CH-53E EMERGENCY FLOTATION SYSTEM DESIGN STUDY

LEVNADC-79256-60

CH-53E EMERGENCY FLOTATION SYSTEM

DESIGN STUDY

BY

KNUTE C. HANSENTHOMAS H. LAWRENCE

SIKORSKY AIRCRAFTDIVISION OF UNITED TECHNOLOGIES CORPORATION

STRATFORD, CONNECTICUT

JULY 1981

CONTRACT N62269-80-C0210

DISTRIBUTION UNLIMITED

PREPARED FOR AT

NAVAL AIR DEVELOPMENT CENTER \ r ,

WARMINSTER, PA 18974

S817 21 ui9I-

NOT ICES

REPORT NUMBERING SYSTEM - The numbering ef technical project reports issued by theNaval Air Development Center is arranged for specific identification purposes. Eachnumber consists of the Center acronym, the calendar year in which the number wasassigned, the sequence number of the report within the specific calendar year, andthe official 2-digit correspondence code of the Command Office or the FunctionalDirectorate responsible for the report. For example: Report No. NADC-78015-20indicate: the fifteenth Center report for the year 1978, and prepared by the SystemsDirectorate.. The numerical codes are as follows:

CODE OFFICE OR DIRECTORATE

00 Commander, Naval Air Development Center01 Technical Director, Naval Air Development Center02 Comptroller10 Directorate Command Projects20 Systems Directorate30 Sensors & Avionics Technology Directorate40 Communication & Navigation Technology Directorateso Software Comp'iter Directorate60 Aircraft & Crew Systems Technology Directorate70 Planning Assessment Resources80 Engineering Support Group

PRODUCT ENDORSEMENT - The discussion or instructions concerning commercial produc*.sherein do not constitute an endorsement by the Government nor do they convey orimply the license or right to use such products.

APPROVED BY: DATE:

-VR WOODSR USN

UNITED North Main S-eet

TECHNOLOGIES S:tatford ocnrc.nrc' u6602SIKORSKY (203) 386-4000

AIRCRAFT

July 15,1981 SEL-5954

Comnander Nawl Air Development CenterWarminster, Pennsylvania 18974Attention: Code 6054(HD)

Via Naval Plant Representative Office, Stratford, Connecticut

Subject: Submittal of Final Technical ReDo:-t, CH-53E Emergency Flotation SystemDesign Study

ReferenLe: (a) Contract V52269-80-C-0210, Contract Data Requirements List DDForm 1423 Sequence Number A003

Enclos-ire: (1) Final Technical Report "CH-53E Emergency Flotation SystemOesign Study", NADC-79256-60 (SER-13452)

(2) Annotated Preliminary Technical Report "CH-53E Emergency Flot-ation System Design Study" SER-13452

Enclosure (1) is suomitted in accordance with Reference (a). Enclosure (1)

incorporates the corrections and comments suggested in Enclosure (2).

Very truly yu,;rs,

• UNITED TECHNOLOGIES CORPORATION

K.C. HansenSIKORSKY AIRCRAFT DIVISION

"KCH : sr

CC: NADC 8131 (3)DDC (12)

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I REPOR2-NImBER 2 GOVT ACCESSION No. 3 IRE( IPIENT*S CATALOG NUMB8R

NADC+79256-6ý J,~~A'. .i 6 1004 TITLE (and S;,btIlle) 5 TYPU OF REPORT 6 P.RIOD COVERED

K" ) CH-53E Emergency Flotation System j Final eport.%Design Study ... 5 PERFORMING ORG. REPORT NUMBER

_ _ _ _ _ _ _ _ _ SER-I 3452.,7 AUTOR) "- 8 CONTRACT OR GRANT NUMBER(@)

Hansen, K. and Lawrence, T. 0. 1 N62269-80-C -J

9 PERFORMING ORGANIZATION NAME AND ADDRESS -0 PROGRAM ELEMENT. PROJECT, TASKAREA 6 WORK UNIT NUMBERS

Sikorsky Aircraft Div. United Technologies Corp.N. Hain St. .. irtas W11090000Stratford, Conn. 06602 k -ii

11 CONTROLLING OFFICE NAME AND ADDRESS 12 REPORT DATE -

Naval Air Development Center 6/10/81_ "iWV _ I-. _ _.Warminster, PA 18974 13 NUMBEROF PAG..5

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Appproved for Public Release; Distribution Unlimited r

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18 SUPPLEMENTARY NOTES

19 K EY WORDS (Continue on reverse arde If necessary mid tden.tly by block n: .nber)

CapsizeFlotation/Stability SystemH-53 Hel iropter(H-53 tlel icopter

0Z ABST 4Cv' (Conirnue on reveres side If necessary end Identify by block number)

Auxiliary flotation and stability systems were studied for use on CH-53Ehelicopters. Inflatable bags were found to offer the capability to evacuatea full complement of troops from a flooded cabin in sea state 5. Logistics,wei-iht and performance penalties were estimated. A description of the 1/10Froude scaled model concurrently built for wave tank testing is included.

DD I °J.ANm73 1473 E.DITION OF I NOV 65 IS OBSOLETE A1, §•9.'.S N 0102-L r -.0 4-660'

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UNITEDTECHNOLOGIES"SIKORSKY NADC-79256-60AIRCRAFT

1.0 SUMMARY

4A study has been conducted to design an auxiliary flotation/stability:.ystem for the CH-53E helicopter which will keep the aircraft uprightand ifloat (with the cabin flooded) long enough to allow the evacu-ation of a full complement of combat troops. Configurations weremade to be compatible with the proposed MH-53E helicopter and MCMequipment as well. The study showed that inflatable flotation bagsprovided the best design solution. Three such systems were designed"in detail, one each for sea states 2, 4, and 5. Increasing systemcapability from sea state 2 to 5 results in only a slight increasein cost. the final systems should have acceptable reliability andmaintainability characteristics, minimal impact on performance, andonly rause a small weight penalty.

In addition, a 1/10 Froude scaled model of the CH-53E and the auxi-liary flotation systems has been designed and constructed. Thismodel will be provided to the U.S. Navy for hydrodynamic testing.

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UNITEDTECHNOLOGIESSIKORSKY NADC-79256-60

FORWARD

This report presents results of a design study of an auxiliary flotation/stability system for the CH-53E helicopter. The program technical directionwas provided Naval Air Development Center, Warminster, Pennsylvania, under thedirection of Harold Dewhirst. Funds for this effort were provided by the NavalAir Systems Command AIR-340B Office.

The following Sikorsky employees made technical cointributions to this report:

I Mr. Edmond Kiely Model Design

Mr. Thomas Lawton Model Design

Mr. Carmen Perruzzi Flotation System Design

Mr. Graham Willoughby Flotation System Design

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TABLE OF CONTENTS

SECTION PAGE

1.0 SUMMARY

FORWARD i

2.0 INTRODUCTION2.1 Background2.2 Study Outline

3.0 FLOTATION SYSTEM REQUIREMENTS 3

3.1 Review of CH-53 Accidents on Water3.2 CH-53E Basic Hydrodynamic Characteristics3.3 Rotor Decay Characteristics

4.0 CONCEPTUAL DESIGNS 10

4.1 Concepts Investigated4.2 Results

5.0 PRELIMINARY DESIGN STUDY 12

5.1 Design Philosophy5.2 Calculation of Righting Moment5.3 Background5.4 System Description

6.0 DESIGN TRADE-OFF STUDY 19

6.1 System Reliability and Maintainability6.2 Reliability and Maintainability Attributes6.3 System Weight6.4 System Drag6.5 System Cost6.6 Final System Selection

7.0 DETAIL DESIGN 24

7.1 Physical Description7.2 Performance Decrements7.3 Maintenance Requirements7.4 Approximate Cost Comparisons7.5 Alternate System Design

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TABLE OF CONTENTS

SECTION PAGE

8.0 SCALE MODEL DESCRIPTION 30

8.1 Model Description8.2 Model Characteristics8.3 MH-53E Simulation

9.0 CONCLUSIONS 34

10.0 RECOMMENDATIONS 35

11.0 REFERENCES 36

12.0 TABLES 37

13.0 FIGURES 52

14.0 APPENDIX A - Review of CH-53A/D Accidents On Water 90

14.1 Accident Data

14.2 Summary of Findings

14.3 Design Guide Lines

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LIST OF TABLES

TABLE NO. DESCRIPTION PAGE

I CH-53E Buoyancy Characteristics Without Cabin Flooding 37

II CH-53E Buoyancy Characteristics With Cabin Flooding 38

Iii CH-53E Rolling Moment Parameter 39

IV Hydrostatic Wind Moment Requirement 40

V Basic Characteristics of Candidate Floats 41

VI Basic Characteristics of Candidate Systems 42

VII Normalized Reliability and Maintainability Ratings 43

VIII Relative System Initial and Life Cycle Costs 44

IX Final System Design - Float Characteristics 45

X Final System Design - Buoyancy Summary 46

XI Final System Design - Summary of Stability 47Characteristics

XII Final System Design - Inflation Systems Summary 48

XIII Final System Desigp - Cost Estimates 49

XIV Comparison of Systems One and Seven 50

XV Scale Model Characteristics 51

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LIST OF FIGURES

FIGURE NO. DESCRIPTION FAGE

1 CH-53E Reference Coordinates 52

2 CH-53E Buoyancy Characteristics 53

3 CH-53E Roll about WL 2.97m. (117 in.) 54

4 CH-53E Righting Moment Calculation 55

5 CH-53E Gross Righting Moment without Cabin 56Flooding

6 CH-53E Gyoss Righting Moment with Cabin 57Flooding

7 CH-53A Sea State Capability 58

8 CH-53E Hydrostatic Wind Requirements vs. 59Sea State

9 CH-53E Net Righting Moment for Roll about 60WL 2.46m. (97 in.)



12 CH-53E Net Rightipg Moment for Roll about 63WL 3.26m. (127 in.)


14 CH-53E Maximum Righting Moment vs. Waterline 65

of Roll Axis

15 CH-53E Rotor RPM Decay Time History 66

16 Auxiliary Flotation System Number One - 67Sea State 5

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LIST OF FIGURES (Cont'd.)

FIGURE NO. DESCRIPTION PAGE

17 Auxiliary Flotation System Number Two - 68Sea State 5

18 Auxiliary Flotation System Number Three - 69Sea State 5

19 Auxiliary Flotation System Number Four - 70Sea State 4

20 Auxiliary Flotation System Number Five - 71Sea State 4

21 Auxiliary Flotation System Number Six - 72Sea State 2

22 System One Hydrodynamic Capability with 73Cabin Flooding

23 System Two Hydrodynamic Capability with 74Cabin Flooding

24 System Three Hydrodynamic Capability with 75Cabin Flooding

25 System Four Hydrodynamic Capability with 76Cabin Flooding

26 System Five Hydrodynamic Capability with 77Cabin Flooding

27 System Six Hydrodynamic Capability with 78Cabin Flooding

28 System One (Sea State 5) Detailed Three-View 79Drawing

29 System Four (Sea State 4) Detailed Three-Viow 80Drawing

30 System Six (Sea State 2) Detailed Three-Vi° 81Drawing

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LIST OF FIGURES (Cont'd.)

FIGURE NO. DESCRIPTION PAGE

31 Alternate Float Configuration for Aircraft 82with AN/ALE-2 Dispenser

32 CH-53E Model - Profile View 83

33 CH-53E Model - Plan View 84

34 CH-53E Model - Door Details 85

35 CH-53E Model - Rotor Head Details 86

36 CH-53E Model - Counterweight System 87

37 CH-53E Model - Float Details, Installation 88

38 CH-53E Model - Float Details, Construction 89

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2.0 INTRODUCTION

2.1 Background

The Sikorsky CH-53E helicopter will provide the U.S. Navy and MarineCorps with a highly capable and versatile platform for performing thefollowing missions:

Long Range DeploymentVertical ReDlenishmentSearch and RescueTroop and Equipment DeploymentEquipment and Aircraft RecoveryAmphibious Operations SupportShip-to-Shore Cargo TransportVertical-On-Board-DeliveryAirborne Mine Countermeasures

In the performance of these missions, the aircraft spends a largeportion of its time operating over water and, therefore, may besubject to emergency water landings.

The CH-53E was designed to be ditchable and stable in water condi-tions up to Sea State 2. This capability was based on the assumptionthat the cabin remained watertight and provided both buoyancy andstability. In addition, there are sealed volumes under the cabin andcockpit ("tubs") and fuel cells in the sponsons which also providebuoyancy and stability.

