AidSpace Blog

Horten H IX V3 “Bat-Wing Ship,” March 2014 Update

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Conservator Lauren Horelick, Post-Graduate Conservation Fellows Anna Weiss and Peter McElhinney, and retired treatment artisan Karl Heinzel continue to prepare the Horten jet wing to move to the Mary Baker Engen Restoration Hangar at the Steven F. Udvar-Hazy Center in Chantilly, VA. We have pushed back the Horten move to early spring in order to concentrate on finishing the Curtiss SB2C Helldiver by March 15.

Conservation is studying four different aspects of the materials used to build the jet: wood, adhesives, metals, and coatings. The conservators have found three types of wood. The outer skin is made of plywood of varying shapes and thicknesses and reinforced in some areas with laminated lumber supports. These supports also serve to affix the plywood skin to the metal structural framework. Artisans during World War II used lumber in the construction of the canopy rear section, and elsewhere such as the aft end of the center section and in the air brake assembly. The small blocks of wood that serve as ‘spacers’ between the plywood skin and the metal airframe represent a third wood type that the conservators characterize as birch based on preliminary analysis. These blocks appear to be layers of thinner veneers stacked and glued under pressure to the required thickness. In this blog update, we will look more closely at the plywood and examine the lumber supports, spacer blocks, metals, and coatings in future updates.


Plywood from the Horten

Here is a small sample cross section of plywood removed from beneath a metal engine cover near the front of the aircraft. The wood is in good condition and is representative of much of the wood used throughout the plywood skin. The cross section indicates the plywood in this area is made from sheets of 5-ply wood that artisans during World War II stacked and glued under pressure to create a wooden panel of the required thickness. Note the grey colored adhesive layer between each 5-ply layer. Conservators examined the sample and photographed it using a Hirox 3-D Digital Microscope. The veneer width and the number of plys used to make the individual plywood layers is consistent with the historical records, see Lacey, P.M.C., Rutherford, H.C., Pollard, G.J.T., Austin, J.B. 1945. Investigation of Targets connected with the German Plywood, Improved Wood, Shuttle Block, and Joinery Industries, British intelligence Objectives Sub-Committee Final Report No. 348. Image by Pete McElhinney.

Identifying the wood species used to produce the plywood proved more complex than originally anticipated. Conservators identify wood by using the microscope to compare features visible in the three different cuts (or planes) from a sample piece of wood- the cross-sectional plane, the radial plane, and tangential plane:



Diagram showing orientation of planes examined for wood identification. Illustration by Pete McElhinney.

The unknown sample is visually compared to known reference samples. Depending on the particular wood species, key diagnostic features, and visual patterns of diagnostic value are visible in each of the three planes described above.

With thin veneers as seen above in the first photo, the exposed surface area of the cross-sectional and radial planes available for analysis is quite small. Furthermore, the penetration of glue into the wood layer, and the pressure used to make the plywood can distort some of the microscopic features useful for species identification.

Identifying the plywood sample above started with the premise that the veneers most likely came from Common Birch (Betula pendula) or European Beech (Fagus sylvatica). Post-Graduate Fellow Pete McElhinney characterized the wood by processing the sample shown above to produce thin tangential sections of the individual veneers. He sliced thin sections through the 0.2 mm thin veneer ends and mounted the sections on a microscope slide.

We can see one of the main differences between the two species of Birch and Beech in the tangential plane. Ray cells are involved in moving materials within the woody stem, and variations in the number of cells comprising the width of the ray can aid species diagnosis. In Common Birch, the ray structures do not exceed four cells in width whereas in European Beech, the ray structure can measure up to twenty cells wide, see Schoch,W.,Heller,I.,Schweingruber, Wood anatomy of central European Species.

photomicrograph of plywood

Reflected light (light source in front of the specimen) photomicrograph of plywood sample. Arrows point to the ray cells in the dark areas of the sample. National Air and Space Museum Conservation photo.


photomicrograph of plywood

Transmitted light (light source behind the specimen) photomicrograph of plywood. The wide ray structure particularly clear on the left side of the image far exceeds the four-cell width of Common Birch, and is more consistent with European Beech. National Air and Space Museum Conservation photo.

