overview of helicopter dynamics and aeroelasticity, and ... of helicopter dynamics and...
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Overview of Helicopter Dynamics and Aeroelasticity, and Autonomous Mini Helicopter Development
C.Venkatesan Department of Aerospace Engineering Indian Institute of Technology Kanpur
Kanpur, India
PRAVARTANA-2016 IIT-Kanpur
February 2016
INTRODUCTION ------------------------------------------------------------------------
• Since the First Successful Flight of Truly Operational, Mechanically Simple and Controllable Helicopter by Sikorsky (1939-42) - Continued R&D Efforts to Improve Helicopter By Incorporating New Technological Developments As and When Matured, and Available • Composites • Automatic Flight Control Systems • Vibration Control Devices • Mission oriented configuration • Advances in Fundamental Understanding of Rotor/ Fuselage Dynamics, and Aerodynamics
INTRODUCTION ------------------------------------------------------------------------------ • Rotorcraft Research Programs - Virtual Aerodynamic Rotorcraft (CFD Based) - Experimental Rotorcraft (Wind Tunnel Testing, Prediction) - Comfortable Rotorcraft (Vibration and Noise) - Active Rotorcraft (Active Rotor Blade Devpt.) - Smart Rotorcraft (Flight Dynamics, ACT Devpt. All Weather Flying) - Safe Rotorcraft (Crashworthy, HUMS) - Specialised Military Rotorcraft (Stealth, Weapons, Display Systems, Avionics etc.) - New Rotorcraft Configurations
My Focus of Helicopter Research Theoretical
• Comprehensive rotorcraft analysis for helicopter design • Flight dynamics and handling quality evaluation • Helicopter dynamics: short courses/ text book
Experimental • Design and development of mini autonomous
helicopter • HILS for helicopter
INTRODUCTION ------------------------------------------------------------------------------ • Challenging Area of Research - Quiet / Comfortable Rotorcraft (Noise, Vibration)
Aeromechanical Problem (Air, Ground Resonance)
COMPLEXITIES OF ROTOR SYSTEM ----------------------------------------------------------------------
- COMPLEX DYNAMICS BLADE MOTION (AXIAL-FLAP-LAG-TORSION) ROTOR-FUSELAGE COUPLING
- COMPLEX AERODYNAMICS COMPRESSIBILITY REVERSE FLOW DYNAMIC STALL RADIAL FLOW BLADE-VORTEX INTERACTION ROTOR WAKE-FUSELAGE INTERACTION
Mathematical Modelling
• Structural modeling of rotor blades
• Aerodynamic modeling
– Wake induced inflow at the rotor disk
– Sectional aerodynamics in attached (classical unsteady theories)
and separated (dynamic stall models) flow regions
• Aeroelastic models and their contribution towards the study of
rotary-wing aeroelasticity
Rotor Blade Geometry
𝛽𝛽p - Precone angle
𝛽𝛽d - Predroop angle
𝛽𝛽s - Presweep angle
𝛬𝛬s - Tip Sweep angle
𝛬𝛬a - Tip Anhedral angle
Review: Structural Modeling
• A structural model for a rotor blade undergoing flap-lag-torsional deformations (Houbolt and Brooks, 1958)
• Nonlinear beam theories applicable for moderate deformation of an isotropic beam (Hodges et al (1974), Friedmann et al(1978)) – Rotor blade is modeled as 1-D Euler-Bernoulli beam and its
sectional properties are evaluated from 2-D sectional analysis
– Higher order terms are eliminated using an ordering scheme
– Did not include the effects of cross-sectional warping and transverse shear
10
Structural Modeling (cont’d)
• From 1980’s, use of composite materials in construction of rotor blades
• Structural models applicable for analysis of composite beams having arbitrary/thin walled cross-sections (Friedmann (1989), Dugundji (1990), Chopra (1991))
• The importance of cross-sectional warping and shear effects have been identified and are included (Worndle(1992), Hodges(1991,1997)
• Models suitable for advanced geometry tip shapes (Chopra (1992), Friedmann (1995), Rohin & Venkatesan (2011))
11
Aerodynamics
Inflow
Local Global
Section Loads
Prescribed Wake
Free Wake
CFD
Uniform Inflow
Drees Model
Mangler & Squire
Perturbation Model
Dynamic Inflow
Dynamic Wake
Classical Unsteady Dynamic Stall
CFD
Theodorsen
Greenberg
Loewy
Leishman-Beddoes
ONERA
Modified ONERA
Gangwani
Aerodynamic Models
Aerodynamic Modeling: Inflow Models
• Wake Induced Inflow
– Prescribed wake/Free wake Computationally extensive – Inflow models Global model, computationally less intensive
• Uniform Inflow based on momentum theory:
13
iλαµλ += tan
)(2 22 λµλ
+= T
iC
χ
µ λ
tan µχλ
=
Rotor Disk
Wake
Inflow models (cont’d)
• Drees Model (1949): Function of radial station and azimuth
• Dynamic wake Model (1989, DW) (Peters-He model):
14
[ ])sin()()cos()()(tan),,(0 3,1
ψβψαφαµψλ ptptrtr pj
pj
p ppj
pj ++= ∑ ∑
∞
=
∞
++=
21]~][[][ 1 mc
npj
Cpj LVM ταα =+ −
21]~][[][ 1 ms
npj
Spj LVM τββ =+ −
( , ) tan (1 sin cos )i x yr k r k rλ ψ µ α λ ψ ψ= + + +
( )[ ]χχµµ cotcsc8.1134;2 2 −−=−= yx kk
χ
µ λ
tan µχλ
=
Rotor Disk
Wake
Aerodynamic Modeling: Sectional aerodynamics loads
