Advice needed on LOC Deployer ground testing

[Joe Bruce]

I built a LOC Deployer (3" all-inclusive dual deploy kit) as a test vehicle for the EggTimer Quantum that I soldered, the MJG e-matches I dipped, and the charge wells I designed and printed in PETG. My real goal is full dual deployment on the LOC 5.5" Patriot I built as my NAR Level 2, but I figured it was better to test with a 2 lb. rocket than a 12 lb. rocket!

I've been using the NASSA deployment charge calculator to estimate the required charge. I started with 0.35g of black powder (deployment charge kit from BuyRocketMotors), and moved up a bit to 0.40g. That seems to give nice separation in ground testing, and has not resulted in any damage to the streamer (protected by a LOC "starter blanket" -- a small hexagonal nomex(ish).

My frustration is with the main chute. First, the payload compartment is about 1-2" too small for the included 28" chute (with a spill hole pre-cut), the mini nomex, and the 15' of shock cord. I can fit everything, but the two 2-56 nylon screws (shear pins) are really holding things compressed by at least 1/2". Second, only 2 of 4 ground tests resulted in separation. I have thin (0.005"?) brass sheets epoxied inside the payload tube to prevent elongation of the shear pin holes, and the cardboard/brass are tapped for the 2-56 screws. The NC has holes sized for the OD of the 2-56 screw, and it works perfectly -- remainder of screws are still in position in the NC shoulder and I just push them into the NC with the tip of a screwdriver.

I started with 0.25g (no separation), increased to 0.363 (NC came off, chute was still stuck in payload tube), increased again to 0.45g (no separation), and increased again to 0.50g (separated but blew a 1/2" hole through the nomex). In all cases, I stuck with 2 shear pins, though I've considered reducing it to 1. Like I said above, the shear pins are needed just to keep the NC on due to the undersized payload tube. I insert the e-match to the bottom the charge well, pour in the BP (barely covers the tip), pack dog barf on top, then end with masking tape over the top and another piece wrapped around the charge well.

The 3D printed charge wells are holding up fine, the Quantum is doing its thing well, the MSW screw switch is properly disconnecting deployment power, and the e-matches are working (except for the ones where the pyrogen flakes off, rats).

Any suggestions? Half a gram of BP seems excessive for the 3" x 4.5" of payload tube left once the e-bay and NC are in place, and I'm concerned how many nomex blankets I'll go through just in ground testing!

 

[GaryT]

Get yourself a 3/8" wood bulkhead, cut off the bottom of the NC, put a small eyebolt in the wood bulkhead, now insert the bulkhead up inside the NC and use 6-8 screws countersunk into the NC shoulder around the outside to hold it in place. You'll gain a few inches and can friction fit the NC or still pin it without it already being under pressure.I'm not a fan of stretching any rockets as they never look right to me. I would also not recommend using only one shear pin, you take the chance of cocking the NC on ejection and getting it stuck.

Edit: You can also have more of the coupler in the booster to gain a bit more space. IE if you have an 8" Coupler have 5" in the booster and 3" in the payload. I've done both these suggestions many times without fail.

 

[richP]

Does the nosecone slide in easily or is there some friction? How tightly are you folding the chute? How tightly are you packing the dog barf over the powder? It's usually better to have the ematch sitting on top, or just barely in the powder. Not at the very bottom.

If I had to guess, based on the hole in the nomex, I would say that the chute/nomex was hindering the charge. I would try to fold it fairly tight and try again.
Also, good advice from GaryT.

 

[Joe Bruce]

@GaryT and @richP -- Thanks to both of you for the advice!

The NC fit is pretty loose -- I would use tape if it was single deploy w/o shear pins. The chute is folded as compactly as possible, though frankly the shock cord takes up almost as much room. It slides in easily, but is then squashed by the NC so probably "plugs" the tube.

I've added a bulkhead into an NC before for adjustable weight, I guess I just hoped that I could follow LOC's instructions on this one. Their 3.0" light e-bay is only 6" long, and I built it as directed w/ 2.5" on either side of the vent ring. If I had it to do over, I would do 2"/3" or maybe even 1.5"/3.5" to gain an extra inch. Guess that's what I get for assuming the all-inclusive design would work out of the box.

