Armstrong (formerly Dryden) Flight Research Center continues it's legacy of exciting work in the area of dynamics and control of advanced vehicle concepts. This status presentation highlights the research and technology development that Armstrong's Control and Dynamics branch is performing in the areas of Control of Flexible Structures and Automated Cooperative Trajectories

Jacobson, Steven R.

NASA Technical Reports Server

NASA Armstrong Status 
Aerospace Control & Guidance Sub-committee 
Meeting 113 
Englewood, CO  
March 2014 
 
Steve Jacobson
661-276-7423 
Steve.jacobson@nasa.gov 
https://ntrs.nasa.gov/search.jsp?R=20140013244 2019-08-31T17:36:21+00:00Z
Abstract 
 The NASA Armstrong (formerly Dryden) Flight 
Research Center continues it’s legacy of exciting work 
in the area of dynamics and control of advanced 
vehicle concepts. This status presentation highlights 
the research and technology development that 
Armstrong’s controls and dynamics branch is 
performing in the areas of “Control of Flexible 
Structures” and “Automated Cooperative Trajectories.” 
Dryden Flight Research Center is now 
Armstrong Flight Research Center 
On March 1, 2014, NASA's Dryden Flight Research Center 
became the Armstrong Flight Research Center in honor 
of research pilot and astronaut Neil A. Armstrong. 
NASA's Western Aeronautical Test Range is now named 
for NACA director and NASA's first deputy administrator 
Hugh L. Dryden. 
CONTROL OF FLEXIBLE 
STRUCTURES RESEARCH 
 
AFC-based high-lift 
t
active controls 
load alleviation 
 
Objective  
Explore and develop aerodynamic, structural, and control 
technologies to expand the optimal wing system drag vs. 
weight design trade space for reduced energy consumption 
Technical Areas and Approaches 
Tailored Load Path Structure 
– Passive aeroelastic tailored structures  
Active Structural Control 
– Distributed control effectors, robust control laws 
– Actuator/sensor structural integration 
Aerodynamic Shaping 
– Low interference external bracing 
– Passive wave drag reduction concepts 
Active Flow Control 
– Transonic drag reduction; mechanically simple high-
lift 
Adaptive Aeroelastic Shape Control 
– Continuous control effector(s) for mission-adaptive 
optimization 
Benefit/Pay-off 
– 20% wing structural weight reduction 
– Wave drag benefits tradable for weight or other parameters  
– Concepts to control and exploit structural flexibility 
– Optimal AR increase up to 50% for cantilever wings, 100% 
for braced wings 
braced 
cantileve
r 
tailored 
multifunction
al 
passive/active 
advanced aerodynamics 
Prop Clean Struc Aero Quiet 
adaptive control 
effectors 
NASA ARMD Fixed Wing Objectives (FY19):  
Optimal Aspect Ratio +50 to +100%, TRL 3 
 
X56A Stiff Wing Envelope Clearance Completion 
Problem 
The X-56A built by Lockheed Skunkworks with AFRL funding is going through initial airworthiness flights using both stiff and 
flexible wings.  After demonstration is completed the aircraft will be transferred to NASA/FW for research in active control of 
lightweight flexible structures that can lead to lighter, more efficient, higher aspect ratio wings.  
Objective 
Demonstrate airworthiness of X-56A vehicle (with stiff and flexible 
wings) and flight systems; assess vehicle dynamic characteristics 
and provide validation of the dynamic modeling process. 
Approach 
Incrementally clear the vehicle through a systematic process of 
envelope expansion through pilot input response testing and 
computer programmed control surface movements, and record 
data with onboard research instrumentation system. 
Results 
• Eight stiff wing flights July-September 
• Vehicle was stable and controllable from takeoff up to 130 knots. 
• Good correlation between flight and predicted dynamic responses, with some model adjustments made. 
• Nose landing gear dynamics were less damped than predicted, requiring a nose landing gear modification. 
• Ship systems checked out well. 
Significance 
• Completion of X-56A Stiff Wing Envelope Clearance is a significant milestone in the progression towards inflight demonstration of 
active flutter suppression. The improved dynamic models resulting from this test will provide the ability to finalize the control system 
gains and proceed to flight with flexible wings. NASA provided range and ground safety and airworthiness advice during this flight 
phase. 
POCs (AFRC): John Bosworth, Gary Martin, Marty Brenner 
Linear Parameter Varying (LPV) Virtual 
Deformation Control 
 
