concepts as well as fuel efficiency and emissions,Penn State for jet noise reduction,Purdue for system of system analysis,MIT for green initiatives,Wyle labs for real-world loudness effects and boom guidance,LM Transportation Security Solutions for air traffic analysis,and Helen Reed and Bill Saric for laminar flow analysis.All required tasks include subsequent subtasks that align with the main task.The WBS encompasses all work necessary to oversee and direct the execution of the N+3 Phase 1 Program. 4.0 Tasks and Trade Studies-Airframe Systems 4.1 Advanced Vehicle Concept(WBS 3.1) 4.1.1 Concept Layout and Design (WBS 3.1.1) 4.1.1.1 Description Before laying out a configuration,we looked at the N+3 goals and addressed design methods and strategies necessary to meet those challenges.Based on our past history designing and analyzing supersonic configurations,we first focused our energy on the sonic boom requirement.The N+3 sonic boom goal of 65-70 PLdB is significantly lower than the state of the art 107 PLdB of the (408,000 Ib,100 passenger)Concorde with a shock strength of 2 psf,or the 102 PLdB of the (12,000 Ib-33 times lighter than Concorde)F-5 with a shock strength of 1.3 psf.Meeting the sonic boom goal requires a minimum shock(ramp signature)shock strength of 0.12 to 0.17 psf.One way of meeting this goal is increasing the fuselage length used by SEEB to calculate the minimum shock signature,as shown in Figure 2.In order to reduce the length required,it is anticipated that the perceived level of noise on the ground can be reduced through shock blending,as shown from 2 methods of varying shock separation in Figure 3,and through taking into account real world absorption and turbulence.Results from Wyle's analysis on Effects of Atmospheric Propagation on Low-Boom Shaped Signatures can be seen in Section 4.2.5. 500 MTOW 450,000 Ib 450 400 350 300 Typical Non- 250 Low Boom 200 450,000Ib 150 100 SST Optimum 50 Length 0 60 65 70 75 80 85 90 PLdB Figure 2. Relation between vehicle length and perceived level of noise (PLdB) The other noise challenge was meeting the airport noise goal of 20-30 EPNdB cumulative below FAR36 Stage 3 limits. Current subsonic airplanes,like the Boeing 777-200 with GE 90-85B and the Airbus A380 with RR Trent 970,already meet this goal at 23 EPNdB and 26 EPNdB cum below stage 3 respectively.However,it is more of a challenge for supersonic aircraft.Using the Concorde as a state of the art(SOA)comparison,its supersonic transport status is 45 EPNdB cumulative above Stage 3.Our strategy for meeting the noise goal was to first require GE to meet sideline-3 EPNdB at 90%power also known as PLR(programmed lapse rate),use the GE Variable Cycle Engine,and optimize takeoff procedures.Second,reduce approach noise with a low-noise fan design,inlet liners and inlet flow choking.Third,investigate other promising advanced technologies. Copyright 2010 by Lockheed Martin,Published by the American Institute of Aeronautics and Astronautics,Inc.,with permission. 6
Copyright 2010 by Lockheed Martin, Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 6 concepts as well as fuel efficiency and emissions, Penn State for jet noise reduction, Purdue for system of system analysis, MIT for green initiatives, Wyle labs for real-world loudness effects and boom guidance, LM Transportation & Security Solutions for air traffic analysis, and Helen Reed and Bill Saric for laminar flow analysis. All required tasks include subsequent subtasks that align with the main task. The WBS encompasses all work necessary to oversee and direct the execution of the N+3 Phase 1 Program. 4.0 Tasks and Trade Studies – Airframe Systems 4.1 Advanced Vehicle Concept (WBS 3.1) 4.1.1 Concept Layout and Design (WBS 3.1.1) 4.1.1.1 Description Before laying out a configuration, we looked at the N+3 goals and addressed design methods and strategies necessary to meet those challenges. Based on our past history designing and analyzing supersonic configurations, we first focused our energy on the sonic boom requirement. The N+3 sonic boom goal of 65-70 PLdB is significantly lower than the state of the art 107 PLdB of the (408,000 lb, 100 passenger) Concorde with a shock strength of 2 psf, or the 102 PLdB of the (12,000 lb—33 times lighter than Concorde) F-5 with a shock strength of 1.3 psf. Meeting the sonic boom goal requires a minimum shock (ramp signature) shock