15
Sources of unsteadiness in helicopter rotor blade
A)
B)
C)
Flapping Motion
Lead-lag Motion
Elastic Torsion
Aerodynamics in Forward Flight: Dynamic stall
ψsin∞+Ω= VrV
16
0 180deg.ψ< <180 360 deg.ψ< <
Advancing side : High velocity Low angle of attack Retreating side : Low velocity High angle of attack
Blade stall occurs in the retreating region. Unsteady motion + High angle of attack DYNAMIC STALL
Advancing Side i.e., Retreating side i.e.,
Sectional aerodynamics loads (cont’d)
• Sectional Aerodynamic Coefficients
– Classical unsteady model (valid for attached flow) (2-D)
• Theodorsen theory (1935)
• Greenberg theory (1947)
• Loewy theory (1957)
– Empirical dynamic stall model (2-D) • Beddoes - Leishman model (1986)
• ONERA model (1989)
– CFD (2-D or 3-D) 17
Dynamic stall (cont’d) • Two distinct directions of research
– Experiments on dynamic stall – Modeling of dynamic stall
• Experiments on dynamic stall
– McCroskey(1973), Carr (1988) and Chandrasekhara(1990) » Oscillating airfoil in pitch
– Carta(1979), Ericsson and Reding (1980) » Oscillating airfoil in pitch and plunge
– Favier and Maresca (1979-1988) » Pitching airfoil in pulsating on-coming flow
• Modeling of dynamic stall
– CFD methods – Semi-empirical models
18
Dynamic stall (Cont’d) • Semi-empirical methods
– Beddoes Model (1976)
– Ganwani Model (1981)
– Beddoes-Leishman Model (1986)
– ONERA (EDLin) Model » Petot’s Initial Model (1980) » Peter’s unified lift Model (1986) » Petot’s extended Model (1989)
– ONERA (BH) Model (1995) – Laxman and Venkatesan – Modified ONERA Model(2007): Combination of Finite state model in attached flow + ONERA
• CFD methods (1995 – )
19
Modified ONERA Stall Model • Lift at quarter-chord point
0
1
,
( );
where
hW VV
W h
θ
θ
= +
=
[ ]
+∆
−=Γ
+Γ
+Γ
+∂
∂+
+
∂
∂
+
+
∂
∂
=Γ
+Γ
+Γ
Γ+Γ++=
0/
2
2
2
22
120112
021
2
3
0
2
31
2
3121
2110
0|
~~21
WbVECV
bVr
bVr
bVa
WAWC
AWbVA
WC
bVAW
bVA
WC
bVA
bVB
bVB
VVWbkWbsSL
VWz
z
z
z
L
L
L
σθ
σ
θσ
θ
ρ
*Laxman, V., and Venkatesan, C., AIAA Journal, January 2007
Modified ONERA Model (contd.)
21
• Replacing first order approximation of Lift Deficiency Function by a second order rational approximation
• Airfoil is assumed to undergo a pitching
Model Expt.
Flight Dynamics 1. Trim, Stability, Control Response, handling qualities, control system design
2. Helicopter Simulation models have grown in sophistication over time -
Flap-only model (Heffley (1988); Gagandeep Singh (2012) ), Flap-lag-
torsion model (Takahashi, 1990)
3. Linearized model needed for stability, handling qualities and control
system design (Kim et al., 1993)
4. Study of maneuvers is more complicated than forward flight.
5. Chen – Kinematic equations for helicopter motion in steady helical turns.
Sideslip angle has a strong influence on the trim equilibrium position.
6. Very little literature on turning/maneuver flight dynamics (Chen, 1984),
(Celi et al, 1991, 2002, 2005), (Rohin Kumar and Venkatesan, 2014)
General Maneuver
23
Flight Dynamics
Ωa
yea
zea
xea
Vf
χ γf
γf
Vf
yb
zb
xb
Rot
atio
n ax
is
xea, yea, zea – Earth-fixed axes
χ - dynamic Track angle
Horizon
Equations of Motion
24
Force Equations
•
•
Moment equations
• (roll)
• (pitch)
• (yaw)
Kinematic Relations
•
•
•
Flight Dynamics
Aeroelastic Formulation
25
Eight rotating modes per blade are considered
four flap modes two lag modes one torsion
one axial mode
Equations of motion in modal space
[ ] [ ] [ ] FKCM =++ ηηη
Helic
opte
r Trim
and
Rot
or R
espo
nse Trim initial
guess Vehicle geometry & aerodynamic data
Loads
Inflow Response
CG loads Empennage aerodynamic loads
Fuselage aerodynamic loads
Trim equations
Trim solver output
Algebraic equation solver
Diff. Eq. solver
Trim outer loop
Main Rotor Trim inner loop
Till convergence
Till convergence
X
X
Over a complete revolution
Mean hub loads
Validation
1. Structural dynamics (SDAR)
2. Whirl tower test (CAFDAR)
3. Straight level forward flight trim (CAFAR)
Sweep Effects University of Maryland Rotating Beam Experiment • Epps, J.J., and Chandra, R., Journal of the American Helicopter Society, 1996 • Hopkins, A.S., and Ormiston, R.A., Proceedings of the American Helicopter
Society 59th Annual Forum (2003) – RCAS validation
Uniform Aluminium Beam Sweep – 0, 15, 30, 45 degrees RPM - 0, 500, 750
28
Ω
2.5”
1”
0.063”
34” 6” 16% Tip Sweep
Validation
Rotating, Swept, Uniform Al beam
29
Effect of RPM on natural frequencies for Λ = 00
Validation
Rotating, Swept, Uniform Al beam
30
Effect of RPM on natural frequencies for Λ = 450
Validation
Frequency vs RPM: ALH
1Ω
2Ω
3Ω
4ΩN
omin
al R
otor
Spe
ed
5Ω
6Ω
7Ω
Freq
uenc
y (H
z)
Rotor RPM
CAMPBELL DIAGRAM
MOSES
IITK CODE
Thrust and Power Curves
Validation
Formulation of lead lag damper model Fluidlastic lead lag damper attachment to the main rotor
blade
Root boundary condition
• Main rotor blade is fixed to hub through radial and conical bearing.
