Madcow "Level-2" Build, 4" Fiberglass Airframe w/54mm Motor

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kevinkal

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This will be a build thread to share, learn through feedback and document my first Fiberglass Rocket Build in an effort to make my L2 Certification attempt with a more advanced Dual Deploy rocket capable of flying I's through low L's.
I selected the Madcow "Level-2" Build because I like the design, layout and quality of the kit, not to mentioned the available detailed assembly instructions complemented by some excellent previous build threads here on The Rocketry Forum.

I ordered the Level-2 kit through Apogee Components on April 12th, 2016. At that time, they had 5 units in stock, today they're down to 1. So perhaps this is indeed a popular kit.

Here's what I received last week:
Box:
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Contents:
All the airframe parts are nicely fabricated fiberglass, I was impressed with how well the nosecone fit the tubes.
There were 2 DVDs with Tim's video instructions for assembly, but no printed assembly instructions. I went to the Madcow Rocketry website and downloaded their instructions to build their 4" Fiberglass Super DX3. This kit is nearly identical except for the fins. The Level-2 uses straight tapered fins, similar to the Nike Smoke.
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It was good that I checked the contents list and verified that each item matched the description. I found that I had received only a 36" main parachute. Not nearly big enough for this rocket.. which without the motor will weight in @ 127 oz, and depending on motor and build will go 12+ lbs. This rocket requires no less than a 48" main parachute if it's kept light and flown on light motors, or larger parachute if heavier. I think the 48" parachute that is supposed to come with this kit is undersized. This is my biggest concern with this excellent kit. This is meant to be a Dual Deployment kit... it should come with a parachute that takes advantage of the second low altitude main deployment and use a bigger chute that will set this bird down softly. What do you think?
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I contacted Apogee, and Amy from Apogee contacted me Monday and is working with Madcow to get the "correct" chute to me. I hope it's at least the 50" chute. Hopefully I'll get the chute before Tripoli Central California's (TCC) DairyAire 3-day HPR Event in May 20-22nd. UPDATE: The replacement Chute Arrived a few hours after I posted this. Apogee and Madcow did an outstanding job to get the correct chute to me fast. Thank you.

The drogue chute is 18", but doesn't appear to be as rugged as I would have expected. Will this drogue hold up to 10 - 12 lbs of falling rocket for thousands of feet before the main opens? I suppose it just needs to hold 10-12 lbs of average force.. plus endure the stresses of flapping at roughly 60-75 ft/sec during freefall.
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I wanted to thank kcobbva for his willingness to share his experience building this exact kit just this month, where he obtained his L2 cert. In a few posts, I'll share the results of implementing his suggestion to me to modify the nosecone to be "avionics sled ready".

I'll be reserving the next few post positions for pictures and other updates. I took a picture of every part while on my gram scale... this helps with mass and cg calculations, making for the best possible Open Rocket / RockSim models.
 
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I'll be using Rocketpoxy from Glenmarc Industries Inc. for all structural bonds in this build I've mixed only a few batches thus far, and am impressed with the working time. A downside to the long working time, is that I tend to stay up far too late working with it. It ships with a bottle of coloring pigment. The kit that I received from Apogee came with black pigment. I'll use it when I wish to see where the epoxy is at, and not use pigment when I want a cleaner/translucent bond.
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One of the first things I did was to dry assemble the major components. They all seemed to be a good fit. There were, however, a few items that I felt needed to be correct before proceeding with the build. These were:
1. Nose Cone shoulder cut was not square. It was close and would have been functional, but I decided to square it up using a wet tile saw with a diamond blade.
Before:
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After:
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2. The slots in the body tube were slightly too narrow. This was easily solved using sandpaper and a popsicle stick to get the sandpaper into the slot. I was careful not to remove too much material and to make sure I removed equal material lengthwise in order to maintain fin alignment.
The G10 fins did not have a bevel on them and were 0.132" thick:
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The slots in the body tube were only 0.004" too narrow, but still preventing the fins from sliding in.0
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Easy fix, only needed a few passes.
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3. Every cut on every tube was not perfectly square. I was most concerned with the motor mount tube, as if I were to have blindly butted up the AeroPack 54mm retainer and bonded it with JB Weld, it would have aligned with the bottom of the motor mount, which was not square to the axis of the tube. The following 2 photos show where I'd marked the high-side of the tube, and used the black marker as a guide to assist in sanding down the correct amount at the correct position, before making a few final sanding strokes across the full cross-section, resulting in a near-perfect flat and square bottom.
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I didn't get a good picture, but before squaring the bottom of the motor mount tube, with the retainer butted up flush to the aft motor mount tube, the motor would be visibly offset relative to the upper diameter of the motor mount tube.
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I used a flat metal table and some 150 grit wet sandpaper to square the motor mount tube. It came out perfect on the first try.
 
