L1/L2 2.6" Madcow DX3 Build

Last week I found time to actually attach fins. Finally. It's been what, 4 or 5 months? More? It's finally starting to look rocket-like. Anyway, here's a quick summary.



Sometime in December I created fin alignment jigs out of foam board and templates printed from payloadbay.com I made three, so that I'd have one spare to support the other end of the tube. This let me pick the two that fit best to use on the fin itself when actually gluing them in. I tried to keep them at a minimal size (thus the 6 sides instead of only 3). The weak points at the tips of the fin cut outs I reenforced with some painters tape. Any tape would have been fine, I just happened to have that sitting next to me that day.



Using a method I've seen described somewhere else on this site, I lightly beveled the fiberglass fins. These fins are only 1/16th thick, so I didn't take much. I tried to only remove about 1/3 of the thickness from each side. I used a 'jig' essentially comprised of a flat board with two more pieces of wood (approx. 1/2" square?) screwed to it. Sandpaper was screwed down to lay flat along the base board. The fixed width/height allowed me to sand a consistent angle on each fin. I had to reposition the sandpaper a few times, I think once for each fin, as the repeated sanding in one location wore it down pretty well along the straight line/corner where the fin made contact. The process generated a lot of fiberglass dust, and as expected, caused a fair amount of itching, even when I did this with latex gloves on. Wrists and arms still got hit a bit. Even for this minimal work, a respirator is essential. Lots of this dust ends up in the air and you don't want to breath it. In my opinion, a dust mask isn't going to cut it for this. It may be tough to see in the photo, but I've also sanded to root edge, tab, and fillet areas of the fin in preparation for epoxy.



I described a while back that I had drilled some extra holes along the fin slot. You can see in this picture how I've used a syringe to inject the epoxy (rocketpoxy / G5000, tinted black for visibility) into the space between the airframe and the motor mount. This process seemed to work very well. I'd mix and fill the syringe, insert into each hole and squeeze out some epoxy in each direction, then move to the next hole. I got great coverage, and as you can see in the photos below, the dams I installed previously on the motor mount worked perfectly. If I was to do it again, I'd have made the dams narrower and saved some epoxy, as they aren't adding any strength past probably 1/8 - 1/4" away from the fins, but I had been worried about alignment of the motor mount and fin slots. Looks like I shouldn't have been worried, everything worked out fine.



You can see here the jig in use. The nice thing about the payloadbay jig template is that it prints fin thickness too, so there's no guess work or sloppy wobble so long as you cut right on the lines. The final fin alignment was near perfect. I did make one little un-fixable error here though. The fin slots in this kit are cut LONGER than the fin tabs. That means there is about 1/8" play forward and back when the fin is in the slot. I had intended to place all the fins hard against the back edge (maximizing the Cp towards the rear). This worked fine on the first fin. On the second fin, I forgot to check that positioning after putting on the fin alignment guides. The friction from putting the rear one on slid the fin to the 'forward' position, and I didn't think to correct it. I noticed as soon as I took the guides off to prep for attaching the third fin, which I put on 'correctly' at the back edge. Thus one of my three fins is about 1/8" further forward than the other two. I don't expect this to make any significant difference in flight characteristics, so I'm going to give it a pass. I caught it long after the epoxy had hardened and was uncorrectable at that point anyway.

Next up is the fin fillets, possible even this week. Because the fin tabs are a tiny bit longer than the gap between the motor mount and the body tube, and I neglected to sand them sufficiently to bring them fully in contact, there is a very small gap, probably 1/64" or 1/32" between the bottom of each fin and the BT. I plan to fill it with some medium CA prior to filleting to stop any epoxy from squeezing through when I form the fillets. Anybody see an issue doing that? I know CA ain't great for bonding strength, but I'm just looking for gap filling. it'll all get encased in fillet epoxy, so I think I'm good. Thoughts?

