Advanced Concept Development Of A Hydrogen
Supersonic Airliner:
Second Iteration
Narayanan Komerath
Daniel Guggenheim School of Aerospace Engineering
Georgia Institute of Technology
Atlanta
PROJECT EXTROVERT: Learning To
Innovate Across Disciplines
Summary
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Advances in curriculum to enable development of advanced concepts.
2010: 3 levels of undergraduate experiences in taking a new look at the prospect for supersonic flight. Including
demographics, economics, environmental business case, and supersonic aerodynamics:
- freshman introduction to conceptual design and making a business case for hydrogen with carbon market predictions
- junior/senior Sears Haack Minimum Wave Drag body calculations for supersonic hydrogen airliner
- team Special Problem leading to a peer-reviewed conference paper
New 2011:
-Concept exploration results from last year are the starting point for this year’s course assignments. The gaps in
learning seen last year are being addressed this year.
- Developing a peer-reviewed paper
- Presenting to industry experts
- Junior Senior high speed aero class asked to start with conceptual design and technical paper, and use supersonic
area ruling to improve the prediction (not the design, just the certainty of the prediction).
- AIAA paper on integrating a simple CAD code with MatLab and classical supersonic aerodynamics to improve
efficiency of conceptual design process and enable radical innovations.
- Experience of bringing “hard” problems back into senior courses, with state-of-the-art technical capabilities.
Project Structure for EXTROVERT:
Learning To Innovate Across Disciplines.
UR
Here
Test case: Can we actually use these resources to
advance undergraduate learning?
Concept Development Exercise
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:
•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
AE3021 High Speed Aerodynamics
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.
Problem Formulation: Predicting the drag of an LH2 SST
Wave drag coefficient becomes very high because of the volume of LH2. Need a good way to estimate wave drag of a
configuration at Mach 1.4.
Objectives:
1. Refine minimum-drag body shape and drag value for the supersonic area rule rather than the transonic (cross
sections) area rule.
2. Devise an efficient technique to couple the supersonic area rule method with an engineering drafting tool such as
CATIA or AutoCAD, or simpler versions. Crucial to enable iterative geometry changes, and do the supersonic wave
drag computation.
3. Estimate the compressible boundary layer drag over the final configuration at the design supersonic and subsonic
Mach numbers, and thus refine the conceptual design numbers.
Final Assignment of course, 6 weeks, weekly reporting in stages
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Form teams of two each (or work alone for no extra credit or consideration)
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Start with published conference version of paper by the Special Problem Team and 1-hour presentation
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Copies of several reports papers, links to supersonic aircraft designs done by student teams in NASA competitions.
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Web-based notes, examples.
Assignment Steps
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Week 1: Start report, analyze problem & conceptual design spreadsheet, develop approach
to design an aircraft configuration including space for the passengers and cargo, fuel,
engines, intake and exhausts, wings and tails.
Week 2: Develop & compare cross-section area distribution with Sears-Haack distribution for
same total volume and length constraints. Find Sears-Haack drag, and percentage error in
area distribution compared to Sears-Haack.
Week 3: Use linear theory to estimate drag and compare with Sears-Haack expression. See
if second order theory for pressure coefficients does better. Explain the differences.
Week 4: Examine supersonic wave drag calculation in several papers, and explore ways to
implement it efficiently using a CAD software package.
Week 5: Implement supersonic wave drag computation by taking intercepted area in Mach
cones rather than oblique planes. Link the Mach cone procedure to CAD package and use it
to iterate projected area distribution towards ideal Sears-Haack.
Week 6: Calculate compressible boundary layer skin friction drag for final configuration using
the Boeing high Reynolds number reference temperature method modified from the Schulz –
Grunow method, for the Mach 1.4 cruise condition and a subsonic cruise condition.
Finals Week: Submit the final report with the initial and improved conceptual design
comparison, and the refined seat-mile cost estimates.
Student performance
Start : Unique and extreme disdain of “derivations”. Many disasters in the first 3 tests.
• Very large spread of performance from superlative to negative points.
• Post-Drop Day class vastly different. Many questions about prospects for supersonic flight.
• Final reports: even the students who did not pay much attention to the assignment, actually did some
exploration and rationalization regarding hydrogen-fueled supersonic airliners.
• The best assignments reflected superlative independent thinking and exploration. Sought and found
and read the classical papers on the subject to a good level of comprehension.
• Sears-Haack body shape easily calculated, but linear theory produced wide spectrum of results.
• Mostly due to arithmetic or logic errors; varying values of reference area and the length in calculating
drag coefficients.
• Compressible boundary layer drag calculations also produced spectrum of answers.
• Layouts were typically revised 4 or 5 times until the designers decided that they could not get any
closer to the Sears-Haack ideal. Often this was still quite far from the Sears-Haack and yielded drag
as much as 30 to 50% higher.
• One finely-formatted report was a regurgitation of unsupported statements from various “System
Design” papers that declared the value of subsonic design optimization, nothing to do with the stated
assignment.
