2 - AVTPE-ConOp-2019-000.pdf

National Aeronautics and Space Administration

Commercial Supersonic Technology Low Boom Flight Demonstration Phase 2:

Acoustic Validation Test Planning, and Execution

(AVTPE)

Concept of Operations AVTPE-ConOp-2019-000

Release date: May 10, 2019

Prepared by:

Larry J. Cliatt, II CST Principal Investigator/ AVTPE Research Lead

LARRY CLIATT Digitally signed by LARRY CLIATT Date: 2019.05.14 10:43:19 -07'00'

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Approved By:

Peter G. Coen CST Project Manager/ LBFD Mission Manager

Craig L. Nickol LBFD Project Manager

Heather A. Maliska AFRC Thrust 2 Project Manager

Jay Brandon LBFD Chief Engineer

Brent R. Cobleigh FDC Project Manager

David M. Richwine LBFD DPM-Technology

Brian K. Strovers CST Chief Engineer

Brett A. Pauer LBFD Lead Operations Engineer

Lori P. Ozoroski LBFD Aero Lead & CST ProVIT Technical Lead

David N. Larson LBFD Lead Pilot

HEATHER

MALISKA

Digitally signed by HEATHER

MALISKA

Date: 2019.05.14 10:52:22 -07'00'

BRIAN STROVERS

Digitally signed by BRIAN

STROVERS

Date: 2019.05.14 11:03:19 -07'00' BRETT PAUER Digitally signed by BRETT PAUER

Date: 2019.05.14 12:32:59 -07'00'

BRENT COBLEIGH Digitally signed by BRENT COBLEIGH Date: 2019.05.14 13:24:45 -07'00'

DAVID LARSON Digitally signed by DAVID LARSON Date: 2019.05.15 08:35:00 -07'00'

DAVID RICHWINE Digitally signed by DAVID RICHWINE Date: 2019.05.16 10:49:07 -04'00'

LORI OZOROSKI Digitally signed by LORI OZOROSKI Date: 2019.05.16 11:32:37 -04'00'

JAY BRANDON

Digitally signed by JAY

BRANDON

Date: 2019.05.16 12:44:08 -04'00'

PETER COEN Digitally signed by PETER COEN Date: 2019.05.22 00:10:12 -04'00'

CRAIG NICKOL Digitally signed by CRAIG NICKOL Date: 2019.05.22 10:52:16 -04'00'

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Table of Contents

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References

1. “Advanced Air Vehicles Program Commercial Supersonic Technology Project Overland

Supersonic Flight FY19 Sub-Project Test Plan.”

2. “Low-Boom Flight Demonstration Mission Research Data Plan (RDP),” LBFD-01-019-RDP.

October 2018

3. LBFD C609 QueSST Configuration Release C Package. Document number: “2004-0031-B

C609 Shaped Boom Performance.xlsx,” March 2018.

4. Richwine, Michael and Dunn, Noah. “Effects of Atmosphere on LBFD Sonic Boom Ground

Loudness,” December 2018.

5. “SonicBAT Program Flight Test Plan for Edwards AFB,” Wyle Technical Note TN 15-32, November.

6. LBFD Delta Preliminary Design Review (DPDR). “Aerodynamics and Performance,” July

2018.

7. “Shock Sensing Probe Objectives and Requirements Document,” June 2018.

8. “Airborne Location Integrating Geospatial Navigation Systems (ALIGNS) for SSP (Shock

Sensing Probe Objectives and Requirements Document,” ALIGNS-ORD-001, 2018.

9. “Airborne Background Oriented Schlieren using Celestial Objects Phase I Objectives and

Requirements Document,” AirBOSCO-ORD-001, December 2018.

10. “Airborne Back Ground Oriented Schlieren Phase 4 Objectives and Requirements

Document,” ABOS4-ORD, August 2018.

