Jet Pack Weight. -- AKA - Boba\'s Hernia!!! PIC!!!

As I near the completion of my MB "old school" JP, I decided to add some "Great Stuff" (expanding foam) to the insides. Is it just me, or does this junk add THAT much extra weight? I was thinking about trimming some of it out.

Also, has anybody tred heating up the back plate to contour it to the curved shape on the JP before attaching it? I figured this would take some of the stress off of the adhesive and make less gaps on the outer seam.

Thanks

I don't know about the foam thing, but you definately need to heat up the back plate and shape it do the open jet pack. It will glue much easier this way. Just bondo the seam it leaves.

I was thinking of 2 part epoxy for the seams. Is Bondo better as far as sealing and sanding?

2 part epoxy is good. I dunno about Bondo as glue.

You used Great Stuff? Did your jet pack explode yet? That stuff is kinda risky to use on vac'd JPs as the expansion of it cannot be controlled. It has a tendency to make JPs look bloated, it not blowing out the seams altogether. It can be used if only very small amounts are added at a time, but I've heard some horror stories from others who've used it. I hope you won't be sharing a similar experience with us as you have spent a long time working on yours. Good luck.

my old one exploded during celebration II

I just got an MB new style JP, this could come in handy..

Seek, got a pic of that

Well, I put the great stuff in last night (8PM) and as of this morning it did expand, but seems ok. I only hope that the expanding is complete and I don't come home to find it all over the place.

Seeker, how did that happen? I thought that once the stuff expands...that's it. Can temperature effect it? If so, I my cut some of it out.

Thanks for the heads up guys.

If the jet pack is sealed up it wont be a problem. but for any chance air gets in there and the stuff is still not completely dried then "BAM"

My pack was wraping and looking all weird from the inner part of the pack. it was like it was morphing or something - very alive and creepy looking.

but after it all dried up and sealed the jet pack shape went back to normal on its own.

Seek, how long after you putting the stuff in did it do this?

that was a couple of months later

Well, that settles that. As soon as I get home, I am going to be removing some of the "stuff". Not all, but enough to not have to worry.

Guys, what would I do without your help!

Thanks

Jedi-Bob...
Great stuff is not a problem if done following the directions of applying in large areas. Put it in a little at a time and sprinkle water on it as this makes it cure faster..
If it is applied all at once, then the middle will not cure and you can have problems as Seeker mentioned.

Also, If it was just sprayed in all at once and there was no "escape" holes drilled in back the areas of the tank that were filled to allow air to get in and also let the foam expand out of the holes, then you would have a problem with the tanks.
Thus the bloated looking JP's...

If you filled the back side of the main body cavity, without the back plate and it has expanded fulley, you should have no problems and no need to remove any of it.

You just gotta becarefull of the stuff....

Lynn

Jedi-Bob wrote:
Is it just me, or does this junk add THAT much extra weight? I was thinking about trimming some of it out.

It shouldn't add that much weight, a 1lb- 2 maybe? Hardley enough to make any difference in the scheme of things.
My MB pack with PVC frame and fully foam filled only weighed in at 14 lbs, my fg RA only weighs in at 15lbs.
Lynn

My JP is completely opened right now. I ripped out some of the stuff and it is now 2 days that it has been in there. As far as the foam in the middle, if I made holes into the foam, do you think that this would help assure that the "inner foam" has fully cured?
I will try and post a pic tonight.

Thanks everyone.

Good idea jedi-bob. Drilling a hole in there.

I followed these exact same directions ( http://www.jedi-academy.com/fett_jet pack1.html ) with my 1999 MB jet pack. I filled it with Great Stuff per those directions and haven't had it break the seams of any of the parts 4 years later.

I don't know why some people's packs will break seams out and some won't because of the Great Stuff, but I've heard it before too.

I just bought some of that great stuff and its minimal expanding (yellow can) Im mounting my rocket today, hopefully there wont be any explosions

DPR

Does this look like too much foam???

I think you'd be safe like that, Bob. I think the expansion problem mainly occurs when people add it to their JPs after they've sealed them up, thus ending up with air pockets in the corners.

JB, that's good enough Great Stuff. Try to remove just a little bit from the areas close to the edges facing the backplate so in the future they don't expand and reach it to make it explode.

I see that you've assembled your JP the same way as I did. Is your JP vacuuformed or Fiberglass? Mine is fiberglass, and I don't see a problem with the inside stuff. I remember that either MB or RA have in the instructions to DO NOT use the "Great Stuff" on their JPacks. I think that If you use just a little or average (as you did), I see no problems at all.

About the backplate, I think that the two-part epoxy works better than anything else, but you still need probably the Bondo, Epoxy Putty, or Bondo Glazing Putty to seal the gaps around.

Robert