NATURAL LAMINAR FLOW AIRFOIL ANALYSIS AND TRADE STUDIES NASA

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This document constitutes the finai report for the 4 1 1 and 4 1 2 portions of Task 4 1. Natural Laminar Flow NLF one of five major tasks covered by the Statement of Work. for Contract NAS1 14742 The report covers work conducted from August 1977 through. June 1978 The NASA Technical Monitor for all contract tasks was Mr D B Middleton. of the Energy Efficient Transport Project Office at Langley Research Center. The investigations were conducted within the Preliminary Design Department of the Vice. President Engineering Organization of The Boeing Commercial Airplane Company. Contractor personnel who participated and their areas of contribution are. G W Hanks Program Manager,C W Clay Task Manager Airfoil and Trade Studies. G R Swinford Configuration,T C Versteegh Airfoil Design. R L Sullivan Aero Performance,3 A Paulson Low Speed Aerodynamics. R N Gornstein High Speed Aerodynamics,K H Hartz Weights. M D Taylor Stability and Control,V D Bess Structures.
A C Wery Loads,C R Pratt Barlow Flutter, Principal measurements and calculations used during this study were in customary units. PRECEDING PAGE BUNK NOT FILMED,1 0 SUMMARY 1,2 0 INTRODUCTION 7. 3 0 SYMBOLS AND ABBREVIATIONS 9,4 0 NLF AIRFOIL AND WING DESIGN 15. 4 1 Airfoil Design Sequence and Procedure 15,4 2 Airfoil Design Evolution 19. 4 2 1 Starting Airfoil Airfoil 1 19,4 2 2 Design Modifications Airfoils 2 3 and 4 22.
4 2 3 Final Airfoil Airfoil 5 26, 4 3 Airfoil 5 Boundary Layer Stability Analysis 29. 4 4 Wing Geometry Selection 30,5 0 AIRCRAFT DESIGN TRADE STUDY 35. 5 1 Trade Study Methods 35,5 2 Trade Study Airplanes 35. 5 2 1 Turbulent Reference Airplane Configuration 35. 5 2 2 N L F Airplane Configurations 38,5 2 3 NLF Wing Structure Design and Analysis 41. 5 3 Airplane Sizing a n d Performance 62,5 3 1 Sizing a n d Performance 64.
5 3 2 Sensitivity Study 67,5 3 3 Mission Analysis 69. 5 3 4 Turbulent Reference and NLF AR10 24,Airplane Mission Analysis Comparison 70. 5 4 Economic Study 71,5 5 Trade Study Results 71,6 0 CONCLUSIONS AND RECOMMENDATIONS 73. 6 1 NLF Airfoil and Wing Design 73,6 1 1 Conclusions 73. 6 1 2 Recommendations 73,6 2 Aircraft Design Trade Study 74.
6 2 1 Conclusions 74,6 2 2 Recommendations 74,7 0 REFERENCES 77. 1 N L F Airfoil Design Criteria 16,2 Airfoil Design Sequence 17. 3 Boundary Layer Stability Analysis Method 18, 4 Airfoil 1 Pressure Distribution a n d Contour 19. 5 Airfoil 1 Pressure Distributions M 0 76 20,6 Airfoil 1 Pressure Distributions M 0 78 20. 7 Airfoil 1 Pressure Distributions M 0 80 21, 8 Airfoil 1 Effect on Mach Number on Pressure Distribution 21.
9 Airfoil 1 Application Boundaries 22, 10 Pressure Distribution Comparison Airfoils 1 and 2 22. 11 Pressure Distribution Comparison Airfoils 1 and 3 23. 12 Lower Surface Pressure Distribution Comparison,Airfoils 3 a n d 4 23. 13 Application Boundary Comparison Airfoils 1 and 4 24. 14 Airfoil 4 Pressure Distributions 25, 15 Pressure Distribution Comparison Airfoils 4 and 5 26. 16 Airfoil 5 Lift Curve 27,17 Airfoil 5 Application Boundaries 27. 18 Airfoil 5 Upper Surface Boundary Layer,Transition Prediction 29.
19 Airfoil 5 Lower Surface Boundary Layer,Transition Prediction Disturbance 30. 20 Effect of Pressure Distribution,o n Disturbance Amplification 31. 21 Effect o f Sweep o n Transition Location 32, 22 NLF Airplane Wing Spanwise t cHldX Distribution 33. 23 Cruise Spanload Distribution 34,24 Design Development Method a n d Sequence 36. 25 Reference Tubulent Airplane General Arrangement 37. 26 Reference NLF AR10 24 Airplane General Arrangement 38. 27 Reference NLF AR12 Airplane General Arrangement 39. 28 NLF Wing Structural Concept 42,29 NLF AR10 24 Wing Aerodynamic Panels 43.
