L3 Winter Build Thread - 3/4 Scale PAC-3 Patriot

Construction of the 4:1 VK nosecone has begun thanks to Python Rocketry. Can't wait to see it.
Now if I can just shake this stupid flu. Stupid vaccine was worthless this year. Bleah.

mccordmw said:

Construction of the 4:1 VK nosecone has begun thanks to Python Rocketry. Can't wait to see it.
Now if I can just shake this stupid flu. Stupid vaccine was worthless this year. Bleah.

Click to expand...

Screw vaccines all you need are anti biotics lol.


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SinfulDarkLord said:

Screw vaccines all you need are anti biotics lol.


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Click to expand...

Antibiotics don't touch viruses. That said, the shot is sometimes worthless, but more likely, he's got a cold, not the flu.

AdAstraPerAspera said:

Antibiotics don't touch viruses. That said, the shot is sometimes worthless, but more likely, he's got a cold, not the flu.

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My point proven still, its just a simple cold and you dont need no shot. If he had the flu, he would be in the hospital.

Viruses are more painful than a simple cold. Oh and yeah shots dont work unless its for what it is. If he got the flu shot for a simple cold then yeah its not going to work.

Sorry for derailing


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mccordmw said:

Construction of the 4:1 VK nosecone has begun thanks to Python Rocketry. Can't wait to see it.
Now if I can just shake this stupid flu. Stupid vaccine was worthless this year. Bleah.

Click to expand...

Your gonna love what Dan gets to you!

AdAstraPerAspera said:

Antibiotics don't touch viruses. That said, the shot is sometimes worthless, but more likely, he's got a cold, not the flu.

Click to expand...

PhD in molecular biology and cellular biology with multiple publications on HIV Integrase (using avian myeloblastosis analogue).

Here's a hallmark publication that led to a lot of followup work on HIV-IN inhibitors. https://academic.oup.com/nar/articl...ient-concerted-integration-of-retrovirus-like

Yep. Antibiotics won't do jack. I tested positive for Influenza A. My 13 yo had it over the weekend, but also only felt awful for a couple days. Nasty strain, but diminished effects due to partially effective vaccine. Still not fair. I got poked. I want my immunity! Waaaah!

Stupid flu sidelined me for much of the weekend, but I did manage to get some build time in.

This weekend, I worked on cutting the coupler tube to create the payload bay plus the coupler. The critical part here is that I get a good, straight cut. Normally, on any tubes less than 4", I can use my chop saw to get a good cut. Unfortunately, this 8" tube won't fit in that, so I had to go old school and use a hacksaw. The method I use works well to give really straight, clean cuts.

I have 48" of coupler tube to cut for both the bay and coupler. The payload bay should be long enough to support a 4" switch band plus one body diameter of coupler for a straight join. So I marked off 20" on the tube (8" + 8" + 4") and used the airframe to scribe the cut line. Since I already made sure the airframe tubes had straight edges, this gave me a good reference line to cut.



If I just use a hacksaw to now cut through the line, it will be difficult to wind up with a really straight edge. I'd have to sand the thing down. Instead, lightly cut into the marked line with the saw and keep going around the tube with gradual cuts over and over until the cut is complete.


The end result is a good, clean cut that needs no sanding.



This video does a far better job than I just did for describing how to make straight cuts on a tube.

[video=youtube;N-ptltp7TIw]https://www.youtube.com/watch?v=N-ptltp7TIw[/video]

Setting aside the 20" payload bay for now, here's how the coupler will fit. It transfers the force of the thrust from the fin can up through the coupler and contacts the bulkhead of the payload bay.



I dry fit assembled the booster, fin can, and coupler to make sure it's all straight.



It's all good. I measured at four points. All the same length, so I know I have a good, straight cut.



Next up will be fiberglassing the bulkheads for the payload bay...

Between everyone in the house sharing colds and flus and a business trip up to Milwaukee, it's been tough to get some time the last three weeks to work on my build. I did make some progress yesterday, though.

I measured and cut the mid airframe section and the payload bay switch band. To make sure I get a perfectly even cut, I use a wrap of butcher paper to give a nice, square edge for marking. I use the same cutting method as posted above.



The mid frame and switch band were dry fit on to the bottom coupler and payload bay tube. You can see that it's all tight and straight. No gaps or sanding adjustments needed.



