A New Look at Hydrogen Fueled Supersonic Airliners

Alex Forbes, Anant Patel, Chris Cone, Pierre Valdez, Narayanan Komerath

Daniel Guggenheim School of Aerospace Engineering Georgia Institute of Technology

Atlanta

IMETI 2010, Orlando, FL June 2010

Overview

•  New look at the prospects for developing supersonic civil airliners

•  Post-1990 global demographics and market intensity of Eastern Hemisphere, climate change, fuel prices and technological advances

•  “Point-to-point” architecture viable with long range mid-size airliners

•  Mach 1.4 cruise makes enough destinations viable for supersonic flight.

•  Conceptual design estimate of cost per seat mile for HC and LH2 fuel

•  No “Hydrogen drag penalty”.

•  Viable aircraft geometries are shown to exist.

•  Hydrogen-fueled airliners can achieve seat-mile costs low enough to open a large worldwide market and justify a viable fleet size.

1960s experience: Concorde and Tu-144

•  Technical marvels, derived from strategic bombers. •  Tu-144 safety issues, <100 civilian flights made. •  Concorde: Expected market >200, but only 12 eventually built. •  Mach 2 sonic boom, small capacity (80-100), 3000 - 4000 mile range, small choice of over-

water routes, very high ticket prices.

High-Speed Civil Transport (HSCT) How did the NASA-Boeing-GE-UTC in the 1990s effort end?

“An HSCT would reduce the flight times from California to Japan to approximately 4 hours”

Lets see some points from NASA’s final report on the HSR program. Source: NASA HSCT Program Final Presentation, 1999

Aeronautics R&T “Three-Legged Stool”

Technology Availability

Policy Supportability Market Acceptability

Potential HSCT Economic Impact - 1990 View 2005-2020 Long Range Over-Water Market

Long range airplane market share could be driven by HSCT Potential for a $200B swing in U.S. sales and 140,000 new jobs

U.S. HSCT Program Offshore HSCT Program

Subsonic Only — No HSCT

HSCT European

Team

Large Subsonic

Medium Subsonic

Medium & Large

Subsonic

HSCT U.S. Team

Large Subsonic

Medium Subsonic

Medium & Large

Subsonic

Large Subsonic

Medium Subsonic

Medium & Large

Subsonic

United States 79%

United States ( 747 / 767 / 777 MD-11 / MD-12 )

65%

United States 49%

Europe 21%

Europe 51%

Europe ( A300 / A330 /

A340 ) 35%

Source: NASA HSCT final 1999

“High-Speed Civil Transport Comparative Perspective”

Concorde HSCT Goals

North Atlantic 1976 2.0 3000 100 400,000 87 Premium Exempt 75 20a

Market Entry In Service Year Cruise Speed (Mach) Range (nautical miles) Payload (passengers) Takeoff Gross Weight (lb.) Required Revenue (¢/RPM) Fare Levels Community Noise Standard Noise Footprint (sq. mile) Emissions Index (gm/Kg fuel)

Atlantic & Pacific 2005 2.4 5000 - 6500 250 - 300 700,000 10 Standard FAR 36 - Stage 3 5 5

Source: NASA HSCT final 1999

“

”

“High-Speed Civil Transport Development Business Implications

•  Studies by Industry have Indicated that HSCT Development Costs Could be more than Twice the Level of Current Subsonic Airplanes

•  If the Product is Successful: –  Industry will Face 15-18 Billion Dollar Negative Cash Flow with a Break

Even in the 7 -10 Year Range assuming Continuous Production •  If the Product is Unsuccessful:

–  High Development Costs and Investments would be Unrecoverable –  The Ability to Compete for Advanced Subsonic Airplane Sales would be

Significantly Degraded –  Significant Impact to Market Share and Balance of Trade

These Technical and Economic Risks Make it Unwise to Commit to a Product Development Program without a Clear Demonstration of Technical and Cost Viability”

Source: NASA

Prevailing View •  Costs too much – no market at those prices. Rising fuel prices increase the gap. •  Would only compete with existing transonic airliner market – no rationale for investment •  Hydrogen airliners are “too far in the future” •  Huge “drag penalty” of using hydrogen •  Sonic boom •  Emission of water vapor at > 20,000 m causes lasting environmental damage •  Hydrogen price has to come down along way

•  NO PROSPECT OF SUPERSONIC AIRLINE FLIGHTS FOR MOST OF US!

