L3 Build - Gratuitous Excess

The Rocketry Forum

Help Support The Rocketry Forum:

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Hi everyone,

Just started my L3 build, figured I'd post here. This is going to be a pretty "standard" build, building a LOC Bruiser EXP. Current plan is to fly it on an AT L1000W for a shakedown flight, then an AT M1350W at Midwest Power at the end of October for the cert. Between now and then, who the heck really knows what will happen, so that's all TBD obviously.

Before starting, the only change I made was swap out LOC's MMAS motor mount system for a straight 75mm mount. I'm lucky enough to work about 20 min from LOC, so I stopped by and swapped the parts out. As usual, Jay at LOC is awesome to work with.

Avionics will be all Eggtimer - I have two Quantum's that were previously flown, thinking of building up either another one of those or a Proton and have triple redundancy. After shoehorning the two Quantums into a 3" airframe for dual redundancy/dual deploy on a different flight, I'm looking forward to working in a 7.5" av bay!!

Thus far, I've laminated one of the body tubes once and the booster body tube twice (just got done applying epoxy actually). I'm using Soller Composite's fiberglass tube/sock/whatever you want to call it. First layer is 6" light glass, the next 2 layers of the 7" light. Each layer is about 10oz, so getting 30oz total. (as an aside - I bought a foot of their 6" heavy sock (26oz), it will NOT fit on a 7.5" LOC tube, and it's not even close). I'm using Aeropoxy Laminating epoxy (PR2032 resin, PH3660 hardener), as I used it before...it might not be "perfect", but for a cert flight I'll take "familiar and successfully applied" over "try 4 new things and have to learn all of them too". In case you're wondering, most of my complaints with Aeropoxy are around 2 things- 1) the hardener can settle out and not work right (fix by shaking first) and b) it needs to be above 70F to cure right, more than that preferred (fix by not laminating in April, wait till July if you're doing it outside like I am).

Some pics of various stages of the laminating process:

Yes - looks like a giant condom, lol. There's a nosecone in there to help guide it on:
IMG_20200627_114006665_HDR.jpg

Hanging dry:
IMG_20200627_114744856_HDR.jpg

Hanging wet:
IMG_20200627_123626557_HDR.jpg

Hanging wet, second layer:
IMG_20200704_114748156.jpg
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Got the 3rd layer of glass put on the bottom section today too, courtesy of the hot air here this weekend.

IMG_20200704_150808487.jpg


I do have one question - I'm planning on starting the booster/fin can section shortly. See drawing below.

Question - would people suggest attached what I have labeled as "drogue tube" to the bottom booster section (as drawn), or should I secure it to av bay and blow the fin can off?

IMG_20200704_191739765.jpg

Thanks!

Dustin
 

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
6,681
Reaction score
2,099
Location
Huntsville AL
Question - would people suggest attached what I have labeled as "drogue tube" to the bottom booster section (as drawn), or should I secure it to av bay and blow the fin can off?
If you want to blow your drogue out instead of pulling it out, fix it to the ebay.

If you want to make it slightly stronger in bending, find where will your center of gravity be. Fix the end thats further away from the CG (range), and leave the closer end sliding. (Less bending moments closer to the CG)
 

Tim51

Well-Known Member
Joined
Jul 4, 2015
Messages
857
Reaction score
144
Location
London, United Kingdom
What!? No pics of the fin slots being re-cut when the 'glass reached the leather stage...? Aways my favourite bit..😊

Seriously - good luck with the build and the L3 cert. Will be following with interest.
 

n3tjm

Papa Elf
Joined
Jan 21, 2009
Messages
7,273
Reaction score
158
Location
Penns Creek, PA
Hi Dustin. Great Build so far. You want the have the drogue tube secured from the fin can. I also want to suggest two alternative plans for your fin can.

Fin Can design.jpg

You can see here two differences. First, you want to have a centering ring butted on the forward end of the fins. This allows for a solid fin connection. This can be done two ways. The simplest is epoxy all the rings forward of the fins to the motor tube. If the "optional ring" fits inside the tube coupler, you can attach the coupler at this point. If not, the coupler should be installed after the mount is glued into the fin can's air frame. Epoxy the fins in. reinforce all the joints, including where the air frame tube makes contact with the fins. Finish the fin can by attaching the rear centering rings.

The second way to do it is cut slots in the two centering rings and fins. Assemble the motor mount completely. Reinforce all the joints. Extend the fin slots on the air frame tube so the air frame can be slid on the forward end of the mount and the fins slide into the slots.

