Filling voids in cluster mounts?

[skyspike1]

When filling voids around motor tubes for clusters inside main airframe,instructions call for mixing tissue w/epoxy. Should I actually mix together,(at what ratio?) or wad tissue in voids 1/2" dwn, then cap with solid epoxy? Rocket is LOC ViperIV instructions are vague at best.

 

[Micromeister]

When filling voids around motor tubes for clusters inside main airframe,instructions call for mixing tissue w/epoxy. Should I actually mix together,(at what ratio?) or wad tissue in voids 1/2" dwn, then cap with solid epoxy? Rocket is LOC ViperIV instructions are vague at best.

Generally it doesn't have to be tissue and epoxy, for years we've used tissue and plain old Elmer's white glue. wrapping paper tissue seems to have a bit better hold together then facial tissue but either will work.
I mostly use Elmers yellow Carpenters glue for ths process these days but epoxy will certainly work it's just a little heavier.

you actually mix the tissue and glue together until you have a mass that has enough body to fill about 1/2 to 3/4" of the length to the openings between the motor tubes. I generally set a riv-nut with screw (extended screw end wrapped with masking tape in the center of 3 and 4 motor cluster with either 10-24 or 1/4-40 round head machine screws to act with a flat washer as motor retainer for the bunch.

Note in the photo below I used yellow tracing onion skin paper with 30minute eposy which gives the hardeded matrial a yellow appearance. So you can see just about any light weight, very thin paper product with glue or epoxy will work to fill the voids. Keep in mind we are just "Plugging the holes" it doesn't have to be all that thick.
Hope this helps.

 

[skyspike1]

Thanx alot! thats about what I was thinking of,(I have plenty of Carpenters Glue) I also thought of mixing "Q-cell" powder(A white,light dust substance mixed W/polyester resin to add volume w/out weight when fixing dings in surfboards.)because I have plenty of it in shop.But I like the tissue paper idea better, I't seems to be a more proven technique. I also noticed your motor retain insert for a 1/4 20 thread bolt and washer to hold all 4. NICE idea! I have some Alum masonry inserts for hurricane shutters with 1/2" long threaded fasteners that have a flat,wide head 1" so no washer needed. I was going to retain motors from ejecting out w/tape wrapped tight,but your bolt technique is perfect, THANKS!

 

[Gillard]

i'll second the use of white glue. i usually use estes wadding and white glue only, used many times not problems yet.

 

[terryg]

I used gorilla glue on my last cluster. It expands as it cures and will fill gaps.

 

[new2hpr]

2-part foam and very quick taping would work as well.

-Ken

 

[Wingnut]

Hey, Micro John-
Out of curiosity, have you ever tried using a nylon screw in that setup? Definitely save a bit of wight over the metal screw, but I wonder if it's burly enough in tensile strength to do the job...
Dave

 

[powderburner]

This tissue/glue thing is an old Estes technique. If you pull up the kit instructions on something like the old Astron Ranger (three BT20 MMTs inside a BT60 airframe tube) there is no mention of centering rings (did they even have such a thing as CRs back then?).

I always thought that most of the purpose of including some tissue was to stiffen the glue, so that it stays put when you pack it into place. (A big plop of glue would simply drain out the end of the MMT.) So, as to the proportion of glue-to-tissue, maybe you should start with a little extra tissue in the mix and if it is too stiff to work with, then start adding more glue a few drops at a time. skyspike1's idea to use "Q-cell" powder (probably microballoons, just like we use to mix with epoxy) would be another good way to go, if combined in a stiff enough mix.

Micromeister has already given you a really good list of ideas and materials. I have also used tissue paper and it works just fine. The only thing I would warn about is the tendency for "white" glue to shrink as it dries, and a big wad of wet tissue/glue could easily cause a wide zone of shrinkage. Use of carpenters (yellow or brown) glues will reduce this effect. The gorilla glue idea from terryg sounds like a really good one---I don't think GG does the same "shrinking" act as it dries.

 

[Micromeister]

Hey, Micro John-
Out of curiosity, have you ever tried using a nylon screw in that setup? Definitely save a bit of wight over the metal screw, but I wonder if it's burly enough in tensile strength to do the job...
Dave

Nope! I'd be very leary of using nylon screws in such a Harsh and HEATED environment. Looking at the abuse the Stainless Truss head machine screw & washer gets after flight makes me suspect even if the thread tensile strength is high enough to hold a nylon Threaded body the HEAD might deform enough to allow motor kickout(s) at ejection.