NASA CR-120909

LF467 CONCEPT DEFINITION

by

GENERAL ELECTRIC COMPANY

prepared for

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

NASA-Lewis Research. Center Contract NAS3-15690 Laurence V. Gertsma - Project Manager 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. NASA CR-120909 4. Title and Subtitle 5. Report Date LF467 CONCEPT DEFINITION 6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No. R72 AEG 207

10. Work Unit No. 9. Performing Organization Name and Address General Electric Company Aircraft Engine Group 11. Contract or Grant No. Cincinnati, Ohio 45215 NAS 3-15690

13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Contractor Report National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, D.C. 20546

15. Supplementary Notes Project Manager, Laurence W. Gertsma Lift Fan Project Office NASA Lewis Research Center, Cleveland, Ohio

16. Abstract

This is the final technical report documenting the LF467 concept definition. The LF467 is an advanced turbotip lift fan intended for application with the YJ97-GE-100 turbojet gas generator on a V/STOL transport research aircraft. The program objective was to define a fan that develops a reasonably high (1.30) fan pressure ratio consistent with propulsion requirements of a V/STOL research transport aircraft and that exhibits the ability to achieve a 100 PNdB overall noise objective through the use of modest additional installation treatment. This report covers the aerodynamic and mechanical designs of this system and presents the resulting configuration, weight, and noise predictions.

17. Key Words (Suggested by Author(s)) 18. Distribution Statement Propulsion, Lift Fan, V/STOL Unclassified - Unlimited Tip Turbine, Aerodynamic Design

19. Security dassif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price* Unclassified Unclassified 121 $3.00

* For sale by the National Technical Information Service, Springfield, Virginia 22151 TABLE OF CONTENTS

PAGE

SUMMARY i INTRODUCTION 5 DESIGN REQUIREMENTS 7 DESIGN POINT SELECTION 7

DESIGN POINT SUMMARY 10

ACOUSTIC DESIGN AND ANALYSIS n

JET NOISE 12

TURBINE NOISE 12

FAN NOISE 12

ACOUSTIC TREATMENT 13

ESTIMATED NOISE LEVELS • 14

AERODYNAMIC DESIGN 16

INITIAL STUDIES 16

DOUBLE STATOR CONFIGURATION 17

SELECTED FAN CONFIGURATION 18

FAN DESCRIPTION lg

AERODYNAMIC DESIGN DETAILS 19 FAN BLADE AND VANE GEOMETRY 20 TURBINE AERODYNAMIC DESIGN 21 AERODYNAMIC FLOWPATH 21

MECHANICAL DESIGN 22 FRONT FRAME DESIGN 22 GENERAL DESCRIPTION 22 DESIGN REQUIREMENTS 22 AERODYNAMIC LOADING 23 MANEUVER LOADS 23 CROSSFLOW CONDITIONS 23 COMPONENT DESIGN DESCRIPTION 24 Hub 24 Struts 24 Bellmouth 25 Dome 25

iii TABLE OF CONTENTS

PAGE

Forward Air Seal Assembly 26 DESIGN STRESS LEVELS 27 SCROLL DESIGN 27 GENERAL DESCRIPTION 27 DESIGN REQUIREMENTS 27 COMPONENT DESIGN DESCRIPTION 27 Inlet Elbow 28 Bubble 28 Torque Tube 28 Scroll Exhaust 28 Nozzle Partitions 29 Scroll/Airframe Mounts 29 Insulation 30 DESIGN SUMMARY 30 ROTOR DESIGN 30 GENERAL DESCRIPTION 30 DYNAMICS 31 LOW CYCLE FATIGUE ANALYSIS 32 LIMITING STRESS AND LIFE 32 FAN BLADE 32 Design Requirements 33 Design Criteria 33 Dovetail 34 Airfoil 34 Shrouds and Seals 35 Siderails 35 TURBINE 36 Design Requirements 36 Design Criteria 37 Bucket 38 Bucket Tip Shroud 38

iv TABLE OF CONTENTS

PAGE

Braze Joint 38 DISK 39 Design Requirements 39 Design Criteria 39 Disk Design 40 BEARINGS AND SUMP 40 Design Requirements 41 REAR FRAME DESIGN 41 GENERAL DESCRIPTION 41 DESIGN REQUIREMENTS 42 COMPONENT DESIGN DESCRIPTION 42 HUB COVER 42 HUB RING 42 FAN STATOR VANES 43 ACOUSTIC SPLITTERS 43 MIDBOX 44 EXHAUST LINERS 45 TURBINE STRUTS 45 INSULATION BLANKET - MIDBOX 45 AFT AIR SEAL 46 FAN CAVITY PURGE 46 REAR FRAME - SCROLL BRACKET 46 DESIGN SUMMARY 46 WEIGHT SUMMARY 47 PERFORMANCE 48 INSTALLATION 50 LIFT FAN INSTALLATION 50 WEIGHTS AND INERTIAS 50 MOUNTING SYSTEM 51 YJ97 INSTALLATION 51 TABLE OF CONTENTS

PAGE

DISCUSSION OF RESULTS 52 CONCLUSIONS 55 NOMENCLATURE 57 REFERENCES 59

vi LIST OF TABLES

TABLE PAGE

I Installation Parameters Used in LF467 Performance, Sea Level 60 Static, Standard Day

II LF467 Fan Design Point Parameters, Sea Level Static, Standard 60 Day

III LF467 Turbine Design Point Parameters, Sea Level Static, 61 Standard Day

IV LF467 Noise Estimates 61

V Design Summary of Rotor Components 62

VI Bearing DN Values 63

VII LF467 Performance (Sea Level Static, Standard Day) 63

VIII LF467 Dimensions for a Range of Ambient Temperature Design 64 Conditions

IX LF467 Weights and Inertias 65

X LF467 Mount Load Table 65

vii LIST OF FIGURES

FIGURE PAGE

1 Typical V/STOL Research Aircraft Mission 66 2 Ducting Schematic of an Interconnected Two Fan, Two Gas 66 Generator System 3 Inter-Duct Pressure Losses for Bleed-out of System 67 4 Inter-Duct Pressure Losses for Bleed into System 67 5 Variation of Engine Airflow with Ambient Temperature 68 at Fan Design Conditions 6 Variation of Engine Fuel Flow with Ambient Temperature 68 at Fan Design Conditions 7 Variation of Engine Discharge Temperature with Ambient 69 Temperature at Fan Design Point 8 Variation of Engine Discharge Pressure with Ambient 69 Temperature at Fan Design Point , 9 Variation of Interconnect Duct Flow with Ambient 70 Temperature at Fan Design Point 10 Effects of Ambient Temperature on Fan Turbine Flow 70 11 Effects of Ambient Temperature on Fan Turbine Temperature 71 12 Effects of Ambient Temperature on Fan Turbine Pressure 71 13 Effects of Ambient Design Point Temperature on Fan Size 72 14 Effects of Ambient Design Point Temperature on Fan Inlet Air 72 15 - Effects of Ambient Design Point Temperature on Fan Pressure 73 Ratio 16 Effects of Ambient Design Point Temperature on Fan Thrust 73 17 LF467 Lift Fan Layout 74 18 Aerodynamic Flowpath for Double Stator Configuration 75 19 Fan Exit Pressure Profiles - Double Stator Configuration 76 20 Rotor Inlet Mach Number Distribution - Double Stator 76 Configuration 21 Rotor Aerodynamic Loading Parameters - Double Stator 77 Configuration 22 Stator Inlet Mach Number Distribution - Double Stator 77 Configuration 23 Stator Aerodynamic Loading Parameters - Double Stator 78 Configurat ion

viii LIST OF FIGURES

FIGURE PAGE

24 Aerodynamic Flowpath for the Selected LF467 Using Loaded 79 Splitters 25 Flowpath Wall Mach Number Distributions 80 26 Rotor and Stator Exit Pressure Distributions 80 27 Rotor and Stator Total Pressure Loss Coefficients 81 28 Rotor Inlet Mach Number Distributions 81 29 Stator Inlet Mach Number Distributions 82 30 Rotor Air and Blade Angle Distributions 82 31 Stator Air and Blade Angle Distributions 83 32 Rotor Aerodynamic Loading Parameters 83 33 Stator Aerodynamic Loading Parameters 84 34 Rotor and Stator Choke Ratio 84 35 Radial Location of Stream Functions 85 36 LF467 Blading Solidities 85 37 Rotor Blade Meanline Geometry 86 38 LF467 Rotor Blade Geometry 86 39 Stator Vane Geometry 87 40 Rotor Aerodynamic Load Distributions 87 41 Stator Aerodynamic Load Distributions 88 42 LF467 Turbine Velocity Diagram 88 43 LF467 Flowpath 89 44 Front Frame Components 90 45 Forward Air Seal Assembly 90 46 LF467 Front Frame Stresses 91 47 Scroll Nomenclature 91 48 Scroll Stresses 92 49 Rotor Frequency-Speed Diagram 92 50 Rotor Low Cycle Fatigue Analysis 93 51 LF467 Blade 93 52 Dovetail Steady State Stress 94

ix LIST OF FIGURES

FIGURE PAGE

53 Blade Dovetail Stress Range Diagram 94 54 Disk Dovetail Stress Range Diagram 95 55 Blade Airfoil Stress Range Diagram 95 56 Blade Natural Frequencies 96 57 Fan Blade Flutter Margin 96 58 Outer Part-Span Stress Range Diagram 97 59 Turbine Configuration and Materials 97 60 Blade Tip Shroud Stress Range Diagram 98 61 Upper Siderail Stress Range Diagram 98 62 Metal Design Temperature ' 99 63 Integral Bucket and Tip Shroud 99 64 Bucket Frequency-Speed Diagram 100 65 Bucket Stress Range Diagram 100 66 Bucket Tip Shroud Stress Range Diagram 101 67 Rear Frame Nomenclature 101 68 Rear Frame 102 69 Stator Vane Insert 103 70 Rear Frame Stresses , 103 71 Stator Vane Torsional Frequency versus Fan Speed 104 72 Stator Vane Flexural Frequency versus Fan Speed 104 73 Weight Ratio for Range of Ambient Design Temperature 105 74 YJ97 Engine Discharge Gas Flow 105 75 YJ97 Engine Discharge Pressure 106 76 YJ97 Engine Exhaust Gas Temperature 106 77 YJ97 Engine Fuel Flow 107 78 Variation of Fan Speed with YJ97 Engine Speed 107 79 Fan Inlet Airflow 108 80 Fan Total Pressure Ratio 108 81 Fan Total Net Thrust 109 82 LF467 Fan Installation Drawing 110 83 LF468 Mounting System 111 SECTION I

SUMMARY

This is the final technical report presenting results of the LF467 turbotip lift fan concept definition, conducted during the period October, 1971 to January, 1972, under Contract NAS3-15690.

The LF467 is a 66.8 inch fan tip diameter advanced lift fan system with a fan aerodynamic design pressure ratio of 1.30 and a design fan tip speed of 1060 feet per second. The fan turbine is designed to accept the exhaust flow of the General Electric YJ97-GE-100 turbojet.

The LF467 concept definition study was conducted to extend low noise lift fan technology to include systems with 1.30 fan pressure ratios. The basic objective was to define a fan system in sufficient detail to enable a sound engineering judgment to be made among the 1.25 to 1.35 pressure ratio fans with respect to noise, size and performance as it would apply to a V/STOL research aircraft system.

The LF467 pressure ratio was set at 1.30 to expand the matrix of study fans between the LF468 a 1.25 design, and the LF460 about a 1.37 pressure ratio design. The remaining critical system parameters (fan tip speed, turbine exit Mach number and turbine exit diffusion) were selected for a balance design with respect to fan and turbine jet noise, yet capable of providing good system transient response. The final selected turbine design has a bucket exit Mach number of 0.55 and a turbine exit diffuser area ratio of 1.30. The resulting fan system cross-section is presented in the figure on the next page.