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ere are some of the hardware items that I picked up to enchance this build.

An Aeropack 54mm Retainer for fiberglass 54mm tubes:
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An Aeropack 38-54mm Motor Adapter:
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An Rouse Tech RMS 38/720 motor (thanks Watermelonman):
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Here's some dry fit integration photos:
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I also like ball swivels. I found these at Apogee, they're good sized and rated to 500 lbs. I'll use one at the base of the main chute bridle. I'm not sure if I need to use the second one for this build or not. Comments from you, time and experience will tell.
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I also picked up some 1/4" stainless hardware including eyebolts rated to 400lbs working load, stainless washers and stainless nylock nuts.
The Eye nut in the left side of this photo looked useful, so I picked up just one. I've not figured a good use for it yet, but quickly put all 4 of the new stainless eyebolts to use.
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Parts scuffed up with 80 grit and batch of Rocketpoxy ready to go with black pigment
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Cleaned mating surfaces after sanding using IPA:
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A nice large fillet was easy using Rocketpoxy, though I had to make sure the parts didn't shift during the long wait for the glue to setup.
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Stainless Eyebolt in and tight. I installed it with this angle to aide in access and to allow for clearance from long motor casings that will protrude through the motor tube.
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I also like ball swivels. I found these at Apogee, they're good sized and rated to 500 lbs. I'll use one at the base of the main chute bridle. I'm not sure if I need to use the second one for this build or not. Comments from you, time and experience will tell.
View attachment 289012

I scratch built my L2 but it is very similar to the "Level 2" in size and weight. I only use one swivel and that is attached to the fin can on the drogue side. I've found that the only shock cord twisting that happens on mine is the fin can spinning while it falls under drogue. The short drop under main never seems to twist anything.

YMMV, but I would highly recommend only using the one swivel and put it on the fin can.
 
I used rocketpoxy without pigment to bond the 2 G10 Altimeter Bay Bulkhead disks. The epoxy would very slowly creep out around the perimeter with applied pressure. I must have scooped the epoxy overflow bead off the edges at least 4 or 5 times before it stopped flowing out. I used a 1/4 eyebolt through the center hole to maintain alignment until the epoxy set.
Sanded mating surfaces with 80 grit:
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The result was a nice clean bond and the G10 remained translucent. It was easy to see any air pockets between the halves, and a simple direct application of pressure would slowly force out the voids, making for a 100% contact area bond. Not that a strong bond is necessary here, but why not make it the best possible?
Here the bulkheads are marked for drilling out the holes for the threaded rod. Using 1/16" drill at 3000 rpm for the pilot hole, then going right in with a 1/4" bit at roughly 2000rpm worked well on my drill press.
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I scratch built my L2 but it is very similar to the "Level 2" in size and weight. I only use one swivel and that is attached to the fin can on the drogue side. I've found that the only shock cord twisting that happens on mine is the fin can spinning while it falls under drogue. The short drop under main never seems to twist anything.

YMMV, but I would highly recommend only using the one swivel and put it on the fin can.

Thanks Handeman. That makes sense.
 
