Multidisciplinary Design Multidisciplinary Design Optimization of a Optimization of a

Composite Amphibious Composite Amphibious Aircraft FuselageAircraft Fuselage

Plamen Roglev, MSc.Plamen Roglev, MSc.Perun TM EOODPerun TM EOOD

P.O.Box 26, 4001 Plovdiv, BULGARIAP.O.Box 26, 4001 Plovdiv, BULGARIAplroglev@mail.bgplroglev@mail.bg

The golden age of seaplanes is The golden age of seaplanes is long gone…long gone…

because of:because of:• Higher weightHigher weight• Higher dragHigher drag• CorrosionCorrosion

Power-to-weight ratio of Power-to-weight ratio of planing boats and airplanesplaning boats and airplanes

0

0,05

0,1

0,15

0,2

0,25

0 100 200 300 400 500

Cruise velocity, km/h

Po

we

r to

we

igh

t ra

tio

, k

W/k

g

Seaplanes

Landplanes

Planing Boats-Calm sea

Planing Boats - Stormy

Empty weight to Maximum Empty weight to Maximum take-off weight of commercial take-off weight of commercial seaplanes and landplanesseaplanes and landplanes

0,4

0,45

0,5

0,55

0,6

0,65

0,7

0,75

0 1000 2000 3000 4000

Range, km

EM

/MT

OW

Seaplanes

Landplanes

Empty weight to Maximum Empty weight to Maximum take-off weight of LSA take-off weight of LSA seaplanes and landplanesseaplanes and landplanes

0,4

0,45

0,5

0,55

0,6

0,65

0,7

0 500 1000 1500 2000

Range, km

EW

/MT

OW

LSA seaplanes

LSA landplanes

Advantages of composite Advantages of composite structures for amphibious structures for amphibious aircraftaircraft• Eliminate corrosionEliminate corrosion

• Reduce weightReduce weight

• Cheaper maintenance and longer lifeCheaper maintenance and longer life

• Improved shape – lower dragImproved shape – lower drag

Sandwich structuresSandwich structures-lighter, because they are stiffer-lighter, because they are stiffer-cost-effective-cost-effective-can be more damage tolerant-can be more damage tolerant-provide flotation-provide flotation

Single Skin Laminate- Blunt Projectile Damage

Sandwich Laminate- Blunt Projectile Damage

Photo by High Modulus (NZ) Ltd.

Application of the progress in Application of the progress in planing boats designplaning boats design

Optimization of planing hullformsOptimization of planing hullforms

• ResistanceResistance

• Longitudinal and lateral stabilityLongitudinal and lateral stability

Experience with composite hull Experience with composite hull structuresstructures

• DesignDesign

• UsageUsage

Amphibious aircraft design is Amphibious aircraft design is multidisciplinary by nature – there are multidisciplinary by nature – there are contradicting requirements for contradicting requirements for aerodynamics, structural performance and aerodynamics, structural performance and

hydrodynamic properties :hydrodynamic properties : PlaningPlaning• Stable Take-off – low drag Stable Take-off – low drag

and spray, longitudinal and spray, longitudinal stability – porpoisingstability – porpoising

• Hull loads during take-off Hull loads during take-off and landing and landing

Displacement regimeDisplacement regime

• Seaworthines – hull Seaworthines – hull volumevolume

• Lateral stabilityLateral stability

Traditional design of Traditional design of seaplanesseaplanes• Use of semi-empirical equations based on Use of semi-empirical equations based on

statistical datastatistical data

• Data obtained from model scale tests Data obtained from model scale tests

• Experience from former projectsExperience from former projects

• Sequential determination of design Sequential determination of design parametersparameters

To explore new designs physics based To explore new designs physics based modelsmodels should be introducedshould be introduced

Challenges for the high-fidelity CAD Challenges for the high-fidelity CAD based analysis methodsbased analysis methods(Navier-Stokes (Navier-Stokes

fluid flow and FEM structural analyses)fluid flow and FEM structural analyses) • High complexity of the flow High complexity of the flow

• Very high computational costVery high computational cost

• Numerical noise due to discretizationNumerical noise due to discretization

• Impossible to explore large design Impossible to explore large design spacesspaces

The solution:The solution:

Use metamodels (models of models) for Use metamodels (models of models) for MDOMDO