• Another team simply quoted statements from some reference to the effect that hydrogen fueled
airliners were far off in the future, with no evidence of any serious calculations. Reminescent of AIAA
journal reviewers.
Student’s Problem Statement
Examples
General shape of the Sears-Haack body, and final configuration. From Durbin and Swits [Ref. 3].
Iterating the cross-section area with components included.
From Dessanti and Ingraham [5]
Configuration before and after supersonic area ruling.
Discussion
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Initial shock: “modern curriculum” seems to be letting engineering students reach final year
with no appreciation for either scientific logic or a sense of numbers ?????
Concept Development exercise is demanding. It does bring out the best in many students:
long list of references, innovation
Supersonic area ruling is difficult, as evidenced by continuing publications in AIAA
conferences of funded project results seeking to improve the iterative procedure.
Top 50 percent of these assignments are impressive in enthusiasm, initiative and sustained
effort .
Conscious decision to not let the top students be dragged down by those on “cruise control”.
No grading miracle: Wide disparity in performance made grade decisions quantitatively
easy, emotionally difficult.
Conclusions and Future Directions
•Completes second iteration of the concept development process.
•Started as a question on demographics and carbon market issues.
•First iteration showed viability with top-level conceptual design in 2009-2010.
•Second iteration refined aerodynamics, students added knowledge on various issues -usability and
cost projections for liquid hydrogen.
•-sonic boom alleviation technology, detailed configuration aerodynamics, internal layout issues.
•Variety of procedures to couple CAD software with supersonic area ruling theory.
•Large dynamic range in skills, capabilities and thinking experience of seniors.
•Identified areas for substantial pre-graduation improvement in several students (up to half the class in
this case),
•Also showed impressive capabilities of the class overall.
•Several innovations and the large amount of knowledge captured from the course
•Sets the stage for professional level advancements in the area of supersonic aircraft development and
aerodynamic design.
Next step:
•Refine sonic boom issues and alleviation techniques at the graduate course level Return to future
iterations where drastically different configurations can be investigated.
•Tough problems remain in all aspects, but this is not surprising.
•Such an exercise removes the superficial appearances and cuts into the issues enough to reveal and
address these problems.
Acknowledgments
• Development of this paper was supported by NASA under the
EXTROVERT cross-disciplinary problem solving initiative. The
technical monitor is Tony Springer, NASA HQ.
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
Conceptual Design at Freshman Level
• 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.
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.
Summary of Issues
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
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.
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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
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.
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
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Conceptual Design Procedure: Freshmen comfortable and pick up quickly.
Project Document for the conceptual design project to counter “last-minutitis”.
Cross-disciplinary exploration comes easily for freshmen, harder for seniors!
Basic knowledge issues persist with seniors and graduate students.
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.
SUMMARY OF OBSERVATIONS
Overall design calculations
Market / demographics issues
Applying “theory” learned in classes
Capturing essence of design approach
Using math to develop bounds
CONCLUSIONS
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.
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.
Potential HSCT Economic Impact - 1990 View
2005-2020 Long Range Over-Water Market
Subsonic Only — No HSCT
United States
( 747 / 767 / 777
MD-11 / MD-12 )
65%
Large
Subsonic
Medium
& Large
Subsonic
Europe
( A300 / A330 /
A340 )
35%
Medium
Subsonic
U.S. HSCT Program
United
States
79%
Large
Subsonic Medium
& Large
Subsonic
Medium
Subsonic
HSCT
U.S.
Team
Europe
21%
Offshore HSCT Program
United
States
49%
Large
Subsonic
Medium
Subsonic
Medium
& Large
Subsonic
HSCT
Europea
n Team
Long range airplane market share could be driven by HSCT
Potential for a $200B swing in U.S. sales and 140,000 new jobs
Europe
51%
High-Speed Civil Transport
Comparative Perspective
Concorde
Source: NASA
HSCT Goals
North Atlantic
Market
Atlantic & Pacific
1976
Entry In Service Year
2005
2.0
Cruise Speed (Mach)
2.4
3000
Range (nautical miles)
5000 - 6500
100
Payload (passengers)
250 - 300
400,000
Takeoff Gross Weight (lb.)
700,000
87
Required Revenue (¢/RPM)
10
Premium
Fare Levels
Standard
Exempt
Community Noise Standard
FAR 36 - Stage 3
75
Noise Footprint (sq. mile)
5
20a
Emissions Index (gm/Kg fuel)
5
High-Speed Civil Transport Development
Business Implications
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Source: NASA
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
High-Speed Civil Transport (HSCT)
Why did the NASA-Boeing-GE-UTC effort fail?
Lets see some slides from NASA’s final report on the HSR program. Source: NASA
An HSCT would reduce the flight times
from California to Japan to approximately
4 hours
Aeronautics R&T
“Three-Legged Stool”
Technology Availability
Market Acceptability
Policy Supportability
Source: NASA
GLOBAL DEMOGRAPHICS AND AIRLINE ROUTES