The noise level objective was established at 92 PNdB, which would permit attainment of a six engine aircraft noise level less than 100 PNdB without inlet treatment. Based on a comparison of noise levels for fan systems having pressure ratios between 1.25 and 1.35, it was concluded that the noise level objective could not be obtained without integration of stator lean with a heavily treated exhaust system. During the aerodynamic design studies, it was determined that 15 degrees of stator lean could be employed through proper contouring of the exhaust splitter system. For this condition, the exhaust splitters are aerodynamically loaded in the radial direction and accomplish some downstream diffusion in order to distribute the aerodynamic loading between the stators and the exhaust flowpath. A double exit stator row system with the two stators leaned in opposite directions, initially considered and shown to be aerodynamically feasible, was abandoned because of mechanical complexity.

The acoustic analysis of the selected configuration, including 15 degrees of stator lean and four exhaust splitters, showed an estimated overall noise level of 94.0 PNdB for a single lift unit. This level is 2.0 PNdB higher than the objective; however, it is felt that with further system optimization in a detailed design study, a reduction of 1 to 2 PNdB could be achieved. Thus, it is reasonable to assume that the 100 PNdB objective for a 6 fan system V/STOL research aircraft could be achieved through the use of a modest amount of installation treatment. The mechanical design approach used in the LF467 is based on previous studies of lift fan systems employing the three strut front frame and single bubble scroll arrangement. The use of the three strut frame and modified scroll represents a significant weight, cost and complexity reduction at the sacrifice of a small amount of increased fan system overall thickness. The three strut front frame system also improves the installation flexibility by removing the requirement that the major strut, be oriented relative to the longitudinal axis of the aircraft.

The LF467 rotor and stator design is essentially the same as used in the LF460 and LF468 fan systems. The rotor system incorporates 88 high aspect ratio blades with two part-span shrouds. The tip turbine employs four turbine buckets per carrier that are integrally attached to the tips of each of the 88 fan blades. Conventional grease-packed bearings are used to support the twin-web disk arrangement.

The rear frame incorporates fifty-four titanium stator vanes with 15 degrees of lean in the direction of rotation. The outer panel stators are leaned 30 degrees against rotation to allow for relative thermal growth of the rear frame outer casings. Four acoustic splitters are included in the rear frame system. Each splitter is one inch thick and incorporates a corrugated core thus providing a two sided single degree of freedom noise suppression system.

The LF467 reference size lift fan is sized to operate using the exhaust gases of the YJ97-GE-100 engine on a sea level static standard day. Design point or maximum control operation is achieved by flow transfer between two interconnected engine systems. The maximum control gas conditions are established by the engine operating limitation of 2060 degrees Rankine exhaust gas temperature and the balanced flow transfer level. Nominal operation is established for the no flow transfer case and engine operation at the rated 1835 degrees Rankine exhaust gas temperature. Static performance of the LF467 fan at the two operating points at the standard day conditions are as follows: Nominal Maximum Rating* Control

YJ97-GE-100 EOT, ° R 1835 2053 Fan Airflow, Ib/sec 702 773 Fan Pressure Ratio** 1.216 1.266 Fan Speed, percent 92.0 100.0 Turbine Inlet Pressure, psia 46.1 53.1 Gas Generator Airflow, pounds per second 69.1 75.4 Gas Generator Speed, percent 101.5 101.5 . Net, Ibs 12885 15692

One phase of this design study was to determine the effects of ambient temperature on YJ97 exhaust gas conditions during the maximum power transfer method of operation. These gas conditions were then used to establish a parametric family of 1.30 pressure ratio lift units that show the effects of flat-rating at different temperature levels. The results of this study are summarized as follows:

Ambient Fan Tip Fan Nominal Maximum Temp Day Diameter Weight thrust Thrust (° F) (inches) (pounds) (pounds) (pounds) I Std1 66.80 947 12,885 15,692 75 64.93 900 12,209 14,881 90 64.22 837 11,348 13,851 100 60.64 795 10,748 13,138

The reference LF467 system, sized for standard day operation, has an estimated weight of 947 pounds. This weight level represents a thrust to weight ratio of 16.6 based on the maximum thrust level.

* Noise Rating Point ** Including acoustic splitter loss. At maximum control, the fan stage pressure ratio is 1.30 SECTION II

INTRODUCTION

The General Electric Company has been conducting a program in con- junction with the NASA to define an advanced lift fan system which would satisfy the requirements of a V/STOL transport research aircraft. Starting in late 1969, major effort was placed on the LF460 lift fan detail design, which was completed in May, 1971.

The LF460 is a 1.37 pressure ratio lift unit sized for use with the YJ97-GE-100 turbojet as the gas generator. Emphasis was placed on achieving low fan noise while maintaining the high thrust/weight capability of a high pressure ratio lift fan system.

In August, 1970, a NASA-sponsored study was initiated to define Remote Lift Fan Systems suitable for commercial applications in the 1980 time period. This study involved cycle and configuration screening followed by component and layout design activity through the preliminary design stage for the selected systems. Provision was included in this study for the projected achievement of greatly reduced noise levels. To achieve these low noise ob- jectives, lift unit pressure ratios of 1.25 and 1.20 were selected for the final designs.

Considering the trends shown in the Remote study, the decision was made to investigate the alternative of a lower pressure ratio lift fan for the research aircraft application to achieve reduced aircraft noise. A concept definition study was conducted under contract to NASA Lewis to investigate a design based on a 1.25 fan pressure ratio. Definition of this study fan, designated the LF468, is documented in Reference 3. The LF468 utilized the LF460 fan as a base but incorporated a single bubble scroll. Where applicable, the design included those noise suppression features identified in the Remote Fan Lift Program which can be used to advantage in the earlier time period. In November, 1971, the conceptual design studies of low noise lift fans were extended to include a design based on a 1.30 fan pressure ratio. Definition of this study fan, designated the LF467, is documented in this report. The LF467 lift fan incorporates all of the desirable design features identified during both studies of the Remote Lift Fan Program and the LF468 design studies. In addition, the design includes fan exit stator lean and additional exhaust acoustic suppression to achieve overall noise levels con- sistent with the requirements for the V/STOL transport research aircraft. The desire to investigate this higher pressure lift fan system is based on the results of aircraft systems studies which indicated large weight and per- formance penalties associated with the lower pressure ratio designs. SECTION III

DESIGN REQUIREMENTS

The LF467 lift fan system is designed to meet the anticipated require- ments of a typical V/STOL research transport aircraft. The design requirements are defined taking into consideration a typical research mission which includes three cycles of vertical take-off, conventional cruise and vertical landing. The total mission, as shown schematically in Figure 1, represents an operating time of 33 minutes per event. The duty cycle representation applied to the design takes into consideration the appropriate system power settings and anticipated power changes for maneuvering control throughout this type of mission.

The limiting components in the LF467 lift fan system are the hot rotating and static parts such as the buckets and scroll. These components are designed for an ultimate life of 1200 hours; thus, the system has the capability of performing about 2000 of the typical missions as defined. This number of missions should adequately meet the requirements for the total V/STOL research program.

A detailed description of the analysis methods and assumptions used in applying this mission analysis to the component design duty cycle is given in the LF460 design description, Reference 1.

Design Point Selection

The LF467 was designed to operate at a 1.30 fan stage pressure ratio. This definition is based on the pressure ratio from the fan rotor inlet plane to the stator exit plane, exclusive of the losses associated with the exhaust acoustic splitter system. The overall fan or nozzle pressure ratio reflects the losses associated with the acoustic splitter skin friction; splitter and stator vane row interaction losses ; and fan inlet bellmouth, bulletnose and strut friction losses. For the LF467 design, the fan nozzle pressure ratio is 1.266 relative to ambient static pressure. Other design considerations included in the LF467 system are:

• Turbine exit velocity equal to or less than 1.10 times the fan jet velocity to assure a low level of turbine nozzle jet noise.

• Minimum fan tip speed consistent with established rotor loading criteria in order to achieve reasonable fan response to transient thrust changes.

These design considerations led to the selection of a fan tip speed of 1060 feet per second with a fan radius ratio equal to 0.454 for consistent design technology employed in the previous LF460 and LF468 lift fan designs.

As an initial part of the LF467 design cycle, the gas conditions available for operating the fan at the design point were evaluated. Design point operation of the LF467 lift unit can only be achieved by transfer of flow between a pair of YJ97 gas generators. These gas conditions were pre- viously determined for an ideal, no loss interconnect duct system. For this study, the design point gas conditions were determined using the off-design computer deck developed during the LF460 study program. This off-design analysis includes a representative interconnect ducting system with losses and provides for balanced flow transfer gas conditions between the two inter- connected YJ97 gas generators. The ducting arrangement is shown schematically in Figure 2. For this arrangement, the performance of the ducting components was estimated as follows:

• Engine diffuser loss coefficient (Station 5.1 to 5.11) 0.15

• Losses associated with bleed-out flow (Station 5.11 to 5.12) Figure 3

• Interconnect duct total pressure loss coefficient (Station 1.4 5.12 to 5.15)

• Losses associated with bleed-in flow (Station 5.12 to 5.IIP) Figure 4

Transition duct pressure loss including wide open valve 0.967 (Station 5.13 to 5.3) During flow transfer for control to achieve design gas conditions, the throttle valves at the inlet to .one of the lift units are partially closed down. This increased back-pressure on the engine produces an increase in both engine exhaust gas pressure and temperature. Flow transfer then occurs between the high and low pressure engine duct systems. This added flow to the un- throttled engine then back-pressures that engine until an equilibrium condition is achieved. The gas energy of both engines are now at an increased level with this higher energy flow entering the unthrottled fan turbine system. The level of flow transfer and throttle position is established by the gas gener- ator exhaust gas temperature limitation of 2060 degrees Rankine.

The maximum power or flow transfer conditions were determined for a system which included two YJ97 gas generators as defined. A range of ambient temperature conditions was used to investigate this design criteria on fan sizing and performance. For each ambient temperature level, the fan turbine nozzle area was sized for rated engine exhaust gas temperature of 1835 degrees Rankine with the assumed installation parameters given in Table I. The engine discharge conditions as shown in Figures 5 through 9 were then obtained for the maximum flow transfer conditions. The engine discharge flow conditions, with modifications for flow transfer and ducting pressure loss produce the fan turbine inlet gas conditions as shown in Figures 10 through 12. These gas conditions then provide the basis for evaluating the effects of ambient tem- perature on a 1.30 design pressure ratio lift fan system.

The results of this lift fan design parametric study are presented in Figures 13 through 16. The effects of design temperature on the fan rotor size is shown in Figure 13. Figures 14 through 16 present fan performance for the three operating conditions:

• Nominal Maximum or high lift fan receiving gas flow without duct throttling.

• Nominal Minimum or low lift fan receiving gas flow with duct throttling.

• Nominal Rated or no flow transfer case where both fans develop the same lift. From this analysis, the reference size lift unit was selected based on a sea level standard day temperature where the fan tip diameter was estab- lished as 66.8 inches, thus this family of lift units incorporating a fan pressure ratio of 1.30 are identified as the LF467.

Design Point Summary

The base or reference size lift unit is established as the LF467. This size lift unit represents a sea level standard day designed system operating on the gas flow from a pair of YJ97 gas generators with about 8.8 percent flow transfer and a limiting exhaust gas temperature of 2060 degrees Rankine. The corresponding temperature on the engine receiving the transfer flow and feeding directly to the lift fan operating at design point conditions is about 2052 degrees Rankine. The fan unit is designed to accept these engine exhaust gases. The significant fan and turbine design parameters for the LF467 lift fan are given in Tables II and III.

10 SECTION IV

ACOUSTIC DESIGN AND ANALYSIS

Design of a family of low noise lift fan systems was initiated with the LF460, a 1.37 fan pressure ratio system. Acoustic analysis of this system, which included only modest levels of exhaust acoustic suppression, showed the 500 foot sideline noise level to be 97.3 PNdB at the noise rating or nominal thrust condition. The noise level for six fans would be 105.3 PNdB. This level of noise generation, when corrected for estimated system installation treatment level, would yield an overall noise level of 100 to 103 PNdB for a typical six fan research transport aircraft.

