Discussion in 'High Power Rocketry (HPR)' started by Steven88, Sep 9, 2019.
Good tips, thanks
And you're going to do a build thread on this when it arrives, right..? Given this discussion so far I think it's safe to assume you'd have alot of people following the build with keen interest!
Maybe I should! I have been impressed with all the help and interest thus far with this build! To have a community of people that share the same passion and give helpful advice is worth a lot and will definitely make this a ‘better’ rocket upon completion! And as always, having fun and being safe is the main thing...
I have a build thread on here of my Big Nuke 3E
Do you have a link for your build, please? Tried searching - plenty of BN builds but couldn't seem to find yours...
Yes, I am interested in it as well. Tks
HERE is an incredible build thread by Neond7, he even used my Blastcaps. Love his paint scheme.
That's a great thread, full of interesting discussion. Thanks for sharing both the BN3E build itself and your L3 journey.
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...
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.
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'.
...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.
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
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.
That looks like a cool cluster engine rocket!
Thanks! These things are always a learning experience. Here's the thread: https://www.rocketryforum.com/index.php?threads/148468/
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.
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:
1) In the rocket I showed in my post, the booster was relatively heavy (3 motors, 3 x retainers, lots of CF etc)
2) As shown in the thread, the NC was also weighted to compensate for the relatively short length of this build (it's a lot shorter than a BN3E) I was therefore concerned about the NC being jolted off prematurely at apogee. Some initial calculations suggested the M2 screws I've used on other, lighter rockets would not be enough. Bigger screws needed bigger ejection charges.
3) *This is really important*: Whatever the calculations suggest, the only way to be sure is to ground test, then ground test more, using exactly the same grade and type of powder you intend to use in the flight. There are always variables from rocket to rocket. So use the calculation as an indicator of a 'start point' to begin your ground testing, not as a definitive.
Maybe someone who has built a BN3E stock can chip in here as to whether shear pins are necessary for the booster section (...?) - a snug fit between the Av coupler and the airframe might be sufficient, I don't know...
Sorry I didn’t reply sooner. Here is what I meant by Z-clip retention.
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 stuff
Rocketpoxy isn’t thin, it’s more of a paste. Typical “quality” structural thin epoxy systems include WestSystems, US Composites, System Three general purpose etc.
Thicker yet still not paste like would be Aeropoxy 6209 and System Three T88
Thanks. 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
that is a fine system
note that i was not saying that you should not use RocketPoxy for your build, just that RockeyPoxy is not a "this epoxy system."
so long as you pay close attention to surface prep and mix your RocketPoxy correctly it will serve you very well. we on TRF tend to make a much bigger deal about glue than is necessary. in all reality, with proper prep, BSI 15min would be more than sufficient to keep a Loc kit together for 97.81% of the flight profiles it will see. yes, to include a cert 3 M flight
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 GREAT news is that ANY epoxy will work with Loc products....yep, I said it! Wood glue works too!
Have used West System, US Composites, Bob Smith 5, 15, 20, 30 mins, Rocketpoxy, Aeropoxy, Pacer (Zap), JB Weld, Proline, etc. They all work!
Personal preference is indeed a system. IE: a base epoxy with low viscosity that can be used for laminating and really soaks in (as you indicate), but can be modified to preference using fillers. My personal favorite resin is West. Fave fillers include colloidal silica, milled fiber, 404 HD filler, fairing blends (typically include phenolic microballons), and so on.
When it comes to epoxies, there is no right or wrong answer for sport flying, only preferences. Pick one or two to try out, and give that Big Nuke a build! Got one to finish up here, myself!
Yep! I’m on the same page with you now! My Loc kit came with those z clips
Use 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.
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.
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 it
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