In the new Mary Baker Engen Restoration Hangar building at the Steven F. Udvar-Hazy Center, several artifacts at a time can be worked upon by the Museum staff of expert specialists, most of whom are certified airframe and power plant mechanics. Many learned their trades in the armed forces before joining the Smithsonian. While each knows the intricacies of working on contemporary aircraft, all have acquired additional skills and expertise from their on-the-job experience. No amount of formal training can teach all of the minutiae of working on a rare World War I wood-and-fabric biplane or an exotic Japanese floatplane bomber. These skills are acquired through years of experience and passed down to new technicians who join the staff when their elders retire. Far more than technicians, these men and women are true craftspeople, specializing in fabric, woodworking, painting, metal working, or a host of other skills. The results are impressive. With painstaking effort, NASM’s conservation staff has saved dozens of aircraft from the ravages of time and deterioration. Their task is a difficult one, eagerly carried out in a spirit of mutual respect, cooperation, and refined specialization.
Aircraft awaiting restoration in the Mary Baker Engen Restoration Hangar
An artifact enters the National Aeronautical Collection after careful consideration by the appropriate curatorial departments. The Aeronautics Division is responsible for deciding which aircraft are brought into the Museum, which ones are placed on loan, which ones go on exhibit, and which ones are removed from the collection. A careful system has evolved to consider every issue before the status of an aircraft is changed.
The acquisition of an aircraft begins with the appropriate curator among the eight currently in the Aeronautics Division. He or she weighs the merits of the acquisition, determines whether it will enhance the collection, and, if so, presents it to the Aeronautics Division’s collections committee. The committee, which consists of all eight curators plus the Division’s chairman, discusses the proposed acquisition based on the guidelines of the Aircraft Collections rationale, a detailed document that outlines the aircraft-collecting plan of the Museum.
Three criteria are used to determine whether or not an aircraft is suitable: historical, technological, and practical. The historical criterion is divided into five subcategories:
1. The aircraft is recognized as a milestone in aviation history, such as the 1903 Wright Flyer, the world’s first aircraft.
2. It represents an important, well-defined era or event in the evolution of aviation, such as Charles Lindbergh’s Ryan NYP, the Spirit of St. Louis, in which he flew solo across the Atlantic in 1927.
3. It represents political or social and cultural factors that have affected aeronautical history, such as the Concorde supersonic airliner.
4. It has had a continuing long-term effect on society and culture, such as the Boeing B-29 Enola Gay, which dropped the first nuclear bomb.
5. It has played a significant short-term role in shaping the course or outcome of a major historical event or era, such as many World War II aircraft
There are four technological criteria:
1. The aircraft represents a significant advance in aircraft performance, for example the experimental Bell X-1 that first broke the sound barrier.
2. It represents a significant advance in the application of technology to a specific aeronautical role, for example the classic Douglas DC-3 airliner.
3. It represents the development of aeronautical technology that has since been widely applied in other fields, for example the North American X-15. hypersonic research aircraft.
4. It represents political and economic factors that influenced the development and application of technology, for example many post-World War II military and civilian aircraft types.
Finally, there are four practical criteria that must also be considered:
1. The aircraft can be obtained, preserved, restored, and exhibited at a reasonable cost.
2. It can be transported to the Museum or to and from temporary storage.
3. It has research, scholarly, and/or educational value.
4. It meets the physical requirements for exhibition.
An extensive archival materials library and a large inventory of original components help ensure accurate preservation or restoration of aviation artifacts, a primary goal of the Museum
If approved by the Aeronautics Division’s committee, the responsible curator makes a formal presentation to the Museum’s official Collections Committee, which is comprised of the chairs of the curatorial departments, two representative curators, the Conservator, the Chief of Collections Management, and other interested parties. This committee weighs the same selection criteria and votes on whether or not to acquire the aircraft. If approved, the committee’s recommendation is forwarded up the chain of command to the director, who ultimately makes the final decision.