strength of 0.12 to 0.17 psf. One way of meeting this goal is increasing the fuselage length used by SEEB to calculate the minimum shock signature, as shown in Figure 2. In order to reduce the length required, it is anticipated that the perceived level of noise on the ground can be reduced through shock blending, as shown from 2 methods of varying shock separation in Figure 3, and through taking into account real world absorption and turbulence. Results from Wyle‘s analysis on Effects of Atmospheric Propagation on Low-Boom Shaped Signatures can be seen in Section 4.2.5. Figure 2. Relation between vehicle length and perceived level of noise (PLdB) The other noise challenge was meeting the airport noise goal of 20-30 EPNdB cumulative below FAR36 Stage 3 limits. Current subsonic airplanes, like the Boeing 777-200 with GE 90-85B and the Airbus A380 with RR Trent 970, already meet this goal at 23 EPNdB and 26 EPNdB cum below stage 3 respectively. However, it is more of a challenge for supersonic aircraft. Using the Concorde as a state of the art (SOA) comparison, its supersonic transport status is 45 EPNdB cumulative above Stage 3. Our strategy for meeting the noise goal was to first require GE to meet sideline -3 EPNdB at 90% power also known as PLR (programmed lapse rate), use the GE Variable Cycle Engine, and optimize takeoff procedures. Second, reduce approach noise with a low-noise fan design, inlet liners and inlet flow choking. Third, investigate other promising advanced technologies
Signature Variations for Loudness vs.Shock Separation 0.8 -15 msec Separation 0.6 -6 msec Separation same Duration 0.4 -6 msec Separation same Expansion 02 30 120 140 160 200 -0.2 -0.4 0.6 -0.8 Time,msec Loudriess vs.Shock:Separation Rise Time =1/AP +14 ■Same Duration Same Expansion 8 Poly.(Same Duration) -Poly.(Same Expansion) 8p7d 'ssaupno] 20364208 10 20 25 Shock Separation,msec Figure 3. Effect of shock separation on loudness As part of the iterative design process,we looked at a number of different vehicle concepts that would integrate features necessary to achieve the N+3 mission requirements and performance goals.Desirable configuration features included items that would provide low boom,low drag,low weight,and good aeroelasticity performance for cruise and off-cruise conditions. Drawing on previous Quiet Supersonic Transport (QSST)experience,our process started with applying the desirable configuration features to a modified inverted-V,"QSST-like"concept.The four-engine inverted V-tail concept was proposed to better capture advantages of the inverted tail concept-particularly greater wing bending moment relief. Preliminary vehicle sizing with QSST and historical data established the weight breakdown necessary to determine engine thrust,wing sizing,and fuselage length for boom.A slight improvement was assumed,giving an L/D of 10 and an SFC of 0.95 Ib fuel/lb thrust/hr.These assumptions were applied to the reference mission of 100 passengers,4000 nm range,and Mach 1.6 cruise.This resulted in a Max Take-off Gross Weight(MTOW)of just over 300,000 Ib,with an efficiency of 3.07 pax-nm/Ib fuel,as shown in Figure 5.However,this did not meet the requirement of efficiency between 3.5 to 4.5 pax-nm/lb fuel.It was calculated that the efficiency could be raised to 3.97 pax-nm/lb fuel if the L/D increased to 11,the SFC improved to 0.90 Ib fuel/lb thrust/hr,and empty weight reduced by 5%.This quantified the N+3 vehicle improvement values to achieve NASA's desired performance goals.These values were status indicators as opposed to targets.N+3 technologies were sought to maximize performance as much as possible and potentially go beyond these goals. Copyright 2010 by Lockheed Martin,Published by the American Institute of Aeronautics and Astronautics,Inc.,with permission. 7
