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For reference, we are never allowed to have a leading edge exposed
counterweight (a la Malibu or Venture) on a large aircraft due to icing.
Ditto for squared off counterweights. The squaring off sounds great for the
"in trim" condition to reduce separation drag, however it causes more drag
when not in perfect alignment. Round is better.
As for the counterweight itself, in commercial aircraft we use depleted
uranium which has a density of over 20 g/cc; tungsten is almost 21; lead is
a little over 9. Epoxy is in the low 2's. Tungsten, uranium or any of the
other high density refractory metals are too hard to work for any
homebuilder. However, some of these materials come in forms that we can use.
There are a couple of ways to save on the counterweight required for a given
control surface that I haven't seen talked about here:
1. Use tungsten rod in the lead pour to increase density by 50 to 60%.
Higher density can allow you to move the CG of the counterweight more forward
of the hinge line, which decreases the weight required for balance. TIG
welding electrodes work fine for this. It is expensive.
2. Tungsten grindings or dust mixed with lead can increase the lead pour
density by 30 to 50%. Mixing the dust with epoxy will yield a "micro" that
has about the same density as lead due to the low density of the epoxy.
3. Move the counterweight as far forward as the design allows. In most
cases, this has been directed in the manual and by the original engineers.
However, I have seen many cases where the counterweights had plenty of room
left to go forward and could have a pound or two shaved off for the same
balance.
Eric Ahlstrom
Star Aerospace LLC
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