Once an aircraft enters the collection, it can no longer be treated as it was when it was in service; it is now an artifact. In the past, the most widely accepted technique was to restore an aircraft to its original factory-delivery condition. This produced beautiful aircraft in resplendent paint but often at the cost of originality. A thorough restoration that replaces numerous parts and strips the paint from the aircraft destroys much of the originality of the artifact. In some cases, for example when the aircraft is in dire condition, this is acceptable, but the desire today is to preserve the artifact as much as possible, for in this way the integrity of the original technology and history can be maintained. Ideally, when new aircraft are acquired, they will be placed in a proper physical environment that will forestall the effects of time and decay. As with any other artifact, objects must be handled as little as possible, whether it is a ruggedly-built aircraft or a fragile work of art. When that is not possible, the Museum must act.
The Museum’s Collections Management Policy details explicitly the Museum’s requirements and responsibilities regarding its artifacts. Preservation is foremost:
NASM is committed to the preservation of all its collections through (1) an active preventive conservation program, (2) the preservation, restoration, and treatment of specific artifacts, employing conservation principles, (3) the responsible exhibition, movement, cleaning, and handling of objects, (4) the provision of quality storage environments, and (5) complete documentation of object condition and treatment. Artifact treatments follow the American Institute for Conservation’s Code of Ethics and Standards of Practice to the degree practical.
The restoration process, when required, must also follow established policy. While the effort is always collegial, the roles and responsibilities of the individuals involved are clearly outlined and must follow established methods:
Artifact restorations are always historically accurate and reflect the technology original to that artifact. It is the combined responsibility of the curator (who takes the lead and has final decision-making authority), restoration foreman, restoration specialists, and conservator, to determine (1) the goals of a specific restoration, (2) the object’s final configuration, and (3) methods of treatment, with an emphasis on reversibility. Original components and materials are always used when available; they are preserved or returned to their original configuration. Repairs are made if necessary and marked as such. Complete documentation, including restoration log books, is maintained in the curatorial files; a summary of treatment given an object is filed in the appropriate accession file.
At work on the starboard wing of the Japanese Aichi Seiran bomber.
How an aircraft will appear after it is restored is also carefully thought out. Unless it is impossible to do so because the history of the particular aircraft is not known and the original markings have been removed, all aircraft must be restored to represent the event for which, or the operating regime in which, they are most well known. The re-marking of the aircraft must be as faithful to the original markings as practical. When presented with a choice, such as a U.S. Navy aircraft that carried several different variations of an approved paint scheme, the choice must be to present the aircraft in its most important scheme. For instance, if the aircraft has a significant combat history it should be painted in the markings in which it fought and not those in which it was delivered before seeing combat. There are cases when an aircraft is a generic type with an insignificant history. In this event, it is appropriate to paint the aircraft in a scheme that best represents the type while in service. It is not appropriate in this case to paint it in the markings of a specific, well-known example, such as the markings of a similar aircraft flown by an “ace.” That would be deceptive and misleading. Because the process is irreversible and damages the aircraft, the earlier policy of mounting a detailed identification plaque on the inside of restored aircraft is no longer appropriate.
When the project is completed, the restored aircraft is rarely flown. According to the Collections Management Policy:
While NASM’s artifacts may be returned to near-flight condition, they are rarely flown, and engines rarely run. NASM will not risk objects in the National Collections in flight demonstrations. Aircraft will only be flown if, in the judgment of the director, flight is the most practical method of movement.
These are the principles of artifact preservation and restoration that have guided the staff for many years and will continue to do so for the foreseeable future.
Aircraft are selected for restoration based on the condition of the aircraft and exhibit requirements. Some aircraft are in better shape than others. Those with the most pressing need for conservation are given preference because any artifact, whether made of metal or of wood, has a limited life, as the forces of decay are constantly and inexorably on the attack. The job of the Museum is to prolong that life for as long as possible, preferably for hundreds of years.