Another not which I always do with my larger rockets is make an anti zipper band on the forward end of the drogue tube and main parachute tube. I do this by wrapping a 2" kevlar band around the top of the tube before fiber glassing the tube. I never had a zipper after I started doing that. But it looks like you already glassed your tubes, but maybe 3 layers is enough strength to prevent zippers. (Personally all my rockets where I fiber cardboard or phenolic tubes tubes, I just use one layer).

Great build. looking forward to seeing more :)
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
If you want to blow your drogue out instead of pulling it out, fix it to the ebay.

If you want to make it slightly stronger in bending, find where will your center of gravity be. Fix the end thats further away from the CG (range), and leave the closer end sliding. (Less bending moments closer to the CG)
Hadn't considered the CG idea, nice!


What!? No pics of the fin slots being re-cut when the 'glass reached the leather stage...? Aways my favourite bit..😊

Seriously - good luck with the build and the L3 cert. Will be following with interest.
Lol, yeah - I asked for and received a dremel tool for Father's Day specifically for the job of trimming all of the glass on this, specifically the fin slots but also the ends. Plus, everyone needs a dremel tool, lol.

Thanks!


Did you put on all three layers of Fg sleeve at once then wet them all out? Or did you put on one fg sleeve wet it out then put on the next fg sleeve and wet out?
Each individually. The first one cured for about a week or so I think. Managed to do layers 2 and 3 in the same day (yesterday) on account of how fast the epoxy cured with it being 85F outside here. 2nd layer went on at 10am, 3rd layer went on an 3pm, everything cured up by 8pm. I couldn't imagine dragging the cloth over the tube if it were tacky yet in any way, shape, or form.
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Hi Dustin. Great Build so far. You want the have the drogue tube secured from the fin can. I also want to suggest two alternative plans for your fin can.

View attachment 423355

Great build. looking forward to seeing more :)
Thanks for all the input and taking the time to draw that up!

Couple of comments/questions-

1) The motor mount tube is 34" long, body tube is 30", coupler is 15". So, the motor mount tube would barely reach into the coupler, which is why I was planning on putting the centering rings up against the bottom of the coupler. I see on LOC's website they do sell rings for fitting inside the coupler, but not with a 75mm tube in the middle - I'll email Jay at LOC and see if he can custom cut something for me.

2) I take it the ring up against the fin is there because basically you're getting things bonded together in every possible direction? I like it.

3) Regarding the body tube on top of the fin can (the drogue chute tube) - does that get epoxied to the fin can and made permanent, or does that bolt together? I can see arguments both ways - if I do bolt it together, I'd probably 3D print some pretty extensive supports to epoxy into the tube to spread the load so that the bolts or whatever don't rip it apart. Epoxying would seem the better solution other than it'd make it a lot harder to attach the recovery hardness. Maybe less of a deal with a 7.5" tube though...should be able to fit my arm into it up to the shoulder, I'm not that ripped, lol.

4) I'd probably make the centering ring in the coupling another double stack. If I end up epoxying the second tube to the coupler, I can use THAT double ring for the top rail guide, should be rocket solid going through coupler, body tube w/ 30 oz glass, and into 2 centering rings.

5) I won't be able to get epoxy to all surfaces when eventually assembling. Would people suggest drilling holes and injecting via syringe? I've seen that done elsewhere. Or, since I'll have possibly as many as 6 centering rings, not a big deal if there isn't a fillet on all sides? Given the name of this rocket and the mentality behind it, I would lean towards holes and syringes and stuff.

Thanks everyone!


Dustin
 
Last edited:

tsmith1315

Well-Known Member
Joined
May 16, 2020
Messages
215
Reaction score
122
Location
Doerun, GA
Hey Dustin, this is a little late now, but for future reference-

You can easily cut glass/epoxy with a razor knife when it is in the green cure stage. That's where it's solid but pliable. Like leather, as Tim51 was talking about.
It makes a clean cut, no Dremel necessary. Fin slots and tube ends are a breeze at that point. For some strange reason, I like that part, too. Maybe it's a Tim thing.
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Hey Dustin, this is a little late now, but for future reference-

You can easily cut glass/epoxy with a razor knife when it is in the green cure stage. That's where it's solid but pliable. Like leather, as Tim51 was talking about.
It makes a clean cut, no Dremel necessary. Fin slots and tube ends are a breeze at that point. For some strange reason, I like that part, too. Maybe it's a Tim thing.
Yeah, I have had good luck there in the past. The way yesterday went, it wasn't in the cards. For the first layer I put on (2nd on the tube), it cured so much faster than I was expecting (went out to check if it was leather yet and it was full up cured), 3rd time was just kinda "whatever" because it was going to suck at that point regardless, lol.
 

