Foam it. You don't need internal fillets with foam for this rocket. Doing your external fillets before foaming, however, will ensure the foam doesn't weep out around the fin slot.
(Personally: internal fillets, no foam needed.. glue joints are stronger than foam. I just glued my Super DX3, so far no issues..)
Whereas an epoxy joint can break, foam makes it impossible for the fin to move. There are merits to using foam; however, it is heavier than epoxy, and should not be used if stability is an issue.
Whereas an epoxy joint can break, foam makes it impossible for the fin to move. There are merits to using foam; however, it is heavier than epoxy, and should not be used if stability is an issue.
Nonsense! I have had two rockets with epoxy foam make hard landings under drogue and the fin(s) broke.
“Impossible” is much too strong of a word. Foamed in fins get knocked out and when they do it’s a chore to repair them.
If the fin tab is a large area then foaming a fin can can add rigidity beyond what epoxy fillets alone can accomplish and could even be used instead of internal fillets, but if the fin tabs are small, such as in any rocket where the body tube and the motor mount tube are close in size, epoxy internal fillets are much stronger. Unfortunately those rockets are the ones that are most difficult to apply internal fillets unless you inject them. Also unfortunate is that the rockets which have large fin tabs will gain the most weight from foam unless fin pockets are part of the design.
Foam is pretty good in compression. It’s not so great in tension.
Personally I’ve stopped using foam anywhere other than in some nosecones if I want to add weight or make the nosecone more impact resistant.
Can't argue with any of that. I guess I used "impossible" like "going to the moon is impossible" ... until somebody did. :grin:
[emoji106]
It does seem impossible to return to the moon though…
Steve Shannon
Hey guys, thanks for the feedback. I had in my head foam was the way to go on bigger rockets. I'm ok with not using it and just using fillets. I suppose its like which glue is better, right?
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