LPV Shape 
Modal Filter 
LPV Inner Loop 
and Modal 
Controller 
LPV Inner Loop Control of X-56A Model 
Fuel Mass (M): 0-70 lb; Speed (V): 50-150 KEAS 
Modal 
displacement 
commands 
Shape 
Commands
Control 
Surface 
Commands 
Pre-processed 
Modal Matrices 
NASTRAN X-56A 
Model w/Fiber 
optics 
 
LPV Strain 
Modal Filter 
Ȳறሺܯሻ 
Ȱறሺܯሻ 
ݍොሺݐሻ 6 fibers 
Pitch, Roll 
 Yaw rate 
 commands 
1000’s of strain 
measurements 
 
Robust Modal Filtering: Tolerance 
to Distributed Sensor Failures 
• Motivation 
Fiber break Outboard 
Sensors 
100s of biased 
sensors 
LPV Inner 
Loop and 
Modal 
Controller 
LPV Inner 
Loop and 
Modal 
Controller 
 
Standard 
Modal Filter 
Ȳறሺܯሻ 
X-56A X-56A 
1000’s of strain 
measurements 
Experimental Fiber Optic Sensor 
Data (Childers et al., 2001) 
Gross  
outliers 
Modal  
commands Modal  commands  Robust 
Modal Filter 
ܴ Ȳ ܯ  
Down-weights 
Biased Sensors Enormous Modal  Amplitude Errors 
Wing Tip Z Deformations 
Failure at 10 seconds 
Failure Failure 
ݍොሺݐሻ ݍොሺݐሻ 
s
t
r
a
i
n
,
 
ߤ
ݏ
 
X-56A 
s
t
r
a
i
n
,
 
ߤ
ݏ
 
Fiber optic sensor station # 
CFS Research and Development Plans 
• Familiarization with Research vehicle (2014) 
– Shadow Lockheed-Martin 
– Develop NASA controller for stiff wing flights 
– Receive the X-56  from Lockheed/AFRL  
• Develop models and release them to the community (ITAR 
restrictions may apply) 
– Aeroelastic models 
– Aerodynamic coefficients (PID) 
– In-flight structural characterization/ mode shapes (PID)  
• Develop flutter and aeroelastic shape control technologies 
(ongoing) 
– Accel and Fiber optic shape sensor based controllers 
• Conduct flight research using NASA and external partner 
developed controllers (2015 and beyond) 
– NASA AFRC Flex Wing controller  
– NASA ARC Aero-efficiency controller (Nhan Nguyen) 
• Dissemination of research (ongoing)  
 
Automated, Cooperative Trajectories 
 
 
 
 
Joe Pahle 
Controls and Dynamics Branch 
NASA Armstrong Flight Research Center 
joe.pahle-1@nasa.gov 
661.276.3185 
Curt Hanson 
Controls and Dynamics Branch 
NASA Armstrong Flight Research Center 
curtis.e.hanson@nasa.gov 
661.276.3966 
What are Cooperative Trajectories? 
Aircraft are separated 
by 1 to 2 NM 
Trail aircraft flies in 
the upwash region 
of the lead’s wake 
CT is a class of Formation Flight with large 
separations between aircraft 
Results: Efficient Commercial 
Transports 
Sustained, trimmed flight within the upwash 
portion of the lead aircraft’s wake reduces the 
trailing aircraft’s total drag by as much as 
10% -15%. 
 Lower Cost per Mile 
 Reduced Particulate Emissions at 
Altitude 
 