The Museum has developed a system to identify the level of treatment required by all the aircraft in the collection. Three different levels were determined and are applied. Level 1 requires the least care. These artifacts are either already restored or have been well preserved since their acquisition and need minimum care for exhibit. Those in Level 2 are in generally good shape as well, and require only minor work such as painting or repair before they are presentable. Those in Level 3, however, are quite different. These artifacts require a thorough treatment involving major disassembly to search for and arrest corrosion and to repair significant damage. Only then would a Level 3 artifact be suitable for display.
Restoration and conservation staff at the Garber Facility at work on various aircraft components.
One other important consideration is weighed before an aircraft is chosen for restoration. Because objects are brought into the collection so that they may be shared with the public, aircraft and other artifacts must eventually be prepared for display. When the Museum decides to create a new exhibit, the appropriate curator assumes the responsibility of selecting the artifacts and preparing the label script. If the artifacts require preservation or restoration treatment, they are placed ahead of other objects that may be in need of more thorough care but are not immediately required for display. Thus, the selection of artifacts for restoration is based on exhibit requirements as well as preservation needs.
To address these questions, members of the curatorial and collections management staff meet periodically to determine restoration priorities. The first step is for the curator to prepare a curatorial package that outlines the extent of the restoration and the appropriate final configuration of, for instance, an aircraft. These guidelines would also include a thorough history of the individual aircraft type and the specific history of the aircraft to be restored. In cooperation with the restoration staff, the appropriate restoration techniques are outlined to serve as a guide. The expertise of the craftsmen is essential, as they best know the correct techniques and materials suitable for the restoration procedures. Once these decisions have been made, the appropriate artifact is moved on to the shop floor and work begins.
The primary concern of the restoration specialist is to assess the condition of the artifact and address the extent to which time and exposure to the elements has caused deterioration. Intergranular corrosion of the aluminum alloys is a common problem, particularly with Japanese aircraft. As the composition of the alloy ages, it is gradually weakened, causing the metal to decompose from within. This is revealed when the aluminum alloy delaminates and flakes off. Surface corrosion occurs when the thin protective layer of pure aluminum is violated by a dent or scratch that exposes the more vulnerable alloy to the air. This often results in pitting which, if not too severe, can be treated with a simple protective coating. The repeated expansion and contraction of metal during the rigors of flight, such as wing flexing or repeated fuselage pressurization, can cause stress corrosion. Over time this weakens the metal and allows corrosion to enter along points of stress, particularly around rivets. The corrosion of steel—rust—is also a serious concern around landing gear and engine mounts.
Deterioration of organic materials such as wood and fabric is also a significant problem. When subjected to humid climates, these materials absorb water and become a breeding ground for fungus. The resulting rot destroys the cellulose that provides wood’s strength. Fungicides can eliminate the problem temporarily but the only long-term solution is to place these aircraft in a dry, climate-controlled environment to prevent a recurrence. Fortunately, if it cannot be salvaged, wood is easily repaired, using standard approved procedures. Only as a last resort will replica parts be fabricated. Then, as with metal parts, the object will be permanently marked as a replacement to prevent confusion and ensure authenticity in the future.
Restoration technicians are expert in fabric, metal, and wood fabrication.
Similarly, fabric, whether cotton or linen, is subject to degradation over time. Humidity and the resulting fungal growth can weaken fabric, but the worst culprit is light, particularly ultraviolet light, which can destroy the strength of a fabric. Currently, restoring fabric is difficult, if not impossible. If small repairs are no longer practical, as a last resort the Museum is forced to make the difficult decision to replace the fabric, as it did with the 1903 Wright Flyer and the Spad XIII. In each case, the fabric was severely damaged by light and humidity. Great care is then taken to find modern fabric that is as correct as possible in type, warp, woof, and thread count. The fabric is then remounted using the same stitching techniques as found on the original, and then treated with the appropriate dope at least twice to tighten the fabric Subsequent coats are used to apply the correct color. Antifungal chemicals are also applied.
The old fabric is not disposed of because it is an important part of the aircraft’s history and can serve as a model for replicating similar fabric in future restorations. It also preserves the original markings and stitching, which are important for future historians and restorers to study. Therefore, the original fabric is carefully mounted on acid-free backing and placed in environmentally-friendly storage for long-term preservation.
