**2.1 Large Aircraft Composite Fuselage (LACF) program**

The LACF program was conducted in part by Northrop and was sponsored by the Air Force Wright Aeronautical Laboratory (AFWAL) during the 1980s. The program was part of an effort focused on manufacturing technology for the Linear Manufacturing of Large Aircraft Composite Primary Structure Fuselage. The multi-phase program was directed toward the definition and demonstration of manufacturing methods for cocuring stringer stiffened fuselage panels using (1) existing, qualified material systems; (2) automated skin fabrication; (3) inner mold line (IML) controlled tooling; (4) non-autoclave curing technology. Like many similar terms, in the 1980s "linear" manufacturing was a code word for "lean" and non-autoclave is referred to today as out-of-autoclave or OOA processes.

The program followed a building-block approach through four phases (**Figure 2**):

• Phase I—methods definition

*Aerospace Engineering*

new aircraft.

**2. Early research and development**

development of composite materials and processes [2].

automated lamination processes such as ATL and AFP.

solid silicone mandrels, on their portions of the program.

(ACT) program in the mid 1990s.

reinforced composites (CFRP) in both commercial and military aircraft were limited mostly to non-structural applications such as fairings and flight control surfaces. Structural applications for military aircraft began to appear in the 1980s as composite usage grew to more than 20% of the weight of the structure. As the industry continued to mature, material and processes became better understood and cost effectiveness improved to the level that commercial aircraft manufacturers incorporated the technology into the latest generation of wide body and other

Research and development of high performance composite materials and processes for aerospace applications in the Unites States was first conducted in the 1940s at Wright-Patterson Air Force Base in Dayton, Ohio [1]. The focus of this early research was primarily for military applications. This research has continued since that time and today, the Air Force Research Laboratory (AFRL), with support from industry, universities and other government agencies such as the Department of Advanced Research Projects Agency (DARPA) and the Department of Energy (DOE), continues to play a leading role in developing advanced materials for military applications. NASA initiated research devoted to the development of high performance composites for commercial aircraft and space vehicles in the late 1960s. Over the years, NASA has worked collectively with industry and academia to develop affordable technologies to improve safety and performance of aircraft and launch vehicles. The paper *NASA Composite Materials Development: Lessons Learned and Future Challenges* provides an excellent historical review of NASA's role in the

A common characteristic shared between AFRL and NASA sponsored programs was the "building-block" approach for research and development programs that progressed through a series of steps, each one having an increase in complexity and cost that built upon the previous step. In general, programs started at a coupon level and looked at a wide range of samples to down select design approaches, materials of construction, tooling and manufacturing processes to build and test coupons, subcomponents and ultimately full scale components. Not unlike the Technology Readiness Levels applied to describe new technologies today, this approach was used successfully in programs such as the Air Force's Large Aircraft Composite Fuselage (LACF) Program in the late 1980s and NASA's Advanced Composites Technology

The B-2 Stealth Bomber program was also taking place during the 1980s and provided many lessons learned related to the manufacture of large composite primary structure. For the B-2, survivability performance was one of the primary reasons for the extensive use of carbon fiber composites—cost and producibility were not the most critical factors. Boeing was a prime subcontractor on the program and built the wing skins using Automated Tape Laying (ATL). This program presented the opportunity to demonstrate the productivity that was possible using

Another program which derived direct benefit from the ACT program is the V-22. Composites have been used extensively and aggressively in helicopters more than any other type of aircraft because weight is such a critical factor. The V-22 uses composites for the wings, fuselage skins, empennage, side body fairings, doors, and nacelles. AFP technology is used to fabricate the aft fuselage skin in one piece. Both Bell and Boeing also incorporate cocured, hat stiffened fuselage structures, using

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As the program moved through various phases, lessons learned where documented and applied to the next phase. Phase I lessons learned included:


**Figure 2.** *LACF program.*


Phase II lessons learned included:


Among the lessons learned as a result of Phases III and IV were the economics related to process scale up for both size and rate. This included ply cutting and kitting time for panel fabrication and backing paper removal and management issues affecting tow placement and stringer laminate preplying (**Figure 5**). Another lesson included gaining a better understanding of cocuring longitudinal "I" beams to the skin of a large fuselage panel. One nice feature of the "I" beam construction is that the tooling is not trapped after cure and the channel details that form the "C"

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**Figure 5.**

*Laminate cross ply equipment.*

*The Evolution of the Composite Fuselage: A Manufacturing Perspective*

of the "I" beam can be removed over any length. Disadvantages were also apparent including the number of laminate preform and tooling details needed to construct

Northrop developed hat stiffened fuselage skin manufacturing technology in support of the YF-23 (**Figure 7**). One critical problem to solve was the removal of hat stiffener mandrel tooling from the cured part. The fuselage tooling was OML controlled and constructed from CRFP prepreg to match the coefficient of thermal expansion (CTE) of the parts. The resin system used for the tooling was bismaleimide (BMI) and the tools were autoclave cured on male, machined monolithic graphite source tools. The hat stiffeners that run longitudinally along the skin were cocured using a silicone

an "I" beam vs. the simplicity of the hat stiffener (**Figure 6**).

mandrel system developed by Northrop using Rubbercraft as a supplier.

*DOI: http://dx.doi.org/10.5772/intechopen.82353*

**Figure 4.**

*"C" channel roll forming machine.*

**Figure 3.** *"I" beam formed from "C" channels.*

*The Evolution of the Composite Fuselage: A Manufacturing Perspective DOI: http://dx.doi.org/10.5772/intechopen.82353*