Summary of Issues In Countering the Prevailing View

•  How have demographics and economic development altered worldwide market projections for supersonic transport ?

•  Viable destinations, flight times, curfew and business implications •  Drag implication of hydrogen, given the lower fuel weight fraction •  Impact of Global Warming on prospects for hydrogen-powered flight •  Noise, ML/D and emissions implications for cruise Mach number

GLOBAL DEMOGRAPHICS AND AIRLINE ROUTES, 2007

Growth of World Wide Air Travel

•  300% rise from 1980 to 2008. •  US deregulation, Eastern Europe, Russian arctic airspace, EU

integration, South Africa opening, MidEast, South America, China, India, Far East, Australia & Pacific.

•  Globalization effects on family travel. •  Long point-to-point flights (14- 17 hours) and aging travelers •  Expected further doubling in coming decade.

Fuel Prices and the Hydrogen Economy

•  “Hubbert Peak Oil” and expected sharp rise in fuel •  Nonlinear effects on jet fuel prices as gasoline demand drops •  Air transportation industry aiming for 50% CO2 reduction below 2005

level (mainly by ticket price increases to fund “green” projects) •  Hydrogen is the only permanent way to cut fleet emissions •  Rationale for funding R&D •  Expected drop in H2 production costs as automotive fuel cells arrive •  Continued drop in H2 prices as more sources become available

Sonic Boom and Noise Considerations

•  Below Mach 1.4, sonic boom expected to be imperceptive even from current airline altitudes (Boeing Sonicruiser research).

•  Northrop nose shape R&D shows reduced boom effects with small increase in drag.

•  Blended wing-body designs now feasible with CFD/CAA/ engine-airframe integration

•  Higher-bypass engines allow lower takeoff jet noise. •  LH2 aircraft will have lower weight and wing loading.

Preliminary Sizing and Performance

•  200 passengers and 6 crew. •  Minimum structure fraction needed to build aircraft was set at 27%. •  Engine technology at the level of F-35 Joint Strike Fighter, •  Thrust-specific fuel consumption was assumed at 1.1 per hour, at the

level assumed in the NASA HSCT project. •  Length limited to 67 m (220 feet). •  Comfort level of modern airline business class seats

Aerodynamics at Supersonic Cruise Sears-Haack body shape: Minimum drag for given volume Supersonic area ruling: Mach cones. Blended airframe shock minimization Compressible boundary layer

There is No Hydrogen Penalty Upper bound on the “hydrogen penalty” is a 50% jump in total drag coefficient. But LH2 airliner weighs much less.

LH2 delivers 3.8 times as much heat per unit mass as Jet-A.

For the same payload and wing loading, total drag of the LH2 SST is only 55% of that of the Jet-A SST.

Gross weight of LH2 SST is only 32% of Jet-A SST for same range and payload – much lower sonic boom footprint.

Lower altitude feasible: less climb cost, and exhaust will disperse.

Actual mass of H2O generated per trip is approximately the same with LH2-SST or Jet-A SST.

Seat-Mile Fuel Costs

Cheapest Transonic, 2009

Prevailing View Our Conclusions

Will Cost Too Much – no market at those prices. Rising fuel prices increase the gap.

