Aerospace & Defense Technology - December 2023 - 31

Tech Briefs
Composite Repair Engineering Case Studies for U.S.
Army Aerostructures
The U.S. Army fields a multitude of aircraft mission design series (MDS) developed by several different
original equipment manufacturers with varying mission requirements and flight profiles. The structural
analysis in this work assumes the materials, tooling, skillsets, and capabilities are organically
available and proper at the repair location.
Army Combat Capabilities Development Command, Redstone Arsenal, Alabama
T
he U.S. Army operates and maintains
several aircraft MDS to meet
the warfighter's multidomain mission.
Aircraft fielded by the U.S. Army originate
from multiple equipment manufacturers.
These aircraft include rotary-wing
configurations such as the
AH-64D/E Apache, CH-47F Chinook,
and H-60A/L/V/M Blackhawk aircraft
which significantly vary in mission
parameters and flight profiles. These
aircraft contain structures made from a
majority aluminum, steel, and titanium
alloys which have dominated aircraft
designs for much of the history of powered
flight. However, the use of
advanced composite material systems
such as fiberglass, carbon, and aramid
fiber reinforcement with high performance
epoxy resins has steadily
increased to optimize structural designs
and improve mission capability.
Fiberglass was first developed in the
1930s, with carbon fiber materials subsequently
developed in the 1980s. The utilization
of polymer matrix composite
material systems such as carbon-epoxy
fabrics and aramid honeycomb core has
significantly increased in civilian and
military aircraft designs. This is a result
of the significant increase in specific
strength and stiffness capabilities and
resistance to corrosion and fatigue that
composites offer to the enterprise. While
composites certainly are not new to aviation,
their uses were primarily limited to
secondary and lightly loaded structures
such as covers, fairings, spoilers, and
antenna. During the RAH-66 Comanche
helicopter development effort, the U.S.
Army made attempts to build a fiber-reinforced
crashworthy airframe structure
through the Advanced Composite Airframe
Program (ACAP). The ACAP effort,
conducted by Bell Helicopter and
Sikorsky Aircraft, was intended to determine
the feasibility of utilizing composVHF
ANTENNA
VERTICLE
STABILIZER
ENVIRONMENTAL
CONTROL SYSTEM
MAIN ROTOR
BLADES
TAIL ROTOR
BLADES
RIGHT HAND
EXTENDED FORWARD
AVIONICS BAY
N0.2 ENGINE
AND NACELLE
HORIZONTAL STABILIZAR
RIGHT WING
AND PYLON
N0.1 ENGINE
AND NACELLE
TADS/PNVS
LEFT HAND
EXTENDED FORWARD
AVIONICS BAY
LEFT WING
AND PYLON
CHAIN GUN
COMPONENTS
Figure 1: Potential composite applications for the U.S. Army's fleet of H-64 Apache helicopters.
Figure 1. H-64 Apache Composite Layout.
ites for fuselages and primary structure.
The driver for this effort was to reduce
weight, eliminate metal corrosion, build
more tolerant battle damage structures,
and reduce aircraft radar cross sections.
While the program was cancelled in February
2004, the Comanche and ACAP
programs demonstrated that composites
would be acceptable for use on miliary
aircraft. Additionally, these programs
helped to set a precedence for future
repairs of composite structures. The
repair methods of that effort included
standard wet layup, for smaller damage,
and replacement of modular components
for larger damage. Replacement of
modular sections accomplished by
removing smaller sub-sections of the
structure and effectively splicing in a
replacement part.
As technologies develop, aircraft
mature, and strides are made in advanced
Aerospace & Defense Technology, December 2023
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materials development and analysis, aircraft
have increased use of advanced
composites within the aerostructure.
These advanced materials are now being
used in highly loaded structures, including
aerodynamic profiles.
Evolving mission requirements led to
the use of unmanned fixed wing aircraft,
such as the MQ-1 Grey Eagle and RQ-7
Shadow, which employ carbon fiber
composites as the bulk of the fuselage
structure. Structurally critical applications
include main rotor blade spars,
bulkheads, fuselage skins, stringers,
walkways, and stabilators. Additionally,
it is suspected that future U.S. Army aircraft
designs will have structures primarily
constructed from advanced composite
materials. The U.S. Marine Corps'
MV-22 Osprey tiltrotor aircraft has an
airframe constructed primarily from carbon
fiber reinforced epoxy material sys31

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Aerospace & Defense Technology - December 2023

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