The requirement to achieve a maximum noise level of less than 100 PNdB, with a possibility of achieving a 95 PNdB level, led to the design of a family of lower pressure ratio lift fan systems. The initial lift fan system design which included extensive exhaust acoustic suppression was the LF468, a 1.25 fan pressure ratio unit. The results of this design study showed a six fan research aircraft to have an estimated 500 foot sideline noise level of 101.3 PNdB without additional aircraft installation treatment. A level of less than 100 PNdB could be achieved with a modest amount of fan inlet treat- ment. Fan exit stator lean was not included in this initial highly suppressed fan design because of difficulties in achieving acceptable stator aerodynamic loading. Later modifications of the aerodynamic design of fans with highly suppressed exhaust systems1indicated that it is possible to have both lean and high levels of exhaust suppression. This encouraging result led to the conclusion that a higher pressure ratio lift fan might meet the objective noise level of 100 PNdB for a six fan research transport.

This design study was then extended to include a lift fan system designed to develop a 1.30 fan pressure ratio. The higher pressure ratio levels are desired for consideration of the aircraft installation and systems compatibility viewpoint. This lift fan system was designated the LF467, and

11 has a fan tip diameter of about 66.8 inches and is designed to include extensive exhaust system suppression, adequate rotor stator spacing, and fan exit stator lean as desired for minimum noise generation.

Jet Noise

The two sources of jet noise which are inherent to the lift fan unit are the fan jet exhaust and the tip turbine exhaust. The fan exhaust jet noise is primarily a function of the fan jet velocity which is established by the fan pressure ratio and corresponding temperature rise. These parameters are depen- dent upon the fan design selected and, as such, are not variables which may be used to reduce noise. With the fan jet noise established, the turbine jet noise was set at a lower level through proper selection of the turbine exit velocity. The resulting contribution of turbine jet noise to the total jet noise floor was about one PNdB. The turbine exit velocity was set at the desired level without major compromises in the turbine rotor design by incorporating an exit diffuser in the turbine exhaust stream.

Turbine Noise

Puretone and broadband noise generated by the tip turbine blades are established by the turbine tip speed and blade number. Both of these variables were selected on the basis of aerodynamic and mechanical design considerations. The noise level of the turbine blading that resulted was not a major noise source and was on the order of the fan jet noise floor; thus, no attempt was made to add acoustic treatment to the turbine exhaust, or to modify the basic design. This noise source does produce an increase of the total floor noise (i.e., all noise except that generated by the fan blades) on the order of three PNdB.

Fan Noise

The major noise source for the LF467 lift fan is the puretone and broadband noise generated by the fan stage. In order to minimize the noise generated by the fan due to interaction of the rotor blade wakes and outlet

12 guide vanes, three specific acoustic features are incorporated into the design:

• High number of rotor blades (88) - A high number of rotor blades is used to insure that the passing frequency is well beyond the 2828 to 4480 Hertz bandwidth most heavily weighted for PNdB calculations and also takes advantage of the higher atmospheric and ground attenuation levels available at the higher frequencies.

• Large axial spacing between the rotor and stator vanes - An axial spacing equal to two rotor chords was maintained to reduce the strength of the rotor wake before interaction occurs with the stators. The short chord, moderate solidity rotor blades aid this design feature since the physical spacing for two chord lengths is minimized.

• Circumferential stator lean - The stator row is leaned circumferentially in the direction of the rotor rotation at an angle of 15 degrees to the hub. By circumferentially leaning the exit stators the rotor wake becomes oblique to the vane, thus producing a slicing type interaction as opposed to a more uniform or radial simultaneous interaction. The tip portion of the blade is leaned opposite to rotation by 30 degrees for mechanical design reasons. This helps in producing a slicing action between the wake and OGV but the effectiveness is not as large as leaning in the direction of rotation.

Acoustic Treatment

Noise suppression by means of acoustically treated splitters is ob- tained most effectively by maintaining the height of the passage through which the noise is propagating at a value approximately equal to the wave length of the treatment design frequency. For the LF467 spectrum shape a design frequency of 4000 Hertz was selected. Maximum suppression will occur at this frequency with decreasing levels at lower and higher frequencies. The extent to which the lower and higher frequencies are suppressed establishes the suppression bandwidth. For the selected design frequency, it is necessary to use four

13 acoustic splitters in the fan exhaust duct to provide the required passage height. The combination of passage height and the requirement to maintain a wide suppression band resulted in selection of a one inch splitter thickness. The inner and outer walls of the flowpath are also acoustically treated. The length of the acoustic splitters is defined by the ratio of length to passage height (L/H). For the LF467, a ratio of four was assumed for the basic con- ceptual design.

An additional three PNdB suppression is assumed to be available by applying acoustic treatment to the exit louvers. This assumption was based on the treatment tests and louver arrangements developed for the LF460 lift fan reported in Reference 1.

Estimated Noise Levels

LF467 noise levels were estimated using the prediction technique and assumptions used for the LF460 and LF468 lift fan systems, References 1 and 3. Reference 1 describes the prediction method.

Table IV presents the estimated noise levels for the LF467 at the Noise Rating Point. Total noise for the lift unit is 94 PNdB which is two PNdB higher than the objective level of 92 PNdB required to satisfy the aircraft objective noise levels. A comparison of the suppressed fan noise of 92.5 PNdB and the total noise of 94.0 PNdB shows only a 1.5 PNdB influence due to the jet noise and turbine noise floor.

One of the most important factors in the overall noise level is the inlet radiated fan noise seen in the aft quadrant. For the estimates presented, it was assumed that the inlet level was 10 PNdB lower than the exhaust radiated noise in the aft quadrant. As seen in Table IV, even though the exhaust treat- ment is reducing the aft generated noise by 20.7 PNdB the overall effect is only a reduction of 9.7 PNdB. Since this assumption of 10 difference between inlet and exhaust radiated noise is such a significant factor, the LF467 noise was also calculated with the assumption that the inlet radiated noise is completely removed. These values are also shown. This would represent the lowest noise

14 attainable by the LF467 as currently designed. The impact of the inlet noise is obvious since the noise level is only 86 PNdB with it removed, which is below the value (87.0 PNdB) required to obtain An overall of 95 PNdB for a six fan aircraft.

15 SECTION V

AERODYNAMIC DESIGN

Initial Studies

Previous fan aerodynamic design studies, the LF468 and advanced remote lift fan, have shown that it is difficult to incorporate both exit stator lean and extensive exhaust treatment into the system design. The basic aerodynamic problem associated with stator lean is that with the stator vanes leaned in the direction of rotation, a radially outward flow component must be accounted for in the inner and hub flowpath. When exten- sive exhaust treatment is included, the blockage associated with the splitter thickness tends to require a radially inward sloping flowpath. Attempts to satisfy both of these criteria were unsuccessful in the previous design studies. The usual problem was excessive stator vane loadings in the vicinity of the hub.

During the initial design phases of this study, it was apparent that the 1.30 pressure ratio fan must include stator lean in order to have a reasonable overall noise level. Two basic approaches were considered to incorporate lean:

• A double stator row with the first row leaned in the direction of rotation and the second row leaned opposite to rotation.

• A single stator row leaned in the direction of rotation with aerodynamically loaded acoustic splitter systems. The annular flowpaths near the hub act as diffusers and tend to unload the stator vanes in the hub area.

The double stator row configuration was carried through the aerodynamic design phase and was shown to be feasible. The configuration was not carried through the mechanical design sequence because of the high mechanical complexity associated with this scheme. The results of the aerodynamic study will be pre- sented to document the design characteristics of this type of lift fan stator design.

16 The aerodynamic design studies of the loaded splitter configuration also showed that a stator system with 15 degrees of lean was feasible without unnecessarily high aerodynamic risk. In addition, this single stator row design offers about two additional inches of acoustic treatment over the two stator design for the same total fan thickness. On this basis, and because of the con- siderable design experience that is available for the conventional highly treated stator configuration, the loaded splitter configuration was selected for this design phase of the LF467 lift fan.

Double Stator Configuration

The double leaned stator configuration incorporates two vane rows closely spaced together. The forward vane row was leaned 15 degrees in the direction of rotation based on the reduced noise levels inherent with lean in this direction. The second vane row was leaned in the opposite direction. For this configuration, the first vane row turns the flow radially outward because of the direction of lean. The second downstream vane row then turns the flow radially inward thus tending to correct the radial outward flow problem of the leaned stator and at the same time meet the acoustic lean criteria. Both stator rows include 30 degrees of outer panel lean opposite to rotation as required to satisfy the mechanical design considerations.

The flowpath developed for this configuration is shown in Figure 18. The details of the aerodynamic design procedures are described in Reference 1. The significant aerodynamic parameters are presented for reference purposes in Figures 19 through 23, as follows:

• Fan exit total and static pressure profiles Figure 19

• Rotor inlet Mach number distribution Figure 20

• Rotor aerodynamic loading parameters Figure 21

• Stator inlet Mach number distribution Figure 22

• Stator aerodynamic loading parameters Figure 23

17 Selected Fan Configuration

The fan design configuration selected for continuation into the mechanical design effort was the 15 degree leaned stator system incorporating the four aerodynamically loaded splitters. The basic aerodynamic procedures defined in Reference 1 were used for this design, resulting in the aerodynamic flowpath shown in Figure 24. This design configuration incorporates the desirable 15 degrees of stator lean in the direction of rotation with a reversed 30 degrees of lean between the outer splitter and the stator tip. Comparison of the double stator configuration, Figure 18, and the final LF467 configuration, Figure 24, shows that an additional two inches of exhaust treatment is included in the design for the same overall fan depth.

Fan Description

The significant design parameters which describe the LF467 fan are presented in Table II. The fan was designed for a nominal total pressure ratio of 1.30. The actual overall pressure ratio from ambient to fan discharge is 1.266 because of the pressure loss associated with the inlet and the four acoustic splitter panels in the exit. Selection of tip diameter, hub radius ratio, airflow and tip speed were discussed previously, under Design Require- ments and Design Point Selection.

The desirable features included in this design are as follows:

• The inlet bellmouth and bulletnose heights have been increased to accom- modate the single bubble scroll and modified front frame. These features are desired for overall system simplicity and reduced component weight.

• The aerodynamic design tip speed was selected as 1060 feet per second consistent with the aerodynamic loading levels at a 1.30 fan pressure ratio. A minimum tip speed consistent with reasonable aerodynamic loading is required for rapid response of the lift unit to thrust changes.

• The stator and exhaust system includes stators leaned 15 degrees in the direction of rotation with four acoustically treated exhaust splitters. These items were included to reduce overall fan system noise levels.

18 • The rotor to stator spacing is two times the rotor tip chord. This level of spacing is required to reduce rotor-vane interaction contribution to the overall noise levels. Increased rotor-vane spacing above the two level is usually not warranted based on the additional noise reductions.

• Aerodynamic loading both upstream and downstream of the stator vane row and additional downstream diffusion is included in the exhaust splitter system so that the stator lean could be incorporated into the design, even with the large blockage due to the four one inch thick exhaust splitters.

Aerodynamic Design Details

The flowpath of the LF467 system as developed during this conceptual design study is shown in Figure 24. The fan aerodynamic design parameters obtained during the design study are presented in Figures 25 through 34. These characteristics represent the results of only an initial conceptual design study. An optimization and smoothing of the parameters would undoubt- edly occur during a final design analysis.

The significant fan aerodynamic parameters for the LF467 configura- tion with stator lean, as presented in the figures, are as follows:

Wall Mach number distributions Figure 25

Rotor and stator exit total pressure profiles Figure 26 I Rotor and stator pressure loss coefficients Figure 27

Rotor and stator inlet velocity distribution Figures 28 and 29

Rotor and stator air and blade angles Figures 30 and 31

Rotor aerodynamic loading parameters Figure 32

Stator aerodynamic loading parameters Figure 33

Rotor and stator choke ratios Figure 34

19 In Figure 35 is presented the radial location of the stream function parameter throughout the fan rotor and stator consistent with the aerodynamic performance parameters previously presented.

