Vibration Behaviour of External Payload on Rotorcraft

Vibration Behaviour of

External Payload on Rotorcraft

Schmid David

RUAG Switzerland Ltd

Division Aviation

Torino, 23.04.2013

03.05.2013 RUAG Aviation 2

Content

About RUAG

ISSYS Pod Purpose and Structure

Project Goal

Dynamic Model

Vibration Tests

Comparison of Test and Simulation


RUAG Holding


RUAG Aviation:

Independent Life Cycle Support Business and military aircraft MRO

Final assembly, MRO and upgrades, authorized service

centre for various aircraft types (F/A-18, F5, Cessna,

Piaggio, Bombardier, Dassault, Dornier 228 and NG

and many more)

Components and subsystems

Development of new structures and products,

engineering of modifications & repairs for existing

aircraft, Static & Fatigue Testing of Coupons and Mid-

Size Components, Wind Tunnel facilities

EASA Part 21 Subpart G, EASA Part 21 Subpart J, EASA

Part 145, FAR-145, Type Certificate Holder Do 228

ISO 9001, EN 9100

Based in: CH, DE, USA, 1980 employees

Net sales: CHF 487 million

EBIT: CHF 22 million

Proportion R&D: 12%


ISSYS Pod

Self Protection System against guided missiles integrated

into a mobile pod

Pod is attached to the aircraft with an interface adapter

customized for each aircraft type

Interchangeable between aircraft in a short time by ground

personnel

Lower cost of pod versus fully integrated system

Pod system remains the same for all helicopter types, only

interface adapter needs to be redesigned


Self Protection System – Flare Firing


ISSYS Pod


ISSYS Pod

Missile Approach

Warning Sensor (2x)

Radar Warner (2x)

Laser Warner (2x)

Countermeasure

Dispenser

Avionics (EWC, PCU,…)

inside Pod


Interface Adapter – UH-1D

2 Milled Brackets

(Pod-Side)

2 Milled Brackets (A/C-

Side) 8 Adjustable Length Push-Pull

Rods


Project Goal

Develop an analysis model to accurately predict eigenfrequencies of

system for new interface adapters and different pod configurations

Challenges:

System non-linearity due to non-linear force-deformation curve of struts

and freeplay between struts and other structure

Short engineering cycle – no time for large engineering tests

Conventional FE analysis (static & eigenmodes) not adequate

Large amount of design constraints & requirements

Solution:

Use MotionView / MotionSolve to simulate vibration behaviour of

system


Design Constraints & Requirements

UH-1D Interface Adapter

Pod position must be adjustable in all 6 degrees of

freedom within certain range

Lightweight (max total weight of LH & RH adapter is 7kg)

Pod position far aft and outboard relative to the hardpoint

positions due to passenger sliding door

Large tolerances of A/C hardpoint positions (absolute and

relative)

Adapter – Pod system must avoid main rotor frequency

bands


Design Constraints – Frequency Bands


Analysis Work Flow

Component (Strut)

Test Data

Static Analysis FE

Models

CAD Model

Dynamic Model

Vibration Test

Dimensions /

Component

Masses

Force –

Displacement

Curve

Deformable

Bodies

(FlexPrep)

Validate

Model


Measured Strut Properties


Dynamic Model – Assembly

Non-Linear

Spring-Damper

Elements

(Struts)

FlexBodies

(from static

model using

FlexPrep)

Point Mass

(Magazine

with Flares)

User Configured

Analysis Flow

Simulating Real

Installation Work Flow

Simulated

Exciter Input

(White Noise)


Dynamic Model – Static Checks

Pod Mass

Static Analysis (1g Gravity) shows good correlation between test and

model

Test Model D

Pod 47.5 kg 47.2 kg <1%

Mag w Flares 9.93 kg 9.93 kg 0%

Total 57.43 57.13 <1%


Vibration Tests

Strain Gage Time History Data

(1 configuration only)

Frequency Response


Sample Result: Z - Axis – Full Magazine

Sensor: Envelope Z-Axis

Configuration: CIDAS 100 Light LH

Full Magazine (36 Standard Flares)


Summary

First two modes predicted accurately without model tuning

(D<5%)

Third mode prediction less accurate (D~15%)

Model is easy to set-up and modify

Model not yet ready for standalone prediction, still some

tests needed for simulation of new interface adapter

designs, but helps tremendously during design phase


Thank you for your attention!

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Vibration Behaviour of External Payload on Rotorcraft

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