It's been another month, must be time to get off my procrastinating rear end and actually post a progress update. Fillets went on nicely with Rocketpoxy during the beginning of May. Still using the black dye for visibility. Not much to say about this other than the practice I had doing the same on my blue big daddy really seemed to pay off. Tape, apply, pull, wait, remove tape and smooth, repeat the next day on the next side. I did get one small void that must have surfaced after I took the tape off one night and went to bed. Not sure how, cause at that point the Rocketpoxy was pretty well set. Anyway, hollowed it out a bit and applied another dab of epoxy, then sanded flush. Seemed to work fine.



I didn't get many mid-process shots, mostly I just forgot. I was also working on another Madcow product, a 38mm cardboard Mini Frenzy, which was getting fillets at the same time. No after shots of that one. For that matter, no after shots of the final fillets on the DX3 before I started sanding it either. Fillets were pulled with a short piece of PVC (1/2" I think) which was probably larger than needed by a good margin, but I think I like the look regardless. Sanding was done with a longer length of the same PVC pipe (about 14") wrapped in sand paper. This worked moderately well, but because of the larger diameter after apply the sand paper, had a tendency to catch the edges and not the middle, somewhat reshaping the fillet. I caught on and did a fair bit with a smaller diameter cpvc pipe that seemed to even things out. Mostly by eye though, so it's probably not as great as I'd like it to be. Oh well, I can live with it. Paint will show/hide all the imperfections.

EeebeeE said:

One thing to consider with microballoons. If you intend to breach Mach 1, you really don't want them. They make the fillets porous and weaker than if you used straight epoxy, and when you go transonic (About Mach 0.8 to Mach 1.2) you will run into a lot of turbulence that will put a lot of pressure on the fins. This rocket is designed for mach speeds so you won't experience as much flutter, but you will still get a little and you want to make sure you have exceptionally strong fillets.

Rocketry Warehouse and Apogee Rockets sell RocketPoxy. This is a very thick epoxy that does very well for fillets. It will take about 4 hours to set, but the fillets are smooth and extremely hard. It has a shear strength of over 14,000 PSI. It bonds very well to FG if you rough up the contact areas on the fins and the airframe. Do 2 fillets at a time by laying the rocket sideways, taping off the areas you do not want, smoothing the epoxy into place and letting it set. You end up with beautiful fillets that are nice and smooth.

Click to expand...

This may be a little late, but for future reference.
From my years of composite fabrication knowledge on aircraft micro is more of a filler. Flox is kind of an in between micro and cabo and cabo is where the strength is.
Sandability is easier to tougher in the same order.
Strength is weaker to stronger, in same order.
Weight is light to heavy, in same order.

This is a fun build to follow. Thank you for the continuous photos and updates.

dford said:

This may be a little late, but for future reference.
From my years of composite fabrication knowledge on aircraft micro is more of a filler. Flox is kind of an in between micro and cabo and cabo is where the strength is.
Sandability is easier to tougher in the same order.
Strength is weaker to stronger, in same order.
Weight is light to heavy, in same order.

This is a fun build to follow. Thank you for the continuous photos and updates.

Click to expand...

Thanks, after the response from EeebeeE, I did a bit more research and found pretty much the same thing, but didn't discover anything about "Flox". I looked a bit further today and discovered that it was synonymous with flocked cotton, which I had heard about as filler previously, but dismissed as likely pretty weak. I guess it's really not. I never did really use the microballoons that I bought for much other than bulking out the fillets on a few LPR rockets. I used chopped silica in a few places where I was mostly looking for thickening on a few kevlar-to-MM connections as 'encasement' where structural strength was still mostly a second though.

It is a bit late, admittedly, but I really appreciate the feedback and I'm glad you're enjoying the (horribly drawn-out) build.

I've made some progress with the avionics portion of the build. Due to the time, this post will be mostly pictures. If anyone is looking for details, let me know. I plan on using a similar pull-pin system for the altimeter that I did for the nosecone tracker (Post #30). This will be a single altimeter bay. If I want to fly a redundant back-up system I'll have to build another sled.