Fan Blade and Vane Geometry

Based on the aerodynamic design parameters previously presented, the blade geometries selected for the LF467 fan design are summarized in Figures 36 through 39. The variation of rotor and stator solidities are shown in Figure 36. These solidity levels were selected to provide adequate stall and choke margins with additional consideration based on mechanical require- ments.

In Figure 37 is shown a plot of rotor blade meanline arc length ratio and meanline arc radius ratio versus radius. At the hub, arc length ratio was set at a 0.5 level. At the tip, the arc length ratio was selected to keep the junction of the meanline arcs downstream of the blade throat. An approximately linear variation was then used from hub to tip. The arc radius ratio was varied from hub to tip in a manner to provide the proper local and rotor average choke margins.

The LF467 rotor blade geometry is summarized in Figure 38. The sudden increase in chord and maximum thickness-to-chord ratio near the tip is the result of mechanical requirements for attachment of the tip turbine bucket carriers. The waviness of the camber and stagger curves is due to the part- span dampers.

The stator vane blade geometry employs circular arc airfoils. The stator vane geometric parameters are shown in Figure 39. The vanes incorporate constant chord, maximum thickness and trailing edge thickness throughout the airfoil span. Variations of camber and stagger are due to the penetration of the acoustic splitters through the blade row.

The radial variation of aerodynamic loading on the rotor blade and stator vane rows for the selected air design and blading geometry is shown in

20 Figures 40 and 41. The discontinuities in the stator vane loading occurs at each of the acoustic splitter locations.

Turbine Aerodynamic Design

The fan turbine system is designed to accept the exhaust gas condi- tions from the two interconnected YJ97 engine systems at the maximum power transfer levels. The reference size LF467 lift fan system is based on these gas conditions representative of sea level static operation on a standard day. The significant turbine design point parameters are tabulated in Table III. The turbine velocity diagrams at this design point are shown in Figure 42.

This turbine design is similar to those used in both the LF460 and LF468 lift fan designs in that the turbine bucket exit Mach number is selected as high as reasonable followed by downstream diffusion. The high bucket Mach number which results in minimum bucket height, is desired to achieve minimum time for response to a given change in thrust level. The downstream diffusion is required to yield a turbine exit velocity almost equal to the fan exit velocity in order to minimize the effects of the turbine jet noise on the overall jet noise. The effects of these parameters, turbine exit Mach number and diffusion, were investigated during the LF468 design and are discussed in Reference 4. Based on these trends, the bucket exit Mach number was selected to be 0.55 at the design point and a 1.30 area ratio diffuser was used down- stream of the turbine bucket exit.

Aerodynamic Flowpath

The aerodynamic flowpath of the fan and turbine streams is shown in Figure 43. This flowpath includes a fan rotor with a 0.454 hub radius ratio and a 15 degree radial inward fan tip slope. The fan flowpath at the hub is almost axial. A rotor exit to stator inlet spacing of 2.0 times the rotor tip chord is used to minimize rotor-stator interaction noise. The fan exhaust flowpath includes four one inch thick acoustic splitters. Two of the splitters extend through the exit stator row and are used to guide the flow along the innerstage hub and tip flowpaths.

21 SECTION VI

MECHANICAL DESIGN

Front Frame Design

General Description

The principle components of the front frame assembly shown in Figure 44 are the struts, hub, dome and bellmouth. The front frame is the main structural support for the rotor, transferring all rotor loads, gyroscopic moments and inertia forces through the scroll to the airframe mounts. The front frame incorporates a center hub for mounting the rotor bearings and three structural struts oriented 120 degrees apart. These struts restrict the relative axial deflections between the rotor and adjacent structure. The struts are pinned at the hub and scroll allowing the struts to follow radial movement of the scroll.

Design Requirements

In addition to the general design requirements discussed in Section III, the following requirements are applicable to the front frame:

1. Provide required stability to maintain adequate clearances and prevent interference between static and rotating parts during all fan operating conditions.

2. Provide a seal between the turbine and fan inlets to limit hot gas leakage into the fan stream.

The fan system is subjected to aerodynamic, maneuver and crossflow loading conditions. The front frame is designed to transmit all rotor loads through the scroll to the airframe mounts.

22 Aerodynamic Loading

Tine resultant static foiroes clwft to> »' *

Axial Force Torque Component (Pounds) (Inch- Pounds)

Bellmouth +5849 0 Bulletnose -1331 0 Struts -20 0 Rotor Hub +1158 0 Rotor Blades . . +7541 218,100 Turbine Carriers and Buckets +124 218,100 Stator Hub and Inner Wall +985 0 Fan Stators and Splitters 41254 218,100 Stator Midbox and Outer Wall -120 0 Scroll Nozzles +1945 220,500*

Air loads on the struts are due to aerodynamic drag only and are assumed negligible during hover operation.

Maneuver Loads

The front frame and mounts are designed to withstand maneuver loads as defined in Reference 1, when applied simultaneously with the aerodynamic loading. Maneuver loads can be applied during conventional flight or in a crossf low environment .

Crossflow Conditions

The front frame is designed to withstand aerodynamic loads experienced during transitional flight when installed with a shallow wing fan inlet.

* Turbine Residual Swirl = 2400 inch-pounds In direction of rotation

23 The design point for crossflow operation is 100 percent fan speed at a flight speed of 150 knots.

Component Design Description

Hub

The hub provides a load-carrying structure to transfer rotor loads to the three struts. A flange stiffened structure is utilized to limit radial deflections. The hub is fabricated from a machined titanium 6-4 forging. Three gussets are located between the two flanges, positioned in line with the strut attachment lugs. Lugs on each flange, drilled and bushed for body-bound bolts, provide attachment points for the struts. The aft flange is drilled to accept bolts to fasten the bearing outer race retainer to the hub. The dome is bolted to the forward flange.

Struts

Three equally-spaced struts provide the loadpath which transfers the fan thrust, crossflow, gyroscopic and inertia loads to the scroll mounts. The struts are structural spars utilizing top and bottom cap strips supported by a continuous shear web, resembling an I-beam with a constant chord of 9.0 inches. Both the top and bottom cap strips transition from an airfoil contour through the fan flow area into machined lugs for fastening to the hub. The lugs are boxed-in on the sides to reduce load-induced deflection.

The struts are NACA 63-618 series airfoils. A honeycomb filler is located between cap strips on each side of the web to form the required airfoil contour. The honeycomb is adhesive-bonded to the web and the 0.010 inch aluminum face sheets. Honeycomb filler is also used between face sheets to form part of the airfoil under the bottom cap strip.

A uniball attachment is used at the outboard end of each strut. This prevents induced bending moments in the strut when loads are transmitted

24 to the scroll mount.

Bellmouth

The bellmouth provides the aerodynamic outer flowpath of the fan inlet. It incorporates the forward air seal assembly. The bellmouth is mounted to the scroll with 36 "A" frame brackets and is fabricated in two sections to allow assembly of the brackets to the scroll.

The bellmouth is a continuous 360 degree titanium 6-4 honeycomb structure. It utilizes 0.010 inch face sheets resistance-welded to 0.0035 inch foil forming a 0.5 inch thick panel. The honeycomb has 0.25 inch cells.

At the outer diameter, the bellmouth is crushed to a reduced thickness to provide a recession for the airframe installation cover. Anchor nuts are provided on the underside for mounting the installation cover.

A machined flange is located at the aft end of the bellmouth to provide mounting for the forward air seal assembly. The seal assembly ring is fabricated from two 0.020 inch titanium 6-4 face sheets separated by a brazed corrugated strip to dissipate heat. A 0.25 inch thick insulation blanket is attached on the scroll side of the bellmouth to limit soak-back temperatures at shutdown.

At the three locations where the scroll mount brackets penetrate through the bellmouth, the honeycomb is crushed to provide a flange for six anchor nuts riveted to the back side. These are used to mount a seal around each scroll mount bracket.

Dome

The dome provides the required aerodynamic contour over the hub region of the front frame. The dome has cutouts at each strut location to allow unrestricted strut motion during fan operation. The dome is formed from

25 0.25 inch thick aluminum 7075 T6 honeycomb sandwich with 0.010 inch face sheets bonded to an internal load-carrying network of ribs. The ribs carry the loads from an aluminum "u" channel at the lower end of the dome to the six mount points at the upper mounting flange. The flange has six 1 inch tubes open at their upper end and blanked-off and drilled at the lower end for attachment to the hub.

Forward Air Seal Assembly

The forward air seal assembly is attached to the aft inner surface of the bellmouth. This seal assembly, shown in Figure 45, restricts the hot gas leakage from the turbine inlet into the fan stream. A slip seal controls leakage from the fan cavity, between the bellmouth and scroll, into the turbine rotor inlet.

The forward air seal has thirty 12 degree segments. Each segment has a 0.030 inch backing plate with each end machined to provide a 0.25 inch overlap from segment to segment. The seal surface is a strip of honeycomb 0.2 inch thick by 0.5 inch wide, which is brazed to the backing plate. The honeycomb utilizes 0.0625 inch cell size and 0.0025 inch foil. The seal sectors are bolted to the seal ring.

The seal ring supports the seal assembly. It is fabricated from two cylinders of 0.020 inch titanium 6-4 separated by a wiggle strip. Cooling air is vented through the wiggle strip. A flange on the forward end bolts to the aft end of the bellmouth.

The bellmouth-to-scroll slip seal is also assembled from 12 degree segments. Each segment consists of two laminated 0.010 inch sheets offset to form an overlap at each end, thus providing an "interlock" between seg- ments. The slip seal is bolted to the seal assembly ring with the insulation sandwiched between.

The air deflector consists of six 60 degree segments. Each segment is

26 bolted between the seal assembly and the bellmouth. The air deflector directs the hot gas leakage rearward to minimize effects on the incoming fan air stream.

Design Stress Levels

In Figure 46 is presented the major component design stresses for the lift fan front frame. Stress levels shown are the maximum which are predicted to occur under combined steady state, cross-flow and maneuver conditions.

Scroll Design i General Description

The turbine scroll distributes the engine exhaust gases through two 180 degree arms to feed the turbine nozzle annulus. The gas leaves the scroll through the nozzle partitions at a constant exit angle to drive the tip turbine. To minimize weight, a simple single bubble scroll is utilized. The scroll provides a loadpath to transfer front frame and bell- mouth loads to the airframe mounts. The scroll is fabricated from Rene" 41 material.

Design Requirements

In addition to the general design requirements discussed in Section III, the following requirements apply specifically to the scroll:

• Operate under engine-out conditions (only one-half of scroll receiving hot gas flow) for a maximum of 4 minutes without adverse structural effect.

• Transfer all front frame loads to the airframe mounts.

Component Design Description

As shown in Figure 47, the scroll assembly incorporates the inlet elbows, bubble, nozzle partitions, a torque tube and exhaust section. All sheet metal skins are stretch formed in right-hand and left-hand sections then masked and chem-milled .to minimum skin thickness after forming. This provides thick weld joints and improved formability, while retaining the advantages of lightweight thin gauge design.

27 Inlet Elbow

Two inlet elbows direct the inlet gas tangentially. These elbows pro- vide a controlled area change to maintain a constant Mach number as the flow is turned and fed to the first section of nozzle partitions. The elbows have a flange at the inlet for bolting to the gas duct system. They are fabricated from 0.060 inch material and chem-milled to 0.040 except where weld joints occur at the bubble, torque tube and scroll exhaust. A one inch thick honeycomb partition with 0.020 inch thick face sheets, separates the two inlets. It provides the structural load path from the front frame strut to the airframe mount beneath the scroll inlets.