Since some of the ab3ve missions require operation at low altitudeswith the personnel door open and/or the cargo ramp down, it may beimpossible to secure the aircraft prior to an emergency water land-ing. In addition, the single-point suspension hatch in the center ofthe cabin may be open, or the cockpit glazing may be shat !red bywater impact upon landing. Any of these eventualities can ead tothe cabin becoming flooded. In this event, the remaining sealedvolumes cannot provide sufficient buoyancy and the aircraft willsink.The U.S. Navy has requested that Sikorsky Aircraft conduct a designstudy to find ways for improving CH-53E sea keeping capabilities

following an emergency water landing. The specific guidelines were:

1. Define systems for maintaining the CH-53E upright and afloatlong enough for the successful evacuation of a full troopcomplement.

2. Systems for performing this task in sea states 2, 4, and 5 withthe cabin flooded should be evaluated.

3. Systems are only required to keep aircraft afloat long enoughfor successful personnel evacuation. However, systems whichwould keep the aircraft afloat long enough to allow recovery aredesirable.

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4. Systems should be practical for the aircraft's operationalenvironment and have minimal impact or aircraft performance.

"5. Systems should be compatible with the proposed M}H-53E heli-copter.

6. Sikorsky shall design and construct a scale model of the CH-53Eand proposed flotation systems for use in towing tank tests.The U. S. Navy will conduct the tests.

The reque-ed study has been completed and is documented in thisreport.

2.2 Study Outline

The study was conducted in five phases, discussed below:

Phase I - Flotation System Requirements (Section 3.0)

This phase involved a review of CH-53A/D water accidents, a deter-mination of basic CH-53E hydrodynamic characteristics with andwithout cabin flooding, and a delineation of the additional buoyancyand stability required to meet study guidelines.

Phase II - Conceptual Design Studies (Section 4.0)

A wide array of systems for improving buoyancy and stability wereinvestigated. This resulted in a decision to use conventionalinflatable auxiliary flotation bags to provide a~ditional buoyancyand stability.

Phase III - Pceliminary Design Study (Section 5.0)

This phase was conducted to define the basic characteristics ofsystems using flotation bags which would meet the study guidelines.

Phase IV - Trade-Off Study (Section 6.0)

In this phase, the preliminary designs were evaluated with respect toreliability and maintainability, weight, drag, and cost. Threesystems were selected as best, one for each sea state.

Phase V - Detailed Design (Section 7.0)

The three selected systems from Phase IV were designed in more detailand system characteristics more precisely defined.

In addition to the analytical studies above, a 1/10 Froude-scaledmodel of the CH-53E was designed and constructed for use in Navytowing tank tests. (Section 8.0)

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3.0 FLOTATION SYSTEM REQUIREMENTS

The flotation system requirements were determined in the followingway. First, CH-53A/D water accidents were reviewed since the CH-53Eis a derivative of these earlier aircraft and has the same fuselagebut larger sponsons. These data were used to derive design guidelines for flotation/stability systems. Next, the inherent buoyancyand stability characteristics of the baseline CH-53E were deter-mined, for cases with and without cabin flooding. These hydrodynamiccharacteristics were then used to determine the additional require-ments for se. states 2, 4, and 5. Finally, the decay in main rotorRPM and control power following an autorotative landing was analyzed.These data were used to determine the time available for systemactuation.

3.1 Review of CH-53 Accidents On Water

The accident data compiled in this report and presented in Appendix Awas obtained from the Naval Safety Center, Norfolk, Va. Thisappendix contains all the Navy/Marine CH-53 accidents occurring onthe water in the time period May 1968 to June 1979.

As a result of the findings of this study of CH-53 Na y/Marinehelicopter accidents, the following design guide lines were estab-lished relative to the design criteria for stability and flotation ofCH-53E.

DESIGN GUIDE LINES

A helicopter flotation/stability system design shall accomplish thefollowing:

1. Accommodate the full range of aircraft weight and center-of-gravity locations.

2. Accommodate the full range of anticipated aircraft configura-tions. Closures, such as doors, windows, hatches, etc. that maybe opened in flight shall not be considered closed in emergencyor accident situations.

3. Keep the aircraft upright in sea state 3 (3 to 5 foot waves)with winds to 30 knots, and keep the aircraft afloat for a timesufficient for the evacuation of a full complement of crew andpassengers in these conditions.

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3.2 CH-53E Basic Hydrodynamic Characteristics

Hydrodynamic characteristics of the CH-53.- were determine( with thecabin both sealed and flooded. The baseline aircraft moieled was aCH-53E in troop transport configuration with external auxiliary fueltanks jettisoned and a full load of internal fuel. This correspondsto a gross weight of 24,444 kg (53,889 lb.) and a center-of-gravitylocation of fuselage station (FS) 9.06m. (356.7 in.), waterline (WL)4.19m. (165.1 in.) and buttline (BL) 0.048m. (1.9 in.). All buoyancyand stability calculations assume fresh water density of 1000 Kg/mr(1.94 slug/ft ). Buoyancy and righting moment were calculated withthe aircraft level in the water and submerged to various depths. Thenose landing gear and main landing gear wells were assumed to beflooded.

Buoyancy

The aircraft has four major sources of buoyancy:

1. A sealed tub under the cab.n t1iuor

2. A sealed tub under the cockpit floor

3. The sponsons

4. The cabin itself

The buoyancy of each of these volumes was calculated for the aircraftlevel in the water and submerged to depths corresponding to WL's2.46m. (97 in.), 2.72m. (107 in.), 2.97m. (117 in.), 3.26 m. (127in.), and 3.48 m. (137 in.) as shown in Figure 1.

Two configurations were evaluated. First, the cabin was assumed tobe watertight as intended in the original design. This large cabinvolume contributes significantly to overall buoyancy. In the secondconfiguration, the cabin was assumed to be flooded. This situationcould arise if the aircraft entered the water with the cargo rampdown, personnel door open or the single-point access hatch uncovered,for example. It should be noted tLat numerous openings exist betweenthe inside of the cabin and the tub under the cockpit; therefore, thenose tub was assumed to be flooded any time the cabin was flooded.

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The external auxiliary fuel tanks were not included in the buoyancycalculation since they are normally jettisoned prior to an emergencylanding. In addition, the tanks and their supporting pylons are notdesigned for water impact loads and would probably be damaged duringan emergency water landing.

The results of the buoyancy calculations are presented in Figure 2and tabulated in Tables I and II. Note that adequate buoyancy willexist if the cabin is watertight and the aircraft will float at WL2.92m. (15 in.). If the cabin is flooded, the only sealed volumesavailable are the cabin tub and the sponsons. These provide a totalbuoyancy of 13,271 kg (29,258 lb.), which is inadequate to maintainflotation and the helicopter will sink.

Therefore, a minimum of 11,172 kg (24,631 lb.) of buoyancy must beprovided by the auxiliary flotation system to maintain the aircraftafloat.

Hydrodynamic Stability

The roll direction is critical for the CH-53 due to the location ofdisplaced volumes at shorter moment arms than those which are avail-able in pitch. For that reason, hydrodynamic stability is assessedby investigating the aircraft's roll characteristics.

A semi-emperical method of analysis developed by Sikorsky Aircraftwas used to evaluate the hydrodynamic roll stability of the CH-53Eand to define the requirements for the auxiliary flotation system.This method of analysis is based on hydrodynamic model test data ofthe CH-53A aircraft. This analysis requires knowing the rightingmoment, the lateral imbalance, and hydrostatic wind capability of theaircraft. The details of the analysis are discussed below.

Basic Stability Characteristics

The CH-53E righting moment was determined as a function of rollangle. The aircraft was assumed to be level in the water at the samedepth increments used in the buoyancy calculations. At each depth,the aircraft was rolled to angles of 3, 6, 9, 12, 15, and 18 degrees,as shown for a typical case in Figure 3. At each depth and rollangle, the gross righting moment was determined by calculating therolling moments due to the various submerged volumes and to theaircraft's mass at its center-of-gravity as indicated in Figure 4.Two configurations were investigated, one with the cabin sealed, theother with the cabin and nose tub flooded. The results are shown inFigure 5 and 6, respectively.

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Without flooding, the CH-53E is inherently stable when submerged to

waterline 2.72 m. (107 in.) and 2.97 m. (117 in.). The instabilityat waterline 2.46 m. (97 in.) is due to the large weight moment sincethe center-of-gravity is so far above the roll axis. The instabilityat waterlines 3.26 m. (127 in.) and 3.48 m. (137 in.), is due to thecomplete submergence of the downside sponson. With the sponsoncompletely submerged, increases in righting moment are not producedas roll angle increases. The only stabilizing forces available comefrom the cabin volume and the effect of rolling the upside sponsonout of the water.

With the cabin flooded, Figure 6, the aircraft is unstable for alldepths investigated.

The curves of Figure 5 and 6 represent the gross righting momentavailable. Two other effects are normally present. One is thelateral center-of-gravity offset of .048 m. (1.9 in.) inherent in theaircraft design and is due to the asymmetry of the tail rotor, engineconfiguration, and auxiliary equipment. This lateral offset reducesthe gross righting moment by 11,568 N-m (8532 ftlb.). The secondeffect normally present with an articulated rotor is the lateraloffset of the rotor center-of-gravity due to the blade lead-lagdegree-of-freedom. The CH-53E lag dampers are preloaded to hold theblades against their lead stops when the rotor is stopped. With allthe blades against their lead stops, the lateral imbalance due tolead-lag is zero. Thus, the net righting moment is equal to the grossrighting moment less the moment due to the lateral center-of-gravityoff-et. This moment represents the true capability of the aircraft.

Analytical Methodology

The method of analysis used to evaluate the sea state capability ofthe CH-53E is shown in Figure 7, which is a plot of wave heightversus wind velocity. The curve denoted "CH-53A capability" isreproduced from the CH-53A hydrodynamic report SER-50296, Reference1, and shows combinations of wave height and wind velocity that theaircraft can sustain without capsizing. The shape of the CH-53Acurve was developed from test results obtained from a 1/20th scalemodel test performed at the Davidson Laboratory of Stevens Instituteof Technology. In this test, an artificial roll moment was placed onthe model ind wave height was varied until a capsize occurred. Thisprocess was repeated until the roll moment was just equal to themaximum righting moment available. (i.e., the point at which theaircraft would capsize without any waves.)

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Each artificial roll moment could be related to a side wind velocitywhich would produce that moment. The maximum righting moment theaircraft can generate can be equated to a maximum side wind cap-ability. This is defined as the hydrostatic wind capability.

For the CH-53A, Figure 7 shows that the aircraft could withstand awave height of 2.2 meters without any wind or a side wind of 20meters/second without any waves, so its hydrostatic wind capabilityis 20 meters/second. To relate this capability to real sea stateconditions where wind and waves act together, a standard sea statecurve is also shown on Figure 7. Its intersection with the CH-53Acapability line defines the CH-53A's sea keeping qualities. In thiscase, the intersection corresponds to a wave height of 1.65 meters(5.4 feet) and a wind velocity of 9 meters/second (1.75 knots),representing a lower sea state 4 capability.

In order to evaluate the effects of different configurations orflotation systems, the maximum available righting moment is det-ermined. This is then equated to a hydrostatic wind capabilityderived from conventional aerodynamic calculations. The resultingwind velocity is then plotted on a graph like Figure 7. A lineparallel to the original curve is then drawn on the graph. Itsintersection with the standard sea state curve then defines the seastate capability of that configuration.

Determination of Required Capabilities

The hydrostatic wind capability is defined as the maximum side windthe aircraft can withstand without capsizing in calm water. Thehydrostatic wind capability is determined by calculating the windmoment that is equal to the maximum net righting moment, using thefollowing equation:

MW = l12/OA CD Se I (Vw) 2

Where:

Mw = wind moment, N-m (ft-lbs)

,= air density, 1.225 Kg/ 3 (.002378 Slug/ft )A m

CD = drag coefficient

S e= equivalent b oadside area abovee waterline, m (ft )

= moment arm from fuselage center-of-pressureto reference waterline m (ft)

V = wind velocity, m/sec (ft/sec)w


Normally, the term CD S e is lumped together as a rolling moment

parameter, L/q, m3 (ft 3 ). When multiplied by the dynamic pressure,

"1/2/0 A (Vw) 2 , it yields the wind moment. The values of L/q for tht

CH-53E at the various depths investigated are presented in Table III.

