Design, Fabrication and Testing of Ornithopter wing

1
Design, Fabrication and Testing of Ornithopter
wing

• By
• V. Krishna chaitanya
• Hemendra Arya K. Sudhakar
• Guide Co-guide

CASDE, IIT Bombay Aerospace Engineering
Department 15th July, 2005.
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Birds Flight

• Gliding or soaring flight

• Resembles Aircraft.
• Only Lift and no thrust.

Flapping or Powered flight

• Flapping of wings for Lift.
• Twisting of wings for thrust

Smart and Adaptive techniques

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• Adaptive technique is used for ornithopter wing.
• Structural member tailored suitably for required
  flexibility.
• Spar is main source of bending and torsional
  stiffness.
• Fabric, ribs and skin contribution is less.

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Introduction

• Spar design.
• Fabrication of spar.
• Structural testing of spar.
• Wing Fabrication.
• Slider crank flapping mechanism.
• Wind tunnel testing of wing.

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Spar Design
Requirements

• Main source of bending and torsional stiffness.
• Sufficiently light and durable to flap.
• Fit within the thickness of the chosen airfoil.
• Match with the dynamic variations of bending and
  torsional stiffness.
• Ease of fabrication.
• Box section and composite material will form the
  candidate design

H height
h is height b is width and t thickness of box
section
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Design Methodology
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Cross section of spar

• EI E(material) (2bt36bth22th3)/12.
• GJ G(material) (2b2h2t)/(bh).
• The height of the spar will be a known
  parameter.
• From the above equations a polynomial in terms
  of width (b) is obtained and solved.
• Thickness is obtained by substituting the width
  and height in anyone of the above equations.

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Analysis of spar

• Spar is modeled as cantilever beam.
• No mass of the structure is considered.
• Walls of the spar are represented as layers of
  orthotropic laminates.
• Modeled as plane stress problem.
• Loads and torques act along the elastic axis of
  spar
• Linear analysis is carried out.

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Spar model

• Bending stiffness of 48.84 N-m2 and Torsional
  stiffness of 4.56 N-m2 is constant through out .
• Taken from the Journal The Development of
  efficient ornithopter wing.
• Commercially available Generic E-glass/epoxy is
  used.
• E1139 GPa. E228.7 GPa. G123.8 GPa.
• µ120.23
• The dimensions of the box section are
• Height 14mm Width 8.4 mm
• Thickness 0.94mm.
• Length of the spar 1.016m crank angle 15.380.

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Spar model created in ANSYS
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Bending Deformation
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Twisting Deformation
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Preparation of Plaster of Paris mold
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Fabrication of spar using Pop mold
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Comparison of Fabricated specimens
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Elements of Structural testing

• To know the properties of spar.
• To check the properties lies close to theory.
• Helps to use the spar for wing.
• Bending and torsional testing for specimen
  properties.
• Testing has to be non-destructive.

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Bending experiment

• End is fixed.
• Load is applied at one station.
• Deflection is measured on other stations.
• Deflection is measured using height gauge.
• Dial gauge is used for stations close to root.

mm/N
Cijhh
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Flexibility matrix for specimen 1
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Flexibility matrix for specimen 2
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Flexibility matrix for specimen 3
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Torsional Experiment

• End is fixed.
• Horizontal bar is glued at each station.
• Equal and opposite load is applied on bar.
• Pulley is used for load transmission.
• Deflection measured using height gauge.
• Dial gauge is used at root.

Cij??
rad/N-m
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Torsional Flexibility of specimen 1
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Torsional Flexibility of specimen 2
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Torsional Flexibility of specimen 3
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Wing Fabrication

• The spar has to be fit within the airfoil.
• The elastic axis be positioned accurately.
• The spar centre of gravity and elastic axis is
  chosen to be same.
• Smooth surface of skin to reduce drag.

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The ornithopter wing spar and airfoil
Spar
S1020 Airfoil
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1. Split the airfoil into two half's and cut the
box section
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3. Spar placed between the two halfs
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4. Glue the spar and the airfoil
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6. Covering the wing with skin
Mass of the wing 43.2 grams
Semi wing aspect ratio 7.8
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Mechanism
Requirements

• The mechanism should weigh less.
• Simple with minimum joints and rigid.
• Flapping kinematics should be harmonic.
• Minimum phase difference between the wings.
• Flapping amplitude should be 300 to -300.

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Flapping Mechanism

• Slider Crank Flapping Mechanism.
• Symmetrical Flapping.
• Less joints but more sliding members.
• Flapping Amplitude 300 to -300.
• Precision machining.

