Research at NASA's NFAC wind tunnels

NASA Technical Memorandum 102827

Research at NASA's

NFAC Wind Tunnels

H. Kipling Edenborough

June 1990 Ng0-Z_?33 (NASA-TM-IO?827) R_SFARCH AT NASA'S NFaC WI_NB TUNNELS (NASA) 9 p CSCt. O18 Uncles 0291O44 _3/ot National Aeronautics and Space Administration

NASATechnicalMemorandum102827

Research at NASA's

NFAC Wind Tunnels

H. Kipling Edenborough, Ames Research Center, Moffett Field, California June 1990 National Aeronautics and Space Administration Ames Research Center Moffett Field, California 94035-1000 ORIGINAL PAGE IS OF POOR QUALITY RESEARCH AT NASA'S NFAC WIND TUNNELS H. Kipling Edenborough Assistant Chief, Full-Scale Aerodynamics Research Division NASA Ames Research Center Moffett Field, CA USA ABSTRACT The National Full-Scale Aerodynamics Complex (NFAC) is a unique combination of wind tunnels that allow the testing of aerodynamic and dynamic models at full or large scale. It can even accommodate actual aircraft with their engines running. Maintaining full- scale Reynolds numbers and testing with surface irregu- larities, protuberances, and control surface gaps that either closely match the full-scale or indeed are those of the full-scale aircraft help produce test data that accu- rately predict what can be expected from future flight investigations. This complex has grown from the vener- able 40- by 80-Foot Wind Tunnel that has served for over 40 years helping researchers obtain data to better understand the aerodynamics of a wide range of aircraft Figure 1. National Full-Scale Aerodynamics Complex from helicopters to the Space Shuttle. A recent modifi- cation to the tunnel expanded its maximum speed Acoustic considerations were given high priority in capabilities, added a new 80- by 120-foot test section the new drive system design. Modern acoustics technol- and provided extensive acoustic treatment. The modifi- ogy was incorporated to reduce drive-system-generated cation is certain to make the NFAC an even more useful noise to extremely low levels. The test sections have facility for NASA's ongoing research activities. This also been acoustically treated, which allows detailed paper presents a brief background on the original facil- noise measurements to be made on the test vehicle ity and the kind of testing that has been accomplished during tests.

using it through the years. A summary of the modifica- tion project and the measured capabilities of the two Before the start of research testing, integrated sys- test sections is followed by a review of recent testing tems tests were conducted with the objective of check- activities and of research projected for the future.

ing operation of the NFAC and calibrating its perfor- mance. The wind tunnel meets or exceeds essentially all 1. |NTRODUCTION performance objectives. In the 40- by 80-foot section, the tunnel runs smoothly at its maximum test section The National Aerodynamics and Space Administra- speed of 300 knots (Mach 0.45). Throughout the operat- tion (NASA) has a wide assortment of wind tunnels.

ing envelope, the test-section dynamic pressure is uni- One of the most interesting and useful is the National form to within _+0.5%, the flow angularity is uniform to Full-Scale Aerodynamics Complex (NFAC) located at within t-0.5 °, and the axial component of turbulence is NASA's Ames Research Center, Moffett Field, Califor- generally less than 0.5%. The low-noise fans and nia. This tunnel, which is actually two tunnels in one, acoustic treatment have resulted in background noise has received considerable attention in the last 2 years as levels for this very large tunnel that are comparable to it has completed an extensive modification, including other (smaller) large-scale acoustic wind tunnels in the repowering, and the addition of a new, large 80- by United States and abroad. In the 80- by 120-foot sec- 120-foot test section. It compliments the original 40- by tion, flow quality in this nonreturn leg is equally good 80-foot section that has been in use since 1944. Figure 1 and is not greatly affected by external wind conditions shows the tunnel as it now exists.

at the inlet.

