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CLEAN SKY 2FRC-IADP

NextGen Civil tiltrotor crashworthiness approaches

presentersLuigi Di Palma

Francesco Di CaprioMarika Belardo

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ContributorsAerosekur, Leonardo Helicopters, Magnaghi Group, SSM, University of Campania “L Vanvitelli”

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Outline

• THE TWO PROJECTS ARE PART OF THE AIRFRAME AND SYSTEMS DEVELOPMENTS TO BE APPLIED TO THE NEXT GENERATION CIVIL TILTROTOR TECHNOLOGY DEMONSTRATOR UNDER DEVELOPMENT AT LEONARDO HELICOPTERS DIVISION

• THE ITALIAN AEROSPACE RESEARCH CENTER IS INVOLVED IN TWO COLLABORATIVE PROJECTS FUNDED BY CLEAN SKY 2 JOINT UNDERTAKING WITHIN THE HORIZON 2020 RESEARCH FRAMEWORK

• THE TWO PROJECTS ARE NAMED “T-WING” AND “DEFENDER”• THEY ARE R&D PROJECTS AIMED AT FLYING THE NGCTR-TD VEHICLE• PERMIT to FLY IS REQUESTED

NGCTR-TD

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T-WING OUTLINE

• T-WING is a collaborative project funded by Clean Sky2 in the framework of EU Horizon2020 program

• AIM: design, manufacturing and qualification up to flight (TRL6) of the WING STRUCTURE of the NGCTR-TD

• BUDGET: 26 M€• DURATION: 2018 - 2023• PARTNERS

Loads & AeroelasticityLoad monitoring design

WTM design

Structural DesignAnalysis

Crashworthiness analysis

Structural Design & stressQualification, Airworthiness

Composite manufacturing, NDI & assembly

Metallic parts manufacturingTools & Jigs

Nacelle primary structure manufacturing

Ground Vibration Test, Noise, Dissemination

Project CoordinationInnovations, Advanced Analyses, Testing, Wing instrumentation,

Dissemination

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DEFENDER OUTLINE

• DEFENDER is a collaborative project funded by Clean Sky2 in the framework of EU

Horizon2020 program

• AIM: design, manufacturing and qualification up to flight (TRL6) of the Fuel Storage

System of the NGCTR-TD

• BUDGET: 1.4 M€

• DURATION: 2018 - 2022

• PARTNERS

Design, analysis and innovations

Design manufacturing and

qualificationProject

CoordinationModeling

strategies and analyses

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CRASHWORTHINESS ACTIVITIES

• T-WING• CRASH ANALYSIS OF THE WING. Requirement is to show that any cabin occupants

are protected in a crash situation from equipment mounted externally above the cabin including the wing. The requirement stipulates that under prescribed vertical down crash load factor, the wing has to fail in a prescribed section (frangible section), this means that the cabin needs only withstand the weight of the remaining portion of the wing above the fuselage and the fire is prevented.

• BIRD STRIKE ANALYSIS OF THE WING LEADING EDGE: The aircraft must be capable of continued safe flight and landing during which likely structural damage or system failure occurs as a result of a bird strike in A/C (4 lb bird) of VTOL mode (2 lb bird)

• DEFENDER: CRASH OF THE MOST CRITICAL FUEL TANK BAY• REQUIREMENT: to show that the most critical fuel tank bay, under a survivable crash

condition, prevents any occurrence of fuel leakage and fire, to let the occupants safely escape from the cabin.

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CRASHWORTHINESS HIGHLIGHTS

• T-WING• CRASHWORTHINESS RELATED TO WING DESIGN: very peculiar requirement dictated

by VTOL capabilities of tiltrotors: the design of the wing that breaks at prescribed section under specific crash load factor requires:

• special structural features to drive suitably the phenomenon (actually under patent evaluation),

• methods to model and aid the design of the wing• experimental validation to extend the solution to a future certified product.

• BIRD STRIKE ANALYSIS OF THE WING LEADING EDGE: in a multi-cells wing box the vehicle capability to “get home” after bird strike should be easily achievable. The safety requirement satisfaction for a VTOL machine is more demanding in order to prevent undesired failure of inter-connecting drive shaft and additionally fire triggering. Special design of leading edge is required.

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CRASHWORTHINESS HIGHLIHTS

• DEFENDER• CRASHWORTHINESS REQUIREMENT FOR THE FUEL TANK (CFR/CS §29.952). For a

“winged” VTOL vehicle having the fuel tanks inside the wing (i.e. tiltrotors), the current airworthiness requirement is followed to design the tank and the surrounding structure (i.e. wing). The prescribed drop test to be passed with no fuel leakage could be conservative for no standard helicopter machine like tiltrotor. What are the more realistic fuel tank crash conditions?

