SBR Fusion Level 2 Build

After assuring my wife I was going to spend the rest of the year building the rockets currently in my build pile and think about Level 2 next winter (down under), I discovered Havoc in the Paddock in Waikato, NZ [https://www.nzrocketry.org.nz/events/Havoc]. With a 10000 ft limit and the chance to show my new found hobby to my family and friends back home - I changed my mind and decided to make a rocket for Level 2.

Actually I’m probably going to make 3 to cover my bases - but will keep this thread for my first one.

I’m also keen to build a dual deploy rocket. I’d seen a couple of build threads for this rocket and was attracted by the all inclusive nature of the kit. We have a good supplier here in Australia but I have discovered stock levels can vary from time to time. So with only a relative few months to get going I pulled the pin and ordered from the US. Postage was quick and it arrived well packed yesterday.


Spent last night reading the very comprehensive instructions including the part about following them exactly..... but I have a few questions about small mods.

It had a LOT of laser burn. How much should I sand off to ensure centring rings are firmly attached etc.

Second, 18 min Epoxy is recommended, but as I have 15 & 30 min BSI, they’ll be my go to. Except, there is no mention of internal fillets. Given its rated for a K motor, would I be wrong to leave out the rear CR and do some internal fillets on the motor mount and inside the airframe? If I use Titebond III for the fin motor interface and internal fillets, my overall weight would be similar to using epoxy for just the fin attachments. For that matter, for a cardboard/plywood interface is epoxy going to be any stronger than TBIII anyway?

Lastly - for tonight - for those that have built it - has anyone used an aftermarket motor retainer. I’m thinking something along the lines of a 54mm PML or Aeropack retainer.

I'll be watching this build... Pointy Side Up!!!

[EDIT]... That's some edit you did...

To answer your questions about the adhesive. 30 minute BSI epoxy is a very good choice for joining or filleting. I'd use JB weld for gluing any retainer in place, but IINM the fusion doesn't need it. Also, after gluing the rear CR in place, on the aft end of it, you might want to use some 30 minute JB weld (thinned with alcohol) to seal the wood for easier clean up after flight.

Hi Nick, Looks like a fun build. My recommendations would be..

You want strong epoxy joints, (that’s why we use epoxy right), so sand off the laser burn for good adhesion, but do not sand away wood or the shape. Same goes for fin edges for primer & paint adhesion.

I always do internal fillets with 5min or 15min. 5min if I am not worried too much about internal fillet neatness. I use 30min for all external fillets.

Installing the aft CR is nearly the last thing I do.. after rail buttons. I also use weld nuts for the rail buttons, which makes it super easy for replacing rail buttons.

As for Titebond III, love it for LPR builds, but the RSO may not like it for a HPR L2 cert flight. I would recommend use of epoxy. Interesting to hear what others think.

I might do a some cut away test joins between epoxy & TB3. Epoxy should be more penetrating into the wood & cardboard. I also always lightly sand the outside body tube where the fillets will be to improve epoxy adhesion to the glassine wrap.

Uh oh, the glue debate already.

(Wood glue and epoxy are both stronger than the paper and ply fibers they're bonding)

No debate since I total agree with you Nytrunner, just about everything is stronger than the wood (in general). I was commenting about what an RSO would think in a cert flight.

FYI: https://woodgears.ca/joint_strength/glue.html

Titebond 3 wins in their tests. .. and has 3ksi shear. While epoxy is generally more "reinforcing" than PVAs.

Dang it ! I build my LOC Doorknob with aliphatic (wood) glue. And no, I'm not giving my L2 back.

Nick my answers to your questions are as follows:

Yes, lightly sand to remove laser burn.

When in doubt, follow the manufacturers recommendation for adhesives. If you have some prior experience with the materials being bonded and the stresses they might encounter go with what you know. If you have developed an epoxy sensitivity stay away from that s___ ! I would fillet the fin tab to motor mount joint with your goo of choice.

If a kit includes motor retention (like the Fusion does) I would tend to use it but that's another personal choice. Many, many, many TRFers go the aftermarket route.

And most importantly never, ever, ever, ever, ever ask a glue question on this forum again.

samb said:

And most importantly never, ever, ever, ever, ever ask a glue question on this forum again.

Click to expand...

So, what's your favorite glue?