n3tjm

Papa Elf
Joined
Jan 21, 2009
Messages
7,273
Reaction score
158
Location
Penns Creek, PA
Yeah, you will need a longer motor tube, but it’s worth it for a stronger connection of the sections. If you want to bolt the drogue tube to the fin can (which I have done with my rockets), you will want to epoxy some blind nuts on the inside of the tube coupler to have something to screw into. If you do that, and you do what I suggest and have a centering ring on the top, you will have to wait until you get the tube cooler installed before you glue in the top centering ring. Bolting the tube on the fin can makes it easier replacing the tube if it gets damaged, or you need a longer drogue tube if you discover you want to fly it on a motor that is to long for that configuration.
If I ever get a chance to fly a N2000 or one of those 98mm O motors, I would need to get a longer drouge tube.
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Yeah, you will need a longer motor tube, but it’s worth it for a stronger connection of the sections. If you want to bolt the drogue tube to the fin can (which I have done with my rockets), you will want to epoxy some blind nuts on the inside of the tube coupler to have something to screw into. If you do that, and you do what I suggest and have a centering ring on the top, you will have to wait until you get the tube cooler installed before you glue in the top centering ring. Bolting the tube on the fin can makes it easier replacing the tube if it gets damaged, or you need a longer drogue tube if you discover you want to fly it on a motor that is to long for that configuration.
If I ever get a chance to fly a N2000 or one of those 98mm O motors, I would need to get a longer drouge tube.
Makes sense. This is a 75mm, the longest hardware Aerotech sells is 36" or so, so it'll work. I'll probably end up epoxying it and just being done with it. If something damages a tube with 30oz of glass, I doubt the bottom of the booster survived anyways, lol.
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Tonight I took the tube to a friend's place who has a better workshop for messy things like dremeling fiberglass...he also has a belt sander volunteered to the effort. Worked out pretty well, very happy with the results.

The T-88 arrived today, I ordered two "custom" centering rings from LOC (fit inside coupling and with a 75mm MMT hole), so I should be in position this week to start actually building the fincan.

...been waiting for this since about 1999, when I took part in Rockets for Schools in Sheboygan, WI as an 8th grader. I saw someone launch on an M and said then that I would someday do that. The time has finally arrived. Awesome.

IMG_20200706_213639825.jpgIMG_20200706_213644834.jpg
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
I see you using some of my suggestions :).
Lol, true. They make sense, so why not. I do need to clear the changes with the TAPs yet. The only real "big" change is moving the top double centering ring to the coupler.

This thing is gonna be solid by the end, that's for sure.
 

DMehalko

Well-Known Member
Joined
Jan 25, 2010
Messages
88
Reaction score
35
Location
Colorado
Nice! I plan to order a Bruiser (non exp) for big fat low altitude flights, watching with interest
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
TAP approved the change, picked up rings today. Here's basically what this is gonna look like in cross section...I couldn't figure out in CAD how to add the fins, they go in that slot on the right.

Booster Cross Section.PNG
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Are you building the structure as a single part instead of an assembly?
That's the plan at the moment....if I'm understanding your comment. Can you elaborate on what you mean by assembly? Are you meaning the upper tube detaching from the bottom, or something else?

I plan on building the motor mount tube, centering rings, and fins attached to the tube, and then slide that assembly into the tube and then epoxy the ever living crap out of all the joints....does that help?
 

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
6,681
Reaction score
2,099
Location
Huntsville AL
Sorry, should have elaborated. You were referring to the solid model of your rocket and the difficulty adding fins. I was referring to the model, not the actual rocket
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Sorry, should have elaborated. You were referring to the solid model of your rocket and the difficulty adding fins. I was referring to the model, not the actual rocket
Yeah, swing and a miss for me there. I was trying to do an assembly with different parts. I have zero formal training on CAD, so I'm just kinda making it up as I go. I drew that pic primarily to show the TAPs what I'm doing with the rings, so that was the important part.
 

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
6,681
Reaction score
2,099
Location
Huntsville AL
Not bad.

Add one fin to the assembly, mate it to the slots (front of tab coincident to slot, side of tab coincident to slot), and tangent mate the root underside to the body tube. Then either repeat the process for your other fins, or seeif your program has a circular pattern feature.
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Not bad.

Add one fin to the assembly, mate it to the slots (front of tab coincident to slot, side of tab coincident to slot), and tangent mate the root underside to the body tube. Then either repeat the process for your other fins, or seeif your program has a circular pattern feature.
Lol...I tried the fin once and gave up pretty quickly, I didn't know of the existence of the tangent mate...that would help!