Acronym/Initialism List

AAMP Airborne Acoustic Measurement Platform AAVP Advanced Air Vehicles Program ADS-B automatic dependent surveillance broadcast AFRC Armstrong Flight Research Center AirBOS Airborne Background Oriented Schlieren AirBOSCO Airborne Background Oriented Schlieren using Celestial Objects ALIGNS Airborne Location Integrating Geospatial Navigation System ARMD Aeronautics Research Mission Directorate AVTPE Acoustic Validation, Test Preparation and Execution BL body lengths BOSCO Background Oriented Schlieren using Celestial Objects CST Commercial Supersonic Technology DATR Dryden Aeronautical Test Range DGPS differential global positioning system EAFB Edwards Air Force Base, CA GPS global positioning system LBFD Mission Low Boom Flight Demonstration Mission LBFD Project Low Boom Flight Demonstrator Project MOE margin of error

AVTPE ConOp Rev. 000 10 May 2019 Page 5 of 28 n number of samples NASA National Aeronautics and Space Administration PLdB Perceived Level in decibels SonicBAT Sonic Booms in Atmospheric Turbulence SSP Shock Sensing Probe TV test and validation TBD to be determined z* factor of confidence

Document Change History

Revision Date Change Page 000 10 MAY 2019 Baseline None

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1 Introduction

NASA’s Aeronautics Research Mission Directorate (ARMD) strategy is guided by six strategic thrusts identified in response to three overarching global mega-drivers that will, in large part, shape the needs of aeronautical research in the coming years. These drivers and thrusts are described in the ARMD Strategic Implementation Plan (SIP) (http://www.aeronautics.nasa.gov/strategic-plan.htm).

In the near term (2015–25), Strategic Thrust 2, Innovation in Commercial Supersonic Aircraft, outlines the ARMD objective of enabling the establishment of a standard for acceptable overland supersonic flight, in cooperation with international standards organizations. ARMD will develop and validate analysis tools and technologies intended to enable the design and development of supersonic aircraft with low sonic boom. In the longer term (2025–35), ARMD will continue research on technologies required to meet the desired boom level in larger aircraft, but will also conduct research in areas related to other challenges to successful supersonic transports.

Under NASA ARMD’s Advanced Air Vehicles Program (AAVP), the Commercial Supersonic Technology (CST) Project provides the research and leadership to achieve ARMD’s objectives in Strategic Thrust 2. ARMD has formed research themes that support the desired outcomes for this strategic thrust (see the ARMD SIP link above). Within these research themes, the CST Project focuses a majority of its research on certain key Technical Challenges that are viewed as enabling to the Strategic Thrust 2 near-term outcomes. The current Technical Challenges are:

1) Integrated Low Boom Aircraft Design;

2) Sonic Boom Community Response Metric and Methodologies; and

3) Low-Noise Propulsion for Low-Boom Aircraft.

Concurrently, the CST Project conducts research in other key areas related to successful supersonic transports, such as improvements in supersonic cruise efficiency, reduced emissions, aero-servo-elasticity, and flight systems.

Based on the long trajectory of supersonic research over the past few decades, a consensus has emerged that the next required step towards achieving the goals of the Strategic Thrust 2 near-term objective and CST Project Technical Challenges is to design, build and test a large-scale flight demonstrator.

To that end, the Low-Boom Flight Demonstration Mission (LBFD Mission) is comprised of work conducted by the Low-Boom Flight Demonstrator Project (LBFD Project) and CST Projects, combined with key capabilities and assets from the Flight Demonstration and Capabilities (FDC) Project. The LBFD Project objectives will be achieved through the design, construction, and flight validation of a research aircraft called the X-59 with the capabilities required to conduct effective community response studies. The X-59 will create a shaped sonic boom signature with a calculated loudness level of 75 PLdB (Perceived Level PLdB) or less during supersonic cruise (Mach ≥ 1.4) flight. Although the aircraft will be smaller in size than future supersonic airliners, its sonic boom ground signature will be traceable to that of the larger aircraft. The X-59 will be capable of meeting the LBFD Mission requirements of performing

AVTPE ConOp Rev. 000 10 May 2019 Page 7 of 28 multiple supersonic overflights of a single community with passes that are nominally 50 miles in length, and up to 20 minutes apart on a single flight.

In preparation for the LBFD Mission community response testing, NASA will conduct a flight research campaign to verify the loudness levels of the X-59 and to validate low-noise sonic boom design tools.1 The results of this effort will go toward determining the readiness for community response testing.

