USAAVRADCOM-TR-82-D-9

AD AllDA18 8 2

SLACK WIRE STRIKE PROTECTION CONCEPTS

BELL HELICOPTER TEXTRON, INC.P. 0. Box 482Fort Worth, Tex. 76101

July 1982

Final Report for Period September 1981 - May 1982

IApproved for public release;distribution unlimited. DTFIC

SEP 0 21982

Prepared for

APPLIED TECHNOLOGY LABORATORYU. S. ARMY RESEARCH AND TECHNOLOGY LABORATORIES (AVRADCOM)

-Fort ti,' Va. 23604

LA-1

APPLIED TECHNOLOGY LABORATORY POSITION STATEMENT

This report is considered to define effective concepts for slack wire strike protection thathave retrofit potential for existing Army helicopters. Prior to implementation of any ofthese concepts, full-scele testing and cost effectiveness analyses are required. Results ofthis contract will be considered in formulation of future programs and aircraft designrequirements.

LeRoy T. Burrows of the Aeronautical Systems Division served as project engineer forthis effort.

I,

DISCLAIMERS

The tindings in this report are not to be construed a an official Department of the Army position unles sodesignated by other authorized documents.

When Government drewings. speclflcatons, or other dataet used for any purpose other then In connectionwrith a definitely related Government procurement operation, the United States Government thereby Incurs noretponsibillly nor any olinigtion whetsoever; end the foci that the Government may have formulated, furnished,or in any way suppiald the said drawings, secilications, or other data it not to be regarded by implication orotherwie as in any manner licensing the holde" Or any other pr or torpoe3tion, or conveying any rights orpermission, to manufacture, use, or sell any patented invention that mey in any way be related thereto.

Trade names cited in this report do not constitute an official endorsement or eop--all of the use of suchcommercial harcdwr or software.

DISPOSITION INSTRUCTIONS

Destroy this report when no longer needed. Do not return II to the originator.

1

-mti~~ ':17.

Unclassified _

SECURITY CLASSIFIC.ATtON )r THIS P-AGE ,'WN.,- Oara Entered)

REPORT DOCUMENTATION PAGEB--ORD COMPLETING S FORMI REPORT NUMBER )2 GOVT ACCCSSION NO.1 I. RECIPIENT'S CAT ALOG NUU F-R

USAAVRADCOM TR-82-D-9 _"_

4. TITLE (an Sub.f1?¶) S TYPE OF REPORT 6 PERIOO COVERFO

Final ReportSLACK WIRE STRIKE PROTECTION CONCEPTS Septemoer 1981-May 1982

C PCRFORMINO ORG. REPORT NUMBER

7, AuTHC.R(•) a : CONTRACT OR GRANT NIMB[CRI(')

DAAK5]-81-C-0034

DAAK9. PERFORMING ORGANIZATION NAME ANO ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK

AREA & WORE UNIT NUUR•FAIBell Helicopter Textron, Incorporated 62209A 1L162209AH76P. 0. Box 482 6Fort Worth, Texas 76101 1 '76E 032II. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

Applied Technology Laboratory, US Army Re- July 1982search & Technology Laboratories (AVRADCOM) 13 mUMEER OF PAGES

Fort Eustis, Virginia 23604 72MONITOnING AGENCY NAME & ADDRESS((I dilIro It In- CoII1olIlrj O fi1*e) 1S SECURITY CLASS. (of IAho .'pc

Unclassi fied

•.* OE .' 1FICATION,'DOWNGAADINGSCInOULIE

I. DISTRISUTION STATEMENT (o W Ie R.potnr)

Approved for public release; distribution unlimited.F

17. DISTRIBUTION STATEMENT (ol Cho 4,II,act ontfoiIJ In 61oft 20, ti diiievit f-om R.port)

I1, SUPPLEMENTARY NOTES

It v We • '.S(ContI,-, M• 6 re 0er id# II ft -0006,y Od Identily by block nn0.rbt)

Helicopter Tail RotorWire Strike Support TestingS'ack Wire FairingsRotating Controls Cutters

Main Rotor Trade-off StudyAWTtr -: -. Wh- M..~ 1 ffa"- -d id.dl~f PI,- E .RI

A desin -tudy has been conductea -• estitli.n slack wire str!.-'eprotect.on concepts. The objectf.., ' the study was to define andinvestigate design concepts thdt could prevent helicopter mishapscaused by main and tail rotor uontroal entanqlemen$ w1ith a slackwir- Ihe stuiv hp]i-,ptcr wcs an Ud-:ý8A equipped with a tatit wire

protection system (WSPS) .~j_______

SDO ,•A 1473 DOMOMO, ,.ov.SoLET Unclassified

SECURI TY CLAS-ItFICATIOR OF THIS -AQGE (Ebo, Date Entered)

I110 11

Unclassif i edSIECUPLTY CI.ASSIFICATION OF ToCIS PA' • .o• . Fl-d)

Block 20. Abstract - (:,.lftinued.

Eight main rotor and five tail rotor protection coJncepts weredeveloped to the extent that their individual characteristics couldbe determined for use i:t a trad!e-off evaluation.

Two of the more promising main rotor concepts were ealuated duringa whirl test. It was cdemonstrated i-. rh.c Lest that both conceptswere feasible and very effective in protectino the rotating controlsfro, entanalement. Frr,m the results of the trade-off evaluationand testing, four main rotor and fout tail rotor concepts wererecommendod for further deveLIopment.

Aeezs3ion ForNTIS 2&DTIC TA.

r BB . . .

o r

--C

TABLE OF CONTENTS

LIST OF' ILLUSTRATIONS ..................................

INTRODUCTION ...........................................

SLACK WIRE PROBLEM DEFINITION .......................... 8

CONCEPT FORM1ULATION .................................... 11

DESIGN CONSIDERATIONS ............................. 11PRELIMINARY ANALYSIS .............................. 15

Potential Concepts identified ................... 15

CONCEPT SELECTION ...................................... 18

SELECTION PROCEDURE ............................... 18CRITERIA FOR SELECTION ............................ 18

PRELIMINARY DESIGN ..................................... 21

LAYOUT DESIGN STU!DIES ............................. 21DESIGN DESCRIPTION ................................ 22

Main Rotor Aerodynamic Fairing .................. 22Main Rotor Pitch Link Ring ...................... 22Main Rotor Actuated Cutter ...................... 23Main Rotor Pitch Link Cutters ................... 29Main Rotor Grip Assembly Cutters ............... 29Tail Rotor Controls Cover ....................... 29Tail Rotor Shaft Cutter ......................... 35Tail Rotor Shaft Cover ........................... 35Tail Rotor Yoke-Mounted Cutters ................. 35Texil Rutor PiLch Link Cutteis ................ 35

DESIGN SUPPORT TEST ............................... 35

Test. Equipment ............................... 35Baseline Test ................................ 42Pý P "t-h Link Ring .............................. 47P tch Link Cutter ............................ 54

I3

TABLE OF CONTENTS (Concluded)

TRADE-OFF EVALUATION ................................... 56

PARAMETER DEFINITION .............................. 56CONCEPT COMPARISONS ............................... 58

Main Rotor Aerodynamic Fairings .............. 58Main RotoL Pitch Link Ring ...................... 63Main Rotor Actuated Cutter ....................... 65Main Rotor Pitch Link Cutters ................... 65Grip Assembly Cutter ............................. 66Tail Rotor Controls Cover ........................ 68Tail Rotor Shaft Cutter and Shaft Cover ...... 68Tail Rotor Yoke Cutters .......................... 69Tail Rotor Pitch Link Cutters ................... 69

CONCLUSIONS ............................................ 71

RECOMMENDATIONS ........................................ 72

4

Ii

,!

