Boeing Unveils Hypersonic Airliner Concept
Boeing Commercial Airplanes (BCA) has joined with hypersonic specialists at the company’s Research & Technology unit to study a Mach 5 passenger transport capable of crossing the Atlantic in 2 hr. or the Pacific in 3.
The initial concept vehicle, unveiled at the American Institute of Aeronautics and Astronautics (AIAA) Aviation 2018 conference in Atlanta, is a preliminary step toward a long-range development plan targeted at both commercial and military applications. Although not yet defined, the concept is provisionally aimed at a passenger capacity larger than long-range business jets, but smaller than Boeing’s 737, with potential entry into service from the late 2030s onward.
Flying at Mach 5, and with a projected cruise altitude of 95,000 ft., the vehicle would travel at more than 2.5 times the speed and 30,000 ft. higher than the supersonic Anglo-French Concorde, which was retired in 2003. According to Boeing, the additional speed would enable same-day return flights even across the Pacific and provide airlines with increased asset utilization.
Emerging from the same internal high-speed vehicle research studies that produced the hypersonic intelligence, surveillance, reconnaissance (ISR) and strike military concept unveiled early this year at the AIAA SciTech conference in Florida, the civil design forms part of a broader Boeing program that may include the nearer-term development of a reusable hypersonic demonstrator. This vehicle, if sanctioned, would be used to prove a wide range of airframe, systems and propulsion technologies for multiple applications, and could be flown as early as 2023 or 2024, says Boeing chief scientist for hypersonics Kevin Bowcutt.
“You have to do these kinds of studies now to know where we have to push the technology and where we have to advance things,” says Bowcutt, whose hypersonic aircraft research studies have usually been related to space access and potential near-term military applications. “Technologically we could have an [operational military] hypersonic aircraft, such as an ISR, flying in 10 years. But there’s a lot that goes into a commercial airplane, including the market, regulatory and environmental requirements, so it will happen when there is a convergence of those things.”
Boeing’s studies indicate Mach 5 as the watershed speed between civil and most nontransport military applications. “When you look at the problem of getting from Point A to Point B anywhere in the world, the question is how fast do you want to go and how fast is fast enough?” says Bowcutt. “Supersonic isn’t really fast enough to go overseas and back in one day. For the business traveler or the military, where time is really important, that’s an interesting point. Mach 5 is where you can do that. You can get across the Atlantic in about 2 hr. and across the Pacific in about 3 hr.”
Working with advanced concept designers at BCA, the Boeing Research & Technology (BR&T) hypersonics group has studied the potential advantages of operating at significantly higher cruise speeds on today’s networks. “If you look at time differences and schedules, you can conceive of going back and forth in a day. It is also interesting from an airline business perspective, because now you can double the rate of income generation [as] you use the asset twice in a day instead of once or even less,” he adds.
Outwardly resembling the hypersonic demonstrator/ISR configuration revealed in January, the commercial concept is a sharply swept delta with twin fins and a prominently humped forward fuselage. The initial configuration also leveraged a raft of earlier Boeing supersonic transport aircraft design work going back five decades to the 2707 SST as well as the High Speed Civil Transport project of the 1990s and the transonic Sonic Cruiser concept of the early 2000s, which ultimately led to the 787. It also includes design lessons from various Boeing low-boom and supersonic business jet studies.
“Several months ago we shared this with BCA and asked if they would be interested in us furthering these studies,” says Bowcutt. “They said yes, so from that we’ve done more studies and the aircraft has evolved quite a bit from the design we are showing. We are not going to share that evolution—but we are sharing the starting point,” he says.
Although sharing design features with Boeing’s proposed military hypersonic demonstrator, the commercial concept has an extended forward fuselage for greater cabin volume. Credit: Boeing
“Our commercial airplane team has been working right alongside the BR&T team as this technology has evolved,” says Mike Sinnett, vice president of BCA product strategy and future airplane development. “We share our insight into the commercial market and where we see it going, as well as the requirements any commercial airplane would need to meet—ranging from passenger appeal to regulatory mandates.”
The combined team has “so far been looking at requirements and flight times,” adds Bowcutt. “And we have some of their advanced concept folks working shoulder-to-shoulder with us. We are trying to get to a point where we have a concept in which we are comfortable with the way the design closes, and then we can start looking at the market and at things like sonic boom and takeoff noise.”
