ZOFE takes the real-time measurements acquired during the flight test and applies a technique to extrapolate the aircraft’s flutter boundary, Chen explains, allowing designers to obtain essential information without potentially endangering the test aircraft or pilot.
ZOFE is in use by the U.S. Air Force for special projects for testing flutter suppression and innovating new kinds of air vehicles. Major aircraft manufacturers are also testing the product.
In the meantime, ZONA is developing an additional innovation in partnership with Dryden that promises potentially significant changes to flutter testing. Through SBIR contracts, ZONA created its Dry Wind Tunnel (DWT) technology for conducting ground flutter testing without a wind tunnel.
“A lot of wind tunnel data is suspect because of tunnel effects,” explains Brenner. Wind tunnels are not big enough to accommodate full-scale test aircraft, so smaller models of the aircraft have to be used instead. While these models still provide valuable aerodynamic information, Brenner says, “some parameters don’t scale up properly to a full-scale aircraft.”
ZONA’s DWT uses shaker devices to mimic the effects of aerodynamic forces on a full-scale wing or aircraft. The system’s software can calculate the aerodynamic forces and give that command to the shaker, which then applies that force to the true structure so engineers can record and observe the effects. The company claims that DWT can thus eliminate the uncertainties inherent in wind tunnel testing.
“DWT is more accurate,” says ZONA project manager Jennifer Scherr, “because you have all of the control surfaces included, you are not making a scaled-down version of the aircraft, and you don’t have the wind tunnel walls adding other variables to the mix.” The technology also helps eliminate significant costs. Chen notes that the wind tunnel flutter test for a recent new aircraft design cost about $3 million to fabricate the scaled-down model and around $50,000 a day for the wind tunnel testing.
“Flight flutter testing of a new or modified vehicle is very expensive and time consuming,” says Starr Ginn, Dryden’s aerostructures deputy branch chief and contract monitor for the Phase II Small Business Technology Transfer (STTR) project to develop the DWT. “It takes roughly 25 people to prepare the aircraft, a large staff in the control room, fuel costs for each flight, and time in-between flights to review the data. Using the DWT will help identify where the flutter sensitivity is on the ground, allowing for a reduced number of flutter test points.”
ZONA continues to work with Dryden to advance the DWT technology, and is planning testing on the AAW aircraft in 2011. The company’s NASA partnerships have been essential for its ability to innovate new technologies, says ZONA engineer and director of operations Darius Sarhaddi.
“Aeroelasticity is not something that everyone needs,” he explains. “This type of technology is very narrow. For our business, government partnership is very important.” It may be a specialized field, but the benefits of ZONA’s NASA partnerships—helping keep flutter confined to flags and seaweed—are very real.