USAAVLASS TECHNICAL REPORT DESIGN ANALYSIS OF INTEGRAL WEIGHT AND BALANCE SYSTEM FOR ARMY CARGO HELICOPTERS

Transcription

1 Mm USAAVLASS TECHNICAL REPORT DESIGN ANALYSIS OF INTEGRAL WEIGHT AND BALANCE SYSTEM FOR ARMY CARGO HELICOPTERS if Stiait L. Vint; u August 1967 U. S. ARMY AVIATION MATERIEL LABORATORIES FORT EUSTIS, VIRGINIA CONTRACT DA AMC-451(T) NATIONAL WATER LIFT COMPANY A DIVISION OF PNEUMO DYNAMICS CORPORATION GRAND RAPIDS, MICHIGAN Distributin f this dument is unlimited Reprdued by the CLEARINGHOUSE fr Federal Sientifi & Tehnial Infrmatin Springfield Va

2 DEPARTMENT OF THE ARMY U. S. ARMY AVIATION MATERIEL LABORATORIES FORT EUSTIS. VIRGINIA The desirability fr a means by whih the grss weight and enter f gravity f a helipter may be nveniently determined, prir t flight, is well established. Fixed-wing airraft weight and balane tehnlgy has advaned t a pint where n-bard weighing systems are mmerially available. The appliatin f these integral weight and balane system nepts t Army arg helipters intrdues unique prblems, the slutins t whih have been frmulated as a result f this study. It Is the pinin f this mmand that the present integral weight and balane system tehnlgy an supprt an aurate, lightweight system fr use in Army arg helipters. Future peratinal tests will prvide the final answers nerning system auraies and suitability t rtary-wing type airraft.

3 Prjet 1F121401A.254 Cntrat Dk AJvIC-451(T) USAAVIABS Tehnial Reprt August 1967 DESIGN ANALYSIS OF INTEGTrU WEIGHT AND BALANCE SYSTEM FOR ARMY CARGO HELICOPTERS Final Reprt by Stuart L. Vamer Prepared by Natinal Water Lift Cmpany Instrumentatin and Cntrl Operatins A Divisin f Pneum Dynamis Crpratin Grand Rapids, Mihigan fr U.S. ARMY AVIATION MATERIEL LABORATORIES FORT EUSTIS, VIRGINIA Distributin f this dument is unlimited

4 ,, ' SUMMARY This study vered an analysis f helipter peratinal usage affeting the design, installatin, and peratin f an integral weight and balane system fr Army arg helipters urrently in existene and thse yet in the planning stage. An analysis f existing integral weight and balane systems and their appliability t helipter usage was als perfrmed. A remmended general system nfiguratin is disussed as the utme f the previusly amplished analysis. Prblems invlving aurate measurement f the grss weight and enter f gravity with rtr(s) in peratin are disussed with the slutin. The appliatin f an integral weight and balane system t Army arg helipters appears t be entirely feasible. n < iii... i

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6 v TABLE OF CONTENTS Page SUMMARY iii LIST OF ILLUSTRATIONS vi LIST OF TABLES viii INTRODUCTION 1 STATEMENT OF THE PROBLEM 3 APPROACHES TO SOLUTION 6 Weight and Balane System Types 6 System Operatinal Requirements 9 DESIGN CONSIDERATIONS 18 System Desriptin Lad Sensing Instrumentatin 18 Calibratin Funtin Cmputer Display 32 Pith Sensr 33 Cntrl 33 System Cnfiguratin Variatins 34 System Limitatins., 44 RECOMMENDED SYSTEM CONFIGURATION Landing Gear Strut Instrumentatin Terrain Slpe Errr in Strut Lad Measurement Terrain Slpe Errr in Center f Gravity Readut Cmpensatin fr Terrain Slpe Errr in Strut Lad Measurement 76 Crretin Tehniques fr Rtr Lift Effet During Weight and Balane Measurement 80 Calibratin/Cmputer Pakage 84 Grss Weight and Center f Gravity Indiatr Pith Cmpensatr 90 Cntrl 93 Carg Hk Instrumentatin System Weight Estimate 95 Pwer Requirements 97 Errr Analysis 97 PROGRAM PLAN FOR ADAPTATION OF INTEGRAL WEIGHT AND BALANCE SYSTEM TO ANY ARMY CARGO HELICOPTER 97 DISTRIBUTION 101

7 MMi - r LIST OF ILLUSTRATIONS Figure Page 1 Hysteresis Plt Ole Pressure Measurement Vs. Lad n Strut 8 2 Integral Weight and Balane System Blk Diagram 19 3 Fres Ating n Landing Gear Strut 21 4 Vertial Lad Fre 22 5 Side Lad Fre 23 6 Drag Lad Fre 24 7 Srub Turn Fre 25 0 Instrumentatin Appliatin t Landing Gear Imprper Tehnique 26 9 Instrumentatin Appliatin t Landing Gear Prper Tehnique Terrain Slpe Errr in Strut Lad Measurement Strut Lad Measurement Errr as a Funtin f Pith Attitude Terrain Slpe Errr in Center f Gravity Readut System Diagram Manual Integral Weight and Balane System System Diagram Eletrmehanial Serv Integral Weight and Balane System, Dual Serv Diagram Weight and Center f Gravity Indiatr Serv Display System Diagram Eletrmehanial Serv Integral Weight and Balane System, Serv and Meter Mehanism Display Weight and Center f Gravity Indiatr Serv and Meter Mehanism Display Weight and Center f Gravity Indiatr Dual Meter Mehanism Display Blk Diagram Slid State Digital Weight and Balane System Weight and Balane Remte Indiatr Integral Weight and Balane System fr the UH-I Cmputatin f Center f Gravity fr Tw-Skid Landing Gear (as n UH-1) Center f Gravity Envelpe UH-1D Integral Weight and Balane System fr the CH Cmputatin f Center f Gravity fr Triyle Landing Gear (as n CH-54) Center f Gravity Envelpe fr CH Integral Weight and Balane System fr the CH vi

8 wmmmm^mmmmm* inn"- F T-«28 Cmputatin f Center f Gravity fr Quadriyle Landing Gear (as n CH-47) Effet f Errr in Grss Weight n Cmputatin f Center f Gravity Latin Defletin Sensr Bar "T" Cnfiguratin Strut CH-47 Frward Landing Gear Strut Test Typial Landing Gear Axle Instrumentatin Hardware "T" Cnfiguratin Strut Instrumentatin Installatin "L" Cnfiguratin Strut C-130 Main Landing Gear Preprdutin Shk Test "L" Cnfiguratin Strut Instrumentatin Installatin "L" Cnfiguratin Strut with Swivel Capability and Ole Strut Supprted Drag Link Suspensin Instrumented Ole Strut Tp Cap Fur-Wheel Tmk Strut C-141 Main Landing Gear Instrumentatin Test Fur-Wheel Truk Strut Instrumentatin Installatin Terrain Slpe Errr in Strut Lrad Measurement Terrain Slpe Errr in Center f Gravity Readut Apparent Center f Gravity Psitin Change Vs. Height f Center f Gravity Mehanizatin f Cmpensatin fr Terrain Slpe Errr Density Altitude Vs. Lift, CH-47 Helipter Crretin f Lift Effet Withut Density Altitude Cmpensatin Ckpit Display and Cntrls fr Integral Weight and Balane System Crretin fr Rtr Lift During Grss Weight and Center f Gravity Measurement Crretin f Lift Effet With Density Altitude Cmpensatin System Cmpnents CH-47 Integral Weight and Balane System Calibratin/Cmputer Pakage Weight and Center f Gravity Indiatr Serv and Meter Mehanism Display Pith Sensr Cntrl Pakage Carg Hk Instrumentatin fr CH vii

9 «PinpmwiHam mi ; / LIST OF TABLES Page I Advantages Offered by Integral Weight and Balane System fr Army Carg Helipters 5 II Cmparisn f Weight and Balane System Types 10 III Operatinal Requirements fr an Integral Weight and Balane System fr Appliatin t Army Carg Helipters 12 IV Operatin Cnditin Variables Affeting the Appliatin f an Integral Weight and Balane System t Army Carg Helipters 17 V Integral Weight and Balane System Cmpnent Cmmnality 47 VI Lift Effet Crretin Chart fr CH-47A 81 VII System Weight Estimate 95 VIII Analysis f Integral Weight and Balane System Errr (Using CH-47 Integral Weight and Balane System as Example) 98 DC General Predure fr Appliatin f Integral Weight and Balane System t Any Army Carg Helipter 99 X Prgram Plan fr Appliatin f Integral Weight and Balane System t Any Army Carg Helipter (Typial) 100 viii

10 I I' MMMI MHHBH M ' """. '" - T-«INTRODUCTION Frm the very first days f airraft, it has been helpful t the pilt t knw the grss takeff weight and the latin f the enter f gravity f his airplane. In mre reent years, it has beme nt nly desirable but als neessary fr military and mmerial peratrs f airraft t knw grss takeff weight and enter f gravity psitin fr reasns f bth safety and prdutivity. In reent deades, preise knwledge f these tw elements has beme a standard preflight requirement. The ldest methd, and the ne mst widely used at present, invlves manual alulatins based upn knwn airraft harateristis and measured (r estimated)arg and passenger weights and psitins within the airraft. Beause f the umbersme nature f the manual methd and its inherent inauraies as a result f human errr r inaurate arg weight and psitin data, the need fr aurate, autmati methds fr determinatin f grss takeff weight and enter f gravity psitin is well established. Varius methds fr weighing laded airraft n fixed r prtable platfrm sales have been tried, but with little suess. Generally, the time nsumed in perfrming this peratin and the st f the equipment have prven t be prhibitive. As lng ag as 1951, attempts were made t devise autmati n-bard systems fr measuring grss weight and enter f gravity psitin fr airraft. The initial attempt generally nsisted f affixing strain gauges t the landing gear; but, beause f the nature f the instrumentatin, it prved t be neither pratial nr reliable. In 1958, Cleveland Pneumati Tl Cmpany, the wrld's largest manufaturer f landing gear, attempted t devise a system based n measurement f the pressure in the le struts f the landing gear. Hwever, beause f the fritin inherent in le stru peratin, it was nluded that any system based n this priniple was bund t give errati results. Thus, this apprah was abandned. In 1959, the Instrumentatin and Cntrl Divisin f Pneum Dynamis Crpratin, wrking with its sister divisin, the Cleveland Pneumati Tl Cmpany, began the develpment f a weight and balane system based n strain sensing within the landing gear struture,utilizing a newly develped sensr. These effrts ulminated in the first suessful airraft integral weight and balane system whih was installed and tested in 1964 in tw USAF C-130 airraft. In Deember 1964, the Instrumentatin and Cntrl Divisin merged with the Natinal Water Lift Cmpany, als a Divisin f Pneum Dynamis Crpratin. In June 1966, the autmati integral weight and balane system beame an perating reality with the first prdutin artile installatin f the Pneum Dynamis Crpratin 1

11 system in USAF C-130 airraft. Sine the histry f pratial rtary-wing airraft is nsiderably shrter than that f fixed-wing airraft, the effrts tward develpment f an nbard weight and balane system fr helipters are f shrter duratin; hwever, the need is ertainly n less ritial, and, under sme nditins, it undubtedly is mre ritial than the requirements n fixed-wing airraft. Frtunately, there is n reasn why the experiene and tehniques develped fr fixed-wing airraft annt be applied diretly t rtarywing airraft. Hwever, there are substantial differenes in appliatin and use, and several new fatrs are intrdued. This reprt vers the results f a study perfrmed by the Natinal Water Lift Cmpany under Cntrat DA AMC-451(T) fr the U. S. Army Aviatin Materiel Labratries, Frt Eustis, Virginia. The initial phase f the study was an investigatin f the peratinal aspets f helipter usage with respet t the appliatin f n-bard weight and balane systems. Next, based n infrmatin gathered in the peratinal investigatin, Natinal Water Lift Cmpany perfrmed an engineering analysis f the general appliatin f integral weight and balane systems t Army arg helipters. Finally, as an utme f the previus effrts, a general remmendatin as t the nfiguratin f a helipter integral weight and balane system is prvided, and a disussin f the ptential prblem areas and their slutins is given. This reprt therefre reunts the need fr weight and balane infrmatin in rtary-wing airraft; it examines the airraft features and the varius basi methds ptentially apable f generating this infrmatin; it analyzes the instrumentatin available fr perfrming the neessary measurements and mputatins; then it presribes a remmended system.