Copyright 2010 by Lockheed Martin, Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 7 Signature Variations for Loudness vs. Shock Separation -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 0 20 40 60 80 100 120 140 160 180 200 Time, msec Ground Overpressure, psf 15 msec Separation 6 msec Separation same Duration 6 msec Separation same Expansion Signature Variations for Loudness vs. Shock Separation -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 0 20 40 60 80 100 120 140 160 180 200 Time, msec Ground Overpressure, psf 15 msec Separation 6 msec Separation same Duration 6 msec Separation same Expansion Figure 3. Effect of shock separation on loudness As part of the iterative design process, we looked at a number of different vehicle concepts that would integrate features necessary to achieve the N+3 mission requirements and performance goals. Desirable configuration features included items that would provide low boom, low drag, low weight, and good aeroelasticity performance for cruise and off-cruise conditions. Drawing on previous Quiet Supersonic Transport (QSST) experience, our process started with applying the desirable configuration features to a modified inverted-V, ―QSST-like‖ concept. The four-engine inverted V-tail concept was proposed to better capture advantages of the inverted tail concept – particularly greater wing bending moment relief. Preliminary vehicle sizing with QSST and historical data established the weight breakdown necessary to determine engine thrust, wing sizing, and fuselage length for boom. A slight improvement was assumed, giving an L/D of 10 and an SFC of 0.95 lb fuel/lb thrust/hr. These assumptions were applied to the reference mission of 100 passengers, 4000 nm range, and Mach 1.6 cruise. This resulted in a Max Take-off Gross Weight (MTOW) of just over 300,000 lb, with an efficiency of 3.07 pax-nm/lb fuel, as shown in Figure 5. However, this did not meet the requirement of efficiency between 3.5 to 4.5 pax-nm/lb fuel. It was calculated that the efficiency could be raised to 3.97 pax-nm/lb fuel if the L/D increased to 11, the SFC improved to 0.90 lb fuel/lb thrust/hr, and empty weight reduced by 5%. This quantified the N+3 vehicle improvement values to achieve NASA‘s desired performance goals. These values were status indicators as opposed to targets. N+3 technologies were sought to maximize performance as much as possible and potentially go beyond these goals
b fraction Empty Weight 148,000 0.492 Reference Mission Payload Weight 22,440 0.075 100pax Fuel Weight 130,200 0.433 4.000 Nmi range Mach 1.6.50.000 ft altitude Max Take-Off Weight 300,600 pax-Nmi/Ibfuel Efficiency 3.07 Figure 4. Initial sizing for reference mission 4.1.1.2 Results The initial configuration was sized with an assumed MTOW approximately equal to 300,000 Ibs,resulting in a wing area approximately equal to 3,000 ft,and a take-off thrust approximately equal to 100,000 Ibs.The benefits of this low-boom configuration include stretched boom signature due the inverted V-tail and nose droop,favorable aerodynamic interference and compression lift for aft-under-wing mounted engines,efficient propulsion integration due to the planform trailing edge sweep and airfoil reflex,aerodynamic efficiency for wing planform design,reduced wing gull roll penalties due to wing tip and inverted V-tail anhedral,and structural flexibility suppression due to inverted V-tail wing bracing.Once designed,these specific elements were considered endemic to the configuration and always a part of the initial configuration technology set. The design was used as the "yardstick"to compare other potential configurations.Figure 5 highlights the overall initial configuration definition and design features that were modelled within CATIA V5. Forebody volume buildup and signature requirements Inverted Vfor structural stability per shaped signature requirements Planform TE for 200ft Wing dihedral elevates lift for stretched boom Tip anhedral reducing signature roll in side-slip,allowing greater inboard dihedral Wing Area--3,000 sqft Aft-under-wing mounted T/O Thrust--100.000 lb engines for favorable Nose droop for stretched boom siqnature aerodynamic MToW--300.000b interference and compression lift 80ft Figure 5.Initial Configuration Definition Once the initial concept was defined,an initial inner mold-line(IML)cabin volume constraint was determined to insert passengers within the loft.The initial configuration held 101 passengers including future projected economy seat sizing comfort improvements relative to the Concorde and other regional jets plus the provision for 10%first class seats.The cabin layout included one galley,two lavatories,one supplemental space,and three emergency constraints.The boom constraints on the fuselage outer mold line(OML)forced cabin camber and cross section pinching on each end.This limitation required one 1s class seat to be removed from the forward section of the cabin,and a unification of the next set of seats.Nine rows in the aft section of the cabin changed from 4 across to 3 across while the cabin was lengthened.Cambered cabin slopes less than 5% have to be reconciled in a future design phase.Figure 6 demonstrates a realistic cabin layout that establishes fuselage IML constraints for the initial configuration. Copyright 2010 by Lockheed Martin,Published by the American Institute of Aeronautics and Astronautics,Inc.,with permission
