The Path to the Modern Era

A strategy began forming in 1972 with the launch of the Air Force-NASA Long Range Planning Study for Composites (RECAST), which focused priorities for the research projects that would soon begin.[700] That was pre­lude to what NASA research Marvin Dow would later call the "golden age of composites research,”[701] a period stretching from roughly 1975 until funding priorities shifted in 1986. As airlines looked to airframers for help, military aircraft were already making great strides with composite structure. The Grumman F-14 Tomcat, then the McDonnell-Douglas F-15 Eagle, incorporated boron-epoxy composites into the empennage skin, a primary structure.[702] With the first flight of the McDonnell-Douglas AV-8B Harrier in 1978, composite usage had drifted to the wing as well. In all,

Air Force engineer Norris Krone prompted NASA to develop the X-29 to prove that high-strength composites were capable of supporting forward-swept wings. NASA.

about one-fourth of the AV-8B’s weight,[703] including 75 percent in the weight of the wing alone,[704] was made of composite material. Meanwhile, composite materials studies by top Grumman engineer Norris Krone opened the door to experimenting with forward-swept wings. NASA responded to Krone’s papers in 1976 by launching the X-29 technology demonstrator, which incorporated an all-composite wing.[705]

Composites also found a fertile atmosphere for innovation in the rotorcraft industry during this period. As NASA pushed the commer­cial aircraft industry forward in the use of composites, the U. S. Army spurred progress among its helicopter suppliers. In 1981, the Army selected Bell Helicopter Textron and Sikorsky to design all-composite airframes under the advanced composite airframe program (ACAP).[706]

Perhaps already eyeing the need for a new light airframe to replace the Bell OH-58 Kiowa scout helicopter, the Army tasked the contrac­tors to design a new utility helicopter under 10,000 pounds that could fly for up to 2 hours 20 minutes.[707] Bell first flew the D-292 in 1984, and Sikorsky flew the S-75 ACAP in 1985.[708] Boeing complemented their efforts by designing the Model 360, an all-composite helicopter airframe with a gross weight of 30,500 pounds.[709] Each of these projects provided the steppingstones needed for all three contractors to fulfill the design goals for both the now-canceled Sikorsky-Boeing RAH-66 Comanche and the Bell-Boeing V-22 Osprey tilt rotor. The latter also drove devel­opments in automated fiber placement technology, relieving the need to lay up by hand about 50 percent of the airframe’s weight.[710]

In the midst of this rapid progress, the makers of executive and "general” aircraft required neither the encouragement nor the finan­cial assistance of the Government to move wholesale into composite airframe manufacturing. While Boeing dabbled with composite spoil­ers, ailerons, and wing covers on its new 767, William P. Lear, founder of LearAvia, was developing the Lear Fan 2100—a twin-engine, nine – seat aircraft powered by a pusher-propeller with a 3,650-pound air­frame made almost entirely from a graphite-epoxy composite.[711] About a decade later, Beechcraft unveiled the popular and stylish Starship 1, an 8- to 10-passenger twin turboprop weighing 7,644 pounds empty.[712] Composite materials—mainly using graphite-epoxy and NOMEX sand­wich panels—accounted for 72 percent of the airframe’s weight.[713]

Actual performance fell far short of the original expectations dur­ing this period. Dow’s NASA colleagues in 1975 had outlined a strategy that should have led to full-scale tests of an all-composite fuselage and wing box for a civil airliner by the late 1980s. Although the dream was delayed by more than a decade, it is true that state of knowledge and
understanding of composite materials leaped dramatically during this period. The three major U. S. commercial airframers of the era—Boeing, Lockheed, and McDonnell-Douglas—each made contributions. However, the agenda was led by NASA’s $435-million investment in the Aircraft Energy Efficiency (ACEE) program. ACEE’s top goal, in terms of fund­ing priority, was to develop an energy-efficient engine. The program also invested greatly to improve how airframers control for laminar flow. But a major pillar of ACEE was to drive the civil industry to fundamentally change its approach to aircraft structures and shift from metal to the new breed of composites then emerging from laboratories. As of 1979, NASA had budgeted $75 million toward achieving that goal,[714] with the manufacturers responsible for providing a 10-percent match.