The total net righting moment (fuselage plus auxiliary flotationdevices) required for sea states 2, 3, 4, and 5 were determined usingFigure 8. A line was drawn from the sea state scale to the standardsea state line, and from this point, a line parallel to the CH-53Acapability line was drawn until it intersected the wind velocityaxis. This intersection point is the wind velocity the CH-53E mustbe designed to withstand to achieve a given level of sea statestability. The corresponding wind moment, Mw, and wind velocity aregiven in Table IV for sea states two, three, four, and five. Forexample, the aircraft must be able to withstand a side wind of 19.6m/sec (38.2 knots) f it is to have a Sea State Three capability. Ifthe aircraft is submerged to WL 2.72 m. (117 in.), the rightingmoment that must be provided is:

MREQD 1/2 /OA (19.6)2 (L/q)WL 2.72

1/ 2 /<A (19.6)2 (123.38)

"MREQD = 29,031, N-M (21,412 ft-lbs)

Thus, the basic aircraft, plus the auxiliary flotation system, musttogether generate a maximum righting moment of 29,031 N-m if theaircraft is to be stable in Sea State Three when floating at WL2.72 m. (117 in.).

The CH-53E stability requirements are summarized in Figures 9 to 13.These figures show the net righting moment versus roll angle for eachdepth increment studied along with the maximum righting momentrequired for various sea states. The most stable case shown is withthe cabin unflooded and the aircraft at WL 2.72 m. (117 in.). Forthis condition the aircraft is stable to Sea State Two. To increaseits capability to Sea State Five, an additional righting moment of99,000 N-m (73018 ft-lb) is required without cabin flooding and126,400 N-m (93228 ft-lb) with the cabin flooded and rolled to 12degrees.

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The peak righting moment without cabin flooding for each WL ispresented in Figure 14. As can be seen when the CH-53E is submergedto WL 2.92 m. (115 in.) which provides neutral buoyancy at a GrossWeight of 2444 Kg (53889 lb.), the aircraft has an inherent Sea StateTwo capability. Thus, even without cabin flooding an additionalrighting moment is required to obtain Sea State Three and abovecapability.

3.3 Rotor Decay Characteristics

One important design feature of any flotation/stability system iswhether or not it is deployed before the water landing. If deployedbefore, it must withstand water impact loads which can be verysevere. If deployed after the landing, the question arises as to howlong the deployment can or should be delayed.

The basic seriario envisioned in this study involves an emergency,autorotative landing on the water. To keep the system weight reason-able, it was decided that any system considered would be deployedafter the landing. In addition, an emergency landing from lowaltitude may not allow time for deployment of the flotation/ stabi-lity system.

After an autorotative landing, the pilot can still control theaircraft with cyclic inputs as long as the rotor RPM is reasonablyhigh; say 70% or higher. The decay of rotor RPM following an auto-rotative flare was determined from CH-53E flight test data.

The decay of rotor speed is shown in Figure 15 with the main rotorcollective at its low position, 10%, following a full engine cut. Ascan be seen, it will take approximately ten seconds for the rotorspeed to decay from 100% to 71% which is the rotor speed where therotor control power will be reduced in half. If the rotor speed isat 90%, which is the approximate rotor speed following an autorota-tive flare, it will take approximately six secoids for the rotor toslow to 71%. Thus, the deployment of the flotation/stability systemshould take less than six seconds.

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SIKORSKY NADC-79256-60AIRCRAFT

4.0 CONCEPTUAL DESIGNS

The traditional method for adding buoyancy and hydrodynamic stabilityto a helicopter is use of auxiliary inflatable flotation bags. Thistechnique has been applied very successfully by both Sikorsky (S-58,S-61, S-62, S-76, SH-60B) and other helicopter manufacturers. Duringthe initial phases of this study, it became clear tnat the inflatablefloats required to support and stabilize the CH-53E in sea state 5would be very large. Therefore, while the detailed hydrodynamiccharacteristics of Section 3.0 were being calculated, a conceptualdesign study was undertaken to determine if there were any otherpractical approaches for providing emergency flotation.

Concepts Investigated

In addition to preliminary layout and sizing of auxiliary flotationbags, a number of other concepts were investigated. These included:

1) Extenda•b'le Weight - This system would have a weight on the endof a folding or telescoping boom. The boom would be lower-ed/extended below the aircraft to lower the center-of-gravityand provide a stabilizing moment and damping.

2) Boom Floats - This concept envisioned the use of small, in-flatable floats on the ends of folding booms. In use, the boomswould fold out from the fuselage and the floats would inflate tocreate stabilizing outriggers. Some attention was paid tohaving the inflation of the floats act to deploy the boom also,so that a separate extension mechanism would not be required.

3) Dagger Boards - Another scheme investigated was the use ofdagger boards on the sponsons to ?rovide stability and damping.

4) Component Ejection - This system would employ pyrotechniccharges to sever the main rotor blades and tail pylon from theaircraft. Technology verified during the design of the RotorSystems Research Aircraft (RSRA) would be used to insure ade-quate reliability. Such a system would significantly reduce theweight of the aircraft, reduce the side area exposed to thewind, and lower the center-of-gravity.

In addition to the schemes outlined above, various combinations ofthese schemes, with and without inflatable floats, were also evalu-ated.

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UNIEDTECHNOLOGIESSIKORSKY NADC-79256-60AIRCRAFT

4.2 Results

As the buoyancy and hydrodynamic stability data in Section 3.0 wasaccumulated, it became obvious that any emergency flotation system

•i would have to, first of all, provide a significant amount of buoy-

ancy, on the order of 10,000 kg (22,000 Ib) or 10 cubic meters (350cubic feet) of displaced volume. This is obviously best done withinflatable floats. Further calculations showed that once floats ofsufficient size to provide the required buoyancy were utilized on theaircraft, the hydrodynamic stability requirements could be achievedby making relatively small increments in the float sizes.

In addition, the schemes proposed above all had some common dis-advantages. These were:

1) They all required some form of mechanization. This would haveincreased maintenance relative to inflatable floats which areessentially passive. In addition, a very real question ofreliability arises with folding/telescoping joints and actuatorsthat sit quiescently for long times in a salt water environment.

2) All of the conceptual systems above would probably involve asignificant weigh' penalty compared to inflatable floats.

3) Inflatable floats are a technology with well established designcriteria, known material characteristics, and proven operationalreliability. The other systems were not, and in some casesmight carry significant devclopmental risk.

Therefore, at the end of the conceptual design study, it was clearthat conventional inflatable flotation bags offered the best solutionfor CH-53E emergency flotation.

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5.0 PRELIMINARY DESIGN STUDY

As indicated in Section 4.0, the result of the conceptual designstudy was a decision to utilize conventional inflatable flotationbags to provide the required buoyancy and stability for the CH-53E.Eight configurations were laid out initially, but two proved to beuaacceptable. Preliminary design of the remaining six systems wascompleted. The results of this effort are discussed below.

5.1 Design Philosophy

The following design philosophy was adopted for all of the auxiliaryflotati n systems:

1) Each system would provide adequate buoyancy and stability forthe given sea state conditions with the cabin and nose tubflooded.

2) Each system would provide a three degree nose-up trim pitchattitude. This increases the clearance between the rotor planeand the water since the aircraft has a five degree forward shafttilt.

3) Each system would provide the required stability and neutralbuoyancy when the aircraft was submerged -o WL 2.97 m. (117 in.)at FS 8.64 m. (340 in.) (except for System Three which hadneutral buoyancy at WL 2.90 m. (114 in.) at FS 8.64 m.). Thisgeometry will submerge the person in the most aft trooD seat upto his or her waist, thus allowing for easy egress eitherforward or aft.

4) Multicompartment floats with check valves would be used toincrease system safety. In the event one compartment wasdamaged, the other compartment(s) would not deflate. Systemswould be designed to maintain buoyancy but have reduced stabi-lity for any single compartment failure.

5) Each system would have an inflation time of four seconds. Thisis practical if helium is used, but would require very largelines if nitrogen is used as the inflating medium.

6) Each system was designed to be compatible with the proposedMHI-53E helicopter featuring "enlarged sponsons". Floats, floatstowage, and inflation systems were all located so as not tointerfere with MCM equipment.

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5.2 Calculation of Righting Moment

The righting moment characteristic of each system was calculated

assuming the aircraft rolled about its trim waterline. The effect ofthe aircraft settling in the water to maintain neutral buoyancy wasalso explicitly modeled. Note that as the airciaft rolls, thebuoyancy from the tub and sponson decreases and the floats mustsettle further into the water to maintain neutral buoyancy. Thissettling reduces their righting moment capability. In calculatingthe righting moment of each system a fresh water density of 1000

3 3kg/mi (1.94 slugs/ft ) was used and it was assumed the floats wereonly 75% effective to account for the deformation of the float as itis submerged.

5.3 Background

The auxiliary flotation systems were designed to meet the buoyancyand stability requirements outlined in Section 3.0. Three configura-tions were designed for sea state 5, two for sea state 4 and one forsea state 2. These are shown in Figures 16 to 21.

In addition to these six float configurations, two other conceptswere evaluated and discarded. The first configuration consisted oftwo large floats, one on each sponson. To obtain the desired stabi-lity and buoyancy the floats had to be longer than the sponsons. Thestructure outboard of the wheel wells is in,,dequate to support thesefloats and would require a great deal of structural modification.Thus, there was inadequate structure available to attach the floatsalong their entire length. Due to this lack of support, the ends ofthe floats would deflect up when submerged and they would becomeineffective.

The other configuration utilized three floats. In this 'ase the nosefloat was wrapped around the cockpit of the aircraft. The other twofloats were located aft of the sponson in a manner similar to thoseshown in configuration one, Figure 16. This configuration wasrejected due to lack of load bearing structure on the cockpit. Ifthe plexiglass shattered, the bag could become torn and buoyancywould be lost. Therefore, both of these designs were eliminated fromfurther study.

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1 AIRCRAFT

5.4 System Description

General

Each float is inflated with helium from its own separate fiber glassbottle and i: designed to operate at pressures between 8.62 kPa (1.25PSIG) and 2#.l kPa (3.5 PSIG). Helium is used as the inflatingmedium to allow for a four second inflation time (derived from thetime of six seconds for rotor RPM decay from 90 to 70 percent). Thefloats used in all systems except six have multi-compartments. Aninflation line runs from each bottle to a manifold. Lines run fromthe manifold to each compartment in the float. Check valves will belocated either in the float or the manifold for each compartment. Inthe event a compartment becomes damaged the check valves will preventthe other compartmeuts from becoming defla.ed. A nozzle in the checkvalve is designed to choke the flow during inflation, so that if acompartment is damaged prior to inflation, all the gas will notescape out through the damaged compartment, but will be available toinflate the other compartments. Inflation bottles, plumbing andfloats for all systems are designed to be compatible with the plannedMCM equipment and enlarged sponsons of the MH-53E helicopter.

The preliminary design results are summarized in Tables V ard VI.Table V gives the float characteristics for each system, includingnumber of float-, float size, and number of compartments. The systemcharacteristics ace given in Table VI, including system weight,buoyancy, inflation bottle number and size, and line sizes.

The specific characteristics of each system are discussed below.

System One

System One is a four float configuration designed to provide seastate 5 stability. The general arrangement is shown in Figure 16 andthe righting moment characteristics in Figure 22.

The four floats are disposed two forward and two aft, one on eachside of the fuselage. All floats are cylindrical with a diameter of1.83 m. (6.0 ft). The forward floats are 2.13 m (7.0 ft.) long whilethe aft ones are slightly longer at 2.65 m (8.7 ft). Each of theflotation bags is divided into three separate compartments viavertical diaphragms.

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Assuming the float volume and buoyancy to be 75 percelnt of thenominal value (in order to account for distortion), system oneprovides an additional buoyancy of 18,867 kg (41,595 lbs.) and givesthe aircraft a total righting moment capability of 70,900 N-m (52,293ft-lbs) at a twelve degree roll angle. This system brings the totalavailable aircraft buoyancy (cabin flooded) up to 3z,395 Kg (71,419ibs) and provides stability to Sea State 5.

The aircraft will float with a three degree nose-up attitude and witha one degree roll to port. This roll is due to the lateral center-of-gravity offset. From a failure standpoint, the aft port float isthe most critical. With a failure of one compartment in this float,the total available buoyancy (aircraft plus floats) is reducedslightly to 29,254 kg (64,493 lbs.), but the righting moment cap-ability is reduced to around 10,000 N-m (7,376 ft-lbs), giving alimiting sea state of 2. This failure would also increase the portroll from one degree to five degrees.

The nose floats are stored within the electronics compartment door.

This requires a new fiber glass door with a bump to accommodate thefloats and modifications to the hinges and latches so that they canreact the float loads.

The aft floats are stowed internally in fuselage compartments between

FS 13.3 m. (522 in.) and 13.8 m. (545 in.). The fuselage wouldrequire structural modifications in the form of cut-outs and doublersin the affected areas, while the floats would be contained in fiberglass boxes.

