Main Rotor Blade Analysis - ASASI Rotor Blade Analysis.pdfEstablish the last flight path, heading, and attitude and of the helicopter Establish the RPM of the main rotor and engine

Main Rotor Blade Analysis inHelicopter Accident Investigation

by Sam Webb

➔Establish the last flight path, heading, andattitude and of the helicopter

➔Establish the RPM of the main rotor and enginepower levels

➔Establish drive train continuity➔Establish sequence of events of the accident

➔Investigator must havea limited knowledge ofthe design of the rotorsystem and blade

➔Wooden symmetricalairfoil

➔Nickel leading edge,wooden filler, steelspar

➔Aluminium spar andskin, honeycomb core

➔Compositeasymmetrical airfoil

➔Uni-directional S-2glass/ epoxy fabric &E glass/ epoxy tape,fibreglass spar

➔Superior fatiguetolerance, notch andcorrosion resistance

➔Normally wider cord /longer length blades

➔Higher main rotorRPM/ higher bladeinertia

Two Bladed Systems,(teetering, semi-rigid)

➔Blades usually lighterconstruction, lesscord, less length

➔Main rotor RPMvalues marginallylower to compensatefor cord areadifferences

Fully articulated, multi-blade systems

➔Blades sameconstruction as multi-bladed system

➔Main rotor RPMvalues same as multi-bladed system

Coaxial- counterrotating, multi-bladesystems

➔Blade bending, notshattering

➔Blades generally intact➔Blade bending inboard

and downward➔High angle of attack=

blade tearing aft ofspar

Tip weights

Low Main Rotor RPM

➔Blade tip weightsintact

Low Main Rotor RPM

Weights

➔Spar fractures, trailingedge separation

➔Honeycomb fracturedand separated

➔Damage mainly tooutboard sections ofblade Fractured spar

High Main Rotor RPM

➔Tip weights �ejected�➔May travels for

kilometres from theimpact site (fartherdistances for multi-bladed systems

High Main Rotor RPM

➔First blade to impactsurface mostdamaged

➔Following bladesexhibit lesser damagedue to main rotorinertia bleed off

High Main Rotor RPM

First impact

➔Damage is in plane

High Main Rotor RPM

Shattering

➔Massive bladedistortion on multi-bladed systems

➔Blades sustain moredamage due to lighterconstruction

➔Articulated systems,dynamic stops fail

High Main Rotor RPM

➔Blade spindling/distortion

➔Spar fracturesdepending on mainrotor RPM

➔Bending of spardepending on angle ofattack

Spar bend

Damage From Water Impact

➔Inertia of the blade- with high inertia will loseRPM slowly with increased angles of attack

➔Higher the helicopter gross weight and/or densityaltitude= more the blade wants to overspeed

➔Manoeuvring- tends to increase RPM due toenergy enhancement of the rotor system

➔Will collaborate otherevidence

➔Distorted or broken➔Direction of force will

collaborate power onor off and autorotation

Main Rotor Controls

P/C rod ends

➔Damage to pitch horn,blade grip, mastassembly on semi-rigid and rigidsystems= indication ofhigh RPM

Main Rotor System

➔Torque-tension strapdamage

Main Rotor System

➔MR Spindle sheardamage

Spindle sheared

Main Rotor System

➔Swashplate duplexbearing damage=indication of high RPM

Main Rotor Swashplate

➔Pitch change rod endattachment damage

➔Static overloadindications= high RPM

➔�Necking� indications=low RPM

Main Rotor Controls

Sometimes you justhave a bad day!

Sometimes you neverunderstand!?!?!?!?!