This presentation describes an unconventional process for analyzing and validating non-linear aerostructures

Herrera, Claudia Y.

Lung, Shun-Fat

Spivey, Natalie D.

NASA Technical Reports Server

Aeroelastic Response of the Adaptive Compliant Trailing 
Edge Transition Section
Claudia Y. Herrera, Aerospace Engineer, and Natalie D. Spivey, Aerospace Engineer
NASA Armstrong Flight Research Center, Edwards Air Force Base, California 93523
Shun-fat Lung, Structures Engineer
Jacobs Engineering, NASA Armstrong Flight Research Center, 
Edwards Air Force Base, California 93523
San Diego, CA
January 4 – January 8, 2016
AIAA SciTech 2016 Structures, Structural Dynamics, and Materials Conference
https://ntrs.nasa.gov/search.jsp?R=20160000699 2019-08-31T04:52:39+00:00Z
Outline
• Introduction
• Test Article Overview
• Ground Testing Approach
• Aeroelastic Analysis
• Flight Testing Approach
• Summary and Conclusions
2AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
Introduction
• Small Business Innovation Research program 
initiative between AFRL and FlexSys, Inc.
• Several aerodynamic benefits of an adaptive airfoil
– Noise reduction
– Structural Load alleviation
– Improve aerodynamic efficiency
– Increase control surface effectiveness
• AFRL/NASA ERA partnership to integrate the Adaptive 
Compliant Trailing Edge (ACTE) Flaps and NASA 
Armstrong’s SCRAT GIII
• Designed to deflect from -2° to 30° in flight, shown in the 
figure
• Accountable for systems integration, flight-test execution, 
and assessing the airworthiness of the integrated flight 
system to support a flight test campaign that occurred from 
November 2014 – April 2015
• Clearance of transition sections and flaps done with AFRC 
airworthiness processes and requirements
The ACTE flaps at 30° of deflection flown on SCRAT
AIAA SciTech 2016 SDM 3NASA AFRC - C. Herrera
Next Gen 
Aircraft
Test Article Overview
Overview of SCRAT, Flight Testbed
– A modified GIII, SubsoniC Research Aircraft (SCRAT), for 
flight research experiments intended for advancing flight 
technologies
– Acquisition of research data, and a telemetry system 
transmits the data to the control room, where researchers 
and engineers monitor research experiments and safety-
related information
– Baseline SCRAT flight characteristics well understood.
– Flight hardware removed from the SCRAT in support of 
integration of the ACTE flaps
4AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
Disney Scrat
NASA SCRAT
Test Article Overview
Overview of the ACTE Flap, Flight Test Article
– Replaced the NASA SCRAT conventional Fowler flaps on both the left and right sides of aircraft
– Employed the same attachment points on the wing as the Fowler flaps 
– Measures approximately 19 ft by 2 ft and entirely replaces a Fowler flap
5AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
– Five main components: 1) inboard transition section (ITS), 
2) Main flap, 3) outboard transition section (OTS), 4) the 
flap spar, 5) the actuation system
– Flaps deflected before each flight
– Actuation system deflected ACTE flaps through operational 
range of -2° (up) to +30° (down), relative to the wing OML
– Created the continuous mold-line as 
the flap was deflected through its full 
range of operation
– Connected main flap section to wing 
OML
– Inboard and Outboard are similar in 
shape; vary in size by wing taper
– Strong but flexible enough to 
withstand the aero loads experienced 
during flight
– Operation exercised flap through 
large deformations
– Potential for supersonic flow, 
increasing chance of failure.
– Monitoring of panel-type responses 
during flight-testing.
Importance of the Transition Sections
Test Article Overview
AIAA SciTech 2016 SDM 6NASA AFRC - C. Herrera
Ground Testing Approach
Build-up Approach to Ground 
Testing
• Model validation in the form of ground 
testing 
• Building of confidence in modeling and 
testing methods
• Insight into the compliant structure 
technology early in the project
• Access to prototype test articles
– Prototype series 2 and 3
– “A” designation referred to main flap
– “B” designation referred to TS’s
• Ground vibration tests highlighted yellow
7AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
AIAA SciTech 2016 SDM 8NASA AFRC - C. Herrera
Prototype - P2.2B Ground Vibration Testing
• The test objectives were:
1) Consider any apparent change in stiffness due to 
changing the flap deflection
2) Evaluate accelerometers as instrumentation on flexible 
structure
3) Evaluate various types of excitation methods and 
instrumentation
4) Evaluate finite element model (FEM) techniques 
employed
• Two test configurations
1) Cantilevered from a milling machine
2) Free-free using bungees
• Lessons Learned
1) Local modes on test structures should be instrumented.
2) Non-structural components should be modeled
3) Certain accelerometer locations were more capable of 
capturing mode shapes
4) Shaker excitation and impact hammer were needed for 
excitation
5) Most favorable excitation location was on the fixed wing 
representative portion
Ground Testing Approach
Ground Testing Approach
AIAA SciTech 2016 SDM 9NASA AFRC - C. Herrera
Prototype - P3.2B Ground Vibration Testing
• Objective: to measure modal characteristics at -2°, 0°, and 
+30°
• Test article: P3.2B (full-scale, right-side ITS)
• Analyzed in two steps
1) Deflection of FEM by FlexSys’ inputs.
2) Modal analysis on deflected FEM
• An equivalent Young’s modulus in a linearized non-linear 
structural analysis
• The test objectives were:
1) Quantify change in frequencies and mode shapes as a 
function of flap deflection with the test article in a free-
free boundary condition
2) Evaluate analytical FEM techniques employed
3) Determine which FEM software (ANSYS® vs. 
Nastran™) is more accurate in analytically deflecting 
the ACTE flap to best represent the ACTE structural 
modes
4) Evaluate various types of excitation methods
5) Determine what design variables to use in potential 
future FEM updates
• Only free-free boundary condition
Ground Testing Approach
P3.2B Ground Vibration Testing
• Lessons Learned and Observations
1) Comparison of ANSYS® vs. Nastran™ deflected FEM
2) Good comparison to GVT results from ANSYS®
3) Analytical results lower than GVT results for critical 
modes
4) Post-test FEM update not required
5) Significant effect on the mode shapes and frequencies 
by deflecting and applying an internal load
6) Required multiple types of excitation
7) Unexpected outcomes - Unpredicted mode observed at 
30 degs due to lack of stiffness caused by missing main 
flap section; high damping levels 
• Decrease in frequencies as a function of increased 
deflection
• Observations from GVT informed the planning of the 
full flap GVT
• Correlation of GVT results to analytical predictions 
informed the model update of the full flap FEM
10AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
Mode 
-2° (Up) 0° (Wing OML) 30° (Down) 
Test 
(Hz) 
FEM 
(Hz) 
% 
Change 
Test 
(Hz) 
FEM 
(Hz) 
% 
Change 
Test 
(Hz) 
FEM 
(Hz) 
% 
Change 
1 31.4 27.2 -13.3% 31.1 26.8 -13.8% 28.5 29.6 4.1% 
2 --- --- --- --- --- --- 29.5 --- --- 
3 38.2 33.5 -12.3% 37.0 33.1 -10.6% 35.5 31.7 -10.7% 
4 42.3 39.3 -7.0% 42.1 38.8 -7.8% 37.7 37.4 -0.8% 
5 46.4 45.1 -2.8% 46.2 44.5 -3.8% 42.3 44.5 5.3% 
6 50.4 46.5 -7.8% 50.4 46.6 -7.4% 45.0 45.3 0.8% 
 