LIST OF ILLUSTRATIONS

Figur e Page

1 Model 206BR helicopter with main andtail rotors entangled by rope ........................ 9

2 Model 206A helicopter swashplatedamaged by monofilament line ........................... 10

3 OH-58 helicopter .................................. 12

4 AH-i helicopter ................................... 13

5 UH-I helicopter ................................... 14

6 Main rotor aerodynamic fairing ........................ 23

7 Main rotor pitch link ring ............................. 25

8 Main rotor actuated cutter ............................. 27

9 Main rotor pitch link cutter ........................... 31

10 Main rotor grip-mounted cutter ........................ 33

11 Tail rotor controls cover .............................. 34

12 Tail rotor shaft cutter ........................... 36

13 Tail rotor shaft cover ............................ 37

14 Tail rotor yoke-mounted cutter ........................ 39

15 Tail rotor pitch link cutter ........................... 41

16 Baseline test hub ................................. 43

17 Pitch link ring concept test har'.qare ............. 44

18 Pitch link cutter concept test hardware .............. 45

19 Pitch link cutter ................................. 45

20 Pitch link sawtoothed cutter ........................... 46

5

LIST OF ILLUSTRATIONS (Concluded)

Figure Page

21 Horizontal wire baseline test ...................... 48

22 Vertical wire baseline test setup ..................... 49

23 Vertical wire baseline test results ................... 50

24 Pitch link ring test with baseline test setup ..... 51

25 Test results of pitch link ring with baselinetest setup ........................................ 52

26 Test results of pitch link ring with modifiedtest setup ........................................ 53

27 Kevlar orientation of cutting duringmodified test ..................................... 55

28 Kevlar orientation at cutting duringbaseline test ..................................... 55

29 Main rotor aerodynamic fairing andgrip-mounted cutter ............................... 62

30 Main rotor pitch link ring andgrip-mounted cutter ............................... 64

31 Effect of pitch link cutter blade shapeon cutting motion ................................. 67

B6

&. •.• ,

INTRODUCTION

With the increased low altitude and nap-of-the-earth operationof U.S. Army helicopters, the danger and number of wire strikeshave also increased. Equipping helicopters with mechanismsthat will cut wires will result in fewer mishaps and casualtiesand improve overall mission effectiveness. The U.S. Army hasprocured a wire strike protection system for the OH-58 heli-copter to provide increased survivability against taut wiresstriking the upper and lower portions of the fuselage. Theremaining areas of concern are main and tail rotor blade wirestrikes and the entanglement of slack wires with the main andtail rotor controls.

Wire strikes have been documented that involve hitting obstaclesranging from string- to steel-reinforced power transmissionlines with diameters of less than 0.12 inch to over 1.1 inch.The larger diameter and stiffer wires are not as likely towrap around rotating controls when these wires become slack.The danger of a mishap due to slack wires generally involvesmonofilament line, string, communication wire, and TOW missilewires that have been broken. These wires are relativelyflexible and lightweight, which makes them susceptible tobeing picked up by the main rotor and wrapped around therotating controls.

The WSPS is very effective on taut wires but will not protectthe rotating controls from slack wire damage. A system isneeded that will protect the rotating controls from bindingand bending from the wrapping of slack wires. This reportidentifies and develops various main and tail rotor protectionconcepts into systems that effectively meet this need forcontrols protection.

I

- 7

SLACK WIRE PROBLEM DEFINITION

There have been many instances of slack wires. strings, andropes that have wrapped around main and tail rotor shafts andcontrols of military and civil helicopters. One or two wrapsof wire would not pose a threat; however, many windings havean additive effect. In the case of rotating controls, verylight wire or string with many wraps can bind or collapse thepitch links causing difficulty or loss of corntrol of theaircraft. Figure 1 shows a rope from a balloon that wrappedaround the main and tail rotor controls. Because it turnsfive times faster than the main rotoz, the tail rotor has manymore windings.

Slack wires could be oriented in any manner in space when theyare "caught" by the helicopter. Taut wires are generallyhorizontal and pose problems for the fuselage (cabin or landinggear). The slack wires can be pulled into the main or tail.rotor by the inflow of air or "dragged" across the fuselageinto the controls. Slack wires that pose the greatest threatfor entanglement with cjntrols are generally small in diameter,lightweight, and very flexible. These wires can be metallic,plastic, or organic in composition and very long.

A particular problem with small diameter wires is that theycan cut bolts and seals and penetrate bearings as well as wraparound controls. Fi-gure 2 shows the nonrotating inner ring ofa swashplate that was damaged when a kite being flown withmonofilament line was struck. The kite line wound around thering and cut a groove 1/8-inch wide by 3/64-inch deep. Ai,-therpotential military threat is the injection of wires or stringsinto the paths of helicopters. The organic fiber, Kevlar,would be a significant threat due to its low density, hightensile strength, abrasion resistance, and fracture toughness.

i4

ii8

I.

CA

2.F

Mod- tail heicojt; with main andtalrotors entanciled by copo.

ýA4

Figure 2. Model 206A helicopter- swashplate damagedby menofilament line.

10

CONCEPT FORMULATION

DESIGrN CONSIDERATIONS

Guidelines and design requirements, which influenced the typeof concepts selected, were initially established in the con-tract. The baseline helicopter was an OH-58A equipped with aWSPS for taut wire cutting. Tne primary design considerationwas to protect the main and tail rotor pitch change links toprevent loss of helicopter control by the pilot. Both activeand passive concepts attached to either the rotating controlsor airframe were to be ccnsidcred. Passive concepts includedfixed cutters, guards, deflectors, and fairings.

Also to be considered was the adaptability of the baselineconcepts to UH-l and Ali-l helicopter usage. As stated earlier,the OH-58A was u-cd as the baseline helicopter for the gener-ation of concepts. Figure 3 shows three-view sketches of theOH-5SA helicopter wit: close-ups of the main and tail rotorcont:ol systems. Figures 4 and 5 show the AH-I and UH-lhelicopters, respectively. The upper fairing of the A1-1helicopter completely shields the fixed controls and swash-plate, thus preventing slack wires from becoming trapped inthis area. The upper fairing of the UH-l helicopter leavesmuch of the fixed controls and swashplate exposed, leaving moreplaces for catching slack wires. The UH-l helicopter also hasa stabilizer bar assembly that further complicates the rotatingcotriuols. The OH-58A and AH-I helicopters do not havestabilizer bars. Consequently, a slack wire protection systemfor the main rotor controls of the OH-58A and AH-i helicopterswould be primarily concerned with the rotating pitch links.Such a system would rot be as effective on the UH-1 helicopter.