12 % STATEMENT OF THE PROBLEM With an aurate knwledge f arg helipter grss weight and enter f gravity nditins, measurable imprvements are derived in bth safety and prdutivity. Therefre, the existing mplement f arg helipters and their flight rews an be nserved, while at the same time their assigned tasks an be perfrmed with greater effiieny. Drasti imprvements in safety are seen in takeff, in flight and landing mdes, in minimizing expsure f men and mahine t enemy fire under mbat nditins, and in minimizing the effet f strutural fatigue indued by peratin at extreme balane nditins. The ritial takeff phase f helipter peratin an be nduted with maximum safe lads, while at the same time aerdynami stability an be maintained when aurate grss weight and enter f gravity infrmatin is available. This apability is partiularly desirable under adverse density altitude nditins under whih nrmal lad-arrying apabilities are redued. Maximum flight perfrmane apability is a diret utme f the knwledge and ntrl f grss weight and enter f gravity in a helipter. Knwledge f this Imprtant weight and balane infrmatin enables avidane f aerdynami stability prblems suh as blade stall at high airspeeds and grss weight. Aurate preplanning f helipter apabilities at an intended landing site is failitated by the aurate grss weight and enter f gravity infrmatin btained prir t takeff. That is, the apability t make a hver apprah r the neessity t land with frward speed an be preplanned. An bvius advantage f an integral weight and balane system abard Army arg helipters Is the ability prvided t lad t ptimum weight and balane nditins in an abslute minimum f time. The redued expsure f helipters and flight rews t enemy fire, while ertainly t be ategrized as a flight safety item, must als be nsidered in the light f the inreased ptential prdutivity. An imprtant faet f the use f an integral weight and balane system in the lading f Army arg helipters is the redutin in strutural fatigue whih results frm peratin at extreme balane nditins. With aurate weight and balane data and the use f the integral system, lading an be amplished at mre nearly nminal nditins f enter f gravity. As illustrated abve, the aspet f safety is interrelated with that f

13 prdutivity. Numerus benefits in the area f prdutivity arue frm the use f an integral weight and balane system n Army arg helipters Areas f benefit are seen in the redutin f materiel handling time, in the redutin f arg lading time, in the utilizatin f full lad apabilities, and in the prvisin f ptimum aerdynami trim and thereby maximum flight range r duratin. Delays in the mvement f helipter-brne arg an result frm the neessity t weigh individual items at the dept frm whih shipment is being made. The manpwer required t perfrm the weighing peratin and als muh f the weighing equipment itself uld be utilized fr ther purpses with the availability f an integral weight and balane system fr Army arg helipter use. Lading time at a dept r in the field is nsiderably redued by using the integral weight and balane system t ntrl lad quantity and psitining. The time thus saved an be utilized in the flight task fr whih the helipter is intended. On eah flight f a helipter equipped with an integral weight and balane system, the maximum safe lad fr the nditins t be enuntered an be arried. Estimatin f helipter lad n the "safe side" results in an unneessary redutin in prdutivity, while lad estimates n the "high side" an ause peratin under ver-lad nditins with attendant aerdynami and strutural prblems indued. Weight and balane ntrl f helipter lading with an integral weight and balane system enables flight peratin under mre nearly ptimum aerdynami nditins. Optimum trim results in redued fuel bum-ff rate, with the diret result being inreased flight range and duratin. Using integral weight and balane systems, the urrent lift apability an be maintained by fewer helipters and persnnel, r an imprved lift apability an be prvided with the present mplement f equipment and rew. The magnitude f the prblems urrently existing with the lak f aurate knwledge f helipter grss weight and enter f gravity infrmatin, while large, an be redued t a great extent with the appliatin f an integral weight and balane system. The benefits in the areas enumerated abve will have a majr impat n the verall apabilities f Army arg helipters bth individually and lletively. The advantages ffered by the appliatin f integral weight and balane systems t Army arg helipters are summarized in Table I.

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15 1^^ / APPROACHES TO SOLUTION The types f weighing systems whih an be emplyed in the ntrl f helipter weight and balane are desribed in this setin. System peratinal requirements are als disussed. WEIGHT AND BALANCE SYSTEM TYPES The diversified methds r systems by whih ntrl f helipter weight and balane is maintained range frm the manual mputatin f weight and balane using weighed r estimated arg lad data, thrugh n-site arg weighing equipment and aerdynami feel emplyed by the pilt at takeff, t equipment installed n bard the helipter whih is available fr use at any time. Manual Cmputatin The standard methd fr the ntrl f helipter lading is urrently the manual mputatin f weight and balane. With this system, the basi weight f the airraft and its aessries is knwn and entered in the mputatin frm. Other weights and their mments are entered fr mputatin f enter f gravity. Often, a majr errr in the estimatin f arg weight exists, partiularly in field peratins. The imprper lading whih an result frm these errrs auses the helipter t be perated in an ineffiient r even a dangerus manner. On-Site Weighing Equipment Platfrm-sale-type weighing equipment is generally available fr arg lad ntrl at the larger depts frm whih arg helipters perate. As disussed previusly, delays in lading and transprting arg an result frm the neessity t weigh materiel prir t lading. Further, platfrmsale weighing equipment is generally nt available in the field due t its umbersme nature. Thus, the use f platfrm sales annt be nsidered the answer t the neessity t weigh arg in the ntrl f helipter lading. Aerdynami Feel The aerdynami feel harateristi f the laded helipter is naturally taken int aunt by the pilt in all flight peratins. Obviusly, this tehnique is mmnly used (mre effetively by mre experiened pilts) t rss-hek manually mputed weight and balane harateristis. While this methd prvides a minimal hek n helipter lading nditins, it annt be relied upn fr a mre extensive rle.

16 I ( On-Bard Weight and Balane Measurement Equipment The strng desirability t make the weight and balane ntrl equipment an integral part f the helipter is evident in nsideratin f the advantages t be gained. With the weight and balane ntrl equipment made integral with the helipter, measurements an be made at any landing site. The equipment apable f prviding lad measurements must measure either landing gear lads r dynami lads in the rtr system. Measurement f rtr system dynami lads is drastially limited in its apability, prviding n stati measurements r enter f gravity mputatins. With this tehnique, measurements are made f lift fres n the supprt struture fr the rtr head r f fres in the rtr drive train. The limitatins f this system make it unsuitable fr peratinal ntrl f helipter weight and balane. When mpared with the previusly desribed methds, it is seen that the instrumentatin f the landing gear struts remains the nly pratial tehnique t be emplyed in the measurement f helipter weight and balane. Instrumentatin f the landing gear struts enables measurements f hellpter lad and lad distributin at any time that the helipter is n the grund. N umbersme platfrm sales need be used in the measurement f individual items f arg. The auray f the system whih instruments the landing gear strut lads an vary widely with the Instrumentatin tehnique emplyed. The tw general instrumentatin methds appliable t landing gear strut lad sensing are the measurement f le strut pressure versus lad and the measurement f mehanial defletin f the strut versus lad. The strut instrumentatin methd whih applies a pressure transduer at the le strut fr measurement f pressure versus applied lad is highly unsuitable fr use n a helipter whih perates n nnlevel terrain in the field. Testing perfrmed by the Instrumentatin and Cntrl Operatins f Natinal Water Lift Cmpany at the failities f the Cleveland Pneumati Tl Cmpany n pressure transduer instrumented struts under idealized nditins shwed pr results. With the struts munted vertielly in a test mahine with rller plates munted under the wheels in bth the fret-aft and side-t-side diretins in rder t eliminate side fres, a hysteresis in the pressure transduer utput f 10% t 15% was seen, as shwn in Figure 1. With the strut psitined nnvertially and with side lading, as in peratinal helipter use, the fritinal fres tending t bind the strut wuld have been greatly inreased. Measurements with errr f this magnitude annt be nsidered useful in a weight and balane system fr appliatin t Army arg helipters. :

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18 Bf Measurement f the lad n helipter landing gear struts by sensing the defletin f strutural members is desirable in that the variable le strut bearing fritin des nt affet the measurement. The instrumentatin, if applied prperly, is apable f aurately measuring the individual strut lad under the widely varied nditins enuntered by Army arg helipters. This instrumentatin, as part f the integral weight and balane system arried abard the helipter, is immediately available at any landing site t prvide aurate measurement f helipter grss weight and enter f gravity. Table II prvides a mparisn f the weight and balane system types previusly desribed. SYSTEM OPERATIONAL REQUIREMENTS The user f an integral weight and balane system abard a helipter needs aurate data displayed in a usable manner fr the ntrl f lading. The equipment must enable rapid determinatin f quantity and plaement f arg. The display and the ntrl pakage shuld be f a size and nfiguratin that an be munted s as t be diretly aessible t the pilt. The mputer pakage need nt be munted in the kpit area, but shuld be aessible t the rew in flight fr system test purpses. In additin t landing gear strut instrumentatin, lads n high-apaity hists r arg hks shuld be sensed and displayed n the weight indiatr. Bth the display pakage and ntrl shuld be self-illuminated t prvide ptimum readability. The integral weight and balane system, t be fully useful, shuld be apable f prviding aurate stati weight and balane readings. This auray under stati nditins is imprtant t enable lading peratins t be mpleted withut the neessity fr rtr peratin t break strut fritin. In additin, an aurate grss weight and enter f gravity referene is prvided fr measurement during rtr peratin. Full rretin fr the rtr lift effet during weight and balane measurement must als be prvided. Full lift rretin must aunt fr helipter rtr lift at the site f the initial mpensatin and fr the variatin in that lift t be enuntered at subsequent landing sites having a density altitude variane. Envirnmental requirements fr the integral weight and balane system must be tailred t the temperature, vibratin, shk, altitude, and attitude nditins enuntered in Army arg helipter peratins.

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20 mmm mm In designing the equipment fr installatin n helipters, ne must take int aunt the nditins enuntered in bth fatry and field installatin, alibratin, and verhaul. Speial nsideratin must be given the landing gear nfiguratin t be instrumented in eah appliatin. Table III prvides a summary f the peratinal requirements fr an integral weight and balane system fr appliatin t Army arg helipters. Operatinal Cnsideratins The appliatin f an n-bard weight and balane system t Army helipters requires a mplete understanding f the envirnment in whih peratin is required. In rder t gather the stre f infrmatin needed in the analysis f the appliatin, Natinal Water Lift Cmpany has interviewed persnnel assiated with helipters in the areas f flight peratin, safety, training, maintenane, design, nstrutin, and test. A nferene held at Frt Ruker, Alabama, prvided a majr ntributin regarding the effet f helipter peratinal predures n the appliatin f integral weight and balane systems. Rated persnnel frm the Army Bard f Airraft Aident Review, the U. S. Army Aviatin Test Bard, and the Department f Rtary Wing Training at Frt Ruker; a tehnial representative frm Being-Vertl; and engineers frm Natinal Water Lift Cmpany attended. A brad range f experiene was available, ranging frm that f several reently rtated helipter pilts frm the Vietnam mbat area, thrugh experiene in flight test, training and safety. The viewpint f a helipter manufaturer's tehnial representative and the Natinal Water Lift Cmpany perspetive n the weight and balane system appliatin were als drawn upn in the disussins. A resume f the infrmatin btained in this nferene whih is partiularly pertinent t peratin in mbat znes fllws. (a) Carg in these areas is nt weighed. N idea exists as t an aurate grss weight figure r enter f gravity latin. (b) The abve nditin is upled with the neessity t land quikly, t disharge passengers and arg, t relad quikly, and t lift ff. Operatin under fire makes a fast, aurate system fr measuring weight and balane highly attrative. () As a result f the desirability t alight, disharge, relad, and lift ff quikly, it is mmn pratie t perfrm the lading peratin 11