Unpredicted mode non-existent in 
other deflections
Ground Testing Approach
Flight Article Right Flap Free-Free Ground 
Vibration Testing
• Test article was right side ACTE flap 
• Objectives were to measure modal 
characteristics at 0°, +15° and +30° with a 
free-free boundary condition
• Test objectives were to:
1) Verify expected trend in frequencies as a function of 
deflection
2) Acquire the data to validate and update the flap FEM 
for 0°, +15° and +30° flap deflections
3) Acquire weight and CG measurements for the flight 
article
4) Evaluate various non-contact sensing methods for 
acquiring GVT data
1) Laser Doppler vibrometer
2) Photogrammetry
11AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
Ground Testing Approach
• Flight Article Right Flap GVT Results
– Increase in frequencies as a function of deflection
– Only first three modes captured based on frequency range of flutter analysis
– Flight test instrumentation locations on the transition sections decided by mode shapes.
– Acquisition of data required to perform FEM update.
• Updated flutter analysis led to foregoing of the last GVT, the Mated SCRAT/ACTE GVT
AIAA SciTech 2016 SDM 12NASA AFRC - C. Herrera
Aeroelastic Analysis
Prototype Model Correlation
• P3.2B FEM extracted from the full ACTE flap FEM
• General decrease in frequencies as a function of increasing deflection
• Analytical method of deflection was established: ANSYS vs. Nastran
• Model update parameters for transition sections
13AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
Mode -2° 0° (Wing OML) 30° 
1 27.2 26.8 29.6 
2 33.5 33.1 31.7 
3 39.3 38.8 37.4 
4 45.1 44.5 44.5 
5 46.5 46.6 45.3 
 