ACEE proposed a gradual development strategy. The first step was to install a graphite-epoxy composite material called Narmco T300/5208[715] on lightly loaded secondary structures of existing commercial aircraft in oper­ational service. For their parts, Boeing selected the 727 elevator, Lockheed chose the L-1011 inboard aileron, and Douglas opted to change the DC-10 upper aft rudder.[716] From this starting point, NASA engaged the manufac­turers to move on to medium-primary components, which became the 737 horizontal stabilizer, the L-1011 vertical fin, and the DC-10 vertical stabi­lizer.[717] The weight savings for each of the medium primary components was estimated to be 23 percent, 30 percent, and 22 percent, respectively.[718]

The leap from secondary to medium-primary components yielded some immediate lessons for what not to do in composite structural design. All three components failed before experiencing ultimate loads in initial ground tests.[719] The problems showed how different composite material could be from the familiar characteristics of metal. Compared to aluminum, an equal amount of composite material can support a heavier load. But, as experience revealed, this was not true in every con­dition experienced by an aircraft in normal flight. Metals are known to
distribute stresses and loads to surrounding structures. In simple terms, they bend more than they break. Composite material does the opposite. It is brittle, stiff, and unyielding to the point of breaking.

Boeing’s horizontal stabilizer and Douglas’s vertical stabilizer both failed before the predicted ultimate load for similar reasons. The brittle composite structure did not redistribute loads as expected. In the case of the 737 component, Boeing had intentionally removed one lug pin to simulate a fail-safe mode. The structure under the point of stress buck­led rather than redistributed the load. Douglas had inadvertently drilled too big of a hole for a fastener where the web cover for the rear spar met a cutout for an access hole.[720] It was an error by Douglas’s machin­ists but a tolerable one if the same structure were designed with metal. Lockheed faced a different kind of problem with the failure of the L-1011 vertical fin during similar ground tests. In this case, a secondary inter­laminar stress developed after the fin’s aerodynamic cover buckled at the attachment point with the front spar cap. NASA later noted: "Such secondary forces are routinely ignored in current metals design.”[721] The design for each of these components was later modified to overcome these unfamiliar weaknesses of composite materials.

In the late 1970s, all three manufacturers began working on the basic technology for the ultimate goal of the ACEE program: design­ing full-scale, composite-only wing and fuselage. Control surfaces and empennage structures provided important steppingstones, but it was expected that expanding the use of composites to large sections of the fuselage and wing could improve efficiency by an order of mag­nitude.[722] More specifically, Boeing’s design studies estimated a weight savings of 25-30 percent if the 757 fuselage was converted to an all­composite design.[723] Further, an all-composite wing designed with a metal-like allowable strain could reduce weight by as much as 40 per­cent for a large commercial aircraft, according to NASA’s design anal­ysis.[724] Each manufacturer was assigned a different task, with all three collaborating on their results to gain maximum results. Lockheed explored
design techniques for a wet wing that could contain fuel and survive light­ning strikes.[725] Boeing worked on creating a system for defining degrees of damage tolerance for structures[726] and designed wing panes strong enough to endure postimpact compression of 50,000 pounds per square inch (psi) at strains of 0.006.[727] Meanwhile, Douglas concentrated on meth­ods for designing multibolted joints.[728] By 1984, NASA and Lockheed had launched the advanced composite center wing project, aimed at designing an all-composite center wing box for an "advanced” C-130 airlifter. This project, which included fabricating two 35-foot-long structures for static and durability tests, would seek to reduce the weight of the C-130’s cen­ter wing box by 35 percent and reduce manufacturing costs by 10 percent compared with aluminum structure.[729] Meanwhile, Boeing started work in 1984 to design, fabricate, and test full-scale fuselage panels.[730]

Within a 10-year period, the U. S. commercial aircraft industry had come very far. From the near exclusion of composite structure in the early 1970s, composites had entered the production flow as both second­ary and medium-primary components by the mid-1980s. This record of achievement, however, was eclipsed by even greater progress in commer­cial aircraft technology in Europe, where the then-upstart DASA Airbus consortium had pushed composites technology even further.

