Project Number : PS 1.3
Development of a Smart Materials Based Actively
Conformable Rotor Airfoil
PIs:
Prof. Farhan Gandhi
Prof. Mary Frecker
Graduate Student:
Andrew Nissly
Penn State University
2005 NRTC RCOE Program Review
May 3-4, 2005
Background/ Problem Statement:
• Develop analysis and design method for conformable rotor airfoil
– achieve significant deformation required to reduce rotor vibration at N/rev
– can be viewed as the successor to rotor blade trailing-edge flaps
– advantage: integral structure (no hinges, linkages, etc.)
Deformable skin
Trailing Edge Flap
Conformable Airfoil
Technical Barriers:
• Smart actuation must have required authority (under airloads) and bandwidth
• weight, volume, and power constraints
• Airfoil cross-section traditionally designed NOT to undergo any deformation
• a fundamental change in design philosophy is required for conformable airfoil
• reduction in cross-section stiffness is required
• Large local surface strains in the skin due to shape change require novel materials
•Highly-specialized sandwiched composite skins
Task Objectives:
• Develop design methodology for a conformable (controllable camber)
rotor airfoil using a passive substructure and a limited number of actuators
– Meet specified trailing edge deflection
(camber)
– Withstand aerodynamic loads
– Consider volume (weight) constraint
Concept presented at 2004 review
Approach:
• Shape optimization starting with passive structure of predetermined topology actuated by
limited number of piezo actuator elements
– max trailing edge vertical deformation (camber) while withstanding airloads
– FEA-based optimization method, gradient-based solution method
Expected Research Results or Products:
• Develop new design methodology and obtain solution(s)
• Demonstrate feasibility of a smart-materials based conformable rotor airfoil
• controllable camber
• flexible skin sections to allow large local strains
• Develop a thorough understanding of the physical issues in this design
• Build and evaluate demonstration prototype
Numerical Testbed
• Rotor Airfoil (NACA 0012)
–
–
–
–
–
Chord length: C = 1.66 ft (50 cm)
Maximum Thickness: 12% chord
Rigid Spar from LE to 25% Chord
Only aft portion is actuated and flexible
High EI, low EA skin
Rigid
D-Spar
Axis of Symmetry
Conformable Airfoil Actuation Mechanism
A Cellular Truss
Mechanism
Active Vertical Members
(Actuators)
Point Moves
up-down as
actuators
extend/shrink
Deformed Configuration
-- Top Skin Extends
-- Bottom Skin Shrinks
Passive Linkage
Left active member
restrained
in vertical position
exaggerated rotation of
right active member
Array of such units along the airfoil chord 
Accumulation of rotation,
Build-up of camber
Limited number of actuators required, Easy to Build
0.1
Design Domain Parameterization
0.05
0
Shape Optimization:
-0.05
-0.1
• Thickness of passive elements
0 < tlower < ti < tupper
ti
-V (Contraction)
• Passive Material Area
Constrained to % of Amax
-0.15
M
Amax   l i t upper
Piezoelectric
Elements
i 1
Passive Elements
-0.2
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
+ V (Extension)
Skin Elements
0.4
0.2
Optimization Problem
0.15
0.1
Objective function
– Maximize Tip Deflection (TD) under
actuation load
J1 = Tip Deflection (TD)
0.05
0
0.2
TD
-0.05
0.15
-0.1
– Minimize deflection under air load
• Air load unchanged with changes in
airfoil shape
0.1
-0.15
0.05
-0.2
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0
J2 = wT K w = Strain Energy (SE)
– Two objective functions considered
-0.05
Kw = fair
-0.1
Single-criteria objective function: Max (J) = J1 = TD
Multi criteria (Ratio) objective function : Max (J) 
-0.15
J1 TD

J 2 SE
-0.2
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Sample Optimized Geometry:
Comparison of Two Objective Functions
0.05
0.05
0.04
0.04
0.03
0.03
0.02
0.02
0.01
0.01
0
0
-0.01
-0.01
-0.02
-0.02
-0.03
-0.03
-0.04
-0.04
-0.05
-0.01
TD Objective Function
Ratio Objective Function
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0
0.09
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.05
0.04
• DActuation ↑ with ↑ Amax using the
TD objective function
0.03
0.02
0.01
0
Y
-0.01
• DActuation ↓ with ↑ Amax using the
Ratio objective function
-0.02
-0.03
X
-0.04
-0.05
-0.01
0
0.01
0.02
0.03
TD Objective Function
25
40
0.04
0.05
0.06
3 mm
0.07
0.08
0.09
20%
3 mmAmax
20%
3 mmAmax
65%
9 mmAmax
965%
mmAmax
3 mm
10
2
9 mm
8
6
4
30
2
0
• DAirload ↓ with ↑ Amax for both
objective functions
Ratio Objective
9 mmFunction
Airload Deflection (mm)
Actuation Deflection (mm)
0
Comparison Of Objective Functions –
Actuation Deflection
45
15
35
40
45
1.6
1.2
0.8
0.4
0
20
25
30
X/Y (%)
35
40
45
15
20
25
30
X/Y (%)
35
40
45
Effect of Actuator Thickness
• DActuation ↑ with ↑ actuator
thickness for both objective
functions
7
6
• Increase in DActuation is smaller
for the TD objective function
because the passive structure is
less rigid and the actuators are
already operating close to their
free strain
Deflection (mm)
Actuation Deflections
5
4
Ratio Objective Function
3
TD Objective Function
2
Airload Deflections
1
0
2
3
4
5
Actuator Thickness (mm)
6
• DAirload ↓ slightly with ↑
actuator thickness for both
objective functions
Discussion & Conclusions
• Choice of optimal design
– Ratio objective function gives solutions with very low
airload deflections.