The original 40- by 80-foot test section maximum Research testing has been under way in the 40- by speed was 200 knots. That section can now be used for 80-foot section since the summer of 1987 and in the 80- tests up to 300 knots. The increase in speed greatly by 120-foot section since the summer of 1988. A wide expands the usefulness of the facility for high-speed scope of tests have been completed ranging from those STOVL aircraft research and for tilt-rotor and high- involving the tilt-rotor and conventional helicopter speed rotorcraft explorations. The 80- by 120-foot test rotors to test of a supersonic VSTOL fighter concept section maximum speed is 100 knots and is large and a parafoil advanced recovery system for rocket- enough to permit full-scale Reynolds number testing on launch-system recovery purposes. The NFAC has a large models, or testing of actual aircraft of the multiyear backlog of tests scheduled and promises to be Boeing 737 size.

ORIGtNAE PAGE BLACK AND WHITE PHOTOGRAPH a key element in many of the important research and development programs only now being envisioned.

z. ItAKKFBl.QI2.N_ The original 40- by 80-Foot Wind Tunnel was designed to accommodate all but the largest aircraft of the time. The facility covered 8 acres and had a circuit length of approximately 1/2 mile. Six 40-foot-diameter fans, each powered by a 6000-hp electric motor, gener- ated airflow up to a maximum test section speed of 200 knots. The construction project was started in 1941 and the tunnel went into operation in June, 1944.

Figure 3. Space Shuttle One-Third-Scale Model, 1976 The early years were spent on a variety of projects, many of which led to increasing the speed of the air- tests, some of which were also accomplished in this craft being tested by means of drag reduction. Wing- tunnel.

flap systems were modified and tested so as to lower the landing speeds and give the pilots better control. During the 1960s and 1970s the tunnel was used This tunnel became the primary facility for investigat- extensively for full-scale tests of helicopters and verti- ing the low-speed characteristics of full-scale aircraft cal and short takeoff and landing (V/STOL) aircraft.

during takeoff and landing. For V/STOL aircraft, special emphasis was placed on the transition from powered hft at low speeds to wing The 40- by 80-Foot Wind Tunnel contributed signif- lift at high speeds. Examples of the types of configura- icantly to jet aircraft stabihty and control systems in the tions tested are shown in Figures 4 and 5. A model of 1950s. Reducing the landing speed of jet aircraft greatly the upper-surface-blowing concept as incorporated in reduced the runway lengths required. the Quiet Short-Haul Research Aircraft (QSRA) is shown in Figure 4. The tih-rotor was extensively tested Testing of swept wings was also the subject of during this period. Following earlier tests of the XV-3 numerous tunnel entries. Even forward-swept wings and components of newer designs, the XV-15 shown in were included. Tests of high-speed supersonic transport Figure 5 was tested in the tunnel prior to its highly suc- configurations such as that shown in F_gure 2 added a cessful flight-test program.

great deal to the understanding of the aerodynamics of such configurations. During its design process the By 1980, the 40- by 80-Foot Tunnel had been used Space Shuttle (Figure 3) was tested in the tunnel at one- in over 550 tests involving several hundred aircraft and third scale. The landing phase of the Shuttle operation models. A wide range of configurations had been researched and much information had been added to was of obvious interest to the designers and pilots. This work was built on the foundation of many lifting-body aeronautical science as a result of investigations in this tunnel.

m m m Figure 4. Quiet Short-Haul Research Aircraft, 1977 Figure 2. NASA SCAT-15F, Supersonic Transport, OR!GINAL PAGE IS OF POOR QUALITY &\ I \\ \-, \\ / \,, .". j,',, </ ";/ Flaps Deflected Louvers Closed/ Vane Set / / ,, / / '_ / \ / _T..___.._2____.._ _ Vane Set _ /// //'Y Vane Set Open Air Exchange Door Vane Set Closed tO- by 80-Foot Test Section (a) 40- by 80-Foot Wind Tunnel