The tail rotor of the OH-58A helicopter is attached to oneside of the tailboom; the vertical fin is attached to theother side and extends above and below the tail rotor. Thetail rotors of the AH-I and UH-l helicopters are attached tothe top of the vertical fin exposing more of the tail rotor atsome cruise attitudes, where the tail rotors are above themain rotor. This increases the probability of picking upslack wire. The AH-I and UH-l tail rotors also employ activecounterweight assemblies that extend much further beyond thetail rotor hub than the OH-58A tail rotor, which has a muchsimpler control system.

T.i

Tail Rotor Controls

Main Rotor Controls

E "

Figure 3. OH-58 helicopter.

12

!0

Tail Rotor Controls

Main Rotor ControlsIi

;w Figure 4. AH-l helicopter.

131

-r rr- ' r ,x' w ri7'

Tail Rotor Controls

A

Main Rotor Controls

'iFigure 5. UH-I helicopter.

14

For the slack wire protection concepts that will be devisedfor the OH-58A helicopter, consideration will be given as tohow these concepts could be employed on the AH-i and UH-ihelicopters. But, the concept development effort and allsubsequent refinements will be limited to the OH-58A heli-copter.

PRELIMINARY ANALYSIS

Potential Concepts Identified

Ideas and approaches for slack wire strike protection conceptswere generated during brainstorming sessions attended byEngineering Design, System Safety, and Stress personnel.Attendees were briefed about the problem of slack wire entangle-ment and the necessary design considerations as discussedearlier. Concepts were not evaluated during the initialsessions to generate a larger base from which to select and toprevent concepts from being deleted prematurely without somedevelopment.

Twenty-four main rotor and sixteen tail rotor protectionconcepts were identified and are briefly described below:

Main Rotor Shielding Devices

- Fairing extending from existing cowl to rotor.

- Rotating spool (attached to pitch links) incorporat-ing flanges to retain wire.

- Coarse mesh wire (shaped similar to fairing) extend-ing from existing cowl to rotor.

Four vertical bars attached to cowl around rotatingcontrols.

Protective cylinder around each pitch link, whichallows controls to work after cylinders are wrappedwith wire.

Slip-jointed tubes attached to the rotor hub andswashplate outside of the pitch link radius.

Main Rotor Passive Cutting Devices. (Cutters do not moverelative to mounting surface.)

15

cutter mounted forward of mast on centerline ofship.

Straight blade on pitch links.

Sawtooth blade on pitch links.

Sharp blades mounted along leading edge of hub.

Sharp blades mounted on hub perpendicular to rotordisc.

Sharp blades mounted on fixed swashplate ring.

Cutters mounted on outside and inside of fairing.

Hook/notch cutter mounted on rotor tip.

Hook/notch cutter mounted at root of blade on leadingedge.

Hook/notch cutter mounted on rotating swashplatering.

Main Rotor Active Cutting Devices

- Scissor mechanism, operated from collective motion,mounted on fixed swashplate and housing.

- shear or reciprocating sawtooth cutter mounted oncenterline forward of mast (manual or automatic).

- Cam-operated blade that would cut wire between pitch

links.

- Centrifugal mechanism that automatically deploys atoperating rpm with cutting done as tension in wireincreases (stowed at static position).

- Cam-operated cutter at swashplate with tubes attachedto rotor hub and swashplate 4%,.o guide wire intocutter.

Main Rotor Advanced Concepts. (Remove wire by burning.)

Laser device.

16

- Electrical discharge.

- Engine bleed air heat.

Tail Rotor Protection Deviceaon

- Fairing around pitch links and yoke.

- Fairing around pitch links.

- Fairing around shaft (mast) mounted onto gearbox.

- Wire mesh (shaped similar to fairing) around pitchlinks.

- Wire mesh device around shaft (mast). i- Rotating cylinder around shaft (mast).

Tail Rotor Passive Cutting Devices

- Hook/notch cutter mounted at. the root of blade onleading edge.

- Sharp blade mounted along leading edge of yoke.

- Hook/notch cutter mounted on rotor tip.

- Blade mounted on pitch links.

- Blade mounted on gearbox along shaft (mast).

- Blade on hub outside pitch link/blade attach pointradius.

Tail Rotor Active Cutting Devices

- Reciprocating sawtooth cutter mounted on transmission.

Centrifugal mechanism automatically deployed atoperating rpm with cutting done as tension in wireincreases (stowed at static posiLicn).

Advanced Concepts. (Remove wire by burning.)

- Laser device.

- Electrical discharge.

- Engine bleed air heat.

17

CONCEPT SELECTION

SELECTION PROCEDURE

A qualitative evaluation was conducted by Engineering Designpersonnel in which concepts suitable for refinement duringpreliminary design were selected from the potential conceptsidentified in the Preliminary Analysis section. Engineerinqsketches of each potential concept were developed into adesign for use in the evaluation. These designs were developedfor effectiveness, low weight, low cost, minimal impact onhelicopter operation, and maximum safety to ground personnel.These sketches depicted major components in each design withenough detail to identify local attachment requirements, areasof protection, and approximate component sizeýs and locationsrelative to the helicopter.

CRITERIA FOR SELECTION

The concepts to be refined were selected based on their ef-fectiveness, technical feasibility, impact on basic helicopteroperation, and adaptability to UH-l and AH-l helicopters.Effectiveness was considered to be a measure of how well aconcept protected main or tail rotor pitch links from variousslack wire threats. These threats included;

- Thin material - TOW wire.6

- Pliable material - monofilament line or Kevlar.

- Thick material - communication wire or loose powerlines.

- Material picked up by rotor wash.

- Horizontal slack material.

- Vertical slack material.

- Material trailing from WSPS or other helicopters.

- Multiple occurrence.

For a concept to be considered effective, -t had to show thepotential of protection from a large number of these threats.

18

Technical feasibility was considered to reflect the amount ofrisk associated with each concept. Concepts that were complexor that relied on unproven technology would require a greatdeal of refinement to arrive at an effective concept andthereby limit the total number of concepts developed. Forthis reason, concepts that could be refined into effectivedesigns in a reasonable amount of time using present technologywere selected.

The effectiveness and feasibility of each concept was theprimary consideration for selection; adaptability and impacton helicopter operation were secondary considerations. Aconcept's impact on helicopter operation included any detri-mental effect it had on rotor vibration, handling qualities,or scheduled maintenance.

Complex mechanisms in most cases received a low rating in bothfeasibility and effect on helicopter operation. The designconcepts that incorporated complex mechanisms were less reli-able and more difficult to install and maintain. If theseconcepts were in the rotating system, they would siqnificantlyaffect vibration if out of adjustment, installed improperly,or worn. The concepts selected for refinement during pre-liminary design are listed in Table 1.