While U. S. commercial programs continued to conduct demonstra­tions, the A300 and A310 production lines introduced an all-composite rudder in 1983 and achieved a vertical tailfin in 1985. The latter vividly demonstrated the manufacturing efficiencies promised by composite designs. While a metal vertical tail contained more than 2,000 parts, Airbus designed a new structure with a carbon fiber epoxy-honeycomb core sand­wich that required fewer than 100 parts, reducing both the weight of the structure and the cost of assembly.[731] A few years later, Airbus unveiled the A320 narrow body with 28 percent of its structural weight filled by
composite materials, including the entire tail structure, fuselage belly skins, trailing-edge flaps, spoilers, ailerons, and nacelles.[732] It would be another decade before a U. S. manufacturer eclipsed Airbus’s lead, with the introduction of the Boeing 777 in 1995. Consolidating experience gained as a major structural supplier for the Northrop B-2A bomber program, Boeing designed the 777, with an all-composite empennage one-tenth of the weight.[733] By this time, the percentage of composites integrated into a commercial airliner’s weight had become a measure of the manufactur­er’s progress in gaining a competitive edge over a rival, a trend that con­tinues to this day with the emerging Airbus A350/Boeing 787 competition.

As European manufacturers assumed a technical lead over U. S. rivals for composite technology in the 1980s, the U. S. still retained a huge lead with military aircraft technology. With fewer operational con­cerns about damage tolerance, crash survivability, and manufacturing cost, military aircraft exploited the performance advantages of com­posite material, particularly for its weight savings. The V-22 Osprey tilt rotor employed composites for 70 percent of its structural weight.[734] Meanwhile, Northrop and Boeing used composites extensively on the B-2 stealth bomber, which is 37-percent composite material by weight.

Steady progress on the military side, however, was not enough to sustain momentum for NASA’s commercial-oriented technology. The ACEE program folded after 1985, following several years of real prog­ress but before it had achieved all of its goals. The full-scale wing and fuselage test program, which had received a $92-million, 6-year budget from NASA in fiscal year 1984,[735] was deleted from the Agency’s spend­ing plans a year later.[736] By 1985, funding available to carry out the goals of the ACEE program had been steadily eroding for several years. The Reagan Administration took office in 1981 with a distinctly different view on the responsibility of Government to support the validation of com­mercial technologies.[737]

In constant 1988 dollars, ACEE funding dropped from a peak $300 million in 1980 to $80 million in 1988, with funding for validat­ing high-strength composite materials in flight wiped out entirely.[738] The shift in technology policy corresponded with priority disagree­ments between aeronautics and space supporters in industry, with the latter favoring boosting support for electronics over pure aeronautics research.[739]

In its 10-year run, the composite structural element of the ACEE program had overcome numerous technical issues. The most serious issue erupted in 1979 and caused NASA to briefly halt further studies until it could be fully analyzed. The story, always expressed in general terms, has become an urban myth for the aircraft composites commu­nity. Precise details of the incident appear lost to history, but the conse­quences of its impact were very real at the time. The legend goes that in the late 1970s, waste fibers from composite materials were dumped into an incinerator. Afterward, whether by cause or coincidence, a nearby electric substation shorted out.[740] Carbon fibers set loose by the inciner­ator fire were blamed for the malfunction at the substation.

The incident prompted widespread concerns among aviation engi­neers at a time when NASA was poised to spend hundreds of millions of dollars to transition composite materials from mainly space and military vehicles to large commercial transports. In 1979, NASA halted work on the ACEE program to analyze the risk that future crashes of increasingly composite-laden aircraft would spew blackout-causing fibers onto the Nation’s electrical grid.[741]

Few seriously question the potential benefits that composite mate­rials offer society. By the mid-1970s, it was clear that composites dra­matically raise the efficiency of aircraft. The cost of manufacturing the materials was higher, but the life-cycle cost of maintaining noncorrod­ing composite structures offered a compelling offset. Concerns about the economic and health risks poised by such a dramatic transition to a different structural material have also been very real.