So, I will:

1. Cut off the end of the NC and add a bulkhead w/ eyebolt recessed into the shoulder, secured w/ epoxy and screws. That'll give me almost 3 inches of space.
2. Maybe fold the chute in half rather than z-fold, and then z-fold and tape the shock cord to minimize its size. Wrap in a new nomex.
3. Consider tweaking the charge well design to reduce the ID (currently 9 mm). A quarter gram of BP barely covers the bottom. Maybe I'll use the ID of the centrifuge vials my current stock came in.
4. Add BP to the charge well, then stick the e-match in, head down. Then pack in some dog barf and finish with masking tape.
5. Buy some BP in bulk -- the 5.5" Patriot will probably use a few grams in each charge well, times 4 (it'll be redundant DD). That'd be a LOT of those $10 ejection charge kits.

I've heard (here and elsewhere) that the e-match should be near the top of the BP (e.g. J-bend so the head is facing towards the mouth again), but the BP layer was so thin in these charge wells... Maybe by constraining the diameter, it will burn better/faster, produce more pressure, and burn my laundry less!

 

[Speaknoevil]

#3 above may be your problem. It is possible with the powder dispersed like that you are not getting a complete, and at least, not an immediate burn, so your blast wave is reduced. If you do use the centrifuge vials, I make it a practice to wrap the sides with metal tape. This increases containment (and subsequent pressure) and provides directionality to the shock wave.

 

[Joe Bruce]

#3 above may be your problem. It is possible with the powder dispersed like that you are not getting a complete, and at least, not an immediate burn, so your blast wave is reduced. If you do use the centrifuge vials, I make it a practice to wrap the sides with metal tape. This increases containment (and subsequent pressure) and provides directionality to the shock wave.

I'm not planning to directly use the centrifuge vials. Interestingly, they have a 9mm ID, so that doesn't fully explain the issue. However, I'm reducing the ID of my charge well to 6mm, and I increased the wall thickness to 2.4mm (I have no idea what the ID or wall thickness is on similar wells from Mach 1 Rocketry, though I'm considering one of their 38mm DD kits -- beautiful e-bay design).

I'm still going to feed the e-match in from the top (I have a cut-out on the rim exactly the thickness of the wires), but I will fill the well with BP first and put the e-match on top, followed by dog barf (as noted in #4). I will also design myself a funnel (9mm ID was hard enough to fill without spilling) and a tamper (round-ish, but with a cutout for the wires). And, of course, it's time to put my SainSmart 3018Pro CNC to use and cut the bulkhead for #1.

Thanks again to all of you for the advice!

 

[Speaknoevil]

I'm not planning to directly use the centrifuge vials. Interestingly, they have a 9mm ID, so that doesn't fully explain the issue. However, I'm reducing the ID of my charge well to 6mm, and I increased the wall thickness to 2.4mm (I have no idea what the ID or wall thickness is on similar wells from Mach 1 Rocketry, though I'm considering one of their 38mm DD kits -- beautiful e-bay design).

I'm still going to feed the e-match in from the top (I have a cut-out on the rim exactly the thickness of the wires), but I will fill the well with BP first and put the e-match on top, followed by dog barf (as noted in #4). I will also design myself a funnel (9mm ID was hard enough to fill without spilling) and a tamper (round-ish, but with a cutout for the wires). And, of course, it's time to put my SainSmart 3018Pro CNC to use and cut the bulkhead for #1.

Thanks again to all of you for the advice!

Oh, I'm sorry, I'm used to the small vials like below that hold just over 1g each. Actually don't have any sitting here, so don't know the dimensions. But as you mentioned, for a small amount of powder you for sure have to use dog barf to contain/concentrate it at the bottom with the match.