+

, _?_/,o,e, Figure 5. Tilt-Rotor Aircraft, XV-15, 1978 80 by 120-Fool _._'_ / 3. TUNNEL MODIFICATION Test Sect,on°_ L ...... Open/ Vane Set //_._/ Even though the 40- by 80-Foot Wind Tunnel was _,_.____ Vane Set_ / / / _ - one of the world's largest tunnels (a Soviet tunnel of '+e Se, approximately the same test section dimensions and a maximum speed of 135 knots had been built in 1938), ! i j the need for larger size and higher speeds had become , ,_._._" l "-r--r ....... J]]j obvious by the late 1960s. Emerging helicopter and I I i ]Jy ',-_",,.£ .... , .---,--, ......... %, V/STOL aircraft designs were targeted for larger size and higher speeds. To minimize tunnel-wall interfer- (b) 80- by 120-Foot Wind Tunnel ence and to test at conditions typical of full-scale flight aircraft Reynolds and Mach numbers, more capability Figure 6. NFAC Modes of Operations was required. In 1977 a decision was made to repower the tunnel and add a new, large, nonreturn test section to the facility. By increasing the total drive system power from 36,000 hp to 135,000 hp, 40- by 80-foot test-section speeds were projected to increase from 200 knots to 300 knots maximum. That same power level was expected to provide slightly more than 100 knots in the new 80- by 120-foot tunnel test section.

Figure 6 shows the facility in each of its two modes of operation. The old 40- by 80-Foot Wind Tunnel closed circuit remains essentially intact. A system of turning vanes and moveable louvers and a moveable set of exhaust louvers allows selection of operation with Figure 7.40- by 80-Foot Test Section Calibration, 1987 flow in either one or the other of the test sections at a time. By 1986 the modifications to the 40- by 80-Foot Wind Tunnel were completed. Integrated systems tests and flow calibrations were conducted, allowing the tun- nel to become fully operational in mid-1987. The 80- by 120-foot section became operational in 1988, after similar systems tests and flow calibrations.

Testing for flow quality as a part of the integrated systems test was completed in both test sections. The calibration instrumentation boom is shown installed in each of the test sections in Figures 7 and 8.

/ Figure 8. 80- by 120-Foot Test Section Calibration, ORIGINAE PAGE SLACK AND WHITE PHOTOGRAPH Thetestsection flowcharacteristics forbothsec- interactions could be measured. This test yielded exten- tions can besummarized as follows: sive data on download as effected by direction of rotor rotation and wing flap angle. The as-designed V-22 rotor direction was found to be optimal (reference 5).

• Speed uniform towithin_+0.25%

• Flowdirection uniform towithin _+0.5 °

Forward flight data obtained up to 220 knots were • Axialturbulence intensity typically <0.5% found to match predictions well with little effect from the wing. Plans have been made for a Phase II test up to

Inaddition tothese characteristics, it was found that

the full tunnel maximum of 300 knots following an forthe80-by 120-foot testsection, atmospheric winds upgrade in the rotor control system hardware.

donothave asignificant effect onflowquality.

A second major test involved the E-7A supersonic The careful attention thatwas given toacoustics in STOVL configuration shown in Figure 10, mounted in thedesign of thetunnel modification andtestsection the 40- by 80-Foot Wind Tunnel. This concept utilizes treatment paid off.The test section noise is 5 to10dB an ejector augmentor system and a variable-angle vec- lower, atequal airspeeds, than it was before the modifi- toring nozzle to provide lift and forward propulsion at cation. Themeasured noise levels ata given tunnel low speeds. The ejector system doors are closed for high-speed forward flight and the concept uses conven-

speed arecloseto thebackground levels of other

smaller tunnels used intheU.S. and abroad foracoustic

tional jet thrust and wing lift. These tests provided research. These good characteristics aresure tomake extensive data on ejector augmentation performance theNFAC ahighly useful tunnel foracoustics research. and combinations of direct jet thrust needed for transi- Details of themeasured flowquality andnoise levels tion to forward flight. Lift and draft polars for the high- areincluded inreferences 1-3.

speed mode were also obtained. The configuration appears to have considerable merit. Reference 6 pro- vides details of these tests.