Copyright 2010 by Lockheed Martin, Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 8 Figure 4. Initial sizing for reference mission 4.1.1.2 Results The initial configuration was sized with an assumed MTOW approximately equal to 300,000 lbs, resulting in a wing area approximately equal to 3,000 ft2 , and a take-off thrust approximately equal to 100,000 lbs. The benefits of this low-boom configuration include stretched boom signature due the inverted V-tail and nose droop, favorable aerodynamic interference and compression lift for aft-under-wing mounted engines, efficient propulsion integration due to the planform trailing edge sweep and airfoil reflex, aerodynamic efficiency for wing planform design, reduced wing gull roll penalties due to wing tip and inverted V-tail anhedral, and structural flexibility suppression due to inverted V-tail wing bracing. Once designed, these specific elements were considered endemic to the configuration and always a part of the initial configuration technology set. The design was used as the ―yardstick‖ to compare other potential configurations. Figure 5 highlights the overall initial configuration definition and design features that were modelled within CATIA V5. Figure 5. Initial Configuration Definition Once the initial concept was defined, an initial inner mold-line (IML) cabin volume constraint was determined to insert passengers within the loft. The initial configuration held 101 passengers including future projected economy seat sizing comfort improvements relative to the Concorde and other regional jets plus the provision for 10% first class seats. The cabin layout included one galley, two lavatories, one supplemental space, and three emergency constraints. The boom constraints on the fuselage outer mold line (OML) forced cabin camber and cross section pinching on each end. This limitation required one 1 st class seat to be removed from the forward section of the cabin, and a unification of the next set of seats. Nine rows in the aft section of the cabin changed from 4 across to 3 across while the cabin was lengthened. Cambered cabin slopes less than 5% have to be reconciled in a future design phase. Figure 6 demonstrates a realistic cabin layout that establishes fuselage IML constraints for the initial configuration
1.Boom constraints on fuselage OML force cabin camber and X-sec plnching on ends 2. One 1 Class seat removed from front,next row 参ats moved to9ther 3.9rows in aft coach changed to 3 across,cabin lengthened 4.Camber slopes below 5 deg,can design workable noor angle垂 Wall encroachment Forward Aft Economy 4X Economy5X (50"pltch) (32"pltch] (32"pitch) Prem.Economy (36"pltch) Galley 165* 70° 58” 月oor camher Ba99(466c not picture 933量 Cabin implications of Low-Boom Area Distribution: 1.Non-uniform seat rows (2+2,3+2) Lowest standing helght 2.Low clearance at forward end Figure 6.Area-ruled cabin layout 4.1.2 Alternative Configurations (WBS 3.1.1) 4.1.2.1 Description The N+3 concept vehicle definition also included exploration of alternative concepts,both conventional and unconventional,to investigate all potential configuration solutions.Figure 7 highlights the various configurations that were studied starting with the family of inverted-v tail configurations and branching off to an oblique wing,a twin-fuselage concept,and a variety of brainstorming concepts. Copyright 2010 by Lockheed Martin,Published by the American Institute of Aeronautics and Astronautics,Inc.,with permission. 9
Copyright 2010 by Lockheed Martin, Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 9 Figure 6. Area-ruled cabin layout 4.1.2 Alternative Configurations (WBS 3.1.1) 4.1.2.1 Description The N+3 concept vehicle definition also included exploration of alternative concepts, both conventional and unconventional, to investigate all potential configuration solutions. Figure 7 highlights the various configurations that were studied starting with the family of inverted-v tail configurations and branching off to an oblique wing, a twin-fuselage concept, and a variety of brainstorming concepts