I prob phrased my glue question wrong. It was more that the instructions don’t specify internal fillets. So any glue inside the fincan would be extra weight. What I am thinking is that TB III internal fillets usually end up weighing quite substantially less by the time they cure properly. Given I’m replacing the included non forged eyebolts with some forged ones with built in shrouds, I’m going to lose some weight there and the whole thing should balance out.

Next thing I decided while running this morning is that the kit only comes with 2 centring rings for the main motor mount. Makes it tricky to just glue in one prior to flying fins. I think I might cut another myself. Will also give an extra glue for the fin tabs inside the fincan. I figure I’m planning this for Level 2. If I lose a few hundred ft with extra weight I will still pass. If I pop a fin on landing, I won’t.

Lastly, my Tapatalk is playing games with me. My major edit last night was retrieving most of my initial post from the internet gremlins. It seems to be a recurring problem for me at present.

Nick Hutton said:

I’m going to lose some weight there and the whole thing should balance out.

Click to expand...

I think you're trading grams for grams here. You could save way more weight by leaving off paint/vinyl wrap

It's a really good kit with a lot of flexibility from what I've heard. You'll do great!

Thanks for the replies. I’ve cracked on and decided to use a combination of epoxy and TBIII.

First up the supplied eye bolts aren’t forged. I had some forged SS eyebolts with shorter stems. Weight wise a comparable switched. Epoxied up and mounted to MMT.



As previously decided, I’ve added a 3rd CR to mate with the top of the fin tabs. Not sure why it’s not included as most of the kits I’ve made and builds I’ve followed have used one. Requires a bit of measuring up to get it all perfect, but will give me another surface to interact with the fins. Additional weight was 12g + glue.



Also deviated from instructions and peeled the glassine from the body tube around fin slots for better fillet bonding later.



Lastly, the instructions specified 3/16 inch MMT below lower CR. This seemed a little short if I had decided to want a retainer, plus the pics in the instructions clearly had a lot more showing, plus the sim fusionrocket sent me had the MMT tube flush with the body tube. As requested in the instructions I emailed SBR for advice. I got a somewhat terse reply and probably wouldn’t bother asking them again. My MMT will be a fraction more exposed.

Roughed up inside of body tube with coarse grit sandpaper and roughed up CR edges prior to gluing in. Also did this for MMT. Instructions don’t specify this but maybe it’s assumed it’s common knowledge. Glued with 15min epoxy incl a fillet on top of fore CR, but left middle CR flat as fin tabs will lock right in and will get internally filleted. I’ve read through the dark star build thread at the top of HPR a few times and I’m adapting some of the really good advice there for this build.

Will follow with interest Nick. Havoc 10,000ft is tempting!

BrendanH69 said:

Will follow with interest Nick. Havoc 10,000ft is tempting!

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Would much rather have been launching today, but I can kinda see why it’s a bit risky[emoji1974][emoji91][emoji91].
I will prob launch this dual deploy on an I at Cedar Grove before going all out on a J at Havoc. It sims close to 5000ft on a small J so would be pushing QRS ceiling.

I built a BSD/SBR Thor kit (the older and better kit with proper 3/16” fins) for an L2 attempt and I used Titebond 3 all the way except for the exterior fillets which were JB Weld and BSI for installing the coupler. While the little hook and screw retainer is definitely proven, I do not trust it. I use Aeropack exclusively now, plus it’s 100x easier to adapt a motor with Aeropack.

Nick, I know what you mean; I was waiting and counting the sleeps to launch day! Have had to quench my rocket thirst with joining TRF and reading loads of interesting stuff instead, including building up ideas on a a "mood board" of design ideas for myself and Dave (my rocket buddy) for a home made launch tower.

samb said:

And most importantly never, ever, ever, ever, ever ask a glue question on this forum again.

Click to expand...

K'Tesh said:

So, what's your favorite glue?

Click to expand...

That is too friggin funny....

So turns out I spoke too soon. Just 24 hrs after lamenting the cancellation of our club launch due to fire risk - a bushfire (wildfire) swept through our little seaside town. My yard even made the world news courtesy of it becoming a charred black mess.



Kinda put a hold on my build. We were evacuated and kept out for a few days. On the plus side, my TBIII internal fillets have been well heat cured!



After a weekend spent cleaning, I’ve now gotten round to masking and doing external fillets. I’ve gone a mixture of BSI30min and silica.