2 Project Scope

The CST Acoustic Validation, Test Preparation, and Execution (AVTPE) effort is the data collection component to complement Phase 2 of the LBFD Project. The primary objective of Phase 2 is to validate that the boom loudness on the ground is acceptable for community response testing and to gather airborne and ground data that will be used to validate sonic boom propagation and acoustics models in a real atmosphere. During Phase 2, the NASA LBFD Project is responsible for X-59 flight planning and operations. The FDC Project is responsible for maturing and providing key airborne research capabilities and testbeds. The NASA CST Project is responsible for the test design, field equipment related to sonic boom measurements, and test execution.

The relationship between CST research themes and LBFD project goals and objectives is shown in Table 1. The orange box illustrates the role that the LBFD project has in supporting CST during Phase 2, and how it traces back directly to the “demonstrate” element of the LBFD project.

Table 1. Relationship between CST research themes and LBFD Project Goals/Objectives.

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• TV-03: Gather lateral ground measurements of the shock signature across width of sonic boom.

• TV-04: Gather measurements of the shock signature in the far-field above the atmospheric boundary layer.

• TV-05: Gather longitudinal ground measurements of the shock signature along sonic boom carpet.

• TV-08: Gather data to validate the test design, instrumentation, logistics, and operational considerations for application to LBFD Phase 3 community response testing.

Figure 2. LBFD Phase 2B.

3.3 LBFD Phase 2C – Flow Visualization of Shock Structure

During LBFD Phase 2C, AVTPE will us a NASA F-15 instrumented with an airborne background oriented schlieren system to:

• TV-06: Gather flow visualization of shock structure in the near-field (<10 BL) of the X- 59.

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Figure 3. LBFD Phase 2C

4 Sonic Boom Ground Measurements (Phase 2B)

Sonic boom datasets that are dependent on ground-based systems are considered ground measurements. These measurements are obtained from microphone arrays on the ground and by the NASA AFRC Airborne Acoustic Measurement Platform (AAMP). The AAMP measurements are compared to the microphone array measurements to determine the effects of atmospheric turbulence.

4.1 Lateral Measurements – Carpet Characterization (TV-03)

The span-wise profile of the sonic boom carpet will be measured using a ground-based microphone array system. Such measurements will use a microphone array perpendicular (lateral) to the aircraft flight path.

4.1.1 Sonic boom carpet width

AVTPE measurements will characterize the full width of the X-59 sonic boom carpet at cruise conditions. While recent analysis of the X-59 carpet width has been shown as approximately 25 nm (Figure 4), this analysis was done with standard atmospheric conditions and no winds.

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Figure 4. X-59 carpet width. Standard atmosphere, no winds.3

A sensitivity study that used historic real-atmospheric conditions showed that the real carpet width can be expected to be over 70 nm in some conditions. Figure 5 shows X-59 carpet width predictions near Edwards AFB with real atmospheres for every day in the year 2017. The weather data was taken at 12:00 Coordinated Universal Time (UTC) and the aircraft heading was due west.

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Figure 5. X-59 carpet width. Real-atmosphere.4

Table 4 lists the average and 90th percentile carpet widths for several combinations of time of day and aircraft heading. Based on this data, AVTPE will target the capabilities to measure a 50 nm sonic boom carpet width.

Table 4. X-59 carpet widths.

Real-atmosphere, as a function of time of day and heading.

4.1.2 Lateral microphone array concept

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SonicBAT,5 both the primary and secondary arrays will be 1500 ft. long with microphones spaced evenly every 100 ft. Since NASA sonic boom prediction tools show that the most variable part of the X-59 sonic boom carpet is at 20° – 30° phi angle (Figure 7), the secondary array will be placed at approximately 25° phi angle. Figure 8 shows candidate locations for the two microphone arrays.

Figure 8. Turbulence measurements microphone array locations.

4.2.1.2 Far-field measurements

Measurements of the shock signature of the X-59 at design cruise conditions will be taken above the atmospheric boundary layer with minimal atmospheric turbulence effects. The NASA AAMP is a TG-14A-149AMT-200S motorized sailplane modified with a wing-tip microphone (Figure

9) and a data acquisition pallet.

The AAMP will be flown up to 14,000 ft. above mean sea level (MSL) to measure the sonic boom above the turbulent boundary layer of the Earth. The measurements will be compared to ground measurements (section 4.2.1.1) to determine the influence of atmospheric turbulence on X-59 sonic boom signatures.

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Figure 9. Wing tip-mounted microphone on TG-14 Motorized Sailplane in AAMP configuration.