System Two

System Two is a four float configuration, also designed to providesea state 5 stability. In this case, two floats are mounted amid-ship, one on each sponsori, and two are mounted aft on the tail boom.The general layout is shown in Figure 17 and the righting momentcapability in Figure 23.

All floats are cylindrical. The sponson floats are 1.54 m. (5.05 ft)in diameter and 5.33 m. (17.5 ft) long with five compartments each.The aft floats are 1.19 m. (3.9 ft) in diameter and 1.62 m. (5.3 ft)long and contain two compartments each.

System Two provides an additional buoyancy of 17,589 Kg (38,777

lbs.), bringng the total aircraft capability (caoin flooded) up to31,117 Kg (68,601 lbs.). The righting moment capability of theaircraft with this system is 69,100 N-m (50,966 ft-lbs) at a rollangle of 11 degrees, giving a sea state 5 capability.

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With the critical sponson compartment damaged, the buoyant capabilityof the aircraft is reduced slightly to 29,254 kg (64,494 lbs.) whilethe maximum righting moment available is reduced to less than 1000N-m (738 ft-lbs.).

The sponson floats are housed in soft covers on the outside of eachsponso.=. in a manner similar to the SH-3A/D/H packaging. Two ex-ternal doublers will be added to the bottom of the sponson to reactfloat loads. In addition, the fairing on the leading edge of thesponson would be modified to accommodate the inflation bottles.

The aft floats are attached to the tail cone and protected with

breakaway fiber glass covers. External doublers would be added to

react the float loads. The inflation bottles for the aft floatswould also be located in the tail cone and appropriate access panelswould be provided.

System Three

System Three is a six float configuration, also designed to providestability in sea state 5. The general arrangement is shown in Figure18 and the righting moment characteristics in Figure 24. There arefour fuselage floats, two forward and two aft, mouited in the samemanner as the floats in System One. There are a so two sponsonfloats, one on the outboard portion of each sponson as in System Two.Again, all floats are cy]indrical with the forward and aft floatshaving a diameter of 1.71 m. (5.6 ft) and lengths of 2.19 m. (7.2 ft)and 2.71 m. (8.9 ft), respectively. The sponson floats are 1.07 m.(3.5 ft) in diameter and 2.68 m. (8.8 ft) long. The fuselage floatshave four compartments each, while the sponsons floats only have twoeact..

System Three floats have a total buoyancy of 20,453 kg (45,090 lbs.),l-inging to total aircraft capability (cabin flooded) up to 33,980 kg,14, 9 14 lb.). The addition of these six bags results in a maximumrighting moment of 103,500 N-m (76,338 ft-lbs) being generated at aroll angle of 12k degrees. This gives the system a substantial seastate 5 capability.

With the critical sponson compartment failed, buoyancy is reduced to32,824 kg (72,365 lbs.) and the maximum righting moment available is78,700 N-m (58,046 ft-lbs.), retaining the sea state 5 capability.

Attachment, stowage, and structural modifications required for thefore and aft floats are tae same as those for System One. Thesponson float st(wage and structural modification requirements arethe same as those for the sponson floats of System Tvo.

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UNITEDTECHNOLOGIE-3SIKORSKY NADC-79256-60AIRCRAFT

System Four

System Four is a four float configuration designed for sea state 4.

It is esentially identical to System One except that the flotationbags and their inflation bottles have been reduced in size to reflectthe lower requirements of Sea State 4. Bag attachment, stowage, andrequired structural modifications are essentially the same as thoseof System One. Figure 19 shows the general arrangement of thisconfiguration while its righting moment curve is presented in Figure25.

The floats all have a diameter of 1.71 m. (5.6 ft). The forward bagsare 2.19 m. (7.2 ft) long, the aft 2.71 m. (8.9 ft,), All bags aredivided into four compai.tments. Total bag buoyancy is 16,854 kg(37,157 lbs.), creating a total aircraft capability of 30,380 kg(66,977 lbs.). The system can generate a maximum righting moment of37,500 N-m (27,659 ft-Lbs.) when rolled nine degrees.

With a compartment in the critical aft port float deflated, thebuoyancy is reduced to 30,123 kg (66,410 lbs.) and the rightingmoment capability is less than 2,000 N-m (1475 ft-lbs.), yieldingonly sea state I stability.

System Five

System Five is a four float configuration for Sea State 4 and isessentially a duplicate of System Two except that the inflatable bagsand their inflation bottles have been reduced in size to reflect thelower requirements. Bag attachment, stowage, and required structuralmodifications are essentially the same as System Two. The layout isshown in Figure 20 and the righting moment curve in Figure 26.

The sponson floats are 1.49 m. (4.9 ft) in diameter and 5.18 m. (17.0ft.) long. They are divided into seven compartments each rather thanfive as in System Two. This increase was necessary to providepositive buoyancy and stability with one sponson compartment flooded.The tail bags are 1.19 m. (3.9 ft.) in diameter and 1.62 m. (5.3 ft.)long, with two compartmaents each. Total buoyancy, aircraft plus bags(cabin flooded) is 29,845 kg (65,797 lbs.), of which the floatscontribute 16,316 kg (35,971 lbs.). The aircraft generates itsmaximum righting moment of 45,000 N-m (33,190 ft-lbs) at a roll angleof ten degrees.

If the critical port sponson compartment fails, buoyancy is reducedto 28,710 kg (63,294 lbs.) and righting moment capability is reducedto around 4500 N-m (3319 ft-lbs). This gives stability only for seastate 1 conditions.

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System Six

System Six is essentially a duplicate of Systems One and Four exceptthat the floats and inflation bottles were sized for sea state 2capability. Bag attachment, stowage, and required structural modi-fications are nominally the same as those for System One. A generalarrangement drawing is provided as Figure 21, while the rightingmoment characteristics are plotted in Figure 27. Note that themaximum righting moment of 21,000 N-m (15,488 ft-lbs) occurs at eightdegrees, and would nominally provide a sea state 3 capability.However, experience and cests indicate that the roll angles aregenerally higher than this; so, the righting moment at 12 degrees ofroll (11,000 N-m (81)3 ft-lbs)) was used to establish a sea state 2capability.

The fore and aft floats are 1.74 m. (5.7 ft.) in diameter and havelengths of 2.01 m. (6.6 ft.) and 2.41 m. (7.9 ft.), respectively.Each float has only one compartment. If they had been designed toprovide positive stability with one compartment failed, this wouldhave required either a large number of compartments or floats largeenough to have a sea state capability greater than 2 with all com-partments inflated.

System Six can generate a buoyant force of 15,726 kg (34,670 lbs.)and increases the total available buoyancy to 29,254 kg (64,494 lb.),cabin flooded. With one aft float deflated, total system buoyancy isreduced to 24,976 kg (55,062 lbs). This is sufficient to float theaircraft modeled in this study, which has a gross weight it 24,444 kg(53,889 lbs.). However, with the aft float deflated, the aircraft isunstable and will roll over.

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UNITEDTECHNOLOGIESSIKORSKY NADC-79256-60ARRAFT

6.0 DESIGN TRADE-OFF STUDY

The design trade-off study was performed to select one configurationfor the upper and mid sea states from those developed in the pre-liminary design phase. Sikorsky's MINICOMP Comparative Life CycleCost Model was used to perform this trade-off study. System reli-ability, maintainability, weight, drag and cost were used as thetrade-off variables. The results are discussed below. Note thatSystem Six was the only system designed for sea state 2, so notrade-off study was required. For completeness, however, theattributes of that system have been provided along with those of theother five candidates.

6.1 System Reliability and Maintainability

The following Reliability and Maintainability (R&M) attributes wereevaluated for the trade-off study of the six flotation systems:

1. Failure Rate

2. Unscheduled maintenance manhours

3. Scheduled inspection time

4. Deployment Reliability

Float deployment failure

Rollover incidence

Sinking incidence

The results of the analysis are presented in Table VII. From an R&Mstandpoint, the configurations employing four fuselage floats(Systems One, Four and Six) were preferred.

Failure rate, unscheduled maintenance manhours and scheduled in-spection time were extrapolated from predicted values for the SH-60Bemergency flotation system, based primarily on relative size andcomplexity factors. The following assumptions were made:

1. The arming and firing circuits have levels ofreliability and redundancy equivalent to the SH-60Band are identical for all six system concepts.

2. The gas bottles, squibs and associated circuitry areindependent in each system and of equal reliability.

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UNITEDTECHNOLOGIESSASIKORSKY NADC-79256-60SAIRCAFT

3. Installation of and accessibility to system componentswould be generally equivalent to that of the SH-6OB.

The R&M attributes for each system are discussed in detail below.

6.2 Reliability and Maintainability Attributes

Systems One, Four, and Six

It is estimated that systems one, four and six will have R&Mcharacteristics slightly better than the other four float configur-ations (systems two and five) and substantially better than the sixfloat configuration (system three), Although systems one, four, andsix have a higher probability of a rollover incident in the event ofa system malfunction, they have sufficient buoyancy with any onefloat deflated to keep the aircraft afloat versus systems two andfive which will allow the aircraft to sink (cabin flooded) if one ofthe sponson floats fails to deploy.

Systems Two and Five

Systems two and five are estimated to have slightly poorer R&Mcharacteristics than systems one, four and six due primarily to thegreater exposure to damage associated with the soft-covered, extern-ally mounted floats. The sponson floats will be particularly vul-nerable to impact damage when the aircraft lands in unprepared areasand during ground handling. Daily inspections would be required toexamine for damage to the covers; if damage were found, it wouldprobably be necessary to unpack and inspect the float for tears andpunctures, a time-consuming procedure.

Systems two and five also suffer the disadvantage of requiring theexternal fuel tanks to be jettisoned before deploying the sponsonfloats. They also suffer a significant disadvantage versus the otherconcepts in that failure to deploy either one of the two sponsonfloats will cause the aircraft to overturn and sink. Even without amalfunction of the flotation system, aircraft stability could bedegraded if one of the two external fuel tanks fail to jettison,causing asymmetrical buoyancy.

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System Three

System Three, the only six-float configuration, is estimated to havesignificantly worse R&M characteristics than any of the other fivesystem concepts. It incorporates the soft-covered, externallymounted sponson floats and the increased maintenance they willrequire. Because of its complexity, system three has a greaterprobability of malfunction. Its one advantage is if any of the sixfloats fails to deploy, it will not roll over, although its stabilitywould be decreased.

6.3 System Weight

The weight of each system is given in Table VI. Systems two and fiveare the lightest with the next lightest solution being the four floatconfigurations mounted on the fuselage (systems one, four and six).Most of the weight increase for the four float fuselage system is dueto structural modification and new electronics bay door required formounting the floats internally in the aircraft. Mounting the floatsinside improves the reliability and reduces the maintenance re-quirements for each system. As would be expected the heaviest systemis the six float configuration of system three.

6.4 System Drag

The estimated drag of each system is presented in Table VI. As canbe seen, the drag increments are small an4 would have a negligibleeffect on aircraft performance. The aft fuselage mounted floats arestowed internally and do not contribute any drag. The sponson floatscontribute to the drag since their soft packaging extends outside theoriginal sponson contours. rhe nose floats are packaged inside theelectronics bay doors. These doors are "bumped out" to accommodatethe floats, and therefore contribute a slight drag penalty.

6.5 System Cost

The relative cost factor of each system is presented in Table VIII.The relative cost factor is based on a preliminary estimate of eachsystem normalized by system one. The recurring cost factor includesthe cost of modifying each aircraft, tooling, maintenance, receivingand transfer inspection of each aircraft and materials required forthe installation of the float system. Engineering design, qualifica-tion ground and flight testing, trial installation, materials andfloat design is included in the non-recurring cost estimate.

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Comparative Initial Costs

Configurations two and five, the four float configuration withsponson floats, have a slightly lower recurring and non-recurringcost factor than the other four float configurations, systems one andfour. It should be noted both four float configurations for seastate 4 have a higher non-recurring cost factor than their counter-parts designed for sea state 5. This is due to the greater com-plexity of thcse systems because a larger number float compartmentsis required to provide stability with one compartment failed. Therecurring cost factor for sea state 4 is lower than the counterpartdesigned for sea state 5 due to smaller size floats.

Due to its complexity the six float configuration, system three, hasthe highest cost factor. System six has the lowest cost factor dueto its simplicity. However, system six dces not provide stabilitywith one float failed. If this capability were to be provided,system six floats would require a large number of compartments andthe cost factor would increase.