4. RECENT R_SEARCH TESTING

As soon as possible after completion of the 40- by 80-Foot Tunnel flow calibration tests, research investi- gations were resumed. The first major test to be con- ducted was an investigation of tilt-rotor aerodynamics using a two-thirds-scale V-22 rotor and wing shown in Figure 9. The test had the dual purpose of measuring the wing download in the hover condition and of sub- stantiating rotor performance in the presence of a wing at high forward speeds. The download work was an extension to full scale of the research reported in refer- ence 4. By mounting the pressure-instrumented wing so that it was not connected to the rotor nacelle, and by Figure 10. E-7A STOVL Configuration in the 40- by having a sensitive rotor balance system, the rotor/wing 80-Foot Wind Tunnel, 1988 The latest test in the 40- by 80-Foot Wind Tunnel was conducted to explore helicopter main rotor and fuselage aerodynamic interactions. This test installation is shown in Figure 11. The rotor, which is a Bell 412, was mounted on the NFAC's Model 576 test stand that incorporates a 1500-hp electric drive motor. This stand allows fuselage body loads to be measured Figure 9. V-22 Tilt-Rotor Tests in the 40- by 80-Foot Figure 11. Helicopter Interactional Aerodynamics Test Wind Tunnel, 1987 in the 40- by 80-Foot Wind Tunnel, 1989 ORIGINAl.: PAGE BLACK AND WHITE PHOTOGRAPH independently from rotor loads through the use of load cells supporting the fuselage shell. The fuselage is represented by a very simple, pressure-instrumented teardrop shape. Smaller-scale model data have already been obtained to aid in this full-scale effort. During the testing a full set of rotor and body performance and loads data as well as acoustics data were obtained up to 0.3 advance ratio at 0.68 tip Mach number for rotor shaft angles ranging from -4 ° to -12 °. Future tests will explore higher advance ratios and will incorporate a separate tail rotor test stand to determine tail rotor inter- action effects.

Figure 13. Base Drag Test in the 80- by 120-Foot Wind The first model test in the 80- by 120- Foot Wind Tunnel, 1988 Tunnel was conducted in the summer of 1988 and involved investigations of two large (30- and 60-foot The drag reduction achieved by the boat-tail plates span) controllable parafoils. This was part of an Air was measured both by use of the tunnel balance and by Force-sponsored study to explore the usefulness of such the use of load cells on the aft flat end of the truck systems for recovery of spent booster rockets. Figure 12 trailer. A 10% reduction of overall drag was measured.

shows the larger parafoil during testing. The primary This corresponds to 500-1000 gal/yr of fuel savings for objectives of the test were to determine the basic aero- a typical truck or up to 1 billion gal/yr for the entire dynamics of the parafoils, their ability to flare for the U.S. fleet of tractor/trailers.

final touchdown, and control mechanism behavior.

Through the use of the tunnel balance and control line Currently, the E-7A is being tested in the 80- by load cells, the basic aerodynamics were measured. The 120-Foot Wind Tunnel. Figure 14 shows the test instal- flare maneuvers were successfully accomplished and lation. These tests are expected to yield valuable data information on the parafoil's behavior was gathered.

on the characteristics of such a configuration in the This testing, combined with drop-test data, has proved speed regime from 0-100 knots with reduced wall of great value to the project.

effects as compared to those of the 40- by 80-Foot Wind Tunnel. These data will also prove of great value in interpreting the aerodynamic characteristics as deter- mined using the 40- by 80-Foot Wind Tunnel in that same speed range.

