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3 Technical Challenges in Wake Turbulence Research
Pages 29-59

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From page 29...
... However, the benefits of vortex alleviation can only be realized in the long term, and even then, only if a particular concept proves viable. If the threat cannot be eliminated, an improved spacing system can enable the next-best solution: Avoid the vortex or ensure that it can be tolerated.
From page 30...
... Supporting studies such as hazard boundary definition, system-level benefit studies, and the development of a system to gather data about wake events will be key to targeting research and eventually implementing solutions. Not only do they require the same supporting research, but alleviation and spacing also are not mutually exclusive -- the best possible system may include elements of each.
From page 31...
... Air traffic spacing system design, combined with progress in other technical challenges such as hazard boundary definition, wake modeling, wake visualization, and wake alleviation (both active and passive) , has the potential to offer capacity increases in the short term and in the long term.
From page 32...
... Any dynamic wake vortex spacing criteria must be applicable a very high percentage of the time. Without this attribute, capacity gains will be offset by the inability to maintain schedule integrity when it is necessary to revert to today's wake vortex spacing separation standards.
From page 33...
... The FAA, assisted by NASA, should continue its current improved spacing programs, which promise results in the short and medium terms. In addition to allowing increased usage of existing runways in IMC conditions, dynamic spacing for CSPAs may eventually support a reduction in the current wake-vortex-related runway separation standards of 3,400 ft for independent approaches (spacing needs to be maintained only between aircraft on the same approach path)
From page 34...
... Recommendation 3-4. The FAA should pursue work in the short and medium terms to determine minimum runway spacing for future airport expansion, which is needed to achieve capacity goals in the long term.
From page 35...
... The accuracy of the wake location prediction will depend primarily on the number and accuracy of the above parameters that are available for inputting to the real-time model. This model can determine the position in three dimensions of the wake danger zone for depiction by neighboring aircraft or air traffic controllers.
From page 36...
... . Most commercial aircraft now have a moving map display that could be used to display the wake danger zone associated with neighboring traffic within a certain altitude (e.g., 300 ft)
From page 37...
... . Vortex alleviation offers the potential to remove the vortex threat within a given distance of the generating aircraft.
From page 38...
... Implied in the assessment of vortex alleviation is a defined "hazard boundary" that can be used to judge if a given encounter is acceptable. The approaches to vortex alleviation can be grouped into two broad categories, one aimed at vortex modificationthat is, making vortices weaker or more diffuseand the other aimed at vortex breakupthat is, forming vortex rings.
From page 39...
... NASA's aeronautics program is well-aligned to conduct wake vortex alleviation work as medium- to long-term foundational research. TABLE 3-3  Milestones for Vortex Alleviation Time Horizon Milestone Short term High-level assessment of alleviation based on effectiveness and viability Multiple concepts explored Systems benefit studies conducted for best concepts Medium term Validation tests conducted for most viable concepts, at Reynolds numbers sufficient to represent an aircraft in flight, preferably via flight tests Assessment of performance under realistic atmospheric conditions for most viable concepts Long term Flight test conducted to demonstrate system effectiveness
From page 40...
... Thus, although forecasts of conditions that would move wake vortices out of the areas of concern could be available in the needed time frame, forecasts of wake decay probably could not be achieved without further funding for model development. European research has demonstrated some short-term forecast model capability at Frankfurt (Gerz, 2007)
From page 41...
... Federal wake turbulence research should engage the Weather Research and Forecasting model effort in order to identify the optimal set of weather parameters needed for predicting wake turbulence. Finding 3-9.
From page 42...
... Direct vortex measurement and detection can be used to supplement the vortex modeling for a dynamic spacing system, but the vortex models (in conjunction with local weather models) will determine how far in advance the airport capacity can be forecast.
From page 43...
... An indicator for how the uncertainty box grows with time as a function of different atmospheric conditions is needed to judge the utility of the predictions for a given application. The second challenge is understanding how the growth of uncertainties depends on the uncertainties in initial wake characteristics, and how this contributes to the scatter in typical flight data.
From page 44...