Bubble

The bubble is fabricated from 0.060 inch material and chem-milled to 0.020 except at the weld joints. The cross-sectional area decreases to maintain a flow Mach number of 0.35 as the gas is distributed to the first 120 degree segment of the nozzle partitions. Diameter is constant from there to the 180 degree point (opposite the inlets) where another partition across the bubble separates the two halves of the scroll.

Torque Tube

The torque tube provides a structural attachment and a contoured inlet flowpath for the nozzle partitions. Locally, at each airframe mount, it provides a load path from the nozzle partitions into the bubble and into the airframe mounts. A short angled strip of 0.030 inch material is brazed within the torque tube and eloxed to accept the nozzle partition at the same time as the exit outer flowpath. The partitions are fitted within the eloxed slots and brazed.

Scroll Exhaust

The scroll exhaust consists of an inner and outer flowpath. The inner

28 flowpath is machined with two radial stiffening rings and butt welded to the bubble. A strip of 0.030 inch material is brazed to the side forming a torque box into which the nozzle partitions are brazed. The torque box has a three-leaf slip seal brazed at its lower end. The outer flowpath is a machined component that has the forward end welded to the torque tube inlet and the bubble. A slip-fit slot is located at the aft end to mate with the rear frame.

Nozzle Partitions

Variation of the gas flow angles inside the scroll requires three different families of nozzle partitions to turn the gas and provide a constant nozzle discharge angle. Each of the 178 nozzle partitions has a 0.005 inch protuberance on the pressure side which establishes the throat area for the convergent-divergent supersonic nozzle design. The nozzles are cast hollow, have a wall thickness of 0.040 inches and are twisted slightly because of the required canting relative to the buckets. The canted posi- tion is necessary in order to carry the bubble membrane loads across the partitions. Each nozzle partition is brazed to the torque box at its inner end and to the torque tube at its outer end.

Scroll/Airframe Mounts

The three mounts, spaced 120 degrees apart, are machined brackets having a one inch diameter uniball for airframe mounting and a 0.375 inch diameter uniball for attachment to the rear frame. The mount between the inlets is welded to the honeycomb partition separating the two halves of the scroll. At the other two positions, the mounts are welded to the torque tube and a flanged ring (0.2511 x 2") around the bubble. The flange provides the principal load path between the strut mounts and the airframe mounts. The front frame mount clevis is welded to the honeycomb partition at the inlets and bolted to the flanged ring at the 120 degree locations. A drag link mount clevis welded to the torque tube is provided 180 degrees from the scroll inlet. This mount accepts one half of the fore and aft fan inertia loads and half of any residual scroll nozzle torque loads.

29 Insulation

The outer surface of the scroll is covered with 0.5 inch thick Min-K. The insulation is contained in two 0.003 inch AMS 5510 foil skins.

Design Summary

The scroll design was based on the LF460 type duty cycle and analyzed as a "Time and Cycle - Dependent Structure." This analysis, presented in Reference 1, is based on the assumption that a linear combination of creep damage and fatigue damage is valid for design purposes. Preliminary analysis indicates that the maximum bubble stress occurs at the mount points. Results indicate that the 1200 hour mission life requirement can be satisfied with the current scroll design. In Figure 48 is shown the overall stress summary for the scroll.

Rotor Design

General Description

The LF467 rotor basic design approach is essentially the same as that used in the design of the UT468 lift fan. The rotor incorporates a single stage fan and a single stage tip turbine. The fan stage has 88 high aspect ratio blades. Each fan blade has two part-span shrouds to control blade vibrations and torsional flutter. Torque transmission is accomplished through these part-span shrouds and a blade tip lockup.

The turbine consists of 88 sectors, each containing four shrouded buckets. The buckets have integral tip shrouds and incorporate improved FOD resistance features compared to previous fan turbines. The turbine bucket carrier assemblies are integrally attached to the tip of each fan blade.

30 The disk utilizes the twin web geometry proven by operation on previous lift fans. The two-piece disk is electron beam welded at the rim and brazed at the internal spacers. The stub shaft is integral with the disk,, elmiminating the need for a mechanical joint.

The rotor is supported by two grease-packed bearings, one angular- contact thrust bearing and one pre-loaded roller bearing. The roller bearing employs an out-of-round inner ring which loads the rollers to prevent skidding. The bearings have inner race rotation similar to the LF1 lift fan utilized in the XV-5 aircraft. Silverplated bronze cages are used to minimize power loss. Vacuum melt M50 bearing material is used in the races, rollers and balls to improve bearing fatigue life. The sump is a self-contained removable subassembly allowing the rotor to be balanced on its own bearings prior to fan assembly.

Dynamics

Lift fan rotors exhibit dynamic characteristics similar to conventional gas turbine rotors, in that both are susceptible to coupled blade-disk vibrations. The rotor dynamic requirement is that no detrimental vibratory mode of the coupled blade-disk be present in the fan operating speed range from 70 to 100 percent rpm. The design criteria are:

• The coupled blade-disk two-wave vibratory mode should be at least 15 percent higher in frequency that the 2/rev excitation at 100 percent rpm.

• The coupled blade-disk three-wave critical speed should be below 70 percent rpm.

The results of the axial vibratory analyses are shown in Figure 49. The two wave resonance satisfies the criteria with a margin of 15 percent. The three-wave resonance occurs at 75 percent rpm, compared to an objective of 70 percent rpm. A reduction to the 70 percent level would not be desirable

31 since any decrease in the three-wave critical rpm would also decrease the 15.0 percent margin of the two-wave resonance. Design and test experience have shown that placement of the two-wave mode above the 2/rev excitation is more important than having the three-wave mode at the bottom of the operating range. The LF336 has a three-wave resonance at 74 percent rpm, yet has experienced no blade stress build-up. The results obtained are, therefore, considered completely acceptable.

Low Cycle Fatigue Analysis

All rotor components were assumed to be subject to 12 start-stop cycles per hour. The stress range for the low-cycle fatigue analysis was defined as the difference between the stresses at the 0 percent speed and the 104 percent speed conditions. Half of this stress range was considered to be mean stress and the other half was considered to be alternating stress, as illustrated in Figure 50. A stress concentration factor was applied to both alternating and mean stresses. In Table V are summarized the results of the analysis.

Limiting Stress and Life

A summary of limiting stresses for all major rotor components is also given in Table V. This table lists the material^.design temperature, type of loading and criteria for limiting stress. Comparisons are made between the design'limit stress and allowable stresses. Margins of safety are given for the limiting stress, either yield, rupture, low or high-cycle fatigue. All margins of safety are positive. The only life limited component is the braze joint. The joint area was set so as to meet the lift requirements-of the rotor. In summary, based on preliminary design analysis, all rotor components meet the objective levels of allowable stress and required life.

Fan Blade

The fan blade configuration is shown in Figure 51. The fan contains 88

32 Rene 95 blades. Each blade has an integrally attached turbine sector at its tip, two part-span shrouds on the airfoil, and a single hook dovetail at the blade root for disk attachment. The fan blades are multiple circular arc airfoils. The inner fan flowpath is established by the integral platforms on the blade root and the adjacent disk dovetail posts. The outer fan flow- path is defined by the fan blade tip shroud. Blade rigidity for frequency control and torque transmission is provided at the root by the dovetail, along the airfoil by part-span shrouds near the 1/3 and 2/3-span points, and at the tip by the tip shroud. Axial blade retention is provided in the forward direction by an integral hook on the dovetail aft face and in the aft direction by a blade retainer ring.

Design Requirements

The blade has been designed to meet the life and cycle requirements defined in Section III. These requirements include:

• Minimum life of 1200 hours.

• Capable of withstanding 14,400 start-stop cycles.

Design Criteria

The blade design criteria are:

• In the fan operating range (70 to 100 percent rpm), there must be a margin of at least 15 percent between any blade natural frequency and any excitation frequency from the front frame and stators.

• Blade flutter must not occur prior to fan stall.

• All blade stresses must be less than:

• 80 percent of ultimate tensile strength at 106 percent speed.

• 0.2 percent minimum yield strength at 106 percent speed.

33 * Minimum rupture strength (Mission Analysis).

* 10' cycles on the stress range diagram at 100 percent speed.

Dovetail

The blade root attachment to the disk is made using a straight, single hook dovetail with a 55 degree flank angle. Straight, single hook dovetails are employed for reliability and ease of manufacturing. Dovetail stresses at 100 percent speed are shown in Figure 52. Strength levels even at over- speed conditions are adequate, as shown in Figures 53 and 54. The dovetail and the dovetail shank extension to the airfoil are progressively stronger than the blade root.

Airfoil

The alternating stress margin for the peak stress point is shown in the airfoil stress range diagram, Figure 55.

Blade vibration from aeromechanical flutter and strut-induced flow distortion is avoided. Resonant frequencies of the blade panels are shown in the blade frequency-speed diagram of Figure 56. All blade natural fre- quencies are more than 15 percent above both the 3/rev excitation of the front frame struts and the 54/rev excitation of the rear frame stators.

Analysis of blade torsional flutter indicates that the three blade panels have the following flutter margins:

Percent of Flutter Panel Margin at Fan Stall

1 28% 2 28% 3 59%

These margins, relative to limiting levels, are illustrated in Figure 57.

34 Shrouds and Seals

The outer part-span shroud is more highly stressed than th

The blade tip section transitions from an airfoil into the blade tip shroud and siderails as shown in Figure 59. The blade tip shroud forms the fan tip flowpath and supports the seal. The siderails support the turbine buckets and transmit bucket loads to the blade. The tip shroud and the siderails are machined as integral parts of the blade.

The blade tip shroud, like the siderails, is tapered to reduce weight. No rupture life is consumed in the blade shroud; therefore, the limiting design criteria is fatigue. The stress range diagram (Figure 60) shows that with a criterion of 10 Ksi alternating stress, there is an alternating stress margin of 1.05 at the peak steady state stress point.

The seals (Figure 59) are 0.015 inches thick and are formed from Rene 41 sheet. These single-tooth running seals rub the stationary honeycomb seal strips on the front frame-bellmouth assembly and the rear frame assembly, blocking hot gas leakage from the tip turbine into the fan. The seals support only their own weight and are, therefore, not highly stressed. The seals are brazed to the fan tip shroud, and are replaceable.

Siderails

The siderails, shown in Figure 59, are tapered along the tangential surface to obtain maximum material utilization and to reduce weight. The outer portion of the siderails is in the same temperature environment as the braze material. At these temperatures, negligible rupture life is consumed; therefore, fatigue is the limiting design criteria for the siderails. The siderail vibratory stress limit is 10,000 psi. The maximum siderail stress and margin of safety are shown in Table V.

35 The siderail stress range diagram is shown in Figure 61.

Turbine

The turbine contains 352 hollow uncooled buckets, arranged into 88 sectors of four buckets each. Each sector is an integral part of one fan blade. This integral blade turbine concept is similar to that of the LF460 and LF468.

A blade-turbine sector, shown in Figure 59, consists of:

• Four buckets, each with integral internal stiffener and integral tip shroud.

• A two-piece sheet metal box section.

• Two one-piece sheet metal air seals.

• One fan blade with integral siderails, part-span shrouds, and blade tip shroud.

The buckets are equally-spaced over the fan blade. The box section positions the buckets and adds structural rigidity by absorbing bucket gas bending loads. The siderails are integral parts of the blade. The attach- ment of the buckets and box section to the siderails is the only structural braze joint in the blade-turbine sector assembly.

Design Requirements

The turbine has been designed to satisfy the life and cyclic require- ments defined in Section III. These include:

• 1200 hours life.

• Capability of withstanding 14,400 start-stop cycles.

36 In addition, the rotor system is designed to provide:

• Minimum axial clearance of 0.45 inches between the turbine and any stationary fan component.

Design Criteria

The following criteria have been established:

i • All stresses must be less than: '

* 0.02 minimum yield strength at 106 percent speed.

* Minimum rupture strength at 100 percent speed derated for thin wall high temperature effects.

* 107 cycles on the stress range diagram at 100 percent speed.

• Bucket uncorrected gas bending stress must be less than 10,000 psi. This is a criterion which regulates the bucket stiffness for accept- able vibratory stress.