4.2.2 Unfocused climb measurements (TV-05)

The X-59 flight profile has been designed to include supersonic climb performance that should minimize a focused sonic boom on the ground. AVTPE will take measurements to validate potential “unfocused climb” profiles that could be used during Phase 3 community testing. It is proposed that such measurements would use a microphone array that runs along the sonic boom carpet, longitudinal to the flight path.

Figure 10 shows a conceptual unfocused climb flight profile of the X-59. It is an integration of concepts from Lockheed Martin6 and NASA. The black rectangle indicates the segment of the climb where the possibility of a focus sonic boom being generated is most likely. In order to validate the capability of acoustic propagation tools to predict the sonic boom ground signature and loudness of X-59 at supersonic acceleration/climb conditions, measurements will be taken during this segment of the trajectory. The segment is approximately 50 nm long. Measurements could be taken at various phi angles where a focus sonic boom is likely to occur.

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Figure 10. Conceptual X-59 unfocused climb/accel schedule area of interest.

4.2.2.1 Longitudinal microphone array concept – Unfocused Climb

The proposed unfocused climb measurements consist of a 25 nm long array to span half of the area of interest illustrated in Figure 10. The details of this array will be described in the AVTPE requirements document (TBD #1). NASA anticipates that microphone array spacing may be customized as a result of refined unfocused climb predictions or initial longitudinal measurements at real-atmospheric conditions. The lateral microphone array concept described in section 4.1.2 could be used. Two separate climbs would have to be performed, with measurements being taken for half of the 50 nm area of interest at a time.

5 Airborne Measurements (Phase 2A/2C)

Airborne measurements are considered to be any dataset, the collection of which is conducted independently from sonic boom measurements on the ground. This includes near-field shock signatures measurements, pressure measurements on the surface of the X-59, mid-field shock signature measurements, and shockwave imaging from airborne systems.

5.1 Near-field Shock Signature Measurements (TV-02)

The characterization of the X-59 near-field shock signature will predominately be done using a specially designed nose boom capable of measuring shockwave overpressures during flight. The nose boom system is called the NASA Shock Sensing Probe (SSP)7 and will be installed on one

AVTPE ConOp Rev. 000 10 May 2019 Page 19 of 28 or more NASA F-15 aircraft. Measurements will be taken in-flight at X-59 design cruise conditions, for a range of body lengths (BL) and phi angle combinations. Body length is based on the X-59 length. Figure 11 shows a table of the 31 proposed test points and a diagram that illustrates where the SSP aircraft (shown in blue) will be locating with respect to the X-59 (shown in red). The test points that are above the aircraft (+/- 130 – +/- 150 degrees) will be within 10 body lengths of the aircraft. The planned separation for measurements above the aircraft is to be determined based on SSP flight results (TBD #2).

Figure 11. Proposed near-field shock measurements.

To help guide the measurement aircraft, a cockpit display called the Airborne Location Integrating Geospatial Navigation System (ALIGNS)8 will provide the pilot with real-time relative positioning data and steer-to points for phi angles below the aircraft. The F-15 will align with the X-59 at the desired test point (separation distance and phi angle). The F-15 will then fly forward through the X-59 shockwave field. Once the entire shockwave field has been measured, the F-15 will reduce speed to fly background relative to the X-59, measuring the shockwave field again. This sequence will constitute a single test point. The plan would be to complete several test points on a single supersonic pass. Given the challenges of obtaining these measurements, NASA anticipates that these test points will be prioritized to ensure that key test points are achieved as resources and schedule permit.

5.2 Mid-field Shock Signature Measurements (TV-07)

Some additional shock signature measurements will be taken farther than 10 body lengths from the X-59. Notionally the measurements will be taken at approximately 20,000 ft. away from the X-59 at phi angles of 0, 10 and 20 degrees. The same approach used for near-field shock signature measurements could be used for the mid-field. However, operations will be more

AVTPE ConOp Rev. 000 10 May 2019 Page 20 of 28 challenging due to the long propagation distances and times. The additional difficulty could possibly result in an undesirable success rate.

Another approach would be for the F-15 to use ALIGNS to position itself at a desired separation and phi angle while flying ahead of the X-59. The F-15 would fly at a slower speed, allowing the X-59 shock signature to overtake the SSP on the F-15.

