Lead Wool vs Lead Shot

[robcaldwell]

Just a post build update...

I was moving my 4 Place B Model last week. I noticed a "swooshing" sound somewhere in the left wing. Narrowed it down to the aileron. I quickly realized that the lead shot I used in the balance tube was leaking out. Not sure how this happened. During construction I sealed one end of the tube with a generous amount of epoxy. I poured in the loose lead shot, then sealed the other end with epoxy. I know that some have used a slurry of lead shot and epoxy, but I could not come up with a clean method for doing that.

I removed the aileron and drilled out the epoxy plug on one end, and poured out the remaining shot. Also had to cut open one of the lightening hole and shake out all of the loose shot.

I am refilling the balance tube with lead wool. If I had to do it over again, I would use lead wool in the balance tubes instead of the bird shot.

https://www.mcmaster.com/lead-wool/.

I suppose one of the rivets used to secure the balance tube in the leading edge of the aileron came loose.

[AKKen07]

I used bird shot but melted it and poured it in. Was quite a bit easier than I expected. Safety precautions exercised of course.

[svyolo]

I almost just melted it but in the end I epoxied a 1" long wood plug in the end of the tube, mixed epoxy a few ounces at a time and roughly mixed the epoxy into the lead shot in a cup. When I was done I put another wood plug in the other end.

The plugs aren't in the end of the tube in my case. They are about 3" from either end. I poured both tubes same day so I did both the same.

[Nev]

This is good to know Rob. I've done mine the same way. Knowing this, I'll keep an eye on the rivets during pre-flight.

When I first made the tubes up, after putting epoxy on the top end, I noticed that the lead shot had compressed and was moving about when I shook the tubes. So I got a 12" long drill bit and drilled right down into the shot. Then I mixed more epoxy, warmed it up, then poured it into the tube so it ran down inside quite a way. Now there doesn't seem to be any movement,

[robcaldwell]

As an update....

I am completely redoing the balance tubes in both of my ailerons.

After repacking the faulty left balance tube with lead wool, the weight of the replacement wool did not match the weight of the shot that I removed. The weight of lead wool I used was surprisingly less, by more than a pound. I would have guessed that compressed lead wool would have weighed more than shot as there should be almost no voids. Apparently not. I obviously have a difference in weight on both sides now.

I built my ailerons at the same time and without the ability (because of space) to static mount them to the hinges on the wings for a proper balance test. https://bearhawk.tips/1899. Now that I have a flying airplane I can remove the current balance tubes, reinstall the ailerons to the hinges with the pushrod disconnected, hang weight on the aileron leading edge until I achieve balance... And use that weight to build and install new balance tubes. This should equal everything out and give my controls better feel.

I have ordered new AL balance tubes (https://www.mcmaster.com/catalog/127/3989) and depending on the amount of weight needed will determine if I use a lead shot and epoxy slurry (get it right this time), or continue with lead wool.

[Chewie]

Rob I'm planning to wait as long as possible to fill my balance tubes, riveting them in but not putting in lead shot until the ailerons are 99% covered. Based on what you're doing now with fabric and such do you think this is still a good idea?

[robcaldwell]

That might work. My concerns would be 1). Working inside the hinge pocket trying to pour the shot. 2). The rivet mandrels inside the tube could cause a restriction / blockage. 3). Any stray shot that gets away from you and inside the covered aileron might be difficult to retrieve. I had a few that got trapped between the fabric and AL surfaces. A real mother to try to get out.

I built a jig to hang my ailerons on, simulating the hinges. I am using this to find the exact weight I need for balance and to build the tubes fully weighted before reinserting them.

Mark said he doesn't think anyone else has ever experienced shot escaping from balance tubes. I'm a pioneer!

[gregc]

A little expensive alternative for 6063 aluminum tubing:

https://www.antennapartsoutlet.com/products/unprocessed-aluminum-tubing?variant=37821963665569