Lag damper
Conical bearing
Radial bearing
WT- whirl tower ABC- ALH boundary condition
PM-point mass DF- damper force
Comparison with whirl tower test data
Mr. Parwez Alam, Master’s Thesis, 2014
Level Flight
SIDE SLIP AT 138 KMPH (DW- AP- WT)
POWER
200
300
400
500
600
700
800
900
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Pow
er (K
w)
Advance Ratio
DW/AP/WT (MR Power)DW/DS/SDM (MR Power)DREES/AP/WT (MR Power)DREES/AP/SDM (MR Power)Flt. Test (Total Power)
10%
Dyn. Wake:DW Airfoil Polar:AP
Wind Tunnel Polar:WT Simple Drag Model:SDM
Sectional Lift @ high speed
Research Puma CT/σ = 0.08
μ = 0.38 r/R = 0.92
Our study CT/σ = 0.076
μ = 0.35 r/R = 0.95
UH-60A CT/σ = 0.079
μ = 0.368 r/R = 0.92
Data from : • Bousman (1999)
• Yeo and Johnson, Journal of Aircraft (2005)
Sectional Pitching Moment @ high speed
Research Puma (swept-tip) CT/σ = 0.07
μ = 0.362 r/R = 0.92
Our study CT/σ = 0.076 μ = 0.35 r/R = 0.95
UH-60A CT/σ = 0.079
μ = 0.368 r/R = 0.92
Data from : • Yeo and Johnson, Journal of Aircraft (2005)
RESULTS
Sectional loads: Azimuthal variation of the sectional lift, drag and moment at 0.95R for
the Inflow states of S= 3,10,15,21 and 45 at µ = 0.30
Harmonic content increase with the inclusion of higher harmonic inflow states.
Minimum pitching moment observed in the second quadrant at higher inflow states.
Lift Drag Moment
BLADE LOADS AT VH (lag moment near root)
0
0
0
0
0
0
0
0
0
0 360 720 1080 1440 1800
PSI (Deg)
ANALYSIS
FLIGHT TEST
BLADE LOADS AT VH (torsion moment near root)
0
0
0
0
0
0
0
0 360 720 1080 1440 1800
PSI (Deg)
ANALYSIS
FLIGHT TEST
Steady Turn
• Weight 4.5 T • Advance ratio 0.14 (30.38 m/s) • CCW main rotor rotation- From top • +ve turn rate is right turn – From pilot view • -ve turn rate is left turn
5
7.5
10
12.5
15
-40 -20 0 20 40
Deg
Turn rate (deg/s)
Main rotor Collective
1.52
2.53
3.5
-40 -20 0 20 40
Deg
Turn rate (deg/s)
MR lateral cyclic
-3.5
-3
-2.5
-2-40 -20 0 20 40
Deg
Turn rate (deg/s)
MR longitudinal cyclic
TRIM in TURN
0
4
8
12
16
-40 -20 0 20 40
Deg
Turn rate(deg/s)
Tail rotor collective
-1
-0.75
-0.5
-0.25
0
0.25
-40 -20 0 20 40
Deg
Turn rate (deg/s)
Pitch Attitude
-75
-50
-25
0
25
50
75
-40 -20 0 20 40
Deg
Turn rate (deg/s)
Roll Attitude
Future Research Directions -------------------------------------------------------------------------------- • OPTIMUM DESIGN OF ROTOR BLADE FOR VIBRATION, NOISE, HANDLING QUALITY, PERFORMANCE • HIERARCHY OF ANALYSIS TOOLS/ CAPABILITIES FOR DESIGN • LIFE PREDICTION/ LIFE EXTENSION / SAFETY • HEALTH MONITORING OF SYSTEMS AND COMPONENTS
• AUTONOMOUS FLIGHT (SENSORS, ACTUATORS, CONTROL LOGIC, COMMUNICATION, POWER PLANT)
• OPERATION UNDER DIFFICULT WEATHER CONDITIONS (OFF-SHORE, SHIP BASED, WINDY MOUNTENOUS TERRAIN) • VARIABLE STABILITY HELICOPTER/ SIMULATOR
• COST OF PROCUREMENT, OPERATION, MAINTENANCE
AUTONOMOUS FLYING VEHICLES
• Autonomous and/or remotely-piloted flying vehicles attracting serious R&D effort - Potential in civil and defence applications • Configurations of vehicles
- Fixed-wing, Flapping wing, Rotary-wing
Rotary-wing type vehicles • Rotary-wing type vehicles
- Unique feature: Hover • Configurations of rotary-wing vehicles
- Conventional (one main rotor + one tail rotor) - Coaxial contra-rotating - Multi-rotor (Quad rotor, tri-rotor, hexa-rotor, octa-rotor)
Conventional configuration
• Our focus on conventional helicopter - Fundamental understanding of flight control - Stabilization of highly unstable vehicle - Correlation of theory and experiment for scale models - Experimental exposure to helicopter study
Autonomous Mini Helicopter Our Motivation: 2005
Challenge in practical design/ development Spectrum of knowledge Helicopter dynamics/stability/control Structural design and analysis Transmission system/ control system Avionics/ Inertial measurement/ signal processing Controller design/ wireless communication Software for on-board computer Display architecture Intelligent tasks (obstacle avoidance/ survey) Hover, Vertical and Forward Flight Capability
WORK MODULES
Electronics Mechanical Control
Sensors RPM, IMU, Sonar, GPS
Actuators PWM generation Communication Ground station
Test rig Load measurements
Engine test Blade design
Engine testing and maintenance Vehicle assembly and maintenance
RPM Yaw-pitch-roll
6-DOF Simulation
Mini-Helicopter Bergen Intrepid Gas EB
Height 467 mm
Length 1370 mm (without blades)
Main blade length 810 mm
Tail blade length 95mm
Fuel tank 0.5 liters high octane gasoline