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kcobbva suggested that I look at modifying my nosecone to enable further avionics upgrades for GPS, Trackers etc.
He pointed me to a nosecone kit bye ape-rc.com.
As it turns out, ape-rc is operated by a new friend of mine, Chris, who is also in my same city. While I didn't need the whole nosecone kit, I did pick up just an Altimeter Bay Mounting Ring.. which is a 3.75" diam G10 ring with a 6 hole mounting pattern and a ~54mm through hole. Chris handed me this part just yesterday and I was impressed with the quality. He even installed 6 PEM nuts with 10-32 button head screws. It dropped right into my nosecone, with a nice slight interference fit... perfect. I used Rocketpoxy that had been sitting for about 1 hour, to bond this into my nosecone. I made sure to create a nice big fillet on both sides to hold forces from ejection and the snap of a fully extended shock cord. It turned out excellent, really making for a professional looking nosecone!

I used the Altimeter Bay Mounting Ring (left) to match drill holes in my stock G10 nosecone bulkhead. I also used a wet tilesaw to remove about 0.20 inches from the radius around the stock bulkhead. Here's the result:
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I sanded both sides of the Mounting Ring with 80 grit before cleaning with IPA and bonding:
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Dry fit, perfect:
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Bonding with Rocketpoxy, note that tape was used to prevent epoxy from getting into threads:
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I peeled off the tape before the Rocketpoxy setup too hard:
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The result, Very nice!
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Last night, in addition to the nosecone mod, I managed to install the motor mount tube with just the forward Centering Ring and Eyebolt into the Body Tube. I probably made it more difficult than it needed to be but I wanted to have a fillet both on the forward side and aft side of the centering ring. To do this required precise application of epoxy using a a stick to reach down a narrow passage 12 inches down. The result was a very strong mount, and a mess that will never be seen once the fin can is closed up.

I first sanded everything carefully and thoroughly with 80 grit:

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Then I applied the Rocketpoxy:
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Then slid the parts together, resulting in a very nice thick fillet above the Center Ring, but little or no Epoxy below the Centering Ring.
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I next carefully applied Rocketpoxy to the backside of the Centering Ring 12" inside the fin can area. Once I was happy with that I temporarily slid the rear centering ring in place to align the motor tube in the body tube, stood the assembly up on it's end, and allowed the Rocketpoxy to cure. The result looks great, and feels very stout.
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Next up.. TBD! Bevel Fins or round them? Fin can or Altimeter bay? I have 2 StratologgerCF's and One Eggtimer Quantum to Consider integrating. I'm planning on redundant altimeters, switches, batteries, and charges.
 
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Kevin - this is looking great !! the drogue size was fine on mine. no doubt yours is going to fly nice!! Did you print and cut a fin guide from payloadbay.com? that really worked well on mine. well done so far. I look forward to watching your progress.
 
Earlier today in this new thread, I posted about my parachute issue and hinted that I was worried I would not have the replacement parachute in time for the May Launch date.
I said that too soon. I just walked in and found that with the mail, I had a package from Madcow Rocketry. Thank you Amy at Apogee and Madcow.

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I measured it to be about 50 inches across on the flat sides. So much better than 36".
It appears to be Madcow's 50" Ripstop Nylon Chute:
- 8 Shroud Lines
- Recommended Descent Weight: 5-9 lbs (I will need to look for a bigger chute when I fly heavier motors.)
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Ok, so I updated my open rocket model with this as a 51" chute to see what it showed for my under main canopy descent rate at ground hit. It appears to be too high, even with the smallest J motor, it's hitting the ground at 24 ft/sec minimum with the smallest motors. So, it would seem this parachute is still too small. Should I buy a new bigger chute for my L2 cert flight or risk ground impact damage? I don't think I want to risk anything. Ok, Gene... time to look at a Fruity Chute. =]

My open rocket sim is not updated for actual weight, just actual components that I've integrated so far.. it does not include lots of odds and ends nor glue or paint.. thus I expect my model to be even heavier and come down faster that what this version is showing below:
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Kevin - this is looking great !! the drogue size was fine on mine. no doubt yours is going to fly nice!! Did you print and cut a fin guide from payloadbay.com? that really worked well on mine. well done so far. I look forward to watching your progress.

