Flight test analysis of the forces and moments imparted on a B737-100 aircraft during wake vortex encounters

FLIGHT TEST ANALYSIS OF THE FORCES AND MOMENTS IMPARTED ON A B737-100AIRCRA]_ DURING WAKE VORTEX ENCOUNTERSChristopher L. RobertsDepartment of Mechanical EngineeringHoward UniversityD. D. Vicroy ÷NASA Langley Research CenterS.T. SmithHoward UniversityAbstractSeveral of our major airports are operating at or near their capacity limit, increasing congestion and delays fortravelers. As a result, the National Aeronautics and Space Administration (NASA) has been working in conjunctionwith the Federal Aviation Adminiswation (FAA), airline operators, and the airline industry to increase airportcapacity and safety. As more and more airplanes are placed into the terminal area the probability of encounteringwake turbulence is increased. The NASA Langley Research Center conducted a series of flight tests from 1995through 1997 to develop a wake encounter and wake-measurement data set with the accompanying atmosphericstate information. The purpose of this research is to use the data from those flights to compute the wake-inducedforced and moments exerted on the aircraR. The calculated forces and moments will then be compiled into adatabase that can be used by wake vortex researchers to compare with experimental and computational results.IntroductionAircraft travel has been a primary form oftransportation over the past four decades. Due toincreased air traffic, major airports are currentlyoperating at or near their capacity limit. This hastranslated into increased congestion and passengerdelay. As early as the 1950s, scientists haverecognized this as a potential problem and soughtmethods to alleviate this condition. Recently, theNational Aeronautics and Space Administration(NASA) has been working in conjunction with theFederal Aviation Administration (FAA), commercialairlines, and aircraft manufactures to increase airportcapacity and improve safety. Several solutions havebeen proposed. The most feasible method is toincrease the production per runway by decreasing theseparation distances between aircraft during takeoffsand landings during inamanent flight rules.Depending upon the flight airspace, weather,visibility,andtheaircraft'sdistancefromclouds,AirTraffic regulations require the pilots to fly undereither Visual flight rules (VFR) or Instrument flightrules(IFR). Under VFR, the pilots are responsible formaintaining safe separation distances. Under IFR,theAir TrafficControllers(ATC) areresponsibleformaintaining the separation distances mandated by theFAA [1]. When conditions require an airport tooperate under IFIL the airport capacity issignificantly diminished. This has led to speculationthat IFR separation may unnecessarily limit theoperating capacity of major airports.In order to decrease IFR separationdistances, it is necessary to address the issue of ahazardouswake encounter. Wake vortices, alsoknown as wing-tip vortices, are created when theairflow over the top surface of a wing meets theairflow over the top of the bottom wing surface. Theair flowing over the top surface of the wing flowinwards towards the wing centerline; whereas, the airflowing over the under-sm'face of the wing flowsoutward towards the wing's tip. When the twoairflows meet at the wing's trailing edge, they join atan angle creating clockwise and counter-clockwiserotating vortices.Vortices are created by all classes ofaircraft: Heavy (300,O001b or more), Large (between12,5001b and 300,O001b), and Small (less than12,5001b) [2]. When a following, lighter load aircraftencounters the wake from a heavy load aircraft, theaerodynamic load of the following aircraft isredistributed. This can result in a loss of control forthe lighter aircraft and is particularly hazardousduring rake-offs and landings. For this reason, theFAA has set specific longitudinal separation distanceguidelines to ensure that the following aircraft will+Aerospace Engineer, Vehicle Dynamics Branch, Senior Member AIAACopyright ©2000 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.