21 »Bffa^wwffw«!! i wmm I 12

22 wmmmmmm. <pf'&*t&?.*w--: with the rtrs running at flight-perating RPM and minimum lletive pith (nditins under whih an integral weight and balane system wuld be required t funtin aurately, as well as under stati nditins). Relatively high lift is attained under this nditin and must be aunted fr if aurate weighing is t be pssible. The magnitude f this lift prdued fr the CH-47A Chink, fr example, is n the rder f 6000 punds. (d) Operatin n nnlevel terrain is quite mmn and is always apprahed t maintain a level lateral nditin. Ammdatin f slpes as high as 10 is pssible. Majr errrs in the latin f lngitudinal enter f gravity psitin wuld result if mpensatin were nt prvided. (e) Operatin with water landings is perfrmed with redued grss weight limits. Fr example, fr the CH-47A Chink, a 28,000-pund maximum limit is impsed rather than the nrmal 33,000-pund limit. (f) Carg hk lad readut, as planned fr the CH-47A, wuld be desirable. N enter f gravity reading is needed in this readut mde. (g) Readut f enter f gravity psitin shuld be made in terms f fuselage statin. (h) (i) Certain smaller helipters suh as the UH-1 series are ritial as t grss weight and enter f gravity latin and shuld be nsidered fr appliatin f the integral weight and balane system. Lad suspensin systems using a single hk r able d nt adversely affet enter f gravity psitin in that the able is nrmally lated at the nminal enter f gravity, and the suspended lad, being pendulus, lates its enter f gravity diretly belw the attah pint. In the nferene, mentin was made f multiable supprt systems nw used n the CH-54 Skyrane and under nsideratin fr use n the heavy lift helipter. With this supprt tehnique, supprt able tensin an be measured by integral weight and balane system mpnents fr lad readut and equalizatin. Operating Charateristi Demnstratin Demnstratin f helipter perating harateristis was made at Frt Ruker using a CH-47A Chink. The previus statement f the persnnel in the nferene that the rtrs prvided lift in even the grund-idle nditin was bme ut, as the fuselage was seen t lift as rtrs were 13

23 brught up t grund-idle RPM. Inreasing rtr speed thrugh flight-idle RPM t perating RPM prdued an inreasing lift effet. The apability t vary the lift distributin frm the frward, t aft rtrs by use f the yli stik was als demnstrated. Attentin was given the landing gear struts during the demnstratin t rughly determine the effet f strut fritin n the ability f the struts t fllw lading hanges. N mtin wss bserved n the struts until the yli stik was exerised, varying the distributin f lletive pith applied t the frward and aft rtrs. It wuld appear that the strut fritin magnitude n this helipter wuld prelude the use f strut pressure variatins in the measurement f lading. Operatinal Variables Operatinal variables enuntered in the helipter appliatin are listed belw and are seen t have majr imprtane in the determinatin f requirements fr an integral weight and balane system fr helipter use. Rtr Cnditin (a) Pwer ff, n rtatin (b) Fixed RPM and speifi pith () Any RPM and any pith With pwer ff and n rtr rtatin, n lift results; thus, the helipter weight and lad distributin an be determined slely by the instrumentatin f the landing gear (assuming that n lading ramps are in ntat with the grund). In weighing the helipter with the rtr at a fixed RPM and a speifi pith setting, the resulting lift must be mpensated fr by adjustments in bth grss weight and enter f gravity readings, preferably by referene t aurate stati readings r, less aurately, by tables rrelating the errr and the variables invlved. Again, instrumentatin f the helipter need nly invlve the landing gear struts. If we desired t btain a helipter weight reading at any rtr RPM and any rtr pith setting, we must then assume that the vehile is mpletely supprted thrugh the landing gear struts n the grund r that it is partially supprted by the grund and partially supprted by the rtr plane r that it is mpletely supprted by the rtr plane. In this ase, we must instrument bth the landing gear struts and the rtr supprt struture. An aurate weight an then be btained by the algebrai additin f the landing gear 14

24 MP instrumentatin signals and the signals frm the rtr supprt plane. system seems far t mpliated t be justifiable. This Landing Surfae Cnditins (a) Hardness (b) Fritlnal nditins () Level nditin (d) Water ver (e) Mtin The hardness r fritinal harateristis f the surfae alighted upn an have an effet n the defletin f landing gear strut struture and thereby an impse ertain requirements n the instrumentatin emplyed therein. Landing n an unlevel surfae auses hanges in the measurement and distributin f weight n the landing gear struts and, if nt mpensated fr, results in errrs in grss weight and enter f gravity readings. Unlevel terrain auses an appreiable inrease in the fritin level seen in the landing gear le struts. In thse ases where a helipter lands in water, the partial r full buyany effet takes ver the supprt f the helipter frm the landing gear struts. Finally, we must nsider that the surfae n whih the helipter is t land an be in mtin, as the dek f a ship. The aeleratins impsed by the mving dek n a helipter whih has landed an be appreiable in their effet n weight and enter f gravity readings. Temperature and Altitude Cnditins (Density Altitude) Bth f the abve nditins mdify the lift apability f helipters. These parameters must be knwn r measured t fully rret rtr lift effet during weighing at landing sites having a variatin in density altitude frm that at the rigin f the missin. Wind Cnditin (a) Weight transfer (b) Lift (psitive r negative) The magnitude f lateral weight transfer frm wind lading is nsiderably higher than that f lngitudinal weight transfer as the result f the relatively large side area f the helipter mpared t its frntal area. The resulting small lngitudinal weight transfer frm winds up t 30 knts indues a negligible errr in the enter f gravity reading. The lateral weight transfer, while readily measurable, has n effet n lngitudinal enter f gravity. 15

25 N requirement is seen fr readut f lateral enter f gravity psitin In the CH-47, the UH-1, r the CH-54. Side area f the CH-54 is small; therefre, wind prdues minimal lateral weight shift. Individual hist able readut may be desirable fr able tensin regulatin. Fuel Slsh Weight transfer as a result f fuel slsh with pith attitude f the helipter is nt seen as a prblem in the UH-1, the CH-47, and the CH-54, arding t manufaturing and military prjet ffie persnnel. Attentin is given t enter f gravity ntrl In the design and plaement f fuel tanks fr helipter appliatin. Servie Histry f Equipment The nditin f the helipter and its ritial mpnents with regard t amunt f servie usage r damage an have a majr effet n the limits applied t grss weight and enter f gravity psitin. This mdifiatin t existing limits by the respnsible pilt is a matter f judgement. As an example, a rtr blade knwn t have sustained damage in a mbat situatin might well ause the pilt t redue his lad and, further, t favr the ptentially weakened mpnent with a hange in enter f gravity. 16

26 1 17

27 DESIGN CONSIDERATIONS SYSTEM DESCRIPTION An integral weight and balane system appliable t arg type helipters will be mprised f the fllwing mpnents, as shwn in Figure 2: (a) Sensing instrumentatin (lad and pith attitude) (b) Calibratin elements () Cmputer (d) Display Eletrial signals analgus t vertial lad n the landing gear struts must be prvided in the system. These signals must be standardized as t sale fatr, either at eah individual strut r in a entral alibratin pakage. The mputatin f grss weight and enter f gravity is amplished in a mputer setin utilizing the standardized strut lad signals. Outputs f grss weight and enter f gravity are fed frm the mputer pakage t suitable indiatrs, whih an be pakaged with the mputer r prvided as remte displays. LOAD SENSING INSTRUMENTATION An area f majr nern in an integral weight and balane system is the lng-term repeatability f the landing gear instrumentatin. The system lad sensr utputs must be stable with respet t envirnmental variatins suh as temperature, vibratin, and shk ver prtrated perids between alibratins. The effet f the varius nnvertial lads whih an be impsed n landing gear struts must be effetively rejeted in rder t ahieve a usable level f auray in the instrumentatin signals. Additinally, the landing gear lad instrumentatin must be apable f aurate measurement under stati nditins in rder t enable lading peratins t be amplished with simultaneus aurate weight and balane measurement withut the need fr rtr peratin t break strut fritin. Further, aurate stati measurement prvides a neessary referene fr use when weighing during rtr peratin. The lad sensing instrumentatin emplyed n struts r rane hks an be ne f the fllwing types: (a) Defletin sensr devie (b) Diretly applied strain gauges (measuring strutural strain) () Pressure transduers (measuring landing gear le strut pressure) 18

28 MMH ^ v 1 i >J i s a. CO =< 0 1 J E A 1 a IM O) a ^ i ^ w ^ 1 s OQ! 2 u i T O >, CO Ü A OQ T3 C s J2 > < a ' s t-h \ u 4 2 CT V 4-> i 1 S M Q < 0 1»-> T <N 1 l CO > ^ ^ IX, 03 i 19

29 The defletin sensing devies emplyed in the instrumentatin an be f semindutr strain gauge type, nventinal fil r wire strain gauge type, r eletrmagneti devies suh as the linear-variable-differential transfrmer (L7DT) r relutane pikff. Semindutr strain gauges ffer eletrial utputs whih are n the rder f 20 t 30 times thse prvided by fil r wire types, thereby greatly enhaning the system input signalt-nise rati and, as a result, enhaning ultimate system auray. Defletin sensing devies are applied in r n a landing gear axle r ther lad-bearing member t enable the attahment f the gauges t the instrumentatin by using tehniques unsuitable fr diret appliatin t highstrength, highly heat-treated strut materials. Gauge appliatin methds must virtually eliminate the reepage prblem seen with rgani adhesives in whih lng-term gauge strains are relieved with an attendant lss f system auray. Further, the appliatin f the defletin sensing devies prvides the pprtunity t btain mehanial amplifiatin f strut. defletin levels and t nfigure the instrumentatin appliatin gemetrially t prvide the rejetin f defletins resulting frm nnvertial lading. The fres ating n helipter landing gear struts are shwn in Figure 3 as vertial lad, side lad, drag lad, and srub turn trque. These fres are individually diagrammed in Figures 4 thrugh 7, and they illustrate the envirnment in whih landing gear sensrs must perfrm their lad measurement. Adaptatin f landing gear defletin sensrs t the axle bre by means f expandable llet members has prven t be apable f the neessary psitinal permanene. Care must be taken when expanding any instrumentatin inside an airraft axle s that pint ntat r small area ntat is nt used t seure the hardware. Small area r pint ntat munting tehniques ause high stress nentratins that struturally weaken the defleting member. Figure 8 illustrates instrumentatin f the type whih will prdue high stress nentratin as a result f the lw ntat area and the resultant high unit pressure. The hp stress prdued by this type f munting, when added t the already high stress level at whih landing gear axles nrmally perate, prdues a stress level whih exeeds the allwable limits. N landing gear manufaturer will guarantee any strut using instrumentatin prduing stress nentratins. Figure 9 illustrates the prper appliatin tehnique fr expansively munted instrumentatin elements. In this appliatin, a relatively large ntat area is used t prelude stress nentratins in the landing gear axle bre. N sharp edges are used in the design f this nfiguratin. On asin, 20

30 mm T f Strut ^= Cylinder n Strut J k Pistn i? 1 r «Helipter Airframe Srub Turn Trque Side Lad Drag Lad Vertial Lad The abve fres ating n the strut are diagrammed separately n the ampanying figures. The defletins shwn n the figures are grssly exaggerated fr the sake f larity. Figure 3. Fres Ating n Landing Gear Strut. 21 *.Mj4ö*jy^jj a^

31 Vertial Lad Defletin / End Lad Figure 4. Vertial Lad Fre. 22

32 *»1 VUUUIll Side Lad Defletin / ^> Cuple & Streth Figure 5. Side Lad Fre. 23

33 fl assssa Drag Lad Trque Defletin End Lad Figure 6. Drag Lad Fre < 24

34 IM -m ' y Smb Turn Trque Resisting Fre Defletin Resisting Fre Figure 7. Srub Turn Fre. 25

35 - mi r Landing Gear Axle Expansively Munted Instrumentatin Element WWWWTsWWWW UVWVAVjWWUWV High Stress Cnentratin (prdued by lw area ntat, nt allwable in already highly stressed landing gear). Figure 8. Instrumentatin Appliatin t Landing Gear Imprper Tehnique. ( Landing Gear Axle T^TT E Expansively Munted 1 Instrumentatin Element SXXXXX5 \uv\\v\m\uu\u v Ü Cntat Area Large (n sharp edges t prelude stress nentratins in landing gear). Figure 9. Instrumentatin Appliatin t Landing Gear Prper Tehnique. 26

