From: AFE12@aol.com
Message-ID: <9a.f0258fd.279c9c69@aol.com>
Date: Sun, 21 Jan 2001 15:11:21 EST
Subject: Weight savings, a matter of scale
To: lancair.list@olsusa.com
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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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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