Comparative Life Cycle Costs

The comparative life cycle cost factor for each system is also givenin Table VIII. The reliability, maintainability, weight, drag andcost of each system previously discussed were included in the lifecycle cost analysis. This analysis was based on thirty aircraft. Aswould be expected the life cycle cost factor of system six is thelowest and system three is the .ighest. The life cycle cost factorof system two and five is lower than the comparable four floatsystems one and four.

One important point to be noted is that a reduction in designed seastate capability results in only a small reduction in life cyclecosts.

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6.6 Final System Selection

Even though systems two and five have a slightly lower life cyclecost factor than systems one and four, the four fuselage float systemone and four were selected for the final design phase of this study.This selection was based primarily on the improved safetycharacteristics of these two systems. With the floats mountedinternally in the fuselage they are protected from ground handlingand damage during water landings. In addition, the external aux-iliary fuel tanks will not interfere or damage the floats duringtheir inflation if they are not jettisoned prior to landing. Thesesystems will also be compatible with the enlarged sponsons beingproposed for the CH-53E without modification to the sponson design ormodification to the float tooling. Also, as previously discussed, afloat deployment failure will result in the aircraft rolling invertedbut staying afloat with systems one and four. In systems two andfive, float deployment failure will cause the aircraft to overturnand sink.

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7.0 DETAIL DESIGN

The trade-off study resulted in the selection of systems one, four,and six for design sea state conditions of 5, 4 and 2 respectively.These systems all have the same basic layout, utilizing two floatsforward and two aft. The float size and number of compartmentswithin each float vary with each system.

This section provides a description of the detail features of thethree systems, including physical characteristics, performancedecrements, maintenance requirements, and approximate cost. Onemajor change between these systems and the preliminary designs wasthe addition of auxiliary support tubes between the floats and theaircraft fuselage. These tubes distribute the float loads to main-tain the bearing stresses on the fuselage structure at acceptablelevels.

Three views of the final systems are given in Figures 28, 29, and 30.System characteristics and specifications are summarized in TablesIX, X, XI, and NMI.

An alternative system which would allow the installation of theAN/ALE-29 Chaff Dispunser and have the same capabilities as systemone is also discussed in this section. This configuration has beendesignated as system seven and is shown in Figure 31.

7.1 Physical Description

Geometry

As previously mentioned, all three systems utilize the same basicfour float configuration. The forward floats are mounted on eachside of the nose, directly under the cockpit. The aft floats aremounted on each side of thE fuselage, just aft of the sponsons. Thedetailed float characteristics are given in Table IX.

Packaging

Both forward and aft floats are housed internally in the aircraft.The nose floats are stored within the electronics bay compartmentdoor. This requires a new five-ply fiber glass door with an externalblister and a modification to the latching system and hinges to reactthe loads produced by the floats. A four-ply fiber glass breakawaydoor cover provides protection for the floats from the elements andpossible damage during ground handling. The door cover is attachedto each float by a lanyard to retain it following inflation.

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The aft floats are packaged in a five-ply fiber glass box approxi-mately 50.8 x 102 x 15.2 cm (20 x 40 x 6 in.) with a four-ply fiberglass cover. Both box and cover utilize strux stiffeners. The coveris attached to the float by a lanyard to allow its recovery followinginflation. These aft ,loat compartments are installed in a 50.8 x102 cm (20 x 40 ii.) cutout between frames at FS 13.26m (522 in.) andFS 13.83m (544.5 in.). An intercostal is added between the framesfrom FS 12.75m (502 in.) to FS 14.40m (567 in.). The lower longeronand the frames at FS 13.26m (522 in.) and FS 13.83m (545.5 in.) wouldbe strengthened to react float loads. In addition, doublers would beadded around the cutouts, A drain line on the port side of theaircraft and an electrical line on the starboard side would have to

be rerouted.

Materials

The floats would be constructed of rip-stop urathane-coated-nylon0.0406cm (0.016 in.) thick. Additional layers of material areprovided in areas where abrasion resistance are required, such asaround the opening of the float compartments and where the forwardfloats would contact the rear view mirrors on the MH-53E version.

Auxiliary Support Tubes

Auxiliary support tubes were added to the upper inboard side of allfloats to distribute the float loads more evenly and thereby maintainthe bearing stresses on the fuselage at acceptable levels. Theseauxiliary tubes are 76 cm (30 in.) in diameter and the same length astheir parent float. As a by-product, the presence of these tubeswill help the floats to maintain their shape as they are submerged.

Inflation System

Each float is inflated with helium from its own separate fiberglassbottle and designed to operate at pressures between 8.62 kPa (1.25PSI) and 24.1 kPa (3.5 PSI). Each inflation bottle is cylindricaland made of wound fiber glass for improved ballistic tolerance. Eachbottle assembly contains a bottle, pressure gauge, relief valve,inflation valve, electrically actuated squib for rupturing a dia-phragm to release the inflation gas, and a port which is connected toa line running to a manifold. The manifold has separate lines toeach floa- compartment. As discussed previously, each compartmenthas a check valve to retain pressure if one of the other compartmentsburst. In addition, the check valve incorporates an orifice to chokethe flow during inflation so that a failed compartment will not allowall of the "aflating gas to escape.

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The squibs are wired to a control panel in the cockpit. This controlpanel would be similar to that used on the SEAHAWK (SH-60B) andincorporate a guarded arming switch, a firing switch, and a test4• circuit.

Buoyancy and Stability

Buoyancy and stability characteristics of the final systems are

summarized in Tables X and XI. As can be seen, all systems provideexcess buoyancy, even with the critical compartment failed. A

I• comparison of Tables VI and IX shows that the total buoyancy of each

system has been increased due to the presence of the auxiliarysupport tubes.

The hydrodynamic stability characteristics of the final systems arethe same as those used in the preliminary design. Figures 22, 25, and27. The effect of the auxiliary support tubes on stability have notbeen considered for conservatism. Systens one and four have areduced sea state capability with the critical compartment failed.System six does not have any capability with a failure, since pro-viding that feature would have required either a large number ofcompartments per float, or floats with a sea state capability greaterthan the design value of two. Recall that all these stabilitycharacteristics are for cases with the cabin flooded.

7.2 Performance Decrements

The aircraft's performance is effected by both the increases inweight and in drag due to having the flotation systems installed.

Effect of Drag

The small parasite drag increase of 0.056m2 (0.6 ft 2) will bave anegligible effect on performance. At the best range speed of 241km/hr (130 kts), the increase in power required is only 1.49 kw (2HP) and this is equivalent to only 0.45 kg (I lb) of fuel over a 278km (150 rim) range mission. This increase in drag will not reduce themaximum speed capability of the CH-53E at its design gross weightsince this value is determined by structural limits, not powerlimits.

26


Effect of Weight

The increase in weight due to the flotation system is more signi-ficant. Under power limiting hovering conditions payload or fuelwill be reduced by an amount equal to the weight change if Lheaircraft is required to hover at a fixed altitude. Alternatively, ifthe hovering altitude capability is of importance, the higher grossweight will reduce the hover ceiling by approximately 79-131m(260-430 ft) depending on ambient conditions. The effect of weighton mission range depends, again, on the type of mission. For amission at a fixed maximum Takeoff Gross Weight (T.O.G.W.) ccndition,the equivalent fuel reduction to allow for the flotation systemweight would reduce a 278 km (150 nm) range by approximately 23.2 km(12.5 nm). For a 278 km (i,0 ruii) range mission at a TOGW less thanthe maximum, the range would be reduced by approximately 0.83 km(0.45 nm) or the fuel for the same range would increase by 5.4 kg (12lb.).

7.3 Maintenance Requirements

The following maintenance effort will be required to provide reliableservice from each system:

1) Each day a walk-around inspection of the float compartmentsshould be made to determine if they nave been damaged. If thereis da..age to the compartment the float should be examined

farther and replaced if necessary. The helium pressure level ineach bottle should be checked daily and if necessary they shouldbe recharged.

2) Every 180 days a functional check of the system is required.the floats should be deployed and checked for leaks. Repairsshould be made to the floats if required. The floats will thenbe deflated, lusted with talc and repacked until the nextfunctional inspection. At this time system lines and hosesshould be checked for wear, leakage and security of attachment.

The manifold, fittings, bottles and pressure gage should bechecked for cracks and corrosion and necessary repairs should beperformed at this time.

3) Every three years the squib will be required to be replaced.

The type of maintenance that can be performed at the organizational,intermediate, and depot levels are listed below:

27

L


Organizational Level

o Remove and replace inflation bottle and valves

o Remove and rep.ace the manifold

o Remove and rep.ace the float assembly

o Remove and replace lines and hoses

o Remove and replace flotation system control panel

o Remove and replace pneumatic valve

o Remove and replace pressure gage

o Fault isolate the control and indicating system

4. o Perform minor repairs to the flotation system control4 panel.

,I Intermediate Level

FT• o Repack and stow the float assembly

0 Repair the float assembly

o Fault isolate the flotation system control panel

0 Repair the flotation system control panel

o Perform functional test of the flotation control panel

Depot Level

0 Repair the inflation bottles and valve assembly

28


7.4 A ppropriate Cost Compariso, of Systems

An approximate cost comparison based on 1961 dollars for developing,procuring and inbtalling each system is presented in Table X1I1. As•an be seen there is lixtle diffprence in the cost of developing,procuring and installing each system. The largest savings in pro-curing cost exists between system four and six (sea state 4 ind 2requirements) due to the smaller size floats and simplicity of systen'six. Based on this cost estimate it is concluded there is littlesavings in total bysteiii Lt-aL beLween sea state requirements for themulticompartment system. If multicompartment requirement is elimin-ated, there is a moderate reduction in the cost of the system.

[1 7.5 Alternate System Design

During the detail design phase of this study an Engineering ChangeProposal (ECP) was received from the U.S. Navy, Reference 2, to1j incorporate a chaff dispenser in the CH-53E. The location selectedfor the chaff dispenser is just aft of the main sponson. This isprecisely where the aft floats for the three final configurations arelocated. It is beyond the scope of this contract to incorporate thechaff dispenser in this study. However, the effects on performance,

relative cost and reliability of moving the aft floats of system onefurther aft and mounting them externally on the side oi the aircraftwere examined.

The alternate locatiLi for the rear floats is shown in Figure 31, andthis configuration is designated System Seven. The total buoyancy

and hydrodynamic stability of this system will remain essentially thesame as system one. Mounting the rear floats -xternally will saveweight but the drag of the system will increase slightly. Therelative recurring cost will be less due to the reduction in toolingrequired for the installation of the aft floats, but their externalmounting will increase failure rate and unscheduled maintenancerequirements. The effect of this increase will be to balance thelower non-recurring cost of this system so that tae relative lifecycle cost of system one and seven are essentially the same.

The survivability characteristics of system one and seven are thesame. If one float does not deploy the aircraft will roll over butwill not sink.

A comparison of sysLemns one and seven is provided in Table XIV.

29


RCRAFT

b.0 SCALE MODEL DESCRIPTION

A 1/10 Froude-scaled model of the CH-53E helicopter has been con-structed to allow an evaluation of the hydrodynamic characteristicsof the aircraft with the three flotation systems selected by thisstudy. Figure 32 shows a profile view of the model, while a top viewis shown in Figure 33. The model was constructed primarily fromfiber glass and balsa wood and incorporates a number of features

which will allow for comprehensive hydrodynamic testing. Thesefpatures are:

1) A significant effort was made to scale the weights of each ofthe major components (fuselage, empennage, tail pylon, main andtail rotor, landing gear and floats) to those of their fullscale counterparts. This not only guaranteed that the totalmodel weight would be correct, but that the model center-of-gravity and moments-of-inertia would also be scaled properly.

2) The personnel door, cargo ramp, and upper cargo door may beopened or sealed to allow evaluation of the aircraft with thecabin sealed or flooded.

3) The rotor blades are represented with the correct number,radius, and static droop. This insures that the effect of rotorcontact with the water is correctly simulated.

4) Detachable floats for all three systems selected by the designstudy are available. Both forward and aft floats for SystemsOne and Four have removable compartments so that the effect of

E single compartment failures can be studied.

5) Provision for instrumentation (e.g., pitch and roll gyre) hasbeen made on an upper deck which should be out of the water and

V- is conveniently accessible.

6) A counterweight system is mounted in the cabin and allows forvariations in gross weight, center-of-gravity location, andmoments-of-inertia.

7) The landing gear may be fixed in the down position or removed tosimulate pear up landings.

The model has been designed to be impervious to water. Access to theinstrumentation and counterweights is provided through an accesspanel in the top of the fuselage. A detailed description of themodel is provided below.