19

---\~- - - - .-.- - - --

TABLE 1. CONCEPTS SELECTED FOR REFINEMENT

Main Rotor Protection Concepts

a. Shielding Devices

1. Fairing extending from existing cowl to rotor

2. Four vertical bars attached to cowl around rotatingcontrols

b. Passive Cutting Devices

1. Sharp blade forward of mast on centerline ofhelicopter

2. Straight blade on pitch links

3. Sawtoothed blade on pitch links

4. Sharp blades on hub perpendicular to rotor disc

c. Active Cutting Devices

1. Powered shear mounted forward of mast on centerline

2. Reciprocating cutter mounted firward of mast oncenterline

Tail Rotor Protection Concepts

a. Shielding Devices

1. Fairing around pitch links and yoke

2. Fairing around shaft fixed to transmissioncase

b. Passive Cutting Devices

1. Sharp blade along shaft mounted ontotransmission case

2. Sharp blade on pitch links

3. Sharp blade mounted on hub outside pitch link/bladeattachment radius

H2Ij! 20

-

PRELIMINARY DESIGN

LAYOUT DESIGN STUDIES

The design concepts listed in Table 1 were refined duringpreliminary design to the extent that their individual charac-teristics could be defined. These characteristics were usedin a trade-off evaluation in which the most p -ising of thedesign concepts were determined. The characteristics identi-fied for each concept during preliminary design were:

- Effectiveness

- Weight

- Cost

- Retrofitability

- Adaptability to UH-l and AH-l helicopters

- Effect on helicopter dynamics

- Effect on helicopter structure

Effect on 1 -Aicopter performance

- Interference with helicopter maintainability

- Effect on helicopter radar cross section

-- Hazard to ground personnel

Quarter-size layouts were made cf each design concept installedon the helicopter with full-size details of local attachments,airframe modifications, and cross sections. Also depicted oneach layout were appropriate fuselage structure, rotatingcontrols, and hub details with control motions. Additionalinformation given on the layouts included:

S- Material type and thickness

S- Fabrication techniques

- Fastener quantities, type and size

21

J.........- - - -

DESIGN DESCRIPTION

The design concepts that resulted from the design studies areshown in Figures 6 through 15 and are discussed below.

Main Rotor Aerodynamic Fairing

The fairing shown in Figure 6 is attached to the cheexisting engine inlet cowl and extends to the lower side ofthe main rotor hub. The main rotor flapping extremes es-tablished the fairing height. The fairing is constructed oflightweight honeycomb core with fiberglass skin. For ease ofremoval during maintenance or inspections, the fairing is madein two pieces and quick-release fasteners are used throughout.Modification to the basic airframe involves installing approxi-mately 21 quick-release fazstener receptacles and a riveteddoubler strip.

Main Rotor Pitch Link Ring

The pitch link ring shown in Figure 7 is attached to the topof the existing engine inlet cowl and extends to the lowerside of the main rotor hub. The design consists of a flatring positioned around the pitch links beneath the hub andsupported by four vertical aluminum tubes. The height andouter diameter of the ring were established by flappingextremes. The tubes are attached to the ring and engine inletcowl with cast aluminum fittings. The upper fittings incor-porate cutting surfaces. The ring is constructed in twopieces for ease of installation. The basic ring is honeycombcore and fiberglass skin with a thin steel cutting edge in themiddle of the frame, which also serves as a doubler at thesplice area. Modification to the basic airframe involvesbonding aluminum doublers that have nutplates attached to themiat each lower attachment fitting location.

Main Rotor Actuated Cutter

The actuated cutter is mounted on the centerline of the engineinlet ccowl forward of the mast. The powered shear and recipro-cating blade cutters were considered to be si.milar designs andare shown in Figure R. The wire guide has ai sharp edge f-zrstatic cutting and the lower blades of each concept are drivenby an electrical ram. The ram for the shear cutter is asolenoid device that recycles after use. The ram for thereciprocating cutter is a motor. The shear cutter incorporatesa switch that detects wice material and activites the ram untilthe material is removed. The recipr:ocating cutter would runcontinuously while in a threat area.

22

Pitch link fairing -

Quick-releasefasteners

Existing f~d -

f4in - Plan View

K'Pitch Link fairingODoublev added~

z~ect A-APitch link

PJ.t-'h linkfairinig

/(fiberglass Ma

with honey- fapnA, comb core) angle

-L-' ka~at t,

~" A ___"'

Z,

ViwLoigInor HSd

Pic ik arn

Fiqu 6 Man rtrardnmcfiig

23_ - ' - - . -- . - ' - -- -

Pitch link fairinq

S.... Quick-disconnect c

fastenersExisting cowl ref

"Doubler (added)

Sect |||

- -- - -" •itch link

ik F Liring

-v1e% Looki'ig Aft

• ; -- Aerodynamic Fairing

\ '\

- Ring fastened together

Skin of ring3-ply fiberglasA -Ring made in two (2)

Doubler in splice area pieces for ease of

(.063 al apieces fr"easeto

Honeycomb core - in""%

Rotated 900 :CW I". -Pitch link

Pitch linkI 2W travel

Cast fitting fastenedto existing cowl (t.yP)

Tubing (tY'P)L Fitting fastened with Cast fitting fastened

cutter - rivets or bond to ring lttyP)(cast aS part Fitting Max flapof fitting) (casting al aly) angle

I)Tubing "1..080 wall al aly) , _ % "

Tubing fastened with RingFitting r rivets or bond . Pitch link(casting al aiyY, I ;

SN , •,ttxing fastened with L - V* or screws

"cBonded doubler7//" with nutplates A

(.063 al aly)

\-A .\

0 1 2 3 4 5

Scale in Inches --

0 5 10 15i I a. l I . ,Scale in Inches

Figure 7. Main rotor pitch link ring.

25--'---a -

Cutout in cowl-

Cowl ref-.Fill shim Base(molded\Basestructural . (.125 al aly sheet)

foam)

Cutter blade-I - - Wire guide removed(.125 steel)

"Wire ciuidu

Cutter mechanism(see full scale)

Wire guide(.125 al aly sheet)

Wire sensor lever(al aly)

Switch ,-, ....

Doubler withnutplates and

/ -RAM mounting for 0 5 1.i--• . switch and AIP4 Scale in In

(.0C3 al aly sheet)

0 1 2 3 4 5

Scale in Inches

Figure S. Na.n rotor actuateu cutter.

27 '" "

Base and mountingsame as wire guide-'

Stationary cutter(.125 steel aly)

Moving cutter(.125 steel aly) "

No sensinr-

device shown -

Hedge trimmer-type

actuated cutter•-0 1 2 3 4 5

Scale in Inches

Wire guide

Cutter nechanism(see full scale) -__

0 5 10 15

Scale in Inches

7Nq

II

Main Rotor Pitch Link Cutters

As shown in Figure 9 the pitch link cutters are mounted alongthe pitch links facing outward. Used in conjunction with thepitch link cutters is a single blade mounted on the centerlineof the engine inlet cowl forward of the mast. The straightblade and sawtoothed blade designs are shown togethet due tothe similarities in their design. Two methods of pitch linkblade attachment are depicted.

In one method, a cutter is meThanically fastened to existingpitch links; the other method incorporates a welded steel tubeand blade assembly. Three configurations of the stationarycutting blade aie also shown. Modification to the basicairframe involves bonding an aluminum doubler and nutplateassembly at the base of the forward stationary cutter.

Main Rotor Grip Assembly Cutters

As shown in Figure 10, the main rotor grip cutters are locatedinboard of the blade bolts and perpendicular to the featheringaxis. The cutter is attached to the main rotor grip with atwo-piece cast aluminum clamp. The blade is bolted to theclamp for easy replacement during maintenance. As shown inFigures 29 and 30, the grip cutters are used in conjunctionwith other concepts discussed in this report to form protectionsystems. No modification is required to the basic helicopter.