Figure 12. Parafoil Tests in the 80- by 120-Foot Wind Tunnel, 1988 The second test conducted in the 80- by 120-Foot Wind Tunnel during its startup phase was a cooperative effort between NASA, the National Science Founda- tion, and industry. It involved obtaining detailed pres- Figure 14. E-7A in the 80- by 120-Foot Wind Tunnel, sure distribution measurements and flow-wake visual- ization behind a bluff body (in this case a truck trailer) and determining the effect of the boat-tail plates that 5. FUTURE RESEARCH AREAS can be seen in Figure 13. Although it is somewhat unusual for NASA to be involved with vehicle aerody- The NFAC maintains an approximately 2-year pro- namics, the opportunity to gather base drag information jection of planned tests that is constantly evaluated to for validation of CFD codes and to experiment with match test hardware and tunnel availability. Priority in, clever ways of reducing that drag has obvious value for the schedule sequence is based primarily on nationa)_ potential aerospace applications. The pressure data need and is also subject to continuing review. Some of obtained were very good, and excellent laser light sheet the planned future tests involve additional phases of the flow visualization was obtained of the wake flow. CFD tests described earlier. For example, the V-22 Tilt-Rotor comparisons are currently under way.

tests will be conducted up to tunnel maximum speed a,; mentioned. Future tilt-rotor exploration may involve a ORIGINAE PAGe' BLACK AND WHITE PHOTOGRAPH full-span model that isnowintheconceptual stage. The Acoustics-related testing is expected to become an interactional aerodynamics investigation isjustthestart increasingly important component of the NFAC's activities in the future. With the excellent acoustic char-

of a series of tests designed to explore themultiple

interactions of helicopter main and tailrotors and fuse- acteristics already built into the facility and with a lage shapes. A rotorteststand isin fabrication thatwill major acoustic treatment modification on the drawing facilitate thepowered testing oflarge rotors (>45-foot boards to further improve the 40- by 80-Foot Wind diameter) inprograms todetermine theiraerodynamic, Tunnel test section, the NFAC's unique position as a dynamic, andacoustic characteristics athighspeeds. prime large-scale acoustics facility is assured.

Other rotor programs will involve such areas asactive

control andindividual blade control.

As evidenced by the research that has been accom- plished since the tunnel modification, and as can be An interesting test now in the planning stages seen from the plans already in place for future projects, involves the use of an F- 18 aircraft to obtain flow-field the NASA Ames NFAC wind tunnels are a key element measurements, aerodynamic forces, and structural in the U.S. aeronautics capability.

response for the aircraft in conditions that are difficult REFERENCES or impossible to maintain in free flight. This is espe- cially true in very high angle of attack conditions such 1. Olson, Lawrence; Zell, Peter; Soderman, Paul; as depicted in Figure 15. In the tunnel, these conditions can be established and the flow studied, whereas in Falarski, Michael; Corsiglia, Victor;, and Edenborough, flight the condition is transient and very difficult to Kipling.: "Aerodynamic Flow Quality and Acoustic Characteristics of the 40- by 80-Foot Test Section Cir- study. For many of the effects of interest, such as fore- body flow, and vortex trajectory and bursting, it is cuit of the National Full-Scale Aerodynamic Complex," SAE Paper 872328, SAE Intern. Powered Lift Conf., important to test at a Reynolds number well beyond Santa Clara, CA, 1987.

critical. The use of an actual aircraft, rather than a sub- scale model, helps markedly in this regard. The use of 2. Zell, Peter; and Flack, Karen: "Performance and long-range laser velocimeter equipment to obtain off- Test Section Flow Characteristics of the National Full- body flow-field information should aid in the continu- ing process of understanding complex flows and of Scale Aerodynamics Complex 40- by 80-Foot Wind improving CFD codes through the correlation of predic- Tunnel," NASA TM 101065, 1989.

tions with experimental data.

3. Zell, Peter; and Gary Papenhagen: "Performance and Test Section Flow Characteristics of the National Full-Scale Aerodynamics Complex 80- by 120-Foot Wind Tunnel," NASA TM (to be published Fall 1989).

