To Foam or not to Foam...That is the question.

rocket sok
Onebadhawk
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
M

Maxter

Well-Known Member
Joined
Jan 13, 2015
Messages
118
Reaction score
8
I'm building a Loc Big Nuke, 54mm Motor.(not the 3E version). However, it will be dual deploy. So, do I foam the fin can or not? How about the nose cone? It will have a GPS tracker bay. Thoughts please.
 
Maxter said:
I'm building a Loc Big Nuke, 54mm Motor.(not the 3E version). However, it will be dual deploy. So, do I foam the fin can or not? How about the nose cone? It will have a GPS tracker bay. Thoughts please.
Click to expand...

No foam necessary. Build with proper fillets or fin pockets, and it will weigh less and be plenty strong for nearly every motor currently made in 54mm (probably even the 54mm M I hear Loki is playing with).
 
I can only speak for myself, but foaming is how I am doing all of my fin cans these days. Just finished the fin can on a new scratch build, and foam is the only thing holding the fins in place. https://www.rocketryforum.com/showthread.php?132158-Whitetip-a-38mm-scratch-build Love the stuff, can't say enough good about it! No alignment worries, no drooping fins, no internal fillets. Just assemble, mix, pour, wait, clean up.

Not sure about the NC - are you concerned about deformation during flight? Or attaching your tracker bay? I've used foam to secure nose weight and a U-bolt in a NC for head-end deployment. Again, love the stuff!
 
I'd love to see destructive testing on foam vs internal fillets with external fillets.

My bet is the foam lets go A LOT sooner.
 
DizWolf said:
I'd love to see destructive testing on foam vs internal fillets with external fillets.

My bet is the foam lets go A LOT sooner.
Click to expand...

I would like to see that tested as well, -especially- on the ones that had been done many years ago. I would imagine the foam would get brittle after being heat cycled so many times...?

I'd imagine CJ (Blackjack) may jump in on this thread, I'm pretty sure he's at least an occasional 'foamer' lol
 
DizWolf said:
I'd love to see destructive testing on foam vs internal fillets with external fillets.

My bet is the foam lets go A LOT sooner.
Click to expand...

Diz,
On my Yank Iris 4" rocket, I foamed the fincan and only external fillets. It's had some pretty hard landings and hasn't popped a fin yet... So far...
I only did it because I was in a hurry to finish it and thought I'd give it a try. Now on a LOC kit, if the fin tabs don't go all the way to the mmt, I'm not sure foam would be much help. Or do they all go to the mmt now? I know my IROC didn't and that one fellow posting on his Mini Mag didn't have full tabs.

Adrian
 
Last edited:
all ya gonna do is add weight and slow you down. Plus foaming can change CP/CG relationships.
 
I asked a similar question not too long ago of my club. Response was unanimous amongst all the members who had gone through the foam fad: Foam is great for a hotel build that you're going to fly tomorrow with a single use that you might or might not get back, but has no place in something you want to keep for a while, and is heavy as a boat anchor in all the wrong area of the rocket.

They pointed out that foam does not age well, and usually gives way without warning, especially when older and pushed hard. The one rocket that I've seen give way was foam and cardboard with tip to tip fiberglass and was quite old, had flown previously routinely on Ms, and gave way on an M and catastrophically re-kitted itself at about 700ft AGL. Post mortem of the wreckage by club members indicated that the foam was brittle and had obviously come cleanly off of the surfaces in most areas.

Since I'm a BAR, I've deferred to their experience and failures and went with epoxy and rocketpoxy fillets.

YMMV
 
Last edited:
I think foaming is highly overrated. The resulting foam isnt very strong and it has a tendency to crumble. I think strong internal fillets are better and lighter.
 