Bonus! When I got back from my business trip, my nose cone from Python Rocketry arrived. The work was beautiful. I won't hesitate to use them again. The real test is in the fit, though. I gave him my measurements down to hundredths of an inch. What I got back matched perfectly. The fit was nice and snug with no sanding needed.



The close-up also showed the outer diameter matched the airframe exactly. I'm really pleased with what he sent me. The final weight was 5 lbs for the nose cone. I'll need to adjust my ORK file and make sure I'm still in a comfortable stability margin.



Next in the build queue is to finish up my payload bay bulkheads and sled. Then it's time to start all the epoxy work in putting it all together.

Ha! I just realized my L3 packet is up to 77 pages.

Woo! Ex-Mother-in-Law is coming in this weekend. That gives me the perfect excuse to disappear in the basement to work on my rocket.

Woo! Last night, I got the last of my airframe tubes fiberglassed. I'll peel it tonight and cut it down to 3.5' per my design. I'm thinking the gratuitous full dry fit is in order. Then it's on to epoxying the whole thing together. Coming along slowly, but coming along.

Ah the sweet smell of progress.

Last night, I was able to work on the bulkheads for the payload bay. Since the bulkheads will need to absorb a large shock on deployment, each bulkhead will be made of 4 layers of 1/8" 3-ply Baltic Birch plywood that was laminated with drain sleeve and epoxy.

The plywood circles are 8" in diameter, so I needed to first sand them to fit. Once I had a good fit, they were marked with a T to indicate the ones for the top of the payload bay. These were all inserted into the 8" drain sleeved on top of mylar for the epoxy treatment.



After the epoxy was brushed on, excess was squeegeed off, flipped, and epoxied on the opposite side. Another sheet of mylar was placed on top, and weighted plywood completed the sandwich.



This morning, I pulled apart the sandwich and checked the results. Everything looks like it had good fabric coverage, no bubbles, and no issues.



Tonight, I'll cut them out, touch up the edges with sandpaper, and them epoxy the layers all together with rocketpoxy. They should then be good to go for drilling out holes for the allthread, charge wire holes, and the u-bolts.

After that, the last structural element to complete are the front fins. Then it will be time to epoxy the whole thing together.

Now that all my structural components are done, it's time to start putting it all together.

First up is the fin can. Unfortunately, I couldn't stop to take pictures as I was spreading in the epoxy, but there wasn't anything special to see there. I followed the steps I outlined earlier:

1. spread a ring of Rocketpoxy just above where the fin slots end.
2. insert the fin can until the first centering ring was in and just before the second one was in the tube
3. spread a ring of epoxy just below the fin slots.
4. push the fin can in until the 2nd centering ring was a few inches in the tube
5. the last smear of epoxy was near the bottom of the tube.
6. insert the fin can all the way in
7. push in the thrust plate so the fin can is at the proper height.

Note: a ring of silicone grease was spread on the aluminum thrust plate so it didn't get accidentally epoxied in. It will ultimately be bolted on to the bottom centering ring.

Here's the whole thing left to cure overnight.



Looking down the tube, it appears that I have good filets set up on the upper centering ring. I did a check of all four quadrants. Looks complete.



I use a cheap borescope to check the internals. The centering ring just below the fin slots also looked good. A quick wipe with an isopropanol-soaked paper towel made sure the slots were clear of epoxy. Here's a phone cam shot looking inside one of the slots. The filets were good, and the fin slots were clear of epoxy drips.



While the fin can was curing, I finished up putting together all my fiberglassed 1/8" Batlic Birch bulkheads for the payload bay. These were clamped together and left to cure.



The image above shows the upper and lower bulkheads clamped together. They aren't epoxied together though. I took the assembly apart this morning, and it all looks good. The bulkheads are hard as a rock. Since they have to take a large shock on deployment, I test my bulkheads by balancing them on a wood dowel and standing on the ends. If it bends even the slightest, I'd be concerned. This didn't budge.

Since each plywood disc was first wrapped in fabric+epoxy before putting together the sandwich, I get 2 layers of epoxied fabric between each layer of wood. Those were then epoxied together and clamped.

So...