Thanks Kevin. No, I haven't printed a find guide.. excellent suggestion. I'll do that!
 
After much thought and consideration on what to do regarding the squared off fins that came with this kit, I made a choice and am moving out on executing the work.
My options were to leave them square, round the edges or bevel them. Square leading and trailing edges would not sit right with me, so that was a non-starter. Rounding the leading and trailing edges would be easy, and add a little performance. However, I wanted more of a challenge for this project. So, I decided to bevel them at 10 degrees, and leave a 0.040 leading edge flat that I'll smooth over with some fine sandpaper to blend into the bevel.
I don't have any good power tools for use with beveling. My table saw and wet tile saw would require a significant buildup of a vertical jig to hold the fins. However, Chris showed me a link where a manual sanding rig could be easily implemented. I chose the manual sanding route to bevel the fins. Here's the setup and first fin off the lline, it turned out EXCELLENT! My table saw turned out to be useful after all.. I used its surface and rip fence as major components in the sanding jig.

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After much thought and consideration on what to do regarding the squared off fins that came with this kit, I made a choice and am moving out on executing the work.
My options were to leave them square, round the edges or bevel them. Square leading and trailing edges would not sit right with me, so that was a non-starter. Rounding the leading and trailing edges would be easy, and add a little performance. However, I wanted more of a challenge for this project. So, I decided to bevel them at 10 degrees, and leave a 0.040 leading edge flat that I'll smooth over with some fine sandpaper to blend into the bevel.
I don't have any good power tools for use with beveling. My table saw and wet tile saw would require a significant buildup of a vertical jig to hold the fins. However, Chris showed me a link where a manual sanding rig could be easily implemented. I chose the manual sanding route to bevel the fins. Here's the setup and first fin off the lline, it turned out EXCELLENT! My table saw turned out to be useful after all.. I used its surface and rip fence as major components in the sanding jig.

View attachment 289115View attachment 289116View attachment 289117View attachment 289118View attachment 289119View attachment 289120

That is nice. What is that green sandpaper? Grit?
 
That is nice. What is that green sandpaper? Grit?

Yes, its 3M 80 Grit. I used 80 grit to rough them in, then stepped down to 220 for the final few strokes. I'm mixing Rocketpoxy now to get them initially mounted.
 
I finished beveling the fins early this morning. They all turned out excellent. I wasn't expecting results this good. The leading edge tip thickness on each fin was a uniform 0.035", with both sides parallel and no visible variation. The bevels were uniform and parallel.
Today, I decided to lightly blunt the sharp edges, since my kids or dog could easily get a nasty cut if they ran into it on accident. I also wet sanded the G10 surface finish with 320 grit.
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Finally, I roughened up the base of the fin where it will bond and fillet to the motor tube and the body tube using 80 grit and a cross hatch pattern.
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I expect the roughed section of the fin extends out from the body enough for a nice strong fillet:
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Kevin - you are doing some amazing work here! These look 100% better than mine! I did the hand/eye coordinated edges and was pleased with the outcome. These look REALLY nice! Well done.
 
I came up with a cardboard jig for use with installing the fins. It's a thin pc of cardboard with a 4.03" diameter hole in the middle, and 4 carefully cut out fin slots. I used packing tape to reinforce the stress points on the cardboard so that it didn't rip. I also used small balsawood wedges stuffed between the fin tip and the cardboard alignment jig to push on the fin and thus hold pressure on the fin-to-motor mount tube glue joint. This make shift thing worked perfectly. I simply put the assembly together dry, and everything held tightly, then I just removed a single fin, put a small bead of Rocketpoxy on it and carefully slid it into the fin slot using the cardboard jig to hold alignment as the fin initially contacted the motor tube. this resulted in a very neat tack down of each fin, in perfect alignment. I will add fillets after this batch of glue hardens.

