My L2 Project

[thzero]

Well, am finally starting a L2 project.

Even created a set of flash cards (https://www.cram.com/flashcards/nar-level-2-12210980) to study with... think there was another one posted some time ago, but didn't really care for it and the process of creating was good study anyways too.

As for the project... its intended to be a LOC 5.5 body and nose cone as a stubby... never really built a stubby before. Except this one will have 3D printed fin cans from my experimentation with 3d printing fins and rocket parts (For reference... https://www.rocketryforum.com/threads/hpr-custom-build.162115/).



I'm thinking of, because I have the fiberglass cloth, of wrapping it as I did my 3" rocket Polaris (for reference... https://www.rocketryforum.com/threads/hpr-custom-build.162115). Because why not? More hassle yeah, but also less hassle when painting as I hate dealing with paper tubes and trying to sand them down and get them smooth (fighting that on another 2.63" rocket). And besides the fins will be layered in fiberglass anyways - the 3d printed is more the 'filler' as even PETG is just too flexible.

Yes, I am planning for semi head end deployment; but only single deploy of the drogue with a JLRC for the main. Yes, I am aware that L2 does not require electronics and people suggested low-n-slow, no electronics, etc, etc. However I feel more than confident I can build a simple 3FNC, fly and recover it. And besides, I did my L1 with a custom fiberglass/wood/cardboard/plastic nose cone build that was recovered on a JLRC anyways. Show increased skills.

 

[FlyBy01]

I like it but remember to ground test your ejection charge and I would try a Level 1 motor before the attempt. This is a Level 2 worthy build with the complexity of the design but it seems to be well thought out. If you are going for Tripoli Level 2 please ensure that you have the updated study guide as it has changed recently. Good luck and please post a video or photos!

 

[thzero]

Thanks. Oh yeah, planning to run it on an I284 once its built, certainly.

Ah, going with NAR just because the groups I fly with are NAR.

 

[thzero]

Started the process....



Chopped off the end. It was about 20.15 ounces on the scale before, and now down to 18.4 ounces.



Next up is to cut a centering ring for the inside of the nose cone; using a CR 5.54 to 3.0 ring. The ring goes inside the nose cone and gets epoxied in where the nose cone and the shoulder meet which also gives some nice mechanical benefits.

Unfortunately the shoulder is short at 3.75". But I think the bottom of the nose cone has consistent diameter for the bottom 3" or so of the nose cone that I'll put the vent holes at the bottom of the nose cone.

I'll note the weight of the original nose cone is 20.00oz (always good to weigh things, since OR database has is at 22) and after the cut its down to 18.5oz

 

[thzero]

Here is the fin mount that is being printed... going to be a long print. Then each fin will be printed and wrapped in fiberglass.



A couple of test prints to get the sizing right...

 

[thzero]

Fin attachment completed printing... came out rather well. Predicted weight based on filament usage was 7.9oz, but came in at 6.89oz so yay!



Now onto mounting the t-nuts into the frame. And putting fin #1 onto the printer.

 

[OzHybrid]

I thought printed fin cans were banned for certification flights. someone correct me if I'm wrong....

 

[thzero]

This is not a fin can, rather its a mounting system to mount fins that allows the fins to bolted to the internal structure through the wall of the tube, which will have a layer or two of fiberglass on it. The fins will have a layer or two of fiberglass also.

Per Steve Shannon

I agree. In November (ed: 2020 I believe) the BoD changed the rule to allow 3D printed fin cans to be made by the flyer and used in their L3 certification flight with prior TAP approval.

https://www.rocketryforum.com/threa...r-l3-certification.153464/page-8#post-2088503

 

[thzero]

And in other news... first fin printed. Again, it came in a bit lighter than expected at 3.31oz instead of 5oz so thats good. It'll gain a bit more weight after fiberglassing, but I've accounted for that via area/volume/density calculations for a thin skin of fiberglass. Its a rough approx. but it gave me a good ballpark on 2.63" building using some of these techniques.

 

[Scott_650]

Looks great! Quick question - did you bother to do a cost comparison between “standard” materials and the 3D printed fins? Not counting the printer of course. Curious to see if the filament costs are comparable to plywood…

 

[thzero]

Looks great! Quick question - did you bother to do a cost comparison between “standard” materials and the 3D printed fins? Not counting the printer of course. Curious to see if the filament costs are comparable to plywood…

I didn't. I'm sure its far cheaper to use some plywood even if going with some quality baltic birch 1/4". This wasn't so much about cost as it was about an idea - I had printed parts for other rockets online (expensive) and then broke down and got a 3d printer (CR-6 SE, and then also got an Ender 3). So it went from printing 3d jigs, and electronic bays to hey I can 3d print fins that I can attach to the rocket.

My first build using some of these techniques in a 2.63" frame (https://www.rocketryforum.com/threads/2-63-formerly-3-mailing-tube-printed-rocket.164180/). I'm actually in process now with that one of building a new body to do DD with it... so I can easily swap the fins and nose cone between at least two body configurations.

Now I'm sorta addicted to this 'modular' thing even if it does end up having more mass.

 

[Scott_650]

I didn't. I'm sure its far cheaper to use some plywood even if going with some quality baltic birch 1/4". This wasn't so much about cost as it was about an idea - I had printed parts for other rockets online (expensive) and then broke down and got a 3d printer (CR-6 SE, and then also got an Ender 3)…Now I'm sorta addicted to this 'modular' thing even if it does end up having more mass.

Thanks - I thought the cost for materials would be higher. Though not needing to sand airfoils and being able to use your modular concept for swaps and repairs looks like a fair tradeoff. As far as added mass goes, from my interested by rather casual observation, that’s not a factor many HPR folks seem to put a huge emphasis on - makes sense, if something is just a bit heavier you can use an even bigger motor

 

[SkyFire]

Cool!
FYI, NAR L2 test questions come directly from the study guide.