36 it has been fund desirable t emply a lw mdulus material suh as adhesive in the interfae between the axle bre and the instrumentatin element in a band n either side f a entral band f high mdulus material. This tehnique prvides axial supprt fr the instrumentatin elements, exludes misture and the attendant rrsin prblem, and als eliminates, wear f the landing gear axle by eliminating the entry f abrasive partiles in the axle t instrumentatin interfae. Instrumentatin applied t landing gear in this manner has been extensively tested in the landing gear labratry f the Cleveland Pneumati Tl Cmpany in envirnmental and repeated drp tests. Further, peratinal tests f airraft in atual use have prven the apability f this design t maintain aurate and repeatable utputs. Design f the defletin sensing instrumentatin hardware must result in mpnents whih are extremely simple in nfiguratin. That is, an ideal design wuld be prvided as ne piee, withut jints whih an mve with respet t ne anther. In general, diretly applied strain gauges will be f the nventinal fil r wire gauge type in the instrumentatin f landing gear struture. Attahment f the fil r wire strain gauges diretly t the landing gear struture by rgani adhesives is extremely diffiult t perfrm in a manner whih yields lng-term stability. Unprteted by any mehanial means, the adhesive bnd is subjet t reepage and peel failure. Nevertheless, mis instrumentatin system is utilized extensively in test prgrams where realibratin an be amplished daily r at greater frequeny. With pressure transduers, the prblem f system inauray as a result f strut fritin must be regnized. In general, the landing gear le struts emplyed n helipters are rugged strutures with a mmn harateristi f high pistn-bearing fritin. This fritin level is inreased when peratin n nnlevel terrain adds binding side and drag lads t the le strut. Lads measured by instrumentatin installed in r n a landing gear struture will be subjet t an errr whih is a funtin f the sine f the angle between the sensitive axis f the instrumentatin and vertial. Figure 10 illustrates the lad relatinship fr this pith attitude errr The errr in strut lad measurement is pltted in Figure 11. Figure 12 illustrates an apparent shift f enter f gravity as mputed by the integral weight and balane system when perating under a terrain pith slpe nditin. 27

37 Vertial Landing Gear s 9 Terrain W sin W e w sin 8 w s 6 Ttal Strut Lad = Terrain Slpe (pith) = Restraining Fre as Brake r Chk = Measured Lad Rll attitude f helipter is stated by peratinal persnnel t be nearly level (± 3 - ) in field use n slped terrain. Nrmal pith attitude ranges frm level t 10 nse up r nse dwn. The errr in strut lad measurement is pltted n Figure 11. Figure 10. Terrain Slpe Errr in Strut Lad Measu:;?-.v.üt. 28

38 Mi ' '"^ M _ _, t _ ^ _ N. ^^^ -t ^r sr I 5,,.,,,,in ^^ 1 ^H s x _: ± s s r _ ^ -- ^ ::±_±' g : s P S^ ^ s a ga> _:_s:: s : s ::_s: «w s _ X 5 u :: ± : 'S, _ ::: > 3^ i: S:.. w ^ 5 :: Ä tl i i 2 gg :. : ^ : O r - 0 P. UJ Si 5 L 1 ^ 1 _ iz! _i s : _ f T ir 5 L 5 :: ;:: : ^ A i. j t j r i 5 X J j j ',_ V T \ ll r u 1 > r-^ 1 i I" LJ 1. J T" "l "1 i l ^ 1 I I s i fe l f ;::::::::::::4::::::l ^ CO CM i-h. T3 3 4-> ~* J th 4-> 0 <: m h x: ü 0 M r*»^ M a. in ti C Ü a ^ -> CO u Oi a> 3 5? S CO 10 It ts 3 b e CO 14 0} 5 <0 E 3 H 2 CO CO J= s. a> 01 2 «t-i 0 TJ "0 3 0» Ü C) 1 >M CO 6 M-l S tt ^ 4J i-h 29,

39 mmmmm^^ "^"^^i" Vertial Apparent CG psitin The distane n the grund that the CG mves as a result f the elevatin h f the CG and the angle 6 is S = h tan 0 s h e Figure 12. Terrain Slpe Errr in Center f Gravity Readut. 30

40 "T"^ m CAXIBRATION FUNCTION The alibratin setin f an integral weight and balane system must prvide standardizatin f strut lad sensr signal sale fatr (eletrial utput versus mehanial strut lad input). As mentined previusly, this alibratin funtin an be prvided either at the landing gear strut instrumentatin latin r in a mmn alibratin area. COMPUTER The primary funtins f the mputer in the integral weight and balane system applied t Army arg helipters are: (a) Summatin f the landing gear strut lad sensr signals t prvide a grss weight analg vltage utput fr display. (b) Summatin f the landing gear strut mment signals in the mputatin f enter f gravity. The sendary funtins perfrmed by the integral weight and balane system mputer are: (a) Crretin f grss weight and enter f gravity mputatin with respet t measured helipter pith attitude t a reading rrespnding t that whih wuld be btained with the helipter in a level r nminal attitude. (b) Self-hek f the system t the extent deemed desirable n the basis f a trade-ff between mplexity and reliability. The mehanizatin f the integral weight and balane system an take the fllwing frms. Manual Serv Cmputatin The manual serv system fr mputatin is relatively light, simple, and lw in pwer requirements, deriving its mtive pwer fr the display and mputatin frm the peratr. A majr drawbak in the use f the manually perated serv mputer is the time required in manually driving the drum unter display fr grss weight t the desired reading with respet t a null indiating meter and then repeating the peratin fr the enter f gravity mputatin. 31

41 Eletrmehanial Serv Cmputatin The eletrmehanial serv system is essentially similar t the manual serv type, with the exeptin that the mtive pwer in this ase is prvided by a mtr. The eletrmehanial serv system an prvide a display f grss weight and enter f gravity psitin whih is nstantly urrent and available fr use at any instant. A variatin f the nventinal dual serv mputatin system an be a hybrid system in whih the grs^s weight serv nt nly drives its fllw-up ptentimeter and drum unter display but als drives a send ptentimeter. The shaft psitin f the send ptentimeter prvides an eletrial grss weight funtin emplyed in the mputatin f enter f gravity, resulting in an eletrial analg f enter f gravity whih is displayed n a meter mehanism. Digital Cmputatin The digital mputer fr an integral weight and balane system prvides the mputatin f grss weight and enter f gravity n an instantaneus basis withut the use f any eletrmehanial parts. The mplexity f the digital system in the number f parts emplyed auses the mputer pakage t be smewhat larger and heavier and, in general, mre expensive than the eletrmehanial serv mputer mehanizatin. Eletrni Analg Cmputatin The advent f small, reliable analg multiplier mpnents will enable the eliminatin f the serv system frm the mputatin mehanizatin f an integral weight and balane system. DISPLAY Display f grss weight and enter f gravity infrmatin an be implemented with a wide variety f hardware. Mst mmnly, this infrmatin is prvided n drum unter displays. Other pssible indiatr nfiguratins inlude hybrid drum unter and meter mehanism indiatrs, r even a pitrial display whih, using rss pinters, wuld give grss weight and enter f gravity nditin at a glane with respet t pitrially presented limits. The manual and eletrmehanial serv mputers nrmally drive drum unter type digital displays r hybrid unter and meter mehanism displays. The digital utput mputer is used with magnetially atuated digit display 32 I

42 wheels, segmental numerial display mdules, r ther standard digital displays. The eletrni analg mputer uld drive the rss-pinter display mentined abve. PITCH SENSOR A pith sensr munted n the helipter prvides an eletrial pith angle analg signal t the mputer pakage whih is used in the mpensatin f the mputed grss weight and enter f gravity fr the errr indued by pith attitude. I Pith angle sensrs an be implemented in a number f nfiguratins invlving sensing f the psitin f a pendulus mass. The mmnly emplyed pikff devies used in the pith sensrs are: (a) Ptentimeter pikffs (b) Eletrmagneti pikffs () Strain gauges Strain gauge and eletrmagneti pikffs, suh as the LVDT r relutane pikff, have the imprtant advantage f n ntating surfaes t ause wear under the high vibratin levels whih are nrmal abard a helipter. CONTROL Appliatin f system pwer, the ntrl f system test, and ther funtins, as neessary, are perfrmed in the ntrl setin f the system. The equipment fr these ntrl funtins an be pakaged in a separate unit r an be inrprated in the mputer r indiatr pakages, as desired. Further, the funtins an be divided in their latin, with thse nerned with the nrmal peratin and ntrl f the system lated near the display, and thse used less frequently in test lated n the mputer pakage. Typial integral weight and balane ntrls are as fllws: (a) Pwer swith (b) Readut mmand swith () Test swith (d) Sensr signal ntrl swithes (e) Lift mpensatin ptentimeter(s) (f) Annuniatr lights The system pwer swith is generally a tw-psitin type enabling the system t remain energized, as required. 33,v - - ^4

43 The readut mmand swith may r may nt be used, depending upn the partiular system nfiguratin. Certain systems are energized fr reading grss weight and enter f gravity n a ntinuus basis, while thers are updated frm a previus reading nly by the engagement f a mmentary readut mmand swith. The system test swith is generally f the mmentary type, ausing the system t perfrm a preseleted mputatin f grss weight and enter f gravity. Readut f system test results is amplished either by referene t the grss weight and enter f gravity displays r, in ertain instanes, by referene t a light r lights annuniating the system nditin. It is smetimes desirable t prvide the apability t ntrl the input f the landing gear strut lad sensr signals t the alibratin and mputer setin f the integral weight and balane system. In this manner, individual lad sensr utputs an be read and used in the peratinal test predures devised fr the given system. Additinal system ntrls, in the system t be remmended later in this dument fr appliatin t Army helipters, are ptentimeters lated n the ntrl pakage whih enable the mpensatin f "rtr lift during grss weight and enter f gravity measurements perfrmed with the rtr(s) in peratin. SYSTEM CONFIGURATION VARIATIONS The general blk diagram fr an integral weight and balane system was shwn previusly in Figure 2. Pssible system variatins are shwn in this setin. In eah ase, the signals frm the landing gear lad sensing instrumentatin are alibrated (standardized) and summed int a single weight summing amplifier and a single enter f gravity mment summing amplifier. In the system diagram shwn in Figure 13, the manual serv integral weight and balane system, and the system diagram shwn in Figure 14, the eletrmehanial serv integral weight and balane system, the utputs f the grss weight and enter f gravity mment summing amplifiers are indiated numerially n drum unter displays. In bth systems, the grss weight and enter f gravity analg vltages are nverted t shaft psitin analgs derived by ahieving a null balane nditin with the serv fllw-up ptentimeter and the analg vltage invlved. Display f grss weight and enter f gravity in these systems results frm a mehanial internnetin f the drum unter readuts with the fllw-up ptentimeter, thus utilizing the shaft psitin analg. 34

44 ! - CO ^ w k2 2 $ CO >-> 1 x: i: > S 35

45

46 The eletrmehanial serv integral weight and balane system display is self-ntained, as shwn in Figure 15. The manual serv display wuld be idential t that in Figure 15 with the additin f hand ranks apable f driving the grss weight and enter f gravity mehanisms. The hybrid eletrmehanial serv drum unter and meter mehanism display system shwn in Figure 16 emplys a unique mputatinal sheme. The grss weight serv, in additin t its fllw-up ptentimeter and drum unter, drives a send ptentimeter whse signal is used in the mputatin f enter f gravity. The display used with this system is shwn in Figure 17. The bvius simpliity f this system is evident in the eliminatin f the enter f gravity serv. Figure 18 illustrates a pitrial indiatr whih presents bth quantitative and qualitative infrmatin n grss weight and enter f gravity. In this display, tw retilinearly atuated meter mehanism pinters are dispsed at 90 t eah ther, and eah is referened t sales graduated in units f grss weight r enter f gravity, as neessary. Additinally, the bakgrund behind the rss pinters is marked with the enter f gravity versus grss weight envelpe fr the partiular helipter invlved. Thus, the user, by referring t the intersetin f the pinters, is prvided an immediate qualitative readut f his grss weight and enter f gravity nditin with regard t the allwable envelpe. If the intersetin shuld apprah either the frward r aft limit lines, readings f the speifi values f grss weight and enter f gravity an be made by referene t the rrespnding sale. Cmputer utputs frm the integral weight and balane system, shwn in Figure 19, are in a digital frmat. The digital signals frm the mputer are displayed n suitable digital readuts. Typial readut devies are eletrmagnetially atuated drums, prjetin type digits, r illuminated segmental digits. Figure 20 illustrates an indiatr emplying eletrmagnetially atuated display drums. The use f arg hk and winh lad lifting presents the pprtunity fr a desirable extensin f the apability f the helipter integral weight and balane system. That is, the system an be made t read ut the lad brne by the arg hk r high-apaity winh when the helipter is in the hver r flight mde. This is entirely feasible by instrumenting the hk r winh and displaying its signal utput r thse f the landing gear instrumentatin as ntrlled by manual swithing r a landing gear le mpressin swith. In this manner, when the helipter is n the grund and the hk r winh lad is zer, the lad n the landing gear will be displayed as grss weight and the enter f gravity will be mputed and 37