Tail Rotor Controls Cover

As shown in Figure 11, the tail rotor controls cover concepttotally encloses the pitch change mechanism. The installationhas four parts: a dome-shaped thermoplastic outer cover, analuminum-stamped support ring, and two aluminum-stamped innercover halves. To install the cover assembly, the support ringis first secured to the shaft. The inne• and outer covers arethen screwed to the support ring and the inner cover halvesclamped to the shaft. Cutouts are provided in the inner coverhalves to allow clearance for tail rotor flapping. The smalldeflectors on the blade root prevent thin wire material fromwrapping around the ends of the yoke at the feathering bearingsand l.ýcking up pitch change of the blade.

29..,

29

S. . . . . . . . .. . .. . . . . .. . .. . . . . . . . . . . .. . . . . .. . .

I)" I) I)- ) I)- I)

Al aly cutter Steel aly cutter Bonded steelfastened with aly cutter

Clamped with bolt, screws

nut, and washer

--Indexing screw andblind nut

A-A A-AWelded cutter Clamped cutter

Indexing screw and Optional.// b l i n d n u t

O p i o a c-_ . - - - . "

L matching c

/'Clamped with , installed

bolt, nut, andwasher

Welded cutter Clamped cutter I) A A; 13

/ \

0 5 10 15- - 3 r i jI:, . . ; .

Scale in Inches

Figure 9. Main rotor pitch link cutter.

31

cutter Bonded steel /

with aly cutter

"--Base-. - (.125 al aly)

"" Optional cutters shown Screw and washermatching cutters to be

installed Cutter

Fill shim" * (.180 al aly)

F -"-

" Doubler with nutplates(.63j al aly sheet)

,;:View G1 0 1 2 3 4

Full Scale 2-1-1 _ I - i __jSScale in Inches

"015

nches

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~~40)

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uj 00

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45.

330

-e cov.Er ard inn,!rcover halves fas renedto support rwna with ><screws and washers t

S-Inner cover halves fastened

o ,. " "C to shaft with clamp

- Wire deflectoron blade root

Inner cover half(al aly .020 stamping)

9B

/ Ci

Outer cover(thermoplast ic '

.060 thick)

Nutpiitos uir

support ringSZjl~por t rinq('i aiy .063stamping) 0 1 2 3 4 5

Scale it. inches

Figure 11. Tail rotor controls cover.

34

k*1

Tail Rotor Shaft Cutter

The tail rotor shaft cutter, as shown in Figure 12, is posi-tioned approximately parallel to and forward of the tail rotorshaft. The cutter is a welded assembly and is attached to thegearbox using existing studs. The length of the cutting bladewas established by tail rotor flapping.

Tail Rotor Shaft Cover

The tail rotor shaft cover is shown in Figure 13. The coveris nonrotating and is attached to the gearbox using existingstuds. The cover is constructed of two aluminum-stamped coverhalves that are screwed together at installation.

Tail Rotor Yoke-Mounted Cutters

The tail rotor yoke-mounted cutters are shown in Figure 14.In the method of fabrication shown, the cutters are attachedto the existing blade pitch arm castings. The cutters arecastings with their attachment holes counterbored to provideclearance with the yoke. In another method of fabrication,which is not shown, the blade is integral to the pitch armcasting and replaces the existing part.

Tail Rotor Pitch Link Cutters

The tail rotor pitch link cutters are shown in Figure 15. Thecutters are mounted along the links and face outward. Twomethods of blade attachment to the pitch links are depicted.In one method, the cutter is mechanically fastened to existinglinks. The other method uses a link with an integral blade.

DESIGN SUPPORT TEST

In support of the preliminary design effort, simplified testswere performed to obtain a better understanding of how slackwire wraps around rotating controls and to verify the feasi-bility of two selected main rotor protection concepts.

Test Equipment

j Test Stand. An existing main rotor whirl stand was con-

* figured with an 0oi-58 hub, pitch links, and associated hardware.* Because of the area available for testing, blades were not

installed on the hub. The pitch links were half the length andstiffer than standard 0H-58 links and, due to the method of lower

iF attechment, provided no pitch change to the hub.

*35

41)

IM c

U, 00

03

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ih

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ul r:

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Cutter (2 reqd)(steel aly)

Fastened with existingpitch arm bolts

", (countersink bolts for clearance)/ Pitch arm

Yoke--- - - -

A' A

0 1 2 3 4 5

Scale in Inches

Figure i4. Tail rotor yoke-mounted cutter.

39 : . ,

S,----S

• • < \ " C .

I / '< .i

4 ~-•, I __••=,;

.,o-

.. •" • •.; -- , ...

-- Cutter fastened! topitch l ink (cuttersteel aly)

Cutter made as part of pitch link(change out pitch links)(pitch link steel aly)

Pitch links with cutters

+,d I . | ': I . .. .. . . .. ,)

0 l 2 3 4 5

., r inches

Figure 1 T iail rotor pitch link cutter.

41

--+•.--,,,, ",.+ , , -

This hub is shown in Figure 16. The hub and pitch links werebelt. driven at 300 rpm by a 75-hp electric moter. .

Protection Concepts. Two protection concepts were selectedfor testing, the pitch link ring and the pitch link cutterssimilar to those shown in Figures 4 and 6, respectively. Thepitch link ring concept, as shown in Figure 17, was fabricatedusing an aluminim upper ring with the outer diameter sharpenedfor its cutting surface. The height of the ring was approxi-mately half of actual size due to the test stand geometry. Asshown in Figure 18, two blade shapes (straight and sawtooth) PV_

were tested on the pitch links to determine which blade wasmore effective in cutting the various materials. The type of -"

cuti-er to be evaluated was selected by adjusting the pitchlink roc ends such that the pitch link could be rotated toposition the desired cutter on the outermost surface of theI';link. As seer, ip Figure 19, the edge on the stra-ght bladewas fairly blunt, approximately a 90-degree included angle.The sawtooth blade, as shown in Figure 20, had a flat slopingcutting surface similar to a shear with the notched area asmooth radius. The sharpness of both blade types was con-side:ed to be realistic and easily maintainable in actual 4service. •*

Wire Material. Three types of wire material were tested -Kevlar, communication wire, and TOW wire. The Kevlar material t4was 60 end count roving with each end containing 134 filaments.Two lengths of commanication wire were intertwined and testedtogether. Each lengtn of wire was composed of tive strands ofsteel wire covered with an insulation material. Two lengthsof TOW wire were also intertwined and tested together.

Baseline Test .54

initial testing was conducted Oh the basic test stand (unpro-tected standard test pitch links) configured as shown inFigure 16. The purpose was to learn more about the mechanisminvolved in pitch link wrapping from horizontal and verticalslack wire material.

Horizontal Wire Material. The first attempt at wrapping wirematerial around the pitch links and generatinq high collapsingforces was unsuccessful. One end of a 10-foot length ofKevlar rov-ina was secured to a pitch link and loosely woundaround the litiks with the other end secur,'d to the mast.There wcas no change in roving tension after hub rctation for

#

42 J

I t.