Engine Zenoah G260puh
Rotor system Bolted at blade root
Stabilizer bar Teetering
Helicopter Model
Test Rigs: Mechanical
3 Axis Test Rig (Inertia estimation,
Control law design and testing)
Mini-Helicopter mounted on 3-axis test rig
4 Axis Test Rig (foreground) and Load Cell Tower for Load Estimation
(background)
Experimental setup
Static and Dynamic Testing of Rotor Blade
0 2 4 6 8 10-0.2
-0.1
0
0.1
0.2
Time (sec)
Volta
ge (V
)
Damping Curve
Damping Ratio: 0.7%
Deflections for procured, blade-1 and blade-2 for 500 gms loading
Failure of Gear / Coupler Engine tuning / starting Centrifugal clutch liner Electrical connectors / wiring Electromagnetic Interference Vibration Fuel Linkages Tail drive shaft Manufacturing of components On board sensors
CHALLENGES FACED
Damage of main gear
57
F A B R I C A T E D
G E A R S
MANUFACTURING: Main Rotor Gear
Nylon 6/6 30% Glass fibre
Nylon 6/6 30% Carbon reinforced gear mounted
Nylon 6/6 30% Carbon reinforced
Gear Weight (gm) Delrin (procured) 73.14
Nylon 6/6 30% glass
67.43
Nylon 6/6 30% carbon
72.13
PEEK 76.0
PEEK- VESTAKEEP 4000CF30(A)
58 58
MANUFACTURING Tail Transmission Coupler
Coupler Weight (gm) Delrin
(procured) 3.60
Nylon 6/6 30% carbon
3.73
Unigraphics 3D Model
• Operating Speed range : 2000 – 8000 rpm
• Max. Shear Stress: 33.49 MPa • Max. Normal Stress: 52.38 MPa
Damaged Coupler Nylon 6/6 30% carbon Coupler
Failed bearing
Engine Test Bed
Fuel Tank
Servo controller
Engine Dynamometer
Cooling duct
Dynamometer blower
Installed Tsubaki NEF02W flexible disc coupling
Safety cover
Coupling safety cover
61
Successfully Resolved Centrifugal Clutch Lining Problem
Thickness of lining: 1 mm
Clutch Lining (damaged) Unused Clutch Lining
Fragments
Purchased clutch bell with lining
Manufactured clutch bell with lining
Effect of Clutch Lining on Main Rotor RPM Regulation
New local clutch lining variation of ±15 RPM
Original clutch lining (damaged) variation ±60 RPM
Local clutch lining (worn out) variation of ±40 RPM
WIRELESS ARCHITECTURE
Mini-Helicopter
PXI – Ground Station Xbee
2.4 GHz 250 kbps max.
Radio Unit 35 MHz
PITCH-ROLL CONTROL-17 Aug. 09
PITCH-ROLL CONTROL 17Sept. 09
Ground Resonance: 30 June 2010
Stray signal effect: 14 Nov. 2012
Drive shaft failure: 26 June 2012
Auto-takeoff landing gear crash 1 May 2015
Landing gear vibration: failure 23 Dec. 2015
Wrong power connection 11 Sept. 2015
Servo Jitter: 14 Oct. 2015
Roll servo problem: 29 Jan. 2016
OUTDOOR FIGHT 24 July 2015
Control mistake: 15 Jan. 2016
Position hold: 10 Feb 2016
FUTURE DIRECTIONS
MEETING USER REQUIREMENTS
AUTONOMOUS CONTROL
VEHICLE D&D
• Semi-autonomous • Payload
• Communication • Ground station
• Fully autonomous
• Free hover/ Fwd Flight • Navigation
• On-board control • Manoeuvre flights
• Simulation •Improved control strategies
• Structural design • Rotor design • Transmission • Power plant
• Manufacturing
Class of Vehicles: all-up weight 10~12kg, 60~80kg, > 500kg
HAL-ADE-IITK to jointly develop a TD model
78
My Observations
General • Science – Engineering – Technology
• Truly challenging
• Excellence: Design-Manufacturing-
Assembly-Operation-Maintenance
Personal • Learning from challenges • Theory is easy – Practical is tough • Aim high – face unexpected • Taught humility • Dedication + Patience • Respect
CONCLUDING REMARKS ------------------------------------------------------------------------------
• SEVERAL ISSUES STILL NOT UNDERSTOOD FULLY • CONTINUED RESEARCH TO IMPROVE HELICOPTER PERFORMANCE • AUTO-TAKE OFF, AUTO LANDING, COORDINATED FLYING, LANDING ON MOVING PLATFORM • VERY FERTILE FIELD FOR CHALLENGING RESEARCH
THANK YOU
Past Team Members
B.B Swaroop, # Project Engineer
V. Ravi # Project Engineer Gaurab Dutta # Sr. Project Associate
Manoj K. Dhadwal # Sr. Project Associate Vaibhav Sharma # Project Associate
K. Santosh Laxmi # Project Associate D. Shashikala # Project Associate
Gokul Bala # Project Associate Layeeq Ahmed # Project Associate Rahul Gupta, # Project Associate Preeti Bagade, # Project Associate
Nikita Srivastava, # Project Associate Shamsheer Mohammed, # Project Associate
R. Thirumurugan, # Project Associate Prateek Jain, # Project Associate
Abhilekh Mukerjee, # Project Associate Sanjeev Kumar Gupta # Project Scientist Vinit Kumar Sahay # Sr. Project Associate
V. T. Arun # Project Associate Atul Srivastava # Project Associate
Kapil Srivastava # Project Mechanic Awadhesh Kumar # Project Technician
# Ex. Project Employees
Project Investigators
Dept. of Aerospace Engg.