30 NLF AR12 Wing Aerodynamic Panels 43, 31 Wing Stiffness Distribution Aspect Ratio 10 24 44. 32 Wing Stiffness Distribution Aspect Ratio 12 0 44. 33 Wing Box Skin Panel 45,34 Tail Off Lift Curve Slope Comparison 46. 35 Structural Design Airspeed Comparison 46, 36 Wing Lift Distribution Comparison in Terms of eg 47. 37 Wing Lift Distribution Comparison in Terms of CgC 47. 38 Wing Design Bending Moments at Elastic Axis Comparison 48. 39 Maneuver Critical Positive Gust Bending Moment Comparison 48. 40 Wing Maximum Thickness Comparison 49,41 NLF AR10 24 Airplane Gust Response at. Maximum Zero Fuel Weight 50,42 NLF AR12 Airplane Gust Response at.
Maximum Zero Fuel Weight 50,43 Airplane Gust Response Comparison 51. 44 N L F Airplane Horizontal Tail Sizing Selection 55. 45 N L F Airplane Flap System Geometry 56, 46 Reference Airplane Low Speed Characteristics 57. 47 NLF AR10 24 Airplane Low Speed Characteristics 58. 48 NLF AR12 Airplane Low Speed Characteristics 59, 49 NLF AR10 24 Airplane Drag Characteristics Summary 60. 50 NLF AR10 24 Airplane Drag Polar 61, 51 NLF AR12 Airplane Drag Characteristics Summary 61. 52 NLF AR12 Airplane Drag Polar 62,53 Reference Airplane Design Selection Chart 64.
54 NLF AR10 24 Airplane Design Selection Chart 66,55 NLF AR12 Airplane Design Selection Chart 66. 56 Wing Loading Trade Study 67, 57 NLF AR 10 24 Airplane Sensitivity to Change in Selected. Airplane Characteristics 68,58 NLF Final Airplane General Arrangement 69. 59 N F Final Airplane Mission Profile 70, 60 Optimized Pressure Distribution Characteristics 75. PRECEDING PAGE BLANK NOT FILMED,J Airfoil Evolution 19.
2 Airfoil 5 Geometric Definition 28,3 Reference Airplane Principal Characteristics 37. 4 Reference NLF AR10 24 Airplane Principal Characteristics 39. 5 Reference NLF AR12 Airplane Principal Characteristics 40. 6 N L F Wing Structure Material Allowables 41, 7 Airplane Characteristics Gust Response Comparison 51. 8 Cantilever Wing Uncoupled Modes 52,9 Wing Flutter Speed Ratios 52. 10 Unsized Airplane Wing Weight Comparison,Constant Area 232 3 m 53. 11 Sized Airplane Characteristics and Performance,Requirements 63.
12 Mission Analysis and Economic Data Comparison 65. 1 0 SUMMARY, This study of natural laminar flow NLF is a segment of a program to investigate the. application of new technologies to large transport aircraft with an objective of providing. next generation energy efficient civil transports The NLF segment consists of two. sub tasks airfoil and wing design analysis and a preliminary evaluation of the efficiency. and economics of an NLF airplane as compared to a conventional turbulent flow. transport The two subtasks were conducted concurrently. Airfoil and Wing Design Analysis The subtask objective was to establish through. application of the latest aerodynamic boundary layer analysis methods the feasibility of. developing an airfoil having a high degree of natural laminar flow. A laminar flow airfoil developed by Boeing prior to this contract was selected as a base. point for airfoil and wing design analysis Effects of thickness ratio off design Mach. number and lift coefficient were evaluated followed by airfoil modification to increase. its thickness and to improve the extent of favorable pressure gradient while minimizing. wave drag The final airfoil has a thickness of 10 1 chord a design section lift. coefficient of 0 5 and is intended to cruise at M 0 78 The pressure distribution for. those conditions is shown below,Final NLF Airfoil, Boundary layer stability was evaluated at the design section lift coefficient and Mach. number for a series of Reynolds numbers It was assumed that transition would occur. when the boundary layer disturbance amplitude ratio e had exceeded any of the several. selected values Numbers of amplification factors n have been established in the past. with results indicating maximum values ranging from 10 to 14 Upper surface transition. location on the final NLF airfoil was quite sensitive to change in the selected values of n. while the lower surface transition location showed little variation On the final. developed airfoil for n 12 transition is calculated to occur at 35 chord on the upper. surface despite a pressure gradient favorable to 60 chord while the lower surface. transition is delayed to 50 chord, Although several iterations were required to evolve the airfoil shown the results indicate. that through the use of advanced boundary layer flow analysis and stability calculations. an airfoil that should provide a high degree of natural laminar flow can be designed. Laminar Flow Wing Design Early transition can be caused not only by surface. irregularities and adverse pressure gradient but also by boundary layer crossflow. instability A wing sweep and boundary layer stability analysis based upon a. representative pressure distribution revealed that crossflow instability could cause. transition on natural laminar flow airfoils at very low sweep angles depending on airfoil. pressure gradient For the particular pressure distribution used in the present analysis. crossflow was found to cause transition for leading edge sweep angles larger than 0 12. rad 7 deg as shown below, Transition Location as a Function of Leading Edge Sweep. Tollmien Schlichting,transition,Transition,0 1 0 2 0 3 0 4 0 5 rad.