European Beech

European Beech, note the wide ray structure. Photo from Schoch, W., Heller, I., Schweingruber, F.H., Kienast,F., 2004: Wood anatomy of central European Species. Online version:


Common Birch

Common Birch. The rays in this tangential section are much narrower than rays in the European Beech sample. Photo from Schoch, W., Heller, I., Schweingruber, F.H., Kienast, F., 2004: Wood anatomy of central European Species. Online version:

The gallery above illustrates the different ray widths of Common Birch and European Beech that implicate Beech (in combination with historical research) as the more likely wood used to produce the Horten IX V3 plywood panels.

Post-Graduate Conservation Fellows Anna Weiss and Peter McElhinney work in the Collections Department; Russ Lee is a curator in the Aeronautics Department of the National Air and Space Museum.

Twenty Years of GPS and Instrument Flight

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On February 16, 1994, a significant milestone in American aviation occurred when the Federal Aviation Administration certified the first GPS unit for use in IFR (Instrument Flight Rules) operations. Twenty years later, GPS has become the dominant form of en route navigation as well as the primary technology for guiding aircraft in low-visibility approaches to landing. The unit first certified twenty years ago was the Garmin GPS 155. Today, the prototype unit used in the certification trials is a featured artifact of the Time and Navigation exhibition.

Garmin GPS 155

The Garmin GPS 155 was the first unit certified for use in non-precision instrument approaches (FAA TSO-C129, Class A1 standard) NASM 2012-02110.

Most of us are familiar with how satellite navigation has made it easier to find our way in daily life, so it should be no surprise that pilots have benefitted more than most from the satellite navigation revolution. What may be surprising to many is the way it is changing aviation. Even though it is often in plain sight, the traditional electronic infrastructure of aviation is invisible to most people, who have no awareness of what they are seeing. However, VOR stations, glideslope shacks, localizer antennas, and radar arrays are obvious to those who know where to look. These systems are expensive to construct and difficult to maintain. They are also considerably less accurate than GPS and are range limited. While GPS has its own complex infrastructure, local operations require little in the way of additional equipment to enable very precise approach systems. By shifting from these 1950s era systems to GPS, many more airports are now open to low-visibility landings while airports with existing “blind landing” approaches now have more options that allow for better low-visibility guidance.


The VOR debuted shortly after World War II as America’s standard air navigation system. These ground-based, line-of sight beacons are now giving way to GPS-based systems.

By last fall, the GPS analog to the venerable ILS (Instrument Landing System), known as LPV (Localizer Performance with Vertical guidance), outnumbered the traditional precision approach system by a factor of two-to-one. Three thousand, three hundred forty one of these low-weather approaches were available at 1,650 airports. This means that towns in remote Alaska that depend on air travel for basic necessities are no longer separated from civilization by extended periods of poor weather. Business aircraft can reach many smaller airfields that were previously off limits in low-visibility conditions. Aviators also have access to a higher level of GPS performance than the typical dashboard GPS installation made possible through WAAS (Wide Area Augmentation System).

WAAS System

The WAAS system depends on the enhancement of GPS signals through a supplementary system of satellites and ground stations.

Most importantly, GPS is allowing greatly improved safety and efficiency in all aspects of air travel. Pilots are not simply receiving better navigational guidance. Under the old system of ground-based radio beacons and radar surveillance, navigation and air traffic control services varied widely by region. Air traffic was routed over networks of “airways” that meandered from one beacon or electronic “fix” to another. Air traffic control depended on radar to see the aircraft, but radar coverage has had many gaps and limitations. GPS is now allowing the untangling of this network of airway bottlenecks and filling in the gaps of radar coverage with a consistently accurate and precise capability.

Airway Map

VOR-based airways have been reliable, but they create inefficiencies and bottlenecks that GPS-based systems are better positioned to resolve. National Oceanic and Atmospheric Administration.

Not only do pilots and controllers now have better positioning, GPS also makes it much easier to share this data. The mechanism for sharing is something known as ADS-B (Automatic Dependent Surveillance – Broadcast). This bewildering acronym of a system is a transponder that can relay, and, in many cases, receive positioning and other critical flight data. With the old infrastructure (known as the “Common System”), data about aircraft movements was largely restricted to the individual controllers in communication with an aircraft. Pilots had to rely on the controllers for information about other air traffic. This inability to share information broadly could, and did, compromise safety in certain situations. Today, pilots, controllers, and virtually anyone else who wants to know, are far better informed. If you want to see how this plays out in real time, a number of third party vendors provide apps and other interfaces to see ADS-B data around the world. A decade ago it was science fiction to imagine that anyone could see exactly what a specific airliner was doing almost at that instant on the other side of the world (see it for yourself here).