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Kinematic Analysis

• Position, Velocity and acceleration with time.
• Simulink model for the Kinematic analysis.
• Crank length a 15 mm.
• Connecting rod length b 60 cm.
• Differentiate angular displacement once give
  angular velocity, twice give angular acceleration

bsin
3(t) acos
2(t)

Displacement of the slider is given by d(t)
bcos
3(t) asin
2(t)
The angle rocker makes with the horizontal
tan(
(t)) (d(t) b)/(1.732a)
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Angular Displacement of Rocker
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Angular Velocity of Rocker
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Angular Acceleration of Rocker
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Fabricated Mechanism

• Rigid to withstand wind tunnel loads.
• No mass optimization
• For testing purpose.
• Length of Crank 15 mm and Connecting rod of 60
  mm.
• In-house fabrication.
• Lubricated to reduce friction b/n sliding members.

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Wind tunnel testing

• Evaluation of aerodynamic performance.
• Calculation of Lift and Thrust.
• Sensor used is load cell.
• Separate fixture for lift and thrust (in-house
  fabrication).

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Lift Measurement by Load cell
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Lift Measurement by Load cell
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Thrust Measurement by Load cell

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Thrust Measurement by Load cell
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Lift results for wind tunnel velocity of 10 m/s
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Lift results for wind tunnel velocity of 12 m/s
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Thrust results for wind tunnel velocity of 7.5 m/s
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Thrust results for wind tunnel velocity of 10 m/s
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Flapping wing preview
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Thank U
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Additional slides
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Performance deciders of Ornithopter wing

• Code developed at CASDE.
• Used the validated code for the analysis.
• S1020 airfoil is used for the analysis.
• Bending and torsional stiffness.
• Position of elastic axis and center of gravity of
  spar.
• Iterative procedure.

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• Mass of the wing has to be minimum for better
  aerodynamic performances.
• Torsion stiffness will be within certain limit.
• Bending stiffness has a threshold value.
• Too high bending stiffness is adding mass to the
  wing.

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Lift Vs GJ
EI 48.84 N-m2
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Thrust Vs GJ
EI 48.84 N-m2
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Lift Vs EI/GJ
GJ 5.04 N-m2
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Thrust Vs EI/GJ
GJ 5.04 N-m2
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Lift Vs Elastic axis
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Thrust Vs Elastic axis
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Cross section of spar

• EI E(material) (2bt36bth22th3)/12.
• GJ G(material) (2b2h2t)/(bh).
• (k2c1 c2)b5 ((k1k2k3)c1)b4
  (c1k1k3(c1)3)b3 (3k1(c1)3)b2
  (3(k1)2(c1)3)b (k1c1)3 0
• Where
• c1 (0.5 GJ)/ (G h2) c2 (6 EI)/ E
• k1 h k2 3 h2 k3 h3
• Solving the polynomial will give the width and
  thickness can be obtained using
• t c1 (bh)/b2

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Results of structural analysis
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Flexibility matrix for specimen 1
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Loss in symmetry - specimen 1
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Flexibility matrix for specimen 2
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Loss in symmetry - specimen 2
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Flexibility matrix for specimen 3
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Loss in symmetry - specimen 3
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Torsional Flexibility of specimen 1
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Loss in symmetry - specimen 1
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Torsional Flexibility of specimen 2
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Loss in symmetry - specimen 2
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Torsional Flexibility of specimen 3
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Loss in symmetry - specimen 3
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Single crank mechanism
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Single Crank mechanism

• Designed by Manish Ranjan of Mechanical Engg.
  Dept.
• Simple and Light.
• Unsymmetrical Flapping.
• Angular displacement is close to harmonic.
• Angular Velocity, Angular Acceleration not close
  to harmonic.

Fulcrum Fixed to the body
Crank
Rocker
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Angular Displacement
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Angular Velocity
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Angular Acceleration
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Statistical analysis of Wind tunnel testing
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Mean and Standard Deviation of Lift for 10 m/s
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Mean and Standard Deviation of Lift for 12 m/s
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Mean and Standard Deviation of Thrust for 7.5 m/s
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Mean and Standard Deviation of Thrust for 10 m/s
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Lower and Upper for Mean Lift at 10 m/s
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Lower and Upper for Mean Lift at 10 m/s
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Lower and Upper for Mean Lift at 12 m/s
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Lower and Upper for Mean Lift at 12 m/s
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Lower and Upper for Mean Thrust at 7.5 m/s
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Lower and Upper for Mean Thrust at 7.5 m/s
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Lower and Upper for Mean Thrust at 10 m/s
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Lower and Upper for Mean Thrust at 10 m/s