• Gas bending stress during one engine-out must be less than twice the gas bending stress during normal operation.

• The endurance limit of all thin-wall high-temperature components must be no more than 70 percent of the material minimum endurance limit.

• All calculated turbine natural frequencies must be at least 15 percent higher than any known per-rev excitation frequency in the operating range of 70 to 100 percent speed.

The turbine mechanical design is based on the metal temperatures shown in Figure 62. These temperatures were calculated based on LF336 turbine carrier heat transfer data measured during recent fan tests, adjusted for the exhaust gas temperature of the YJ97-GE-100 gas generator.

37 Bucket

The bucket cross section is shown in Figure 63. The one-piece bucket and tip shroud (Figure 59) is manufactured from a Udimet 700 forging. Electric Chemical Machining (ECM) and Electric Discharge Machining (EDM) are used to generate the external contours and surfaces. The inside cavities with integral stiffener are formed by ECM. This manufacturing process eliminates critical leading and trailing edge welding, brazing, and bend-forming problems. The leading edge suction surface wall thickness is twice as thick as the other walls. This added thickness and the solid leading edge provide added resistance to foreign object damage compared to previous bucket designs.

The turbine frequency-speed diagram is shown in Figure 64. As indicated, no critical excitations exist throughout the turbine operating range of 70 to 100 percent rpm.

The bucket steady state stress is given in Table V. Based on this stress, the bucket uses no appreciable amount of its rupture life during its operation. Fatigue is the limiting design criteria for the bucket. The stress range diagram for Udimet 700 at 1300°F is shown in Figure 65. As shown in Figure 65 and in Table V, the bucket meets the requirements of both the steady state and the one engine-out operating conditions.

Bucket Tip Shroud

As in the bucket, fatigue is the limiting design criteria in this com- ponent. Figure 66 is the stress range diagram for Udimet 700 at 1400°F. As indicated in this figure, there is adequate alternating stress margin for the fatigue sensitive area of the shroud.

Braze Joint

The buckets are held by the siderails and by the vertical walls of the

38 box section. The horizontal box members and the braze fillets are con- servatively considered as having no major load carrying ability. A rupture stress limit of 11,000 psi at 100 percent rpm, based on a 100 percent life consumption, was set for the braze. The braze area was selected so that the stress level was within this rupture life requirement.

Disk

The disk and shaft transmit blade and bucket loads to the bearings, and must have sufficient strength to limit rotor tip deflection to reasonably small clearance variations with the non-rotating parts.

Design Requirements

The disk and shaft are designed to satisfy the following requirements:

• Design speed of 100 percent rpm (3637 rpm)

• Burst speed not less than 122 percent rpm

• Design life of 2400 hours

i • Able to withstand at least 28,800 start-stop cycles I

Design Criteria i The following criteria have been established:

• The steady state meanline stress must be less than the material 0.02 percent yield strength at 106 percent speed.

• The steady state bore stress and the maximum maneuver surface stress must be less than the material 0.2 percent yield strength at 106 per- cent speed.

39 • Minimum material properties. :

Disk Design

The disk halves are welded together using electron beam welding. The stub shaft is integral with the forward disk. The disk rim is contour- machined to form the hub flowpath. The blade retainer hooks are located on the aft face of the rim. The disk material (titanium 6-4) was chosen for its machlneability and weldability. The welded joint properties of titanium 6-4 are greater than 90 percent of those of the parent material.

As seen in Table V, the limiting design criteria for the disk is low cycle fatigue. The disk is stiffness-limited rather than stress-limited due to system dynamic requirements.

Bearings and Sump

The bearings and sump maintain rotor concentricity and alignment with non-rotating parts with minimum friction loss. The bearings and sump transmit rotor thrust, maneuver loads, and other dynamic loads to the fan frame.

The LF467 bearing arrangement is similar to the LF1 configuration, consisting of one deep-groove angular-contact, split-inner-ring ball bearing and one light-weight roller bearing. The bearings are grease-lubricated (Unitemp 500) as are all other General Electric lift fan bearings. The bearings are sealed by four radial lip seals.

The LF467 has a common bearing housing similar to that of the LF460 and LP468, This packaged bearing concept offers the following advantages:

• Bearings are sealed from the environment.

• Improved maintainability of bearings and seals.

40 • Sump hardware can be assembled on the disk shaft and stored until needed.

• Rotor assembly onto the frame is facilitated.

• The rotor can be balanced on its own bearings.

Design Requirements

The bearings and sump have been designed to meet the following require- ments :

• Minimum life of 600 hours.

• Minimum regrease cycle of 10 hours.

• Ability to withstand a minimum of 7200 start-stop cycles.

Table VI shows the LF467 bearings DN values compared with those of the LF336.

Rear Frame Design

General Description

The major components of the rear frame (Figure 67) include the fan stator vanes, the fan and turbine exit flowpath liners, the midbox structure and the fan stream acoustic treatment. Air loads induced on the fan stators are transferred to the midbox. From the midbox, the loadpath goes through the three turbine struts to the rear frame scroll brackets and the airframe mounts. The rear frame is designed to accept all stator aerodynamic and maneuver loading. Noise suppression features included in the rear frame are two chord spacing, acoustic treatment on the fan flowpath walls and four acoustic splitters in the fan stream. Isometric cutaways of the turbine

41 exhaust liner and the fan stator vane row with the acoustic splitters are shown in Figure 68.

Design Requirements

In addition to the general design requirements previously discussed in Section III, the following requirements are specifically applicable to the rear frame:

1. Maintain adequate clearance during all fan operating conditions to prevent interference with rotating parts.

2. Maintain the design gap of the aft air seal to control leakage.

Component Design Description

Hub Cover

The hub cover provides a seal across the hub of the fan and allows access to the hub instrumentation. The cover is a spherically-shaped single sheet of 0.020 inch aluminum (7075 T6). It has a flange at the outer radius and is bolted to the hub.

Hub Ring

The hub ring retains the inboard end of the fan stator vanes and provides structural stiffness at the hub for mounting the inner fan flow- path. It is fabricated from 0.010 inch thick titanium (6A1-4V).

The inner fan flowpath forward of the hub ring is a 0.5 inch thick fiberglass honeycomb-bonded section, having 0.030 inch face sheets and 0.375 cell size fiberglass honeycomb.

The inner fan flowpath aft of the hub ring is a 1 inch thick

42 bonded fiberglass honeycomb section having 0.030 inch face sheets and 0.5 inch cell size. The face sheet forming the flowpath incorporates 0.062 diameter holes with 15 percent surface porosity for acoustic suppression.

Fan Stator Vanes

Fifty four fan stator vanes are incorporated into the rear frame. The vanes are hollow titanium 6-4 double circular arc airfoil sections with a thickness/chord ratio (tm/c) of 5.0 percent. Actual vane chord is 2.93 inches. The vanes are fabricated in two sets; one set spans from the hub to the outermost splitter, the other set spans from the splitter to the midbox. All vanes are equally-spaced circumferentially with the outer set having a 30 degree lean angle relative to the midbox and the inner set having a 15 degree lean angle in the opposite direction.

The outer set of vanes have skin thicknesses of 0.020 inches. The inner set has 0.020 inch skins between the outer two splitters and at the splitter box braze joints, thickness changes to 0.015 inches between the second and third splitter and to 0.010 inches between the inner splitters. Shown in Figure 69 is the die formed 0.005 inch thick internal stiffener which is brazed into each hollow vane. Two full-span hat sections provide stability for the vane skins to preclude buckling. The corrugated portions of the stiffener provide a loadpath across the vane at each of the structural boxes.

Acoustic Splitters

Four acoustic suppression splitters are included in the fan flowpath. In addition to noise level reduction, the splitters also provide aeroelastic stability for the fan stator vanes as well as turn the fan flow toward the hub. The splitters are acoustically treated aft of the stator vane trailing edge. The forward portion is untreated.

All of the splitters are of similar construction, but have different aerodynamic contours. Acoustic treatment consists of 0.062 diameter holes

43 having a 15 percent porosity for all treated surfaces. A corrugated strip separates the splitter skins providing the acoustic chambers for noise sup- pression. Through the vane row, the splitters are structural boxes fabri- cated from 0.020 inch thick titanium 6-4 face sheets. Forward of the stator vane leading edge, the splitters are fiberglass honeycomb fabrications having 0.030 skins and 0.375 inch honeycomb cell size. The titanium portion of the splitter is brazed to the stator vanes and the fiberglass bonded to the titanium. A 0.010 inch thick AMS 5510 stainless steel leading edge is bonded to each splitter for added FOD resistance.

Midbox

The midbox separates the fan and turbine exhaust streams. Stator vane loads are transferred through the midbox to the three turbine struts. The structural portion of the midbox is a brazed circumferential box section fabricated from 6-4 titanium into which the stator vanes and turbine struts are brazed. The inner and outer face sheets are 0.020 inches thick except for local areas 15 degrees on either side of the turbine struts where the thickness is increased to 0.040 inches. A 0.010 inch thick "u" channel closes out the midbox at the forward and aft ends. The fan forward outer flowpath and the acoustically-treated aft outer flowpath are brazed to the channels.

The fan forward outer flowpath is a honeycomb structure having 0.010 inch titanium 6-4 face sheets and 0.375 inch honeycomb cell size. A flange with gusset supports is located on the forward edge with 0.1875 inch anchor nuts riveted on for retention of the aft air seal and exhaust liner.

Brazed to the aft side of the midbox is the one inch thick titanium 6-4 honeycomb acoustically-treated aft outer flowpath. It also has 0.010 inch face sheets and 0.50 inch honeycomb cell size. Acoustic treatment is 0.062 holes with a 15 percent porosity.

44 Exhaust Liners

The exhaust liners provide the flow passage for the turbine ex- haust. The inner and outer flowpath surfaces are 0.25 inch thick Hastelloy X honeycomb with 0.005 inch face sheets. The forward edge of the inner liner is bolted to the flange on the fan outer flowpath panel. The aft side is riveted to the aft fan outer flowpath panel. The exhaust liner has nine equally spaced fairings which separate and stabilize the inner and outer flow- paths. Three of these fairings also provide a thermal shield around each turbine strut. The fairings are 0.25 inch thick Hastelloy X honeycomb with 0.005 inch face sheets and are brazed to the inner and outer flowpaths. After the thermal shields are positioned over each strut and the liner attached to the midbox, a "U" channel is riveted to the aft side of the strut fairings to seal the midbox and strut from the turbine exhaust gas.

Turbine Struts

The three turbine struts transfer the rear frame loads into the airframe mounts. The uniball connection between the struts and the rear frame - scroll brackets assures that only axial and tangential loads (no moments) are transferred into the mounts while allowing unrestricted radial growth.

The hollow bolts which bolt the struts to the rear frame - scroll brackets also function as ducts to pass fan cavity purge air through the struts for cooling. The hollow strut is fabricated from 0.04 inch titanium 6-4. Within the strut are "U" channels with stock thicknesses of 0.010 inch. The channels provide added strength and stabilize the thin strut skins. The turbine struts are brazed to the midbox.

Insulation Blanket - Midbox

Three Min-K insulation blankets each spanning 120 degrees between the turbine struts insulate the midbox structure. The insulation is bagged in a quartz cloth blanket. The forward edge of the blanket is bolted be- tween the exhaust liner and the forward edge of the midbox.

45 Aft Air Seal

The aft air seal restricts the flow of hot gas from the turbine stream into the fan stream. The aft air seal bolts to the forward end of the midbox. It is fabricated from Hastelloy X material in 22.5 degree segments (16 pieces).

The seal is an angle section 0.020 inches thick with two slotted holes at each end to allow for thermal growth. A hole in the middle pro- vides for attachment to the midbox. The seal has 0.060 inch cell size honeycomb brazed to the inner face of the angle.

Fan Cavity Purge

Some of the fan cavity purge air is used to cool the turbine struts while the remaining air is vented to the turbine exhaust through holes in the outer turbine flowpath. This, purge system is designed for approximately one pound per second flow.