As I'm new to Rocketpoxy, I learned a little more today. For this job, I mixed more than I needed, then waited 20 minute for it to firm up before I started mounting the fins. Well.. after the 2nd fin, the Rocketpoxy was getting a bit too tacky for me. I managed to get the last fin bonded before the Rocketpoxy became too hard, which was roughly 30 minutes after mixing. I think the larger volume allowed it to heat up and accelerate it's cure. In hindsight, I wish I'd mixed up just 1/4 that amount. The good news is that I think all the bonds are solid and I can verify good connections using a flashlight and looking through the motor tube at each of the 4 bond lines. Here's some pictures:

Cardboard Fin Alignment Jig, first dry assemble then one-at-a-time drop a fin, apply epoxy, reinstall and tighten the fit using a balsa wedge.
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Simple wedges to apply inward force to hold the fin glue joints to the body tube.
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Results... Nice bonds visible through motor tube. Not too much push-out, leaving clean bonding area for fillets to follow.

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The picture below of the Rocketpoxy shows how stiff it was after just 40 minutes.
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Kevin - you are doing some amazing work here! These look 100% better than mine! I did the hand/eye coordinated edges and was pleased with the outcome. These look REALLY nice! Well done.

Thanks Kevin. I can only hope my build will fly as nicely as yours. I still remember the video of your maiden L2 flight, your Level2 didn't even rotate all the way up! That's craftsmanship!
 
I layed applied the first round of Fillets this evening. I'm getting a little better with the Rocketpoxy, but I'm still having trouble being neat inside the tube. I put the black pigment in since I like seeing the bond through the fiberglass.

Fillet interfaces roughed up nicely.. time to mix some glue.

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I started placing the smaller radius fillets right after mixing the Rocketpoxy.. I could feel the Epoxy heating itself up after I mixed it thoroughly.
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I'm not sure how common it is to fillet the inside interface between the body tube and the fin. I figure it would only make it stronger. The only downside I could think of would be increase difficultly replacing a fin... but I figure if I have to replace a fin, I'd have bigger problems to worry about.
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It's going to take some time to complete the remaining fillets... 2-3 more days. I guess I'll have to work on something else while the Rockepoxy cures.
 
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I always fillet the fin tabs inside the rocket, both on the motor mount tube and the ID of the body tube. As long as you rough up the surfaces to accept epoxy you'll never lose a fin unless you shred the rocket. Very nice build!


[emoji1010] Steve Shannon, P.E. [emoji1010]
 
I can only manage one quarter fin can per day doing fillets with the commute and work day. I completed the 3rd quadrant last night. With the rocketpoxy setting up, I was inspired to assemble the Eggtimer Quantum I've had on my desk for a few weeks now.
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It wasn't a fast fabrication, but I was able to complete it in a few hours and connect via WiFi last night using a tablet. Tonight I fired some test e-matches remotely. It's working very nicely. The matches fired fine with a 1 second firing pulse with the system powered using a single 2S 450mAh 25C LiPo. However, I'm not sure how or if I can test the barometer... I'll have to read up on that.

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Nice work Kevin. One thing I would recommend for RocketPoxy that was pointed out to me a long time ago. After mixing, I pour it on to some cardboard and spread it out thinly. Helps to remove the bubbles. After 15-20 minutes, I then use it to make the fillets. Worked perfectly. I found that using a cup actually worked worse than spreading out. Here's where I posted some of that previously: https://www.rocketryforum.com/showthread.php?130899-First-RocketPoxy-Fillets - Post #19
 
Nice work Kevin. One thing I would recommend for RocketPoxy that was pointed out to me a long time ago. After mixing, I pour it on to some cardboard and spread it out thinly. Helps to remove the bubbles. After 15-20 minutes, I then use it to make the fillets. Worked perfectly. I found that using a cup actually worked worse than spreading out. Here's where I posted some of that previously: https://www.rocketryforum.com/showthread.php?130899-First-RocketPoxy-Fillets - Post #19

If you're getting lots of bubbles your mixing technique is either too vigorous or you are pulling your mixing stick out of the epoxy mixture and then pulling air into the mixture when it goes back in. You shouldn't be whipping it, just stirring it. Also, having your hardener and resin slightly warm makes those few bubbles that seem to come from nowhere rise to the surface more quickly.
You're exactly right about using a cup to mix. You can do it, but you want to transfer to a shallower container right away to avoid cooking off.
 