C. Venkatesan Principal Investigator Abhishek
C.S. Upadhyay A. Kushari
SUPPORTING POWER
Current Team Members
Haritha Pathuri Sr. Project Associate Sanjay Kumar Viswas Project Associate
Sandeep Prajapati Project Associate
Avanish Kumar Bajpai Technical Officer Smita Mishra Dy. Project Manager Vinod Bhaduria Project Technician Vinay Kumar, Project Technician
S. S. Parihaar Sr. Project Mechanic Prameet Tiwari Sr. Project Mechanic
81
NEW HELICOPTER LABORATORY
82
VISIT BY DST REVIEW COMMITTEE ON 05 Oct. 2009
Helicopter Configurations
NOTAR (No Tail Rotor)
McDonnell Douglas-Explorer 1994
Single main rotor + 1 tail rotor MI-24 Co-axial rotor KA-27
Fenestron (Fan-in Fin)
Dauphin , Euro copter EC-155
*Rainald Loehner et al., Extending the Range and Applicability of the Loose Coupling Approach for FSI Simulations, Fluid-Structure Interaction - Modelling, Simulation, Optimisation, Springer Publications, 2006
Sectional aerodynamics loads
• Quasi-Steady Greenberg Model (1947) • The unsteady lift acting normal to the resultant velocity is a combination of circulatory and non-circulatory lift
85
CNC LLL +=
+= 10 2
~21 WWbSLNC
ππρ
[ ]10 22~21 WWVSLC ππρ +=
( )VhVW /0+= θ θbW =1and
Sectional aerodynamics loads (Cont’d)
0
2~21
DCVSD ρ=
Moment on the airfoil
Drag acting along the resultant velocity
CNC MMM +=
−−−= 110 16
344
2~21 WbVWWbbSM NC
πππρThis image cannot currently be displayed.
( )VhVW /0+= θ θbW =1
INTRODUCTION (CONT’D)
-------------------------------------------------------------------------- • BOUSMAN (INTERNATIONAL WORKSHOP ON DYNAMICS AND AEROELASTICITY OF ROTOR SYSTEMS, 1999) “NOT MADE ANY SIGNIFICANT PROGRESS IN THE LAST THIRTY YEARS IN THE ACCURACY OF OUR PREDICTION METHODS. ……. SINGLE MOST IMPORTANT REASON: THE TREMENDOUS DIFFICULTY OF THE PROBLEM WE ARE DEALING WITH.”
Structural Model of Blade • Beam type finite-elements used; 14 degrees of freedom
• Cubic Hermite interpolation polynomial – bending displacement
Lagrange interpolation polynomial – torsion / axial displacements
• Non-linear transformation at the junction between straight blade and
tip
• Free vibration analysis -
88
Panda, B., Journal of the American Helicopter Society, 1987
[ ] [ ] 0=+ qKqM
ELASTOMERIC BEARINGS AND DAMPERS ----------------------------------------------------------------------------- • ELASTOMERIC MATERIALS REPLACE CONVENTIONAL BEARINGS AND DAMPERS • ADVANTAGES - MECHANICAL SIMPLICITY - NO LUBRICATION AND MECHANICAL SEALS • COMPLEX MATERIAL CHARACTERISTICS - TEMPERATURE - AMPLITUDE - FREQUENCY - MEAN STRESS LEVEL
AMPLITUDE DEPENDENCY -----------------------------------------------------------------------------------
-STIFFNESS AND DAMPING CHARACTERISTICS OF ELASTOMER -SINGLE FREQUENCY EXCITATION (3.3Hz, 4.0Hz, 5.4Hz, 6.6Hz)
STIFFNESS Vs AMP. DAMPING Vs AMP.
AMPLITUDE DEPENDENCY --------------------------------------------------------------------------- • DUAL FREQUENCY EXCITATION (3.3Hz and 5.4Hz)
STIFFNESS DAMPING
• CURRENTLY SEVERAL RESEARCH STUDIES FOCUS ON MODELING THIS INTERESTING PHENOMENON
Dynamic stall (Cont’d)
92
( )
)0
2 2 2
0
20
1 1 2
2
2
0
12
m m m
wt L m mv
m m m
m m
wm m mV
M S c V Cm d bW
s VW s bW V
V Va rb b
V Vr V C E Wb b
ρ σ= + +
+ + + Γ
Γ + Γ + Γ = − ∆ +
0 2
0 2
2
,;
;;
Wherea a a Cz
r r r CzE E Cz
= + ∆
= + ∆= ∆
Pitching moment at quarter-chord point:
93
Petot (ONERA EDLin) Extended Model (1989):
α
Lift at quarter-chord point:
If is zero, equations lead to initial model
( )
2 2 2
0
0 1 1 2
1 1 0 1
0 1
2
2
0
12
L
L
wzV
L S sbW kbW V V
CzV V VW Wb b b
Cz d W W
V Va rb b
V Vr V C E Wb b
ρ
λ λ λθ
α ασθ
= + + Γ + Γ
∂ Γ + Γ = + ∂ ∂ + + + ∂
Γ + Γ + Γ = − ∆ +
0
1
,
( );
where
hW VV
W h
θ
θ
= +
=
Rotor Blade Aeroelastic Studies
• Aeroelastic analysis – 3 Distinct Categories
- ONERA stall model + Dynamic wake model (Peters, Dowell, Gaonkar, Venkatesan et al...)
