Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value...

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Design for RVSM Compliance RSSE & 3σ Error Evaluation James Egberg Aerospace Engineer This document does not contain any export controlled technical data.

Transcript of Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value...

Page 1: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

Design for RVSM Compliance RSSE & 3σ Error Evaluation

James Egberg

Aerospace Engineer

This document does not contain any export controlled technical data.

Page 2: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

DESIGN FOR RVSM COMPLIANCE

Presentation Overview

Company

Experience

RVSM compliance

Systematic altitude error & SSEC

Random altitude error & estimation

RSSE & 3σ Error Evaluation

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Page 3: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

UNITED TECHNOLOGIES AEROSPACE SYSTEMS

UTC/UTAS

Formerly, Goodrich

Formerly, Rosemount Aerospace (current legal identity)

Air Data Products (RVSM Related) Pitot-Static Probes Flush-Static Plates SmartProbe® Air Data System Air Data Computers

Air Data Products (Other) Pitot Probes AOA/AOS Vanes TAT Probes Ice Detectors And More…

Burnsville, Minnesota

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Page 4: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

JAMES EGBERG

B.S. from U of MN in Mechanical Engineering

11 years experience at UTAS (Goodrich) with Pitot-static probes and altimetry systems.

Extensive work on altimetry system of 19 different aircraft designs from a number of aircraft manufacturers. 11 Of these currently have, or plan to obtain RVSM certification.

Expertise:

Flight test data processing and evaluation (10 Aircraft)

SSEC calibration (15 Aircraft)

Pitot/static system performance evaluation (9 Aircraft)

Wind tunnel testing and evaluation

Aerospace Engineer

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Page 5: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

RVSM COMPLIANCE

System Design

Probe design

Probe placement

Estimation of altimetry systems accuracy

Flight Test Evaluation

Calibration of altimetry system

Evaluation of residual altitude errors

RVSM Certification

Produce material for RVSM certification package

Our Role in RVSM Compliance

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Page 6: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

RVSM REQUIREMENTS

Requirement: 91.180, Appendix G of Part 91

Appendix G, Section 2, (e)(1): “At the point in the full RVSM envelope where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.”

Appendix G, Section 2, (e)(2): “At the point in the full RVSM flight envelope where mean ASE plus three standard deviations reaches its largest value, the absolute value may not exceed 200 ft.”

Informational Document: A-C 91-85

“This AC describes an acceptable means, but not the only means, for authorization of aircraft and operators to conduct flight in airspace or on routes where RVSM is applied”

Overview

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Page 7: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

MEAN ASE < 80 FT

ASE: The difference between the pressure altitude calculated by the air data system and the free stream (true) pressure altitude.

Mean ASE: The average ASE across the fleet at a given flight condition. (UTAS interpretation)

Definitions

-100

-50

0

50

100

150

200

0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75Alt

itu

de

Err

or

(ASE

) ft

Mach

Example ASE Plot (10 Aircraft)

29kft-Light29kft-Heavy41kft-Light41kft-Heavy

-100

-50

0

50

100

150

200

0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75Alt

itu

de

Err

or

(ASE

) ft

Mach

Example Mean ASE Plot (Mean of 10 Aircraft)

29kft-Light29kft-Heavy41kft-Light41kft-Heavy

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Note: All data presented herein is generated for educational purposes

Page 8: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

MEAN ASE < 80 FT

SSEC (Static Source Error Correction): Correction of the pressure

sensed by the static system to the undisturbed ambient pressure

Static Source Error Correction

-100

-50

0

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100

150

200

0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75Alt

itu

de

Err

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(ASE

) ft

Mach

Example SSEC Plot

29kft-Light29kft-Heavy41kft-Light41kft-HeavySSEC

-40

-30

-20

-10

0

10

20

30

40

0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75

Alt

itu

de

Err

or

(ASE

) ft

Mach

Example Mean ASE PlotSSEC Applied29kft-Light

29kft-Heavy41kft-Light41kft-Heavy

SSEC is typically a Mach based correction (at minimum)

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Page 9: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

MEAN ASE < 80 FT

Relationship between measured static pressure and freestream static pressure can change as a function of aircraft AOA.

This may also be considered an altitude, weight or W/delta effect AOA = ƒ(Speed, Altitude, Weight, … )

Example: AOA Effect

Reducing Mean ASE

Probe Placement

Probe Design

AOA/Altitude/Weight

Compensation.

