January-February 2022 - 31

said. " These substantial cockpit windows are typically
electrically heated. Windows with outer plies of
plastic, as opposed to glass, might have some type of
organic clear coating for abrasion and environmental
protection. "
Passenger cabin windows and helicopter windows
are typically less complex, according to Wright. " In
fact, cabin windows are usually produced from
acrylic or PPG Opticor material. They may or may
not have clear scratch coatings or other types of films,
depending on the aircraft, " he said. " Dimmable windows,
instead, may or may not be an integrated part
of the structural cabin window. In the case of the 787,
the dimmable window resides inboard of the actual
cabin window and is integrated into the aircraft's
interior wall panel. "
Most aircraft window openings have two different
types of transparencies, observes Research Frontiers.
" The outbound transparency is the structural window,
which is typically two stretched acrylic panels.
The most outboard panel is flush with the fuselage
and contacts the outside " , according to Research
Frontiers. " The next transparency in a 'traditional'
aircraft window opening is the panel that the passenger
can touch. This goes by various names including
'scratch pane,' 'scratch lens' or 'dust cover.' This is not
a structural window and is typically polycarbonate. "
Suspended particle device (SPD) tech can be used
in what the industry calls an electronically dimmable
window (EDW), observes Research Frontiers. " An
SPD EDW uses chemically strengthened glass, and
it replaces the polycarbonate scratch lens. An SPD
EDW offers the advantages of electronically controlling
light, glare and heat being transmitted through
the window opening, " says Research Frontiers.
Maintenance Approach
All maintenance performed on an aircraft window
is to be performed in accordance with the applicable
aircraft maintenance manual (AMM) or component
maintenance manual (CMM), points out Wright with
PPG's aerospace division. " Coated windows cannot
normally be polished as this will degrade or damage
the coating. Dimmable elements may be comprised
of very thin glass with a gel inside, " he said. " These
elements are often held in place with clips so the
removal and installation of the panels must be done
with care. Breaking an element is an expensive error. "
Removing and installing dimmable windows
requires a certain degree of care with respect to the
elements themselves, affirmed Wright. " The associated
controller, electrical connections and switches
require checks beyond a pull-down shade, " he said.
" Trouble shooting methods such as voltage checks
might be employed. All such methods are covered
in the applicable AMM/CMM " .
According to Research Frontiers, an SPD EDW
is more robust and durable than a typical scratch
lens. " A polycarbonate lens scratches very easily from
many sources such as a ring on a finger or a zipper on
a coat. Its optical properties also degrade quickly. The
result is that a typical scratch lens requires a great
deal of maintenance and needs to be replaced often, "
says Research Frontiers. " In contrast, an SPD EDW
uses thin/lightweight, scratch-/impact-resistant
chemically strengthened glass. It is scratch-resistant,
and its optical quality does not degrade over time. "
The use of an SPD EDW can eliminate the need for
any other type of window shading system, according
to Research Frontiers. " A typical commercial aircraft
utilizes a thin pull-down shade referred to as a 'knifeblade'
shade, located inboard of the scratch lens and
manually operated by the passenger. The knife-blade
shade assembly consists of many parts within the
window opening plus the fuselage. Some of these
parts move, " says Research Frontiers. " Typical aircraft
shades are well known to be highly maintenanceintensive
in many areas - cleaning, part replacement,
complete assembly replacement, etc. "
SPD EDWs have few components, no moving parts
and a durable substrate, they therefore require less
repairs, observes Mike LaPointe, vice president -
Aerospace Products at Research Frontiers. " Every
time a shade is moved up to down to up, takes the
name of 'cycle.' For each of these cycles, the shade
www.AviationPros.com 31
A defining
feature of
dimmable
windows is
that they are
designed to
be nearly
maintenancefree.
SPD
EDWs
have few
components,
no moving
parts and
a durable
substrate,
they therefore
require less
repairs.
RESEARCH
FRONTIERS
http://www.AviationPros.com
January-February 2022

Table of Contents for the Digital Edition of January-February 2022
