SAMPE Journal - September/October 2016 - 7

Feature Article
Thermoplastic Orthogrid Fuselage Shell
J.W. van Ingen
Fokker Aerostructures, Hoogeveen, The Netherlands

Abstract
In this article a thermoplastic fuselage shell concept is discussed, featuring stingers in two directions; an orthogrid. State of the art composite
fuselage shells use a lot of fasteners to integrate skin, stringers and frames. Using thermoplastic composites, this might change. Thermoplastics
are very tough and have a high out of plane strength. This enables new stiffening and joining methods, without the use of fasteners (Figure 29 ).
TAPAS Project
A fuselage shell is constructed from a skin which is
supported by stringers and frames. The stringers and
frames are both continuous members and intersect
each other.
Current state of art composite fuselages use fastened
clips to connect the frame to the stiffened skin (Figure
1). This solution however appears to be costly due to the
amount of parts and fasteners used.
In the framework of the TAPAS2 project1, thermoplastic
fuselage shells are developed by Fokker. The goal is to
create a composite fuselage shell without fasteners for
the frame to skin joint for a 1.5 to 2m fuselage radius.
No Fastener Fuselage Shell Design Drivers
Two aspects drive the stringer intersection joint design
when considering a composite fuselage shell without
fasteners: cabin pressure and impacts, for instance by
tool drop.
If the fuselage is pressurized, the skin and stringers
expand in radial direction like a balloon. The frames
partially follow this expansion and loads are generated
in the frame to skin joint. Generally there will be a
"mouse hole" in the frame for the stringer to pass. This
discontinuity can generate high peel forces in the frame
to skin joint, just next to the mouse hole. If a fuselage
shell is to be made without fasteners, this will be a
critical point, since composites generally have a low out
of plane strength.
The other driving load case is impact from the outside
of the aircraft, as well as from the inside. The frame acts
as a hard point for impacts in the panel, meaning that
high loads are to be expected in the frame to skin joint
due to impact.

Thermoplastic Orthogrid
One way to obtain a fuselage shell without fasteners
might be to use a composite material with a high
toughness and out of plane strength in combination
with a design without the peel peak at the mouse hole.
This has led to a thermoplastic composite orthogrid,
where the thermoplastic material (AS4D PEKK) has the
required toughness and the grid creates the continuity
without peel peaks, since there is no mouse hole.
The panel shown in Figure 2 was the first thermoplastic
orthogrid made in 2013. It has continuous longitudinal
T-stringers. The longitudinal and circumferential stringer
caps are continuous and overlap at the corner, while the
circumferential web is discontinuous.
To use this panel in a pressurized fuselage shell with
a 3 to 4m diameter, a frame needs to be attached to
increase the bending stiffness. This is shown in Figure

Figure 1. State of art composite fuselage: Frames attached to
omega stiffened skin with fastened clips.
SAMPE Journal, Volume 52, No. 5, September/October 2016

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