Aeroelastic Analysis
Flight Article Model Update
• Linearized analysis
– Material properties validated by P3.2B GVT; applied to TS of 
the full flap FEM
– An individual FEM for each deflection
– FEMs updated to match GVT results
– Compliance to FEM update requirements (NASA-STD-5002)
14AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
Mode 0° (Wing OML) 15°  30°  
1 13.7 14.1 14.9 
2 17.4 18.5 19.2 
3 22.8 23.8 23.8 
 
Mode 
0° (Wing OML) 15° (Down) 30° (Down) 
FEM 
(Hz) 
GVT 
(Hz) 
Delta 
FEM 
(Hz) 
GVT 
(Hz) 
Delta 
FEM 
(Hz) 
GVT 
(Hz) 
Delta 
1 13.7 13.4 -2.2% 14.1 14.1 0.0% 14.9 14.8 -0.7% 
2 17.4 17.7 1.7% 18.5 18.3 -1.1% 19.2 18.8 -2.1% 
3 22.8 22.9 0.4% 23.8 23.9 0.4% 23.8 24.9 4.6% 
 
• Analytical mode shapes and frequencies from Nastran
• General increase in frequencies versus increasing 
deflection
Aeroelastic Analysis
Pre-flight Analytical Predictions
• Provided trends across flight envelope and 
informed flight-testing
• Development of structural and aero models for 
two fuel conditions and various flap deflections
Structural Modal Analysis
• Model integration and analysis using Nastran
• GVT-correlated SCRAT empty/full fuel FEMs 
baseline aircraft GVT 
• SCRAT modeled as simple stick model
• Fowler flaps modeled as point masses
– Removed for integration of ACTE
– Attachments to aircraft modeled as spring 
elements
15AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
Baseline SCRAT FEM SCRAT with ACTE flaps
SCRAT FEM modes with ACTE flaps
ACTE 
attachments 
to aircraft 
Aeroelastic Analysis
Flutter Analysis
• Performed using the ZAero code
– Matched point analysis
– Mach numbers 0.6, 0.7, and 0.8
• Encompassed full fuel and empty fuel 
conditions with the ACTE flaps at 
various deflections
• Flutter crossing at 2.0% damping
• High flutter margins 
– Sensitivity analysis was also done with 
varying spring connection stiffness 
values
• Show flutter speeds increase with 
increasing flap deflection
• Provided frequencies that can be 
compared against flight measurements
16AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
Flight Testing Approach
Pre-flight Frequency Predictions
• Developed for each fuel condition/flap deflection.
– Anchor points: Frequencies as a function of dynamic 
pressure for flap deflections analyzed
– Spot checks: Frequency trends as a function of flap 
deflection
Project Approach
• Build-up approach
– Low/slow => high/slow => high/fast => low/fast
– Small deflections => max Mach and max dynamic 
pressure conditions
– Large deflections => reduced envelope, M0.55
• Safety chase usage
• Staffed AFRC control room
• Wide-ranging suite of flight test maneuvers
– 2-1-1’s, Wind-up turns, POPU, raps, etc.
– Raps excited low frequency modes
– A variety of other maneuvers excited higher frequency 
modes: 2-1-1’s, turbulence and other anti-symmetric 
maneuvers
AIAA SciTech 2016 SDM 17NASA AFRC - C. Herrera
Pre-flight Analytical Predictions for ACTE 0°
Flight Testing Approach
Transition Section Results
• Transition section instrumentation determined by 
motion observed in mode shapes
• Right side instrumentation mirrored on left side
• Monitored all accelerometers
• Strain gages sampled at 1000 Sa/sec for monitoring
• InterActive Display Software (IADS) software usage:
– Monitor data
– Calculate PSDs
– Perform HPD estimations.
• High frequencies tracked for panel-type responses
AIAA SciTech 2016 SDM 18NASA AFRC - C. Herrera
   Left Side Flap Right Side Flap 
Mode Description 
Flight Freq. 
(Hz) 
Damping 
(%) 
Flight Freq. 
(Hz) 
Damping 
(%) 
1 ACTE ITS symm 19.1 2.4% 19.3 8.3% 
2 ACTE ITS anti 18.3 7.4% 18.3 5.5% 
3 ACTE OTS symm 21.4 6.3% 21.4 4.5% 
4 ACTE OTS anti 22.4 11.8% 22.4 7.6% 
 