-40

-30

-20

-10

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0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75

Alt

itu

de

Err

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(ASE

) ft

Mach

Example Mean ASE PlotSSEC Applied

29kft-Light = Min W/δ = Min AOA29kft-Heavy41kft-Light41kft-Heavy = Max W/δ = Max AOA

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Page 10: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

MEAN ASE < 80 FT

AOA Effect Mitigation – Probe Design

Probes can be custom designed to minimize AOA effects caused by A/C aerodynamics

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

-4 -2 0 2 4 6 8

ΔP

s/Q

c

Angle of Attack (AOA) °

AOA Compensation with Probe Design

Result

WT (Probe)

CFD (A/C)

The probe can also be designed to reduce the magnitude of the Mach-based SSEC

correction.

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Page 11: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

MEAN ASE < 80 FT

Pneumatic AOA used for SSEC correction

AOA Effect Mitigation – SmartProbe® Air Data System

Multiple RVSM compliant systems with SmartProbe® ADS

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Page 12: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

MEAN ASE < 80 FT

Un-calibrated Aerodynamic Effects:

Mach effect

AOA effect

Altitude effects (related to Reynolds number)

Optional A/C components which affect pressure field

Imperfections in SSEC:

Unmitigated random errors of flight test aircraft

Errors in reference system of flight test aircraft

Transducer aging

Sources of Mean ASE

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Page 13: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

3-SIGMA RANDOM ERROR

Aircraft Manufacturing

Probe/Port Manufacturing

Probe Mounting

Pressure Transducer

-200

-150

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0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75

Alt

itu

de

Err

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(ASE

) ft

Mach

Example ASE Plot (30 Aircraft)

41kft-Heavy

Mean & 3-σ

Mean ASE + 3σ < 200ft

3-σ

Mean

Random error sources

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-80

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0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75

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itu

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) ft

Mach

Example ASE Plot (30 Aircraft)

29kft-Light29kft-Heavy41kft-Light41kft-Heavy

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Page 14: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

3-SIGMA RANDOM ERROR

A/C Manufacturing Tolerance

Skin Waviness Steps & Gaps

Quantifying the effect: Theoretical computation, wind tunnel, flight testing, and/or CFD

0

50

100

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0.2 0.4 0.6 0.8

Alt

itu

de

Err

or

(ft)

Mach

Skin Waviness and Standoff Height

0"2"4"6"8"

Static port Standoff

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Page 15: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

3-SIGMA RANDOM ERROR

Probe Manufacturing

Probe Contour Static Port Placement

Static Port Finish Probe Alignment

Quantifying the effect: Wind tunnel testing

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Page 16: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

3-SIGMA RANDOM ERROR

Probe Mounting

Quantifying the effect: Theoretical computation, wind tunnel, flight testing, and/or CFD

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Page 17: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

3-SIGMA RANDOM ERROR

Typically a small error contributor

200 ft error at 41kft correlates to 1.71 mbar

Commonly accepted measurement accuracy of static

pressure is near 0.25 mbar (EUROCAE ED-140, ARINC

738)

Pressure Transducer Accuracy

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Page 18: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

3-SIGMA RANDOM ERROR

Statistical analysis to compute 3-σ random altitude error

Flight test data verifies this estimation – but a statistically representative sample will

not be available until after RVSM certification is complete.

Due to RSS’ing, the impact of large error sources are disproportionately large.

1002 + 252 + 252 + 252 + 252 = 112

Quantify effects of Random Error

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Page 19: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

SUMMARY

The systematic error (Mean ASE) and random error (3-σ) can

be estimated by analysis in the design of the altimetry

system.

Aerodynamic effects are the primary sources of ASE

(especially at high Mach), while transducer accuracy is a

minor source of error.

There are many sources of error that must be accounted for in

the evaluation of RVSM compliance. This requires

extensive analytical effort and flight testing in order to show

compliance to RVSM requirements.

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Page 20: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

QUESTIONS

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Page 21: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

3-SIGMA RANDOM ERROR

Quantify Effects of Random Error

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Example: Mach 0.7, 35kft, Light Weight

Error Type 3-σ Error Level (ft) Effect on RSS (ft) Typical level of error (1-σ)

Skin Waviness 120 49 40

Steps&Gaps 90 26 30

Probe Repeatability 60 11 20

Probe Mounting 45 6 15

Pressure Transducer 30 3 10

RSS 170

Although large sources of error tend to dominate the 3-sigma

analysis, smaller sources of error can impact the accuracy of

an individual unit.

Page 22: Design for RVSM Compliance...where mean ASE reaches its largest absolute value, the absolute value may not exceed 80 feet.” Appendix G, Section 2, (e)(2): “At the point in the

FLIGHT TESTING

Typically done in with Mach sweeps

Either done at a range of W/delta, or a range of weights and

altitudes

Typically a trailing cone used as reference static system

RVSM Airspace

Each Point at

Heavy and Light

Weight

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