ADS-B is the networking of air traffic data in entirely new ways.

The Federal Aviation Administration calls the transition from ground-based to satellite-based navigation and control services “NextGen.” Other benefits arising from the revolution launched by the Garmin GPS 155 include lower environmental impacts, improved traffic flow at busy airports,  and accommodation of weather diversions in dense air traffic environments. Also, the current demand for integration of unmanned aircraft into the national airspace systems is only technically possible with the flexibility of a system like NextGen. One area where the advantages of GPS might not be obvious is the use of something called RNP – Required Navigation Performance. This opaque acronym describes the ability to fly flight paths that are far more precise, which in turn allows much more efficient approach procedures into busy airports, reducing time in the air and air traffic delays. In simple terms, instrument approach paths previously required turns and other maneuvers guided by the intersection of radio beams. This created angles which, because airplanes cannot turn on a dime, required either an overshoot or undershoot. Air traffic controllers had to allow for both scenarios and accommodated them by blocking out large sections of airspace. GPS combined with modern flight management systems now allows aircraft to precise curved paths and eliminates much of the previous ambiguity. If this alphabet soup of acronyms is confusing, at least know that GPS is changing the way we fly – to make it more accessible, more affordable, more efficient, and safer.

Environmental Impacts:

Improved Traffic Flow:

Weather Diversions:

Roger Connor is a museum specialist in the Aeronautics Department at the National Air and Space Museum.

Robert A. “Bob” Hoover, The Greatest Stick and Rudder Man, is Honored in Hollywood

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On the evening of Friday, February 21, friends of legendary pilot Bob Hoover will gather with him at Paramount Studios Theater in Los Angeles to celebrate his “Lifetime of Achievement.”  We doubt this Red Carpet event will make Access Hollywood but of course that is not the point.  Instead, these friends will gather to honor an exceptional man with extraordinary flying skills and, hopefully, to hear Bob tell a few more of his incredible stories.

Bob Hoover

Bob Hoover always travels in style with a straw hat – this one is now displayed in a nearby case with his air show flight suit.

It was an earlier legendary pilot, General James “Jimmy” Doolittle, leader of the Doolittle Raid into China in World War II and of 1930s air racing fame, who anointed Bob Hoover as the greatest stick and rudder man who ever lived. It means he really knew how to handle an airplane and an acknowledgment such as this only happens when a real gift is discovered, honed, and played out over a lifetime. You can read about Bob’s career in his own book, Forever Flying, and in countless other chapters, essays and online links, including the National Air and Space Museum, and numerous Halls of Fame and military and honorary medal citations: self-taught aerobatic pilot who overcame air sickness; World War II fighter pilot and POW; military and civilian test pilot charged with flying propeller and first line jet aircraft beyond their limits; aerobatic, air racing, and air show pilot. These are the nuts and bolts of Bob’s career. The Distinguished Flying Cross is perhaps his highest military honor but that was only the start.  His career is the stuff of Hollywood legend and indeed there are at least two documentaries ready to spread the word.

Bob Hoover

As an 18-year-old Tennessee Air National Guardsman, Hoover trained as a tail gunner in Douglas O-38 observation craft.

Admittedly, many other skilled pilots have had remarkable careers so why is Bob Hoover so respected by his peers and beloved by the aviation community?  It is the combination of his extraordinary flying skills, a diverse and enduring aviation career, and his interest in and commitment to people of the aviation community.  Beyond the instructional and flight test efforts, beyond his practical knowledge of the art of flying and his intuitive aeronautical problem solving, is his genuine enthusiasm for his craft, his life, and people.

Bob loves to share his experiences with readers and live audiences as much as they love hearing him.  You are with him as he repeatedly attempts escape from a German prison camp, finally commandeers a Luftwaffe FW-190, and then realizes he must be the “dumbest Army Air Force pilot ever to be flying an enemy plane into Allied airspace.”  You are with him at the infamous test pilot watering hole, the Happy Bottom Riding Club near Muroc (later Edwards)Air Force Base, California. You are with him as he loses the chance of a lifetime — to become the first to fly the speed of sound. You are with him for “forty minutes of stark terror” in the cockpit of an out-of-control F-86 that he miraculously brings safely to ground. You are with him when his airmanship outshines the Soviets in Moscow and only the divine intervention of cosmonaut hero Yuri Gagarin saves him from Siberia. And you are with him when he gently convinces the notoriously crowd-adverse Charles Lindbergh to relax and enjoy himself with the Society of Experimental Test Pilots.