This is the focus of the current NASA 
cooperative trajectory research activities 
Cooperative Trajectory (CT) 
Concept 
 Two or more aircraft using ADS-
B data-link communication  
 reduced separation (1 – 2 NM) 
 Automatic control to maintain 
relative location and separation 
 Probabilistic vortex models to 
estimate the initial wake 
location 
 Sensor fusion used to refine the 
wake location  
Experimental Validation 
12
10% Power 
Reduction 
F/A-18 DO-228 
1995 
Cooperative Trajectory Flight Research on the G-III SCRAT 
Goal: Develop key technologies for commercial CT operations and mature their 
TRL through demonstration in a relevant flight environment. 
Key Technologies 
 An automated CT architecture based on commercial off-the-shelf civilian data-link and 
autopilot systems 
 A robust wake-avoidance algorithm to prevent wake crossings and wake-induced upsets 
 An on-line sensor-fusion algorithm to enable robust, accurate estimates of the size and 
location of the lead aircraft’s wake structure 
Approach 
 Outfit the SCRAT G-III with a platform precision autopilot and ADS-B In 
 Additional instrumentation on the SCRAT enables exploration of wake characteristics 
German  Institute for 
Fluid Mechanics 
NASA Dryden Flight 
Research Center 
14% Fuel 
Savings 
2001 
Air Force 
Test Pilot School 
9% Fuel 
Savings 
2001 
T-38 C-17 
NASA DFRC / 
USAF FTC 
7-8% Fuel 
Savings 
2010 
C-17 
DARPA / AFRL / 
Boeing / NASA DFRC 
10% Fuel 
Savings 
2012-2013 
G-III 
NASA AFRC 
Planned for 2015 
Close Formation Flight Research Cooperative Trajectory Flight Research 
SCRAT wing pressure ports 
and hot-film sensors 
SCRAT wing structural instrumentation 
Proposed GIII CT System Configuration 
G-III INS/GPS 
and 
Instrumentation 
PPA  
OPERATOR 
STATION 
AUTOPILOT 
INTERFACE 
COMPUTER 
VIR-31A 
NAVIGATION 
RECEIVER 
FLIGHT  
DIRECTOR AUTOPILOT 
ILS 
ANTENNAS 
PPA COMPONENTS 
PPA INTERFACES 
EXISTING GIII SYSTEMS 
GAIN / ISOLATION
CIRCUIT  
RELAY 
LOC 
GS 
FLAG 
PILOT INTERFACE 
CT controller 
RS-232 
Ethernet 
Tablet 
Display  
Ethernet 
NEW CT COMPONENTS 
ADS-B in 
CAN Bus 
ADS-B 
antenna 
PPA – Platform Precision Autopilot 
AIAA 2008-6461 
G-III SCRAT CT Control Development 
 Use ADS-B from the lead, estimated winds/vehicle state from the trail, 
and probabilistic low-order vortex models to estimate the initial wake 
location region at trail distance (1-2 nm back) 
 Estimate closest distance from trail to vortex system  
 
 Control cross track to vortex, vertical track to vortex, and along track to 
lead using roll command, altitude command, and speed command 
 Adaptive roll trim gain for steady-state flight within the vortex area of influence 
 NASA G-III lacks an auto-throttle, so PLA commands are displayed to the pilot 
 
 When the trail is within the lead’s vortex area of influence, use an on-line 
sensor fusion approach to refine the estimate of the vortex core 
locations relative to the trail, and “sweet spot” estimation [in 
development] 
 
 Use the updated vortex core locations and ADS-B information from the 
lead in   the wake-avoidance algorithm to prevent wake crossings and 
wake-induced upsets [in development]  
 
Request for Information (RFI) for FAST/853 
• NASA will be releasing an RFI on FAST/853 usage in an effort 
to understand research community requirements and develop 
partnerships 
• Research and flight test capabilities for FAST 853 
– Control system research and evaluation in a single string, dual 
string,  or quad redundant environment 
» Inner loop control 
» Outer loop guidance 
» Autonomy 
– Piloted flying qualities evaluation  
– Pilot interaction with adaptive systems 
– In flight sensor development/evaluation including integration into 
the primary flight control sensor 
• RFI release spring 2014 
To Fly What Others Imagine … 


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