Y.A.B.B. - my biggest build yet

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EXPjawa

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OK, I posted this at lunchtime, only to have it disappear into the server fits the site was having earlier. :eyeroll:

Anyway, I know everyone has upscaled the Big Bertha at some point; I've cloned the Super Bertha myself. But I've been toying with a larger one yet. With the announcement that this year's National Sport Launch being local, and then that Vern & Glenda would be attending, I decided that now is the time. As I gained some experience in building and flying, the design evolved from BT101 to LOC tubing to MAC 4" tube. Along the way, it went from launching on moderate G to needing an H at minimum (an I to get to 2000 ft). The design is single deploy (with JLCR), 38mm mount. So, yeah, its Yet Another Bigger Bertha.

I have pulled together what amounts to being more a kit than a scratch build; I'm not really actually cutting out or custom making any parts myself. Late last season, I bought a 4" fiberglass Bertha nose cone from Ken at Performance Hobbies. This is, BTW, my first dealing with fiberglass. I asked Nat Kinsey of Upscale CNC to cut out the fins. Then I gave the fins to Mike Crupe from MAC Performance, and he whipped up the airframe set slotted for the fins. He also ran the fins through his beveling machine, so that saves me a step too. So, its a kit of mixed manufacture.

I am not planning on rushing through this build, as I have a few months. But I am also not anticipating any real complications in building. In some ways, it really is just skill level 1 kit, rendered at 2.5X scale, with some nuances of fiberglass, epoxy and kevlar thrown in. Right now, I've just spread the parts out on the work bench to get a sense of it. Baby Bertha is supervising the job...

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This will be the physically largest rocket I've built to date. Hopefully, I'll be able to fly it at NSL, then again at URRF5.
 
The YABB needs an I600, I will even lend you the hardware. Looking forward to seeing this one fly Rick.

I may hold you to that, though I am not yet versed the ways of "I" motors. I'm barely dabbling in 38mm to begin with at this point. Is the I600 CTI or AT? My current assumed flight profile is for low and slow, dramatic lift offs. I'm hoping to keep it light enough to lift off with an H100, but it'll probably need every inch of rail to do it.
 
Mmmmm. I600R. Perfect motor for this.

for reference it put my 4” Emerald dragon to 2700’
 
I may hold you to that, though I am not yet versed the ways of "I" motors. I'm barely dabbling in 38mm to begin with at this point. Is the I600 CTI or AT? My current assumed flight profile is for low and slow, dramatic lift offs. I'm hoping to keep it light enough to lift off with an H100, but it'll probably need every inch of rail to do it.

Rick I am pretty sure you took a pic of this rocket on the I600 at one point. I am not sure if it was your pic but the I600 was my go to motor for my 3" PML Bull Pup. If you know this rocket it has relatively thin fins for the span and I am surprised the I600 didn't rip the fins off of it, but she handled the motor without issue. This is right up to her last flight, where I didn't swap out the "M" delay grain for the "L" and she popped at 10 seconds or 225'/s.

That motor in that rocket was reliably a mile high rocket where I could count on 5300 AGL most of the time. My guess is that with that big blunt nose cone and a 4" airframe, that you would be somewhere in the 4K range @ 500ish mi/h. A reasonable alt for that rocket on our fields. However as qquake2k said, this is most definitely not a low and slow profile, but she's not likely going to weathercock off the rail ;)

 
The I600 is a six grain, 38/720 AT Redline reload. It may be too much for YABB, if you want to keep it low and slow.

Well, low & slow is where my comfort zone lies. I'm only L1 at this point in time, and still lack any sort of tracker, so I like the rockets to stay where I can see them. With that said, that doesn't have to be the only answer...

Do you have a Rocksim, or Open Rocket file for YABB?

Yep, there's a screen shot from the Rocksim file above. I'll post the file later.

Rick I am pretty sure you took a pic of this rocket on the I600 at one point...That motor in that rocket was reliably a mile high rocket where I could count on 5300 AGL most of the time. My guess is that with that big blunt nose cone and a 4" airframe, that you would be somewhere in the 4K range @ 500ish mi/h. A reasonable alt for that rocket on our fields. However as qquake2k said, this is most definitely not a low and slow profile, but she's not likely going to weathercock off the rail ;)

Low & slow is just one profile, but not a limitation. I don't think that the rocket will have structural issues with bigger motors, as long as I stay in a reasonable speed zone. The fins are quite large, but they are 3/16" ply. I was specifically thinking of slow liftoffs when I designed it, but I still simmed several I-class motors (and a couple J's). The I600 was not one of them, because I really only looked at CTI options, since that's the hardware I have.
 
Well, low & slow is where my comfort zone lies. I'm only L1 at this point in time, and still lack any sort of tracker, so I like the rockets to stay where I can see them. With that said, that doesn't have to be the only answer...



Yep, there's a screen shot from the Rocksim file above. I'll post the file later.



Low & slow is just one profile, but not a limitation. I don't think that the rocket will have structural issues with bigger motors, as long as I stay in a reasonable speed zone. The fins are quite large, but they are 3/16" ply. I was specifically thinking of slow liftoffs when I designed it, but I still simmed several I-class motors (and a couple J's). The I600 was not one of them, because I really only looked at CTI options, since that's the hardware I have.

Clearly then, you need an I297 Skidmark (CTI 5G) for this baby for slowness if not lowness. :) The J316 Pink or J270 Green would also be nice cert motors if you want to jump to L2. Do you have the full CTI 38mm starter set?

4" rockets are pretty easy to see up to about a mile if the weather is good and you have a person or two to help you out.
 
The sim file says the I600 kicks it to 3600', stable in 14". Max speed 700 fps. The drawback is that the indicated delay is only 10 seconds, which is probably 3-4 seconds too short for apogee deploy. This rocket will rely on motor deploy.