Family of Configurations Initial Configuration Definition-Inverted-V Oblique Flying Wing Configuration Engine Over Wing Configuration Twin Fuselage Configuration Mother/ Blue Sky Daughter Session T-Tail Configuration Mother/Daughter,Blue Sky Alternatives Figure 7.Alternative configuration concepts chosen for further analysis "Blue Sky"Configurations After the initial ideas listed above were considered,further brainstorming sessions,called "blue sky,"were conducted with leading experts from outside the program,to identify more revolutionary concepts.However,no further configurations were discovered that could reasonably outperform those concepts already being considered. Engines-Over-Wing Configuration The engine-over-wing configuration was considered to address potential structural benefits (shorter landing gear)and noise level reductions possible with engine placements above the wing.When the engines are placed over the wing,engine spillage shocks are blocked from the ground by the wing.However,this results in higher pressure on the upper surface of the wing predicted to reduce L/D by 2 points. In order to assess the need for noise reduction with the engines over wing configuration,it needed to be determined how low the noise could be for the engine under wing configuration. This was done through a wing configuration study to address propulsion/airframe integration (PAI)issues of a low-boom design.Figure 8 exhibits the trailing edge design study used for favorable interference drag.The wing trailing edge was swept to capture maximum nacelle shock compression lift and airfoil reflex for shock (and drag)cancellation.The nacelle shock was substantially countered;it met a 65-70 PLdB equivalent area target as easily as above the wing engine placements. The high pressure caused by the nacelle shock on the lower surface of the wing resulted in higher efficiency (lower angle-of- attack)through an increased L/D.Since it was possible to meet the sonic boom requirement with the higher efficiency of the engines-under-wing concept,further development of the engines-over-wing configuration was discontinued. Copyright 2010 by Lockheed Martin,Published by the American Institute of Aeronautics and Astronautics,Inc.,with permission. 10
Copyright 2010 by Lockheed Martin, Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 10 Figure 7. Alternative configuration concepts chosen for further analysis ―Blue Sky‖ Configurations After the initial ideas listed above were considered, further brainstorming sessions, called ―blue sky,‖ were conducted with leading experts from outside the program, to identify more revolutionary concepts. However, no further configurations were discovered that could reasonably outperform those concepts already being considered. Engines-Over-Wing Configuration The engine-over-wing configuration was considered to address potential structural benefits (shorter landing gear) and noise level reductions possible with engine placements above the wing. When the engines are placed over the wing, engine spillage shocks are blocked from the ground by the wing. However, this results in higher pressure on the upper surface of the wing predicted to reduce L/D by 2 points. In order to assess the need for noise reduction with the engines over wing configuration, it needed to be determined how low the noise could be for the engine under wing configuration. This was done through a wing configuration study to address propulsion/airframe integration (PAI) issues of a low-boom design. Figure 8 exhibits the trailing edge design study used for favorable interference drag. The wing trailing edge was swept to capture maximum nacelle shock compression lift and airfoil reflex for shock (and drag) cancellation. The nacelle shock was substantially countered; it met a 65-70 PLdB equivalent area target as easily as above the wing engine placements. The high pressure caused by the nacelle shock on the lower surface of the wing resulted in higher efficiency (lower angle-ofattack) through an increased L/D. Since it was possible to meet the sonic boom requirement with the higher efficiency of the engines-under-wing concept, further development of the engines-over-wing configuration was discontinued