Aerospace Team ONLINE
UPDATE #19 - April 17, 1998
PART 1: Upcoming Chats
Tuesday, April 21, 10:30 a.m.- 11:30 a.m. Pacific Time: David Picasso, Deputy Director of Aeronautics. David knows about all of the Aeronautics programs going on at Ames Research Center. Registration information is at http://quest.arc.nasa.gov/aero/chats/#chatting Read his biography prior to joining this chat. http://quest.arc.nasa.gov/aero/team/picasso.html Thursday, April 30, 1:00 p.m.- 2:00 p.m. Pacific Time: Estela Hernandez, Flight Simulation Engineer Estela is a flight simulation engineer. She uses math to build computer models that simulate flying airplanes. This chat will be in English and Spanish. Registration information is at http://quest.arc.nasa.gov/aero/chats/#chatting Read her biography prior to joining this chat. http://quest.arc.nasa.gov/aero/team/hernandez.html Monday May 4, 1998 9:00 a.m. to 10:00 a.m. George Kidwell, Deputy Director of R & D Services for Operations, George is responsible for directing the wind tunnel operations at Ames Research Center. There are three major national wind tunnel complexes at Ames, and each involves many skilled people, very large amounts of electrical power, a lot of high pressure and high speed air, and the need to run as quickly as possible while still maintaining safety and data accuracy. Registration information is at http://quest.arc.nasa.gov/aero/chats/#chatting Read his biography prior to joining this chat. http://quest.arc.nasa.gov/aero/team/kidwell.html
CONTEST ENTRY DEADLINE EXTENDED
As you know we are holding two contests: "Draw a Picture of an Airplane" and "Write an Essay Describing the Airplane You Would Like to Design", http://quest.arc.nasa.gov/aero/events/index.html We have received some wonderful entries to date. The spring break schedules caused several people to ask for extensions. The final deadline is now April 24, 1998. There will be no more extensions.
[Editor's Note: Steve Smith is an Aerospace Research Engineer. He spends one third of his time in wind tunnels and two thirds doing computational research. Read his bio at http://quest.arc.nasa.gov/aero/team/smith.html ]
by Steve Smith
February 18, 1998
This project is an effort to resolve a problem with two different sets of wind tunnel data for the same airplane, using computer flow simulations of the airplane model inside the tunnel and also flying in free air. Last year, I worked on a project to design a new, better winglet to put on the wing tips of the MD-11 jetliner. I got to test my winglets on a small wind tunnel model (4.7% scale) of the MD-11 in the Ames 12 foot wind tunnel. At the same time, I tested the original winglets so I could compare them. Later on, after the test was over, I got the idea that I should have tested the model with a standard wingtip ( no winglets) for comparison. It turned out that a bigger model (7.25% scale) of the MD-11 was going to be tested soon, so I arranged to make the comparison of the original winglet with a normal wingtip during that test. So now, I have one comparison on the small model, and one comparison on the big model. I want to combine the results so I can compare everything together. But the wind tunnel effects on the two models were different, and the comparison doesn't work well unless I can correct for this size difference. Effects of model size When air flows over an object, it can tell how big the object is by how long it takes to flow past it. To compensate for the difference in size, you can just make the flow go faster. This becomes a problem because the speed gets close to the speed of sound, and the flow is distorted by compressibility effects. It turns out that you can also compensate for the model size by changing the air density. The relationship of model size, flow speed, and density that is used to compare similar flows is called Reynolds number. Theoretically, the flow over two objects of different size is the same if the Reynolds number is the same. Wind tunnel results before corrections For the two different scale models that were tested, the tunnel conditions were adjusted so that the Reynolds number and the Mach number were the same. If the influence of the wind tunnel itself can be compensated for, both these models should produce the same force coefficients. Force coefficients are basically the forces divided by the wing area of the airplane model. It is customary to compare force coefficients instead of actual forces, because the basic effect of size (a bigger wing makes more lift) is compensated for. This correction is not the same as the more subtle effect of Reynolds number, which affects the details of the fluid motion. Without the tunnel wall effects corrections, a comparison of lift and drag characteristics for the two models showed about 20% difference in drag for the same lift. This is a huge difference! I hope the wall corrections will compensate enough to make the results for the two models the same, as they should. We will see!
[Editor's Note: Chris Sweeney is a Flight Simulation Engineer. He works at the Vertical Motion Simulator, the largest one in the world. Read his bio at: http://quest.arc.nasa.gov/aero/team/sweeney.html ]
THE BEGINNING OF THE HIGH SPEED CIVIL TRANSPORT SIMULATION
by Chris Sweeney
February 6, 1998
Our preparations for the two High Speed Civil Transport (HSCT) simulations have started. This year we will run back-to-back HSCT simulations beginning on June 1 and running through the end of July. The first simulation will study how a pilot will interact with the displays and controls on the flight deck. The second simulation will study more of the handling quality of the HSCT as well as some more display issues. The latest version of the "bare" airframe for the HSCT was just delivered. It takes up four full binders. This model is called the "bare" airframe because it does not have any of the computer controlled flight control system with it yet. The "bare" airframe shows how the aircraft will react if there were no computers onboard. It strictly displays the pure aerodynamics of the vehicle. We will start implementing this "bare" airframe immediately and receive the flight control system at a later date.
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