Wing span 6.0 m

Example 1 Example 2

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WING CRASHWORTHINESS APPROACH

SIMPLIFIED PROGRESSIVE FAILURE ANALYSIS

HIGH FIDELITY NONLINEAR ANALYSES MAKING USE OF EXPLICIT CODES

2018 2020 2021 2023WING CDR

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SIMPLIFIED PROGRESSIVE FAILURE OF THE WING, BASED ON LINEAR STATIC ANALYSIS

1) SELECTION OF CRITICAL WING SECTION

2) DEMONSTRATION OF PROGRESSIVE FAILURE OF FRANGIBLE SECTION

TWING CRASH ACTIVITY

1) SELECTION OF CRITICAL WING SECTION

WING + Wing to Fuselage link

FEM

APPLY 12 g VERTICAL LOADING

LINEAR STATIC

ANALYSIS

CRITICAL AREAS VS REQUESTED FRANGIBLE

SECTION

• Detailed FEM• Model is constrained at the base of the

wing links• Inertia loads applied via GRAV card on

entire model• Fuselage-wing links included

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SIMPLIFIED PROGRESSIVE FAILURE OF THE WING, BASED ON LINEAR STATIC ANALYSIS

1) SELECTION OF CRITICAL WING SECTION2) DEMONSTRATION OF PROGRESSIVE FAILURE OF FRANGIBLE SECTION

TWING CRASH ACTIVITY

2) DEMONSTRATION OF PROGRESSIVE FAILURE OF FRANGIBLE SECTION

WING + Wing to Fuselage link

FEM

APPLY PRESCRIBED VERTICAL LOADING

LINEAR STATIC

ANALYSIS

CRITICAL AREAS VS MATERIAL STRAIN

LIMITS

prescribed vertical loading is a vertical g-level between ditching and fuselage link max load

REMOVE FAILED ELEMENTS

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TWING CRASH ACTIVITY1) SELECTION OF CRITICAL WING SECTION

UPPER/LOWER PANEL (composite material only)

Peak strains zones at 12g

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TWING CRASH ACTIVITY2) DEMONSTRATION OF PROGRESSIVE FAILURE

Max strain criterion

REFERENCE ALLOWABLE STRAIN:

• OHC RTD for compressive strain

• FHT RTD for tensile strain

Black colour: elements that exceed allowables

LOWER SKIN

UPPER SKIN

compression

tension

LOOP 1 : 5 g

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TWING CRASH ACTIVITY2) DEMONSTRATION OF PROGRESSIVE FAILURE

PROGRESSIVE FAILURE

Animated Gif (please see in presentation mode)

FAILED ELEMENTS LOOP 1




LOWER SKINUPPER SKIN

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T-WING CRASH ACTIVITY

• The wing has been designed to withstand specific inertial load to prevent any relevant composite failure in order to protect the fuel tanks from fuel spillage (fire protection requirement)

• The wing will adopt the necessary features to induce the wing breaking at relevant sections in order to reduce the inertial loads on the fuselage during the crash (escaping requirement)

• A possible improvement to increase the maximum sustainable inertial load by wing structure will be investigated by using high-fidelity numerical methods taking into account the L/G and fuselage kinetic energy absorption capabilities during crash.

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WING LEADING EDGE BIRD STRIKE APPROACH

Metallic leading edgeABAQUS model of the entire wingABAQUS sub-model

Bird strike analysis for a set of impact angles and LE thicknessIdentification of the thickness compliant with the reqmts

Inclusion of the hydraulic and electrical lines in the model Assessment of lines strengthMost critical impact condition

Complete scenario of bird strike analyses by including the linesWeight optimization

2018 2020 2021 2022WING CDR

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TWING LEADING EDGE BIRD STRIKE APPROACH

• Demonstration of A/C “get home condition” in case of bird strike

• Prevention of double failure of hydraulic and electrical lines in case of bird strike

• Weight reduction of LE

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• Bird material model calibration

• Bird impact analysis on entire wing of

the Next Generation Tilt Rotorcraft

(NTGRT)

• Comparison Full-Model vs. Reduced

Model

• Sensitivity Analysis respect to leading

edge thickness

Upper skin

Leading Edge

Tip Rib

Root Rib

Adopted strategy - Workflow

• Damage status Evaluation on

internal sub-systems

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0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Proj

ectio

n Di

amet

er [m

]

Time [ms]

Projection Diameter

Experimental

Numerical

0

20

40

60

80

100

120

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Velo

city

[m/s

]

Time [ms]

Velocity

Experimental

Numerical

T = 0 ms T = 0.66 ms T = 1.32 ms T = 1.98 ms

Num

eric

alEx

perim

enta

l

• The numeric model was calibrated w.r.t experimental literature data: Bird's substitute tests results and evaluation of available numerical methods. M.A.Lavoie, A. Gakwaya, M. Nejad Ensan, D.G.Zimcik, D.Nandlallc. Int. Journal of Impact Engineering, Vol 36, Issues 10–11, 2009