30

"" E -- - .t- - - - - - 1 / " *" -

UNITEDTECHNOLOGIES

SIKORSKY NADC-79256-60

8.1 Model Description

Fuselage and Sponsons

The fuselage shell was constructed in two halves (port and starboard)by molding five layers of 0.025 cm (0.010 in.) thick fiber glass overa 1/10 scale mandrel of the CH-53E. Each half was removed from themandrel, trimmed and then the two halves were bonded together to forma completely watertight shell. The sponsons were molde& integrallywith the fuselage contours. The engine nacelles were not includedsince they make no contribution to vehicle hydrodynamics, but theirw.eight and inertia were properly accounted for. An access panel wascut into the top of shell between FS 6.18 cm (243.6 in.) and FS11.68m (460 in.) at WL 4.32m (170 in.) as shown in Figure 32. Aninternal doubler was provided around the opening so the access panelcould be attached to the model with screws.

A cabin floor was made from styrofoam and covered with three plys of0.025 cm (0.010 in.) fiber glass. It was bonded into the fuselage atthe correct scale height. This construction insured that the sealedvolume of the fuselage "tub" was correctly modeled. The floor alsoacts to stiffen the fuselage and provides a mounting location for thecounterweight assembly.

The sponsons were sealed internally to provide the correct watertightvolume. In addition, the main landing gear wells were moldei fromthree layers of 0.025 cm (0.010 in.) fiber glass and bonded into thesponsons. A balsa block, sealed with one layer of fiber glass, wasbonded into each of the wells to act as a mounting poin for mainlanding gear. The nose landing gear well was constructed in the sameway and bonded into a cutout at the appropripte location in the nose.

The personnel door, cargo ramp, and ulper cargo door were simulatedas shown in Figure 34. Appropriate cutouts were made in the fuselagewhile the doors were made from the fuselage knock-outs. These doorsmay be removed to allow cabin flooding or taped in place for studiesrequiring a sealed cabin. An uppe'- deck was made from two plys of0.025 cm (0.010 in.) fiber glass and bonded in place in the upperportion of the fuselage as shown in Figure 32. This deck serves asthe mounting point for the main rotor assembly and provides space forthe instrumentation well above any anticipated water level.

The landing gear was carved from wood and is detachable. If renovedto simulate a gear up condition, its weight must be compensated for.

31


Tail Pylon, Empennage, and Tail Rotor

The tail pylon is a carved block of solid balsa, hollowed out andcovered with one layer of 0.008 cm (0.003 in.) fiber glass. Thehorizontal and vertical tails were carved out of balsa and coveredwith one-ply of 0.008 cm (0.003 in.) fiber glass. A plexiglass diskwas used to model the tail rotor. The complete tail assembly isbonded to the fuselage.

As noted befe-e, the weights of the tail rotor, horizontal andvertical tails, and the tail pylon were kept as close as possible tothe scale values of the actual aircraft.

Main Rotor Assembly

The main rotor assembly is shown in Figure 35. The blades aresimulated with aluminum channels since no attempt was made to modeltheir aerodynamic contours. These channels are bent to provide thesame static droop as the actual blades and, of course, there areseven blades of the correct scale rodius so that the rotor contactenvelope with water is correctly modeled.

The rotor blades are bolted between two aluminum disks to form theenvelop- of the rotor while a steel weight is used to simulate itsmass. This counterweight and rotor itself fit over a threaded steelrod which has been welded to a mounting plate with the correct shafttilt of five degrees. This entire assembly bolts onto the upper deckin the fuselage.

Counterweight System

The gross weight, center-of-gravity (c.g.) location, and moments-of-inertia of the model can be varied using a counterweight systemshown in Figure 36. This consists of a long threaded steel rodsupported on a steel mounting plate which is bolted to the cabinfloor.

Gross weight is adjusted by selecting the numbet of weights to beused. Longitudinal c.g. is adjusted by selecting the fore and aftlocation of the weights, while lateral c.g. offsets are modeled bysliding the entire assembly sideways. Vertical c.g. adjustment ismade by sliding the counterweight rod up or down within the slotsprovided.

32


Roll inertia can be varied by adjusting the weight distributionbetween the counterweight assembly and the rotor head weight. Pitchinertia can be adjusted by varying the longitudinal weight distribu-tion on the threaded rod. The yaw inertia will vary as the pitchinertia is adjusted, but experience has shown that yaw inertiascaling is not nearly as important as pitch and roll.

Floats

Floats for all three final designs (systems one, four, and six) wereconstructed for use with the helicopter model (see Figures 37 and38). The floats were cut from styrofoam, hollowed out, and coveredwith a 0.008 cm (0.003 in.) fiber glass skin for protection. The

floats are attached to the fuselage in the appropriate location withthrough-bolts. Both the forward and aft floats for systems one andfour have removable compartments so that the hydrodynamic stabilitywith a failed bag compartment can be studied.

It should be noted that the model floats have smaller than scalediameters so that their buoyancy is 75 percent of the free volumevalue. In this way, the buoyancy and stability characteristics ofthe model and the analysis are comparable.

8.2 Model Characteristics

The basic model characteristics are given in Table XV. The totalweight and c.g. location of the model without the counterweights isgiven in the last column. The scale values of weight, c.g. locationsand inertia for the study configuration are in the middle column.

8.3 MH-53E Simulation

It may be desirable to study the hydrodynamic characteristics of theMH{-53E with enlarged sponsons at some time in the future. Theexisting CH-53E model can be used essentially as is. The currentintention is that oversize sponsons would be constructed so as to fitover the existing ones. This would allow the MH-53E to be studiedwithout destroying the integrity of the CH-53E model. In this case,the auxiliary tank support pylons would have to be removed from theexisting model.

33

S- - - -


19AIRCRAFT

49.0 CONCLUSIONS

9.1 The CH-53E is stable in sea state 2 with the cabin sealed. Noauxiliary flotation is required.

9.2 The CH-53E requires both additional bucyancy and additiona stabilityto float upright in sea state 2 with the cabin flooded.

9.3 After an autorotative landing, & .ficient main rotor control isavailable to keep the aircraft upright for approximately six seconds.This is sufficient to allow full deployment of the auxiliary flota-tion bags if helium is the inflating medium.

9.4 The best method for prov-ding additional buoyancy and stability isthe use of inflatable, at, .iary flotation bags.

9.5 The best auxiliary flotation bag configuration utilizes four fuselagemounted floats, two forward and two aft. Such a system can provideall the required buoyancy and insure stability in sea states from 2to 5. Sea state capability depends on bag size selected.

9.6 Increasing system capability from sea state 2 to sea state 5 in-creases system cost. only slightly.

9.7 An auxiliary flotation system utilizing inflatable bags can providethe CH-53E with buoyancy and hydrodynamic stability to sea state 5conditions. Such a system would have a small weight penalty, accept-able reliability and maintainability, and minimal effect on aircraftperformance.

34


10.0 RECOMMENDATIONS

10.1 The scale model CH-53E constructed by Sikorsky should be used tovalidate the results of this study.

10.2 An analysis should be conducted to determine the effect of each ofthe final design systems on CH-53A/D sea keeping qualities.

10.3 An analysis of the basic hydrodynamic characteristics and sea statecapability of the C/MH-53E with enlarged sponsons should be con-ducted.

10.4 A scale model of the C/MH-53E ;ith enlarged sponsons should behydrodynamically tested. This model could be a modified version ofthe CH-53E model constructed for this study.

I

35

Ia

• ~ UNITED

CHNOLOGIESASIKORSKY NADC-79256-60: ~AIRCRAFT

11.0 REFERENCES

1. Lowry, D.W.; Pisano, J.; Olson, J. "CH-53A Hydrodynamic Loadsand Hydrodynamic Stability", SER-50296, 16 May, 1963.

2. ECP 2006R1, Authorized 30 October 1980.

36

UNITEDTECHNOLOGIESSIKORSKY NADC-79256-60AIRCRAFT ....

TABLE I

CH-53E BUOYANCY CHARACTERISTICS

WITHOUT FLOODING

WATER- FUSELAGE NOSE CABIN SPONSON TOTALLJNE "TUB" "TUB" BUOYANCY

m kg kg kg kg kg(in) (Ib) (lb) (Ib) (Ib) (Ib)

2.21 0 0 0 0 0(87) 0 0 0 0 0

2.46 5473 381 0 609 6463(97) (12066) (841) 0 (1342) (14,249)

2.72 5473 90C 6900 2635 15908(107) (12066) (1985) (15,212) (5809) (35,072)

2.97 5473 1505 14249 5072 26299(117) (12066) (3319) (31,414) (11,181) (57,980)

3.26 5473 2164 21912 7174 36723(127) (12066) (4772) (48,309) (15,815) (80,962)

3.48 5473 2880 29935 8055 46353(137) (12066) (6371) (65,996) (17,759) (102,192)

37

UNITEDTECHNOLOGIESSIKORSKY MADC-79256--60AIRCRAFT-- .

TABLE II

CH-53E BUOYANCY CHARACTERISTICS

WITH FLOODING

WATER- FUSELAGE NOSE CABIN SPONSON TOTALLINE "TUB" "TUB" BUOYANCY

m kg kg kg kg kg(in) (Ib) (Ib) (Ib) (Ib) (Ib)

2.21 0 0 0 0 0(87) 0 0 0

2.46 5473 609 6082(97) (12066) (1342) (13408)

2.72 5473 2635 8108(107) (12066) (5809) (17875)

2.97 5473 5072 10545(117) (12066) (11,181) (23247)

3.26 5473 7174 12647(127) (12066) (15815) (27881)

3.48 5473 8055 13528(137) (12066) (17759) (29825)

38


TABLE III

CH-53E ROLLING MOMENT PARAMETER

WATERLINE ROLLING MOMENT PARAMETER

m m"(in) (ft 3 )

2.46 138.6(97) (4896)

2.72 123.4(107) (4357)

2.97 108.9(117) (3845)

3.26 95.26(127) (3364)

3.48 82.52(137) (2914)

39


TABLE IV

HYDROSTATIC WIND MOMENT REQUIREMENT

SEA HYDROSTATIC HYDROSTATIC MOMENT REQUIREDSTATE WIND N-m (Ft-lbs)CONDITION REQUIREMENT

WL WL WL IAWL WLrm/sec (Kts) 2.46 2.72 2.97 3.26 3.48

5 40.3 137913 122733 108307 94760 82087(78.3) (101719) (90523 (79883) (69891) (60544)

4 26.0 57404 51085 45081 39442 34167(50.6) (42339) (37678) (33250) (29091) (25200)

3 19.6 32622 29031 25619 22414 19417

(38.2) (24060) (21412) (18896) (16532) (14321)

2 12.9 14131 12576 11097 9709 8411(25.0) (10422) (9276) (8185) (7161) (6204)

40

[ UNITEDTECHNOLOGIES SI•.,W JSIKORSKY

SAIRCRAFT NADC-79256-60

TABLE V

BASIC CHARACTERISTICS OF CAI

( Ln C7 n FORWARD FLOATS oo: AFT FL

( (Do 0 f Dia. Length Buoy. = -.h Dia. Len

Sm m kg m m( (ft) (ft) (lbs) f(ft) (

4 3 1.83 2.13 4206 3 1.83 2.(6.0) (7.0) (9273) ,(6.0) (8.

2 5 4 - -- 2 1.19 1- - - (3.9) (5.

3 5 6 4 1.71 2.19 3769 4 1.71 2.(5.6) (7.2) (8308) (5.6) (8.

4 4 4 4 1.71 2.19 3769 4 1.71 2.(5.6) (7.2) (8308) (5.6) (8.

5 4 4- - 2 1.19 1.- - - (3.9) (5.

6 2 4 1 1.74 2.01 3579 1 1.74 2.(5.7) (6.6) (7891) (5.7) (7.