– TD objective function solutions have a higher airload
deflection, however the actuation deflection is considerably
higher
Best choice is an airfoil optimized using the TD objective
function where the deflections due to the airloads are
constrained by an upper limit.
• Displacement of 6–8 mm under actuation achieved
using four compliant mechanism units
– 18-22% change in lift (calculated using X-FOIL)
Prototype design
Wire EDM Machining
• Main Structure: 6061-T6
Aluminum (Fatigue
Strength: 95 MPa)
• 10 PICA-Thru Piezo Stack
Actuators: P-010.20H
Pro-Engineer Model
Prototype Part
Actuator Selection
Physik Instrument Tubular Piezo Stack Actuator: P-010.20H
Length: 27 mm, OD: 10 mm, ID: 5 mm
Blocking Force: 1800 N
Max Voltage: 1000 V
Advertised Displacement at 1000 V: 30 μm
Measured Displacement at 1000 V: 25-30 μm
Vendor Data
Measured Data
Displacement (μm)
30
25
20
15
10
5
0
0
200
400
600
Voltage (V)
800
1000
ANSYS: Finite Element Analysis
Active Elements
Maximum Stress in Flexures:
35 MPa < 95 MPa Fatigue Strength
Predicted Deflections
- MATLAB Code: 5.6 mm
- ANSYS: 4.0 mm
Skin Design:
Camber under Actuation Loads
Moment applied at this section
M = 200 N-m/m span
(Low actuation load)
Deformations due to
o
aerodynamic loads < 1
Change in EI 
less effect
aEI
Decrease skin EA 
more camber
(unless baseline EI
was very high)
Skin bubbling
aEA
EI increased by factor of 10
EA reduced by factor of 100
M1 = 400 N-m/m span
Deformations due to
o
aerodynamic loads < 1
SBB
aEA
M2 = 800 N-m/m span
aEI
aEI
Camber under Moderate Actuation Loads
Buckling
boundary
under
actuation
loads
SBB
aEA
If skin has low EA, as actuation load increases, need higher EI to avoid buckling
If EA reduced by factor of 50, and EI increased by factor of 600
Camber of ~ 3o for M1
o
Camber
due
to
air
loads
<
1
Camber of ~ 6o for M2
Skin Design Conclusions
Process used is analogous to inverse design
What should the properties of the skin be? ….such that
-- global (camber) deformations under air load are not excessive
-- local deformations due to surface pressure are not significant
(no skin ‘bubbling’)
-- local sections do not buckle under actuation loads
-- actuation forces are not excessive for a desired camber
The process followed gives us EA, EI, and max strain specs
We can then go about designing a composite skin using these specs
Low Modulus (silicone) face-sheets
Spacer Flex-Core (Foam?)
Composite Skin has low EA, but high EI,
and can undergo high max strains
Accomplishments since the last (2004) review
• Shape optimization of series of compliant mechanisms within
airfoil:
- Examined effects of passive material constraint, mechanism
geometry, and actuator thickness
• Started construction of a bench-top model
• Optimized skin properties to avoid buckling and localized
transverse deflections under surface pressure loading while keeping
actuation requirements low
Planned Accomplishments for the remainder of 2005
• Complete prototype and conduct bench-top test
• Optimization using dynamic analysis
Technology Transfer Activities :
• Paper accepted for publication in the 2005 AHS Forum 61 Proceedings
• Presented paper at 2004 ASME Design Engineering Technical Conference, Salt Lake City,
Utah
• Presented paper at The 15th International Conference on Adaptive Structures and
Technologies, October, 2004, Bar Harbor, Maine
Recommendations at ‘04
review:
• The task is a tough
problem and shows potential,
but needs to look at skin
structures as to whether it is
practical. It is appreciated to
pay attention to last year
comments. The task is
unique, however potential
payoff or practicality is
debatable.
Actions Taken :
• Completed comprehensive study
of optimal skin properties
• Completed detailed design of
practical design
• Demonstration prototype has been
constructed and will be evaluated in
the lab under quasi-static and
dynamic operating conditions
Overall Accomplishments of Task 1.3
• Developed finite element models and optimization algorithms for
trailing edge camber control
– Topology optimization
– Geometry optimization
– Concurrent optimization
• Calculated Lift/Drag increment of optimized designs using XFOIL
• Developed a shape optimization method for simpler design
• Studied flexible skin designs
• Developed practical actuation system
• Built prototype and bench-top testing
Forward Path
• Demonstrated that a controllable camber airfoil can be
designed and fabricated.
• Controllable camber, as a rotor morphing concept, is ready
to move to CRI (formerly RITA) or other 6.2 type
activity. The lessons learned and experiences gained can
be used in industry-type development and testing activities.
• The lessons learned on how to design structures compliant
to actuation loads, stiff to aerodynamic loads, with
deformable skins, and requiring modest actuation efforts,
should be applied to other rotor morphing concepts.
• Of particular interest to us (and we will propose as an
RCOE renewal task) is the use of bistable mechanisms for
control of blade twist and blade chord in the outboard
regions. Bistable mechanisms provide large stroke with
small actuation effort.