Rear Frame - Scroll Bracket

Three "A" frames connect the rear frame to the scroll. At the apex of each "A" frame is a uniball for bolting to the three rear frame struts. The two ends of the "A" frame are bolted through rod ends incor- porating uniballs to clevises attached to the scroll mounts and torque tube. This arrangement allows radial expansion between the scroll and rear frame while maintaining concentricity. The "A" frames are constructed from Rene* 41 tubing utilizing threaded rod ends for axial adjustment.

Design Summary

The preliminary stresses evaluated for the rear frame stator vanes, turbine struts and structural rings are shown in Figure 70. Vane torsional and flexural frequencies are presented in Figures 71 and 72.

46 Weight Summary 6 In the initial phase of the LF467 study, consideration was given to elimination of the bellmouth as a lift unit component since it is function- ally dependent on the installation. The component weight breakdown is shown below, based on that assumption. For comparison, a weight breakdown is also given including the bellmouth and associated insulation since that feature was included in the LF460 and LF468 designs.

Weight (Ibs) Excluding Including Bellmouth Bellmouth

Front Frame 110 140 Scroll 220 220 Rotor 281 281 Rear Frame 244 244 Sub-Total 855 885 Development Margin 60 62 Total 915 947

The above weight breakdown is given for the reference size LF467 fan that is sized for design operation on a standard day. This size lift unit has a 66.8 inch fan rotor tip diameter. During the initial sizing studies, a family of lift fans with a 1.30 pressure ratio were investigated for various ambient temperature conditions at the design point. As a separate phase of the LF467 design activity, the weights for this family of lift fans was evaluated. The weight scaling factors as a function of the design temperature is shown in Figure 73. These data plus the appropriate performance give the aircraft designer the option of evaluating different levels of lift fan flat rating as reflected by the design ambient temperature conditions.

47 SECTION VII $ PERFORMANCE

The LF467 lift fan is designed to operate with a pair of inter- connected YJ97-GE-100 engines. The installation is shown schematically in Figure 2. The reference configuration of the LF467 is designed for opera- tion at sea level static standard day conditions. A family of 1.30 pressure ratio lift fans was designed covering the range of ambient temperatures usually considered. These designs are based on a flat-rating at all ambient temperatures below the design conditions. This flat-rate design approach permits the use of a smaller fan system if the design requirements are based on hot day criteria. For example, a standard day fan system will have a 66.8 inch fan tip diameter while a fan designed for 90 degree conditions will have a 62.2 inch diameter. The difference in required fan size reflects the lower gas energy at the hot day condition. The thrust levels also reflect this difference in energy levels. For example, at standard tempera- tures the 66.8 inch fan will develop about 12,885 pounds of thrust but the 62.2 inch size will produce only 11,348 pounds of thrust because of the flat-rate criteria. The payoff comes during operation at the hot day condition where both fan sizes will develop about the 11,348 pound thrust level.

Off-design performance was obtained for two typical designs, the standard day and 90 degree day systems. Performance is presented only for the nominal or no power transfer condition with the engine trimmed at the nominal exhaust gas temperature level of 1835 degrees Rankine. Operation at the maximum flow transfer conditions have previously been presented in Figures 13 through 16. The installation assumptions used during the off-design per- formance estimates were as listed in Table I. The ducting losses between the YJ97 engine discharge and the fan turbine inlet, including the fan scroll losses, were 10.8 percent of the inlet total pressure. The scroll loss in- herent to the lift fan system accounts for 5.8 percent of the total losses and is not chargeable to the system ducting.

48 Fan system sea level static off-design performance for a range of engine power settings is presented in Figures 74 through 81. The engine operating characteristics for both the standard and 90 degree day are shown in Figures 74 through 77. The engine for both cases is trimmed for an exhaust gas temperature of 1835 degrees Rankine at the design speed of 101.5 percent. Figure 78 relates fan speed to engine speed and Figures 79 through 81 present the fan operating characteristics for the two designs.

49 SECTION VIII

INSTALLATION

The LF467 lift fan and the YJ97-GE-100 turbojet engine comprise the basic V/STOL propulsion system. The LF467 is designed to operate primarily in a shallow inlet installation where the upper structure surface blends into the lift fan inlet bellmouth. The lift fan exhaust system was designed for operation in combination with thrust vectoring louvers, not included as an integral part of the lift fan structure. Installation of the lift fan with a deep fuselage inlet or as a cruise fan is possible provided that the inlet diameter is not less than 68.1 inches and blends smoothly into the 15 degree tip slope of the fan rotor. For a deep installation such as in a cruise or fuselage installation, a modified fan bulletnose contour will also be required as shown in Figure 43.

Lift Fan Installation

The LF467 lift fan system was designed to accept the exhaust gas from the gas generator through a double entry scroll. The fan installation drawing is shown in Figure 82. Requirements for connections to the aircraft duct system, and sealing and clearance provisions are similar to those pre- sented in Reference 1 for the LF460. This installation represents the ref- erenced LF467 system designed for standard day conditions. Installation dimensions covering a range of design temperatures to 100 degrees Fahrenheit are listed in Table VIII. These dimensions reflect the changes of fan size with varying design temperatures and flat rating at all temperature levels below the design value.

Weights and Inertias

Weight and inertia data for the basic LF467 fan system are presented in Table IX. These data are applicable for evaluation of the particular mount reactions under maneuver load conditions. Representative weight scaling data for a range of different design temperatures are shown in Figure 73.

50 Mounting System

The fan mounting configuration is shown in Figure 83. The mounting system must maintain concentricity between the front frame, rotor and scroll while providing for thermal expansion of the hot scroll and the large piston load acting on the scroll at the inlets.

Mount B reacts all fan loading in the Y direction and is designed as a scroll-to-airframe mount to provide a direct loadpath to the airframe for the 9,600 pound scroll piston load. This mount also acts as the hardpoint for thermal growth of the hot scroll. Mounts A, B and C react to all fan loading in the Z direction and are designed as direct loadpaths to the airframe for the rotor thrust, scroll and rear frame lift, and axial gyroscopic loads. Mounts B and D react to all fan loads in the X direction. Mount D is a drag link mount which is necessary to provide in-plane stability to the scroll during an engine-out operating condition.

Tabulated in Table X are the mount reactions for the various types of loading conditions.

YJ97 Installation

Installation requirements for the YJ97-GE-100 are presented in References 1 and 2.

51 SECTION IX

DISCUSSION OF RESULTS

The program requirement was the concept definition of a 1.30 pressure ratio lift fan using the LF460 and LF468 fan systems as a basis for the design. The objective was to combine a reduction in jet noise floor with extensive fan acoustic treatment to achieve an acceptable fan noise level consistent with a six fan system objective of 100 PNdB at 500 foot sideline. A simple single- bubble scroll and three strut front frame were used to minimize the weight associated with the large fan diameter and massive exhaust suppression system.

At the noise rating point, the LF467 fan jet velocity is 594 feet per second and the turbine jet velocity is 642 feet per second. A comparison of the LF467 jet velocities with the jet velocities of the previous LF460 and LF468 designs is given in the following table. The resulting Jet noise char- acteristics are also compared.

LF460 LF468 LF467

Fan Jet Velocity, ft/sec 682 560* 594 Turbine Jet Velocity, ft/sec 678 574* 642 Fan Jet Noise (500 ft), PNdB 85.4 75.1 78.8 Turbine Jet Noise (500 ft), PNdB 75.4 65.3 72.6 Total Jet Noise (500 ft), PNdB 85.9 75.6 79.8

The suppressed noise of the LF467 fan system was reduced to 92.5 PNdB through the use of exit stator lean and extensive exhaust suppression. Total fan system noise including both jet and fan noise is 94.0 PNdB, including acoustic exit louvers. This level, that is comparable to the 93.5 PNdB level of LF468 lift fan, a 1.25 design fan pressure, is possible primarily because of

*It is noted that the jet velocities presented for the LF468 are for a 90°F day, while the LF460 values are for standard day conditions. On a standard day, the LF468 jet velocities would be slightly lower than the values shown.

52 the additional acoustic feature of 15 degrees of exit stator lean. The diffi- culty of including stator lean in a heavily suppressed fan system was overcome in the LF467 design by the use of aerodynamically loaded splitters plus the addition of diffusion within the exhaust suppressor flowpaths.

The use of the single bubble scroll and modified three strut front frame, as identified during the LF468 design study, helped to minimize the increase in fan weight due to the increased diameter and heavy exhaust treat- ment. A comparison of the three lift fans in LF4XX family is made in the following table:

Standard Day LF460 LF468* LF467

Max Thrust 15057 14818 15692 Weight 789 897 947 Thrust/Weight 19.1 16.5 16.6

The above comparison shows a slight increase in thrust/weight with the increase in fan pressure ratio for the comparable LF467 and LF468 systems. The reduction in thrust/weight as compared to the LF460 is due to the addition of the exhaust suppression system that was partially compensated for by the use of the lighter weight scroll and front frame. A weight savings of about 70 pounds is anticipated for the LF460 when modified to include the revised scroll and front frame system.

The major disadvantages of the family of heavily suppressed low noise fans, the LF467 and LF468, is the increase in envelope dimensions associated with the increased fan diameter and added length for the exhaust suppressor. A comparison of maximum envelope dimensions is given in the following table;

*The weight and thrust of the LF468 are based on a lift fan with a flat rating between standard and 90 degree days. Results of the LF467 study show that a system designed for flat rating will exhibit almost constant thrust/weight ratios even though the thrust levels change significantly.

53 LF460 LF468 LF467

Max Thrust 15057 14815 15692 Fan Tip Diameter 60.0 68.5 66.8 Max Depth 19.32 34.2 36.4 Max Lateral Dimension* 89.9 94.8 93.3 Max Longitudinal Dimension 85.5 92.6 91.2

^Lateral dimension is along axis aligned with scroll inlets. Longitudinal dimension is normal to inlets.

54 SECTION X

CONCLUSIONS

1. Stator lean, 15 degrees in the direction of rotation, can be included in lift unit designs that have a large number of acoustic splitters. Radial loading of the acoustic splitters plus diffusion in the annular flowpaths downstream of the stator are required to achieve reasonable stator aerodynamic loading. This is an improvement over previous de- signs where stator lean with heavy treatment did not appear feasible.

2. The inclusion of stator lean in a 1.30 pressure ratio system resulted in an estimated overall noise level of 94.0 PNdB. This level is com- parable to a 93.5 PNdB for a 1.25 fan without stator lean. Thus, with the assumption of a possible 1 to 2 PNdB noise reduction during detailed optimization studies plus a modest amount of fan inlet treatment, it appears feasible that the overall noise level for a 6 fan research air- craft could achieve the objective level of less than 100 PNdB.

3. Additional analysis and design of the three strut front frame and single bubble scroll did not indicate any mechanical design deficiencies or increases in weight over previous concept definition studies. The weight advantage for this type of system is achieved at a small sacrifice of a deeper fan installation.

4. Design of lift fans for above standard day temperatures and with flat rating yields fan sizes significantly smaller than comparable standard day designs. A 1.30 pressure ratio fan system using the YJ97 will have a tip diameter of 66.8 for a standard day and 62.2 for a 90 degree design, There is very little difference of thrust at the 90 degree day for the two designs. Thus, it is important to consider the aircraft design criteria during the design of the appropriate V/STOL propulsion units.

55 5. A fan system with a design pressure ratio of 1.30 and incorporating stator lean with extensive exhaust treatment represents a reasonable compromise between the desirable high pressure ratio system, greater than 1.35, based on aircraft system requirements and the noise require- ment of less than 100 PNdB for a six fan research aircraft.