However, from a technological challenge perspective, it is speed that sets the research agenda. “To get from Mach 0.8 to Mach 5 is a sixfold [600%] increase in speed, but from Mach 5 to 6 is only a 20% increase. After Mach 5 you get diminishing returns and increasing costs, so what I am looking for are technical cliffs, or step changes. If you go much faster, eventually you are going to hit a step change in propulsion or materials,” explains Bowcutt. Unlike the Concorde, which achieved a top speed of just over Mach 2 by adopting an aluminum airframe, Boeing believes a Mach 5 cruise speed is achievable using an advanced titanium airframe structure.
The choice of Mach 5 also simplifies the propulsion option, says Bowcutt. “We know we don’t need a scramjet because we can do it with a kind of turboramjet: a turbofan that transitions to a ramjet at Mach 5.” In contrast, the propulsion system for the higher-speed, Mach 5+ ISR vehicle will require a more sophisticated turbine-based combined cycle (TBCC), which combines conventional turbine engines with dual-mode ramjet/scramjets (DMRJ). The turbine engines operate up to a sufficiently high Mach number to enable transition to the DMRJ. The engines will share a common inlet and nozzle, with the turbine cocooned after transition and then restarted once the hypersonic vehicle slows down for return to a runway landing.
The turboramjet for the commercial variant, on the other hand, is more akin to the Pratt & Whitney J58 engine developed for Lockheed’s Mach 3-plus-capable SR-71 Blackbird, but takes the concept further by completely shutting off the turbine element at higher speeds. Boeing envisions an annular turboramjet in which a turbine engine, developed from an existing commercial turbofan core, accelerates the vehicle to a transition speed at which the ramjet element takes over and the turbine section becomes partially or fully cocooned.
Similar to the three-stream adaptive-cycle XA100/101 military engines in early development by General Electric and Pratt, the engine will have a single inlet and nozzle and be integrated, with an axisymmetric annular layout. This would incorporate a bypass duct around the turbine engine that would bypass air into a combination afterburner/ramjet at the back of the engine. “It’s not a new idea, but what’s different is that the J58 was limited in Mach number because it was always putting some air through the turbomachinery. When you go to Mach 5 you can’t really do that. You have to deal with cocooning and perhaps some flow through the engine which would have to be cooled.”
Bowcutt says advanced cooling technology will be key, for controlling the thermal environment of the cabin, systems and propulsion system. The heat exchanger technology in development by Reaction Engines for the UK company’s SABRE propulsion system could play a part, he adds. Boeing, which along with Rolls-Royce announced in April that it was investing in Reaction, says the British developer is “supporting our study.” According to Bowcutt, who first discussed the possibility of a commercial hypersonic derivative at the Wharton Aerospace West Coast conference in early June, the heat exchanger could be a “nice synergy and might have a great application.”
For the overall propulsion system, Boeing will also likely need to partner with other industry players beyond the current "big three" commercial engine-makers GE, Pratt and Rolls. Development of the military hypersonic vehicle concept is continuing under DARPA’s Advanced Full Range Engine (AFRE) initiative and a TBCC flight demonstration concept study run by the U.S. Air Force Research Laboratory (AFRL). Boeing’s engine partner for the concept is Northrop Grumman Innovation Systems (formerly Orbital ATK), which in September 2017 was awarded a $21.4 million contract for the AFRE program. Boeing began work on the AFRL TBCC flight demonstrator concept study, with Orbital ATK as subcontractor, in 2016.
Boeing is also studying using liquid methane as another key component of the cooling system as part of a dual-fuel architecture incorporating conventional Jet A for turbine operations. “The nice thing about methane is you can use it for cooling as well as fuel. Methane has higher energy per pound than Jet A, so you get an ISP [specific impulse] boost out of it, but it is less dense so it takes up more volume. That is why it will be an interesting study to optimize the split between the fuels. It could be 100% methane or a split—we just don’t know yet.”
Boeing is on firmer ground with the aerodynamics of the concept, which will leverage the company’s extensive experience with hypersonic waverider configurations. A waverider rides the shockwave attached to the leading edge, thus benefiting from lower induced drag. “We are doing a lot of that aero work right now, trying to look at what the theoretical limits of the lift/drag ratio are in cruise, and there are some key things we’ve learned about how to configure waveriders to get the right ratio, and to get high performance with an integrated propulsion system,” says Bowcutt.
For slower-speed flight and reducing takeoff noise, Boeing is “looking at technologies like flow control to enhance wing lift, and ways to keep the engine noise quiet enough,” he adds. “Do you derate on takeoff? We certainly would not afterburn on takeoff. We have some innovative things we are doing there, and I’m not going to divulge them. We have tons more work to do, but we have some very neat ideas.”
http://aviationweek.com/commercial-aviation/boeing-unveils-hypersonic-airliner-concept
Boeing Commercial Airplanes (BCA) has joined with hypersonic specialists at the company’s Research & Technology unit to study a Mach 5 passenger transport capable of crossing the Atlantic in 2 hr. or the Pacific in 3.