 

[David Schwantz]

Your problem is a directional blast. Your charge wells are acting like a barrel of a gun. Your Nomex is so close to them that the blast is blowing a hole in them. As others pointed out, try using the vials. This will allow the blast to radiate in all directions and not just into the blanket. Also as in post #3, with the match at the bottom of the well you are blowing BP out that has not yet burnt and it is igniting as it is outside of the well.

 

[Joe Bruce]

So would I be better off just using a glove tip filled with BP? If I'm looking for an omnidirectional blast? Just printed a new well and the funnel is currently printing, but maybe I'm just reducing the caliber.

We're talking about the same centrifuge vials. The ID is actually 9 mm (I was surprised too), the OD is about 10.4 mm.

EDIT: I assumed people who used the vials were putting the vial into a well, still yielding a directional blast...

 

[Speaknoevil]

So would I be better off just using a glove tip filled with BP? If I'm looking for an omnidirectional blast? Just printed a new well and the funnel is currently printing, but maybe I'm just reducing the caliber.

We're talking about the same centrifuge vials. The ID is actually 9 mm (I was surprised too), the OD is about 10.4 mm.

EDIT: I assumed people who used the vials were putting the vial into a well, still yielding a directional blast...

I do not put my vials into wells.

 

[Joe Bruce]

So... the vials are single use? I imagine they shatter, right?

 

[Speaknoevil]

So... the vials are single use? I imagine they shatter, right?

No, I don't reuse them. Others may. Years ago I just bought them in bulk on eBay. In fact, I have sizes up to 6g of powder. Saying that, I have used nitrile glove tips too, frankly most any containment system will work as long as it is, well, contained.

 

[Joe Bruce]

Thanks. I know I've seen charge wells like this in other designs, but it isn't working for this rocket, it seems. Or maybe the root problem is still that there isn't enough space for the laundry?

Cut the end off the NC, now to CNC two 3/16" ply bulkheads, glue 'em together, and epoxy/screw in place.

 

[David Schwantz]

As Speak said, I do not put them in a well either. Nor are they able to be reused. I bought like 500 for 12.00 bucks or so. If you want a couple to try out PM me and I can send you some. Have never used the glove tip.

 

[David Schwantz]

What is the point of cutting the NC off? Are you just trying to get more space in the bay?

 

[GaryT]

I only use charge canisters Blastcaps, The Blastcaps were my Co., sold them for years. My ematch goes on the bottom always has always will. Like Speaknoevil said the vial is directional and acts like a shotgun blast, years ago it blew a perfect dime size hole through the phenolic wall causing the bird to flat spin in.

 

[Speaknoevil]

I have a few of Gary's Blastcaps in my larger rockets. I use those too. Frankly, I don't mind directional blasts as long as the direction is in line with airframe (not into it's side), and there is enough space in the bay. As you experienced, very tightly packed bays can lead to damage with a directional charge. In this case, I find it better to use the glove tip option.

 

[Joe Bruce]

What is the point of cutting the NC off? Are you just trying to get more space in the bay?

Yes. As noted in the first post, the chute + shock cord + nomex bundle (tightly packed) doesn't really leave enough clearance for the NC. The shoulder would stick out 1/2" at least, so I push it down tightly while I screw in the shear pins. There is only 3" diameter by about 4" for the laundry, and that's too little for a 28" chute, 15' of shock cord, and a nomex to protect it all.

 

[Joe Bruce]

I have a few of Gary's Blastcaps in my larger rockets. I use those too. Frankly, I don't mind directional blasts as long as the direction is in line with airframe (not into it's side), and there is enough space in the bay. As you experienced, very tightly packed bays can lead to damage with a directional charge. In this case, I find it better to use the glove tip option.

Thanks for the clarification! I've been confused between "too directional" advice and "not burning completely" advice. Maybe the charge wells would work okay if the laundry isn't so tight (e.g. on my 5.5" Patriot). But I'll try glove tips next on the Deployer once I finish the NC modifications.

 

[David Schwantz]

Just like you see on TV, when you hold the muzzle to close to the skin the powder that burns outside of the barrel leaves a stippling effect. I have also burnt holes in blankets like this. I did find some flame proof treatment that I have sprayed on some blankets. But have not been able to try it out yet. Hopefully someday we will launch again.