Primary wood parts (1/8" craft balsa), prior to assembly. Shown here as a partial-sub assembly, it turns out that I rather forgot that I needed the baseplate off-axis. I needed to re-cut the slots on the end caps, as shown in later photos.


The momentary switch I installed in the tracker bay used a piece of copper wire to secure it. I realized afterwards that toothpicks would be lighter. A bit of chopped silica was used to thicken the epoxy here.


Again similar to the tracker bay, I used a piece of aluminum tubing which just fits my 1/8" pull pins as a guide assembly, epoxied to a piece of ply. Prior gluing, this was a continuous piece of tube. The center was cut out after the epoxy had set-up pretty well, but prior to becoming rock hard. It was enough to hold it in place while I used a razor saw to remove the center portion of the tube, but soft enough to clean up the run-over with a hobby knife afterwards.

No further progress on this part so far. I got sidetracked with primer, altimeter testing, pvc field stand contruction, paint/finish polishing, real (non-rocketry) life, etc. Further updates as I find time. Probably tomorrow, as I have to take the day off to care for my son who's sick (again). Nothing serious though. Heck, it even sounds hilarious. Coxsackievirus. Come on, who's not laughing, right? Too bad it comes with a fever and pimple/blister like sores all over his hands, arms, feet, legs and mouth. We're past the fever stage, but still have to deal with the semi-open sores. No daycare till everything scabs over. Luckily he's in good spirits most of the time. Anyway, I'm rambling. Goodnight!

Ok, can't sleep. (clowns will eat me) Not much else, but I thought I'd post one quick 'reflection' picture. Let's just say that this thread by Nathan inspired me to try my hand at polishing a paint job. No before shot for this one, but I can safely say that the nosecone of my Estes V-2 nosecone is now shiniest thing in my fleet.



Along the way I found out that imperfections in the paint (or just using a single coat as I did here, with no clear coat) will result in emphasized imperfections, but still, things look pretty good. The reflections visible in the black paint make me want to use black as a primary color on this L1/L2 build. I've been debating paint schemes and I still haven't settled on anything yet. I'm leaning towards black with (some set of related colors) in a semi-random helical stripe pattern. Any thoughts or suggestion for paint color / patterns, etc. (no matter how off-the-wall!) are warmly encouraged.

MCriscione said:

Ok, can't sleep. (clowns will eat me) Not much else, but I thought I'd post one quick 'reflection' picture. Let's just say that this thread by Nathan inspired me to try my hand at polishing a paint job. No before shot for this one, but I can safely say that the nosecone of my Estes V-2 nosecone is now shiniest thing in my fleet.

View attachment 291919

Along the way I found out that imperfections in the paint (or just using a single coat as I did here, with no clear coat) will result in emphasized imperfections, but still, things look pretty good. The reflections visible in the black paint make me want to use black as a primary color on this L1/L2 build. I've been debating paint schemes and I still haven't settled on anything yet. I'm leaning towards black with (some set of related colors) in a semi-random helical stripe pattern. Any thoughts or suggestion for paint color / patterns, etc. (no matter how off-the-wall!) are warmly encouraged.

Click to expand...

That nose cone iz EPIC!
I follow this build pretty close because I think it may be my future L1L2 build.
I like very much!:wink:

dford said:

That nose cone iz EPIC!
I follow this build pretty close because I think it may be my future L1L2 build.
I like very much!:wink:

Click to expand...

I'm glad you like it dford. I think that it makes for a nice kit that you can build 'your way' pretty easily. I could have opted for a number of easier/simpler choices in construction, or could have made my life even more difficult. I suppose you could say that for any kit, but I like the bones of this one.