The initial concept vehicle, unveiled at the American Institute of Aeronautics and Astronautics (AIAA) Aviation 2018 conference in Atlanta, is a preliminary step toward a long-range development plan targeted at both commercial and military applications. Although not yet defined, the concept is provisionally aimed at a passenger capacity larger than long-range business jets, but smaller than Boeing’s 737, with potential entry into service from the late 2030s onward.
Flying at Mach 5, and with a projected cruise altitude of 95,000 ft., the vehicle would travel at more than 2.5 times the speed and 30,000 ft. higher than the supersonic Anglo-French Concorde, which was retired in 2003. According to Boeing, the additional speed would enable same-day return flights even across the Pacific and provide airlines with increased asset utilization.
Emerging from the same internal high-speed vehicle research studies that produced the hypersonic intelligence, surveillance, reconnaissance (ISR) and strike military concept unveiled early this year at the AIAA SciTech conference in Florida, the civil design forms part of a broader Boeing program that may include the nearer-term development of a reusable hypersonic demonstrator. This vehicle, if sanctioned, would be used to prove a wide range of airframe, systems and propulsion technologies for multiple applications, and could be flown as early as 2023 or 2024, says Boeing chief scientist for hypersonics Kevin Bowcutt.
“You have to do these kinds of studies now to know where we have to push the technology and where we have to advance things,” says Bowcutt, whose hypersonic aircraft research studies have usually been related to space access and potential near-term military applications. “Technologically we could have an [operational military] hypersonic aircraft, such as an ISR, flying in 10 years. But there’s a lot that goes into a commercial airplane, including the market, regulatory and environmental requirements, so it will happen when there is a convergence of those things.”
Boeing’s studies indicate Mach 5 as the watershed speed between civil and most nontransport military applications. “When you look at the problem of getting from Point A to Point B anywhere in the world, the question is how fast do you want to go and how fast is fast enough?” says Bowcutt. “Supersonic isn’t really fast enough to go overseas and back in one day. For the business traveler or the military, where time is really important, that’s an interesting point. Mach 5 is where you can do that. You can get across the Atlantic in about 2 hr. and across the Pacific in about 3 hr.”
Working with advanced concept designers at BCA, the Boeing Research & Technology (BR&T) hypersonics group has studied the potential advantages of operating at significantly higher cruise speeds on today’s networks. “If you look at time differences and schedules, you can conceive of going back and forth in a day. It is also interesting from an airline business perspective, because now you can double the rate of income generation [as] you use the asset twice in a day instead of once or even less,” he adds.
Outwardly resembling the hypersonic demonstrator/ISR configuration revealed in January, the commercial concept is a sharply swept delta with twin fins and a prominently humped forward fuselage. The initial configuration also leveraged a raft of earlier Boeing supersonic transport aircraft design work going back five decades to the 2707 SST as well as the High Speed Civil Transport project of the 1990s and the transonic Sonic Cruiser concept of the early 2000s, which ultimately led to the 787. It also includes design lessons from various Boeing low-boom and supersonic business jet studies.
“Several months ago we shared this with BCA and asked if they would be interested in us furthering these studies,” says Bowcutt. “They said yes, so from that we’ve done more studies and the aircraft has evolved quite a bit from the design we are showing. We are not going to share that evolution—but we are sharing the starting point,” he says.
Although sharing design features with Boeing’s proposed military hypersonic demonstrator, the commercial concept has an extended forward fuselage for greater cabin volume. Credit: Boeing
“Our commercial airplane team has been working right alongside the BR&T team as this technology has evolved,” says Mike Sinnett, vice president of BCA product strategy and future airplane development. “We share our insight into the commercial market and where we see it going, as well as the requirements any commercial airplane would need to meet—ranging from passenger appeal to regulatory mandates.”
The combined team has “so far been looking at requirements and flight times,” adds Bowcutt. “And we have some of their advanced concept folks working shoulder-to-shoulder with us. We are trying to get to a point where we have a concept in which we are comfortable with the way the design closes, and then we can start looking at the market and at things like sonic boom and takeoff noise.”