• JetA -fueled SSTs are not viable for 8000 km range . • At today’s costs, LH2 SST ~ 3 x cheapest economy tickets

Compete with existing transonic airliner market – no rationale for investment

•  Demographics & economics have increased market. •  Carbon savings of a fleet of 500 LH2 SSTs would provide

over $2B in a decade, as investment rationale

Huge “hydrogen drag penalty” Drag is lower as weight is << Jet-A SST

Sonic boom Not an issue at Mach 1.4. Overland flight achievable

Water above 20km unacceptable No need to go above 15,000m

Hydrogen price has to come down LH2 SST is already more cost-effective than Jet-A SST. Mass production for automobiles can bring prices down

Hydrogen airliners are NOT “too far in the future”

“Call your local congressperson, NASA, ESA, JAXA, industry and airline executives”

Conclusions

ACKNOWLEDGEMENTS

The work reported in this paper was made possible by resources being developed for the “EXTROVERT” cross-disciplinary learning project under NASA Grant NNX09AF67G S01. Mr. Anthony Springer is the Technical Monitor.

Valuable technical resources on high speed aircraft aerodynamics came from the Boeing Company, courtesy of Dr. B. Kulfan.

Exercise in challenging “conventional wisdom” and taking a fresh look at a global challenge problem.

Aim:

Make supersonic airline travel viable for the mass market.

Approach:

Concept Development Exercise

• Conceptual design at several levels, combining technical knowledge with global demographics, economics, sustainability and public policy issues.

• Validate calculations by confirming present day conclusions, then challenge assumptions and show alternative path to viability.

• Go from requirements definition to “ticket price per seat mile”

• Refine technical design and economics

Organization of this presentation

• Introduction to the project

• 5 different levels at which concept development has been pursued. - AE1350 Freshman Introduction to Aerospace Engineering - AE3021 High Speed Aerodynamics - AE2xxx Special Problems - AE4xxx Special Problems -  Undergraduate thesis

• Technical issues & results

• Observations regarding evolution of student experience

• Conclusions

• Acknowledgements

• For given specifications, estimate payload using common sense (e.g., “What is the average weight of a passenger on an airliner? How much food and water should be carried per passenger?”) • From benchmarking guess Payload Fraction. Find Take-Off Gross Weight. • Wing Loading from benchmarking, find planform area. Fix span, find Aspect Ratio. • For selected cruise altitude and speed, find CL and CDi. • Guess low speed CD0. Find cruise L/D and Speed for Minimum Drag. • Use thumb-rules to select a suitable engine and number of engines. • For the selected engine, find thrust-specific fuel consumption from published data, and estimate thrust at altitude. • For specified range, find the fuel weight fraction needed at takeoff. • Given engine thrust-to-weight ratio, see if structure weight fraction is enough to build the aircraft. • Once the cruise point design is shown to close, find the steady flight envelope, against aerodynamic stall, thrust available, and maximum climb rate. • Find takeoff and landing distances.

Implemented on spreadsheet for iteration, integration and plotting.

Conceptual Design at Freshman Level

AE1350 Freshman Introduction to Aerospace Engineering

2 hour freshman course, taught in Spring 2010. Several prior teachings since 1997, using Conceptual Design as the gateway to aerospace engineering.

Major assignment, done in teams of two:

Conceptual design of a short-haul (~1000 mile range) subsonic airliner to carry 150 passengers. Spreadsheet calculation procedure, with range and structure fraction used as metrics of viability.

Revise to incorporate liquid hydrogen fuel. Compare performance of the two versions. Calculate lifecycle carbon savings at today’s Carbon Market prices.

•  Designing a Flight Vehicle: Road Map •  Force Balance During Flight •  Earth's Atmosphere •  Aerodynamics •  Propulsion •  Performance •  Stability and control •  Structures and Materials •  High Speed Flight •  Space Flight

AE 2xxx and 4xxx Special Problems

2 sophomores (alumni of AE1350, Spring 2010) and 3 seniors (all following completion of Aircraft Design capstone design course, 2 after AE3021 as well) signed up for 3-hour Special Problems, across 2 semesters.

1 other student signed up for an Undergraduate Thesis project.