41

TABLE V

BASIL CHARACTERISTICS OF CANDIDATE FLOATS

RWARD FLOATS ____ AFT FLOATS SPONSON FLOATS~~0

Length Buoy. 0 0 Dia Length Buoy. D iia. Length Buoy.

m kg m m kg ( m m kg(ft (f___) (f___) _______ W___

(f) ((ft) It (ftbs) s ( t)(ft) (Ibs)

2.13 4206 3 1.83 2.65 5227 ---(7.0) (9273) (6.0) (8.7) (11,525) - -

2 1.19 1.62 1346 5 1.54 5.33 7449L (3.9) (5.3) (2966) (5.05) (17.5) (16422)

2.19 3769 4 1.71 2.71 4659 2 1.07 2.68 1799(7.2) (8308) (5.6) (8.9) (10,270) (3.57) (8.8' (3967)

2.19 3769 4 1.71 2.71 4659 - - -

(7.2) (8308) (5.6) (8.9) (10,270) - - -

- 2 1.19 1.62 1346 7 1.49 5.18 6813- - (3.9) (5.3) (2'66) (4.9) (17.0) (15,019)

2.01 3579 1 1. 74 2.41 4284 - - -

(6.6) (7891) (5.7) (7.9) (9445) -

ECHNOLOGIESSIKORSKY NADC-79256- 6 0AIRCRAFT

TABLE VI

BASIC CHARACTERISTICS OF CANDI

SBuoy.(2 0 a- SystemM System Total(2) Failed M, 0,

U % V Weight Drag Buoy. Comp. V a

SKg m2 Kg Kg Li

S(Ibs) (ft) (Ibs) (Ibs)

1 5 200 .06 18,867 17,12 4

(442) (.0056) (41,595) (38,7'/)

2 5 181 .03 17,589 16,099 4(399) (.0028) (38,777) (35,492)

3 5 244 .08 20,453 18,653 6'538) (.0074) (45,090) (41,124)

4 4 196 .06 16,854 15,689 4(433) (.0056) (37,157) (34,590)

4 180 .03 16,316 15,343(397) (.0028) (35,971) (33,826)

6 2 191 .06 15,726 II1,442 4(421) (.0056) (34,670) (25,226)

(1) System weight will increase by approximately 15% if nitroger

inflation medium.

(2) Based on 75% of the free Volume.

42

Tt

TABLE VI

ASIC CHARACTERISTICS OF CANDIDATE SYSTEMS

2)Forward Sys. Aft Sys. Sponson Sys.Buoy."2 -* ___

otal(2) Failed c D Bottle Line Bottle Line Bottle Lineuoy. Comp. (D Vol. Size Vol. Size Vol. Size

V)0

.Kg Kg Liteý cm Liter cm Litsr cmibs) (Ibs) (in) (in) (in-) (in) (in) (in)

,867 17,125 4 35.4 2.54 43.8 2.86 -

,595) (38,777) (2163) (1.00) (2670) (1.13) --

,589 16,099 4 - - 11.0 2.22 62.7 3.49,777) (35,492) - - (672) (.875) (3826) (1.38)

,453 18,653 6 31.6 2.54 38.9 2.86 14.8 1.27,090) (41,124) (1926) (1.00) (2372) (1.13) (906) (0.50)

,854 15,689 4 31.6 2.54 38.9 2.86 -

,157) (34,590) (1926) (1.00) (2372) (1.13) -

,316 15,343 4 - - I11.0 ?.22 57.0 3.49*,971) (33,826) - - (672) (.875) (3480) (1.38)

,726 11,442 4 29.8 2.54 35.8 2.54 --,670) (25,226) (1817) (1.00) (2182) (1.00) -

pproximately 15% ;f nitrogen is used for

-------------------------------------------

K UNITEDTECHNOLOGIESSIKORSKY

A RAFT NADC-79256-60

TABLE VII

NORMALIZED RELIABILITY AND MAINTAINABILITY RATINGS

RELATIVE PROBABILITY

SYSTEM INSP. FAILURE UNSCHED. DEPLOYMENT ROLLOVER SINKINGTIME RATE MAINT. FAILURE* INCIDENT INCIDENT

MAN-HRS.

1 1.05 1.0 1.0 1.0 2.0 1.0

2 1.10 1.15 1.10 1.0 3.0 **

3 1.45 1.45 1.45 1.5 1.0 1.0

4 1.05 1.0 1.0 1.0 2.0 1.0

5 1.05 1.15 1.10 1.0 3.0 **

6 1.0 1.0 1.0 1.0 2.0 1.0

*One bottle failing to discharge

**Insufficient buoyancy if sponson float fails

Notes:

1. Value 1.0 indicates best system relative to that attribute; hiqher valuesproportionately worse

2. Baseline Values:

Inspection Time: 9.5 manhours ea. 180 days or180 flight-hours

Failure Rate: 3.5 failures/103 flight-hours

Unscheduled Maintenance: 3.7 manhours/10 3 flight-hours

43

-UNIT ED~TECHNOLOGIES

S rlAIRCRAFT NADC-79256-60

TABLE VIII

RELATIVE SYSTEM INITIAL AND LIFE CYCLE COSTS

SYSTEM C0TS

INITIALSYSTEM DESIGN LIFE

StA RECURRING NON-RECURRING CYCLESTATE

1 5 1.000 1.000 1.000

2 5 0.914 0.974 0.960

3 5 1,203 1.280 1.285

4 4 0.992 1.017 0.990

5 4 0.910 0.985 0.958

6 2 0.918 0.959 0.897

44

SUNITEDTECHNOLOGIESSIKORSKY NADC-79256-60AIRCRAFT

TABLE IX

FINAL SYSTEM DESIGN

FLOAT CHARACTERISTICS

SYSTEM SYSTEM SYSTEMPARAMETER ONE FOUR SiX

.(FINAL) (FINAL) (FINAL)

PORWARD FLOA-S

No. of Compartments 3 4 1Diameter, m (ft) 1.83 (6.0) 1.71 (5.6) 1.74 (5.7)Length, m (ft) 2.13 (7.0) 2.20 (7.2) 2.01 t6.6)Buoyancy*, Kg (Ibs) 5182 (11,425) 4750 (10,471) 4452 (9816)Location**

FS, cm (in) 340.6 (134.1) 340.6 (134.1) 342.1 (134.7)WL, cm (in) 233.2 (91.8) 221.0 (87.0) 216.4 (85.2)

AFT FLOATS

No. of Compartments 3 4 1Diameter, m (ft) 1.83 (6.0) 1.71 (5.6) 1.74 (5.7)Length, m (ft) 2.65 (8.7) 2.70 (8.9) 2.41 (7.9)

Buoyancy*, Kg (Ibs) 6405 (14,121) 5853 (12,809) 5347 (11,787)Location**

FS, cm (in) 1381 (543.7) 1386 (545.5) 1370 (539.2)WL, cm (in) 288.3 (113.5) 280.7 (110.5) 271.8 (107.0)

NOTE: All auxiliary support tubes are 0.76m (2.5 ft) in diameter and

the same length az their parent float.

* Based on 75% of the free volume.

**Center of Float

45

STEUNITEDTECHNOLOGIESSIKORSKY NADC-79256-60AIRCRAFT

TABLE X

FINAL SYSTEM DESIGN

BUOYANCY SUMMARY

SYSTEM SYSTEM SYSTEM

CONDITION ONE FOUR SIX(FINAL) (FINAL) (FINAL)

NORMAL

Floats, Kg (Ibs) 23,175 21,206 19,598(51,092) (46,750) (43,206)

Total, Kg (Ibs) 36,446 34,477 32,869(80,350) (76,008) (72,464)

% Study GW 149 141 134

CRITICAL COMPARTMENT FAILED

Floats, Kg (lbs) 21,040 19,742 14,251(46,385) (43,524) (31,419)

Total, Kg (lbs) 34,311 33,013 27,522S(75,643) (72,782) (60,677)

% Study GW 140 135 113

NOTE - Total buoyancy based on an aircraft buoyancy of 13,271 Kg(29,258 lbs.) with the cabin flooded.

46

UNITEDTECHNOLOGIESSIKORSKY NADC-79256-60r ARRFT

F!TABLE XI

FINAL SYSTEM DESIGN

SUMMARY OF STABILITY CHARACTERISTICS

SSYSTEM SYSTEM SYSTEMSCONDITION ONE FOUR SIX

_ _(FINAL) (FINAL) (FINAL)

NORMAL

Sea State Capability 5 4 2Maximum Righting Mom., N-m 70,900 37,500 11,000

(ft-lbs) (52,293) (27,659) (8113)@ Roll Anale, degrees 12 9 12

j CRITICAL COMPARTMENT FAILED

Sea State Capability 2 1 0Maximum Rightiig Mom., N-m 10,000 2,000 f

@ olAge (ft-lbs) (7376) (1475)@ Roll Angle

NOTE: Stability calculations based on the following assumptions:

1) Cabin flooded

2) Floats have 75% of their free volume

3) Aux. support tubes make no contribution to stability

47


TABLE XII

FINAL SYSTEM DESIGN

INFLATION SYSTEMS SUMMARY

SYSTEM SYSTEM SYSTEMPARAMETER ONE FOUR SIX

(FINAL) (FINAL) (FINAL)

FORWARD FLOATS

No. of Bottles 2 2 2Vol. per Bottle, liters 41.6 37.9 35.6

(in 3 ) (?538) (2311) (2170)Inflation Line Size, cm 2.54 2.54 2.54

(in) 11.00) (1.00) (1.00)

AFT FLOAT

No. of Bottles 2 2 2Vol. per Bottle, liters 51.4 46.7 42.7

(in 3 ) (3135) (2849) (2605)Inflation Line Size, cm 2.86 2.86 2.54

(in) (1.125) (1.125) (1.00)

NOTE: All systems have a design operating pressures of 20,684 kPa(3000 PSI).

48

.A A

UNITEDTECHNOLOGIESSIKORSKY NADC-79256-60AIRCRAFT . ..

TABLE XIII

FINAL SYSTEM DESIGN

COST ESTIMATE

SYSTEM SYSTEM SYSTEMONE FOUR SIX

(FINAL) (FINAL) (FINAL)

DEVELOPMENT COST 2,150,000 2,153,000 2,146,000

RECURRING COST

Procuring 49,700 51,400 42,000Installation 100,300 102,200 97,500

TOTAL 150,000 153,600 139,500

49

UNITEDTECHNOLOGIESSIKORSKY NADC-79256-60V E AIRCRAFT

TABLE XIV

COMPARISON OF SYSTEMS ONE AND SEVEN

SYSTEM SYSTEMSYSTEM ATTRIBUTE ONE SEVEN

WEIGHT, Kg 201 189(2bs) (442) (416)

DRAG, m2 2 .056 .065(ft (0.6) (0.7)

RELATIVE COST

Recurring 1.00 1.00Non-recurring 1.00 0.98Life-cycle 1.00 1.01

RELIABILITY AND MAINTAINABILITY

Inspection time 1.05 1.05Failure Rate 1.00 1.10Unscheduled Maintenance Man-hrs 1.00 1.10Deployment Failure 1.00 1.00Roll-Over Incidence 2.00 2.00Sinking Incidence 1.00 1.00

50

I UNITEDTECHNOLOGIESSIKORSKYAIRCRAFT

NADC-79256-60

TABLE XV

MODEL CHARACTERISTICS

PARAMETER FULL SCALE 1/10 SCALE MODEL ASVALUE VALUE DELIVERED*

Gross Weight, Kg 24,444 24.44 13.60

(Ib) (53,889) (53.89) (30.00)

C.G. Location

FSCG, m 9.06 9.06 10.47(in) (356.7) (356.7) (412.3)

WLCG, m 4.19 4.19 4.97(in) (165.1) (165.1) (195.6)

BLCG, m -048 .048 (0)(in) (1.9) (1.9) (0)

Moments-of-Inertia

Ixx, Kg-mr2 2 43,699 .4370(slug-ft 2 ) (59,248) (.5925)

Iy,, Kg-mr2 230,317 2.3032(slug-ft 2 ) (312,267) (3.1227)

I Kg-mr2 2 217,138 2.1714(slug-ft,) (294,398) (2.9440)

*Without Instrumentation

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14'.0 APPENDIX A - REVIEW OF CH-53A/D HELICOPTER ACCIDENTS ON WATER

The accident data included herein was obtained from the Naval SafetyCenter, Norfolk, Va. Included are the reported statistics of tenaccidents involving CH-53 Navy/Marine cargo helicopters and whichoccurred on water in the time period May, 1968 through June, 1979.

It should be noted that the author of this review did not participatein any on-site investigation of the reported accidents. Thus, littleor no first-hand knowledge of the circumstances, occurrences, post-accident investigations or conclusions is available, nor is anythingknown about the pilots and crews or maintenance of the helicopters.

14.1 Accident Data

The computerized data made available by the Naval Safety Center,Norfolk, Virginia on CH-53 Navy/Marine helicopter accidents thatoccurred on water has been reviewed. It was found to contain limitedinformation on eight accidents that resulted in the destruction ofthe helicopter and one which resulted in only limited damage when thehelicopter struck, but did not enter, the water. Two additionalaccidents resulting in destruction of the helicopter were previouslyknown to have occurred.

In August, 1980, Sikorsky personnel visited the Naval Safety Centerto review the records of the ten accidents that resulted in the lossof the helicopters. The records of one of the accidents were notavailable because of litigation and the records of another wasreported in summary form only.

The following data then constitutes the best available data on thesubject accidents. The only way to obtain desired information notcontained in the accident records would be to submit a questionnaireto the crew members involved, but this is considered beyond the scopeof this investigation.