However, from a technological challenge perspective, it is speed that sets the research agenda. “To get from Mach 0.8 to Mach 5 is a sixfold [600%] increase in speed, but from Mach 5 to 6 is only a 20% increase. After Mach 5 you get diminishing returns and increasing costs, so what I am looking for are technical cliffs, or step changes. If you go much faster, eventually you are going to hit a step change in propulsion or materials,” explains Bowcutt. Unlike the Concorde, which achieved a top speed of just over Mach 2 by adopting an aluminum airframe, Boeing believes a Mach 5 cruise speed is achievable using an advanced titanium airframe structure.
The choice of Mach 5 also simplifies the propulsion option, says Bowcutt. “We know we don’t need a scramjet because we can do it with a kind of turboramjet: a turbofan that transitions to a ramjet at Mach 5.” In contrast, the propulsion system for the higher-speed, Mach 5+ ISR vehicle will require a more sophisticated turbine-based combined cycle (TBCC), which combines conventional turbine engines with dual-mode ramjet/scramjets (DMRJ). The turbine engines operate up to a sufficiently high Mach number to enable transition to the DMRJ. The engines will share a common inlet and nozzle, with the turbine cocooned after transition and then restarted once the hypersonic vehicle slows down for return to a runway landing.
The turboramjet for the commercial variant, on the other hand, is more akin to the Pratt & Whitney J58 engine developed for Lockheed’s Mach 3-plus-capable SR-71 Blackbird, but takes the concept further by completely shutting off the turbine element at higher speeds. Boeing envisions an annular turboramjet in which a turbine engine, developed from an existing commercial turbofan core, accelerates the vehicle to a transition speed at which the ramjet element takes over and the turbine section becomes partially or fully cocooned.
Similar to the three-stream adaptive-cycle XA100/101 military engines in early development by General Electric and Pratt, the engine will have a single inlet and nozzle and be integrated, with an axisymmetric annular layout. This would incorporate a bypass duct around the turbine engine that would bypass air into a combination afterburner/ramjet at the back of the engine. “It’s not a new idea, but what’s different is that the J58 was limited in Mach number because it was always putting some air through the turbomachinery. When you go to Mach 5 you can’t really do that. You have to deal with cocooning and perhaps some flow through the engine which would have to be cooled.”
Bowcutt says advanced cooling technology will be key, for controlling the thermal environment of the cabin, systems and propulsion system. The heat exchanger technology in development by Reaction Engines for the UK company’s SABRE propulsion system could play a part, he adds. Boeing, which along with Rolls-Royce announced in April that it was investing in Reaction, says the British developer is “supporting our study.” According to Bowcutt, who first discussed the possibility of a commercial hypersonic derivative at the Wharton Aerospace West Coast conference in early June, the heat exchanger could be a “nice synergy and might have a great application.”
For the overall propulsion system, Boeing will also likely need to partner with other industry players beyond the current "big three" commercial engine-makers GE, Pratt and Rolls. Development of the military hypersonic vehicle concept is continuing under DARPA’s Advanced Full Range Engine (AFRE) initiative and a TBCC flight demonstration concept study run by the U.S. Air Force Research Laboratory (AFRL). Boeing’s engine partner for the concept is Northrop Grumman Innovation Systems (formerly Orbital ATK), which in September 2017 was awarded a $21.4 million contract for the AFRE program. Boeing began work on the AFRL TBCC flight demonstrator concept study, with Orbital ATK as subcontractor, in 2016.
Boeing is also studying using liquid methane as another key component of the cooling system as part of a dual-fuel architecture incorporating conventional Jet A for turbine operations. “The nice thing about methane is you can use it for cooling as well as fuel. Methane has higher energy per pound than Jet A, so you get an ISP [specific impulse] boost out of it, but it is less dense so it takes up more volume. That is why it will be an interesting study to optimize the split between the fuels. It could be 100% methane or a split—we just don’t know yet.”
Boeing is on firmer ground with the aerodynamics of the concept, which will leverage the company’s extensive experience with hypersonic waverider configurations. A waverider rides the shockwave attached to the leading edge, thus benefiting from lower induced drag. “We are doing a lot of that aero work right now, trying to look at what the theoretical limits of the lift/drag ratio are in cruise, and there are some key things we’ve learned about how to configure waveriders to get the right ratio, and to get high performance with an integrated propulsion system,” says Bowcutt.
For slower-speed flight and reducing takeoff noise, Boeing is “looking at technologies like flow control to enhance wing lift, and ways to keep the engine noise quiet enough,” he adds. “Do you derate on takeoff? We certainly would not afterburn on takeoff. We have some innovative things we are doing there, and I’m not going to divulge them. We have tons more work to do, but we have some very neat ideas.”
http://aviationweek.com/commercial-aviation/boeing-unveils-hypersonic-airliner-concept