Document
Assessment of Off - Design Low - Boom Characteristics
of a Low - Boom Supersonic Transport
Wu Li and Karl Geiselhart Aeronautics Systems Analysis Branch NASA Langley Research Center SciTech, January 2024
Outline
• Motivation • Minimum Requirements for Low - Boom Concepts • Optimal Mission Profile for Low - Boom Supersonic Aircraft • Assessment Method for Off - Design Low - Boom Characteristics • Undertrack Low - Boom Characteristics of Low - Boom Concept • Off - track Low - Boom Characteristics of Low - Boom Concept • Conclusions
Motivation
• Multiple studies indicate that the ban on overland supersonic flights has a detrimental impact on the economic viability of supersonic transports.
• NASA has been developing low - boom technologies to enable commercial supersonic overland flights, which will be demonstrated by the X - 59.
• Two supersonic transport concepts with 40 passengers were successfully developed to satisfy a conceptual - level low - boom constraint and achieve the required mission performance goals. (Published in 2021 and 2022 ) • How could we generate a supersonic transport concept that has the potential to have the desired low - boom characteristics over the primary boom carpet for the entire cruise segment?
Minimum Requirements for Low - Boom Supersonic Transports Low - boom constraint at start of overland cruise • Overwater range 3600 nm for transatlantic flights, cruise Mach 1.8 • Overland range 2500 nm for airport pairs in continental US • Overland supersonic flight with cruise Mach 1.4 and sonic boom ground noise level below 70 PLdB (NASA N+3 goal) Unrestricted supersonic overwater flight (using the optimal altitude for min fuel burn) Low - boom overland flight with undertrack ground noise level below 70 PLdB at the start of overland cruise
Sonic Boom Analysis Using CFD Off - Body Pressure
1. Use CFD off - body pressure at the location of 3 body lengths (3BL) below the aircraft.
2. Use an augmented Burgers equation to propagate the CFD off - body pressure through the atmosphere to the ground.
3. Compute the perceived level of decibels (PLdB) of the ground signature.
3BL below aircraft Propagation using augmented Burgers equation ground
Sonic Boom Analysis Using Reversed Equivalent Area
1. Reversely propagate the off - body pressure to 50 ft below the aircraft.
2. Convert the reversely propagated pressure to equivalent area.
3. Propagate the equivalent area to the ground and compute its PLdB value.
Conversion of reversely propagated pressure to A using Whitham’s F - function e,r Reverse propagation using augmented Burgers equation Reversed equivalent area A e,r (Equivalent body of revolution) ground Finding a configuration with Finding a configuration with low - boom low - boom undertrack signature shape for the reversed equivalent area
Low - Boom Concept at Start of Overland Cruise (SOC)
Concept Passenger No. MTOGW OL Mach OL Range OW Mach OW Range 46 - PAX 46 147,600 lb 1.7 3317 n m 1.8 3671 nm Body length = 232 ft, Wingspan = 60 ft Target sonic boom noise = 69.9 PLdB
Optimal Mission Profile for Low - Boom Supersonic Concept
Two advantages of the low - boom mission profile with fixed angle of attack for cruise: • Easier to retain the designed low - boom characteristics at the start of cruise.
• Better fuel efficiency for cruise.
Fixed cruise altitude vs fixed angle of attack (or fixed lift coefficient)
Benefits of Optimal Mission Profile for Low - Boom Concept
OL Cruise Constraint Passenger No. MTOGW OL Mach OL Range OW Mach OW Range Fixed Altitude 46 147,600 lb 1.7 3317 nm 1.8 3671 nm Fixed AoA 46 147,600 lb 1.7 3725 n m 1.8 3671 nm For same dp/p, higher alt lower PLdB
Assessment of Off - Design Low - Boom Characteristics
Find an equivalent area target with the lowest PLdB value while having an acceptable inverse design error.
(acceptable inverse design) subject to (Whitham’s theory) The design vector d consists of coordinates of control points of a Bezier curve as a parametric form of A .
e
Undertrack Low - Boom Characteristics for Cruise Segment
For the 46 - PAX concept, the low - boom characteristics at the end of low - boom cruise are better than those at SOC. This is due to the reduced cruise weight and increased cruise altitude.
Off - Track Sonic Boom Analysis
1. Use CFD off - body pressure at the location of 3BL below the rotated aircraft.
2. Use an augmented Burgers equation to propagate the CFD off - body pressure along the azimuthal direction through the atmosphere to the ground.
3. Compute the perceived level of decibels (PLdB) of the ground signature.
Propagation using augmented Burgers equation ground
Off - Track Low - Boom Characteristics at Start of Cruise (I)
• The 46 - PAX concept behaves like a body of revolution for effective distance < 120 ft.
• The aft low - boom characteristics starts to deteriorate for off - track angle = 30 deg.
Off - Track Low - Boom Characteristics at Start of Cruise (II)
• The 46 - PAX concept behaves like a body of revolution for effective distance < 120 ft.
• The aft shape of the equivalent area target has an almost linear area increase for off - track angle 35 deg.
Conclusions
• This work suggests that within the low - boom design space, there
exist configurations capable of retaining favorable low - boom
characteristics throughout cruise, while maintaining a constant - CL
cruise state that maximizes range.
• The analysis method for assessment of off - design low - boom
characteristics can be used to screen out supersonic configurations
not feasible for robust low - boom design over the primary boom
carpet for the entire cruise segment.
Acknowledgement
This work is funded by the NASA Commercial Supersonic Technology (CST) Project.