Other materials pose unique problems of their own. Since the Second World War, more and more parts have been made with plastics, particularly Plexiglas aircraft canopies. Plastics are subject to the development of minute cracks called “crazing” and can also develop clouding, turning opaque. Careful polishing can reduce the severity of these problems but unfortunately cannot eliminate them. Rubber is similarly difficult to work with; both ozone in the atmosphere and ultraviolet light cause rubber to dry and harden. The opposite can also happen: Rubber can revert to a liquid and flow slowly as it permanently deforms. Once that happens, nothing can be done to restore it. This is true for tires, hoses, and other fittings. Long-term preservation problems presented by the exotic new materials being used increasingly in aircraft and particularly in spacecraft are yet unknown. In this case, proper preservation in a benign environment is the only practical solution.
When preservation or restoration cannot replace a damaged or missing part, the Museum must attempt to locate its suitable replacement. Through the many personal and professional contacts of all involved staff members, as well as advertisements placed in appropriate trade journals and thorough internet searches, even the most obscure part can often be located. As a last resort, the highly trained specialists at the Garber Facility are able to fabricate virtually any part that is required.
A British World War II Hawker Hurricane sits next to a French Nieuport 28 from World War I, both restoration works in progress at the now-closed Garber Facility restoration shop.
The complex treatment given to the famous Boeing B-29A Enola Gay well illustrates many of these complicated issues. On August 6, 1945, this massive, long-range strategic bomber dropped the first atomic weapon, destroying the Japanese city of Hiroshima and thus hastening the end of the Second World War. It entered the NASM collection on July 3, 1949, when Colonel Paul Tibbetts, commander of the 509th Composite Group and pilot of the Enola Gay, flew it to Orchard Place Army Air Field near Chicago. When the Smithsonian was evicted from its Park Ridge location, the Air Force flew it first to Pyote Air Force Base, Texas, early in 1952 and eventually to Andrews Air Force Base near Washington, D.C., on December 3, 1953. It remained at Andrews until 1961 when space was finally made available at Silver Hill, just a few miles down the road.
Despite its historical importance, the Enola Gay languished until December 5, 1984, because of its size. The mighty bomber was then carefully retrieved from storage for its restoration. It is the largest restoration project ever undertaken by the Museum. Large though the restoration shop may have been, it was far too small for a B-29. This single artifact most clearly demonstrates the need for the new restoration shop that will eventually be built at the Udvar-Hazy Center.
Already in parts, the Enola Gay was moved through the shop piecemeal, with the forward fuselage and cockpit receiving priority. Though the aircraft had been stored outside for much of its life, it had fortunately not suffered too severely from exposure. The forward fuselage was in remarkably good condition, although some instruments were missing.
To determine the level of corrosion that needed to be treated, the aircraft was first cleaned. In the past, most of the aircraft would have been disassembled, treated, and rebuilt, but because of the Enola Gay’s large size and improved restoration techniques, the aircraft was disassembled only as far as necessary. Careful examination, using borescopes and other instruments, allowed the technicians to perform equally effective but less invasive procedures.
To prevent damaging the artifact while searching for corrosion, the disassembly was limited to the wings, control surfaces, engines, and turrets. The wing proved a particular challenge because, in addition to the nests and debris left by birds and other animals, it was attached directly through the fuselage. Removing the carry-through wing required the staff to take off the surrounding sheet metal and a series of massive, tapered bolts, a difficult and time-consuming task. Inside the fuselage, the quilted insulation was found to be in tatters from the ravages of mice and was not salvageable. Instead, the craftsmen fabricated new linings and padding using the old material as a pattern.
Expert knowledge and craftsmanship are required for working with aircraft materials. Every effort is made to preserve originality.
Consulting technical manuals borrowed from the Museum’s extensive archival collection, NASM’s craftsmen carefully inspected and treated every section of the massive bomber. The manuals were especially helpful in locating the proper location and direction of the B-29’s intricate wiring and plumbing systems. Some parts of the aircraft, such as the astrocompass, were in such poor condition that a better example was retrieved from the Museum’s large parts inventory and installed in place of the damaged article.