Bird numerical model calibration

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• Bird Mass = 4 lb (1.8 kg)

• Impact velocity: Vmax in Airplane Mode = 243.6 knots; (127 m/s)

• No. of impact Station: 4

• Impact angles: 0° with respect to the angle of incidence of the wing (which is 3°) @ the L.E. apex

point

• The projectile is 226mm long and 113 mm wide (diameter)

• Impact Energy: 14.5 kJ

S1 S2 S3 S4

D D/2D/2

D/2

Impact Conditions

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• The main structural part is, the wing box that is joined to the fuselage by means of 4 metallic fittings which are bolted on the spars and on the root tip.

• The wing box consisting in: front spar, the middle spar, the rear spar, the upper and lower stringer, four inner ribs, the tip rib and the root rib, two upper stringers and one lower stringer.

Inner Trailing edge

Flaperon

Manoeuvrable Surface

Wing Box

Leading EdgeFusulage-wing fitting

Tip Rib

Spars of Central Wing Box

Upper skin

Leading Edge

Upper Stringers

Lower Stringer

RibsCentral Wing Box

Tip Rib

Root Rib

Access Panels

FittingLower skin

• The entire structure is made in composite material with the exception of the leading edge, the spars in the central wing box, the tip and root ribs and the fittings (and other smaller parts like lags and splices).

• The model consisting in more than 60 parts which are connected each other by means of tied constraints.

Full model vs. Reduced Model

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• In order to reduce the computation cost a reduced model has been used.• The Sub-Model consists in: Leading edge, nose ribs, partial rid, partial tip and root ribs, partial upper skin, partial lower

skin, front spar.• The entire structure is made in composite material with the exception of the leading edge, the spars in the central wing

box, the tip and root ribs and the fittings (and other smaller parts like lags and splices).• The model consisting in about 30 parts which are connected each other by means of tied constraints.

Upper skin

Leading Edge

RibsCentral Wing Box

Tip Rib

Root Rib

Lower skin

Front Spar

• The sub-model was constrained (fixed support) on the cut section, which lead to consider rigid the no-modelled wing parts


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Global Displacements - USUM

Time 0.42 ms Time 0.9 ms Time 6 ms

Full

Mod

elSu

b-M

odel


• The comparison has been performed considering fixed the impact angle (0° with respect to the angle of incidence of the wing )

• Impact station S2 and impact angle equal to 0° with respect to the angle of incidence of the wing (which is 3°) @ the L.E. apex point

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S1 S2 S4

Max displacement @ LE Apex (x-Dir) [mm] 87.01 88.01 87.97

Tip-Wing Displacement (USUM) [mm] 1.04 8.20 11.84Without RIB With RIB

2.37 6.42

Internal Energy of the Remaining Wing [kJ] 0.09 0.34 4.52 0.48 0.54

Internal Energy - Remaining Wing respect to Impacted bay [%]

1.30% 5.51% 190.43% 7.48% 8.68%

Summary Results

80.05

6.87

S3

6.176.236.57Internal Energy of Impacted bay (only LE) [kJ]

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 5 10 15 20 25 30

Dis

plac

emen

t [m

m]

Time [ms]

Displacement Time-History - ALL Impact Points

S1 - USUM - Tip

S2 - USUM - Tip

S3 - USUM - Tip

S4 - USUM - Tip

S4

Ductile damage initiation criterion @ 30 ms

S1 S2

S3 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 5 10 15 20 25 30

Ener

gy [k

J]

Time [ms]

Internal Energy Time-History - ALL Impact Points

S1 - ALLIE Wing

S2 - ALLIE Wing

S3 - ALLIE Wing

S4 - ALLIE Wing

• Considering different impact conditions theamount of energy absorbed by the entire wing(without leading edge) is a very small respect tothe total energy absorbed only by the leadingedge.

Full model

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S4 – Bay5

S1 - Bay 1 S2 – Bay 3

S3 – Bay3/Bay4

Global Displacement – Section viewFull Model Results


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Deleted elements


Sensitivity analysis w.r.t. leading edge thickness• Bird Mass = 4 lb (1.8 kg) • Impact velocity: Vmax in Airplane Mode = 243.6 knots; (127

m/s)• No. of impact Station: 4• No. of impact angles/points: 4 angles; 4 impact locations• Total number of impact scenarios: 16• Leading edge thickness: T1, T2, T3, T4, T5

The final thickness configuration and hence thepotential weight saving opportunity of the leadingedge will be defined w.r.t the acceptable damagestate on the front spar.

In order to evaluate the most conservative solution in each bay a large zone of leading edge and frontal spar were removed and the most critical loading conditions were investigated. The wing is still able to sustain the applied loads.

