JEC COMPOSITES MAGAZINE - Issue #109 - November/December 2016 - 62

TECHNOLOGY certification

Structural certification analysis
and reports for aircraft interiors

DR. WARReN leigh phD,
Responsible for Course
Contents and Structure
High Peak Courses Ltd.

This article explains the process of creating an interface loads certification report and its required contents. This report provides the loads
the airframe will experience at the attachment points of the interior unit
depending on the various aircraft loadcases.
For new graduate engineers, it is worth noting that this industry is always looking for certification stress engineers.

he aircraft interiors market includes Galleys, Stowage units (Figure 1) and Flight Crew Rest Compartments (FCRCs). This
growing market is predicted to be worth $10b by the year 2020.
Aim Aviation, BE-Aerospace, Zodiac and Jamco are amongst the major aircraft interiors manufacturer companies. To ensure flight worthiness of their products these companies have to supply two important
structural certification reports that provide the Interface load derivations and the stress analysis respectively.

CAD construction and stowage design
Predominantly, CatiaV and Solidworks 3D CAD software by Dassault
are generally used to design aircraft interiors. However, many aircraft
interiors units have been designed using Unigraphics 3D-CAD.
The Stowage unit example described is generically a cupboard with a
vertical central partition panel creating two compartments accessed by
side doors (Fig.1). Other configurations of Stowage unit are available.

The Stowage unit is fastened by its four feet attachments to the seat
rails of the aircraft floor. Its design should allow for floor baggage and
one coat per compartment. Other items such as magazine racks, baby
bassinet and video display units can be attached externally to the Stowage unit panels. However, other contents may include first aid kits, oxygen cylinders, breathing equipment, folding trolleys and wheelchairs.

Construction of the FEA model
The Stowage unit is primarily made from phenolic glassfibre composite honeycomb flat panels that share common geometric boundaries.
Each panel is fastened together at specific points and pitch. The completed unit is about 1700mm high, 350mm deep and 1500mm wide.
Rather than importing the 3D CAD model into the FEA software, the
Stowage unit FEA models have traditionally been built by referring to
the 2D drawings of the 3D-CAD model and noting the mid-ordinate
geometry coordinates of each corner of the respective panels. These
edge coordinates are entered manually into the pre-processor of the
FEA software. A surface is made by using the four corner points of
each panel. Panel autonomy must be maintained by allocating a specific coordinate for each of the panel's four corners. Although, adjacent
panels will share a common point in space they will not share the same
gridpoint (Figure 2).

Panel meshing

Fig. 1: Aircraft stowage unit
(2 side door version) outside
CAD rendition

Fig. 2: Individual panel FEA
models each with a uniform
density mesh

The MSC-Patran FEA or Siemens Femap NX-Nastran FEA software
contains an isomesh tool that usually generates an acceptable Quad4
mesh into the rectangular panel shapes. Each panel is meshed with a
uniform mesh density of Quad4 elements of equal aspect ratio based
on a grid of mesh seeding no greater than 30mm (Figure 2). It is important that each panel maintains its individuality from the adjacent
panel by ensuring that respective nodes which share a common geometric position are not merged by the tolerance set. The panels are
only connected by the use of mpc-elements which represents the fasteners. Because of the consistent mesh size chosen the nodes of the
mesh of one panel should align to those of the next panel, a sort of
mirror image.

jec composites magazine / No109 November - December 2016

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #109 - November/December 2016