The respect that oozes from the public is palpable because he is telling stories about incredible success and tragedy, and he is telling stories on himself and his acquaintances.  He’s advising us all to do whatever it takes to accomplish our goals, including swapping paperwork or going around authority, but to do so in a purposeful manner.  He is not a saint.  He will give you an honest account of a person or situation; he does not have an agenda. Fighter pilots are known to be an arrogant bunch, but you won’t find that with Bob.  What you will find are determination, courage, self-inflicted wounds, compassion, and humor. Most of all, day after day, Bob Hoover is a true gentleman.

Shrike Commander

Flown by R.A. “Bob” Hoover for 20 years, N500RA is the most recognized Shrike Commander in the world. Hoover used his extensive test pilot and fighter pilot skills to become a legendary airshow pilot and brought a simple business aircraft to international attention.

The Museum is proud to display Bob’s last airshow aircraft, a stock North American Rockwell Shrike Commander 500S, in which he flew the final iteration of his trademark energy management routine, accomplished with two-, one-, and no-engine maneuvers.  You can look it up on You Tube where you will also find footage of him perfectly rolling his plane around its axis while pouring a glass of ice tea and not spilling a drop. Bob’s final flare of air-showmanship occurred in the fall of 2003 when he and his ferry pilot delivered the Shrike to the Museum’s Steven F. Udvar-Center in Virginia.  After his approved fly-by of the Hazy Center’s Donald Engen Tower, he taxied the aircraft up and, much to everyone’s surprise, directly into the north entrance of the Center.  Then Hoover, always the gentleman, calmly walked away after a distinguished career of test flights, crashes, performances, and perfect landings to airshow center. Bob, we join all your friends in saluting you!

Shrike Commander

After landing at Dulles Airport, Bob Hoover makes the final taxi in his Shrike Commander to the Udvar-Hazy Center, October 2003.

Dorothy Cochrane is a curator in the Aeronautics Department of the National Air and Space Museum.

Love is in the Air

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Aerial weddings may now be considered quite commonplace.  Just a quick online search turns up a number of places that provide skydiving services.  But in the nineteenth century, the idea of flying at all was still exciting.  Balloon weddings?  Those were spectacles!

Mary West Jenkins and Dr. John F. Boyton intended to be married on November 8, 1865, in Thaddeus Lowe’s balloon, high over New York City.  Reverend H.W. Beecher would not perform the ceremony in the air, so the vows were said on solid ground in the Fifth Avenue Hotel.  According to Harper’s Weekly, almost six thousand spectators crowded into Central Park to witness the married couple take flight.  The bride did not wear pure white; her dusky pink “ashes of roses” dress was “peculiar, to suit the exigencies of the occasion.”  The contract was signed in the air and after a “delightful trip,” the balloon “landed as gently as a snow-flake” in Mount Vernon, New York.

Jenkins-Boynton wedding

The Jenkins-Boynton wedding with aeronaut Thaddeus Lowe in Central Park. The wood engravings in Harper’s Weekly were based on photographs taken by famous photographer Mathew Brady. NASM 7A47488.

On October 19, 1874, Mary Elizabeth Walsh and Charles M. Colton said their vows in the balloon P.T. Barnum in the air over the Cincinnati, Ohio, Hippodrome—the first actual aerial wedding in America.  The wedding marked the 98th ascension of aeronaut Washington Harrison (W.H.) Donaldson. Details of the wedding were recorded by M.L. Amick in the fantastically titled book History of Donaldson’s Balloon Ascensions: Laughable Incidents, Frightful Accidents, Narrow Escapes, Thrilling Adventures, Bursted Balloons, Trapeze Performances, Mock Suns, Parasalenaes, Mirages, Paper Balloon Ascension, Passengers and Passengers’ Description of Cloud Land, etc.  Renowned showman (and employer of the bride and groom) P.T. Barnum and his brand new wife attended the ceremony, along with an estimated crowd of 50,000 spectators.

