Ballast Boxes for FPV

Often, especially when flying FPV, there's a tendency to have a horizontal weight imbalance on an airplane. VTXs and control RXs tend to work better out on the wings, and with tractor prop aircraft the wing is often the only place for a camera that won't have a frame full of propeller. All this can make it hard to get the center of gravity centered along the fuselage of the craft.

There are ways to mitigate this issue, of course--a small amount of asymmetry can be cured with a few clicks of aileron trim. Too much of this, however, decreases both efficiency and roll authority, and it can only go so far. My friends and I have also been known to employ more primitive methods--namely, taping a rock to the wing.

Believe it or not, the rock has a few drawbacks--a draggy shape, imprecise weight, and general inelegance among them. But there's a better way--a way I've used to great effect with several aircraft.

It starts with two boxes--I use some little polyeurethane boxes I sourced from Tap Plasics, each of which is 1¼" (32mm) on each side and ¾" (19mm) deep. They were less than a buck each.

This is large enough to hold about 7.5oz (200g) of lead. That gives us plenty of weight to work with, but there's no reason to carry more weight than necessary. To that end, we should put them as far out on the wingtips as possible to maximize our moment of force.

My SkyHunter's wings are nice and thick, even at the tips, but for other planes you want to make sure that you have enough meat to hold the box.

I took measurements to ensure that the two wings' boxes were placed symmetrically, then traced the outline of each box with an ink pen.

I've got a rotary tool (Dremel) with a cutting bit and collar that lets me adjust the depth, but this could also be done with a hobby or utility knife; just use a permanent marker or piece of tape to mark the balde so you won't cut deeper than your box is tall.

First, cut the outline you'd marked on the wing. Doing this first will give you a nice clean edge you won't accidentally mess up later.

Next, clear out the inside. If you're using a hobby knife, cut a grid pattern into the foam to be removed and use tweezers, hemostats or needle-nosed pliers to pluck out the resulting columns of foam. With my cutting bit, it's a much simpler task.

Finally, glue the box in. I would use a glue that will cure with a consistency that's less brittle and more rubbery, since vibrations could be an issue this far out on the wing. Hot glue would work fine, as would several other types.

Repeat on the other side and you're done! a few little fishing weights in the proper box will balance out virtually any weight skewing your plane to one side or the other. Or, if you find yourself in the field without such weights, any dense objects will do--small stones (or even sand), nuts and bolts, etc.

Since the moment of force is so far out, extremely dense weights aren't necessarily required, though they're nice to have.

Happy flying!