47 & A WEIGHT 3] IH i 0 0 LSS FUS. STA CENTER OF GRAVITY a # Figure 15. Weight and Center f Gravity Indiatr Serv Display. 38

48 39

49 *»U"OS GROSS WEI8HT «"TER OF ft*virr-fu8. SJA J "'.IMMIMMI. 17. Weight and Center f Gravity Indiatr. Serv and Meter Mehanism Display. 40

50 wm ( a (a w E I G H 22 \- 300 CENTER OF GRAVlT/ FUS STA $ Figure 18. Weight and Center f Gravity Indiatr Dual Meter Mehanism Display. 41

51 I! Q) > Q) ^i mt ipla a äs mt Spl US i I I Ä u aauaaut) a/v.^ 1 Q ^^ "^ *«/ VA/ «J Q» x> CO >- > ITun ßuTUOTiipu leußts g a, 10 appeal utjbjqttbo & O u Ü t 10 CQ 10 4-J JC 0> 3 ^ -H 10 ti 5» ' i... jtf i 8 s s t s & WJ Ä 1 ä rh & > H h, 1 SJOSU9S utia jaa 42

52 GROSS WGT LBS * 1000 t9> t Figure 20. Weight and Balane Remte Indiatr (shwn atual size). 43

53 displayed. The required pith attitude errr rretins an be applied in bth the grss weight and the enter f gravity mputatins. When the helipter lifts ff the grund (unlading the landing gear struts and atuating the le swith), the lad lifted by the hk r winh is indiated n the weight display withut pith attitude rretin applied. Center f gravity annt be mputed under this hver r flight mde nditin beause distributin f the lad ther than that n tne hk is nt measured. This des nt present a prblem thugh, beause the enter f gravity f the helipter (measured while n the grund) annt be adversely affeted by the additin f lads thrugh the nminal enter f gravity latin f the arg hk r high-apaity winh. As previusly stated, winhes f lw apaity munted ff the nminal enter f gravity latin d nt prvide majr enter f gravity shifts. After the ttal grss weight is lifted, that f the helipter and its arg hk supprted lad is btained by manually adding the grss weight reading btained n the grund and the arg hk lad readut. Multipint hist systems fr the CH-54 and the heavy lift helipter enable the lifting and transprting f lads in a manner whih prvides greater restraint than that with single able systems. In this way, bulky lads an be arried lser t the fuselage f the lift helipter withut danger f interferene with landing gear r ther helipter struture when the lad swings. The integral weight and balane system an prvide readut f lad n eah f the multiple ables and enable the display f lift weight. Readut f individual able tensin an allw lad equalizatin if desired. Further, if required, the enter f gravity f the lad uld be mputed while the lad is mpletely supprted by the ables. SYSTEM LIMITATIONS Certain peratinal nditins will nt be mpensated fr in the systems nsidered in this study fr these reasns: (a) Fltatin A partial r full buyany effet relieves lading frm the instrumented landing gear struts and makes aurate weighing with the system impssible. (b) Mving Alightment Area Mtin f the alightment area suh as that urring n shipbard imparts aeleratin t the helipter, ausing the readings derived 44

54 frm landing gear instrumentatin t flutuate between ver-atual and under-atual weights. It shuld be feasible t nte maximum and minimum readings t and use an average value fr grss weight. Aeleratin effets an ause randm variatins in landing gear lad distributin and, therefre, an adversely affet the auray f the enter f gravity mputatin. () Lateral Center f Gravity Measurement The measurement f lateral enter f gravity psitin serves n useful funtin n the CH-47 and the UH-1 helipters. Cable tensin measurement an be prvided n the fur-pint lad attahment system used n the CH-54 t enable lad equalizatin. Determinatin f the enter f gravity f the able-supprted lad an be prvided, if desired. Persnnel winhes, while ften displaed laterally frm the allwable enter f gravity envelpe, are nt a majr ntributr f lateral unbalane due t their limited lift apaity. 45

55 RECOMMENDED SYSTEM CONFIGURATION The fllwing system nfiguratin is based n the knwledge gained in the peratinal analysis and the experiene f this ntratr. The helipter integral weight and balane system is muh like that fr fixed-wing airraft, but at the same time it ffers prblems whih are slely existent in helipter peratin. In this setin, the instrumentatin tehnique remmended fr varius landing gear strut strutural nfiguratins will be desribed. The resultant lad sensr signals are ruted t the alibratin/mputer pakage fr alibratin and summatin f strut lad and mment signals. The system remmended herein has the apability f aepting landing gear strut lad sensr signals frm any number f struts withut regard t their strutural nfiguratin r gemetri relatinship. The grss weight and enter f gravity eletrial analg signals are then fed t the display fr presentatin. System mmnality in mpnents is shwn in Table V. It will be nted that fr the UH-1, CH-47, CH-54, heavy lift helipter arg versin, and heavy lift helipter persnnel versin, the integral weight and balane system mpnents are idential frm appliatin t appliatin, with the exeptin f the value and quantity f ertain iruit elements and the lad sensr adapter hardware. This hardware, naturally, must be designed fr the speifi strutural instrumentatin required. In Figures 21 thrugh 29, integral weight and balane systems are illustrated fr the UH-1, the CH-54, and the CH-47. Eah integral weight and balane system mpnent and its latin abard eah helipter type are illustrated. Als inluded is a figure shwing the landing gear instrumentatin nept and the mputatin f enter f gravity fr eah f the three helipters. The enter f gravity envelpes fr eah appliatin are als prvided fr mparisn n separate figures. It will be nted n the illustratin f the enter f gravity envelpe fr the CH-47 that errrs in grss weight whih might reasnably be expeted t exist in field peratin with estimated weight (5% and 10% grss weight errr) ause majr departure frm the speified enter f gravity flight envelpe. The use f an integral weight and balane system will prvide aurate grss weight and enter f gravity measurements and will assure peratin f helipters at maximum safe lads in the speified enter f gravity envelpe. 46

56 m * >i * * * * 10 * * «* * a 73 a XI X) T3 CO 4-1 * > *-> M 4-> ^ a> t CO CO CO Q ^ s *-> 6 T3 a X) M +-> 4-> 4J S CO CO CO CO CO E-t \ w 2 0 <U ^«, 4-1 CD w H +J CT H Q) i 3' K * * * k 4-> 2 [0 a J«; E IB O -a -a a 73 4-) 4-> *-> CO CO CO CO Ü CO CO Calibi Cm Pa u ^«g "O Ö m J w X) T3 X) X) M M M M 4-> CO CO CO CO CO (U -a -a 4-" M 4-> 4-> CO CO CO CO CO >.? 3 E 'S Ü x> 8 g ra J 5 IM II 0 10 Sens ipter dware Ü ri O Ü»-4 H Ü & K s. -H a 3 r 'S E 10 4-> CO CO CO CO CO s s H) ^ Landin Gear Cnfiq 3 1 a> 4-i > D> ^ «j 4-> T M CO CO CO ge ippli ge ippli «: (N ^r CO CO CO II s r H *- n -S -< Ü ^ Q GröS Weigh Ranqe (lb.) <Tt 00 CO CO T 3 & «^ CO 00 *J w 5 4J ^ CO i w I O M O M. -< H w w a) ^2 ^3 a. 2 ^ sl O * CO <T> r^ Ü t-i T)< -* i-h CO v * t ^^ M 1 K a tv T " 0 > i-h ^p m H X L ll & U Ü af 47 HLH (Carg

57 I x: S QJ M CO <u u JO CQ x: u n 0 OJ u 3 48

58 Sensrs (4 required) / w t 1 /P777/T W i Center f Gravity W, TfZTYTTY Frnt View Side View F - Latin f frward strut D - Distane between frward and aft struts X - Distane frm pint F t enter f gravity Wp, - Weight n frward starbard strut Wp 2 - Weight n frward prt strut Wp - Weight n frward struts = Wp. + Wp. W^, - Weight n aft starbard strut W A 2 - Weight n aft prt strut W A - Weight n aft struts = W Al + W A2 Rear View W T - Ttal weight f airraft + lad = W F + W A Purpse: T determine X distane frm frward strut t enter f gravity S Mments abut pint F = 0 DW A - XW T = 0 Figure 22. Cmputatin f Center f Gravity fr Tw-Skid Landing Gear (as n UH-1). 49

59 & 6700 n 8 Ö Fuselage Statin (inhes frm ref. datum) Figure 23. Center f Gravity Envelpe (UH-1D). 50

60 , - " " "'^ "^ WWPW mmm 'S C m 8 -H b 0 O -H J= C w fl> Tl 0 m -O 1-t P r axle, rt able inputs) withes ehanis w E 1 > a w ndi ad J2 ^ "H S- «1^81 - Ö E CO r <-. :s 1 ^? E in ea ultipi T3 C «1 - S 1 OMPUTER indard (pw luniatr, dard (serve 3 i CO Z w w CO CO Ski g Q Ü a. rion/c L Sts am Stan CALI CON DISP in i a x: IM 6 a> + > 0Q t i 4 G a> 3.-t (M CO ^ m 51

61 Mw- HIHI m i 1^- ' «-- "*,IL mam.> Sensr in eah axle (3 required) W T WZ JP T W, f w, 'Ax "A2 Rear View F - Latin f frward axle D - Distane between frward and aft axles X - Distane frm pint F t enter f gravity W^. Weight n aft starbard wheel W» - Weight n aft prt wheel {f\ *- X is\ ^"^sp 1 Center f Gravity >vnnnn7ttj w t Side View w. W A Wp W T - Ttal weight n aft wheels = W^, + W A - Weight n frward wheel - Ttal weight f airraft + lad = W A + W F Purpse: T determine X distane frm frward strut t enter f gravity Mments abut pint F = 0 DW A -XW T = 0 Figure 25. Cmputatin f Center f Gravity fr Triyle Landing Gear (as n CH-54). 52

62 1 <mm 1 (MW ' *^mmmwv imm^mmmp 43, M I'M i ' < Mi i 11 i r M ' J*J J 1 M 1 ' i 'ill i < i 1 < i 1.1 < 1 11 ' 1 r- ' 1 i i.., i, i i i I 38,000 ^ 33,000 (A 3 O a. 28,000 m 8 ü 23,000 i i Ml, L i i i ' ' ii X' i M/ i / 1 i i ; I ' ' I : r ' I [1 i i ( 1, 1 i 1 U ; i i ' 1 f i 1 j / Mliiii - I'l'ilil T i u / r i i i 1 I 1 '! M! * ' / U, UUU 1 r l t 1 1 I M M \ \ ' ' \\\\\\\'\\\\\\\\\\\ Mi J TA T 1 < M M \ M 1 \ \ N i I n n n i ' \ ). [ [ i IJ i i ^ j ^r^ i I i i l i Lji III i i i I i '! i " ' : i L i i!!! i j i i i rf 18,000 'iit [jiu ii 1 ' n i n 1 ' 1 M ! J 24 Fuselage Statin (inhes frm Ref. Datum) Figure 26. Center f Gravity Envelpe fr CH

63 m mi i i i -. i. ii I X u a e *-> >- w 0Q T3 *J X I t & (1) 3 a 1 PL, 54

64 mmmmmm UMP 1 - Sensr in eah side f _L strut (4 required) Frward F D Sensr fr arg hk (1 required) Sensr Requirements; 7 fr airraft + arg hk W 1_ ^*- x -f Fl W F2 2 ^3^4 r 3 V? X w Fl w F2 W F3 WF 4 W F WAi W A2 W A w T Center f Gravity Frnt View Side View Latin f frward axle Distane between frward and aft struts Sensr n eah aft strut (2 required) Aft W. i ii r w A w Al w A2 Ä1 Rear View Distane frm pint F t enter f gravity Weight n starbard frward utbard wheel Weight n starbard frward inbard wheel Weight n prt frward Inbard wheel Weight n prt frward utbard wheel Ttal weight n frward wheels «Wpj + Wp- + Wp, + Wp 4 Weight n prt aft wheel Weight n starbard aft wheel Ttal weight n aft wheels = W Al + W^- Ttal weight f airraft + lad = W A + W F i Purpse: T determine X distane frm frward strut t enter f gravity 2 Mments abut pint F» 0 DW A - XWp = 0 Figure 28. Cmputatin f Center f Gravity fr Quadriyle Landing Gear (as n CH-47). 55

65 mm in i /. MHHMVMPWMMHEMW Ä IQ 3 a x: a> I* S Ü Fuselage Statin (inhes frm ref. datum) Legend: Current CG Flight Envelpe 5% GW Errr CG Envelpe 10% GW Errr CG Envelpe The urrent flight envelpe fr enter f gravity psitin an be exeeded when manual mputatin is made with the grss weight value in errr by the perentages shwn. Operatin utside the presribed flight envelpe an ause dereased peratinal life f the helipter as a result f the inrease in strutural fatigue. Obviusly, an integral weight and balane system prviding aurate grss weight and enter f gravity measurements an be used t assure peratin f helipters at maximum safe lads in the speified enter f gravity envelpe, prviding ptimum flight trim and therefre maximum flight range r duratin. The abve plt shws mputatins using the CH-47A enter f gravity envelpe as an example. Figure 29. Effet f Errr in Grss Weight n Cmputatin f Center f Gravity Latin. 56.