Each bulkhead is a multi-layered sandwich of:

fabric
1/8" birch 3-ply wood
2 layers fabric
1/8" birch 3-ply wood
2 layers fabric
1/8" birch 3-ply wood
2 layers fabric
1/8" birch 3-ply wood
fabric

The fabric is cheap, but is soaks up a lot of laminating epoxy! The downside is that each bulkhead weighs about 300 g. Not an issue for this large rocket, though.

Tonight, I'll epoxy on the switch band.
Then, it's time to make the fin alignment jig.

Onward and (hopefully) upward.

Question for the masses...

I'm looking for suitable materials for my deployment charge holders. The BP calculator says I'll need about 4 g of 4f BP. Normally, I use PVC pipe caps to hold my centrifuge tubes, but I've only gone as high as 2.5 g BP. At 4 g, I'm worried the PVC would shatter.

I came across this copper pipe cap that looks suitable.

https://www.homedepot.com/p/1-in-Copper-Tube-Cap-C617/100347737



I can get it in diameters that would work well. However, I'm not sure about the softer metal.

Anyone used this for deployment charges?

I'm aware of the nice commercial options out there, but the largest seems to max out a holding just over 4 g. If I need closer to 5 g after ground testing, I don't want to have a holder that's too small.

mccordmw said:

Question for the masses...

I'm looking for suitable materials for my deployment charge holders. The BP calculator says I'll need about 4 g of 4f BP. Normally, I use PVC pipe caps to hold my centrifuge tubes, but I've only gone as high as 2.5 g BP. At 4 g, I'm worried the PVC would shatter.

I came across this copper pipe cap that looks suitable.

https://www.homedepot.com/p/1-in-Copper-Tube-Cap-C617/100347737

View attachment 316478

I can get it in diameters that would work well. However, I'm not sure about the softer metal.

Anyone used this for deployment charges?

I'm aware of the nice commercial options out there, but the largest seems to max out a holding just over 4 g. If I need closer to 5 g after ground testing, I don't want to have a holder that's too small.

Click to expand...

I've done it. The only issue is that it starts looking scuzzy after the first use.

mccordmw said:

Question for the masses...

I'm looking for suitable materials for my deployment charge holders. The BP calculator says I'll need about 4 g of 4f BP. Normally, I use PVC pipe caps to hold my centrifuge tubes, but I've only gone as high as 2.5 g BP. At 4 g, I'm worried the PVC would shatter.

I came across this copper pipe cap that looks suitable.

https://www.homedepot.com/p/1-in-Copper-Tube-Cap-C617/100347737

View attachment 316478

I can get it in diameters that would work well. However, I'm not sure about the softer metal.

Anyone used this for deployment charges?

I'm aware of the nice commercial options out there, but the largest seems to max out a holding just over 4 g. If I need closer to 5 g after ground testing, I don't want to have a holder that's too small.

Click to expand...

You need to get some surplus 50 caliber shell casings .

Lets see, copper has a 20 ksi yield, hoop stress is P*radius/(thickness) [assuming closed ends, thin-walled vessel], and your 4 gram charge generates how much instantaneous pressure?

BDB said:

I've done it. The only issue is that it starts looking scuzzy after the first use.

Click to expand...

For some reason, I'm cracking up at your second statement lol.
Most things that partially contain small explosions tend to look "scuzzy" in my opinion

If I pack 4 g of FFFFg BP in a 1" copper cylinder with a height of 1", pack it with dog barf, and seal with tape, I calculate that it will generate about 9870.06 psi. I'm assuming the tape will burst well before that pressure is obtained.

The caps are cheap enough. I'll pick some up, screw it on to a board, drop a scrap fiberglassed tube on top, and give the test a whirl.

mccordmw said:

If I pack 4 g of FFFFg BP in a 1" copper cylinder with a height of 1", pack it with dog barf, and seal with tape, I calculate that it will generate about 9870.06 psi. I'm assuming the tape will burst well before that pressure is obtained.

The caps are cheap enough. I'll pick some up, screw it on to a board, drop a scrap fiberglassed tube on top, and give the test a whirl.

Click to expand...

Yep. Path of least resistance.

mccordmw said:

Question for the masses...

I'm looking for suitable materials for my deployment charge holders. The BP calculator says I'll need about 4 g of 4f BP. Normally, I use PVC pipe caps to hold my centrifuge tubes, but I've only gone as high as 2.5 g BP. At 4 g, I'm worried the PVC would shatter.

