Blowing in the wind

Small tunnel yields good data quickly and economically

BY BOB HOWARD


Aerospace design engineers have to have good data—especially the kind they get from a wind tunnel. In fact, they won't leave the ground without it.

Even the Wright brothers used a wind tunnel to perfect their designs. Two years of initial research led the pair to abandon most aerodynamic notions of that day and build a wind tunnel to obtain their own data.

Tops-in-their-class Boeing designers are just as exacting. And increasingly, to gather good data quickly, they use a small and popular company wind tunnel, tucked away in Southern California, to do initial conceptualization. At the North American Aviation Research Tunnel, in Seal Beach, they get good data quickly and inexpensively as they create the country's next generation of air and reusable space vehicles.

Boeing Integrated Defense Systems Vice President of Engineering Thad Sandford certainly appreciates the value of NAART data. "This is exactly the type of tool needed," he said. "It is cheap, quick and very useful, with no personnel overhead."

Two significant Boeing programs that conducted early conceptual work in the NAART are the Unmanned Combat Air Vehicle and the X-31A VECTOR.

UCAV Aero Team Leader John Hoef Jr., explained, "This tunnel is certainly one of the reasons that we won the X-45A program. The NAART test results gave us the aerocredibility we needed to win the initial competition. It has been absolutely vital in our UCAV low-cost development efforts."

Much of its favor with users resides in the extreme operational simplicity, which gives minimal cost and one-person operation. Repeat customers generally rave about the fulfillment of their needs for accessibility, schedule flexibility, data accuracy and repeatability, as well as productivity and security.

The users have excellent results in matching up NAART data with what they obtain later in larger tunnels. The roster of past and present users is a veritable "who's who in aero design" of jetfighter, space-vehicle or hypersonic air- and space-vehicle programs.

Why is this tunnel becoming so popular with Boeing aerodynamicists? "We have an entrepreneurial attitude here. When someone needs something important to their program, we find a way to get it done," explained Pat Hayes, an advanced aero scientist in Huntington Beach, Calif., who both uses and manages the tunnel for Boeing.

"Because the tunnel is small, it is less complicated. So I can train in one day a single aerodynamicist or team to use it. This really keeps costs down," he noted. "We also have a machine shop on site for model modifications, and the facility can accommodate secure operations."

Researchers can easily repeat data from the NAART, which is just 48 feet long, in larger tunnels, in math models and in the computational fluid dynamics analysis programs that they will use later in the design process. Tests range from two weeks, which is typical, to one day, to one month, Hayes said. These tests usually support several design phases:

• Conceptual level trade studies make up 70 percent of the business. Here, designers sort through a wide variety of design options quickly.
  
  
• In configuration refinement, engineers optimize the baseline configuration. Some 20 to 25 percent of NAART customers use the tunnel accordingly.
  
  
• Finally, about 5 percent of users do what researchers call an aero dataset buildup. Here, their work generates a database for performance and flying-qualities simulation. The data lead to a computer flight simulator that helps engineers develop control systems.

Hayes likes to tell another success story of when X-31A VECTOR engineers performed a first-of-its-kind "powered test" in the tunnel. The idea was to simulate a jet exhaust close to the ground at high angles of attack, to investigate ground effects.

"Using NAART saved us dollars and substantially reduced risk on the X-31A VECTOR Program," explained Steven N. White, chief program engineer. "Normally, the cost of a test like this would be way too much for a small program like VECTOR."

They rigged the model with compressed air, which they blew through a high-fidelity nozzle mounted to the X-31A model, to simulate thrust pressures. Then, they built a floor that could move up and down, as if the stationary model was landing.

This work in NAART allowed the Boeing X-31A VECTOR team to successfully prove the craft could land on shorter runways or roads at 24 degrees, or twice its normal angle of attack, and touch down at only 121 knots, more than 30 percent slower than the normal landing speed.

The NAART helps engineers make initial discoveries quickly and inexpensively, much as Orville and Wilbur Wright did a century ago.

robert.howard@boeing.com