 

[thzero]

I've been using OVERTURE PETG Filament 1.75mm to print with which is like $23 on Amazon. According to the slicer the fins take 113g and the 227g so like 8 bucks? Although I think the slicer is overstating the filament used.

 

[OzHybrid]

I've been using OVERTURE PETG Filament 1.75mm to print with which is like $23 on Amazon. According to the slicer the fins take 113g and the 227g so like 8 bucks? Although I think the slicer is overstating the filament used.

Check the filament dia exactly. Get a sharpie mark exactly 50mm. Warm up and tell it to extrude 50 mm manually. You’ll probably be under extruding by the % difference in your weights. Put all the data back your slicer. If filament is 1.74 instead if 1.75 use that in slicer. Measure dia in a few places. Adjust your extrusion to be correct. Might as well do a test cube and adjust your xyz so you print the exact size. I usually start by using the depth gauge on the verniers and telling it to move 50 mm one direction note difference. Then other axis then calibrate. Then print test cube and dial in settings. Whole process takes about an hour. Once done what you print will match what your slicer says.
of course now you’re accurately set up dimensionally and extrudally( new word). You’ll have to dial in nice prints again. Another hour.

 

[thzero]

As I need some nose weight, about 5-10 oz depending on motor, to get the stability (per OR) around .5 calibers. With the tailcone trick (https://www.apogeerockets.com/education/downloads/Newsletter154.pdf) its 1.5 calibers.

Surprisingly its hard to find threaded t connectors. This one is brass and 3/8" threaded rod. Was looking for 1/4" or 3/16" threaded rod.



Went out and got some 5/8" and 1/4" rod as well as some brass tubing I could find. Other thought is to braze myself a tee connector. Won't be, obviously as heavy, so more of the weight will be suspended but it won't be as big of holes needing to be cut in the nose cone either.

 

[thzero]

Fins are done printing... look pretty good.

 

[OzHybrid]

Have you got a picture of the fins being printed? I'm interested in what orientation you printed them? The body mount parts look like you printed as shown above. The fin looks like you printed on an angle to get max strength like you would with a balsa grain. How did you do it?

 

[thzero]

Unfortunately I did not... here is screenshot from Cura.... and yes, I printed with the root edge on the horizontal axis.

 

[OzHybrid]

Did you add the support manually? Congrats on the surface finish. Pretty good for PETG. Looks to be well bonded inter-layerally.

 

[Bruce Hoffman]

I didn't. I'm sure its far cheaper to use some plywood even if going with some quality baltic birch 1/4". This wasn't so much about cost as it was about an idea - I had printed parts for other rockets online (expensive) and then broke down and got a 3d printer (CR-6 SE, and then also got an Ender 3). So it went from printing 3d jigs, and electronic bays to hey I can 3d print fins that I can attach to the rocket.

My first build using some of these techniques in a 2.63" frame (https://www.rocketryforum.com/threads/2-63-formerly-3-mailing-tube-printed-rocket.164180/). I'm actually in process now with that one of building a new body to do DD with it... so I can easily swap the fins and nose cone between at least two body configurations.

Now I'm sorta addicted to this 'modular' thing even if it does end up having more mass.

Just ordered a ender 3v2. It’s going to be here Friday. Worried a little about the software to make stuff but we shall see. Awesome looking project.

 

[OzHybrid]

Just ordered a ender 3v2. It’s going to be here Friday. Worried a little about the software to make stuff but we shall see. Awesome looking project.

Thingiverse, SCAD, Cura. Calibrate printer. All free.

 

[thzero]

Did you add the support manually? Congrats on the surface finish. Pretty good for PETG. Looks to be well bonded inter-layerally.

Yeah, the supports were added manually. It was printed with at .28 layer height and yeah came out fairly well.

 

[thzero]

Just ordered a ender 3v2. It’s going to be here Friday. Worried a little about the software to make stuff but we shall see. Awesome looking project.

Yup... I'm using Cura slicer (not the one that Creality provides). I also use onshape.com (its free if you dont mind designs being public) and also using SCAD; been meaning to start converting some of my onshape designs over to SCAD.

 

[thzero]

Busted out the drill press to work to try and cut some custom centering rings. I found that a double headed circle cutter (i.e. https://www.amazon.com/Yosoo-300mm-...eywords=circle+cutting&qid=1628040836&sr=8-74) worked better than a single. Still was a pain getting the measurements just right, very fiddly and the tools are not that precise.



Obviously one is a LOC ring.. but one is a thrust ring, and the other two are centering rings for inside the fin mount. These four will sandwich the fin mount and the two inner centering rings will be glued to the motor tube.

 

[thzero]

This is one of the recovery attachment points. It'll get glued to the motor tube, and then bolted to the airframe. Even includes a handy mounting point for the rail button.

 

[thzero]

Well reprinted the fin attachment structure to make it a bit lighter weight.





Set of rings for the fin can.

 

[thzero]

For the nose weight attachment, didn't really like the other idea. So I got some coupler nuts for 5/8ths rod and used a 1/4 bit and some cutting fluid to drill a nice cross-hole on the drill press.





Obviously it needs cut down and need to drill some holes in the nose cone for the rod. Then dump epoxy in and I'll have a nice attachment point for nose weight.

 

[thzero]

Cut the motor tube... and pulled off the glassine in the area that is being epoxied.



Epoxying the lower centering ring in using Rocketpoxy. The glassine was removed for the upper centering rings too.

 

[thzero]

Attached the thrust ring to the bottom centering ring. The Aero Pack 54mm motor retainer will be epoxied with JB Weld.