Nose Cone Weight

I'm building a couple of squat clusters with full length BT-80 body tubes and PNC80B nose cones. One has a 3x18 motor mount and 3 large fins and the other has a 2x24 motor mount and 4 large fins. Rocksim tells me they are very unstable, so I'll have to add at least 1.5 oz of weight to the nose cones. I'm considering playing it safe and adding 2 oz to each.

I've thought of adding clay and tamping it down into the tip of the nose cones, but what happens when it dries? Will it continue to adhere to the plastic? Will standard modeling clay be OK?

Another option I've thought of is pouring some Daisy BB's into the nose cones and injecting some expanding foam. I've read that epoxy could soften the plastic while it's curing, so foam sounds like a better idea to me.

How much weight will the foam add if I fill the nose cones? I can subtract that from the weight of the BB's. Also, if I add too much foam, can it tear open the nose cone or will it just push its way out the small hole at the base?

Easiest way i've found to ensure the Noseweight stays where it's supposted to and NOT melt Styrene nosecones is do use a Water bath or even Ice water bath while installing Shot and Epoxy noseweight.

First it is important to use a round file or some other scarping device to rough up the inside of the Plastic NC regardless of Noseweight material involved.

I ususally tape a couple Kevlar loops or drill 1/8" hole in the shoulder to allow a piece of old launch rod to be used to suspend the NC in the bowl of water after the noseweight and epoxy have been added. Either way I've not had any problem adding whatever amount of weight and epoxy was needed to the largest thin wall PNC-80K Nosecones without distortion to the NC. Leave the cone in the water bath over night to be sure everything is completely cured.

Hope this helps

Ps: Same method works very well on PMC model nose pieces and other parts where epoxy or CA filling become desireable.

Thanks John. I imagine that slow cure epoxy would keep the heat down?

Tronman said:

Thanks John. I imagine that slow cure epoxy would keep the heat down?

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I haven't seen any appreciable difference.

I generally use Devcon 5 miniute or 30minute 2-ton epoxy for these operations.
I've also used medium CA which can ruin styrene plastic if allow two stay in contact to long without cooling. I don't recomment it's use this way but sometimes when that's all you have handy

It is important to remember to rough up the inside surface well before trying to stick anything to the interior surface of styrene plastic Nosecones.

If you can't or don't want to bother with roughing up the interior of the NC, *and* there is an appreciable shoulder around the access hole, you can use expanding foam to lock the shot/epoxy mixture in place.

Some caveats:

1. The water bath is still a good idea, as the foam does generate heat while curing
2. It is better to pour several layers of foam than to try to fill the entire NC at once
3. The fill hole needs to be large enough to ease the pressure during your final pour, I've cracked smaller NCs by trying to use a little tiny fill hole for 2-part foam

If you don't want to fill the NC with foam, one option is to use 3 1/2" to 3/4" drywall screws. Screw them into the NC a little bit forward of where you anticipate the shot/epoxy mass to end up, with the head and a bit of the shaft sticking out. Once the epoxy is poured and cured, cut the heads off with a hacksaw or dremel, then grind the shaft down to just below the surface of the NC. Fill in the divots with putty, then sand, prime and paint.

G.D.

I've done this with a bunch of plastic NC's and never has the weight broken free yet. 1st take a hole saw and drill like a .5" to .75" hole in the NC's shoulder, Then rinse the inside out with acetone or something similar.

Depending on the size of the NC drill a series of small holes around the tip to about 1-1.5" down the NC, With the NC is tip down drill the holes on an angle, Cover the holes with tape, Mix your epoxy and add your weight to the epoxy (I use BB's) Pour the mixture in the NC, The epoxy will fill the holes on the angle creating a type of barb when right side up.

Ive done this with up to like 3lbs of nose weight and it has never broken free. Once you pull the tape off the epoxy will be nice and smooth and level with the exterior of the NC.

PS I've never used the cold water bath and never had a problem but I also used a slow cure epoxy, If you use the water just put the NC in a plastic bag 1st so the tape stays on.

A couple of things:

The first is that the further toward the tip of the nose, the more efficient it is at moving the CG. That means you do not to use as much.

The second is that the more dense the material is per given volume, the more efficient it is at moving the CG. The most cost effective material is tungsten. Sometimes you can find tungsten weights at your LHS, near Pinewood Derby building material.

Greg

Gorilla Glue (a polyurathane) will also work very well ,and does not generate heat (exothermic reaction)

Just pour in your weight (lead shot or clay) put in a few drop of water or pre-moisten you balast ,then pour in the glue.It cures with moisture and will foam up a bit.

Done and done !!

Works on styrene or poly plastic cones.

HTH

Paul T

The small hole in the end of the nose cone, I put a screw into it and it works for me...

sodmeister said:

Gorilla Glue (a polyurathane) will also work very well ,and does not generate heat (exothermic reaction)

Just pour in your weight (lead shot or clay) put in a few drop of water or pre-moisten you balast ,then pour in the glue.It cures with moisture and will foam up a bit.

Done and done !!

Works on styrene or poly plastic cones.

HTH

Paul T

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+1
I do this all the time.

I honestly never thought of Gorilla glue, but I've used it lots to repair my Super Cub RC airplane. Awesome tip.

sodmeister's idea to try gorilla glue is a good one, that stuff sticks to EVERYTHING and I am sure it would do a good job holding any loose ballast into the tip of the NC

One more idea, and this is one that makes the ballast removeable in case you want to re-use the NC later with another design (that doesn't need all the ballast); make a hole through the base of the NC big enough for a length of BT5 or BT20 to pass through (snugly), put a plug into one end of the selected BT and slide that end through the hole into the tip of the NC, trim off most of the rest of the tube (just leave enough to keep the BT contained in the hole). Then you can fill the tube with ballast and pour in epoxy or GG to make an 'aft' plug to contain the ballast. When you secure the BT in the hole with a wrap of tape it can still be removed later.