USA — Wind Tunnel Explores Dynamics of High-Speed Flight

SILVER SPRING, Md., June 17, 2010 — Wind tun­nels, the tools used to sim­u­late air­speed envi­ron­ments to test flight capa­bil­i­ties, have come a long way since the Wright broth­ers built a box with fans to test a kite mod­el.

At the Air Force’s Arnold Engi­neer­ing Devel­op­ment Cen­ter White Oak site here, the breadth of that change is appar­ent. The orig­i­nal super­son­ic tun­nel, cre­at­ed by Wern­er von Braun and oth­er Ger­man sci­en­tists to test weapon aero­dy­nam­ics in World War II, sits in a lob­by a few yards away from its most-recent descen­dent, Hyper­ve­loc­i­ty Wind Tun­nel 9, which can pro­duce wind con­di­tions sim­u­lat­ing hyper­son­ic speeds, up to Mach 14.

Site direc­tor Dan Mar­ren said Tun­nel 9 is unique in the truest sense of the word: there are no wind tun­nels like it any­where else. The tun­nel uses a 200,000-cubic-foot, sev­en-sto­ry sphere as a vac­u­um on one end, and nitro­gen com­pressed to 30,000 pounds per square inch and heat­ed to 3,000 degrees Fahren­heit to cre­ate a pres­sure ratio of about 1 mil­lion, which is need­ed to cre­ate hyper­son­ic wind con­di­tions.

“Any­thing that goes fast will prob­a­bly come to us [for test­ing],” he said.

The tun­nel is rev­o­lu­tion­ary because of the amount of high qual­i­ty data it pro­duces, Mar­ren said. It can run two tests dai­ly, and record large amounts of data while mov­ing the mod­el dynam­i­cal­ly. Pri­or to its cre­ation, he not­ed, it might take two months to gath­er the data from a day’s work with Tun­nel Nine. It’s espe­cial­ly impor­tant, he added, because nei­ther the research nor the sci­en­tists involved can be repli­cat­ed.

“If you moved this [wind tun­nel] any­where in the world, you couldn’t use it unless you brought these peo­ple with it,” he said. “My staff is unique.”

A com­mer­cial air­lin­er gen­er­al­ly flies between 500 and 600 miles per hour – well below the super­son­ic thresh­old. A bul­let fired from a gun flies at Mach 2, twice the speed of sound. The SR-71 Black­bird, the fastest manned air­craft, trav­els just over Mach 3.

In Tun­nel 9, air trav­els near­ly 4,800 feet per sec­ond, well beyond human expe­ri­ence, Mar­ren said. A human could not sur­vive flight at that speed, he added, because the fric­tion would melt skin and tear a body apart.

“At these speeds, one wrong fac­tor can mean dis­as­ter,” Mar­ren said. “So we have to pre­scribe exact spec­i­fi­ca­tions based on our gath­ered data to make sure our peo­ple and equip­ment sur­vive at high speeds.”

Mar­ren said the test­ing here has been crit­i­cal to the devel­op­ment of mis­sile defense sys­tems that are cur­rent­ly being test­ed over the Pacif­ic Ocean, and in the devel­op­ment of a “prompt glob­al strike” sys­tem that would allow rapid response to emerg­ing threats glob­al­ly, either through satel­lite recon­nais­sance or weapons deliv­ery.

“The stuff we do is aimed to short­en a cam­paign, or elim­i­nate the need for it,” Mar­ren said. “If what we do can elim­i­nate the need to have a for­ward oper­at­ing base or to send peo­ple into harm’s way, we’re all about it.”

Among the devices that have been test­ed in Tun­nel 9 are the X-37B Orbital Test Vehi­cle, an unmanned space vehi­cle, and the Hyper­son­ic Tech­nol­o­gy Vehi­cle, a waverid­er-based unmanned hyper­son­ic vehi­cle that flies near­ly 500,000 feet above sea lev­el at the upper edge of the atmos­phere.

Marren’s crew tests the vehi­cles to ensure their equip­ment and pay­loads won’t be destroyed by the heat or pres­sure of air at hyper­son­ic speed.

“Once you do all of that, you have to come home,” Mar­ren said. “We cov­er the ‘come home’ part.”

Mark Lewis, the for­mer chief sci­en­tist for the Air Force and a pro­fes­sor of aero­space engi­neer­ing at the Uni­ver­si­ty of Mary­land, said the beau­ty of the test­ing done at White Oak is in the appli­ca­tion. He said hyper­son­ic flight gives the Air Force the capa­bil­i­ty to respond faster than ever before.

“Hyper­son­ics allow us to get more infor­ma­tion on a bad sit­u­a­tion before it becomes a full-blown bad sit­u­a­tion,” Lewis said. “If we need some­thing to be some­where, I can get there faster than any­one.”

Lewis added that the research pro­gram at White Oak is an excel­lent oppor­tu­ni­ty for stu­dents pur­su­ing degrees or a career in aero­space engi­neer­ing, and pro­vides an excel­lent envi­ron­ment to bring the­o­ries from aca­d­e­m­ic research to test­ing and eval­u­a­tion.

He said new ideas about how to use wind tun­nels to test con­cepts and the­o­ries have come from hav­ing aca­d­e­m­ic access to Tun­nel Nine, and the exper­i­ments per­formed there have vast­ly increased the sci­en­tif­ic community’s knowl­edge of high-speed flight and space access.

“What bet­ter way is there to get stu­dents inter­est­ed in this career?” Lewis said. “It’s the most amaz­ing moti­va­tor for stu­dents; to see the work they’re doing applied in real life and used by the mil­i­tary.”

U.S. Depart­ment of Defense
Office of the Assis­tant Sec­re­tary of Defense (Pub­lic Affairs)