... TABLE 3-5  Milestones for Wake Vortex Modeling Time Horizon Milestone Short term Flight test requirements defined based on modeling needs Probabilistic model developed based on the state of the art Vortex uncertainties predicted for different weather conditions Medium term Flight test conducted (as necessary) to support/validate modeling Wake models evaluated using flight data Range of applicability estimated for models Models applied to support recategorization efforts Long term Models applied to support dynamic spacing system
From page 45...
... For instance, some sensors are used to measure aircraft wake vortices, and others are used to measure the meteorological conditions for inputs into the wake vortex and weather prediction models. In addition, there are two fundamental roles that wake measurement systems serve: • Sensors for real-time models are required to detect the presence of aircraft-generated vortices in a volume of interest, typically in the approach or departure corridor.
From page 46...
... of wake vortices and provide wake vortex modelers with the empirical data they need to validate their computational models. Laser Doppler velocimetry -- pulsed coherent and continuous wave lidar -- systems are able to detect and measure wake ­vortex characteristics from the ground.
From page 47...
... TABLE 3-6  Milestones for Wake Vortex Measurement Time Horizon Milestone Short term Complete feasibility studies to develop high-resolution, all weather wake vortex measurement system Develop functional requirements that are consistent with wake vortex modeling needs Medium term All-weather wake vortex measurement system Airborne wake vortex sensor Wake vortex measurement network Long term High-resolution, all-weather wake vortex measurement system High-resolution, all-weather wake vortex measurement network
From page 48...
... It is difficult to quantify acceptable reductions in wake turbulence spacing because there is no agreed metric for, nor definition of, hazard boundaries for wake encounters. Recommendation 3-11.
From page 49...
... Strategies implemented to reduce the capacity constraints brought about by wake turbulence must not compromise safety. Concepts such as dynamic aircraft spacing, which have been proposed as long-term solutions to achieve NextGen capacity goals, clearly require explicit definitions of hazard boundaries and acceptable levels of risk.
From page 50...
... must be completed with the annotation, "Wake Turbulence." The Supplemental Form is used only to report the reduced vertical separation minimums (RVSMs) in domestic airspace between 29,000 ft through 41,000 ft (flight
From page 51...
... This participation and communication will be crucial in gaining acceptance of any spacing modification as a result of the total wake turbulence research effort. Additionally, data collected in this effort could be utilized in establishing agreed-on metrics for defining hazard boundaries for the wake encounters.
From page 52...
... These factors will greatly affect the willingness to submit such data and their accuracy. Depending on the level of the data eventually obtained by this methodology, they could be used to correlate the operator input with detailed research data obtained from other elements of future wake turbulence research in the United States.
From page 53...
... If any degradation of safety were detected, separation requirements could be modified accordingly. Flight simulator training for wake vortex encounters could become part of a pilot's initial and recurrent training and could be modified in concert with any advances or changes in wake turbulence alleviation.
From page 54...
... For example, identifying the potential benefits of reduced aircraft spacings in different operational settings requires first determining the relative impact of different options that may be applicable only at certain airports or under certain weather conditions. A number of potential improvements in wake vortex separation efficiency could be realized in the short and medium term that have been identified by the FAA.
From page 55...
... Ultimately the goal is to consider capacity, environment, safety, security, and costs, although initial analysis has been limited to capacity and environment. Another example is a study conducted to determine whether runway occupancy time or in-trail separation on final approach due to wake vortex constraints is the most binding constraint on capacity for SFO.
From page 56...
... System-level studies are an essential element of a wake turbulence research program. They are basic to ensuring that (1)
From page 57...
... 2007. Wake vortex research in Europe, presentation to the Committee to Conduct an Independent Assessment of the Nation's Wake Turbulence Research and Develop ment Program, April 2, 2007, Washington, D.C.
From page 58...
... 2007. Modeling of atmospheric and ground effects on aircraft wake vortices, presentation to the Committee to Conduct an Independent Assessment of the Nation's ��������������������������������������������������������������� Wake Turbulence Research and Development Program, May 15, 2007, Washington, �������������������������� D.C.
From page 59...
... 2004. Real-time safety advising system in re duced wake vortex separations operation, in 2nd WakeNet2-Europe Workshop: ­Capacity Gains as a Function of Weather and Weather Prediction Capabilities, ­Langen.


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