In checking over where I left off here, which is lagging behind construction a bit, I see that I have a bit to catch up with. I'll start with the AV-bay. I wanted to include a GPS connection indicator light on the my nosecone tracker bay, but never got there. I think construction has surpassed that option at this point, but I'm not certain. I could probably retrofit a power indicator at least. Regardless, I was CERTAIN that I wanted some indicator lights for the AV bay to provide external diagnostics / confirmation that all is well. Luckily, the Eggtimer that will be flown in this rocket has some options for that, namely a status indicator light and A/B deployment channel continuity lights. I wanted an additional Power indicator (which will just be run inline with the main power switch. That's 4 channels in all, so I started hunting down 8 conductor connectors. I couldn't find much around the house, but I did stumble on an abundance of network cable. Long story short, an old nonfunctional laptop was completely demolished in the process of scavenging a female network connector. A short while later and the female connector was soldered to a small piece of colorful ribbon cable (26 agw I think? maybe smaller) with some yellow shrink sleeve over it for protection.



I drilled 4 equally spaced holes for the 3mm LEDs that I'll be using. I placed a piece of tape over the holes for later alignment when soldering the LEDs. Pro-Tip, place the tape on the inside next time, as the wall thickness contributes significantly to the spacing and I had to re-work the LEDs later to be closer spaced so they would fit in the holes. I then transferred the tape to a scrap piece of foam board (liberated third of a fin alignment jig) and shoved the LEDs in based on the holes in the tape. I transferred a couple details regarding where I wanted the connector placed based on some trial fits inside the AV-bay coupler.



I bent the leads around and taped it all down, then soldered on the LEDs as best I could (with those tiny leads). Stripping leads that small was nearly impossible. I ended up resorting to melting off some of the plastic sheath with my soldering iron. MISTAKE. It took me nearly an hour of careful cleaning to get the iron re-tinned to the point it was functional again. I may still end up needing to buy a new tip, but for the time being everything looks okay. The soldering job is more that a bit messy, but a quick trial fit into the AV-bay coupler showed that (with a little tweaking of wire lengths by bending with some long nosed tweezers) everything fit. Eventually everything will be permanently epoxied into place, but not until after paint is complete.



A trial of the wiring required a bit of hacked up cat5 patch cord, adding resistors to each of the 4 circuits, continuity checking with my multi-meter, realizing that the 90 degree turn in the cable caused it to flip and I had all my connector polarities labeled backwards, realizing the patch cables swap the center pair striped cables (which nearly caused me a heart attack thinking of having to find the break in the line), and finally, hooking up the 4 pairs onto bus wires and connecting a JST connector for the battery. All the work was a success however, and the final test shows all the LEDs lit. They appear to be plenty bright, and if I did my checking right, this is approximately the brightness they will be after connection to the Eggtimer.

I plan to use the first two green lights as power and status indicators and the two red lights as deployment channel continuity indicators.

I'm still looking for paint scheme ideas. Anybody?!

Well, color me confused. I thought I posted a few minutes ago, then I start browsing the HPR forum and find the reply never went through. I guess I didn't hit submit? Now I have to retype/think everything. :eyeroll:

This is another catch-up post. The rocket has been primed, sanded (120), primed, sanded (220), primed, sanded (220), primed, and sanded (400). Uggg. So much sanding on the fillets. They look about 95% of the way to perfect. Good enough for me. So the rocket is ready for paint. In fact, it got it's first (partial) coat this last weekend with a second coat yesterday. I finally settled on a paint scheme. It's fairly atypical, so I hope you all end up liking it. I guess we'll see. I've got another 4+ colors left to shoot with a whole lot of masking left to be done. I asked everybody here in a separate thread for some recommendations on methods for painting what for me will be a fairly complex masking scheme. It looks like I'll be doing a lot of assembling/disassembling over the course of the next few weeks (weather permitting). Once for every one of those paint colors. I hope the first few layers of masking tape comes back up nicely after sitting for 2-3 weeks.

Before I could do any of that though, I needed to add some kevlar to the nosecone, to act as a retention point for the recover system.



I didn't have any 1/2" kevlar left to match the rest of the rocket, so I used 1/4". This shouldn't be an issue, as the 1/2" was overkill anyway. I knotted each end of the kevlar 3-4 inches from each end and positioned the ends so the knots would be right at the back of the nosecone bulkhead. The kevlar was (5 min) epoxied in place, and then smothered in (20 min) epoxy with chopped silica mixed in to a peanut butter consistency. This all stayed put pretty well. I epoxied in the bulkhead too, but forgot pictures. As the nosecone is on the rocket right now, I can't grab any, but maybe later.

