witth the grroves in the combustion chamber
  • scaloping in the combusion chamber, it is pretty obvious from the texture that there was a lot of turbulance coming out of the neck section, thats agood thing.
  • The color change is really interesting. To the left of the neck the O/F ratio would be high, and lower to the right, im not sure what is really going on but it is obvious that there is a transition right at the neck.

View attachment 690663
So this is the nylon grain in a 54mm motor. Fired in a test stand.
Not the Rattworks..? The Rattworks K240 is 64mm od 59mm I'd.
What grain was in the k240 with the crossflow nozzle?
 
So this is the nylon grain in a 54mm motor. Fired in a test stand.
Not the Rattworks..? The Rattworks K240 is 64mm od 59mm I'd.
What grain was in the k240 with the crossflow nozzle?
the test grains on the test stand were not the same as the RATT.
  • Ratt used a stock grain + X- flow injector
  • test grains were 48mm OD tested in a 54 mm OD tube (stock tube not DOM motor case) using a straight injector
 
I used thermite but put it into a lacquer to dip igniters. Not so aggressive then. I did mix up a magnesium powder based thermite, put 1.7grams of it in a canister and used a nichrome igniter to light it electronically at 20 feet away. Blew like the largest M-80 I ever heard and I quickly packed up and went inside in case someone called the cops. No one did but scared the heck out of me. I expected it to just quietly "flare up" but had a rude surprise. Did well in a lacquer based igniter and the lacquer probably retarded the burn so it just flared up. Other forms of thermite are less aggressive and easier to work with. I used those to dip igniters thereafter. Oh, the burn left a stain on the cement driveway that took 4 years before it faded completely! Kurt

I used thermite but put it into a lacquer to dip igniters. Not so aggressive then. I did mix up a magnesium powder based thermite, put 1.7grams of it in a canister and used a nichrome igniter to light it electronically at 20 feet away. Blew like the largest M-80 I ever heard and I quickly packed up and went inside in case someone called the cops. No one did but scared the heck out of me. I expected it to just quietly "flare up" but had a rude surprise. Did well in a lacquer based igniter and the lacquer probably retarded the burn so it just flared up. Other forms of thermite are less aggressive and easier to work with. I used those to dip igniters thereafter. Oh, the burn left a stain on the cement driveway that took 4 years before it faded completely! Kurt
Safety distances require a 100 feet minimum for all certified hybrids over J motor increases the required distance.
Experimental motors require a doubling of distance.
The code says all hybrids that includes micro hybrids. Safety is critical in our hobby. It also requires that you be a L2 to do any experimental motors.
If I am wrong about these requirements please let me know.
 
Safety distances require a 100 feet minimum for all certified hybrids over J motor increases the required distance.
Experimental motors require a doubling of distance.
The code says all hybrids that includes micro hybrids. Safety is critical in our hobby. It also requires that you be a L2 to do any experimental motors.
If I am wrong about these requirements please let me know.
I've scoured the TRA unified safety code, NAR safety code, NFPA 1122, NFPA 1125 and 1127 - can't find a reference to doubling of distance for experimental motors, but I suspect it was a thing previously. I found this article on TRA's site that was posted when the unified safety code came in to effect, which mentions:
"Under this safety code, there are no longer Commercial launches or Research launches, just Tripoli launches. There are some changes to the current safety code, such as a common safe distance table, a safety code for both model rockets as well as radio-controlled boosted gliders as well as other changes."
...I certainly don't think it's a terrible idea if anyone wanted to go ahead and double the distance when flying untested motors anyway, doubt any RSO would disagree with anyone wanting to do that. I know I've flown certified F motors from high power pads before simply because I wanted to use a rail...

As for micro hybrids, that seems a bit hazy at first, because TRA and NFPA only make reference to high power hybrid motors, or refer to hybrids as a special type of high power rocket motor. In other words, there's no direct statement along the lines of "all hybrids are high power rocket motors". BUT, upon a bit more digging, I did note that NFPA 1125 only defines model rocket motors as being solid rocket motors, therefore, I would interperet that as "all hybrids are to be treated as high power motors", so minimum distance for micro hybrids is 100ft/30m (unless you've somehow managed to a J impulse out of one...) Also not a bad idea anyway, since micro hybrids are WAY louder than any solid motor of the same impulse that I've flown. Micro hybrids are research/experimental motors under the TRA code, so to launch one at a TRA affiliated does indeed require L2.

Note: For those outside the US, the following is in the context of legislation that applies in QLD, Australia only, and this legislation could change at any time. ALWAYS CHECK YOUR LOCAL LAWS, and if you are unsure, SEEK APPROPRIATE ADVICE.