Iz

11

._ Fiqure 16. Baseline test hub.

43• i• !

L -

Figure 17. Pitch link ring concept test hardware~.

44

W21-

Figure 18. Pitch link cutter concept test hardware.

Fiur 19. Pic ikutr

~~45

F'igure 20. pitch link sawtoothed cutter.

46

approximately 4 minutes. However, high collapsing forces wereproduced when 4 to 5 pounds of tension was applied to theKevlar as it wrapped around the pitch links. The means ofapplying this tension and the results of this test are shownin Figure 21. The material was unwound from a spool thatincorporated a disc and spring-loaded calipers to cause re-sistance to rotation. The amount of tension in the roving wasdetermined with a spring scale.

Vertical Wire Material. The basic test stand wasconfigured as shown in Figure 22 to evaluate vertical slackwire material. The spool used to apply the tension to theKevlar was positioned below the hub and the free end securedto the overhead cable. This position was selected for thespool because the material above the hub does not wrap aroundthe pitch links. After the material was positioned, the motorwas started. The results of the test are shown in Figure 23.The Kevlar wrapped approximately one turn around the pitchlinks and the remainder was coiled around the mast between thelower link attach plate and the upper test stand, which is theinterface between the rotating and nonrotating system. Thiswrapping pattern is very similar to that experienced in theactual mishap shown in Figure 1. These results indicate thatfor material oriented vertically at contact the lower portionof the rotating controls will receive the majority of wrappedmaterial. This fact is also suggested by the damaged swash-plate shown in Figure 2, which is located on the helicopter atthe interface of the rotating and nonrotating portion of thecontrols.

Pitch Link Ring

Two tests were used to evaluate the pitch link ring conceptfor the protection it provided against vertical wire material.The first test used an identical method to introduce theKevlar as in the baseline test and is shown in Figure 24. Forthe second test, the free end of the Kevlar was secured to theoutboard portion of the hub instead of the overhead cable.The results of the first test are shown in Figure 25. TheKevlar was cut immediately after the motor was started. Theresults of the second test are shown in Figure 26. The Kevlarwound around the upper ends of the pitch links and was cutafter approximately 30 seconds of hub rotation.

It was felt that the different cutting results of the twotests were related to the orientation of the Kevlar withrespect to the cutting surface at the time cutting occurred.

4

Figure 21. Horizontal ware baseline test.

48

Figure 22. Vertical. wire basr-1ine test zCtup.

49

*~-'.r--

Figure 23. Vertical Wire baseline test results.

50

Figure 24. Pitch link ring test with baseline test setup.

51

V*14

Figure 25. Trest results of pitch link ringwith baseline test setup.

52

Figure 26. Test results of pitch link ringwith modified test setup.

53

The Kevlar in the second test was secured on the hub outboardand above the cutting ring outer surface, and with hub rotationwrapped around the pitch links above the ring. As representedin Figure 27, the wrapping of the Kevlar around the pitchlinks caused it to slide over the cutting edge at an unfavor.-able orientation for efficient cutting. However, in the firsttest the Kevlar was forced inboard into the center of the hubat initial rotation and, as represented in Figure 28, formed amore vertical and efficient cutting angle.

The results of these tests would suggest that the cutting edgeof the ring should be modified to cut material at any orien-tation.

Pitch .Link Cutter

The standard test pitch links were removed and the pitch linkcutters shown in Figure 18 were installed. The pitch linkcutters were evaluated for wire material entering horizontally.Three types of wire material were tested - TOW wire, communi-cation wire, and Kevlar roving for each of the cutter bladetypes, straight and sawtooth.

The wire material was introduced using the same method asdiscussed for the horizontal wire baseline test. For eachtest, the free end of the wire material being evaluated wassecured to a pitch link and the motor then started. Thestraight blade cutter cut all three types of wire materialimmediately, not allowing any additional material to be wrappedaround the pitch links. The sawtooth blade cut the Kevlar andTOW wire immediately but did not cut the communication wire.

The communication wire started filling in the notched area scthat the wire was being wound on wire and the sharp edges werenot contacted. This result was largely due to the lack ofsharpness and configuration of the edge in the notched area.The sawtooth blade was smooth in the notched area and did notcut the wire on initial contact. It is felt that it would bepremature to eliminate the sawtooth blade concept based onthis test configuration without addition .1 edge development.The sawtooth blade offers potential features that. are discussedlater in the report.

54

- ---------

Main rotor hub

P~m 9 1 --- Pitch link

tfc-Kevlar

Fiqure 2"). Kevlai- orientation at cutting duringmodified test.

Main rotor hub

CUtt I • -~ _ ____-__

Ring-

sur lace

Pi c) 3 n

'F---evlar

ILTFigure 26. Kevlar orientatior. at cuttinq during baseline test.

55

TRADE-OFF EVALUATION

After the concepts were refined during preliminary design, atrade-off evaluation was conducted to determine to what extentthe desired characteristics were inccrporated into each design.:'his was performed by establishing the important parameters AIand assigning a relative grade for each parameter. Comparisons ' Ibetween the concepts will be made qualitatively based on howtheir individual parameters are judged.

PARAMETER DEFINITION

The individual parameters and methodology for establishingtheir relative ratings axe described below.

Effectiveness. The effectiveness of a concept was con-sidered to be a measure of how well it protects the rotorcontrols from bending or failing. Each concept wascategorized as excellent, good, or marginal. An excellentrating applied to a concept that cut or shielded alltypes of slack wire from the entire control system. Agood rating applied to a concept that was effectiveagainst most types of slack wire and/or protected most ofthe control system. A marginal rating applied to aconcept that was effective against one type of slack wireand/or protected only one portion of the control system.

weight. The weight of a concept is a function of itssize, materials, attachment, and necessary modificationsof the aircraft. The weight of a concept wý.s charac-terized as negligible if there were no structural changesto the aircraft, there was minimal attachment hardware,and if the weight of the protection device was less thanfive pounds (e.g., sharp edges on the pitch links). Amoderate zating applied when the device weighed over fivepounds, attachment assemblies were recuired, and somestructurai changes to the aircraft were necessary. A 4significant rating applied when the device weighed overfifteen pounds and the basic structure of the aircraft .slrequi:-ed reinforcing.

Cost. The cost of a concept is a function of the partscount, materials, fabrication techniques, complexity, andmodifications to the aircraft. A minimal cost ratingapplied when common materials were used, minimal changes

56I

4,

t

to the aircraft were red, and the device had few andsimple parts. A mo rating applied when the device

complexity was apprec. _ie and aircraft changes wererequired. A signiticant rating applied to a device thatwas complex, had an ap~reciable parts count, and requiredreplacement or additional aircraft structure.

Retrofit Suitability. The suitability of a concept forretrofit on an OH-58 was rated as good or poor. A concepthad good retrofit suitability if a minimum amount ofmodification was required for its installation and poorsuitability if extensive helicopter changes were necessary.

- A Adatability. The adaptability of theUH-l and AH-l d~oaOH-5q devised concept to UH-l and AH-1 helicopters wasrated as good or poor. A concept had good adaptabilityif the OH-58 concept could be used with little or nochange and poor adaptability if major changes were re-quired.