66 I A majr requirement fr an integral weight and balane system suitable fr Army helipter peratins is the apability t prvide aurate grss weight and enter f gravity readings under the nditins enuntered with the rtr(s) running r at rest. The system remmended herein pssesses this apability in that the grss weight and enter f gravity f the helipter an be determined aurately with the rtr(s) stpped and that these values an be used fr referene in mpensating fr this appreiable errr. (The C-47A at 230 RPM and minimum blade lletive pith f +3 prdues a lift n the rder f 20% t 30% f helipter grss weight. Obviusly, a pratial means f mpensating fr this effet must be prvided.) The envirnment t whih the helipter integral weight and balane system equipment is subjeted in peratin impses imprtant requirements whih must be ammdated in the system and mpnent design. Fr example, the existing lw-frequeny vibratin levels must be taken int aunt in the design f the alibratin/mputer and display pakages, bth In their strutural apabilities and in the signal respnse harateristis prvided t minimize display flutuatin during rtr peratin. The salt water r mud immersin f the landing gear struts must als be ammdated. The remmended system nfiguratin has been previusly shwn in Figure 16. As stated earlier and shwn n the shemati, this system uses single weight and enter f gravity summing amplifiers whih aept signals frm any number f landing gear struts withut regard t the strutural nfiguratin f the struts r t their gemetri relatinship. This system utilizes the serv-driven unter fr grss weight display and the meter mehanism display fr enter f gravity. Obvius advantages are btained in th? use f this hybrid system nfiguratin; namely, the eliminatin f the enter f gravity serv system and the attendant redutin in system mplexity. Lgially, the reliability f the system is enhaned by the eliminatin f the enter f gravity serv mpnents by substitutin f the meter mehanism display fr enter f gravity. Further, st f suh a system is smewhat redued. Referring t Figure 17, the display pakage, the suitability f the meter mehanism displa/ fr enter f gravity is apparent. Graduatins n the sale, shwn in this instane fr the CH-47 Chink, are in terms f inhes (fuselage s+atin). Graduatins are prvided in 2-inh inrements, and, withut questin, an adequate readut reslutin is prvided. Details will als be prvided in this setin n the pith sensr used in the mpensatin f the grss weight and the enter f gravity mputatin with regard t pith angle f the helipter and n the ntrl and arg hk instrumentatin. 57

67 LANDING GEAR STRUT INSTRUMENTATION The varius landing gear strutural nfiguratins desribed in this setin are all instrumented by the defletin sensing devie develped by Natinal Water Lift Cmpany. The defletin sensr (Figure 3 is an ally steel antilever beam instrumented n tw ppsite sides, parallel t its lngitudinal axis, with semindutr type strain gauges and the neessary mpensating elements, prviding stability f null and sale fatr with temperature variatin. This devie has been prdued in quantity and has prven t be reliable in its appliatin t the Air Fre C-130 integral weight and balane system. High signal levels are available (30 mv/o.lo-in. defletin) and prvide a high signal-t-nise rati input t the alibratin/mputer pakage. System auray is thereby imprved as a result f the signal levels available. Figure 30. Defletin Sensr Bar. The sensing tehnique remmended fr use in the integral weight and balane system desribed herein prvides sensitivity slely t applied vertial shear lad. The eletrial utput f the defletin sensr assembly in an axle is a funtin f its gemetry, the setinal prperties f the axle, and the applied vertial shear lad. Other lad inputs t the strut, as previusly shwn in Figures 3 thrugh 7, reslve int rthgnally dispsed mpnents and uples t whih the remmended system is insensitive. The applied vertial shear lading is measured by the defletin sensr assembly as shear displaement and as the vertial mpnent f the bending displaement. It shuld be nted that the relative magnitude f the shear defletin is small when mpared t the vertial mpnent f the bending displaement. The remmended system sensr signal utput is high, sine the sum f signals resulting frm bth defletins is used. Thse systems measuring shear defletin alne are penalized in their lw utput 58

68 Signal level by dependene upn the minr shear defletin. One f the mst mmn landing gear strut strutural nfiguratins is the "T" type shwn in Figures 31 and 32. Instrumentatin f this type f strut requires the measurement f the defletin f bth axles. This is neessitated by the lak f pivting apability t enaule equalizatin f lad distributin n the tw axles. That is, in the extreme ase with ne wheel ver a hle, the ther wheel an supprt the full strut lad. The equipment shwn in Figure 33 typifies the instrumentatin t be emplyed within an axle bre. Tw permanent instrumentatin elements are shwn whih are apable f expansive munting within the axle bre. These devies are psitined lngitudinally, axially, and -tatinally within the bre by means f a simple lating tl fr eah devie. The sensr and its munting devie are lated within the permanently munted adapter in the axle and are srew-adjusted and lked t prvide the prper ntat between the tungsten arbide spherial tip n the defletin sensr and the tungsten arbide surfae n the prelad anvil. The permanene f the instrumentatin munting thus ahieved has been thrughly prven in landing gear labratry drp testing and in atual airraft installatin. Figure 34 depits shematially the installatin f bth defletin sensr assemblies within a "T" type axle strut. A. single-wheel "L" nfiguratin antilever landing gear strut is shwn in Figures 35 and 36. Figure 37 illustrates the Installatin f landing gear axle instrumentatin hardware similar t that shwn in Figure 33 in the "L" type antilever strut. Figure 38 illustrates a single-wheel antilever strut apable f 360 swiveling while supprted by a pair f drag arms and a diagnally munted le strut. An bvius prblem exists in the instrumentatin f an axle with full swiveling apability; that is, it is highly undesirable t arry defletin sensr signals thrugh slip-ring arrangements due t their tendeny t indue a high nise ntent in the signal. With this prblem in mind, anther slutin t the instrumentatin is desirable and is fund in the replaement f the tp ap f the le strut with an assembly nfigured as shwn in Figure 39. This instrumentatin methd prvides a diaphragm that deflets under landing gear lads; it als prvides measurement f this displaement by the defletin sensr shwn. It will be nted that, as the landing gear lads inrease, the sensr prelad defletin is dereased, prteting the defletin sensr frm verlad nditins. This enables the use f the full defletin sensr range fr instrumentatin rather than neessitating a large ver-defletin safety fatr. 59

69 m^mmmmmmmmmmmm nw^h» * - > Figure 31. "T" Cnfiguratin Strut. 60 i ^^^^^H

70 Figure 32. CH-47 Frward Landing Gear Strut Test

71 62

72 mmmmmmm^mt^mmmmmmmmmmk^m'^'m ^i^*mm mmmmmammmmjmm MMMMMMMMM M4 M \ g gfe m^ F^SSSSSS^ Figure 34. "T" Cnfiguratin Strut Instrumentatin Installatin. 63

73 ^ '" '» '. wi [ji laniiotinm 1^1,1 Figure 35. "L" Cnfiguratin Strut. 64

74

75 ^ ^^p^ ppi i IHHII-IW mil - -" zy^^^fe VZZZZZTZf^^Z Figure 37. "L" Cnfiguratin Strut Instrumentatin Installatin. 66

76 i \ Figure 38. "L" Cnfiguratin Strut with Swivel Capability and Ole Strut Supprted Drag Link Suspensin. 67

77

78 -""- II I ^^^^ i»» m w^ww^w^h 4 ^»»t mi m\mmuik tmm*m The larger helipters t be manufatured in the future may well utilize the fur-wheel truk landing gear strut nfiguratin shwn in Figures 40 and 41. In this strutural nfiguratin, the lad is nentrated n the hinge pin between the vertial strut and the lngitudinal truk beam, supprted at either end thrugh the axles, wheels, and tires. This lading prvides a defletin f the lngitudinal beam whih is prprtinal t the vertial lad applied. Instrumentatin f the lngitudinal beam defletin is prvided as shwn in Figure 42 by using the previusly desribed defletin sensr and instrumentatin hardware relatively similar t that shwn in Figure 33, with the exeptin that munting is amplished by mehanially lamping and adhesively augmenting the installatin t the exterir f the beam, as shwn. This instrumentatin tehnique has been prven in test in the setup shwn in Figure 41. i 69

79 ...._....,_, Figure 40. Fur-Wheel Truk Strut. 70

80 71

81 11 i MPW Figure 42. Fur-Wheel Truk Strut Instrumentatin Installatin. 72

82 TERRAIN SLOPE ERROR IN STRUT LOA.D MEASUREMENT The gemetri effet f pith slpe n measured lad is shwn n the illustratin, Figure 43. Vertial Landing Gear W Cs e Terrain W Sin W e W Sin 0 w s e Ttal Strut Lad Terrain Slpe Restraining Fre (as brake r hk) Measured lad Figure 43. Terrain Slpe Errr in Strut Lad Measurement. Helipter rll attitude is stated by peratinal persnnel t be nearly level (±3 ) in field use en slped terrain. Nrmal pith attitude ranges frm level t 10 nse up r nse dwn. Cmpensatin fr sine errr in strut lad measurement whih affets the mputatin f grss weight and enter f gravity will be disussed in the setin entitled "Cmpensatin fr Terrain Slpe Errr In Strut Lad Measurement". 73

83 1 TERRAIN SLOPE ERROR IN CENTER OF GRAVITY READOUT The gemetri effet f pith slpe n mputed apparent enter f gravity psitin is shwn n the illustratin, Figure 44. Vertial Figure 44. Terrain Slpe Errr in Center f Gravity Readut. APPARENT CENTER OF GRAVITY POSITION The distane n the grund that the CG mves as a result f the elevatin h öl the CG and the angle 0 is S = h tan 6 = h e Crretin f the mputatin f CG is made t prvide a reading equivalent t that whih wuld be btained with the helipter in its nminal hrizntal attitude. The mpensatin signal derived frm the pith sensr, as (h 8), is a linear funtin apable f full mpensatin fr this apparent CG psitin hange> S. Implementatin f this rretin is disussed in the setin entitled "Cmpensatin fr Terrain Slpe Errr in Strut Lad Measurement." Apprximatin is made fr the nminal CG height h in the heavily laded nditin where CG auray is mst imprtant. The urve (Figure 45) shws the apparent CG hange haral fisti and illustrates the effet f the departure f the atual CG height frm the predetermined nminal, using the CH-47 as an example. 74

84 X) 2 en $ O Xi t CO s: > s Ü J2 C-X " "T f j \_ r j r / 4 :::: J _ f gq ::: : ti x -i t A, t» m H«hf i n Ti n n fi n Nminal CG Heigh t i \\n-ni) (ru~ai\ -jf SL PCI " iiir - ^ V*.l<w CC neigni lli ah* ittot~ / F y i /t /1 i /1 i : :._2i 'T L«. *!" J g, k ' f ll ' 1 / L 70" "" # r i nf- H* - -- / t i r / 11 ^ C r ^ f / 1 1 tl C.L s A's Apparent CG Psitin Change, S (inhes) Ah 0 = 10 t 9 e.. * 1/2 " (As) fr +3 " CG height errr 1/2 " (As) fr -3 " CG height errr Cnditins: Pith Slpe f 10 Figure 45. Apparent Center f Gravity Psitin Change Vs. Height f Center f Gravity. 75 -t"«i4t'4i

