No abstract

No abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503 Wind or "rotorwash" generated by rotors, ducts, or jets effect the operational suitability and utility of future Vertical Takeoff and Landing (VTOL) aircraft. As the aircraft's physical size, weight, and disk loading increases beyond the range of current systems, the risk increases that rotorwash operational impact(s) may compromise an aircraft's ability to satisfy the Warfighter's needs. Early definition of anticipated rotorwash conditions will permit an assessment of operational suitability and determine whether specific design changes are warranted and/or if acceptable operational tactics, techniques, and procedures can be established. 1.AGENCY USE ONLY REPORT DATE July 2014 REPORT TYPE AND DATES COVERED Final TITLE AND SUBTITLE Rotorwash Operational Footprint Modeling FUNDING NUMBERS AUTHOR(S)JohnThis report documents the assessment process, environmental limits, rotorwash modeling, and output display supporting the rotorwash operational footprint model. These elements graphically combine to display the rotorwash operational impact assessment on the ground environment as contour plots or "footprints." The tools developed are for the single main rotor helicopter, tandem helicopter, and tiltrotor configurations, but they can be extended to encompass additional configurations. The rotorwash operational footprint displays the effect of winds generated by rotor thrust on the surrounding environment. These footprints can be used to evaluate compliance with aircraft performance specifications, verify safe separation distances, or inform design trade studies. Wind or "rotorwash" generated by rotors, ducts, or jets effect the operational suitability and utility of future Vertical Takeoff and Landing (VTOL) aircraft. As the aircraft's physical size, weight, and disk loading increases beyond the range of current systems, the risk increases that rotorwash operational impact(s) may compromise an aircraft's ability to satisfy the Warfighter's needs. Early definition of anticipated rotorwash conditions will permit an assessment of operational suitability and determine whether specific design changes are warranted and/or if acceptable operational tactics, techniques, and procedures can be established. SUBJECT TERMSThis report documents the assessment process, environmental limits, rotorwash modeling, and output display supporting the rotor...

The United States Army helicopter fleet experiences deformation of rotor blade contours from sand erosion and the implementation of technologies to protect against it. An investigation was performed to determine the effect of a typical erosion protection coating on the main rotor performance of a UH-60A Blackhawk utility helicopter. Computational fluid dynamics was used to calculate aerodynamic coefficients for representative coated airfoil sections. Hover analyses were performed to evaluate the impact of the coated airfoils on main rotor performance. The results show that airfoil erosion protection coatings can cause a decrease in the rotor's aerodynamic efficiency. Nomenclature= National Advisory Committee on Aeronautics R = rotor radius SLS = sea level standard atmospheric conditions X = airfoil ordinate in the chord-wise direction y + = dimensionless, sublayer-scaled, distance Z = airfoil ordinate normal to the chord  = angle of attack, deg  = rotor solidity

Results of an experimental investigation into the behavior of laminar jet diffusion flames, produced using micro-slot burner ports, are presented. Under certain conditions, the cross-sectional shape of micro-slot flames is qualitatively similar to the cross-sectional shape of circular burner port flames produced in an environment where molecular diffusion is the primary transport mechanism. An order of magnitude analysis reveals that, over the range of experimental conditions examined, the behavior of the experimentally observed micro-slot flames is not necessarily diffusion-controlled. A comparison of the experimental data with an accepted theoretical model shows that current theoretical models do not accurately predict the experimentally observed flame heights. A theoretical expression for purely diffusion-controlled micro-slot flame height is developed and compared with experimental micro-slot flame data. The region where this theoretical expression is valid is identified through an examination of the diffusion to buoyancy parameter. A qualitative discussion of micro-slot flame structure is also presented.