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It is interesting to hear all of the different items we want to save weight
on in our aircraft.  When I was racing motorcycles and hydroplanes, we used
to calculate bolt stress, then go up a size and drill the center out.  It was
lighter than a solid bolt by grams.  Of course, grams make more of a
difference in a 400 lb. motorcycle than they will in and 2200 lb. aircraft.

We should stick the things that are relevant to the scale of the aircraft.  I
tend to go for the "low hanging fruit" first.

Washers that bear on fiberglass or carbon are there to spread out load on
what is essentially a very low modulus surface (we're not in the fiber axis,
remember?), so even firewall fittings could (in washer compression) use
aluminum washers to better spread the loads to the composite fittings than
steel.  In commercial aircraft, we do this in areas where we have fiberglass,
but not carbon.  Carbon is the most electronegative of all airframe
construction materials.  In any direct contact with aluminum (one of the most
electropositive materials) the aluminum will corrode.  Quickly.

In commercial aerospace, we are not even allowed to use steel in direct
contact with carbon.  Anti corrosive paint, nickel or titanium plating is
required;  cadmium is good, but we are trying to be eco friendly these days.  
Anodizing is effective for only a short period of time;  1 to 10 years
depending on climate and salt exposure.

A far better place to save weight is the literally hundreds of pounds of
adhesives, flox, and resin that gets slathered all over the inside of the
aircraft and the 50+ pounds of filler that goes into that show finish.  I
have spoken to builder assist centers that have taken literally 100 lb. off a
Lancair IV in excess filler.  If you're going for a two tone paint job,
simply painting only one color coat over the primer instead of covering all
areas in a base color and then overcoating in the two tone will save at least
20 pounds.

It would take quite a few aluminum washers to make up what you could do with
a little care and masking in just your finish or a few of your basic bonding
and smoothing tasks.

We will be furnishing a set of wing root fairings and wing tips next year
after our aerodynamic optimization is complete.  They will be lighter than
the stock fairings and tips (in addition to lower drag) because they will not
require large amounts of filler to make a smooth surface finish.  The weight
savings from these fairings alone will probably exceed the weight of all
those washers.  Steel or not. <LOL>

Go for the big stuff first.  It's a big airplane.

Eric Ahlstrom
Star Aerospace LLC

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Please send your photos and drawings to marvkaye@olsusa.com.
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