UPDATE # 4 - December 12, 1997
NEW WEB CHAT SCHEDULE TO BE ANNOUNCED NEXT WEEK
We are putting together a schedule of Web chats that will be held starting in January. Hopefully this will give classrooms plenty of time to plan to attend one of the upcoming chats. If teachers have suggestions as to the best times for chats we would appreciate hearing from you. Send email to firstname.lastname@example.org Remember our flexabilty is somewhat limited by our experts' schedules as well.
[Editor's Note: Larry is working on the Tilt Rotor Aeroacoustic Model project. He specializes in rotorcraft aeromechanics research. (that means the aerodynamics, dynamics and mechanical aspects of helicopters and tiltrotor aircraft.)]
Wind Tunnel Testing & Rotorcraft
by Larry Young December 11, 1997 Rotorcraft (helicopters and tiltrotor aircraft) are tested in low-speed wind tunnels (speeds roughly less than 350 miles per hour). Wind tunnels are generally classed in terms of their test section size and speed capability (usually in terms of four different speed regimes: low speed, transonic, supersonic, and hypersonic). The world's largest wind tunnel is a part of the low-speed 40-by-80 and 80-by-120 Foot National Full-scale Aerodynamics Complex (NFAC) at NASA Ames Research Center. The NFAC has been used to test many low-speed aircraft but, in particular, it is used to test rotorcraft and powered-lift aircraft (such as the Harrier jump-jet). Large- and full-scale rotorcraft can easily be tested in the NFAC. I work in and consider the NFAC 'home.' Wind tunnel testing is conducted for various reasons for -- and at different stages of -- an aerospace project. Testing can be conducted to study: fundamental aerodynamics and fluid mechanics; small-scale testing of complete, or partial, models to support preliminary design efforts for new aircraft; large- or full-scale testing of complete, or partial, wind tunnel models (or, sometimes, actual aircraft) to support aircraft production launch decisions or pre-flight risk reduction; and, even after an aircraft is flying, it sometimes desirable to perform wind tunnel tests of the aircraft -- or a key aircraft component -- to identify and correct problems observed in flight or improve the overall performance/capability of the aircraft. Rotorcraft researchers at NASA Ames Research Center conduct wind tunnel tests for all four general types of experimental investigation to support aircraft technology development. Rotorcraft researchers at Ames also are involved in the development of new analytical and computational prediction tools to model and improve the performance and flight characteristics of rotorcraft. A good engineer/scientist always tests their theory/predictions against high-quality data from well-thought-out experiments. I have personally conducted tests of small-scale models in small wind tunnels. I have also tested large-scale helicopter and tiltrotor models in large wind tunnels. Not all of these tests have been at wind tunnels at NASA Ames, though. I have also participated in, or supported, wind tunnel tests at NASA Langley Research Center, at Boeing Helicopter in Pennsylvania, and the Duits-Nederlandse-Windtunnel (DNW) in The Netherlands. Often times one wind tunnel has unique advantages over another tunnel for a given set of test objectives. Also, wind tunnel access is sometimes difficult to get and so a wind tunnel may be selected for a test on the basis of its availability. The planning, pre-test preparation, conduct, and post-test data reduction and analysis of data from rotorcraft wind tunnel tests takes a long time. This whole effort can range from a few months to several years. Rotorcraft researchers, wind tunnel test teams, and aerospace professionals in general, have to be very patient, dedicated, and persistent people. The TRAM project that I manage has been in existence for over seven years. I and the people and contractors that I manage or oversee had to design and build the TRAM models from scratch. This took a lot of time. It is only now that the initial wind tunnel testing has begun. This testing is currently underway in the DNW wind tunnel in The Netherlands. After this initial set of tests is complete the TRAM 1/4-scale wind tunnel model will be tested in the NFAC at NASA Ames. This follow-on testing will happen in a couple years. Safety is an important part of wind tunnel and rotorcraft testing. Test models and wind tunnels are very expensive facilities and great care has to be taken to insure that no damage is caused to these facilities during testing. And, always, care must be taken to insure that people are not put in harm's way. A typical rotorcraft test requires thousands of pages of documentation to be generated during test preparation phase -- most of this documentation is required to insure safety during the test. This documentation includes the test plan (defines the test objectives and the run "matrix"), the Operations Plan (it outlines how to operate and maintain the test model and the wind tunnel), the Design Analysis Report (contains design drawings and structural analyses to make sure the model can handle the expected loads during the test), as well as many other documents. All of this material is written and reviewed by several people. In the end, after successfully completing a test program, the project/test team can feel justifiably very proud of their efforts. The test results are studied and then reported in various types of formal reports including technical conference papers and NASA-distributed reports. Most NASA reports are openly available to the public. Industry engineers, or other researchers, use this information to plan new follow-on tests and/or use the current results to develop new -- or refine existing -- aerospace products. NASA engineers usually support multiple test/research programs at a given time. So as one test program comes to a close, the NASA engineer will quickly ramp up to work on one of the other programs he is on.
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