We Need a Vision for Wind Tunnels—Not Tunnel Vision

By Philip S. Antón

Philip Antón is a senior information and computer scientist at RAND.

Today, we take it for granted that we can fly—and fly safely. But it was not until 1871, when Frank Wenham built the world’s first wind tunnel, that scientists and engineers truly began controlled analysis and aeronautic prediction for the science of flight. Wind tunnels have since been among the most important tools of aeronautical research, playing an instrumental role in everything from the Wright brothers’ first flight at Kitty Hawk to the recent parachute landings of two Mars rovers.

Despite the demonstrated importance of wind tunnels, there is a growing belief that the nation no longer needs the wind-tunnel capacity it has built up over the decades. This belief is based on the view that the aeronautics industry has matured, production has tapered, and whatever needs we have for aeronautic prediction capabilities can be met through other means, such as sophisticated computer simulation technology.

There is an element of truth to these arguments. Aeronautics is relatively mature. When RAND researchers looked at design and production counts over the past five decades, they found that the number of new aircraft designs reaching production—both military and civilian—had declined from more than 50 in the 1950s to about 10 in the current decade. But this decline hides a more subtle point: No class of aeronautic vehicles (e.g., jetliners, fighters, bombers, or helicopters) has gone away, and the nation must continue to predict airflow behavior across a range of design considerations for each vehicle class.

Design and production needs are not the only considerations. Research continues to advance aeronautic performance, to reduce environmental effects, and to explore new system concepts. Numerous concepts for military and commercial aircraft, space systems, and missiles are in the pipeline through the year 2020, ensuring the need for aeronautic prediction capabilities into the future.

But perhaps most important of all are the strategic needs that are derived from long-term national goals and strategies, such as “national security” writ large. Do we, for example, want national security–related programs to depend on sources beyond our national control because we do not have the capability to conduct the programs ourselves? Anticipated strategic needs include everything from space access to commercial vehicles to military weapons.

To meet these needs, we have to rely on multiple test capabilities—subsonic, transonic, supersonic, hypersonic, hypersonic propulsion integration, and directconnect propulsion—in both general-purpose and specific-purpose categories. When RAND researchers assessed whether the existing capabilities in those categories were still needed, they found that, with only a few exceptions, the capabilities were needed for strategic reasons.

But does the nation really need wind tunnels to provide these capabilities? It is true that sophisticated computer simulation technology, like computational fluid dynamics (CFD), has made inroads in reducing some empirical test simulation needs. But CFD is not yet reliable for predicting the characteristics of the complex separated airflows that still dominate most critical design points for new and modified aircraft. Although CFD technology may become a comprehensive solution in the future, we will not realize that potential for decades. Moreover, attaining that potential will require, ironically, many precise wind-tunnel experiments. We cannot hope to replace wind tunnels down the road without maintaining high-quality wind tunnel testing facilities now.

With pressing budget concerns, it is tempting to abandon or to mothball wind tunnels as a way to make ends meet. But given the continuing importance of aeronautic vehicles and the critical role wind tunnels play in their creation, we need to make sure that our decisions are not shortsighted. We should not allow budget concerns to blind us to the national infrastructures that serve important national needs.

PHOTO CREDIT: DIANE BALDWIN