That's all for now. Back again soon with an update on the AV bay sled, which is coming along slowly but surely.

Alright, update time!

We've got more paint down on the rocket, color #2's second coat went on today. No pictures, as it's a surprise. Did I say that already?

Bigger news, the AV-Bay is essentially complete. I can't quite assemble it, due to the air-frame being painted, but the sled is actually all done and everything is mounted up, ready to go. In the interest of my free time, I'm going to post pictures without anything labeled, at least for now. If anybody is confused regarding any of the layout, please just ask. I'll be happy to answer questions or add some labels to the photos if anyone is actually interested.



The initial construction shown in post #65 served as an acceptable start. I started by adding the piece of network cable that will act as the connector to my LED indicator lights shown in post #68. I had also added some wire for the reset (pull-pin) switch. Then the deployment channel power and charge wires and battery (mounted by ziptie but not shown, as I didn't get a shot of the bottom) were installed. One battery for both channels. Wires will eventually pass through the fiberglass bulkheads (not shown).



I meant to take some more intermediate stage pictures. I got rather engrossed in the build work though and forgot. The rest came together over two nights, but by the end of the first, the entire thing looked like a mess, with extra wire everywhere and nothing really tied down. Not photogenic at all and not worth your time. Anyhow, the final sled is as shown above. Again, the deployment charge wires will eventually pass through the fiberglass bulkheads (not shown) and are temporarily being passed through holes in the sled that will eventually contain the threaded rod that holds the whole bay together.

I'd really love some feedback on this one. Things to improve or do differently next time would be great.

mark thanks for the updates, still watching the progress!

Looks good so far, waiting to see pictures of the finished rocket.

I am also just finishing a 2.6" DX3. I think we bought them at the same time, at the Black Friday sale.

I'm glad you're all enjoying it. I'm anxious for the paint to be complete and get some finished pictures up too. Right now it's on it's first coat of it's second to last color. Total color count, including black and white comes out to six. each at two coats for coverage, then the [many feet of] tape comes off and I'll see how I did. It's killing me to wait so long to see where I screwed up. (I'm sure I did somewhere) 19 days gone so far, painting every 2nd or 3rd day, probably another week and a half until tape gets pulled off. Then it's cleanup work, as needed and a few good coats of clear. Hopefully it will done in time for the CMASS Acton launch on July 16th. It won't fly there, but I'll get to show it off and officially join the club / inform them I'm coming to cert in August or September.

I suppose I could at least give you a preview photo on paint in action:



OK, a couple actual question, referring back to the AV bay and my need for deployment charges. First, is standard 1/2" PVC strong enough to hold up to a few grams of BP? I don't know how much I need yet, I haven't calculated, but I figure a few grams at most. What kind of volume is a few grams of FFFF powder? And lastly, where in the world can I purchase black powder in Metrowest Boston / Southern NH near where I live, any idea?

Mass is going to be harder to get 4f. I drive to PA to get mine.

I fly fly my screech on 1.5 grams a side. I'd reccomnd some alum charge cans from MAC, but pvc can work too. 1.5 grams is small. So far I e flown mine in 2 ml vials. ml is approx a g.

BP is controlled. The ATF has waived restrictions on buying up to 50 pounds for use in antique firearms. Take that for what it's worth

That's right, I nearly forgot about it's controlled status. I'll ask around at the next local launch and see what people are using and where they're procuring it. Thanks for the feedback Dave.

I think I got the ejection charge situation settled. I've been asked in the past (and again today, to post the .ork for the rocket, so here it is. CG is still to be confirmed, but this is a pretty close estimate of final weight.

Also, a quick preview of the paint scheme. More black in it than I had originally hoped. Plus, I ended up painting the nosecone a bit differently as a concession to my better half. Anyway, this is the e-bay, just having one more day drying.

