**Figure 4.**

*Aerospace Engineering*

and location.

ment downtime.

(**Figure 4**).

tools.

4.IML provides very easy tool loading and bagging

channels ready for tool loading (**Figure 3**).

Phase II lessons learned included:

5.Continuous roll forming can be used to preform preplied material into "C"

1.Non-autoclave cure has risks associated with consumable bagging materials.

3.Confirmed IML tooling is excellent for controlling stringer/skin dimensions

5.Flat preplied laminates can be drape formed on gentle contours using IML cure

6.Automation can be applied but presents reliability risks and potential equip-

7.Automation can produce a laminate that does not require additional debulking.

8.Roll forming of stringer "C" channels is important for linear manufacturing

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"

4.Confirmed IML tooling and "I" beam stringer for part and tool removal.

2.Integrally heated tooling strongly supports linear manufacturing.

**98**

**Figure 3.**

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

*"C" channel roll forming machine.*

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

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 mandrel system developed by Northrop using Rubbercraft as a supplier.

**Figure 6.** *"I" beam vs. hat stiffener.*

**Figure 7.** *YF-23 fuselage structure.*

The silicone based solid mandrel system included a solid rubber mandrel, a butterfly caul and a resin end dam. The silicone mandrel was designed to be removed from the cured part after pulling and elongating the mandrel to reduce the cross section enough to release from the part. The butterfly caul was designed to help consistently control the OML of the hat stiffener. It also helped to greatly simplify the bagging process which allows for the use of a broader range of operators instead of relying solely on a highly skilled mechanic. The end dam was designed to be cheap and disposable and replace much of the inner bagging process complexity of sealing off the hat stiffener to prevent resin bleed during the cure cycle (**Figure 8**). This is not a hard process, but is critical and tedious.

Northrop subsequently applied this hat stiffener fabrication process technology to the fuselage of the F/A-18E/F as a prime subcontractor to Boeing on the program (**Figure 9**).

During this time period, it was recognized by many of the R&D programs that liquid molding processes presented the opportunity to use resins and fibers in their lowest-cost state by eliminating prepreg from the fabrication process. Other advantages included minimizing material scrap, simplifying raw material storage, and supporting non-autoclave fabrication processes. The development of net shape

**101**

**Figure 9.**

*F/A-18E/F fuselage structure.*

**Figure 8.**

*Solid mandrel system.*

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

damage-tolerant textile preforms and the development of innovative liquid molding tooling concepts supported this opportunity. The Advanced Composites Technology (ACT) program included processes such as resin transfer molding (RTM) and pultrusion in the development efforts. The technologies have progressed to state-ofpractice processes with both the 787 and the A350 programs using liquid molding

The objective of the ACT fuselage program was to develop composite primary structure for commercial airplanes with 20–25% less cost and 30–50% less weight than equivalent metallic structure [3]. The Advanced Technology Composite Aircraft Structure (ATCAS) program was performed by Boeing as the prime

and textile preform technology for fabricating fuselage frame elements.

**2.2 Advanced Composites Technology (ACT) program**

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

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

*Aerospace Engineering*

**Figure 6.**

**Figure 7.**

*YF-23 fuselage structure.*

*"I" beam vs. hat stiffener.*

**100**

(**Figure 9**).

The silicone based solid mandrel system included a solid rubber mandrel, a butterfly caul and a resin end dam. The silicone mandrel was designed to be removed from the cured part after pulling and elongating the mandrel to reduce the cross section enough to release from the part. The butterfly caul was designed to help consistently control the OML of the hat stiffener. It also helped to greatly simplify the bagging process which allows for the use of a broader range of operators instead of relying solely on a highly skilled mechanic. The end dam was designed to be cheap and disposable and replace much of the inner bagging process complexity of sealing off the hat stiffener to prevent resin bleed during the cure cycle (**Figure 8**).

Northrop subsequently applied this hat stiffener fabrication process technology to the fuselage of the F/A-18E/F as a prime subcontractor to Boeing on the program

During this time period, it was recognized by many of the R&D programs that liquid molding processes presented the opportunity to use resins and fibers in their lowest-cost state by eliminating prepreg from the fabrication process. Other advantages included minimizing material scrap, simplifying raw material storage, and supporting non-autoclave fabrication processes. The development of net shape

This is not a hard process, but is critical and tedious.

damage-tolerant textile preforms and the development of innovative liquid molding tooling concepts supported this opportunity. The Advanced Composites Technology (ACT) program included processes such as resin transfer molding (RTM) and pultrusion in the development efforts. The technologies have progressed to state-ofpractice processes with both the 787 and the A350 programs using liquid molding and textile preform technology for fabricating fuselage frame elements.
