That's a great thread, full of interesting discussion. Thanks for sharing both the BN3E build itself and your L3 journey.
It keeps them from fluttering by increasing the rigidity. Fluttering, not aerodynamic drag, is most often responsible for the rapid removal of a fin at Max Q. If acceleration is rapid enough to even be a factor, the laminating of the fins across the motor mount is where you would want the reinforcement, due to, in that extreme example, the body tube junction acting as a fulcrum.How does glassing the fins keep them from ripping off under extreme acceleration? The videos I’ve watched on glassing show glassing the fins before gluing them into the rocket. It would still be the epoxy that holds the fins in place then right not the glassing, so what is the purpose of glassing? Wish I understood it better...
As Demonian said, after filleting you can also lay a continuous sheet of 'glass or CF from the tip of one fin, across the fincan section of the airframe, to the tip of the other fin opposite (and repeat the same around the whole fincan) to increase rigidity and spread the loading. This is referred to as 'tip to tip' or sometimes 'T2T'.How does glassing the fins keep them from ripping off under extreme acceleration? The videos I’ve watched on glassing show glassing the fins before gluing them into the rocket. It would still be the epoxy that holds the fins in place then right not the glassing, so what is the purpose of glassing? Wish I understood it better...
I've done it with others just using FG but that particular build has flown twice so far on big J + Hs and K + I motors.Yes, I can see how putting a layer of CF down one fin over the MMT and back up the next fin would greatly help hold everything together for
That looks like a cool cluster engine rocket!...this is an example where I laminated these large 4mm ply fins individually with 200g FG then did a susequent tip to tip lay up with CF. I cut shaped sheets of 2/2 3k twill CF that I wrapped over the fins, airframe and outboard fairings. This is 5.5" Loc tubing like the Big Nuke.View attachment 395670
I'm not sure what size 2-56 shear pins are (here in Britain UNC gauges are available, but I choose metric) but I used 3 x M2 nylon screws to keep the booster section on, and 3 x M3 for the nose cone. However here are some really important points to consider:I plan to use shear pins to prevent premature separation in both the booster and main section of the Big Nuke 3E. For a 5.54” airframe like this, will three 2-56 shear pins be enough per section or would you recommend more, or should I use 4-40 shear pins instead? I looked for a calculator online for this and all I found was one for the amount of black powder to use based on the amount of shear pins and volume.
Sorry I didn’t reply sooner. Here is what I meant by Z-clip retention.I like what you’ve done there, it looks great! May I ask what Z-clip retention is?
I have RocketPoxy 5000 from Apogee that I planned to use on this build. Will that be a quality thin resin epoxy for where the fins butt the mmt or do you recommend something else. If so, where could I get it at? Walmart, Home Depot etc seems to mainly carry the generic stuffWe've seen the 3E take small M's without reinforcements. Just be sure to remove the glassine layer on the MMT and use a quality thin resin epoxy that will soak in. If you choose to glass the tubes, it would add roughly a pound over all. And of course, remove the glassine from the airframe as well.
that is a fine systemThanks. Does this look like some good glue for where the fins will butt the mmt? Also, I could use the RocketPoxy 5000 for the rest of the build, correct? https://www.aircraftspruce.com/catalog/cspages/gflex3.php
The GREAT news is that ANY epoxy will work with Loc products....yep, I said it! Wood glue works too!Ok. That’s nice to know, seems I can get bogged down at times with getting the perfect glue. On the other hand, I was wanting to get an epoxy with a thin resin so it would soak into the mmt and make a super strong bond to the fin edge as I was advised to do in an earlier thread. If that’s important than I want to find the proper one. It’s a learning curve for me. Before now I thot epoxy was epoxy, and now I’m learning there’s thicker paste like epoxy and thin resin, but ya I don’t want to get too carried away with the glue process either
The shorter motor and adaptor will likely move the CG reward a little. It is likely the kit has enough static margin, but it should be checked anyway. You can always counteract with a small amount of nose weight if it is marginal.What would the disadvantages be for building it with a 75mm motor tube and just running a 54-75 adapter in it if I want to fly 54’s for now? Surely it wouldn’t add that much weight?
Ya, I purchased a thrust plate from apogee and also purchased an Aeropack flanged retainer ring which cost over half of what the whole kit did but I think I will love itUse BSI 30 minute to install couplers and the motor mount into the tube and use Gorilla Wood Glue to put the centering rings on and to glue the fins in. Don't need any fancy epoxy like Aeropoxy/RocketPoxy or West Systems. Make the fin fillets out of BSI or even JB Weld (personally I use JB Weld as it's very smooth and doesn't run). While those clip things might be old school and proven by many people, I don't trust them. I'd rather spend the money on an Aeropack.