5.3 Surface Pressure Measurements (TV-02)

Provisions for pressure sensors will be installed into the X-59 aircraft for surface pressure measurements that will complement near-field measurements if needed. The measurements will be collected using strip-tubing pressure ports, to be installed if near-field measurements and predictions do not agree. Along with the near-field shock measurement described in section 5.1, the surface pressure measurements will help characterize the shock signature of the aircraft and provide insight into tailoring of the aft lift distribution of the aircraft.

Figure 12. Locations and count of pressure ports/tubing on X-59.

There are a total of 100 pressure ports and tubing.

5.4 Airborne Shockwave Imaging Measurements (TV-06)

While near-field and aircraft surface measurements will provide quantitative data to characterize the X-59 sonic boom pressure signature, schlieren photography will be used to provide a qualitative visualization of the near-field shock structure for comparison to computational solutions. NASA has developed the capability to take high-quality, side-view schlieren images of an aircraft in flight using a process and system called Background Oriented Schlieren using Celestial Objects (BOSCO).9 Figure 13 shows an image taken using a ground-based BOSCO system on a T-38 airplane 6.5 miles away.

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Figure 13. Ground-based BOSCO images of a T-38. 6.5 mile range.

NASA is developing the capability to take BOSCO images much closer to the target aircraft by putting the optical system on an airborne platform. The Airborne Background Oriented Schlieren using Celestial Objects (AirBOSCO)9 will place the optical system on the F-15 for AVTPE measurements. Table 6 lists the proposed AirBOSCO test points, where body length (BL) and phi-angle are defined in Figure 14. Note that the 160- and 180-degree points refer to fields of view above the aircraft. The separation between the X-59 and the imaging aircraft is to be determined (TBD #3). The separation is dependent on the size of the desired imaging field and final AirBOSCO capabilities.

Table 6. Minimum airborne shockwave images for AVTPE.

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Figure 14. Schematic of AirBOSCO imaging variables. Not to scale.

In addition to AirBOSCO, NASA is developing another technique to take side-view schlieren images. Airborne Background Oriented Schlieren (AirBOS)10 is a system that has been shown to provide high-resolution air-to-air shock imagery from above the aircraft.10 Previous AirBOS images have only been taken from above the target supersonic aircraft, which is not applicable for AVTPE. However, future concepts of AirBOS will include a side-view capability that could be used for AVTPE.

To help guide the AirBOSCO and AirBOS systems, ALIGNS will provide the F-15 pilot with real-time relative positioning data and steer points.

6 Aircraft and Range Operations

LBFD Phase 2 will use the NASA AFRC Dryden Aeronautic Test Range (DATR) facilities and capabilities. The DATR will be used to monitor surface pressure measurements, aircraft closure rates during near- and far-field measurements, and for situational awareness when multiple aircraft are involved.

7 Meteorological Measurements (TV-03, -04, -05, -07)

Shock signature development and sonic boom propagation are both dependent on atmospheric conditions from the nearfield to ground level. The knowledge of atmospheric conditions is necessary for both sonic boom flight planning and post-flight analysis.

7.1.1 Pre-flight atmospheric profiles

Pre-flight weather profiles will be used for AVTPE waypoint planning. This data would come in the form of local weather models (primary) or pre-flight global positioning system (GPS) sonde weather balloons launched from EAFB or remotely in the general area of planned X-59 sonic

AVTPE ConOp Rev. 000 10 May 2019 Page 23 of 28 boom propagation paths (secondary). EAFB services can launch weather balloons from EAFB, while NASA AFRC personnel can launch weather balloons from EAFB and other identified locations. Waypoints should be delivered to aircrew prior to pilot step.

Both weather model or balloon data would provide data to an altitude of at least 60,000-feet and with at least 1000-ft vertical resolution.

7.1.2 In-flight atmospheric profiles

Weather profiles during flight will be used for post-analysis. This data would come in the form of GPSsonde weather balloons launched from EAFB or remotely in the general area of planned X-59 sonic boom propagation paths. All balloons will be launched near aircraft take-off time.

EAFB services can launch weather balloons from EAFB, while NASA AFRC personnel can launch weather balloons from EAFB and other identified locations.

Balloon data would provide data to an altitude of at least 60,000-feet and with at least 1000-ft vertical resolution.