Problem is, in the rush to leave and the chaos that occurred when we returned to a house full of soot and smoke, I’ve mislaid the instructions.

Has anyone who has made one of these got a copy of the instructions they could scan? I’m kinda stuck at this point as the next step is going the couplers and I need to confirm the measurements!

First of all I am not sure the BSD Thor kit is necessarily "better" than the newer SBR Thor version, its different and reflects the changing design philosophies of the original designer. Yes the newer kit has thinner fins than the original kit, it also will fly on a larger variety of motors and in different configurations (middle break single deploy, traditional dual deploy, and nose cone blow single deploy). Any builder worth their cert level has learned to build for their intended motors, I have personally seen the prototype SBR Thor flown on motors up to and including the K550 (and the reason the K550 is not recommended). If you want to fly the SBR on K550 then it needs the fins laminated with FG the rest of the rocket will be fine, but the fins need to be a bit stiffer.
The new kit is also much more complete than the older one, including chute, motor adapters and other bits including vinyl wraps. Lastly the older kit is no longer available

Arsenal78 said:

I built a BSD/SBR Thor kit (the older and better kit with proper 3/16” fins) for an L2 attempt and I used Titebond 3 all the way except for the exterior fillets which were JB Weld and BSI for installing the coupler. While the little hook and screw retainer is definitely proven, I do not trust it. I use Aeropack exclusively now, plus it’s 100x easier to adapt a motor with Aeropack.

Click to expand...

Wow, close call! Glad to hear everyone safe and home intact!

Close call Nick, guess this means you are off mowing the lawn for a bit. More time for rockets !

On a positive note, these arrived in the mail yesterday



H’s thru to middle sized J’s pretty much covered with this lot.

No wonder we have an AT hardware shortage, it's all going to australia!

These ones are all thanks to Audi_Driver for the sales yard forum. Postage is a killer from the US, so makes sense to buy in bulk

A fairly productive rocket day today. Coated the ebay bulkheads in bsi 20min finishing resin plus coated my already assembled CAM 1 sled.




One small issue that I have discovered is that the instructions only specify that the key holes for the camera mount line up. They are off centre. What they don’t post out is that they need to be on the left. Mine are on the right. I’ll have to file them out to fit a GoPro hero 3, otherwise the key will cover the lens.



I’ve done another step not in the instructions and wicked thin CA into all of the cardboard tubes ends and inside the leading edge surfaces to increase its resistance to damage on landing.



Lastly, I’ve drilled the rivet holes to fix the camera bay. I’m now trying to work out exactly where to put the vent holes for the altimeter. The instructions say 2 inches below the top of the altimeter bay, but I’m buggered if I can work out which edge they are referring to. And there is no photo to guide. Anyone have ideas, preferably pics.



Off on holiday now for 10 days. When I get back I should have this completed fairly quickly. I need to lock in my motor orders for Havoc ASAP. I was hoping for a 54mm Baby J such as a J180T to go in my new 54/872 case, but Ausrocketry probably not going to have it. May have to settle for a 38mm J350, which won’t give quite as slow a lift off unfortunately.

Have a great Holiday Nick, better not be Bali, as that's where I shall be with family from Monday for 14 days or so...

Level 2 Cert completed!

After 3 months of cancelled launches, I ventured to Havoc in the Paddock in NZ. After my pre ordered motors didn’t materialise I was helped out in a big way by a local member who had some J motors he hadn’t used.

A CTI J330 for its maiden launch. I used dual altimeters. An eggtimer quark for the main and the supplied RRC3 for backup as it was more programme able with its settings.

After some discussions and reading online, I added two shear pins to the nose and completed charge testing.

Looking at the flight profile, it looks like the main deployed at 300 ft on the backup charge. Or it just didn’t open till 300ft?

I had an eggtimer tx in the nose, but I could see the whole flight and it landed less than 1/2 a mile away.

Well done Nick!

Nick Hutton said:

On a positive note, these arrived in the mail yesterday

View attachment 393590

H’s thru to middle sized J’s pretty much covered with this lot.

Click to expand...

Sweet.

All appear to be in pristine condition. Almost all closures included, too.

Reminds me that back in 1973 I actually met “Ms” Pristine Condition from the cast of ”Beach Blanket Babylon”.

Well done Nick, great to meet you onsite. Safe travels home !