Benefits of metamodels:Benefits of metamodels:

• Merging of data from simulation and Merging of data from simulation and experimental analysisexperimental analysis

• Filtering of numerical noise and Filtering of numerical noise and experimental errorsexperimental errors

• Low computational cost – rapid exploration Low computational cost – rapid exploration of the design spaceof the design space

• Possible to use Possible to use gradient-based gradient-based optimization methodsoptimization methods

• Visualization of the dependenciesVisualization of the dependencies

Flying boat hull definitionsFlying boat hull definitions

• Beam load coefficientBeam load coefficient

• Displacement Froude NumberDisplacement Froude Number

3bC

3

g

VF

Comparison of the hull resistance of planing boats and Comparison of the hull resistance of planing boats and hydroplaneshydroplanes

Speed Regimes of Hull

0 1 2 3 4 5

Displacement Froude Number

Res

ista

nce

Planing Boats

Hydroplanes

Flying boat design is determined by Flying boat design is determined by the take-off conditionthe take-off conditionMost important parameter - beamMost important parameter - beam

• Classic approach – empiricalClassic approach – empirical

Munro[2]Munro[2]

ΔΔ – weight [kg] – weight [kg]

b- beam [m]b- beam [m]

3132,0 b

Application of planing boats data:Application of planing boats data:Diehl[1]Diehl[1]

Determination of beam from the

hydrodynamic lift coefficient

Beam

K=K(β, Clmax)S – wing surface

22

2b

VChl

SKb

Determination of beam for lateral Determination of beam for lateral stability in planingstability in planing

bmin (β, Δ)[m] = 0,5 + 0,0004 Δ[kg]-0,55 β[rad]bmin (β, Δ)[m] = 0,5 + 0,0004 Δ[kg]-0,55 β[rad]

Longitudinal stability in planingLongitudinal stability in planingForebody length/beam>3Forebody length/beam>3

Seaworthiness requirementsSeaworthiness requirements

Hull volume>3*displacementHull volume>3*displacement

MDO methodologyMDO methodology

• Create physics based metamodels for the drag Create physics based metamodels for the drag and weight of a seaplane hull as functions of and weight of a seaplane hull as functions of length to beam ratio and deadrise anglelength to beam ratio and deadrise angle

• Determine the constraints from the hull Determine the constraints from the hull volume requirements and the necessary volume requirements and the necessary forebody lengthforebody length

• Calculate the design pressures(CS-23)Calculate the design pressures(CS-23)• Build a Pareto front and select the design Build a Pareto front and select the design

parameters according to mission and parameters according to mission and seaworthiness requirements.seaworthiness requirements.

Response surfaces Response surfaces

• Weight / min weight (L/b, Weight / min weight (L/b, ββº)º)• Constant volume of hullConstant volume of hull

• Cx / Cxmin (L/b, Cx / Cxmin (L/b, ββº)º)

Pareto frontPareto frontDrag-Weight tradeoffDrag-Weight tradeoff

Pareto Front

0,995

1

1,005

1,01

1,015

1,02

1,025

1,03

0,95 1 1,05 1,1 1,15 1,2 1,25 1,3

W/Wmin

Cx/

Cxm

in

Drag

Weight

Design Study – Design Study – Composite Composite amphibious aircraft amphibious aircraft investigationinvestigationThe benefits from replacing The benefits from replacing

the Al alloy structure with the Al alloy structure with CFRP sandwich one and CFRP sandwich one and optimizing the geometry of optimizing the geometry of the planing hullthe planing hull

0 500 1000 1500

MTOW

AL EW

C EW

Weight, kg

Series1

0

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Al alloy Composite

Em

pty

wei

gh

t fr

acti

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Series1

Future WorkFuture Work

• Improve the metamodels with Improve the metamodels with application of kriging or radial basis application of kriging or radial basis functionsfunctions

ReferencesReferences

1.Diehl, W. – The application of basic 1.Diehl, W. – The application of basic data on planing surfaces to the data on planing surfaces to the design of flying-boat hulls, NACA rep design of flying-boat hulls, NACA rep No 696, 1940No 696, 1940

2. Munro, W2. Munro, W.. – – Проектирование и Проектирование и расчет гидросамолетоврасчет гидросамолетов – – Москва Москва 19351935