90

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UNITEDTECHNOLOGIESSIKORSKY

RAF• T NADC-79256-60

The ten accidents involving CH-53 helicopters on water are:

NO. IDENTIFICATION MODEL LOCArION TIME TYPE OF ACCIDENT

1. 680501 CH-53A S. Vietnam Night Flew into water atmoderate speed

2. 691101 CH-53A S. Vietnam Night Uncontrolled crash

3. 701030 CII-53D S. Vietnam Day Rotating descentfrom hover

4. 730127 CH-53D Phillipines Dusk Autorotation intowater

5. 730318 CH-53D N. Vietnam Day Rotating descent(MCM) with severe

impact.

6. 730402 CH-53A N. Vietnam Day Autoretation with(MCM) soft impact

7. 730702 CH-53D N. Vietnam Day Emergency landing(MCM) with moderate

impact

G. 740719 CH-530 IN LITIGATION

9. 761104 CH-53D Okinawa Day High speed impact

10. 790617 CH-53D N. Carolina Day Helicopter ditchedfollowing lossof engine

41

Previous studies of CH-53 Navy and Marine helicopter accidents resultingin destruction or substantial damage have shown that accidents on landoccurred almost six times more frequently than those on water.Reference Figure Al, SER-13298, "Crashworthy Fuel System Design Criteria".

91J

UNITEDTECHNOLOGIESSIKORSKY

KARCRA Y NADC-79256-60

The reported events that occurred and the general circumstances under

which the accident took place are:

NO. REPORTED ACCIDENT EVENTS WIND VISIILITY AIRCRAFTOCCURRING BEFORE IMPACT WEIGHT

__._POUNDS

I Pilots distracted during approach to ,oight land- 7 knots One mile in 2?000ing - at 15' attempted to climb with full power hazebut struck water nose down.

2 Pilots practicing night TACAN approaches - 9 knots 7 miles 22700engine failure and explosion - caused helo 810Fto become uncontrollable, fell approx. 1200ft. before impacting water. _

3 Hovering at 2 ft. with RAMP down over bunker Gusts to 1/2 milesurrounded by flood - tail blades hit bunker - 30 knots in heavyhelo. made several flat turns before impacting rain.water. _1

4 Dual engine flameout due to fuel contamination - 8 knots Unlimitedentered autorotation at 90 knots, 800'.

SFlared at 100'.5 Flying at 150', 12-14 knots with MCM Tow. - 12 knots 8 miles

tail vibrations were followed by loss of tail 650Frotor which almost severed tail pylon - helo.made several flat turns before impactingwater. ._____

6 Tail rotor problems caused vibrations during toioperation - hovered at 100' - lost tail rotor -autorotated onto water - used all availablecollective to cushion landing.

7 Engine failure during tow operation at 150' Light 30660aircraft began to descend, rotor RPM at55%; at 50' leveled aircraft, released towand applied collective to cushion landing.

8 IN LITIGATION

9 Picked up passepger on island, during return 9 knots 10 milesflight, both engines believed to have flamed 730F"only due to fuel starvation, steep descentfrom 500',.flared fell from 100'

10 Took off from ship, engine failed- rotor RPM 8 knots 7 miles 35000dropped to 85%, dropped collective, leveled 720 Fhelo. and cushioned landing for controlledditching with rotor at 80% NR.

92

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UNITEDTECHNOLOGIESSIKORSKY9R NADC-79256-60

The reported helicopter configuration, attitude and velocities atimpact with the water are:

NO HELICOPTER CONFIGURATION SEA STATE IMPACT IMPACTOR ATTITUDE VELOCITY

WAVES.

I Probably .;,eels down - Calm, 450 50-55 knots1 - 2 ft. waves Nose down Fwd. speed

2 Probably wheels down - 4-5 ft. waves Tail low In autoro-10/minute tation

3 Ramp open - Probably Flooded Upright Low speed -wheels down River making flat

turns

4 4 internal aux. fuel tanks 1-2 ft. waves Upright Flew 100 ydsin Cabin wheels down - after flareupper ramp door was up - at 40 knotspersonnel door was open. with tail

hittingwater -settled intowater.

5 Wheels up - MCM configura- Calm Upright Right descend-tion ing spin -

violent im-Pact.

6 MCM Configuration. Ramp Unknown Slightly Autorotationraised - Boom stowed - tail low with fullDAM in place, tail pylon collectivebroken off - low speed into

water7 Cockpit windows open - cargo Sea State 1

hook well door open - Ramp 3' waves Level 200-300 fpm.level, wheels down - some 2 seconds 3-5 knots fwdcabin windows missing (Ramp speed.separated on impact).

8 IN LITIGATION

Gear down Unknown Presumed Fell from 100'upright violent impact.

10 Ramp open, cargo in cabin, Sea State 2 Level Zero airspeedgear down cushioned

ditching

3

Ii 93

UNITEDT= TCHNOLOGIESSIKORSKY

SAI ,CRAFT NADC-79256-60

The reported events immediately following impact with che water are:

NO. REPORTED EVENTS AFTER IMPACT WITH WATER

1 On impact, pilot in seat went through nose, tail broke off, helicopterrolled over and floated inverted for approximately 20 minutes, thensank in 120' of water. "Water was full of gas".

2 Fire started, burned for 10-15 minutes, aircraft sank rapidly inupright attitude, many pieces of floating debris.

3 Pilot secured engines and applied rotor brake. Crew and passengersabandoned aircraft which sank in 15 ft. of water. Aircraft rolledon right side after rotor blades stopped.

4 Lower nose windows broken - cockpit filled with water - helo rockedback, came to rest - rolled inverted seconds after - internal fueltanks kept floor 30 inches above water - remained afloat for aconsiderable time, then sank.

5 After violent initial impact, main rotor blades hit water, began todisintegrate, aircraft rolled inverted (to left) and filled withwater. Sank in 2-3 minutes in 63 ft. of water. Tail section severedby tail rotor.

6 After gentle landing, rotor RPM decayed and blades hit water. Arcraftrolled left, pitched nose down. Crew evacuated helo which sank in1-1 1/2 minutes, tail pylon section broke off. MCM DAM failed allowingbig influx of water.

7 After landing on water, helicopter rolled steadily to left. Pilot'swindows were open, cockpit and cabin filled with water. Helicopterrolled inverted, crew climbed on it until rescued 10 minutes later.Floated w~th two ft. of fuselage above water. Sank in 37' water.

8 IN LITIGATION

9 After violent impact, helicopter sank at once. Cabin section found onbottom. Cockpit not found. Water 200-260' deep, strong currents.Debris in water included tail pylon, right landing gear, crew chief's seat.

10 After ditching, floated with rotor at 80%. Secured engines, applied rotorbrake, turned 2000 counterclockwise. Crew and passengers egressed,aircraft was sitting undamaged in water. Ship struck port side - helicop-ter sank after collision.

94 V

SUNITEDTECHNOLOGIESSIKORSKYAIRCRAFT NADC-79256-60

The occupants and their injuries, if any, are tabulated below:

NO NO. OF UNINJURED MINOR MAJOR INJURIES FATALITIESOCCUPANTS INJURIES

1 5 Crew 1 I- Crew Chief 2- Pilot, cut 1- Injuriesthrown leg when thrown & causefrom jump thru canopy. of deathseat by Co-pilot, cut not deter-impact, leg from mined.bruises, control panel.sprainedankle. I

2 5 Crew 0 0 1- Co-pilot, major 4- 3 drownedinjuries receiv- I not founded on impact- All wearingHand released flak vests,restraint prior not lifeto impact. vests.

3 5 Crew 4 Crew 0 0 1- Crew,Gunner found

35 Passengers 35 Passeng- drowneders.

4 5 Crew 12 0 0 0

7 Passengers 0_,__I

5 5 Crew 0 0 6- Pilot-sprained 0

1 Passenger back; Co-pilot-aspiration pneu-monia; Crewchief fracturedvertebrae-ribs;i

Ist mech.-fracturedvertebrae-ribs;Rad. Op.- possiblefractured ribs;Passenger- Facialcuts, broken teeth

6 5 Crew 3 2-Crew - cuts,bruises andgabrasions |frem collap'se of troop|seats inogentle impact.

7 4Crew I I

8 IN LITIGATION

9 4 Crew 4 missing

10 4 Crew 4 Crew5 Passengers 5 Passengere

9

95

LUNITED

TECHNOLOGIESSIKORSKYAIRCRAFT NADC-79' 5o-60

One item of significance in water accidents is the availability of rotorcontrol at the time of the accident. The following table contains thebest estimates of that available ja the ten accidents.

NO. ESTIMATE OF AVAILABLE ROTOR CONTROL

1 Complete control available.

2 Helicopter Uncontrollable

3 Main Rotor Control available, but not directional control.

4 Complete control available.

5 Main Rotor Control available until the blades impacted water - Nodirectional control.

6 Main Rotor Control available until the blades impacted water - Nodirectional control.

7 Little control available as rotor speed dropped to 55% NR.

8 IN LITIGATION

9 Complete control available

10 Complete control available, rotor RPM dropped to 85% NR

96

rUNITD

TECHNOLOGIESSIKORSKYAIRCRAFT NADC-79256-60

14.2 Summary of Findings

1) Accidents, as might be expected, occurred at any time and had

several different causes. The surveyed accidents includedmechanical problems such as loss of directional control, loss ofpower due to engine problems, fuel contamination, and fuelstarvation, all of which resulting in the crew having to make anautorotational descent and subsequent ditching. In otheraccidents the helicopters were inadvertently flown into thewater.

E

2) The weight of the aircraft involved in the accidents varied

considerably; some flights involved crew training and practicemissions with no cargo or passengers, while other operationsinvolved full loads of cargo and personnel. Other accidentsinvolved helicopters equipped for Mine Counter Measures (MCM)operations at intermediate gross weights.

3) The majority of the accidents were reported to have occurred insea state 2 wave conditions (1 to 3 foot waves) with one in calmwater, also one in Sea State 3 (3 to 5 foot waves). However,with one exception, recorded wind conditions were below 12knots. In that accident, gusts to 30 knots were .:corded.

4) In the accidents involving autorotation and ditching, a widerange of impact velocities was recorded. In some of theaccidents, both the vertical and horizontal velocities were lowand water entry was gentle. In one accident, the helicopter wasflying at 40 knots while the tail skag was hitting the water,while in other impacts the forward speed was low but thevertical velocity caused a violent impact. Other accidents

occurred in which the helicopter entered the water while rota-ting about the axis of the main rotor.

5) In the majority of the accidents, the helicopter attitude atimpact with the water was essentially upright with little or noroll and from zero to 150 nose up pitch. In one account inwhich the helicopter was inadvertently flown into the water, theimpact attitude was recorded to be 450 nose down.

6) In most of the accidents the landing gear was down, beingreported as retracted in only one of the MCM mission accidents,In one-third of the accidents the rear ramp was open. In oneaccident the upper ramp door and the personnel door were open,while in another, the cockpit windows and cargo hook well doorwere open and some cabin windows were missing.

97

UNITED S• ~TECHNOL.OGIESSI1KORSKYA NADC-79256-60

7) All of the helicopters involved in the surveyed accidents sank.One broke up on impact and sank at once. One was on fire andsank rapidly. Six others rolled inverted and floated for timesranging from Ilk minutes to 20 minutes. A ninth, which wasfloating on the water undamaged, was struck and damaged by ai ship and then sank.

8) In 9 accidents with 42 crew members, 21 were uninjured, 3received minor injuries, and 8 received major injuries and 10fatalities occurred, 4 known drowned, 1 undetermined, and 5missing. In 4 accidents in which 48 passengers were carried, 47were uninjured, while the 48th received major injuries in theform of focial cuts and broken teeth.

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SUNIIITED

TECHNOLOGIESs ,• . SIKORSKY lIRMA" NADC-79256-60 H

14.3 Design Guide Lines

As a result of the findings of this study of Navy CH-53 helicopteraccidents, the following recommendations are made pertaining to thedesign criteria for stability and flotation of large transporthelicopters.

A helicopter flotation/stability system shall be designed to:

1. Accommodate the full range of aircraft weight and c.g. posi-tions.

2. Accommodate the full range of anticipated aircraft configura-tions. Closures, such as doors, windows, hdtches, etc., that may

be opened in flight shall not be considered closed in em- -gencyor accident situations.

3. Keep the aircraft upright in Sea State 3 (3 to 5 foot waves)with winds to 30 knots, and keep the aircraft afloat for a timesufficient for the evacuation of a full complement of crew andpassengers in these conditions.

- -

Documents

CH-53E EMERGENCY FLOTATION SYSTEM DESIGN STUDY