 

[GaryT]

Another thing that works great for a charge canister and especially on smaller rockets is a shell casing, either a .380, 9mm whatever you need. Pop out the primer and you can screw/bolt it right to your Av-Bay lid. Needless to say the sizings are basically limitless.

My Blastcap Canister I sized in 4, 8 and 12g capacity's, E-Match goes in 1st then your BP then fill the remaining space with dog barf, pack it in and tape shut, just a good push with your thumb doesn't have to be super! packed in.

 

[David Schwantz]

I would advise against a shell casing. Rocket came down with a mess of gouges in it. Had no idea what had happened, until I saw this.

 

[GaryT]

I would advise against a shell casing. Rocket came down with a mess of gouges in it. Had no idea what had happened, until I saw this.

What the heck did they use a 45-70 LOL that thing was way to long or a short shock cord. Casing isn't going to do much more damage than a charge canister. Had to be some kind of anomaly? Why was it so close to the BT from apogee eject?You using a switch band where the coupler ends up by itself?

 

[David Schwantz]

Good eye, that is a 45-70. 25' of kevler, both ends. The sharp brass ends took several chunks of air frame. Could not see it a 10,000', all I know is I took them off my other rocket and installed wells kind of like the ones you posted. Have not had missing chunks since

 

[GaryT]

Good eye, that is a 45-70. 25' of kevler, both ends. The sharp brass ends took several chunks of air frame. Could not see it a 10,000', all I know is I took them off my other rocket and installed wells kind of like the ones you posted. Have not had missing chunks since

45-70 I figured, I have a brand new Marlin 1895SBL 45-70 that I haven't had the chance to get to the range yet. You know what maybe tomorrow? Thanks D. lol

 

[David Schwantz]

Love mine, 1895 CB 24" oct barrel. 19 bears later, never a jam. Gotta love levers.

 

[Joe Bruce]

Unfortunately, our range in MD is closed. Someday I'll be back to flying AND shooting!

Thanks again for the advice. Having trouble with the stupid cheap CNC. Makes me wish I sprang for the Shapeoko / Carbide 3D they have at our local hackerspace.

 

[Joe Bruce]

Just following up... Thanks for the great advice here and in PM.

I found two more BP calculators via old TRF threads (https://www.rockethead.net/black_powder_calculator.htm and https://coastrocketry.com/ejection_charges.htm). In both cases, they recommend a higher pressure for the smaller 3" diameter. So I just finished doing three successful ground tests with 0.7g FFFFg charges contained in nitrile glove tips wrapped in blue tape (~2 wraps around) and masking tape (once over top to label charge).

Clean deployments, shear pins worked as expected, brass shear plates work great, NO damage to streamer or parachute (now wrapped in a new 9" blanket).

Now we just need to get back to launching again!

 

[Joe Bruce]

Wow, never thought it would take so long to get my Deployer in the air! It finally took its maiden flight last Sunday, 3/7 on a G77-7R to 865'. Dual deploy worked perfectly. Flew it twice more today at my daughter's TARC team's launch, on G76-7G (917') and G77-7R (815') again. Perfect both times!

I like the DD setup on my 5.5" LOC Patriot better, since I put screw terminal blocks on the bulkheads and have screw switches wired to the power for the Quantum and Quark (backup). Much easier to swap than on this Deployer, where the charge wires run through small holes in the bulkhead to the Quantum, which has a screw switch to enable the charges. I have to disassemble the AV bay between launches, which drastically increases the turn-around time.

But the extra space I created in the main chute bay did the trick. No damage to the chute after 3 launches, 2-56 nylon screws sheared perfectly (and drogue streamer deployed perfectly) every time with 0.7g Graf 4Fg charges.

Now on to the 5.5" LOC Patriot with its redundant DD -- hopefully at Red Glare XXI! Maybe even on the J450DM for my L2 cert!

 

[cbrarick]

Hey Gary:

Where are you shooting? I usually go to blue trails for rifle.

rick