- Rational function approximation (attached flow) +
ONERA stall model (separated flow) + Free wake model (Friedmann et al.)
- Combination of CSD + CFD
(Johnson, Chopra, Ormiston et al..)
Flight Dynamic Equations • 6 degrees of freedom • 9 equations –
• 3 force equilibrium, • 3 moment equilibrium eqs • 3 kinematic relations
95
• Translational velocity components ue, ve, we • Angular velocity components pe, qe, re
• Steady spin rate Ωa • Orientation angles θh, Φh
• Pilot input angles θ0, θ1c,θ1s, θ0t
• Vfe Flight speed
• γfe Flight path angle • Ωa Turn rate or spin rate
• βfe Side slip angle
Equilibrium Equations
96
Force equations
• X = m(w q – v r) + m g sin Θ
• Y = m(u r – w p) – m g cos Θ sin Φ
• Z = m(v p – u q) – m g cos Θ cos Φ
Moment equations
• L = (Izz – Iyy) q r - Ixz p q (roll)
• M = (Ixx – Izz) r p - Ixz (r2 – p2) (pitch)
• N = (Iyy – Ixx) p q - Ixz q r (yaw)
Kinematic Relations
• p = -Ωa sin Θ
• q = Ωa cos Θ sin Φ
• r = Ωa cos Θ cos Φ
Flight Dynamics
Helic
opte
r Con
trol
Res
pons
e Trim
Vehicle geometry & aerodynamic data
Loads
Inflow Response
CG loads Empennage aerodynamic loads
Fuselage aerodynamic loads
Vehicle Equations of motion
Vehicle states u, v, w, p, q, r,
θ, φ, ψ
Diff. Eq. solver
Diff. Eq. solver
Main Rotor
X
Perturbation in control angle
For every time-step
For every time-step
AIRFOIL --------------------------------------------------------------------------------
• OPERATING CONDITIONS - HIGH DYNAMIC PRESSURE ON ADVANCING SIDE - HIGH ANGLE OF ATTACK IN RETREATING SIDE • DESIRABLE CHARACTERISTICS - HIGH LIFT TO DRAG RATIO - HIGH CL MAX - HIGH DRAG DIVERGENCE MACH NUMBER - LOW PITCHING MOMENT - GOOD STALL BEHAVIOUR
AIRFOIL (CONT’D) --------------------------------------------------------------------------------
• GENERAL OBSERVATIONS ON AIRFOIL CHARACTERISTICS - SYMMETRIC AIRFOILS (LOW PITCHING MOMENT) - POSITIVE CAMBER (HIGH CL MAX) - THIN AIRFOILS (GOOD DRAG DIVERGENT MACH NUMBER BUT MODEST CL MAX) - INCREASE IN MACH NUMBER REDUCES CL MAX - HIGH REYNOLDS NUMBER DELAYS FLOW SEPARATION
AEROELASTIC STABILITY AND RESPONSE OF BLADES --------------------------------------------------------------------------------
• INTENSELY PURSUED BY ACADEMIA AND INDUSTRY • CONSIDERABLE PROGRESS IN THE PAST 40 YEARS • STILL SEVERAL DISCREPANCIES EXIST BETWEEN THEORY AND EXPERIMENT • MODEL TESTS AND FLIGHT MEASUREMENTS PROVIDE DATA FOR CORRELATION • IMPROVE UNDERSTANDING OF THE PHYSICS OF THE PROBLEM • MODIFY, DEVELOP SUITABLE MATHEMATICAL MODELS
AIRFOILS OF SEVERAL TYPES -------------------------------------------------------------------------------
RAE VERTOL
ONERA
EFFECT OF TIP SHAPE ON PITCH LINK LOAD -------------------------------------------------------------------------------
µ = 0.375
STATUS OF VIBRATION PREDICTION ------------------------------------------------------------------------------
• HIGHLY COMPLEX PROBLEM
• VIBRATORY LEVEL AT COCKPIT • MEASUREMENT (4/REV) LEVELS COMPARED WITH THEORY • REASONS FOR POOR PREDICTION - MOMENT AND SHEAR AT BLADE ROOT
ARTICULATED ROTOR HUB -----------------------------------------------------------------------
• ADVANTAGES
- HINGES IN FLAP AND LAG TO RELIEVE LARGE BENDING LOADS AT THE ROOT (EFFICIENT ENGINEERING SOLUTION) - PITCH CONTROL BEARING
ARTICULATED ROTOR HUB -------------------------------------------------------------------------------
• DISADVANTAGES - COMPLEX ROTOR HUB - LARGE NUMBER OF MOVING PARTS (ORDER OF 500, SEVERAL LUBRICATION POINTS) - FREQUENT MAINTENANCE - REPLACEMENT OF PARTS DUE WEAR OUT - CANNOT GENERATE LARGE CONTROL MOMENTS HENCE RESTRICTED C.G. TRAVEL
HINGELESS ROTOR HUB -------------------------------------------------------------------------
• WITH DEVELOPMENT OF COMPOSITE TECHNOLOGY EMPHASIS ON HINGELESS ROTOR DEVELOPMENT(1980’s) - ABSENCE OF FLAP AND LAG HINGES - PITCH BEARING FOR PITCH CONTROL
HINGELESS ROTOR HUB ----------------------------------------------------------------------------
- LESS NUMBER OF PARTS (OF THE ORDER OF 200) - LARGE CONTROL MOMENTS, HENCE FAVOURABLE VEHICLE CONTROL - LARGE DYNAMIC LOADS (VIBRATION) • BOTH ARTICULATED AND HINGELESS ROTORS HAVE EXTERNAL LEAD-LAG DAMPERS TO AVOID AEROELASTIC/ AEROMECHANICAL INSTABILITY