56 NOMENCLATURE

SYMBOL DEFINITION UNITS

C Chord DFT Fan Tip Diameter in D-Factor Diffusion Factor in

Fn Net thrust Ibs 2 g Gravitational acceleration (32.174) ft/sec h Enthalpy ... or Btu/lb Passage height in J Joule's constant (778.16) ft-lb/Btu M Mach number "- MR Relative Mach number - N Speed % or RPM PNdB Perceived noise level decibels q Velocity head pressure psi R Relative velocity ft/sec te Edge thickness - *m , Maximum thickness - T Total temperature °R U Velocity (also u) ft/sec ft/sec or knots V0 Aircraft flight velocity V Velocity ft/sec

WFT Fuel flow Ibs/hour a Angle of gas flow leaving turbine nozzle degrees (relative to circumferential direction) h Angle of gas entering blade row degrees 02 Exit angle of gas leaving blade row degrees 01* Blade leading edge angle degrees 02* Blade trailing edge angle degrees

Note: Where more than one set of units is shown, refer to specific use of symbol.

57 NOMENCLATURE

SYMBOL DEFINITION UNITS

r Angle of gas flow leaving turbine degrees (relative to axial direction) 6 density lbs/ft3

Subscripts

0 Ambient 2 Engine inlet 5.1 Engine Turbine Discharge 5.11 Upstream of Cross-duct Bleed Port 5.12 Bleed Port 5.13 Bleed and Main Stresses Mixed 5.3 Fan Scroll Inlet 5.4 Fan Turbine Inlet 10 Fan Rotor Inlet 11 Fan Stator Exit B Bleed E Engine F Fan

58 LIST OF REFERENCES

1. LF460 Detail Design. General Electric Company 71-AEG-297. NASA CR-120787, under Contract NAS2-6056, September, 1971.

2. Model Specification E-1155. Engine, Aircraft, Turbojet, YJ97-GE-100, October 15, 1969. General Electric Company, Lynn, Massachusetts.

3. LF468 Concept Definition, General Electric Company 71-AEG-362. NASA Contract NAS3-15690, October, 1972.

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64 Table IX. LF467 Weights and Inertias.

With Without Bellmouth Bellntouth

Fan Weight, Ibs 915

Mass Moments of Inertia

2 About Vertical Axis U )* lb-ft-sec 212 208 ZZ 2 About Fore-Aft Axis (I ), lb-ft-sec 107 105 Normal to Fore-Aft Axis (I yy), lb-ft-sec 106 104 o Rotor Polar Monent of Inertia, lb-ft-sec 32

Center of Gravity '

Vertical 1.2 in (below rotor centerline) Fore-Aft on rotor centerline Sidewards 1.9 in (towards scroll inlet)

*Axis of Scroll Inlet is Assumed Normal to Fore-Aft Direction. See Figure 83.

Table X. LF467 Mount Load Table.

(All loads in Pounds)

Load Direction Mount (A) Mount (B) Mount (C) Mount (D)

X Steady State - Thrust at Y -9950

100% Speed Z -4727 -6238 -4727

Crossflow at X -3100 - -3100

150 Knots Y - Z -8877 -4516 -3607

Gyro Acting X -

About X-X Axis Y - (1 Radian) Z ±1200 ±2400 ±1200

Gyro Acting X - About Y-Y Axis Y -

(1 Radian) Z ±2075 0 ±2075 g - Loads (1 g) X ±496 - ±451

(1 E) Y ±947

(1 g) Z ±300 ±347 ±300

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76 O O. • -H St rH H •oP a -P CO «

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77 0.5 \Static Pressure Rise Coefficient --- \D-Factor

Stream Function

Figure 23. Stator Aerodynamic Loading Parameters - Double Stator Configuration.

78 •0p) -P

CO •d 0) 03 0

M C

•O •0p) u 0) i-H 0) CO

o

-P al OH

I

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al -P

in -P •Op afi) ClJ -H +j o CO -H

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81 bO C

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saqouj '

85 1.0

0.8

o 0.6

0.4

0.2

10 14 22 26 30 34 38 Mean Radius, inches

Figure 37. Rotor Blade Meanline Geometry.

100 r 0.20- 5

80 0.16

60 - "E0.12

40 0.08

20 0.04

18 22 26 30 34 38 Mean Radius, inches

Figure 38. LF467 Rotor Blade Geometry.

86 100 0.20

80 0.16 • 4

m X Chord C 3 / •5 60 0.12 - •H •o O ^_-^ Camber 6 ~ V~^-. / 40 r -0 0.08 - 2 \ — *^ f

tm/c

20 o 0.04 - 1 _ ^_ Stagger __ t /C "•""* — • — — _ _ ^ /J , .

O1- e 8 12 16 20 24 28 32 3 Mean Radius, inches

Figure 39. Stator Vane Geometry.

1000

800

400

200

10 14 18 22 26 30 34 38 Mean Radius, inches

Figure 40. Rotor Aerodynamic Load Distributions.

87 1000

800

Tangential c •H \ 5 600

•o oi 3

400

Axial 200

I-'

12 16 20 24 28 32 36 Mean Radius, inches

Figure 41. Stator Aerodynamic Load Distributions.

Velocities, ft/sec Angles, deg Mach Numbers V = 2772 a =21.5 M = 1.490 R! = 35.1 R = 1763 MR1 = .948 R = 1569 B2 = 41.4 V^ = 1038 UR2 = .832 T = 2.2 U U = 1138 2 = .550

Figure 42. LF467 Turbine Velocity Diagram.

88 Figure 43. LF467 Flowpath.

89 Figure 44. Front Frame Components.

Bellmouth

Air Deflector

Forward Air Seal —/ El

Figure 45. Forward Air Seal Assembly.

90 Effective Stress Location (KSI) 1 0.5 2 120.0 3 32.2 4 32.2 5 7.0

Figure 46. LF467 Front Frame Stresses.

Nozzle Partition

Slip Seal

Scroll Exhaust

Figure 47. Scroll Nomenclature.

91 W) nl

•O (1) & CO

0 0" 0) !H

O •P O

Is

Ol 00 00 01

W H to e0n) r 01

-P w

u K ra BW H oo

92 12 Cycles per Hour Stress at 104% Speed

Range of 'Alternating / Stress Total Mean Stress Stress Range

4J 03 Range of Alternating Stress at Stress 0% Speed

Time

Figure 50. Rotor Low Cycle Fatigue Analysis.

15.17 R

Figure 51. LF467 Blade.

93 Stress at 100% Speed Dovetail A. Blade Fillet Stress Disk 45 Ksi B. Face Crush Stress 32 Ksi C. Disk Fillet Stress 43 Ksi

Figure 52. Dovetail Steady State Stress.

Ren£ 95 with Estimated Processing Effects 15O°F, 10O Hours Life, 107 cycles

Alternating Stress Margin

Margin for Maneuver

Design Limit Steady State Stress 60 80 100 120 20O Mean Stress, Ksi

Figure 53. Blade Dovetail Stress Range Diagram.

94 60

Alternating Stress Margin

Design Limit Steady State Stress 40 60 80 1OO 12O 140 Mean Stress, Ksi

Figure 54. Disk Dovetail Stress Range Diagram.

Rene 95 with Estimated Processing Effect; 150°F, 100 Hours, 10? cycles

Iternating Stress Margin

Margin for Mi J-

Design Limit Steady State Stress

20 60 8O 10O 120 140 160 180 200 Mean Stress, Ksi

Figure 55. Blade Airfoil Stress Range Diagram.

95 2OOO

1500

3 D1 £ h

500 3/rev Margin

2O 40 60 80 1OO Rotor Speed, percent

Figure 56. Blade Natural Frequencies.

Unstable Region

A Steady State O Stall ~~^"~~~ Inner Panel ———— Middle Panel ™ Outer Panel

Incidence Angle

Figure 57. Fan Blade Flutter Margin.

96 Rene 95 with Estimated Processin Effects 15O°F, 1OO Hours Life, 1O7 cycle

ng Stress Margin

rMargin for Maneuver

Design Limit /'Steady State Stress •80 100 120 180 2OO Mean Stress, Ksi

Figure 58. Outer Part-Span Stress Range Diagram.

Four U-700 Buckets Each with Integral Tip Shroud and Integral Stiffener

Two Piece R-41 Box Section

One R-95 Blade With R-4I Forward Seal Integral Tip Shroud, Integral Siderails and Integral Tip Lockup

R-Jti Aft Seal

Figure 59. Turbine Configuration and Materials.

97 80

Rene 95 with Estimated Processing Effects 60 10OO°F, 1OO Hours Life, 107 cycles

a g 0) Alternating Stress Margin 3 20

Design Limit State Stress 20 6O 8O 1OO 120 140 160 180 Mean Stress, Ksi

Figure 60. Blade Tip Shroud Stress Range Diagram.

Rene 95 with Estimated Processing Effects o 12OO F, 1OO Hours Life, 10 Cycles

•Alternating Stress Margin

60 80 100 120 140 Mean Stress, Ksi

Figure 61. Upper Siderail Stress Range Diagram.

98 •a o

03 a. •H H

-p 0)

iH O "~~ O H,-/ cii fc bO O01 tH O O O II II CO to a

. a) l1 9H

•P at

H a •H S g 01 a

CM (O

99 14000

12000 178/rev (Nozzles) 10000

8000

6000

4000

18/rev 9/rev (Vane Struts) 2000 3000 4000 Rotor Speed, RPM

Figure 64. Bucket Frequency-Speed Diagram.

50

40 Udimet 700 Forging 1300°F, 100 Hours Life, 10* Cycles

30

Criterion for One Engine Out 20

for Normal Operati 10

0 •OO 10 20 40 50 60 70 80 90 Mean Stress, KSI

Figure 65. Bucket Stress Range Diagram.

100 50

Udimet 7OO Forging 14OO°F, 1OO Hours Life, 1O? cycles

30

£ 20

10

1O 2O 30 4O Mean Stress, Ksi

Figure 66. Bucket Tip Shroud Stress Range Diagram.

Turbine Strut Aft Air Seal Fan Flowpath Rear Frame Outer Forward Scroll Bracket

Fan Flowpath Inner Forward

Midbox Fan Flowpath Fan Flowpath Outer Aft Inner Aft Insulation Turbine Strut Fairing

Figure 67. Rear Frame Nomenclature.

101 m fc, o> •p •p o. ra

I

0)

oo CD

102 Figure 69. Stator Vane Insert.

84.0 KSI 58.9 KSI 59.0 KSI 62.6 Turbine Stator 59.1 KSI 56.8 KSI Stator Vanes 55.3 KSI 61.2 KSI

35.3 KSI 20.5 KSI 13.8 KSI

25.6 KSI KSI

Splitters

Figure 70. Rear Frame Stresses.

103 0) CO 3 9

o -a to 0) fi § HI 03 CM Q. 05 h >. •0p Ofl 01 0) -P 3 W 0*

N

o o o o o o o

1-1 m rt O. 8 Cft O •H C 0) 03 SH (H 0 H w 0) V) C ^ a) V

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t^ 0> o o o 3 o o bO ID eg •H '/touanbajj

104 CO 03 O

u to

fi W • t> ? Ol O

a •H

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o g

105 0 h 3 +J aj a e 0) H tn ai O

w 0) •H M

C- O)

co t» o o o o o 10 0) §^>

tn a0>)

o en •H Q 0) •H M C

Oi

in t* 0) h bC •H

106 CT)

•P •H s •O 0 O. CO

Aa) •H -H FH bD oj A

00

0)

psads

I

0)

(U a •H bC •o o a g. Oi

(1) h 5

'(^M) *ou

107 cd A

W CO

0)

O CO a •H o o

( d/ d) aansssjj

O rH

CD i-l a a nl

ONJ 0) ah

o o o o CO m

'(OTM) 131"!

108 14000

12000

10000

8000

01 3 6000

4000

2000

85 90 95 100 105

Engine Speed (NJ, percent

Figure 81. Fan Total Net Thrust.

109 •H £ cd fn Q a o •H •P 0)

0) -P CO

a

oq

0> h bO •H

<}

110 Mount A

Mount B

Mount D

Mount C—I

Mount D ZMount C Mount B

Figure 83. LF468 Mounting System.

Ill