[VACList] Fwd: RE: Question about aluminum

[John Leggett <pklhead2@xxxxxxxxx>]

Hi folks.
While RJ has previously answered the question about
recycling aircraft aluminum, I also received this
response from an old college roommate working at
Boeing and thought the VAC would find it interesting
and educational.

John Leggett
1968 Safari
WBCCI 1154

--- "Rick" <xxx@boeing.com> wrote:
> From: "Rick" <xxx@boeing.com>
> Subject: RE: Question about aluminum
> Date: Mon, 25 Nov 2002 06:39:49 -0800
> 
> Hi John - 
> 
> The answer to the 747 aluminum alloy and potential use on Airstreams is a
> bit more complicated than one unfamiliar with aircraft design may think, but
> here goes.  Most of the fuselage panels on aircraft are made from 2024 clad
> material.  The cladding, as you probably know is 1100 alloy, basically pure
> aluminum, and is there not for strength but for corrosion protection.  This
> is also what allows the mirror polished surface which Airstream people like
> so much and that we who build the aircraft hate so much due to the potential
> for dings during the long path of assembly.  The cladding is a mechanical
> bond with the 2024 alloy and it is produced by sandwiching a slab of 2024
> between two slabs of 1100 and rolling, and rolling, and rolling.  The
> average skin thickness of our 747 fuselage is .063 inch.  As a comparison,
> the average skin thickness of our narrow body aircraft, (727, 737, 757) is
> about .050. inch.  The crown skin of the 747 is a different story since it
> is a 7000 series alloy and I would speculate that it is 7075 alloy in that
> older airframe.  The crown skin is quite thick since it is a compression
> loaded component and probably wouldn't be of interest to you folks.  The
> window belt area in also an extremely thick structure so loads can be
> transfered around the windows.  (Designers hate windows!)
> 
> I would foresee several problems using existing aircraft skins for trailer
> applications.  First is the thickness.  Our skins are stretch formed for
> contour but them chem milled to take away as much weight as possible.  This
> makes the interior of the skin very "sculptured". The OML is masked and the
> IML is progressively masked in the chem milling process for the transition
> areas between thicker and thinner. There tends to be built up areas at each
> frame.  Ribs, by the way, are in the wing structure and that design really
> gets complicated as far as use of different alloys, thicknesses, etc..  
> 
> Another problem I see is the high quantity of fasteners, mostly rivets, in
> an existing skin panel.  Since an airplane is really just a bunch of rivets
> flying in formation, they pose another interesting issue.  The rivets are
> easy to drill out, not that we ever make an incorrect installation and have
> to replace any, but I would recommend not trying to drill out the titanium
> bolts.  Using a split point drill for easy centering and a drill diameter
> equivalent to the rivet shank diameter, the rivet heads are easy to drill
> off and the rivet then pops right out.  The issue is that since the rivet is
> most likely a flush head design, the hole needed to clean up the countersink
> and install a protruding head fastener will be rather large and probably
> won't match the other rivets in the trailer.  As for the titanium bolts, the
> easiest way for removal is to cut the collar off and punch the bolt out from
> the inside.  Many bolts aren't threaded, they are grooved, so don't go batty
> trying to unthread something that isn't treaded.  The older aircraft,
> however, did use more threaded fasteners than grooved fasteners.  The
> grooved bolts (lockbolts) are faster for us to install and therefore save
> money.
> 
> I would also suggest avoiding trying to salvage any of the belly skins.
> That tends to be an area with corrosion problems and can get rather ugly
> depending who owned the aircraft and what was in the cargo hold.  A cargo
> hold full of goats is not uncommon.  You can envision the rest!
> 
> Stripping the paint without damaging the cladding is my final area of
> concern.  Since the cladding is 10% of the skin thickness, an .063 skin
> obviously only has .006 inch of cladding on a side.  That doesn't leave much
> room for scratch repair.  Also, the cladding is easy to move around with
> power buffing and it is easy to buff right down to the base alloy material.
> While the base alloy can be buffed to a high polish, it will never match the
> mirror finish obtainable with the 2024 clad.  You may already know about
> this and the darker spots that appear with excessive buffing.
> 
> So much for the short answer so pass it on as you see fit and finally - GOOD LUCK!!!!!
> 
> Rick