Improved aircraft wing designs using composite aeroelastic

tailoring

Jonathan Cooper

RAEng Airbus Sir George White Professor of Aerospace Engineering

www.bris.ac.uk/composites

2/14Outline• Overview of current work on use of composites to improve

wing designs

• Carl Scarth– ACCIS DTC (yr2)– Embraer

• Olivia Stodieck– CASE award student (yr2)– Airbus

• Guillaume Francois– ACCIS DTC (yr1)– Part funded by EOARD

Composite Aeroelastic Tailoring

3/14EU Initiatives for Aerospace Industry• 2020 Vision

• 50% reduction by 2020 of:– aircraft fuel use, – emissions – noise

– Flightpath 2050– 75% reduction in CO2,

90% NOx, 65% noise– Emission free taxiing

• Environmental friendly aircraft

• Fast design and certification methods

Composite Aeroelastic Tailoring

4/14Range Equation and Composite Design

R= 𝑉𝑉𝑓𝑓𝑓𝑓

𝐶𝐶𝐿𝐿𝐶𝐶𝐷𝐷𝑙𝑙𝑙𝑙 𝑊𝑊1

𝑊𝑊2

Achieve desired shape throughout

flight envelope Reduce weight through loads

alleviation

Reduce weight by increasing flutter speed

Determination of sensitivity to variations in structure, manufacturing and aerodynamics

L/D

Weight

Improvement through better

Aerodynamics

WeightEngines

Composite Aeroelastic Tailoring

5/14Structural Design

•Structure must be strong enough to withstand loads encountered in lifetime and also aeroelastic effects

Trade-off between strength and weightUse anisotropic composite properties to influence loads and aeroelastics - composites are NOT just a “black metal”

Composite Aeroelastic Tailoring

6/14Aeroelastic Tailoring

• Aeroelastic Tailoring – Structural and Aerodynamic behaviours are optimised by

varying composite fibre angles and layup sequence

>> Wing bending and torsion stiffness >> Passive elastic coupling between wing bending and torsion deformations

Optimisation Objectives:• Weight • Lift to Drag ratio• Static strength • Flutter & Divergence

airspeeds• Control effectiveness• Gust load alleviation

Grumman X-29

Fibre angle

Composite Aeroelastic Tailoring

7/14Tow-Steered / VAT Composites• Fibres follow curvilinear paths within the plane of the ply • First investigated in the early 1990s

Effect of Fiber Waviness, Kuo et al. (1988) Buckling Resistance, Hyer and Lee (1991) Variable Stiffness Concept, Gurdal and Olmedo (1993)

• Improved, more flexible manufacturing methods are being developed (AFP, CTS)

• Application here to aeroelaticity

Continuous Tow Steering (CTS)

Composite Aeroelastic Tailoring

8/14

TipRoot

Maximum Instability Airspeed

Optimum VAT laminate

0 50 1000

100

200

300

Freq

uenc

y (H

z)

Mode 1Mode 2Mode 3Mode 4Mode 5

0 50 100-100

0

100

Airspeed (m/s)

Dam

ping

Rat

io (%

)

InstabilityAirflowRoot Tip

0

1

-1

Composite Aeroelastic Tailoring

9/14Internal Wing Structural Design

Spars

Ribs

• Novel aircraft configurations

CFRP Composite Wing Structure

• Conventional wing

• Better to use curved spars and ribs?

Composite Aeroelastic Tailoring

10/14Optimisation Results - Shapes

DecisionVariable Set

Full ShapeOptimisation

Spar ShapeOptimisation

Cost = 0.9219Vdivergence = 180.2 m/s

Mass = 47.48kg

Cost = 0.8362Vdivergence = 166.6 m/s

Mass = 34.84kg

Both Ribs and Spars shape control offer advantagesBoth should be considered in wing design

Composite Aeroelastic Tailoring

11/14Uncertainty in Composite Designs• Increasing use in aircraft

structures– Use bend-twist coupling to offset

aeroelastic instability

• Manufacturing processes prone to variability e.g.– Layup tolerance– Thickness and geometrical tolerance– Fibre waviness

Boeing 787

PD

FCritical Air Speed

Design Instability Speed

Deterministic Design

Robust Design

Material uncertainty

UncertaintyQuantification

Minimise failure probability

Composite Aeroelastic Tailoring

12/14Uncertain Flutter Prediction

Feasible Region

• Approach using lamination parameters, PCE and Bayesian emulators enables fast prediction of probability bounds

Composite Aeroelastic Tailoring

13/14Response Mechanisms: [452-452 02 902]S

• Plot of aeroelasticresponse in ξ11–ξ12space

• Assume deterministic values for ξ9 and ξ10

• Discontinuities caused by switch in response mechanism

• ξ11–ξ12 PDF crosses discontinuity

• PDF peaks attributed to divergence & flutter

Divergence

Flutter 1Flutter 2

Flutter Peak

Divergence Peak

Composite Aeroelastic Tailoring

14/14Conclusions and Future Work• Design techniques show promising results for

improvement of composite wings• Tow-steering

– Application to high aspect ratio and forward swept wings

• Novel internal composite structures– Application to high aspect ratio and forward swept wings– Experimental testing

• Uncertainty quantification– Application to full aircraft test case– Robust design

• Plenty of room for further ACCIS PhD work for those interested

Composite Aeroelastic Tailoring