As noted in the CMASS thread, I'm scheduled to launch for my L1 cert attempt flight on August 6th on a CTI 38mm 5 grain I350 Smokey Sam. That's right, an I for an L1 cert. It should push to about 4,500' (500' shy of the waiver). I'm hoping no trees eat it, but otherwise the Eggfinder should get it back to me. No point in going low and slow if I'm planning to put a long burn J in the same rocket for my L2 a bit later this summer in Berwick, right?

This thread should be a lot more active over the next week and a half as the final pieces come together. I still have the final paint job to reveal, final AV bay building, and ejection charge testing coming up. Stay tuned. :wink:

MCriscione said:

As noted in the CMASS thread, I'm scheduled to launch for my L1 cert attempt flight on August 6th on a CTI 38mm 5 grain I350 Smokey Sam. That's right, an I for an L1 cert. It should push to about 4,500' (500' shy of the waiver). I'm hoping no trees eat it, but otherwise the Eggfinder should get it back to me. No point in going low and slow if I'm planning to put a long burn J in the same rocket for my L2 a bit later this summer in Berwick, right?

This thread should be a lot more active over the next week and a half as the final pieces come together. I still have the final paint job to reveal, final AV bay building, and ejection charge testing coming up. Stay tuned. :wink:

Click to expand...

You are overflying the field with that motor. It's not going to launch in Amesbury unless there is no wind as the chance for an infield recovery is slim to none.

Please have an alternate low H impulse motor ready, or you'll have to wait for a Maine launch.

+1
Since that will be your first flight of the rocket and also your level 1 attempt, in my opinion it would be better to fly it on a 2 or 3 grain 38mm motor initially. Once you successfully get your L1 there is plenty of time to push the limits of the waiver and lose rockets in the trees.

Still waiting for pics of the finished paint job!

Bob, Nathan, thank you for your advice. I've been to the field only once, and seem to have badly mis-remembered it. I just rechecked the site dimensions (thanks google maps) and see now that it's only about 1,000 ft. square. It just seemed so large that day, that my recal made it seem closer to 2k, which would be much more reasonable for the altitude I had expected on the I350. I neglected to check the field size and only read your waiver. Critical mistake. Thank you again for calling me on it.

Bob, I'm going to reach out to you by PM and ask a few questions, but it looks like I'll be substantially scaling back the size of my first flight motor. Specifics to follow...

And Nathan, I did finally get the rocket out and assembled (temporarily) as part of getting the e-bay assembled and the Stickershock decal applied.

It's official, the rocket is named: AZURE BLAST




The paint job came out pretty well. Unfortunately, the layering method I used meant a lot of paint build up. There are noticeable thickness differences between the early and late colors, white to black is the worst. (white went on first, black last) It would take way too much effort / clear coat to even it out, so essentially all the color transitions have a bit of an 'edge' to them. The 3 coats of clear helped to smooth them out a bit though. Still, over all a nice finish. The nosecone is a fade of the same Rustoleum metallic blue that I used on my Estes Big Daddy.

Looks good!

What does it weigh?

I've weight all the component piece parts, but not actually assembled and 'ready to fly'. It looks like the dry weight is going to be somewhere around 4.75-5 lbs. Give me a couple days and I'll be able to say for certain. Actual added weights right now are coming to 2098g, but I've probably forgotten to throw a couple odds and ends on the scale, like the keychain camera / shroud.

You need to remember that in NAR you need to recover your cert rocket or it didn't happen. You probably have over $400 in your rocket as it sits on the pad. If you went to 4500' in Amesbury, it is highly probable that you wouldn't recover your rocket and get your L1, and would be out $400.

Our field is the minimum HPR required 3000' in diameter from North to South, with 4000'+ to the Southeast, and even more to the West over the swamp.

CMASS allows dual deployment flights up to 3900' and single deployment flight to 2,500' when the wind is light and not from the Northeast to the Southeast. The altitudes are reduced if the wind pipes up because we do not allow rockets to recover outside the field, and when the winds are from the Northeast to Southeast, we will restrict all flight, both high power and model rocket, to altitudes where they will not drift to or overfly the 375 kV power transmission lines that cross the west side of the field.