I have 3 & 4 grain 38mm cases, plus a couple spacers. But that still gives a lot of options in those sizes.


View attachment Bertha 4inB.rkt
 
The sim file says the I600 kicks it to 3600', stable in 14". Max speed 700 fps. The drawback is that the indicated delay is only 10 seconds, which is probably 3-4 seconds too short for apogee deploy. This rocket will rely on motor deploy.

I have 3 & 6 grain 38mm cases, plus a couple spacers. But that still gives a lot of options in 3, 4 & 5 grain reloads.


View attachment 337526

There is a long delay option. I purchased some 14 second long delay grains for the I600 Redline from Sirius Rocketry. https://www.siriusrocketry.biz/ishop/aerotech-38mm-complete-reload-delay-kit-crdk38-04-1714.html

If you are interested in launching the I600 I will throw a 14 second delay in with the hardware.
 
There is a long delay option. I purchased some 14 second long delay grains for the I600 Redline from Sirius Rocketry. https://www.siriusrocketry.biz/ishop/aerotech-38mm-complete-reload-delay-kit-crdk38-04-1714.html

If you are interested in launching the I600 I will throw a 14 second delay in with the hardware.

I'll keep that in mind, maybe at URRF. We'll see... :cool:

Did you sim the CTI I255 Red Lightning? It wouldn't get you as high, but would still be an awesome flight. It's a four grain.

https://pro38.com/products/pro38/motor/MotorData.php?prodid=517I255-16A

I don't seem to have a file for that reload. I'll have to download it and give it a look.
 
I211 is a very nice motor... You'll like it. What does it sim on the I211?
 
I211 is a very nice motor... You'll like it. What does it sim on the I211?

Looks like about 2500' - it actually looks like a near perfect motor for it. That all, of course, assumes that the sim is accurate and worth much. I guess we'll see sooner or later...
 
OK, my first actual step here (and its just a small one) has been to mark out the motor tube as to where the centering rings go:

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Not very exciting, I know. However, I also brought all the parts into work, where I have a scale in the metallurgy lab that measures mass to the 1/1000th of a gram. So I can get very accurate measurements of the components to feed back into the sim. So, i have updated the model and rerun my flight sims. The area that is a guess is the added mass of the epoxy & paint. I won't be able to dial that in, obviously, until the thing is built and finished...
 
OK, time for an update. I had some time to work on this project this weekend. I decided to start at the top, with prepping the nose cone. The cone is fiberglass, so the wall thickness at the shoulder varies a bit. The nose bay kit that I got from Mike Crupe has a centering ring that's stepped to fit into the end of the shoulder. So, I had to trim the edge of the shoulder for that ring to fit it into. I bought myself some new sanding drums for my Dremel, and ground it down until I got a good fit:

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I then used the same on the mold line on the exterior of the cone:

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The next step was foam fill. I get that a glass cone probably doesn't need the reinforcement of the foam, especially within the flight profile I'll probably stay in. But, I think using the foam to support the nose bay rather than trying to fit another ring done in the shoulder. Plus, the foam is fun to play with and doesn't weight too much.

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The volume of the cone took probably 3 oz of each part of the foam; I used about 3.5 oz, and thus had to trim some off the top. I then sliced a grid pattern in the top of the foam with my hobby knife, and used a screwdriver to break them off about 1/4" down. Then I used a hole saw to core out the center for the bay tube, in several steps of cutting, breaking out the foam, cutting, etc. I also had to trim out a slightly larger diameter at the top of the hole, so that close out of the nose bay kit had a place to fit.

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The hole at the 12:00 position is just an inclusion in the foam. But at this point, the bay tube has a good fit. So now, the bay kit needs to be assembled.

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A little sanding was needed to get a good fit of the bay tube into the cap close out piece. Some 20-minute epoxy was mixed up, and the end bulkhead was installed, then the tube to the close out, then the centering ring attached to the close out. I had some extra epoxy left over, so I also attached the centering rings to the motor mount tube:

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All of this is curing now. I also had to do a little bit of sanding to achieve a nice slip fit of the mount into the body tube. Once the epoxy was well set, I test fit it into the tube and got it stuck. Some guys joke about Mike's kits fitting together so precisely that it could fly without epoxy. This was so tight into the tube that I couldn't turn it or pull it back out; I was wondering if I'd need a rocket motor to get it loose. But I made due with a heavy paper roll tube and knocked it out. But a little 120 grit made everything alright.

Next steps are to install the motor mount into the tube and the nose bay into the cone.
 
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My fin jig is far too small for 4" tube. But flipping the rails inside out makes a nice cradle to sit it on in a stable fashion. The fins do all have a very slight twist, so that does make visually aligning them a little harder. But I don't think anyone will casually spot an issue. The fins are, however, thick enough (and cut straight enough thanks to Nat) that they seem to sit squarely just by holding the tip down on the body tube. Or at least as far as i can see. This seems to be working so far...

Oh yeah, I epoxied in the motor mount the other night (obviously). I must have gotten ahead of myself on that one, no pics. Not that they'd have been exciting. I also affixed the nose bay assembly into the cone.
 
Forgot to update - this was done a couple weeks ago. I finished attaching all fins. It now at least looks like a complete rocket:

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As of yesterday, I finished the epoxy fillets on the fins. Next step is to closeout the fin can with the aft ring.
 
Finally! A day warm enough to paint! I primed the YABB when I got home from work, shown here after the first pass:

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With any luck, I'll get to sand it a little bit later in the week and go for primer round 2 on Friday, when the next decent day is forecast...
 
Sanded, with a second prime coat:

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I need to get moving on this; I want to have it finished and flying at NSL...
 
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