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Foam weight

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ActingLikeAKid

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I'm making the leap into fiberglass (Thanks, TopRamen!) and I think I have a project where I can use 2-part polyurethane foam. US Composites has a variety of weights; I'm 99% sure I need the lightest (the 2lb per ft^3) ... right?

http://www.uscomposites.com/foam.html
 

RocketFeller

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I would think so, but don't have any experience with this particular product. PML makes an adjustable density foam that is good stuff, if you want to check out different options.
 

ActingLikeAKid

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I just had a moment of "Hm, maybe not". Did some quick calculations on how much foam I'd need.... and it came back with "2 ml". Maybe I'll stick with internal fillets ;)
 

TopRamen

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There are a couple of types of foam in the materials list in Openrocket, and I've been developing some interesting ways to reinforce foam with lightweight glass cloth, but it's a side project, and until I have flown a model and have the video to prove it, I will not openly discuss the methods, as they would be ridiculed to the point that it would discourage me from making any progress with the research and testing.
If the wacky ideas I'm trying to make work do work, then the proof will just be in the video when I weigh the rocket and then fly it, so any one that would have prevented it from becoming a reality won't have that chance.
I'll just be like, "Hey, look what I did."
This is not entirely a new concept, and I have privately asked for help and advice from folks that are very knowledgeable in the area.
If you want peak performance, then no, this concept I'm working on is not the best way, but if you want a new and more interesting way to make a rocket, and like to try new materials because that's what keeps you interested in the hobby, then yes, it might be fun.

There are thousands of videos on Youtube about how aircraft and boat components are fabricated using foam and composite structures, and I intend to watch each and every single one of them and apply those methods to model rocketry in whatever way I deem enjoyable.
I really don't mind if folks don't like it because it is not the typical way to build. As long as they are enjoying their methods, good for them.
Like I said, rather than face criticism and discouragement, I'll just do it, and if it turns out to not be worth sharing, I might even be able to show why, so others don't have to walk the path I'm currently on.

We're all here to have fun and be safe first and foremost, and if my ideas can meet that criteria when shared with others, I will share them.

In the meantime, since you are L1, the added weight of maybe a foamed fin can on a 4" 38mm 3FNC bird might be worth experimenting with for you, just so you can have some experience with the materials involved.
Maybe make a simple mold for a faceted fin then lightweight glass it?

As long as you're having fun, right?:wink:
 

MikeyDSlagle

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Foam doesn't add a whole lot of weight, but how much is too much depends on the rocket and motor. Say you have 4" rocket with 38MMT, and you want to foam 8 inches of fin can. With 2lb foam you will add around 1.6 oz, unless my math is wrong. On shorter rockets it will make a difference no doubt, but on long super stable birds, it may actually help by bringing the CG rearward a bit.

I use 4lb foam quit a bit. Does it really do any good being in the fin can? No clue. On paper rockets I can see it giving the tube extra strength, but not sure in glass birds. Where I can I always go with at least one set of internal fillets anyway.

I've gotten to where I assemble my fin can outside of the bird and then slide it in, on some birds that is..case by case basis. Helps get good fillets on the fin to MMT connection. I extend my fin slots all the way out the aft end. A piece of coupler aft the rear ring will stiffen it back up. All really depends on the rocket and build techniques.

Mikey D
 
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