Nice work Kevin. One thing I would recommend for RocketPoxy that was pointed out to me a long time ago. After mixing, I pour it on to some cardboard and spread it out thinly. Helps to remove the bubbles. After 15-20 minutes, I then use it to make the fillets. Worked perfectly. I found that using a cup actually worked worse than spreading out. Here's where I posted some of that previously: https://www.rocketryforum.com/showthread.php?130899-First-RocketPoxy-Fillets - Post #19

If you're getting lots of bubbles your mixing technique is either too vigorous or you are pulling your mixing stick out of the epoxy mixture and then pulling air into the mixture when it goes back in. You shouldn't be whipping it, just stirring it. Also, having your hardener and resin slightly warm makes those few bubbles that seem to come from nowhere rise to the surface more quickly.
You're exactly right about using a cup to mix. You can do it, but you want to transfer to a shallower container right away to avoid cooking off.

Thank you for the tips! I should have posted each day I put down a fillet quadrant, as my technique seems to be improving and gravitating to a method that resembles spreading the epoxy thin before it generates too much heat in the cup and gets too thick as it did with the initial fin installation. What I found worked best for me was to first tape off the exterior fillet area, including a very small "dam" of tape near the edges of fin where the epoxy could ooze out. Then I measure 16g of resin and 16g of hardener then slowly mix in a cup. When it just starts too look well mixed and I feel the epoxy's viscosity reduce a little, I put in 3-4 drops of pigment, and mix that. Then I clean my mixing stick and the top lip of the cup of any epoxy components that could possibly be poorly mixed, using a paper towel and some IPA. Then, I immediately pour a line of epoxy down into each fillet and allow it to ooze into position, keep cool, and allow any bubbles to come to the surface. The trick seems to be getting it down before it starts getting thick. At this point, I have a much thinner layer left in the cup, and two thin layers of epoxy filling the fillet area. I then use a long wooden dowel to carefully apply fillets to just two of the remaining internal fillets. I've learned that if the house is at 68F, I can't work fast enough to comfortably get all the fillets in before the epoxy gets thicker than I like. I think that if I'd spread it out like you're suggesting, I would have been able to finish all fillets. However, my work-around was to initially mix less epoxy and only fill 4 fillets with that first batch. Then, while the first batch is setting up, I mix a smaller batch and apply the last pair of internal fillets. They've turned out very well, and air bubbles have mostly not been an issue. I did have to pop just a few before the epoxy setup too thick.. and the fillets settled out nicely afterward. I pull the tape after about 40 minutes.. and use my finger dipped in IPA to smooth things out and blot with a paper town soaked in IPA. I never used to use the IPA dipping finger trick.. but wow it's a powerful last step to making a perfect fillet.
I finished the last quadrant last night! I must say, I've had enough fillet work for a while! =] I saved the unused epoxy as a method to estimate how much epoxy I've added to the fin can. I averaged 30 to 35 grams per quadrant.. thus I added 120 to 140g to the rocket.
 