Outside of the US, NFPA does not apply - local laws supercede these and you must abide by whatever those are, as they may have different requirements. Perfect example of this is QLD Australia, where we have 2 sets of explosives legislation governing rocket motors, and CASA legislation governing flights - individuals without a permit to manufacture explosives CANNOT make solid rocket motor propellant, and that's basically impossible to obtain for individuals, so we can't do EX solids whatsoever, even if TRA and NFPA permits it. But, building and flying experimental hybrid motors is less restrictive, as these are not classified as explosives under our legislation. TRA certification levels are only relevant in QLD for two things: rules for who can fly what at TRA affiliated clubs (which QRA is), and L1 certification is just something that is recognised as satisfying the requirement of demonstrate competency with using explosives when you first apply for a licence to purchase and use explosives (the licence required for buying and using HP solid propellant here).

Outside of that, CASA legislation does not restrict who launches rocket motors nor what type they're allowed to launch, and focusses on safe operation in airspace (i.e - don't launch it with planes flying overhead, don't cause unreasonable risk to people/buildings/property etc.) Result being that here in QLD, we absolutely are allowed to fly micro hybrids as if they were model rocket motors when not launching with a club. That being said, I HIGHLY recommend that TRA safe distances and procedures for launching are followed anyway, and also HIGHLY recommend experience in reloadable solid motors as well. Finally, although we're permitted a greater degree of freedom on this, please, be sensible and do not be the reason for a change in our legislation. Just because something is allowed, it does not mean throwing safety to the wind.
 
I've scoured the TRA unified safety code, NAR safety code, NFPA 1122, NFPA 1125 and 1127 - can't find a reference to doubling of distance for experimental motors, but I suspect it was a thing previously. I found this article on TRA's site that was posted when the unified safety code came in to effect, which mentions:
"Under this safety code, there are no longer Commercial launches or Research launches, just Tripoli launches. There are some changes to the current safety code, such as a common safe distance table, a safety code for both model rockets as well as radio-controlled boosted gliders as well as other changes."
...I certainly don't think it's a terrible idea if anyone wanted to go ahead and double the distance when flying untested motors anyway, doubt any RSO would disagree with anyone wanting to do that. I know I've flown certified F motors from high power pads before simply because I wanted to use a rail...

As for micro hybrids, that seems a bit hazy at first, because TRA and NFPA only make reference to high power hybrid motors, or refer to hybrids as a special type of high power rocket motor. In other words, there's no direct statement along the lines of "all hybrids are high power rocket motors". BUT, upon a bit more digging, I did note that NFPA 1125 only defines model rocket motors as being solid rocket motors, therefore, I would interperet that as "all hybrids are to be treated as high power motors", so minimum distance for micro hybrids is 100ft/30m (unless you've somehow managed to a J impulse out of one...) Also not a bad idea anyway, since micro hybrids are WAY louder than any solid motor of the same impulse that I've flown. Micro hybrids are research/experimental motors under the TRA code, so to launch one at a TRA affiliated does indeed require L2.

Note: For those outside the US, the following is in the context of legislation that applies in QLD, Australia only, and this legislation could change at any time. ALWAYS CHECK YOUR LOCAL LAWS, and if you are unsure, SEEK APPROPRIATE ADVICE.

Outside of the US, NFPA does not apply - local laws supercede these and you must abide by whatever those are, as they may have different requirements. Perfect example of this is QLD Australia, where we have 2 sets of explosives legislation governing rocket motors, and CASA legislation governing flights - individuals without a permit to manufacture explosives CANNOT make solid rocket motor propellant, and that's basically impossible to obtain for individuals, so we can't do EX solids whatsoever, even if TRA and NFPA permits it. But, building and flying experimental hybrid motors is less restrictive, as these are not classified as explosives under our legislation. TRA certification levels are only relevant in QLD for two things: rules for who can fly what at TRA affiliated clubs (which QRA is), and L1 certification is just something that is recognised as satisfying the requirement of demonstrate competency with using explosives when you first apply for a licence to purchase and use explosives (the licence required for buying and using HP solid propellant here).

Outside of that, CASA legislation does not restrict who launches rocket motors nor what type they're allowed to launch, and focusses on safe operation in airspace (i.e - don't launch it with planes flying overhead, don't cause unreasonable risk to people/buildings/property etc.) Result being that here in QLD, we absolutely are allowed to fly micro hybrids as if they were model rocket motors when not launching with a club. That being said, I HIGHLY recommend that TRA safe distances and procedures for launching are followed anyway, and also HIGHLY recommend experience in reloadable solid motors as well. Finally, although we're permitted a greater degree of freedom on this, please, be sensible and do not be the reason for a change in our legislation. Just because something is allowed, it does not mean throwing safety to the wind.
Outside the US NFPA does not directly apply. But it's been used as reference material for pretty much all rocketry regulation, where there is one.
The safety distances were, at one point doubled for experimental motors.
This was pulled back to the regs today, as the safe distance for an accident is pretty much the safe distance. Something going bang, can only travel so far. There is an argument that something flying in the wrong direction could do something, but again that is the same for any rocket.
 
