Air Force Memorial a Tribute to Flight and Engineering

Illustration of the Air Force Memorial by Arup's 3D Media Group - For The Washington Post (Illustration by Arup's 3D Media Group - For The Washington Post)

When architect James Ingo Freed set out to conceive a memorial for the Air Force, he faced a problem of weight and wisp: How to design a monumental structure that evokes that most structureless of mediums, the air itself?

Inspiration came while Freed was watching television. He happened upon footage of a team of Air Force jets performing the dramatic bomb-burst formation, in which several planes shoot skyward in unison and then peel off from each other, creating high-rising vapor trails that curl over at their tops.

Three years and more than $30 million later, stainless-steel versions of those tapering trails are rising on a promontory just west of the Pentagon. When the project is completed in September, three towering tendrils -- the tallest reaching almost 300 feet in the air -- will arc with spectacular grace into the wild blue yonder.

That these 17,000-ton fingers of glistening metal seem impervious to gravity is a tribute to Freed, who also designed Washington's Holocaust Museum. (He died in December.) But it is equally a tribute to a battalion of engineers who worked with the architect and his colleagues at Pei Cobb Freed & Partners to overcome not only gravity but also the treacherous forces of wind and vibration.

Early in the design process, it turns out, wind-tunnel tests revealed that those forces could send the silver spires into a series of oscillations that could lead to catastrophic failure. The solution involved an exotic trick of physics.

Hidden high inside those elegant metallic spires are 13 steel boxes -- a stack of six in the tallest spire, four in the next and three in the last, which, although it is the shortest, still rises 201 feet above the ground. The boxes are about 2 1/2 feet on each side, and each contains a single, free-rolling, metal ball that is 20 inches in diameter and weighs nearly a ton.

Those balls in boxes provide a unique energy-damping system that, although invisible to visitors, promises to keep the monument's swaying within tolerable limits well into the 22nd century.

Even seasoned construction workers say they are in awe of the novel design. "Ain't nobody ever worked on anything like this before," one sweaty worker recently exclaimed to a visitor with an apparent mix of exasperation and pride at the bustling site.

The memorial honors those who served in the Air Force and its predecessor services dating back to the U.S. Army Air Corps of the early 1900s, and it aims to inspire visitors by creating the illusion of escape from Earth's bonds.

That required keeping the trio of arching, hollow, triangular spires as narrow as possible. The largest starts as a triangle just 13 feet wide on each side at its base and tapers to two feet per side at its cantilevered tip, 270 feet in the air.

Adding to the sense of weightlessness, and in defiance of architectural convention, the spires are not weight-bearing skeletons clad in metallic skin. Each is just skin -- albeit three-quarter-inch-thick stainless-steel skin -- almost two-thirds filled with reinforced concrete.

Although the three stainless contrails bend radically outward, like bananas curving away from one another, each is in perfect equilibrium -- when there is no wind.