The last time I foamed anything I was trying to add moderate weight and do a non-structural buildup in a nosecone so I could fit a bulkhead. Worked well but was there just to be a spacer. Structural integrity thanks to an all thread....
 
cbrarick said:
The last time I foamed anything I was trying to add moderate weight and do a non-structural buildup in a nosecone so I could fit a bulkhead. Worked well but was there just to be a spacer. Structural integrity thanks to an all thread....
Click to expand...

In a nosecone it's another story. Good place for weight, and adds some support for plastic cones....but it's not being used as an adhesive really here. Totally different use I believe.
 
Absolutely correct. But it is the best application.

Having said that I do have some "foam and fly" mini rockets, but we're talking about reinforcing CA with foam on a rocket that only flys on Fs and Gs.
 
I built the big nuke kit with out foam.. due to a bad motor delay setting, i sort of crashed the booster tube.

everything else held together just fine.

I guess it's up to you, if you wants to add weight to the nose or not.
internal and external fillets work good for the flying I did with it.
 
cbrarick said:
Having said that I do have some "foam and fly" mini rockets, but we're talking about reinforcing CA with foam on a rocket that only flys on Fs and Gs.
Click to expand...

I want use cbarick's point above as a segue into some math and a tool you can use to decide whether "To Foam or Not to Foam?"

Yes, you are definitely adding weight with foam if you just build the rocket the way you normally do and add foam on top of it. BUT to cbarick's comment above, if you use foam to substitute for internal fillets (certain applications work well for this like the mini-kits from Wildman that I believe he is referencing above utilizing the foam & fly method introduced by Crazy Jim a way's back), then the application may be perfectly acceptable. Personally I would still use some sort of adhesive on the root edge, then you can decide the tradeoff for the internal fillets based on the size/volume and resultant weight of the fillets versus the volume of the airframe cavities you are filling. The attached spreadsheet is your tool to do just that!

I entered data for a typical 4" dia. rocket with a 54mm motor mount and 6" TTW root edges (you want to enter the TTW length and the spreadsheet assumes you have CR's on each end). For those parameters, internal fillets using RocketPoxy are more than 2.5 times heavier than foam in the same application. In fact, you have to go to a 6" dia. airframe before the foam solution would be heavier (indicated by a red "NO" as your answer in the spreadsheet). As for comments on the foam's durability, keep in mind that the foam has to pass government regulations for gas/oil/water intrusion and degradation and this stuff is used for years by the Coast Guard and Navy (think repeated shock/impacts in boat hulls - 33 CFR 183.114)--I think it will stand up to most of our applications.

Disclaimer: Although the tool calculates weight impact of attachment options and provides a ballpark on when to consider use of foam, there are many other factors involved in a rocket design such as flutter propensity, velocity of flight, fin shape/exposure upon landing, etc. In short, use common sense.

View attachment To Foam or Not to Foam.xlsx
 
Last edited:
dixontj93060 said:
I want use cbarick's point above as a segue into some math and a tool you can use to decide whether "To Foam or Not to Foam?"

Yes, you are definitely adding weight with foam if you just build the rocket the way you normally do and add foam on top of it. BUT to cbarick's comment above, if you use foam to substitute for internal fillets (certain applications work well for this like the mini-kits from Wildman that I believe he is referencing above utilizing the foam & fly method introduced by Crazy Jim a way's back), then the application may be perfectly acceptable. Personally I would still use some sort of adhesive on the root edge, then you can decide the tradeoff for the internal fillets based on the size/volume and resultant weight of the fillets versus the volume of the airframe cavities you are filling. The attached spreadsheet is your tool to do just that!

I entered data for a typical 4" dia. rocket with a 54mm motor mount and 6" TTW root edges (you want to enter the TTW length and the spreadsheet assumes you have CR's on each end). For those parameters, internal fillets using RocketPoxy are more than 2.5 times heavier than foam in the same application. In fact, you have to go to a 6" dia. airframe before the foam solution would be heavier (indicated by a red "NO" as your answer in the spreadsheet). As for comments on the foam's durability, keep in mind that the foam has to pass government regulations for gas/oil/water intrusion and degradation and this stuff is used for years by the Coast Guard and Navy (think repeated shock/impacts in boat hulls - 33 CFR 183.114)--I think it will stand up to most of our applications.
Click to expand...