85 tfr^^^r^vmrnmrn COMPENSATION FOR TERRAIN SLOPE ERROR IN STRUT LOAD MEASUREMENT Grss Weight and Center f Gravity Equatins Level Terrain Equatins 2 and 5 define the relatinship between the measured strut fres in the mputatin f grss weight and enter f gravity n level terrain. GW -^ Wn 0- Grss weight equatin. W_ - F - F = 0 (1) W T = F F + F A (2) Center f gravity equatin. Sum mments abut pint "Y" IM Y =O XW T -rf A = 0 (3) (4) (5) 76

86 ^ p- Grss Weight and Center f Gravity Equatins ~ Slped Terrain Equatins 6 thrugh 18 define the relatinship between the measured strut fres and pith angle in the mputatin f grss weight and enter f gravity n nnlevel terrain. sin 6 F A s e Grss weight equatin: (nnlevel terrain) summatin f fres perpendiular t the grund plane. W s 6 = Fp s 0 - F. s 6=0 W T s 9 = (Fp + F A ) s 9 (6) (7) Sine Fp s 9 and F» s 9 are the measured fres, the errr due t slpe 9is ^ A Errr = W T - W^ s 9 = W T (1 - s 9) (8) Therefre, t btain true W T we must mpensate fr the errr due t pith angle 9 as fllws: True Weight = Measured Weight + Errr W,, T = [Fp s 9 + F A s 9] + [W T (1 - s 9)1 (9) 77

87 Center f gravity equatin: (nnlevel terrain) My = 0 XW T s ö + hw T sine-rf A s e = 0 _ = rf^ s 6 _ h tan e w T s e (1 (ID (12) Frm equatin 9, W T s 9 is rreted t W T. Equatin 12 bemes Xs rfft. s 9 W T "" - h tan 9 (13) The errr in enter f gravity resulting frm pith slpe is Errr = X sl p e - X Level rf A s 9 - h tan 9 - WT (14) (15) = _JL. F A (s9 - l)-- h! iw T tan9 (16) r Therefre, t btain true enter f gravity psitin (X), we must mpensate fr the errr due t the pith angle 9 as fllws: True X = Measured X + Errr (17) X = TTA s 9 WT r WT 'T k (s 9-1) - ^ W T tan 9 (18) Mehanizatin f mpensatin fr terrain slpe errr is shwn in Figure

88 Frward Strut Sensr Signals Aft Strut Sensr Signals V\AA^ 1 VW\A Csine Crretin WVSA W Surriming Amplifier Cmpensated ^ Grss Weight Analg Signal Pith Cmpensatr Tangent Crretin Aft Strut Sensr Signals Csine Crretin WW ' CG Summing Amplifier Cmpensated CG "^ Analg Signal Figure 46. Mehanizatin f Cmpensatin fr Terrain Slpe Errr. 79

89 Cmpensatin fr terrain slpe errr is ahieved by using a pith sensr mbined with suitable eletrnis t prvide the required funtins f the measured airraft pith angle. The errr indued in the measurement f strut lad as a funtin f pith attitude is shwn in Figure 11. The measurement errr an be fully mpensated by using a nnlinear (sine) rretin. \ linear apprximatin f the(l - s errr an mpensate fr pith angles up t 10 within 0.25%. CORRECTION TECHNIQUES FOR ROTOR LIFT EFFECT DURING WEIGHT AND BALANCE MEASUREMENT Weight and balane measurements btained during rtr peratin will have large errrs due t lift effet. Lift effet varies as a funtin f rtr speed, yli pith, lletive pith, pressure altitude, and temperature. Crretin fr lift effet an be ahieved by using lift rretin harts, eletrial lift rretin withut density altitude mpensatin, r eletrial lift rretin with density altitude mpensatin. Fr maximum utility, the apprah using eletrial rretin with density altitude mpensatin is preferred. The three lift errr rretin methds are disussed in this setin. Crretin Charts A hart an prvide rtr lift rretin values fr speifi temperature and pressure altitude nditins. These values must be manually added t the grss weight reading btained with the rtr perating frm an Integral weight and balane system withut integral lift rretin apability. The disadvantages f this rretin methd are the need fr manual mputatin and the attendant pssibility f errr r negleting t perfrm the rretin. Table VI illustrates a typial frmat fr this rretin data, using the harateristis f the CH-47A as an example. A hart wuld be prvided fr aretin f errr at eah RPM under whih weighing wuld nrmally take plae. Crretin f measured enter f gravity fr rtr lift effet wuld require a means apable f prviding a fixed yli pith stik lngitudinal ntrl psitin. An annuniatr light an be used t indiate the manual return f the yli pith stik ntrl t a preseleted lngitudinal psitin. This ntrl psitin will mmand a fixed prprtin f lift n the frward and aft struts and will enable mputatin f the apparent enter f gravity psitin. The apparent enter f gravity psitin read n the indiatr must be rreted fr the effet f density altitude by means f a hart similar in frmat t that fr the grss weight rretin. 80

90 w** TABLE VI LITT EFFECT CORRECTION CHART FOR CH-47A GROSS WEIGHT INCREMENTS Rtrs at 230 RPM and +3* Clletive Pith Pressure Temperature C Altitude (ft.) Eletrial Lift Crretin Withut Density Altitude Cmpensatin This methd will fully rret fr rtr lift effet during weighing at the pint f rigin f the missin. The magnitude f this effet fr the CH-47, fr example, is n the rder f 6,000 punds. Variatin in density altitude at the rigin f the missin mpared t that at eah landing area within the missin will prvide errrs in the weight and enter f gravity readings. The gradient f this errr is 187 punds f lift per 1000 ft density altitude fr the CH-47A, as shwn in Figure 47. Crretin f the density altitude errrs an be made if desired by referene t harts similar t thse disussed in the (setin entitled "Crretin Charts." Figure 48 illustrates the appliatin f rretin ptentimeters fr mpensatin f grss weight and enter f gravity readings fr lift effet. Offset signals frm the ptentimeters are fed t the rrespnding summing amplifiers t restre stati grss weight and enter f gravity readings during rtr peratin. The simple adjustment tehnique is desribed in the setin entitled "Eletrial Lift Crretin With Density Altitude Cmpensatin. " The lift rretin swith enables the rretin signal t be applied during rtr peratin (swith in "ON" psitin) r t be remved fr stati weighing (swith in "OFF " psitin). This apprah fr lift rretin prvides a-system with smewhat limited utility. If the helipter missin is perfrmed within an area having a 81

91 8 3 CO III j 1 1 L 4 '! 1 Li - ' 1 i i ' 1 '1 1 1!! I [ UUU r ll l" I I 1 \ A 12003! M ' ' T 1 ' ' \ 1 \\\ i i i! i j j \\\ M 1 1 i l\l i I i i i i 1 \ i 1 " r 11 I '' Vi I! M i! i \ M K \ M L \ L 4000 f " M\ n L pj zuuu! i ' 1 1 i ' tj \ \ J s**«' ' ' \\ t 1 11 I IN Level 1 " " " Hi M \ I - ] ] J'l"] 1 ' III ! G C Lift (punds) Gradient 187 lb /1000 ft. D.A. Cnditins Rtr Speed: 230 RPM 3 Clletive Pith Figure 47. Density Altitude Vs. Lift, CH-47 Helipter. 82

92 r " Frward Strut Sensr Signals v/wv* I Aft Strut Sensr Signals Cmpensated Grss Weight Analg Signal Supply Lift Crretin Swith Grss Weight Lift Crretin Ptentimeter Center f Gravity Lift Crretin Ptentimeter Aft Strut Sensr Signals CG Summing Amplifier Cmpensated CG Analg Signal i Figure 48. Crretin f Lift Effet Withut Density Altitude Cmpensatin (fr weighing during rtr peratin with fixed lletive pith and fixed RPM). 83

93 variatin in density altitude f less than ± 2000 feet, the resulting grss weight errr, in the ase f the CH-47B, is less than ±1% at maximum lad. Eletrial Lift Crretin With Density Altitude Cmpensatin Crretin f the rtr lift effet during weighing an be made t inlude mpensatin fr density altitude variatins frm the rigin f the missin t the subsequent landing sites used. Basi lift rretin ptentimeter adjustments fr grss weight and enter f gravity are made by the pilt at the start f the missin. Data are prvided frm a pressure altitude sensr and a temperature sensr t mpensate fr density altitude hanges. An alternative t the use f the pressure altitude and temperature sensrs exists, sine density altitude data (pressure altitude and utside air temperature) are available frm instruments present in the helipter kpit. These data uld be used in setting individual ptentimeters against graduated sales t mpensate fr density altitude hanges enuntered in the missin. The illustratin f the kpit display and ntrls fr the integral weight and balane system in Figure 49 shws the lift rretin ptentimeter ntrl knbs fr grss weight and enter f gravity rretin, the lift rretin swith, and the lift balane annuniatr (LIFT SAL). The step-by-step predure fr rretin fr rtr lift during grss weight and enter f gravity measurement is shwn in Figure 50. The appliatin f the lift rretin ptentimeters t the system is shwn in Figure 51. CALIBRATION/COMPUTER PACKAGE The alibratin/mputer pakage in the remmended helipter integral weight and balane system is shwn in Figure 52. Its relative size with regard t the indiatr and ntrl pakages is indiated. Figure 53 is an installatin drawing f the alibratin/mputer pakage. Internnetin f this pakage t the ther system mpnents is prvided thrugh a pair f nnetrs n the rear surfae f the unit. Aess t the plug-in mdules ntained within the pakage is gained by remving a single retaining srew and pulling the frnt plate and hassis frm the tubular prtetive ver. Munted n the hassis is a plug-in alibratin ptentimeter mdule whih is remvable fr reinstallatin in a replaement alibratin/mputer pakage. This allws retentin f the alibratin adjustments whih have been made with respet t the harateristis f 84

94 Grss Weight Display Pwer Swith Test Swith f Gravity Display Sensr Signal Cntrl Swith Psitin Annuniatr Lift Balane Annuniatr CG Crretin Ptentimeter Lift Crretin Swith GW Crretin Ptentimeter Figure 49. Ckpit Display and Cntrls fr Integral Weight and Balane System. 85 t, m>mmmwshi

95 (1) Obtain aurate stati grss weight and enter f gravity readings immediately prir t starting rtr with lift r- ^v retin swith in OFF psitin. ^ Ö IQ. 3I[II? 0 0 y^m&ei SO luiilliulmjlllllllllllll 1UÜ Ö [O O] mal TIST k^/ ) [utiskhoj (2) Start rtr, set lletive pith t 3 detent psitin, and set RPM t a fixed value at whih subsequent measurements will be made. Plae lift rretin swith in ON psitin. 1(51 [flllll 300» iliinlimlinll (3) Adjust GW CORRECTION POTENTIOMETER t restre stati GW reading n display. gi [ma li li iliiiiliiliinl By (4) Adjust yli stik lngitudinal ntrl t preseleted psitin annuniated by LIFT BA1 light ON. (5) Adjust CG CORRECTION POTENTIOMETER t restre stati CG reading n display. BILDBlllll 500 A) 320 iw All readings f GW and CG at all landings within the missin until the rtr is stpped are made using the abve lift rretins. Figure 50. Crretin fr Rtr Lift During GW and CG Measurement. 86

96 Frward Strut Sensr Signals VW\A vvxaa Aft Strut Sensr Signals Cmpensated Grss Weight Analg Signal Supply^ Off 'On Lift Crretin Swith Pressure Altitude Sensr (r manual adjustment) V\AAA WW CG Lift Temperature Sensr Crretin (r manual adjustment) Ptentimetir Grss Weight Lift Crretin Ptentimeter f(k/w T ) Aft Strut Sensr Signals 1 vaaa/^ f vwv^ CG Summing Amplifier Cmpensated ^CG Analg Signal Figure 51. Crretin f Lift Effet With Density Altitude Cmpensatin (fr weighing during rtr peratin with fixed lletive pith and fixed RPM). 87