You should check our your rocket with the thrustcurve.org sim with the following inputs. (I guesstimated the empty rocket weight to match your sim.)

I get an ~1600' apogee for a minimum Pro38 H and an ~2500' apogee for a full H for a rocket that would apogee at 4500' with a 5G Pro38 601I350.

A 2G Pro38 243H143 Smoky Sam will apogee ~1600', and a 2G Pro38 273H225 should apogee ~2100'. That's the range of motors you should plan to use for your L1 cert on your 2.6" FG MC DX3 in Amesbury.

Good luck on your cert flight.

MCriscione said:

I've weight all the component piece parts, but not actually assembled and 'ready to fly'. It looks like the dry weight is going to be somewhere around 4.75-5 lbs. Give me a couple days and I'll be able to say for certain. Actual added weights right now are coming to 2098g, but I've probably forgotten to throw a couple odds and ends on the scale, like the keychain camera / shroud.

Click to expand...

I didn't realized your rocket was that heavy! I reran TC, and your OR sim, and your safe L1 motor, the 3G Pro38 364I212-14A, is fine for Amesbury. The 2G Smoky Sam I suggested would be marginal with a 4.75 to 5 pound rocket.

Seems like after discussion with Bob here and via PM, I've settled on the 3G Pro38 I212, targeting about 2,400'.

Playing catch up here, but I got the AV bay assembled over the weekend:



I think I need to extend the motor side charge well with a short piece of cpvc (1" should do) as I'm currently estimating a 2g charge to break the shear pins between the sustainer and the av bay. I'll be prepping for ejection charge test tonight and performing them tomorrow, assuming all goes well. Also, from the pic, it looks like one of my vent ports is being partly blocked by something yellow. I'll figure that out and fix it too.

2g will be plenty.

That is an outstanding paint job. Nice work!

crossfire said:

2g will be plenty.

Click to expand...

Bob pointed out, and I agree, that a 2G smokey sam has a borderline thrust-to-weight ratio for my rocket. Any other CTI propellant, except maybe a skidmark, and i would probably be fine with a 2 grain, but I really have my heart set on the SS. Its still not clear if one is availible, and if not I'll try to get my hands on a 2G Blue Streak or Classic, maybe a White Thunder.

watheyak said:

That is an outstanding paint job. Nice work!

Click to expand...

Thanks! I was somewhat aiming for an abstract barrage of blue fireworks. I think i mostly achieved what i aimed for. It took a prettty long time, mostly due to the number of colors, but i think it was worth it.

crossfire said:

2g will be plenty.

Click to expand...

MCriscione said:

Bob pointed out, and I agree, that a 2G smokey sam has a borderline thrust-to-weight ratio for my rocket. Any other CTI propellant, except maybe a skidmark, and i would probably be fine with a 2 grain, but I really have my heart set on the SS. Its still not clear if one is availible, and if not I'll try to get my hands on a 2G Blue Streak or Classic, maybe a White Thunder.

Click to expand...

I think I wasn't thinking straight last night when I replied and still had motors on the mind. I didn't recognize until this morning that you were talking about charge size in grams and not motor size in grains. Ah, the difference a capital letter makes. Sorry about that.

I'm hoping that 2 should be plenty, but I haven't done any ejection charge sizing that used shear pins previously, so I'm probably a bit high. Hopefully not excessively. For the test, as I don't have a motor case yet, I've simply stuffed the 38/54 adapter with dog barf and capped the ends with cardboard which should be sufficiently resisting to the pressure. Because of this, I have a bit more empty volume back there than a typical flight.

For what it's worth my 4" dx3 only required .8 grams of black powder to separate the drouge. I have not yet tested the main, but I think I'm only going to fly with one or two shear pins as I do not think it should require more then that and at most I'm thinking 1.2 grams bp. All this is in a 4" rocket. At 2 grams in a 2.6" rocket I think you are over charging. Have you ran a bp calculator to figure out how much bp you need?