Right on, dixontj9360. This is the absolute correct approach. Calculations needed. Foam vs. internal fillets depends on the volume and density of each.

Foaming a Loc Mini Magg? Probably not a good idea. Foaming a Loc Vulcanite? Probably a very good idea and a lot easier than trying to spread internal fillets.
 
Foam is a tool just like any other.
Used correctly it has great value. You just don't start pouring it everywhere to save time, or it will bite you.

Speed builds always used 3 holes in fins & WIRE-TIED through holes & around motor mount before foaming. When done this way, you will NOT ever get them out, unless experiencing a " nuk-le-are " event....lol.he
I broke fin in Gizmo way back....sledge hammer beating on fin with rocket in welder's vise trying to remove, flat-bar, chisels, hammer, nothing could knock the remaining fins loose. Was trying to salvage the other fins, motor mount & CR's. No joy, ended up using saws-all.

Still when flying near water I have several with foam in NC, to make them float [with tracker inside]. They have proven their worth at Bong 3 times. rest of rocket was sunk. Nc & tracker just happily bobbing on the surface, so I could find them.
I like to fill about 1/3 of molded NC's with the foam to stiffen them up, so hard landings don't crack the paint or surface.

I now use packing peanuts to lighten the mix. pour some foam in throw in handful of P-nuts add more foam on top. In a large NC [6in & above] it saves a great deal of weight.

Rockets that have difficulty in getting to some area of internal fillets involving tail-cones.....V-2, Talon, Eagle-Claw etc I will use just enough foam to cover area I could not get epoxy in.

It is really great in the mini's as we even have it in the instructions & I use a small amount to attach shock cords in small NC tips.
You still must epoxy the root in place, or foam can push the fin root sideways, or lift it during the expansion phase. [that's always fun]
It makes building mini's so easy & quick. There have been several contests building mini's with foam,and most are still in one piece, flying to my knowledge.
I never just fill up a fin can with foam in a normal build.[except mini's & amount is so small, weight no issue.]
I still think foam has it's place, for the right use, not to exclude using epoxy or wood glue.
 
Last edited:
blackjack2564 said:
Foam is a tool just like any other.
Used correctly it has great value. You just don't start pouring it everywhere to save time, or it will bite you.

Speed builds always used 3 holes in fins & WIRE-TIED through holes & around motor mount before foaming. When done this way, you will NOT ever get them out, unless experiencing a " nuk-le-are " event....lol.he
I broke fin in Gizmo way back....sledge hammer beating on fin with rocket in welder's vise trying to remove, flat-bar, chisels, hammer, nothing could knock the remaining fins loose. Was trying to salvage the other fins, motor mount & CR's. No joy, ended up using saws-all.

Still when flying near water I have several with foam in NC, to make them float [with tracker inside]. They have proven their worth at Bong 3 times. rest of rocket was sunk. Nc & tracker just happily bobbing on the surface, so I could find them.
I like to fill about 1/3 of molded NC's with the foam to stiffen them up, so hard landings don't crack the paint or surface.

I now use packing peanuts to lighten the mix. pour some foam in throw in handful of P-nuts add more foam on top. In a large NC [6in & above] it saves a great deal of weight.

Rockets that have difficulty in getting to some area of internal fillets involving tail-cones.....V-2, Talon, Eagle-Claw etc I will use just enough foam to cover area I could not get epoxy in.

It is really great in the mini's as we even have it in the instructions & I use a small amount to attach shock cords in small NC tips.
You still must epoxy the root in place, or foam can push the fin root sideways, or lift it during the expansion phase. [that's always fun]
It makes building mini's so easy & quick. There have been several contests building mini's with foam,and most are still in one piece, flying to my knowledge.
I never just fill up a fin can with foam in a normal build.[except mini's & amount is so small, weight no issue.]
I still think foam has it's place, for the right use, not to exclude using epoxy or wood glue.
Click to expand...