8 Flight Test Approach

Since the lateral microphone array concept only spans half of the carpet width, two supersonic passes will be used to capture the entire carpet width (see section 4.1.1). It is best to perform both passes with similar atmospheric conditions to best simulate a full carpet measurement. To do so requires: (1) both passes are done as close together in time as possible, and (2) both passes are done with the same aircraft flight path course.

8.1 Proposed Airspace and Flight Path

8.1.1 Airspace – Lateral measurements

Figure 15 and Figure 16 show the proposed flight path and airspace use for lateral measurements (TV-02). The proposed aircraft flight path course maximizes the sonic boom carpet width, providing more valuable data for acoustic validation. Half the sonic boom carpet profile will be measured during each individual pass. This approach will allow the most effective full-carpet measurements since both passes can be done during the same flight, with similar atmospheric and flight conditions. This approach will require coordination to be able to fly the X-59 supersonically outside of the R-2508 complex and high altitude supersonic corridor. Such a flight path would likely result in the densely populated region of southern Los Angeles County to be exposed to sonic booms as the X-59 transitions to its design cruise conditions. Measurements can also be taken using an east-to-west flight path, but it would result in a much narrower carpet. The LBFD Mission will need to consider the cost-benefit of data quality versus exposing the region to sonic booms.

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Figure 15. Proposed airspace and flight path for lateral sonic boom carpet characterization measurements (left).

Figure 16. Proposed airspace and flight path for lateral sonic boom carpet characterization measurements (right).

8.1.2 Airspace – Airborne shock signature and turbulence measurements

Figure 17 shows the proposed airspace to be used for airborne shock signature and turbulence measurements:

• Near-field shock signature measurements (TV-02)

• Mid-field shock signature measurements (TV-07)

• Effects of atmospheric turbulence measurements (TV-04)

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Figure 17. Proposed airspace and flight path for airborne and turbulence measurements.

8.1.3 Airspace – Airborne shockwave imaging

Figure 18 shows the proposed airspace to be used for airborne shockwave imaging (TV-06).

Figure 18. Proposed airspace for airborne shockwave imaging

The planned flight path changes throughout the day depending on sun position and elevation.

Coordination with the Air Force will need to be done to fly outside of the high altitude supersonic corridor, especially since these measurements include an F-15 that will produce loud sonic booms.

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8.1.4 Airspace – Unfocused climb measurements

Figure 19 shows the proposed airspace to be used for unfocused climb measurements (TV-05).

Figure 19. Proposed airspace and flight path for longitudinal sonic boom measurements.

Coordination with the Air Force will need to be done to fly outside of the high altitude supersonic corridor.

8.2 Flight Conditions and Maneuvers

All test points (except unfocused climb points) will be performed at design cruise conditions, nominally Mach 1.4 at 53,000 ft.

Detailed flight conditions will be presented in the AVTPE flight test plan.

8.3 Test Point Matrix

Table 7 lists the conceptual minimum number of test points and flights for each measurement type of LBFD Phase 2 and AVTPE measurements. The table also traces the measurements to their respective CST objectives. The number of test points and number of flights are based on minimums assuming ideal research data collection. This does not take into consideration any reserve flights, repeated test points for accuracy, or additional data for improved analysis. Given the challenges of obtaining these measurements, NASA anticipates that these test points will be prioritized to ensure that key test points are achieved as resources and schedule permit.

The AVTPE flight test plan will take into consideration the effects of resolved TBDs (section 9), and legacy sonic boom flight research considerations.

Table 7. AVTPE Minimum Test Point Matrix.

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Phase 3 community response testing requirements will add additional flights to the test point matrix (TBD #7). During Phase 2 it should be demonstrated that the X-59 can produce sonic booms with a relevant range of PLdB.

8.3.1 Minimum test point number rationales

The minimum number of test points for a specific ground measurement is four (4). This is based on:

(Equation 1)

Where n is the number of samples, z* corresponds to the desired confidence level and MOE is the margin of error. z* becomes 1.96 for a desired confidence level of 95%. For a worst-case scenario, if the success criterion is defined in such a way that the measurements lie within a standard deviation from the mean (i.e. assume the margin of error (MOE) to be the same order as standard deviation), then equation 1 becomes:

(Equation 1)