I came across this copper pipe cap that looks suitable.

https://www.homedepot.com/p/1-in-Copper-Tube-Cap-C617/100347737

View attachment 316478

I can get it in diameters that would work well. However, I'm not sure about the softer metal.

Anyone used this for deployment charges?

I'm aware of the nice commercial options out there, but the largest seems to max out a holding just over 4 g. If I need closer to 5 g after ground testing, I don't want to have a holder that's too small.

Click to expand...

That's all I use. For 4" rockets I use a 1/2" copper pipe cap and 3/4 to 1" of pipe soldered into the cap. For bigger rockets I use 3/4" copper pipe caps with 1 1/2" to 2" of pipe soldered into the cap. I'm working on a doughnut AV bay for my L3 rocket (my booster tube is too short for a 98/15360 case). On these AV bay lids, there is 1" copper pipe caps (that's what came with the lids bought from a buddy). I have yet to see how much the 1" cap holds, but my 3/4" cap/pipe holds 7.5 grams with plenty of room for a dog barf plug and tape over the top. The one drawback I see for the 1" caps is I'll need 2 or 3 strips of tape to close the opening. Yes, they are a little green and charred, but there's no reason to think that will affect deployment. Just appearance...

mccordmw said:

Question for the masses...

I'm looking for suitable materials for my deployment charge holders. The BP calculator says I'll need about 4 g of 4f BP. Normally, I use PVC pipe caps to hold my centrifuge tubes, but I've only gone as high as 2.5 g BP. At 4 g, I'm worried the PVC would shatter.

I came across this copper pipe cap that looks suitable.

https://www.homedepot.com/p/1-in-Copper-Tube-Cap-C617/100347737

View attachment 316478

I can get it in diameters that would work well. However, I'm not sure about the softer metal.

Anyone used this for deployment charges?

I'm aware of the nice commercial options out there, but the largest seems to max out a holding just over 4 g. If I need closer to 5 g after ground testing, I don't want to have a holder that's too small.

Click to expand...

Yes, all the time. I use 1/2in caps and pipe. But, my charges include a length of tube. Here are the charge tubes on my Level 3.



They are 9in long because I needed to get them above the main chute D-Bag. For a traditional dual deploy I use 3 inch long sections. I like having at least a 3in long tube so the powder has a chance to fully burn. I drill a hole in the bottom for a #4-40 screw to attach to the bulk plate. That screw is then sealed with epoxy. There is also a hole on the side (see 2nd pic) that goes through the cap and tube for the E-Match. When I make the charge, I insert the match and then hot glue to seal the hole. Add powder through the top, then stuff with dog barf and tape with masking tape.

Time for the maths!

The cap is 2.54 cm high with a radius of 1.27 cm.
Cap volume is 12.87 cc.

Googling for FFFFg BP dry density turned up 1 cc volume = 14.9 grains
1 g FFFFg BP = 15.432 grains

So...

12.87 cc * 14.9 g/cc = 191.763 grains
191.763 grains * 1 g/15.432 grains = 12.4 g BP

If I need up to 6 g BP, I'll be filling almost 50% of the cap volume with BP. That's too much for my comfort. I don't want to eject a bunch of BP before it all ignites. So I'll solder on a 3" pipe into the cap. I'm not sure of the ID of a pipe that will fit, but I'll assume it's 0.75" ID (1.9 cm ID). That has a volume of 28.96 cc.

That can hold up to 28 g FFFFg BP. So I'll only fill about 18% of the tube. Let's say 1/5th of the tube height. Plenty of room to stuff in an ematch plus dog barf.

Got home. Cut up some 1" copper tuning in 4" lengths.

I taught my 13 yo son to sweat the caps on. This is his first solder. I think he did pretty well.

This weekend, I wrapped up the payload bay. I like things to be symmetrical, so I start with a paper template. I trace out the bulkhead on paper, cut it out, and fold it i half 3 times to give me 8 evenly spaced radial lines from the center. Drill points are noted.



And then, it's taped on to the bulkhead.



Then, it's on to the drill press, and I've got a pretty, drilled out set of bulkheads.



All the components are screwed on, and the nuts will be locked down with some epoxy.



Not seen, but important here is the u-bolt is supported by a metal bar between the connection points on the underside. This distributes the weight evenly.

Next up is to add the internal filets to the reinforcing stringers in the fin can and to epoxy on the top centering ring.