BEARINGLESS ROTOR HUB -------------------------------------------------------------------------
- NO FLAP AND LAG HINGES - PITCH BEARING REPLACED BY FLEXIBLE STRUCTURAL ELEMENT MADE OF COMPOSITE MATERIAL - ELASTOMER WITH HIGH LOSS FACTOR AS DAMPER
BEARINGLESS ROTOR HUB --------------------------------------------------------------------------
• LESS NUMBER OF PARTS (OF THE ORDER OF 50) • COMPLEXITIES - DESIGN OF FLEX BEAM - MULTIPLE LOAD PATH - AEROELASTIC COUPLINGS - NONLINEAR EFFECTS OF ELASTOMER • CONCEPT KNOWN IN MID –60’s - DEVELOPMENT TOOK SEVERAL YEARS - BEARINGLESS MAIN ROTORS IN EC-135 AND RAH-66
ROTOR BLADE MODEL ---------------------------------------------------------------------------- LONG-SLENDER-TWISTED BEAMS UNDERGOING IN-PLANE BENDING (LAG), OUT-OF-PLANE BENDING (FLAP), TORSION AND AXIAL DEFORMATIONS
xi
zi
yi
k j •
•
w
vui
x
φ
Derivation
111
dxddG
GE
U
x
x
xxl
A
T
x
x
xxe
ζηγγε
δγδγδε
ζ
η
ζ
η
=∂ ∫ ∫ ∫
000000
0
∫ =∂−∂−∂2
1
0)(t
te dtWTU
Hamilton’s Principle
where
∫ ∫ ∫=∂ dxddVVTA
ζηδρ .
eW∂ Work due to external aerodynamic forces
Solution Technique • Trim and Blade response obtained simultaneously • 3 sets of differential equations solved sequentially in time-
domain – Sectional aerodynamic loads (evaluated at 15 radial stations from
0.25R to 0.95R in increments of 0.05R) – Inflow – Blade elastic deformations
• Number of states for 4-bladed rotor – Aerodynamic states: 15*8 = 120 per blade – Inflow : 3 – Structural dof : 2*8 modes = 16 per blade Total number of states = 4*(120+16)+3 = 547
112
AEROELASTIC RESPONSE ------------------------------------------------------------------------------
• LOAD VARIATION ON ROTOR BLADE AND PITCH LINK (1999)
NOTE: PHASE SHIFT
• TORSIONAL DEFORMATION PLAYS SIGNIFICANT ROLE
Research Directions --------------------------------------------------------------------------------
ROTOR BLADE • IMPORTANT PARAMETERS GEOMETRY AND OPERATING CONDITION - ROTOR RADIUS - BLADE CHORD - TWIST AND TAPER - TIP SHAPE - AIRFOIL SHAPE - R.P.M
AEROELASTIC STABILITY ------------------------------------------------------------------------------
• STABILITY IN LEAD-LAG MODE OF ROTOR BLADE (Maier and Abrego, 2000)
IMBEDDED SMART STRUCTURE -------------------------------------------------------------------------------
ACTIVE PIEZO FIBRE FOR TWIST CONTROL
CAMBER CONTROL USING SMART LAYERS
117
Vehicle Classification
Autonomous flying vehicles: Unmanned / Mini/ Micro Air Vehicles
UAV 200 kg – 1000 kg Long flying hours
Long range
MINI AV Size 1500mm
6kg – 10kg ½ hr – 1 hr flying
Short range
MICRO AV Size 150mm
½ hr – 1 hr flying Short range
NANO AV Size 50-75mm
MAJOR
Procurement / Laboratory space
Design - Calibration – Integration
of sensors / actuators
Measurement systems (PXI)
RPM control
Heading – Pitch – Roll control
Design / Development of Test Rig
Wired / Wireless communication
Hover test
MINOR
Blade manufacture
Fuselage structure
Load test
Engine test
Landing skid
Avionics box
Power management
PLANNED ACTIVITIES
ROTOR HUB DEVELOPMENT -----------------------------------------------------------------------
6-December 2014 outdoor flight
6-December 2014 outdoor flight
[email protected] flap [email protected] lag [email protected](Nm) (Nm)
-1.8 8110 11830.2 6406 9992.2 5503 7454.2 3679 2566.2 1231 -4657.2 -148 -8958.2 -1608 -1365
10.2 -4721 -240812.2 -7998 -3561
Theta flap [email protected] lag [email protected](Nm) (Nm)
-1.8 3300 3530 2900 4243 2100 1046 800 -3939 -600 -1299
Whirl tower data
Comparison with whirl tower test data
WT- whirl tower ABC- ALH boundary condition
PM-point mass
Steady Turn (180 kmph, 5.5T)
BLOWING SCHEMES --------------------------------------------------------------------------
CL Vs α
CL Vs CD
Team Members
V. Ravi Project Engineer
B. B. Swaroop M.Tech Student Haritha Pathuri Project Associate Gaurav Dutta Project Associate
Avanish Kumar Bajpai Sr. Project Mechanic
Vinod Bhaduria Project Mechanic Smita Mishra Sr. Project Assistant
Manoj K. Dhadwal # Sr. Project Associate
Vaibhav Sharma # Project Associate K. Santosh Laxmi # Project Associate