Effect of Sweep on Transition Location, However a different airfoil pressure gradient could allow a higher leading edge sweep. but also adversely affect the Tollmien Schlichting stability The integration of a natural. laminar flow airfoil into a three dimensional swept wing is a very complex task requiring. in depth studies of optimum pressure distribution versus sweep angle Reynolds number. effects and Mach number effects Since such in depth studies were beyond the scope of. the present work it was necessary to choose a leading edge sweep angle that would. provide some margin from crossflow instability based upon the representative. distribution developed for this study Therefore a leading edge sweep angle of 0 09 rad. 5 deg was chosen for the present study, Aircraft Trade Studies The aircraft trade studies were conducted on the assumption. that insect contamination of the wing leading edge was nonexistent i e either the bug. problem was greatly exaggerated or some system was installed on the airplane to prevent. contamination,Final Airplane General Arrangement, Using the results of the airfoil analysis low sweep low thickness ratio etc a transport. with an NLF wing was configured and compared with a conventional turbulent flow. transport Both airplanes were designed to perform the same mission transport 196. passengers over a range of 3704km 2000 nmi Fuel consumption and direct operating. cost were compared using a Boeing proprietary computer program The computer. program determines the airplane size weight thrust and fuel required to satisfy the. range requirement and other operational constraints and computes the resultant direct. operating cost, Gust load conditions determined the structural strength of the unswept NLF wing and. analysis showed it to be free from flutter To provide a smooth aerodynamic surface. bonded aluminum honeycomb construction was selected even though it proved to be. structurally less efficient than a conventional skin and stiffener wing in this application. To obtain laminar flow as far inboard as possible the NLF wing thickness ratio at the. side of the body was limited to 11 of gross chord as compared to 15 for the turbulent. reference airplane To eliminate wing pressure variations due to engines and struts the. engines were located on the aft body When compared to the wing engine installation of. the turbulent reference airplane the NLF configuration showed a wing and aft body. weight increase The aeroelastic effects associated with unswept wings are found to. increase wing root bending moment over that of a rigid wing For these reasons the. NLF wing was heavier on a weight per unit area basis than the swept wing of the. turbulent reference aircraft, To avoid gaps and discontinuities on the forward portion of the wing the NLF airplane.
was configured without leading edge devices resulting in a maximum landing lift. coefficient lower than that of the turbulent reference wing When the 231 5 km hr 125. kt approach speed constraint was applied during the sizing program the result was a. substantial increase in the NLF wing area causing a large weight increase This negated. the 20 improvement in lift drag ratio attributable to NLF. Results of the final mission analysis and economic study are listed below. Mission Analysis and Economic Data Comparison,Reference airplane NLF final airplane. Payload kg Ib 18225 40180 18 225 40 180,Still air range km nmi 3704 2000 3 704 2 000. cruise 0 78, Operating empty weight 76861 169450 91 290 201 260. Manufacturer s empty 71690 158050 86119 189860,weight kg Ib. Brake release gross 121985 268930 137490 303070,weight kg Ib.
Block fuel kg Ib 20600 45415 21310 46980,Block time hr 4 769 4 885. Reserves ATA domestic 6681 14730 7058 15560,Relative direct operating Base 107 8 base. Based upon 1967 ATA DOC equations adjusted to 1976 costs. This study has demonstrated that the combination of boundary layer stability analysis. techniques with standard airfoil design techniques can be used to satisfactorily define a. two dimensional airfoil having natural laminar flow over a major portion of a wing chord. typical of a large contemporary civil transport However it has also demo. nasa contractor report 1 natural laminar flow airfoil analysis and trade studies energy efficient transport program boeing commercial airplane company

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