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I'm soon to drill shear pin holes in both the booster-to-avionics bay and the payload tube-to-nosecone joints. The video instructions for this model describe installation of Three 2-56 nylon shear pin screws for the nosecone only. However, I would like to run shear pins at both separation points. I am considering if I want to run 4 pins over 3. I'm thinking that the maximum force the pins will see is at the apogee shock cord full extension will be less than what just 2 pins would shear at. I've read that the 2-56 pins shear at forces between 22 and 35 lbf. I'm not sure how to accurately quantify the deceleration, given some unknowns such as the relative velocity between the booster and payload section and the energy absorption capability of my 15' tubular nylon shockcord. I'll just estimate 25 G's peak shock load, unless someone convinces me otherwise. The empty FG nosecone + laundry will total about 2 lbs. So max force would be around 50 lbs. With these numbers, two 2-56 nylon screw shear pins would be marginal at best, and 3 would be the optimal number.
However, given that this is a 4 fin rocket, and the statement in the StratologgerCF Altimeter instructions that says that 4 vent holes are better than 1, I want to put in 4 vent holes. Having the symmetry of 4 fins and 4 vent holes then makes me want to use 4 shear pins so that I can have the line of shear pins inline with the rocket fins, and the altimeter bay vent holes shifted out of the potential turbulence from the shear pins and tube connector rivets by 45 degrees. Is this a good reason to run 4 shear pins? I know I'll need to increase my BP charges to accommodate the additional shear pin. Roughly, the calculator I used shows I'll need about 1.2 g of 4F Black Powder to shear four 2-56 nylon screw shear pins at 12 psi, as opposed to 0.9 g Black Powder to shear three 2-56 nylon screw shear pins at 9psi. (This is using a 3.9" ID by 16" long empty volume in the booster tube.) Now, I also know that the increased pressure will increase the separation velocity and thus increase the ejection cord shock load at apogee... but I'm still going to assume that load will be less than 25 G's. Does that sound reasonable?

So, in summary, I am confident that I need no less than three 2-56 nylon screw shear pins to hold the laundry during a 25 G apogee ejection shock load. However, I'm thinking of using 4 pins for symmetry with my 4 fin FG rocket and having them offset at 45 degrees from my 4 vent holes.

Are these good reasons to go to 4 pins vs. just 3? I just don't like the thought of 3 lines of pins/holes at 120deg separation, when the fins are at 90 degree separation.

I plan to drill these holes later this week, so that I can start ground testing during the weekend.

Hopefully this thread has enough visibility to get some good feedback regarding my shear pin questions. I know there are plenty of threads regarding shear pins, but I didn't gain confidence after reading about 1 hours worth of widely varied discussion.
 
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Kevin - Here's what I did: three pins in the nosecone. 2-56
TWO shear pins in the lower body tube attached to the Ebay 2-56

As for the Ebay Band I drilled three equally spaced holes: two 3/32" and one 7/64 to allow the screw driver to go through.

As for the Blackpowder: GROUND TEST! I also came up with 1.2 for the lower half and it just sat there and I heard "POP" when I ground tested. I believe I ended up with 1.4 or 1.5 for a decent separation with the two pins during the ground test.
 
4 pins should be fine, and your load estimations seem quite reasonable. I run 3 in the main section on both a 3" MAC canvas rocket and a 4" cardboard, and one on the drogue section on the 3" rocket (friction fit on the cardboard rocket). So far that has held well including some somewhat aggressive flights on the 3" (CTI J760 to 6800'). The fit on the canvas is tighter than fiberglass though, so extra pins can't hurt.

One note since you are already going to run redundant altimeters and charges, definitely consider making the charges connected to the backup altimeter a bit bigger. For example, on the 3" rocket I mentioned above I run 1.4g on the primary drogue and main (the drogue compartment has a larger volume than the main but only 1 shear pin), but 2g on the backups. That way if for some reason a charge isn't enough to separate the components, the backup has a better chance of deploying the chute.

This actually has saved my 4" cardboard rocket on one flight-I was using masking tape instead of shear pins and the nose cone separated at apogee, but not enough to deploy the main. The 1.5 gram main charge fired but since the nose cone was separated already, the main didn't deploy-but the 2g backup got the chute out just in time!

+1 to ground testing as well.

Good luck on the testing and flights-looking forward to seeing it fly at DA!
 
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