This is my 'favorite' picture of the fired grain. Lots going on in here In this picture the injector is on the left and the nozzzle on the right.

I used a turbulator insted of a a pre combusion section. The idea of the turbulator is to have some burning and have the flow from the simple nozzle become spread and turbulant. There is regression in this area, but less than 'down stream'

Far left, you can see the krytox line on the bore where the fitting sealed to the bore of the grain, no evidence of any blow by

Preheater ring - (the area to the right of the bore and before the swirls) this started out as one ofthe thinner sections, looks likethere was minimal regression in this area - that is what i was planning on

RTV Bond - I put a bond in using red RTV, I wanted to see about sealing grains or other features together, there is a stright and a taper. Looks like it worked well. The missing RTV in the gaps, pulled out whan I was cutting the sample.

Turbulator - The grain includes a molded in place turbulator section that runs from the preheater ring down. I added a 'neck down' feature in the grain as part of the turbulator, where the swirls fair into the minor diameter and then flare back out inti the spiral pattern. The neck is at approximately from 3.5 - 4 " (seethe ruler below the part)

It is really interesting to look at the three zones, turbulator (1.25 - 3.5) neck (3.5-4), combustion chamber (4.0 plus)
Observations
  • the burned surface looks very different on each side of the neck in the turbulator section the nylon is 'glassy and black' on the combustion chamber side it is pocked and has the grey - brown color. Obvious difference between the two zones.
  • The neck has obvious erosion lies that start at the end of the turbulator groves, transit the neck at a more axial angle, then reconnect with the groves in the combustion chamber
  • scalloping in the combustion chamber, it is pretty obvious from the texture that there was a lot of turbulence coming out of the neck section, thats a good thing.
  • The color change is really interesting. To the left of the neck the O/F ratio would be high, and lower to the right, im not sure what is really going on but it is obvious that there is a transition right at the neck.

View attachment 690663

Grain showing regression

1600 cc of NOS at 700 psi
NOS Table gives;
  • 63.5 degree F
  • 692.13 PSI
  • .803 g/cc ( 50.16 lb/ft^3)
  • 1,280 grams of NOS used
  • 4.8 O/F ratio
grain weight before firing 504 grams - 240 after firing - 264 grams consumed

I used a 1600 cc tank because I wanted to see what the grain looked like partway through a burn. On this grain, it was split at the turbulator (centered at 4.0 inches.)

0-.75 injector sealing area
.75 - 1.25 preheater
1.25 - 3.5 swirled section of the turbulator
3.5-4.5 straight neck section of the tubulator
- 4.85 split between grain sections
4.5 - 10.75 swirled combustion chamber
10.75 - 11.5 straight section
11.5-12.5 Nozzle
The green lines are 1mm spacing

1737844421354.png
Detail of Turbulator section
1737845080606.png
Detail of combustion chamber below turbulator
1737845293600.png
Detail of combustion chamber aft end
1737845376132.png
 
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I'll probably focus more on liquids this year, but the idea is to have the same monotube casings for all. Since my lathe is only 10*22" I am limited in the length of casing I can machine... So far!

Yesterday I machined an expanding arbor for 54mm casings so that I can machine them on the outside close to the chucks.

Next up is a second steady rest that I'll modify to take axial loads so that I can machine casings using a milling attachment and turning them by hand (for internal snap ring grooves)
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I'm assuming this is primarily to square and clean up the ends from a saw cut?

TP
That and external threads like on CTI Pro54 casings. I really like having one end of the casing without any internal features (snap ring groove, holes for bolts/pins) for ease of assembly. Maybe it's a skill issue but I have shredded way to many o-rings :D tbh I haven't tried to machine o-ring grooves with more depth than the standard recommendations you get from manufacturers.
 
That and external threads like on CTI Pro54 casings. I really like having one end of the casing without any internal features (snap ring groove, holes for bolts/pins) for ease of assembly. Maybe it's a skill issue but I have shredded way to many o-rings :D tbh I haven't tried to machine o-ring grooves with more depth than the standard recommendations you get from manufacturers.
Yeah, I can totally relate. That's also my preference for smaller-medium sized casings.

TP
 
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