Thank you for post on Floating nose cone , here in the land of Lake Icky we fly with extra long shock cords just in case

My son lost a 3" darkstar within a hr
My darkstar jr spent close to 3 weeks in and was recovered , long shock cord didn't sink the nc
 
blackjack2564 said:
F
Still when flying near water I have several with foam in NC, to make them float [with tracker inside]. They have proven their worth at Bong 3 times. rest of rocket was sunk. Nc & tracker just happily bobbing on the surface, so I could find them.
I like to fill about 1/3 of molded NC's with the foam to stiffen them up, so hard landings don't crack the paint or surface.

I now use packing peanuts to lighten the mix. pour some foam in throw in handful of P-nuts add more foam on top. In a large NC [6in & above] it saves a great deal of weight.
Click to expand...

Another set of handy tips from CJ. Thanks!
 
michigander said:
Thank you for post on Floating nose cone , here in the land of Lake Icky we fly with extra long shock cords just in case

My son lost a 3" darkstar within a hr
My darkstar jr spent close to 3 weeks in and was recovered , long shock cord didn't sink the nc
Click to expand...

Heh, first flight of my 3" Darkstar took a swim in an irrigation ditch. Our tree climber happened to be out there with Gary T and they pulled it out of the toxic mess. Said it looked like a beaver chasing a jelly fish as it floated by....
 
dixontj93060 said:
I leave that to the reader. :)

Well, OK, I could figure that out too, but no time tonight...
Click to expand...

I saw your underreporting and pulled mine, but you quoted me, drat.

I think this is one we're going to have to test by ripping some fins out.
 
DizWolf said:
Heh, first flight of my 3" Darkstar took a swim in an irrigation ditch. Our tree climber happened to be out there with Gary T and they pulled it out of the toxic mess. Said it looked like a beaver chasing a jelly fish as it floated by....
Click to expand...

LOL

Glad you got it back.
 
I have never foamed anything, so if the following is 'common knowledge', I was not aware of it :/

I will verify my source later, but I recently read that adding a few -drips- of water to the foam mix will make it expand more, and I presumed, not as dense.

They showed the difference between 1 to 5 drips in small cups, and it was a pretty substantial difference in the increase of volume.

Maybe an option for those that do NC foaming?
 
McKailas Dad said:
I have never foamed anything, so if the following is 'common knowledge', I was not aware of it :/

I will verify my source later, but I recently read that adding a few -drips- of water to the foam mix will make it expand more, and I presumed, not as dense.

They showed the difference between 1 to 5 drips in small cups, and it was a pretty substantial difference in the increase of volume.

Maybe an option for those that do NC foaming?
Click to expand...

For the PML foam, that is the case. Not sure if that works for Giant Leap foam (I'd test it, but I gave my cans to my buddy)...
For my Yank IRIS that I referenced before, I used the full 5 drops to get the most expansion/reduced weight in the fin can.

Adrian
 
For US Composites foam you purchase the individual densities from 2 lb/cu-ft @ 40 psi to 16 lbs/cu-ft @ 380 psi.
 

Similar threads

P
LOC 4" Phoenix Payload Bay Options
Replies
18
Views
991
b.wieting
b.wieting
cerving
Ballast
2
Replies
34
Views
2K
cerving
cerving
Porkchap
Customized Madcow 2.6" *Super Pike XL-54* maiden flight photos and videos
Replies
15
Views
600
Porkchap
Porkchap
burritoman1
How to add nosecone weight?
2
Replies
34
Views
2K
BABAR
B
jcampb81
Run Away To Mars - Post Flight Report
Replies
4
Views
507
Hobie1dog
Hobie1dog

Latest posts

Back
Top