Thanks!
 

richP

Well-Known Member
Joined
May 23, 2019
Messages
138
Reaction score
123
Looks stout. Not really sure what the 3rd forward ring is giving you here, and if it's even possible to get it bonded to the airframe without drilling holes.

Just an option, but in the past, when installing a pre-assembled MMT thru the rear, like you are; I liked to use a syringe and put a bead of rocketpoxy in the airframe about an inch short of the forward rings final position, begin sliding the MMT into the airframe until the fwd ring clears the fin slots, and then put another bead around the airframe right where the slots begin. Once the MMT/rings are pushed all the way forward, you get a nice fillet on the front of those 2 rings.
Plenty of ways to skin a cat, so just throwing it out there. Obviously, only your TAPs input really counts.
 
Last edited:

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Looks stout. Not really sure what the 3rd forward ring is giving you here, and if it's even possible to get it bonded to the airframe without drilling holes.

Just an option, but in the past, when installing a pre-assembled MMT thru the rear, like you are; I liked to use a syringe and put a bead of rocketpoxy in the airframe about an inch short of the forward rings final position, begin sliding the MMT into the airframe until the fwd ring clears the fin slots, and then put another bead around the airframe right where the slots begin. Once the MMT/rings are pushed all the way forward, you get a nice fillet on the front of those 2 rings.
Plenty of ways to skin a cat, so just throwing it out there. Obviously, only your TAPs input really counts.
The 3rd ring is against the bottom of the coupler tube. The idea was to provide some load handling there. I'm not a structural engineer, so I'm not sure if that makes sense.

I've started working my way through how to assemble this thing. It's gonna be a trick and a half. Think I'm just going to accept the fact that I'm drilling holes and using a syringe to get some of the interfaces. Makes things less difficult, and with 30oz glass I can't imagine it's going to suddenly make the airframe catastrophically weak.

I'm going to 3D print a guide for holding fins in place while the initial epoxy sets up. 3D printer is currently being used for printing flowers for my wedding in less than a month, so that's not happening right now. For the moment, contemplating it.
 

GalantVR41062

Celebrate Recovery
TRF Supporter
Joined
Oct 25, 2017
Messages
248
Reaction score
163
Location
Plymouth MN
You could glue the MMT and centering rings together similar to what I did in my 1/4 scale Viking 7 build.

I left the aft ring off, glued the 2nd one up that the fin root sits on, then the 3rd one to the MMT. Then I installed my all thread and set the height for the top ring but left it off until the MMT was glued in, I used the aft ring to help hold it centered and set the depth. After that dried I removed the aft ring, installed the very top ring with the recovery attachment points.

20200212_225234.jpg


Very nice build, a local hobby store has a Loc Bruiser EXP hanging from the ceiling and has inspired me for a long time.

~John
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Last night I peeled the motor mount tube, which is an amusing thing to say.

Today I dremeled the motor mount rings, basically the edges so they slide onto the tube (and into the tube) better. Put one ring in the front, put another in front of the fins, and then inserted a fin.

I 3D printed some guides to basically make sure the fins are close enough to proper alignment. Put the fin in, taped the guides on, and added a couple of dabs of 5 minute epoxy to hold the fin in place. Once that hardened, I put a bunch of T-88 in, as far as I could reach, now letting that cure. Tomorrow will do the same on the other side (or later tonight if the stuff I just put in cures up enough to allow it to be rotated).

Once that is done, I'm planning to pull the tube with the one fin on out, then put the ring that the front of the fins bond to - get that at least lightly epoxied on and square to the motor mount tube. Reinsert that assembly and use that ring to make sure the fins are all in the same position along the length of the tube.

...gotta remember to drill the holes for the all-thread first though!!


IMG_20200714_190018343.jpg
IMG_20200714_190816924.jpg
IMG_20200714_190820754.jpg
IMG_20200714_191214976.jpg
IMG_20200714_191220687.jpg
IMG_20200714_194105295.jpg
 

Attachments

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Found out the T-88 cures overnight, so I laid down another fillet this morning before going to work. It's like 64 degrees in my basement, so it curing up was excellent...not all epoxies do in that temp. T-88 is advertised for being able to cure at 35F, which is half the reason I went with it. Good stuff.
 

Dustin Lobner

Well-Known Member
TRF Supporter
Joined
Sep 3, 2019
Messages
198
Reaction score
83
Been carrying on - tomorrow morning should have the last internal fillet on and will be able to pull the mmt tube and fincan out of the body tube...then the epoxying really begins, lol. Should be fun.

...still sitting here kindof in awe this is finally happening, been wanting to since I saw a guy fly an M back in 1999 when I was in 8th grade. Woot. This is awesome.
 
Top