4. Felker, Fort: "A Review of Tilt Rotor Download Research," Presented at 14th European Rotorcraft Forum, Milan, Italy, Sept. 20-23, 1988.

5. Felker, Fort; Shinoda, Patrick; Heffernan, Ruth; and Sheehy, Hugh: "Wing Force, Moment and Pressure Data From a Hover Test of a 0.658-Scale V-22 Rotor and Wing," NASA TM (to be published Fall 1989).

6. Corsiglia, Victor; Farbridge, Joseph; Dudley, Michael; and Smith, Brian: "Large-Scale Wind Tunnel Tests of an Ejector-Lift STOVL Aircraft Model," Figure 15. F-18 Testing in the 80- by 120-Foot Wind AIAA 89-2905, AIAA/ASME/SAE/ASEE 25th Joint Tunnel Propulsion Conf., Monterey, CA, July 10-12, 1989.

ORIGINAU PAGE BLACK AND WHITE '_' t HOTOGRApN

Neton41 A_onau_s and Report Documentation Page

Sp4mc_ Admmi_abon 2. Government Acoession No.

1. Report No. 3. RecipJent's Catalog No.

NASA TM- 102827 4. Title and Subtitle 5. Report Date Research at NASA's NFAC Wind Tunnels June 1990 6. Performing Organizatmn Code 7. Author(s) 8. Performing Organization Report No A-90170 H. Kipling Edenborough 10 Work Unit No.

505-61-51 9. Performing Organization Name and Address 11. Contract or Grant No.

Ames Research Center Moffett Field, CA 94035-1000 13. Type of Report and Period Covered Technical Memorandum 12 Sponsoring Agency Name and Address National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, DC 20546-0001 15. Supplementary Notes Point of Contact: K. Edenborough, Ames Research Center, MS 247-3, Moffett Field, CA 94035-1000 (415) 604-5036 or FTS 464-5036 Presented at the International Session of the Japan Society for Aeronautical and Space Sciences (JSASS) 27th Aircraft Symposium, Oct. 18-19, 1989, Chikushi Campus of Kyushu Univ., Fukuoka, Japan.

16. Abstract The National Full-Scale Aerodynamics Complex (NFAC) is a unique combination of wind tunnels that allow the testing of aerodynamic and dynamic models at full or large scale. It can even accommodate actual aircraft with their engines running. Maintaining full-scale Reynolds numbers and testing with surface irregularities, protuberances, and control surface gaps that either closely match the full-scale or indeed are those of the full-scale aircraft help produce test data that accurately predict what can be expected from future flight investigations. This complex has grown from the venerable 40- by 80-Foot Wind Tunnel that has served for over 40 years helping researchers obtain data to better understand the aerodynamic s of a wide range of aircraft from helicopters to the Space Shuttle. A recent modification to the tunnel expanded its maximum speed capabilities, added a new 80- by 120-foot test section and provided extensive acoustic treatment. The modification is certain to make the NFAC an even more useful facility for NASA's ongoing research activities. This paper presents a brief background on the original facility and the kind of testing that has been accomplished using it through the years. A summary of the modification project and the measured capabilities of the two test sections is followed by a review of recent testing activities and of research__P_L0_cted for the future.

18. Distribution Statement 17. Key Words (Suggested by Author(s)) Unclassified-Unlimited Helicopter research, Tilt-rotor research, STOVL (Short takeoff, vetical landing) research, NFAC Subject Category - 01 (National Full-Scale Aerodynamics Complex) wind tunnel, Acoustic test facilities 19. Secudty Classif. (of this report) 20. Security Classif. (of this page) 21. No of Pages 22 Price Unclassified 10 A02 Unclassified NASA FORM 1626 OCT86 For sale by the National Technical Information Service, Springfield, Virginia 22161