Description: US aerospace systems need improved performance and reduced costs to satisfy military and commercial customers and improve US worldwide competitiveness. This issue is common to a wide range of products that include large military cargo and commercial aircraft, fighter aircraft, military and commercial helicopters, and launch vehicles for both military and commercial missions. The airframe or structure makes up from 30 to 40 % of the vehicle hardware cost for these systems. One thing these airframes have in common is extensive use of aluminum alloy. This suggests that a solution that improves the performance and reduces the cost of aluminum structures will have a payoff potential for a wide range of aerospace systems. These goals can be achieved in a coordinated aluminum-lithium technology development effort that addresses all of the elements that contribute to the cost and performance of aluminum aerospace structures. These include (1) the development of improved alloys and a material property design data base, (2) the development and validation of low cost design and fabrication processes, (3) the development and validation of innovative joining concepts , and (4) application of modeling and analysis activities to alloy processing optimization.

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Advantages: Recent studies and the Advanced Launch System (ALS) and National Launch System (NLS) programs have shown that launch vehicle weight savings of 30 % are possible with the application of al-li to replace aluminum alloys in use today. Cost savings of up to 50 % have been demonstrated for launch vehicle propellant tanks using low cost design, fabrication and assembly concepts, which serves to demonstrate the payoff that can be achieved. Similar assessments of al-li alloys for aircraft, while not as dramatic, show a significant payoff. The high specific strength of this alloy also makes it ideal for reusable launch systems and SSTO system applications. Robert White at NASA has stated, `The benefits of using al-li are huge. Mastering of al-li is a key technology in building future reusable launch vehicles.`

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Challenges: Attempts to introduce al-li alloys into operational US systems have been delayed because of deficiencies in the available US alloys. The poor short-transverse properties of the 2090 alloy causes cracking when integrally stiffened panels are formed in the fabrication of Delta propellant tanks. Material deficiencies caused its removal from the C-17. Fabrication and welding problems continue with the 2195 alloy selected by NASA for development of a lightweight Shuttle external tank. In contrast to the US, Russia has been involved in al-li development for over 30 years and has successfully introduced these alloys into operational fighter aircraft, cargo aircraft, helicopters and missiles. All modern Russian fighter aircraft employ extensive welded aluminum-lithium alloy. The MIG-29 was able to achieve a 24 % weight savings with this approach. The Russian studies concluded that greater weight and cost savings could be achieved with welded al-li than with their composites and it could be introduced rapidly without having to develop a new design and manufacturing infrastructure. Foreign competitors , Airbus and Deutche Aerospace, have recognized the potential of the Russian al-li technology and are employing Russian alloys in commercial aircraft under development. The Russian success in the application of al-li alloys and welding to aerospace structures demonstrates that the cost and performance goals that have been proposed can be achieved and reduces the development risk. In addition, the time and costs to achieve US technology readiness can be significantly reduced by taking advantage of what the Russians have accomplished.

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Possible Applications: While the near term payoff potential is very high, the US R&D resources invested in al-li technology have been limited. An aluminum-lithium technology program aimed at building upon, coordinating and extending current technology in the areas of alloy improvement, development of a design data base, development and validation of low cost al-li fabrication processes will permit early application of this technology to a wide range of products that will enable increased performance and reduced costs.