Transition 
Section 
Sensor 
Freq. 
(Hz) 
ITS FL2006A 282.8 
OTS FL2016A 241.6 
OTS FL2016A 282.8 
 
TS flight-test response for ACTE 0°
Right TS High 
frequency response
Right ACTE Instrumentation
Flight Testing Approach
AIAA SciTech 2016 SDM 19NASA AFRC - C. Herrera
Age old battle: Analysis versus Test
• Anchor point results compared directly to analysis
• Spot check results for result trend comparisons
• Good correlation for ITS and OTS low frequency 
results
– Were in line with empty/full fuel values, considering 
the fuel and flight condition variations
• Similar good correlation for ITS and OTS high 
frequency results
– Multiple frequencies were measured 
– No gross deviations from analytical predictions
Right TS High 
frequency response
TS analysis/test comparison for 0°
Description 
Analytical 
Empty Fuel 
Freq. (Hz) 
Left Side 
Flight Freq. 
(Hz) 
Right Side 
Flight Freq. 
(Hz) 
Analytical 
Full Fuel 
Freq. (Hz) 
ACTE ITS symm 19.28 19.1 19.3 18.44 
 ACTE ITS anti 19.34 18.3 18.3 16.45 
ACTE OTS symm 21.8 21.4 21.4 20.05 
ACTE OTS anti 23.2 22.4 22.4 20.23 
 
Sensor Flight Analysis
FL2006A 282.8
295FL2016A 241.6
FL2016A 282.8
Summary and Conclusions
• Successful structural integration of two non-conventional control surfaces into an existing testbed
• Need for non-linear analysis created by large deflections applied to compliant structure
• Build-up ground testing approach applied:
– Allowed for investigation and validation of ground test techniques
– Validated modeling and analysis methods
• A set of TS testing/FEM development iterations was exercised
– Development of accurate flight article FEM
– Ensured accurate final flutter analyses
20AIAA SciTech 2016 SDM NASA AFRC - C. Herrera
• Final flutter analyses were performed:
– Showed compliance with the 20% flutter margin requirement
– Development of pre-flight flutter predictions for the flight test 
campaign
• Flight test results used to complete airworthiness process.
– Various types of comparisons performed
– Analysis to test comparison showed acceptable results
• Follow-on work is being planned:
– Extension of Mach
– Acoustic signature evaluation
• Potential to reveal unstable panel responses


Aeroelastic Response of the Adaptive Compliant Trailing Edge Transition Section

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server