**4. Conclusions**

*Aerospace Engineering*

alone can be daunting.

world is always cost.

downtime for manual inspections.

presentations on multifunctional composites [12].

Wings are one area of implementation for composites on the single aisle upgrades and new aircraft of the future. The Boeing 777X has incorporated a composite wing into the design. A composite wing allows for a very high degree of laminate tailoring and can be designed and built for maximum efficiency. This creates an elegant wing that is incredible to watch in-flight, but appears alarmingly thin compared to conventional metal aircraft wings. But composite wings for high rates present challenges. Production rates of 12–14 per month for wide bodies have proven to be achievable. Building composite wings to support production rates as high as 60 aircraft per month for narrow bodies has not. Costs related to rate tooling

Remarkable advances in OOA technology might help provide a solution. Bombardier chose an OOA process for wings of the C-series and the MRJ is using an OOA system for the vertical tail wing box, a similar process to what United Aircraft (Russia) has announced for their MS-21 wing. Still, there are complex issues to resolve that will affect the timeline for OOA system usage on next generation, commercial, single aisle aircraft wings and fuselages. The industry is risk adverse and OOA systems are in their infancy compared to autoclave systems. The autoclave process has proven to be very forgiving and tolerant of variabilities that exist in raw materials, support materials, supply chain manufacturing processes and through final part fabrication. The effect of manufacturing variability is well understood and incorporated into efficient designs that contain minimal penalties for the unknown or less well understood. The same will not be true of OOA systems until more lessons learned have been earned. Many of these lessons will continue to come from military applications that are more aggressive in implementing new technologies. The benefit for the military is usually not cost; the benefit for the commercial

On a little longer timeline affecting future composite fuselage construction is sensor and technologies related to structural health monitoring (SHM). This is a very large field with growing interest by many OEM's in many applications by many industries, including aerospace, automotive, and power generation. Advances in this technical arena could be one of the next revolutionary changes or "step changes" (vs. evolutionary) to advance the industry. Advanced sensor technology could supplant many NDT applications by supporting in-situ "structural health monitoring." Installed on or within composite structures, such systems would continuously monitor a component and detects degradation and damage as it occurs. This could eliminate the possibility of damage being overlooked and reduce costly

The future of SHM and other smart composite structures includes morphing technology that changes part shape in-flight to create optimal flight conditions. Built-in sensing, computing, and actuation are emerging new frontiers for structures that self-tailor their properties for changing flight conditions. Similar developments include multi-functional composites—laminates that not only provide lightweight, load-bearing structures, but also perform additional functions such as energy harvesting and storage. The 20th International Conference on Composite Materials (July 19–24, 2015, Copenhagen, Denmark), featured more than 100

3-D printing is another emerging technology that will impact the future of composite fuselage construction. Already making an impact in prototyping, early design and development, and tooling applications. Small, highly complex parts will follow the path being created by 3-D printed metallic parts. Larger applications are sure to follow. Nano technology may also develop as a viable standalone technology or perhaps integrated with 3-D printing. Remarkable innovations are surely on the

**122**

horizon.

The state-of-practice for dual aisle, wide body commercial aircraft fuselages has evolved over the past generation from minor aerodynamic composite fairings and flaps to entire composite fuselage structures. It has been a methodical, tenacious process that has included determined efforts by resources from the military and defense department, academia and many industry participants. It has been a global race between teams in the US and Europe with both competitors realizing a winwin outcome. Enormous technical advances were required on many fronts, from tooling to transportation. Equally enormous advances were requisite on the cost competitiveness of manufacturing and assembling composite materials in order to earn their way onto commercial aircraft platforms. New mid-market aircraft platforms from both sides of the Atlantic will be the launching pad for the next wave of technologies that have earned their way onto dual aisle commercial aircraft. After that, the industry anticipates direction on long awaited replacement designs for workhorse single aisle aircraft—composite fuselage or not?