During reconstruction of the fuselage and wings, mechanics worked on the aircraft’s powerful Wright R-3350 engines. Two of the engines were refurbished on the shop floor of Building 10. All told, the responsible craftsman spent more than 6,000 hours over many years on these two engines. Expert technicians at the San Diego Aerospace Museum restored the other two. NASM has often allowed other qualified museums to perform restorations, on condition that they meet our exacting standards. This is ensured through a restoration contract that all participating museums must honor. The results are worth the effort. San Diego delivered two immaculately restored engines.
Every available personnel resource was used to restore the Enola Gay. In addition to highly trained staff members from NASM and the San Diego Aerospace Museum, summer interns enrolled in college airframe and power plant courses learned proper preservation techniques under careful guidance while restoring the Curtiss Electric reversible-pitch propellers. Other interns tackled the difficult restoration of the aircraft’s radar systems.
Proving their mettle once again, the specialists at the Garber Facility discovered that the aircraft was no longer equipped with the proper bomb shackle used on its historic mission on August 6, 1945. The correct shackle was located through a convoluted but typical set of serendipitous circumstances. A visiting U.S. Air Force captain learned of the missing shackle and informed the Museum staff that he believed that the original plans still existed at the Sandia Laboratories in New Mexico, near Los Alamos, where the first atomic bombs were developed. Further inquiries revealed that the British had developed the shackles, and that they were still in use by the Royal Air Force five decades later. Correct shackles were installed with accompanying supports built from scratch at the Museum.
As the 50th anniversary of the end of the Second World War approached, the Museum stepped up the Enola Gay restoration. Though the entire aircraft was not completed in time, the forward fuselage, engines, and tail section were. This was sufficient to create an exhibit that was more than adequate for the millions of visitors who were eager to see this historic aircraft.
After many grueling hours polishing the bare aluminum of the bomber, it was almost ready for display. The only question that remained concerned the final appearance of the aircraft. The Museum strives to preserve the accuracy, integrity, and originality of all of its artifacts. When the Museum accepted this special B-29 into the collection, it still bore some of the markings of its last mission, flown well after the Hiroshima raid. As these markings were an integral part of the aircraft’s history, it would have been inappropriate to destroy the originality of the aircraft’s markings just to recreate its appearance during one flight, no matter how significant that flight was. After much consultation, the team of curators and restoration specialists agreed to preserve the markings of the Enola Gay as it was when it flew its war-ending mission.
Normally, microcrystalline wax is used to preserve the original aircraft markings. In this case, because the markings of the Enola Gay had been reapplied several times during its Air Force career and were no longer original, it was decided to forgo the wax. All of the markings were carefully photographed and meticulously traced in order on marking paper. The paint was then removed and the aircraft polished to its stunning, gleaming finish. Using the photographs and tracings, the markings were then carefully reapplied and the aircraft prepared for exhibit.
The restoration of the Enola Gay was completed in time for its move and installation at the Udvar-Hazy Center. It is a fine example of the restoration technicians’ craft and the multidisciplinary work from all corners of the Museum that goes into every project of this kind. The Enola Gay represents most of the methods and procedures that have been developed over the years, and will continue and develop well into the future. The final assembly of the divergent parts of this historic bomber took place only when it was moved into its new and final home at the Museum’s new Steven F. Udvar-Hazy Center near Washington Dulles International Airport.
The Enola Gay and the other remarkable aircraft, almost all of which shared space at the cramped Garber Facility, cover the entire scale and scope of aviation’s history. It is a comprehensive collection that has a new home where millions of visitors are able to view many significant aircraft that changed the course of history. Moved from Garber, recalled from loan to other museums, and retrieved from desert storage, these aircraft are now available for all to see. Their story is that of the National Air and Space Museum and of the central role in aviation played by the manufacturers and operators, military and commercial, private and executive, experimental and sporting, and principally of the United States of America.
The restored Boeing B-29 Enola Gay being lifted into place during its installation at the Udvar-Hazy Center.