Questions for consideration by undergraduates:

• Drag implication of using hydrogen, given lower fuel weight fraction

• Effect of post-1990 demographics and economics on market projections

•  Viable destinations, flight times, curfew and business implications

• Impact of Global Warming/ Carbon emission reduction initiatives

• Noise implications of hydrogen-powered SST?

• Radical concepts to take advantage of the different features of hydrogen fuel, supersonic flight, and airport logistics

Summary of Issues

Technical issues & results

Issue #1: Lack of market. No incentive to build SST, because the passengers would be the same ones who now pay for first/business class tickets that make transonic airline routes profitable.

Response: Post-1990 changes in air routes, global demographics and economics.

Issue #2: SST not viable in 1960s, certainly not viable today with high fuel prices.

Response: True for hydrocarbon-fueled SST. Not viable at all.

Issue #3: LH2 requires large volume causing unacceptable supersonic body drag.

Response: Not true. Large improvement in payload fraction due to high heating value of H2 means that the airplane is much lighter, and hence drag is not higher.

Issue #4: Mach 2.5+ flight requires advanced materials. M<1.7 is inefficient.

Response: M>1.4 not needed for mass market. Overall architecture is efficient at 1.4 Sears-Haack transonic drag estimate provides upper bound for ideal drag.

OBSERVATIONS REGARDING EVOLUTION OF STUDENT EXPERIENCE

1.  Conceptual Design Procedure: Freshmen comfortable and pick up quickly. 2.  Project Document for the conceptual design project to counter “last-minutitis”. 3.  Cross-disciplinary exploration comes easily for freshmen, harder for seniors! 4.  Basic knowledge issues persist with seniors and graduate students. 5.  Implementation Experience: •  Undergraduate thesis student decided that taking courses was easier. •  Taking advanced courses confuses students! Only a few build the trait of

thinking about the methods that they learn. •  Students from AE3021 and Capstone Design reluctant to use simple conceptual

design process given in AE1350. Eventually realized that their complex formulae gave the same results when used correctly.

•  When faced with unacceptable numbers, hesitant to do anything about it! (L/D <3 – but “only in cruise”!) AIAA Student Conference paper withdrawn. •  Poster prepared and discussed with better results. •  Paper to peer-reviewed conference done successfully. 6. Vertical Integration aspects: After enough iterations, and given examples,

students do pick up and do an excellent job.

Overall design calculations

Market / demographics issues

Applying “theory” learned in classes

Capturing essence of design approach

Using math to develop bounds

SUMMARY OF OBSERVATIONS

1. Multilevel process to explore a high-risk concept using undergraduate participants. 2. Vertical and horizontal knowledge integration aspects explored, with differing levels

of success and difficulty. 3. Simple conceptual design procedure permits students to explore advanced aircraft concepts and see what is needed to make the design close. 4. Process then used as starting point for detailed configuration analysis. 5. Conclusions on the LH2 SST:

•  Huge change in Eastern Hemisphere demographics, politics and economics •  Large rise in engine T/W and drop in TSFC since Concorde days •  Fossil-fuelled SST is still not viable at today’s fuel prices •  LH2 drag penalty is absent, due to large gain in payload fraction. •  LH2 becomes more attractive as fossil costs rise and H2 costs decrease. •  LH2 SST development costs can be partially met by carbon market savings.

6. Opportunities to improve depth and breadth of learning, and project performance. 7. Iteration helped students reach a good level of project completion.

CONCLUSIONS

Final 3-hour core course in aerodynamics/fluid dynamics/gas dynamics, following 3 hours of AE2020, Low Speed Aerodynamics, and 4 hours of AE3450, Thermodynamics and Gas Dynamics.

Compressible potential flow for subsonic and supersonic aerodynamics. Shock/expansion analyses, compressible boundary layer calculations.

Major Assignment (teams of 2): Select an airplane configuration and analyze one subsonic and one supersonic design point, calculating lift to drag ratio without resort to CFD.

Used Sears-Haack body and compressible boundary layers to estimate minimum drag for supersonic aircraft.

AE3021 High Speed Aerodynamics