It was up to the aviation industry, with Government support, to answer these vital questions before composite technology could move further.

With the ACEE program suspended to study concerns about the risks to electrical equipment, both NASA and the U. S. Air Force by 1978 had launched separate efforts to overcome these concerns. In a typi­cal aircraft fire after a crash, the fuel-driven blaze can reach tempera­tures between 1,800 to 3,600 degrees Fahrenheit (°F). At temperatures higher than 750 °F, the matrix material in a composite structure will burn off, which creates two potential hazards. As the matrix polymer transforms into fumes, the underlying chemistry creates a toxic mix­ture called pyrolysis product, which if inhaled can be harmful. Secondly, after the matrix material burns away, the carbon fibers are released into the atmosphere.[742]

These liberated fibers, which as natural conductors have the power to short circuit a power line, could be dispersed over wide areas by wind. This led to concerns that the fibers would could come into contact with local power cables or, even worse, exposed power substations, leading to widespread power blackouts as the fibers short circuit the electrical equipment.[743] In the late 1970s, the U. S. Air Force started a program to study aircraft crashes that involved early-generation composite materials.

Another incident in 1997 was typical of different type of concern about the growing use of composite materials for aircraft structures. A

U. S. Air Force F-117 flying a routine at the Baltimore airshow crashed when a wing-strut failed. Emergency crews who rushed to the scene extinguished fires that destroyed and damaged several dwellings, blan­keting the area with a "wax-like” substance that contained carbon fibers embedded in the F-117’s structures that could have otherwise been released into the atmosphere. Despite these precautions, the same fire­fighters and paramedics who rushed to the scene later reported becom­ing "ill from the fumes emitted by the fire. It was believed that some of these fumes resulted from the burning of the resin in the composite materials,” according a U. S. Navy technical paper published in 2003.[744]

Yet another issue has sapped the public’s confidence in compos­ite materials for aircraft structures for several decades. As late as 2007, the risk presented by lightning striking a composite section of an aircraft fuselage was the subject of a primetime investigation by Dan Rather, who extensively quoted a retired Boeing Space Shuttle engineer. The question is repeatedly asked: If the aluminum structure of a previous generation of airliners created a natural Faraday cage, how would composite materials with weaker properties for conductivity respond when struck by lightning?

Technical hazards were not the only threat to the acceptance of com­posite materials. To be sure, proving that composite material would be safe to operate in commercial service constituted an important endorse­ment of the technology for subsequent application, as the ACEE projects showed. But the aerospace industry also faced the challenge of estab­lishing a new industrial infrastructure from the ground up that would supply vast quantities of composite materials. NASA officials anticipated the magnitude of the infrastructure issue. The shift from wood to metal in the 1930s occurred in an era when airframers acted almost recklessly by today’s standards. Making a similar transition in the regulatory and business climate of the late 1970s would be another challenge entirely. Perhaps with an eye on the rapid progress being made by European com­petitors in commercial aircraft, NASA addressed the issue head-on. In 1980, NASA Deputy Administrator Alan M. Lovelace urged industry to "anticipate this change,” adding that he realized "this will take consid­erable capital, but I do worry that if this is not done then might we not, a decade from now, find ourselves in a position similar to that in which the automobile industry is at the present time?”[745]

Of course, demand drives supply, and the availability of the raw mate­rial for making composite aerospace parts grew precipitously through­out the 1980s. For example, 2 years before Lovelace issued his warning to industry, U. S. manufacturers consumed 500,000 pounds of com­posites every 12 months, with the aerospace industry accounting for half of that amount.[746] Meanwhile, a single supplier for graphite fiber, Union Carbide, had already announced plans to increase annual out­put to 800,000 pounds by the end of 1981.[747] U. S. consumption would soon be driven by the automobile industry, which was also struggling
to keep up with the innovations of foreign competition, as much as by the aerospace industry throughout the 1980s.