overview of helicopter dynamics and aeroelasticity, and ... of helicopter dynamics and...

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

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))

Aerodynamics

Inflow

Local Global

Section Loads

Prescribed Wake

Free Wake

Uniform Inflow

Drees Model

Mangler & Squire

Perturbation Model

Dynamic Inflow

Dynamic Wake

Classical Unsteady Dynamic Stall

Theodorsen

Greenberg

Leishman-Beddoes

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:

iλαµλ += tan

)(2 22 λµλ

tan µχλ

Rotor Disk

Inflow models (cont’d)

• Drees Model (1949): Function of radial station and azimuth

• Dynamic wake Model (1989, DW) (Peters-He model):

[ ])sin()()cos()()(tan),,(0 3,1

ψβψαφαµψλ ptptrtr pj

pj ++= ∑ ∑

21]~][[][ 1 mc

Cpj LVM ταα =+ −

21]~][[][ 1 ms

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

tan µχλ

Rotor Disk

Aerodynamic Modeling: Sectional aerodynamics loads

Sources of unsteadiness in helicopter rotor blade

Flapping Motion

Lead-lag Motion

Elastic Torsion

Aerodynamics in Forward Flight: Dynamic stall

ψsin∞+Ω= VrV

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

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 – )

Modified ONERA Stall Model • Lift at quarter-chord point

−=Γ

Γ+Γ++=

120112

WbVECV

VVWbkWbsSL

*Laxman, V., and Venkatesan, C., AIAA Journal, January 2007

Modified ONERA Model (contd.)

• 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

Flight Dynamics

χ γf

xea, yea, zea – Earth-fixed axes

χ - dynamic Track angle

Horizon

Equations of Motion

Force Equations

Moment equations

• (roll)

• (pitch)

• (yaw)

Kinematic Relations

Flight Dynamics

Aeroelastic Formulation

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

r Trim

nse Trim initial

guess Vehicle geometry & aerodynamic data

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

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

2.5”

0.063”

34” 6” 16% Tip Sweep

Validation

Rotating, Swept, Uniform Al beam

Effect of RPM on natural frequencies for Λ = 00

Validation

Effect of RPM on natural frequencies for Λ = 450

Validation

Frequency vs RPM: ALH

Rotor RPM

CAMPBELL DIAGRAM

IITK CODE

Thrust and Power Curves

Validation

Formulation of lead lag damper model Fluidlastic lead lag damper attachment to the main rotor

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)

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

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)

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)

0 360 720 1080 1440 1800

PSI (Deg)

ANALYSIS

FLIGHT TEST

BLADE LOADS AT VH (torsion moment near root)

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

-40 -20 0 20 40

Turn rate (deg/s)

Main rotor Collective

-40 -20 0 20 40

Turn rate (deg/s)

MR lateral cyclic

-2-40 -20 0 20 40

Turn rate (deg/s)

MR longitudinal cyclic

TRIM in TURN

-40 -20 0 20 40

Turn rate(deg/s)

Tail rotor collective

-40 -20 0 20 40

Turn rate (deg/s)

Pitch Attitude

-40 -20 0 20 40

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

Time (sec)

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

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

Nylon 6/6 30% carbon

PEEK 76.0

PEEK- VESTAKEEP 4000CF30(A)

MANUFACTURING Tail Transmission Coupler

Coupler Weight (gm) Delrin

(procured) 3.60

Nylon 6/6 30% carbon

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

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

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

NEW HELICOPTER LABORATORY

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

CNC LLL +=

+= 10 2

~21 WWbSLNC

ππρ

[ ]10 22~21 WWVSLC ππρ +=

( )VhVW /0+= θ θbW =1and

Sectional aerodynamics loads (Cont’d)

DCVSD ρ=

Moment on the airfoil

Drag acting along the resultant velocity

CNC MMM +=

−−−= 110 16

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

• Free vibration analysis -

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)

wt L m mv

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 = − ∆ +

Wherea a a Cz

r r r CzE E Cz

= + ∆

= + ∆= ∆

Pitching moment at quarter-chord point:

Petot (ONERA EDLin) Extended Model (1989):

Lift at quarter-chord point:

If is zero, equations lead to initial model

0 1 1 2

1 1 0 1

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

λ λ λθ

α ασθ

= + + Γ + Γ

∂ Γ + Γ = + ∂ ∂ + + + ∂

Γ + Γ + Γ = − ∆ +

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

• 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

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

e Trim

Vehicle geometry & aerodynamic data

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

Main Rotor

Perturbation in control angle

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

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

k j •

Derivation

ζηγγε

δγδγδε

=∂ ∫ ∫ ∫

000000

∫ =∂−∂−∂2

te dtWTU

Hamilton’s Principle

∫ ∫ ∫=∂ 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

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

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

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

Blade manufacture

Fuselage structure

Load test

Engine test

Landing skid

Avionics box

Power management

PLANNED ACTIVITIES

ROTOR HUB DEVELOPMENT -----------------------------------------------------------------------

6-December 2014 outdoor flight

Theta0@0.7R flap moment@0.435m lag moment@0.8m(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 moment@0.435m lag moment@0.8m(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

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

Effect of tip sweep on natural frequencies for Ω = 750 RPM

Validation

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

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

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

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.

Moment

-40 -30 -20 -10 0 10 20 30 40

Turn rate(deg/s)

Tail rotor collective

-40 -30 -20 -10 0 10 20 30 40

Turn rate (deg/s)

Pitch Attitude

-40 -30 -20 -10 0 10 20 30 40

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