97 I# ss 1 Is? ; s s a> +J >. I- W 7 a) K O «i I 10 CQ t TJ C O 10 "S H> fh 2 > t ^ CO M (M «H PH 88

98 D> U m a. u M 3 a 6 I O CO i n 89..,^lg ^ jha

99 the partiular landing gear strut strutures invlved. Summing amplifiers are prvided n a separate plug-in mdule, as are pwer supply mpnents n the third mdule. Sensr signal ntrl swithes are prvided n the frnt panel f the alibratin/mputer pakage t permit the individual readut f strut sensr signals, as desired, fr test purpses. An additinal apability prvided is that f substituting a dubled signal utput frm a sensr t replae that lst in a failed sensr, if this shuld beme neessary. Thus, at a smewhat redued auray, it is pssible t ntinue with the integral weight and balane system. GROSS WEIGHT AND CENTER OF GRAVITY INDICATOR Display f helipter grss weight and enter f gravity in the remmended integral weight and balane system is prvided n the indiatr shwn in Figures 17, 52 and 54. The pakage emplyed is a standard 3-1/4-inhsquare aernautial instrument ase in ardane with MS This ase allws the Installatin f the integral weight and balane system readut n the helipter instrument panel fr reading by the pilt r pilt prir t takeff r In flight with a lad n the instrumented arg hk. Additinal display pakages an be munted fr remte use. The instrument is internally lighted fr night use. The grss weight serv drives a tw-gang ptentimeter. One ptentimeter is used as the serv fllw-up and the ther is used in the mputatin f enter f gravity fr display n the meter mehanism. The meter mehanism used in this instrument has been designed fr high vibratin envirnment and has a pinter natural frequeny f ver 80 ps. The high trque mehanism is apable f driving rugged mving il bearings whih prvide immunity t vibratin and shk failure. The pinter display prvides exellent stability with vibratin input. Parallax prblems are avided as a result f the pinter perating adjaent t a sale whse urvature is that f the pinter radius. Figure 52 shws that the readability f the display is exellent. The grss weight is read ut in inrements f 100 punds, and the enter f gravity is read ut in inrements f 2 inhes. PITCH COMPENSATOR Cmpensatin f the grss weight and enter f gravity mputatins fr errrs indued by nnlevel pith attitude f the helipter is amplished in the remmended system nfiguratin by using the pith sensr shwn in Figure

100 ' >, SI 6 > w fi Ü «O Q) m * a) a) % O S f ID f ^ CO 0> 91

101 Mta u w x: u in Si 5 92

102 This devie emplys a reed-suspended mass immersed in siline damping fluid in a hermetially sealed pakage. Strain n the reed is instrumented by semindutr strain gauges nneted in a bridge iruit. The eletrial utput f this devie is summed int the input f the grss weight summing amplifier and the enter f gravity indiating meter. The reliability f this devie, having n wearing parts, shuld be exellent under the high vibratin envirnment t be enuntered in helipter appliatins. The pith mpensatr als emplys suitable eletrni iruitry t nvert the pith sensr signal t the required trignmetri funtins f the pith angle. These signals are utilized by summing int the rrespnding grss weight and enter f gravity amplifiers, as shwn in Figure 46. CONTROL The ntrl shwn in Figure 56 failitates the appliatin r remval f system pwer; the mmentary appliatin f self-test; the adjustment, appliatin, r remval f lift effet rretin;the display f lift balane nditin; and the display f sensr ntrl swith psitin. The pwer swith is a "push-n", "push-ff" type. The test swith is f the mmentary type and remves the sensr signal inputs t the grss weight and enter f gravity summing amplifiers and substitutes preset referene vltages. The resultant mputatin f grss weight and enter f gravity is read n the rrespnding displays. The deviatin seen in eah ase is mpared with an allwable reading errr tlerane. An illuminated amber indiatr is prvided n the ntrl t annuniate a nnstandard sensr ntrl swith psitin; that is, if any f the sensr ntrl swithes n the alibratin/mputer pakage is in ther than the psitin dented STD, the indiatr is illuminated. Tw lift rretin adjustment knbs are prvided n the frnt fae f the ntrl. Eah knb an be manually lked in the seleted psitin and ntrls a single turn ptentimeter. The signals frm the ptentimeters are used t rret the grss weight and enter f gravity readings btained with the rtrs running. The lift rretin signals an be applied r remved frm the rrespnding summing amplifier inputs as required fr measurement with the rtrs perating r nnperating. A speifi lngitudinal psitin f the yli pith stik ntrl is indiated by the illuminatin f the LIFT BAL annuniatr. This annuniatr enables the pilt t ahieve a fixed lngitudinal lift vetr diretin t prvide a fixed rati f lift n the frward and aft struts teax

103 SE 'vs):. ^ V '}) LIFT CORRECTION Figure 56. Cntrl Pakage. 94

104 ^ w CARGO HOOK INSTRUMENTATION The arg hk r winh instrumentatin nfiguratin will depend in eah ase upn the detail design f the unit t be instrumented. In general, instiumentatin f a devie f this srt an be amplished either by measuring an existing strutural defletin r by adding a mpnent whse defletin an be measured. The eletrial utput f the defletin sensr is summed int the grss weight hannel f the mputer. Instrumentatin f arg hk lading n the CH-47 is amplished by substitutin f the unit shwn n Figure 57 fr the existing adapter blk whih is urrently part f the arg hk assembly. In this unit, the defletin f the lateral beam under lad is measured using a defletin sensr f the type shwn en Figure 30. A landing gear le mpressin swith applies the arg hk r winh lad sensr signal t the grss weight summing amplifier when the helipter is airbrne. The swith simultaneusly remves all landing gear strut sensr signals and the pith mpensatin rretin signal frm the grss weight summing amplifier. The swith als deativates the enter f gravity display. SYSTEM WEIGHT ESTIMATE This estimate is prvided using the appliatin f the remmended system t the CH-47, Chink, as an example. Quantity per Ship Set TABLE VII SYSTEM WEIGHT ESTIMATE Cmpnent Desriptin 4 Frward Landing Gear Instrumentatin 2 Aft Landing Gear Instrumentatin 1 Display Pakage 1 Calibratin/Cmputer Pakage 1 Cntrl Pakage 1 Pith Cmpensatr 5 Sensr Pwer Supply TOTAL Estimated Weight Estimated Weight per per Cmpnent System Üb.) (lb.) NOTE; The abve estimated weight is exlusive f abling weight

105 Figure 57. Carg Hk Instrumentatin fr CH li

106 POWER REQUIREMENTS System eletrial pwer requirements are AC 115 V, 400 ps, single phase 45 W, pwer fatr DC 28 V (lighting pwer nly) 20W ERROR ANALYSIS Table VIII is an errr analysis using the CH-47 integral weight and balane system as an example. Values are given fr errrs in grss weight and enter f gravity in bth unmpensated and mpensated frm. Errr sures are listed, and the methd f mpensatin fr eah is nted. The resultant integral weight and balane system errr (RSS) shwn fr grss weight and enter f gravity simultaneusly inludes maximum values fr eah errr sure listed and therefre an be assumed t be wrst-ase errr values. Naturally, the magnitude f these errrs will derease fr peratin f the integral weight and balane system under mre nearly nminal nditins. PROGRAM PLAN FOR ADAPTATION OF INTEGRAL WEIGHT AND BALANCE SYSTEM TO ANY ARMY CARGO HELICOPTER The adaptatin f the remmended integral weight and balane system t any Army arg helipter mainly nerns the appliatin f the standard defletin sensr t the strutures t be instrumented. Eah landing gear strut and arg hk r able hist is instrumented by using the tehniques previusly desribed in this reprt. The general predure fr appliatin f an integral weight and balane system t a helipter is shwn in Table DC. A typial prgram plan defining the integral weight and balane system appliatin tasks, their sequene In the prgram, and their duratin is shwn in Table X. 97

107 1 T3 O ^ a 1 2 E OZS Kin«) Oi ö,0 ffl Ü j= C i; Ü 3 O 3 fe «T3 C C (V O (D 0 C Q. I * ^H «-«p C (u (O ^ u in tn >- C si -' Q. ta _ a.2-«a x «a 2 «w V "» 2 a E ia O CO i e 8 3 (V x> a S E C 9) ' C -. i ei O 4-> u E t (U t < (ü U) w C U.2 «E a ID E X E X V) O a. 2j d in -' C ^> Ö H -^ ^ in E - 0 «O w 2 >- ^ s CM "O d ( 1 10 > -H *-» 8 10 a, ' 10 Oi t i i d a» O SI.13 Ul in -1 XI t FH ^^ a t *-» 2 ja X) tn 10 Ö 0 3 ^ 4 a? tt tt a tt I/) CO Ü 2 -S.U) n 8«in tm a«4 in a«cm J3 y ^3 ^4 10 (U i 2 i 2 Is S 2 CM a t x p --4 U \ a * 2- tm,5 8«in t > ^^ 4-t i 5 ^ 10 I, T3 t i XI "a a 10 4-» 2 ja t ^^ a a t 4-t O 2 ja a t 4-» 0 2 a«m O u 3 0 w M 2 & > *-» t U 'I 4-» -"4 x; a S. 4-> -, S Ä 8 Si t ^4 01 C 8 Ul a A^ C 4-».a > >- Ü E O O 0 W H. 1? i 5 5 S U i 4-> IM 0 5 g to -4 C E 10 > 3 01 W -4 *-?> - C 4-* " u 0> 3 O ui C Ü s O 'T 10 in "-i g M E s «10» «2 «u.s O i JH O VI C <u CO -a ^ 01 a 4-. Q. ^ 3 i -s a i in O till l 8 98

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110 Unlassified Seurity CI«i«in«Un DOCUMENT CONTROL DATA -R&D (Smeurity Uaatltmtin t tltlm, bdy l mbilrml mnd Indexing annljffn mull b9 mntmnd mhmn Ihm vmrmll rmprl la tl*»9lll*ä) 1- ORIGINATING ACTIVITV (Ciprmf authr) Instrumentatin & Cntrl Operatins Natinal Water Lift C. Divisin 3000 Kraft Ave.,S.E..Grand Rapids, Mih REPORT TITLI u. nk^nt tunity CLA» FICATION Unlassified Ik. GROUP Design Analysis f Integral Weight and Balane System fr Army Carg Helipters «. DCtRiRTivi Hrt» (Typ* l npri mnd Inlulw dmi) Final Reprt t. AuTHOMIlifnniiwM, mimi Inlllml, Imlnmm) Stuart L. Varner * RCPORT DATE T«. TOTAL NO. OF RAGC«109 August 1967 a. CONTRACT OR GRANT NO. DA AMC-451{T)». PROJECT NO. E OltTRISUTION STATEMENT Distributin f this dument is unlimited., OTHER REPORT NOI«l (AUT I M» lprt) USAAVIABS Reprt ' km Hfnd 11. tponsorlng MILITARY ACTIVITV Department f the Army U.S.Army Aviatin Materiel Labratries Frt Euatis. Viraim? Thts study vered an analysis f helipter peratinal usage affeting the design, installatin, and peratin f an integral weight and balane system fr Army arg helipters urrently in existene with thse yet in the planning stage. An analysis f existing Integral weight and balane systems and the appliability t helipter usage was als perfrmed. A. remmended general system nfiguratin Is disussed as the utme f the previusly amplished analysis. Prblems Invlving aurate measurement f the grss weight and enter f gravity with rtr(s) in peratin are disussed with the slutin. The appliatin f an integral weight and balane system t Army arg helipters appears t be entirely feasible. DD., (»LACS«DO PC rj473 KS I I JIM M, «NICN If Unlassified Emlir CES3l

111 Unl l!^. laasiriatlfi KKY WORD! Integral Weight and Balane System (IWBS) On-Bard Weight and Balane System Grss Weight Center f Gravity Rtr Lift Effet Density Altitude Terrain Slpe Landing Gear Lad Instrumentatin Pith Angle Instrumentatin Carg Hk Instrumentatin Weight and Center f Gravity Display Defletin Sensing Strain Gage Calibratin Cmputer Summing Amplifier Serv Amplifier Side Lad Fre Vertial Lad Fre Drag Lad Fre Srub Turn Fre Ole Strut»OLl «T HOL««T ROLE WT Unlassified " itraritr Oatalflatla 6g33-«7