D. Shashikala # Project Associate Gokul Bala # Project Associate
Layeeq Ahmed # Project Associate Sanjeev Kumar Gupta # Project Scientist Vinit Kumar Sahay # Sr. Project Associate
V. T. Arun # Project Associate Atul Srivastava # Project Associate K. Srivastava # Project Mechanic
Awadhesh Kumar # Project Technician
# Ex. Project Employees
Students
Dr. V. Laxman Dr. M. Rohin Kumar Mr. Lokeswara Rao
Mr. M. Sakthivel Mr. Prashanth
Mr. Bharti Swaroop Mr. Vishnu Prasad
Mr. H. Ravinder Mr. Gagandeep Singh
SUPPORTING POWER
Rotating, Swept, Uniform Al beam
127
Effect of tip sweep on natural frequencies for Ω = 750 RPM
Validation
Rotating, Swept, Uniform Al beam
128
Effect of tip sweep on natural frequencies for Ω = 0 RPM
Validation
Result and discussion :
Damper effect on natural frequency
Mode Natural Frequencies (non-dimensional)
Without Damper With Damper
1st Lag 0.672 0.692
2nd Lag 5.954 5.924
3rd Lag 16.600 16.101
1st Flap 1.089 1.088
2nd Flap 2.792 2.785
3rd Flap 5.730 5.685
1st Torsion 4.748 4.748
2nd Torsion 17.292 17.292
1st Axial 62.251 62.320
130
Main Rotor Gear
Main Gear – Unused (Procured) Material – Delrin
Damaged Spur Gear Damaged Bevel Gear
Main Gear Model in Unigraphics
• Gear Ratio (engine – main rotor – tail rotor): 7.5 : 1
: 4.67
• Max. Engine Power: 2.4 HP
• Engine RPM range: 3000 – 13000
Material Test for Tensile Stress.
Spur Gear Bevel Gear
Static Stress (MPa)
19.63 25.88
Dynamic Stress (MPa)
42.4 56.52
131
MATERIAL Requirements of Main Rotor Gear
Loads :
• Max. Design Stress: 60 MPa
Materials Tested: • Delrin (Annealed )
• Nylon 6/6 30% Glass Fibre o Annealed and Non – annealed
• Nylon 6/6 30% Carbon o Annealed and Non – annealed
o Yield Stress: 70 MPa
132
FABRICATED GEARS
Polycarbonate
Delrin
Cotton fibre reinforced plastic
Main Rotor Gear
LEVEL FLIGHT (4.5T, 2KM, MID CG)
RESULTS
Sectional loads:
Significant increase in 3/rev, 5/rev Harmonic content with higher inflow states.
An increase of 2 to 8 times in 3/rev and 5/rev sectional loads is observed w.r.t the 3 inflow states.
Convergence in loads 3/rev harmonic content after 10 inflow states.
Lift
Drag
Moment
0
4
8
12
16
-40 -30 -20 -10 0 10 20 30 40
Deg
Turn rate(deg/s)
Tail rotor collective
-1
-0.75
-0.5
-0.25
0
0.25
-40 -30 -20 -10 0 10 20 30 40
Deg
Turn rate (deg/s)
Pitch Attitude
-75
-50
-25
0
25
50
75
-40 -30 -20 -10 0 10 20 30 40
Deg
Turn rate (deg/s)
Roll Attitude
TIP SHAPE – GENERAL OBSERVATIONS -----------------------------------------------------------------------------
• TIP SWEEP AND TAPER IMPROVE PERFORMANCE OF ROTOR DEPENDING ON SPEED CONDITION • SYSTEMATIC STUDIES ON EFFECT OF TIP ON TRAILING EDGE VORTEX AND ITS INFLUENCE ON ROTOR LOADS AND NOISE ARE STILL TOPICS OF RESEARCH • WHAT IS THE OPTIMUM TIP SHAPE IS STILL A FUNDAMENTAL QUESTION?
EUROCOPTER BLUE EDGE BLADE REDUCED NOISE
HOVER INDOOR 21 July 15
Past Team Members
B.B Swaroop, # Project Engineer
V. Ravi # Project Engineer Gaurab Dutta # Sr. Project Associate
Manoj K. Dhadwal # Sr. Project Associate Vaibhav Sharma # Project Associate
K. Santosh Laxmi # Project Associate D. Shashikala # Project Associate
Gokul Bala # Project Associate Layeeq Ahmed # Project Associate Rahul Gupta, # Project Associate Preeti Bagade, # Project Associate
Nikita Srivastava, # Project Associate Shamsheer Mohammed, # Project Associate
R. Thirumurugan, # Project Associate Prateek Jain, # Project Associate
Abhilekh Mukerjee, # Project Associate Sanjeev Kumar Gupta # Project Scientist Vinit Kumar Sahay # Sr. Project Associate
V. T. Arun # Project Associate Atul Srivastava # Project Associate
Kapil Srivastava # Project Mechanic Awadhesh Kumar # Project Technician
# Ex. Project Employees
Project Investigators
Dept. of Aerospace Engg.
C. Venkatesan Principal Investigator Abhishek
C.S. Upadhyay A. Kushari
SUPPORTING POWER
Current Team Members
Haritha Pathuri Sr. Project Associate Sanjay Kumar Viswas Project Associate
Sandeep Prajapati Project Associate
Avanish Kumar Bajpai Technical Officer Smita Mishra Dy. Project Manager Vinod Bhaduria Project Technician Vinay Kumar, Project Technician
S. S. Parihaar Sr. Project Mechanic Prameet Tiwari Sr. Project Mechanic