Undamaged model Model with removed elements

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TWING LEADING EDGE BIRD STRIKE APPROACHTh

= T

1Th

= T

2Th

= T

3Th

= T

4

Step Time 1 Step Time 2 Step Time 3

Th =

T5

Lead

ing

Edge

Thi

ckne

ss

Sensitivity analysis w.r.t. leading edge thickness

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TWING LEADING EDGE BIRD STRIKE APPROACHTh

= T

1Th

= T

2Th

= T

3Th

= T

4Th

= T

5

Lead

ing

Edge

Thi

ckne

ss

Sensitivity analysis w.r.t. leading edge thicknessStep Time 1 Step Time 2 Step Time 3

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Damage Evaluation on the internal systems • New solution with intermediate shield

Hydraulic (x2)Electric (x2)

Leading Edge

FEM Details

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Damage Evaluation on the internal systems • The most critical configuration is reported (minimum leading edge thickness)

Skin Damages Status

Displacement (UX) Shield Damage status

Skin Damage Status

Without Shield With Shield

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Hydraulic and Electric Damage status

Displacement Displacement

Hydraulic Damage status


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t =

1.5

ms

t = 3

ms


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t =

1.5

ms

t = 3

ms


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FUEL TANKS CRASH APPROACH

Tank mat coupon testsTank mat numerical calibration

Cube drop simulationHigh fidelity analysis of most critical fuel tank bay

Cube drop testCube num-expcorrelation

Full scale drop test of most critical fuel tank bayExperimental validation of the model

2018 2020 2021 2022FSS CDR

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D. Cristillo, F. Di Caprio, C. Pezzella, C. Paciello, Comparison of Numerical Models for the Prediction of Bladder Tank Crashworthiness, MEDYNA 2020

• numerical investigation on the crashworthiness of CUBE bladder tank (MIL-DTL-27422)

• Material model calibration based on coupon tests

• Comparison between two commercial codes (Ls-Dyna and Abaqus)

• Experimental test from literature

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numerical-experimental calibration of thebladder flexible materialCoupon tests:• Tensile test on Nylon fabric layer• Tensile test on NBR layer• Tensile test on complete Fuel Tank structure

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• Comparison between two commercial codes (Ls-Dyna and Abaqus)

• Experimental test from literature• Material model calibrated with exp tests

Ls-Dyna vs Abaqus

time histories of the impact force exerted on the soft fuel tank

• Abaqus smaller difference with respect to the experimental data

• Ls-Dyna seems more rigid than Abaqus

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C. Paciello, C. Pezzella, S. Magistro, G. Lamanna, F. Di Caprio, M.Belardo, L. Di Palma, Crashworthiness of a Tiltrotor Fuel tank bay,Int. Workshop on Engineering for Rotorcraft Safety, 7-9 April 2021

Preliminary high fidelity model of the most critical fuel tank bay• Model including: surrounding structure; fuel lines; fuel

systems inside the tank, 80% fuel filling (SPH approach)• Material model calibrated by tests (nylon fabric + nitrile

rubber• Drop is simulated through a dynamic analysis performed

with Ls-dyna, by imposing the pulse acceleration derivedfrom experimental data from Leader past experience

• Surrounding wing structure: rigid vs deformable

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C. Paciello, C. Pezzella, S. Magistro, G. Lamanna, F. Di Caprio, M.Belardo, L. Di Palma, Crashworthiness of a Tiltrotor Fuel tank bay,Int. Workshop on Engineering for Rotorcraft Safety, 7-9 April 2021

Surrounding wing structure: rigid

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• Surrounding wing structure: deformable• Drop test simulated by imposing free

vertical drop from 50 ft on rigid surface• PRELIMINARY RESULTS

Evolution of damage in thesurrounding structure (CFRP): LS-DYNA material models MAT58 basedon Matzenmiller’s damage mechanicsmodel with four Hashin’s failuremodes criteria

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NEXT STEPS

• CUBE DROP EXPERIMENTAL TEST

• NUMERICAL CUBE DROP CORRELATION

• FULL SCALE EXP. DROP TEST OF THE MOST CRITICAL FUEL TANK BAY

• FULL SCALE MODEL VALIDATED

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DEFENDER Project

Prof. Erasmo Carrera CoordinatorMatteo Filippi [email protected]@polito.it

Marika Belardo, PhD, DEFENDER Project [email protected]

Francesco Di Caprio, PhD, Project [email protected]

This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovationprogramme under Grant Agreement number: 738078 — DEsign, development, manufacture, testing and Flight qualification of nExtgeNeration fuel storage system with aDvanced intEgRated gauging and self-sealing capabilities (DEFENDER)

THANK YOU!T-WING Project

Eng. Luigi Di Palma [email protected]

Marika Belardo, PhD, Project [email protected]

mailto:[email protected]






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