Dynamics. The effect of the concept on helicopter dynamiccharacteristics was rated as minimal or siqriificant. Theconcept had a minimal effect on helicopter dynamics ifthe concept component natural frequencies were such thatonly occasional local vibrations resulted. The concepthad a significant effect on helicopter dynamics if air-frame or rotor frequencies were changed such that ob-jectionable or damaging vibrations could result.

Structural. Helicopter structural effects of a conceptwere considered to be any increase in airframe or rotorcomponent loads or decrease in existing structure strengthdue to its installation and were rated as being minimal,moderate, or significant.

Performance. Helicopter performance as described herein1s constlued as relating to static and dynamic handlingquaiities and power requirement changes due to a concept'sincrease in helicopter frontal and/or profile areas.These effects were rated as being minimal, moderate, orsignificant.

Maintainabilitv. The impact of a concept on helicoptermaintainability is a function of the interference thatthe concept will have on routine inspection'; and main-tenance. Concepts that hide or prevent access to cetLainareas of the helicopter would include fairings or shields.Each concept was rated to have a minimal, moderate, or

57

Il

signriificant effect on the overall helicopter maintain-abi lity.

Radar Cross Section. The amount of additional helicopterradar cross section attributable to a concept was con-sidered to be a function of its size, location, and shapeand was rated as minimal, moderate, or cignificant.

Personnel Hazard. The hazard presented by a concept wasconsiderFed to be a function of the danger it presents toground personnel. The amount of hazard present was ratedas no hazard, some hazard, or very hazardous.

CONCEPT COMPARI SONS

To bimplify the presentati-n of the relalive grade of eachconcept, symbols were assigned to each oi the iaramete. ratingcategories. These symbols and their meaning for each parameterare shown in Tdble 2.

The p•arameter iatiigi J oi each concept. are shown in Table 3for ma-n rotor concepLi and in Table 4 for tai) rotor concept.b.A demcription of thUe technical characteristict; of each concept)b given below, 3n which advaxitageii and disadvantages of thedesign at.e discussed. Also, recommendations are made As towhether a concept sihould he rejected or further leveloped andteu ted.

M.in Untoi Aerodynamic Fairpings

The Ia ring offeirs prctcction fer :i-. but a umil] port).on ofthe upper ends of the HLtUfl ]J,' . a-id a majority of the s&ackwirv Ltiieats. Huwevei, vciticl wire material encounteredcould become wrapped around the pitch links similar to thatexperienced during testing of the pitch link ring concept'hown in Figure 29. For this reason, the effectiveness of thefairing received a "good" rating.

The operation of the helicopter is degraded due to the sizeand location of the fairin.. Maintenance of the helicopterwvuld be nioderately affected because an additional cowlingwould have to be removed during scheduled maintenance. Also,more time would be required for preflight inspection of therotating controls.

Jt is felt that the fairing would cause a significant deg-radatic-n in perf:rr,,ance and handling qualities of the heli.copter.

TABLE 2. PARAMETER RATING SYMBOLS

RATING SYMBOL MEANING

Effectiveness Excellent Good Marginal

Weight Negligible Moderate Significant

Cost Minimal Moderate Significant

Retrofitability Good Poor

UH-i and AH-ladaptability Good Poor

Dynamics Minimal - Significant

Structural. Minimal Moderate Significant

Performance Minimal Moderate Significant

Maintainability Minimal Moderate Significant

Radar cross section Minimal Moderate Significant

Personnel hazard No hazard Some Veryhazard hazardous

w9

59 59

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The additional cross-sectional area of the fairing would causea reduction in the maximum attainable airspeed in level flightand a possbile increase in turbulent airflow over the tailrotor and vertical fin. The actual performance and handlingquality effects of the fairing would have to be evaluated in aflight test program.

The adaptability of the fairing was considered poor. Thehigher airspeed of the AH-1 helicopter and the greater distancebetween the rotor and fuselage on the Uqi-i helicopter wouldpossibly cause a greater degradation in performance and handlingqualities than the OH-58 helicopter.

Variations in the fairing concept were considered to improveits overall rating. The grip assembly cutter wac combinedwith the fairing, as shown in Figure 30, to protect the upperportion of the pitch links. The effectiveness of the systemis considered to be excellent, but the cutter added anadditional degree of hazard and degraded the operation of thehelicopter. The fairing shape and helicopter configurationcould be developed during a flight test program to improve orto correct the reduced performance and handling qualities;however, it would be expensive and have a risk associated withit. It was felt that the excellant effectiveness of thefairing system did not offset its known deficiencies andpotentially high development cost and, therefore, should notbe considered a viable concept.

Main Rotor Pitch Link Ring

The feasibility and effectiveness of the pitch link ring wassuccessfully demonstrated during testing. The concept has thepotentiil .,) rrt-:Lon for the pitch links andswashplate from wire material oriented vertically. Protectionfrom horizontal (parallel to swashplate rotation plane) wirematerial would be good with a small portion of the upper pitchlinks exposed. Marginal protection would be offered formaterial encountered parallel to the centerline of the heli-copter.

The concept is lightweight, low in cost, and has minimaleffect on helicopter operation. Installation of the design issimple, and retrofitability and adaptability would be good.

The structural strength and stiffness of the support tubeswould have to be evaluated during additional developmenttesting. Any possible threats should be identified that mightcause high loads and deflect the ring into the rotatingcontrols.

63

_r

4J,

So1

A-,"

04.

/ 1•

I 04

54

Variations in the concept were considered to improve itsoverall rating. The grip assembly cutter was combined withthe pitch link ring to protect the upper portion of the pitchlinks and is shown in Figure 30. The effectiveness of theresulting system would be excellent for vertical and horizontalthreats and would not significantly affect the other parameters.

The pitch link ring concept and its variation are both prom-ising concepts and should be developed and tested further.

Main Rotor Actuated Cutter

The effectiveness of the shear cutter or reciprocating cutterwould be marginal. Protection from horizontal (perpendicularto helicopter centerline) wire material would be good. Hori-zontal wire that draped and trailed across the upper guideblade could become entangled in the pitch links before thetension in the wire became sufficient to cause cutting on thesharp guide. The cutters would offer marginal protectionagainst vertically oriented material or material aligned withthe helicopter centerline. The cutter would be effective forthose cases in which vertical wire material was caught on thehub and rotated forward of the guide blade and across it. ForcaseEý similar to those tested in which the material was forcedinto the center of the hub, the cutte. would be useless.

Additional design development would be required to define theinternal mechanism of the rams and electrical installation.The design would involve modifications to airframe structureand electrical panels and make retrofit complicated. Themechanism would require periodic lubrication and cleaning and

* pose a serious hazard to ground personnel.

It is felt that the effectiveness of the actuated cutters does* not offset the other major deficiencies and, therefore, should* not be considered a viable concept.

Main Rotor Pitch Link Cutters

* The ftasibility of cutting slack wire as it wraps around therotati.ng controls was successfully demonstrated during testing.These results are discussed on page 58. All materials identi-

S fied for testing were cut. The concept offers excellentprotection from horizontal wire material and has the potentialof excellent protection from vertical wire material.

