Elevator Counterweight

I made the decision ages ago to make the elevator counterweights using tungsten instead of lead.  And I have been putting off making them.  The plan is to encase tungsten shot in epoxy.

I first tried to make the mold from wood.  Could not get the shape I wanted;  Abandoned that idea.

I want the weight as far forward as I can possibly make it, so the front needs to be curved.

FYI - tungsten is 1.7 times heavier than lead.  My theory is I would need less of it, could get the weight farther forward.  Overall lighter.

Weighted the arm of the elevator after paint.  I need 7.2 lbs of tungsten.

Mold version 2 is aluminum clecoed together.  I made it 3" tall - which will fit under the elevator tip fairing.  With tungsten only in the mold (as a test) it needs to be 2".

I applied packing tape to the inside of the mold (sides, bottom and back).  Waxed all the clecos.  Then a bead of clear silicone around the bottom.  Then a thin layer of epoxy on the inside of the mold, and let it dry.  My theory is this will seal up the mold so when the tungsten shot and epoxy go in it will not leak.

At this point I'm really wishing I had just made it out of lead.  Alas no... 

3.5 lbs is 1.59 KG.  The mold weights 410 grams, so the two together need to be 2 KG.  i overshot the mark slightly.

No leaks from the mold.

I added 3/4" of resin, then tungsten (there is actually a lead bullet in the bottom a friend gave me), and repeated until I got to the weight.  A bit more resin on top so everything is fully encased.

I am worried about tungsten falling out, which is why I put a thin coat of epoxy on everything first.  I may wrap the whole unit in fiberglass to ensure that doesnt happen.  Will see what it looks like when it comes out of the mold.

Bolts are all waxed.  Packing tape over the heads to stop leaks and keep them straight.  

Used West Systems.  Fast hardener on the skim coat, and slow on the main pour.  That should reduce any cracking.

Now the 24 hour wait...

Well it worked, and it fits under the fairing.

Now I need to make a 2nd one... already started.

2nd one done and test fit... slightly too long up front and will interfere with the elevator tip fairing.  So grinding in process.  Will have to fiberglass it back up.  Not a big deal.

First one drilled for the other two holes and dimpled.  All good.

Fiberglassed the second one up... not dry yet.  Cold in the hangar (well, relatively).

First one attached with bracket / captive fasteners.  My theory is (a) adds a bit of weight, and (b) you can check the bolts without taking the fairing off.

And the fairing fits too!

Am going to have to add some lead to the right side.  Just not heavy enough.  5 pieces of lead cut.  Will be darn close.

Cut, fit, fairings installed.  Just need to tighten down the screws.  Almost perfect balance (elevator pushrod disconnected in the pic... just hanging from the weights).

Done.  One list thing on the list.