Walsh-Colton wedding

The Walsh-Colton wedding party with aeronaut W.H. Donaldson, October 19, 1874. Photographic copy of a wood engraving, based on original drawings by W.H. Donaldson, from History of Donaldson’s Balloon Ascensions. NASM 76-4448

The balloon initially held six people—Donaldson, bride and groom, attendants Anna Rosetta Yates and W.C. Comp, and the Rev. Howard B. Jefferies.  When it was determined that the basket could hold one more, David Thomas, “the best of ‘press agents,’” who had tirelessly promoted the event, “was taken in bouttainiere [sic] and all.”  The bridal party sent a parachute announcing the completion of the vows to the spectators below and the balloon continued its flight over Cincinnati, finally landing so that the couple could go to the cathedral for a second ceremony and the reception.

The Buckley-Davis Wedding

The Buckley-Davis wedding party with aeronaut James Allen, September 27, 1888. NASM 7A47391

Though not a Barnum production, the September 27, 1888, wedding of Margaret Buckley and Edward T. Davis also drew quite a crowd, as it was held at the Rhode Island State Fair at Narrangansett Park in Providence. An article in Frank Leslie’s Illustrated Newspaper estimates that 40,000 watched as Davis and Buckley entered the “specially prepared ‘bridal car’ of the mammoth balloon Commonwealth, held down by 24 men at the guy ropes.”  After the ceremony, aeronauts James Allen and his son James K. directed the balloon skyward.

The Buckley-Davis Wedding

The Buckley-Davis wedding party and aeronaut James Allen reenact their September 27, 1988, balloon wedding in a studio. NASM 2001-5327

The Davis’s honeymoon, or “bridal trip,” did get off to a bit of a rough start.  At dusk, the balloon landed in a swamp near Easton, Massachusetts, about thirty miles away from Providence.  The wedding party was “obliged to cling to the ropes above the basket to keep out of the water.”  Finally rescued, the balloon tied safely to a tree, the couple completed their trip by rail.  Afterwards, Allen and the Davises reenacted their wedding for a photographer in a studio.

Elizabeth Borja is an archivist at the National Air and Space Museum.

Double Word Score: CURATOR says YES

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It was not on Valentine’s Day, but love was in the air at the Udvar-Hazy Center on Veteran’s Day in 2005. Two and a half years into dating, my then-boyfriend Ben came up with a very creative and meaningful way to propose to me. He knew how proud I was of setting up our display of a Skylab era Scrabble board, and he used that as a starting point for linking my dedication to work with our acknowledged interest in a future together.

During installation of the small artifact display case in the human spaceflight exhibit area in the Space Hangar, I was on the ladder when it came time to install a magnetic Scrabble board and letters. To make it look interesting on the shelf, I placed the bag of letters on its side with particular letters spilled out: those that represented the Museum (N-A-S-M) and my department, Space History (D-S-H). I also placed letters spelling out three spaceflight-relevant words on the tile racks, which are there even today. Every time friends or family wanted to tour the building, I pointed out my little “inside joke.” Ben had heard the story dozens of times when he leveraged my attachment to that display to his advantage.

Unbeknownst to me, Ben contacted the object’s curator and my colleague, Valerie Neal, to see what she could do. Valerie put the wheels in motion and got the right people involved to complete Ben’s plan. On Veteran’s Day, under the guise of wasting some time before heading to a ski and snowboard exhibit at the Dulles Expo Center, we walked around the Museum for a bit. I thought the Museum visit was strange, but suspicions were raised when at one point I noted that his hand felt sweaty as I held it. Ben passed it off as moisture from his drink at McDonald’s. As we came around towards the center of the Space Hangar, ready to head out, I walked purposely to avoid going to the Scrabble display and telling the story again. Ben gently guided me in that direction anyway. As I got closer, I noticed the letters on the tile racks looked different, and actually started to get mad. The closer I got, the more I realized what the words now spelled out: “Jen will you marry me.” I stopped dead in my tracks, shook my head in disbelief, and holding Ben’s hand, walked slack jawed towards the case.

The story has a happy conclusion of course, and a humorous ending to the proposal itself. As he opened the ring box, which was hidden in a pocket of his pants for hours, the ring fell out and danced across the floor towards the rails that surround our major artifacts. My museum employee mind worried that we might have to get security to get the ring back, but thankfully, it was within our reach! The following September, we got married in front of friends and family, many of whom knew about this amazing proposal before I did.

So next time you’re at the Udvar-Hazy Center, think of my fantastically creative husband Ben when you look at that Scrabble board.

I said yes.

I said yes.

 Jennifer Levasseur is a museum specialist in the Space History Department at the National Air and Space Museum.