65

The concept is lightweight, low in cost, and has minimaleffect on helicopter ope'ration. Installation of the design issimple, and retrofitability and adaptability would be good.The sharp edges -,:uld be covered with a simple sheath toprotect ground ., kiaintenance personnel from injury.

The contribution of the forward blade to the overall effective-ness of the pitch link cutters was not tested. The forwardblade installation is a major portion of the concept weight,and additional testing could establish if the chance in ef-fectiveness it piovided was worth the weight and cost penalty.The forward blade in some cases could provide the necessaryten-ion required for cutting vertical or horizontal wirematerials by the pitch link cutters. Horizontal wire thatbecame draped over the forward blade and wrapped around therotating controls could be cut by its edge or the pitch linkblade. The forward blade would also be effective for thosecases in which vertical wire material was caught on the huband rotated forward of the blade wrapping around it and thepitch links.

Additional development of the sawtoothed pitch link bladeshape could improve cutting effectiveness on thicker diameterand vertical wire materials. As shown in Figure 31, theselected angle of the sawtooth blade could cause relativemotion between the cutting surface and the wire material as itwrapped and cut more efficiently. The blade edge shape testedfor the sawtooth configuration was less refined than thestraight blade edge. Cutting efficiency of the sawtoothedblade could also be improved if a cutting edge similar to thestraight blade were used in the notched area.

Variations of the pitch link cutter concept should be evalu-ated during additional testing. Swashplate protection forvertical wire material could be improved by adding a low pitchlink ring concept. The 3- to 4-inch-tall ring would eithercut the wire or redirect the wire to the pitch link cutteredge at a more favorable orientation for cutting.

Grip Assemby Cutter

The grip assembly cutter concept as discussed earlier was pri-marily used in conjunction with other concepts to form a pro-tection system. As an individual concept, the grip cutterwould have poor overall effectiveness; however, when combinedwith other concepts, it offers excellent protection for the

66

Motion alonocutting surface-. • Tension in wire

- ------ 4- material caiusescutting mot~ion

Blade angle

Horizontal Wrapping Matcrial

STension in wirematezial causescutting motion

H0

F "/

,. /// -

//

Motion &long 1

cutting surfa.e.-,

Vertical Wrapping Material

v

Figure 31. Effect of pitch 1z2k cutter blade shapeon cutting mrition.

67

upper pitch links against all threats. The blades are angledIsuch that wire material would not collect and bind the feather-ing axis of the blade.

The cutters are lightweight, low in cost, and have minimaleffect on helicopter operation. Installation of the design issimple, and retrofitability and adaptability would be good.The sharp edges could be covered with a simple sheath andstrap to protect ground and maintenance personnel from injury.

The grip cutters as an individual concept should be rejectedbut. should be considered in the development and testing ofother concepts.

Tail Rotor Controls Cover

The tail rotor controls cover would offer excellent protectionfor the pitch change mechanism against all threats. However,material can become wrapped around the shaft and have adverseeffects on tail rotor flapping. For this reason, the overalleffectiveness was considered to be only good.

The weight and cost of the cover would be moderate. Theweight calculations for all tail rotor concepts included theballast adjustments required at the nose to keep the center ofgravity of the helicopter unchanged with the concepts installed.

Maintainability of the helicopter is moderately affectedbecause additional covers would have to be removed duringscheduled maintenance, more time would be required for pre-flight inspection of the pitch change mechanism, and tailrotor balancing would require more time.

Variations in the cover concept were considered to improve itsoverall rating. Either the shaft cutter or the shaft coverwould combine with the controls cover to protect the areabetween the gearbox and the yoke. The effectiveness of theresulting system was considered to be excellent and not detri-mental to the other parameters.

The tail rotor cover and its variations are all promisingconcepts and should be developed further.

Tail Rotor Shaft Cutter and Shaft Cover

The shaft cutter and shaft cover concepts as discussed earlierwere primarily used in conjunction with other concepts to iorm

68

a proLection system. As individual concepts, the shaft cutterand shaft cover would each have poor overall effectivity.But, when combined with other concepts, they offer excellentprotection for the area between the gearbox and the yoke.

The cover and cutter are each lightweight, low in cost, andhave minimal effect on helicopter operation. Installation ofthe designs is simple, and retrofitability and adaptabilitywould be good.

The shaft cutter and shaft cover as individual concepts shouldbe rejected but should be considered in the development andtesting of other concepts.

Tail Rotor Yoke Cutters

The yoke cutter would have marginal overall effectiveness. Itwould provide excellent protection for the pitch change bear-ings and the ends of the yoke. However, little protectionwould be offered the pitch change mechanism'.

Although the cutters are lightweight and low in cost, theycould cause a moderate increase in pilot effort. The addedweight of the cutters on the pitch arm ring would combine withthe existing balance weights to cause an increase in pedalforces and more pitch link bearing wear. These effects couldbe minimized by additional design and analysis.

The adaptability of the cutters is poor because the designwould have to be significantly modified for use on UH-l andAH-I helicopters.

The yoke cutter would require a moderate amount of additionaldevelopment, but it off'rs the potential of excellent pro-tection for the pitch change bearing area. It could be usedin conjunction with other concepts to imprcve overall effective-niess and, for this reason, the yoke cutters should be developedand tested further.

Tail Rotor Pitch Link Cutters

The pitch link cutter would have marginal overall effectiveness.It would provide excellent protection for 'he pj ch changemechanism but little protection fom the pitch charge bearingsand yoke endc.

?. !

i 6£9,

The concept is lightweight, low in cost, and has minimaleffect on helicopter operation. InstalJation of che design issimple, arid retrofitability and adaptability would be good.The shaip edges could be covered with a simple sheath toprotect ground and maintenance personnel from injury.

variations in the pitch link cutter concept were considered toimprove its overall effectiveness. The yoke 3nd shaft cutterswere combiaed with the Ditch link cutters to form a systemthat could provide excellent overall protection with minimaleffect on weight and cost.

The pitch link cutter as an individual concept should berejected but should be considered in the development andtesting of other concepts.

70

CONCLUSIONS

The two most promising wire protection concepts selected forfull-scale testing were the pitch link ring and pitch linkcutters. Two iitch link cutter configurations were tested.Three types of wire material, aligned vertically and hori-zontally, were tested. It was demonstrated by these teststhat both concepts could cut wires before a disastrous buildupcould form. In addition to validating the concepts, the testsdisclosed some useful information regarding the behavior ofthe wires during different encounter situations.

SV

71

Its

RECOMMENDAT IONS

Based on the results of this effort, it is recommended that:

'.. The following concepts be fabricated and tested.

For main rotor protection:

- Pitch link ring

- Pitch link ring with grip cutters

- Pitch link cutters

- Pitch link cutters with modified pitch linkring

For tail rotor protection:

- Controls cover

- Controls cover with shaft cutter

- Controls cover with shaft cover

- Pitch link cutter with shaft cutter and yokecutter

2. The functional testing of the main rotor protectiondevices continue and expand in scope to include allactual rotating hardware and measurements of the non-rotating input control forces.

3. The functional testing of the tail rotor protectiondevices include all actual rotating hardware (includingblades) and measurements of the nonrotatirig input controlforces.

2883-82

72