Next up is the epoxy filets for the internal reinforcement stringers. This is a long, narrow gap, so I had to set up a pole to reach in with a syringe loaded with Rocketpoxy. So I give you the "Epoxy Reacher-Squirter™" It's not pretty, but it works pretty well.



I mixed 30 g of resin and 30 g of hardener and scooped it into the 50 ml syringe. That's enough to do two filets. I found it worked best to squirt most of the epoxy deep into the stringer and then to use the opposite end of the dowel to drag out the filet.

In the end, I got pretty good coverage of the area.



The excess that dribbled over the end was wiped up since I need to put the top centering ring on that once all the filets harden. I got half of them done last night. The rest go tonight then the top centering ring.

What's left then:
- front fin beveling
- all fin attachments
- nosecone eyebolt
- payload bay sled
- sand/prime/pain
- laundry
- ground testing

Almost done! Already thinking about the next build. Likely a clustered L1/L2 range. Must...focus...

More progress last night. And finally, a full-stack money shot!

After the top centering ring cured overnight, I added a filet of Rocketpoxy on top. This would also serve to bind the couplet to the ring. Before inserting the coupler for permanent placement, the bottom tube had 30 g of Rocketpoxy randomly smeared around the walls. Following that up, a generous coating of phenolic wood glue was used to coat the tube and provide a solid bond with the coupler.

Here you can see the filet at the bottom where the couple contacts the top centering ring. This creates a double-wall on top of the fin can. It's veyr sturdy.



The whole assembly is left upright to cure straight and true.



While this cures, I was able to epoxy on the switch band to the payload bay. The way the airframe is set up, the bottom coupler runs from the top of the centering ring, up through the middle airframe (which gives room for the drogue and shock cord), and butts up against the bottom bulkhead of the payload bay. To get an exact fit for the switch band contacting the middle airframe, I assembled the rocket partially to check the fit.

First up, slide on the middle airframe on top of the coupler. Not much to see here.



Here, you can see the payload bay in place as it sits in the middle frame and rests with the bulkhead on the top centering ring. The switch band is slid up to the top and out of the way. Epoxy was applied to the wall of the payload bay, and the switch band was slid down until it contacted the airframe. After the switch band was slid down on the epoxy, I taped the band to the payload bay to prevent sliding. The whole thing was pulled out, and excess epoxy was wiped clean from the payload bay and middle coupler. I work sloppy. :



In the post-cure fit (not shown). The switch band sits tightly against the airframe. When I knock on the top bulkhead, there is no echo beneath. The bottom bulkhead sits flush against the top of the coupler. As an additional test for a flush fit, I took a black crayon and colored the top of the coupler. After sliding in the payload bay and tapping (not twisting since this can just show marks if there is one high spot!), the bulkhead showed signs of crayon transfer all around.

Here's a full stack test fit. All the tubes are flush with no gaps, and straight. Money shot! You can see bondo spots on the top tube where I'm starting to sand things smooth.



As a test for tightness of the fit and straightness, not shown here, but I can hold the booster tube horizontal. The whole airframe does not bend at any joint by more than enough top open up a gap greater than 1-2 mm. The couplers and payload bay are straight and tight. I'm being extra cautious since I'm concerned about bending moments on such a large rocket.

Charge testing will make sure it's not all too tight, but I am able to pick up the sections and shake lightly to get them to separate, so I'm not worried.

It's hard to get the scale of the bottom fins, but I have 4 with a 7" span. Stability with the motor in is currently estimated to be 1.2. I need to buy the chutes and deployment bag to get a better estimate. That cuts it a bit close for me, so I'll likely put 1-2 pounds of mass in the nose cone to put me closer to 1.5 (where I'm most comfortable).

Not shown are the stubby middle stabilizer fins. They don't do much beyond being true to the look of the MEADS PAC-3 Patriot.

That is a large rocket

It looks great!

Nytrunner said:

That is a large rocket

Click to expand...

Hence its name, "The Compensator". :grin:

It's a good feeling, isn't it?

Bat-mite said:

It's a good feeling, isn't it?

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Yep. I'm at that good feeling phase. Once I'm done building, it will be replaced with the anxiety phase. Will it buckle on thrust? Will the retainers hold? Is it stable enough? Deployment? Will the hardware and shock cords hold? Ahhhh!