United States Army Aviation Center Fort Rucker, Alabama April 2007

Transcription

1 United States Army Aviation Center Fort Rucker, Alabama April 2007 Student Handout TITLE: AH-64D Rotor System FILE NUMBER: PROPONENT FOR THIS STUDENT HANDOUT IS: COMMANDER, 110 TH AVIATION BRIGADE ATTN: ATZQ-ATB-AD Fort Rucker, Alabama FOREIGN DISCLOSURE STATEMENT: The materials contained in this student handout have been reviewed by the course developer, in coordination with the USAAVNC foreign disclosure authority. This student handout is releasable to foreign military students without restrictions. D-3

2 Terminal Learning Objective Action: Identify the components and operation of the AH-64D rotor system Conditions: Given an AH-64D helicopter or training device and TM Standards: In accordance with TM Safety Requirements Risk Assessment Level Environmental Considerations None Low NOTE: It is the responsibility of all soldiers and DA civilians to protect the environment from damage. Evaluation NOTE: Before presenting this lesson, instructors must thoroughly prepare by studying this lesson and identified reference material. You will be given a written test PFN 1050A-1 or 1050B-1 containing questions concerning this block instruction. You will be given 60 minutes to complete this examination, it will be given in a classroom in Blg Instructional Lead-In The rotor system consists of the main rotor assembly and the tail rotor assembly. It interfaces with the drive system and flight control system to provide lift, thrust, directional flight control, and anti-torque control for the helicopter. As an AH-64D Longbow pilot, you will need to be able to identify rotor system components, determine their suitability for the intended flight and respond to rotor system operating indications. In this lesson, we will first discuss the main rotor system components then discuss the tail rotor system components. D-4

3 A. ENABLING LEARNING OBJECTIVE ACTION: CONDITIONS: Identify the characteristics of the main rotor assembly Given a written test without the use of student notes or references STANDARDS: In accordance with TM Learning Step / Activity 1. Rotor System D-5

4 a. Main rotor assembly (1) The main rotor assembly provides lift and directional flight for the helicopter. It is mounted on the static mast and is driven by the main rotor drive shaft. (2) The main rotor assembly is four bladed, has a diameter of 48 feet, is fully articulated, and ballistically tolerant. (3) The main rotor assembly is controlled by the cyclic and collective flight control system through a swashplate, scissors links and pitch change links. (4) Main rotor assembly major components (a) Main rotor hub assembly (b) Strap pack assemblies (4) (c) Feathering bearing assemblies (4) (d) Pitch housings (4) (e) Lead-lag dampers (8) (f) Lead-lag links (4) (g) Droop stop follower assemblies (4) (h) Droop stop ring (i) Ground brush assemblies (2) (j) Hub retention nut (k) Lock ring (l) Main rotor drive plate (m) Drive plate close out assembly (n) Derotation unit (o) Blade attachment pin assembles (4) (p) Main rotor blades (4) D-6

5 (5) Main rotor hub assembly (a) The hub allows feathering, flapping, and lead-lag motion of the rotor blades and system. It holds the entire main rotor assembly to the static mast and accepts driving torque transmitted to the hub from the main transmission by a steel driveshaft inside the static mast. (b) The hub assembly consists of the hub, upper and lower retention plates, the lower shoe, the droop stop ring, and the roller/follower assemblies. The hub and lower shoe are machined from aluminum alloy forgings. (6) Strap pack assemblies (a) The strap pack assemblies permit flapping and feathering motion and transmit centrifugal loads from the main rotor blades to the hub. (b) The strap pack assemblies are attached to the hub assembly at its inboard end by two bolts. The two bolts sandwich the strap pack assembly between the upper hub, upper steel retention plate and the lower steel retention plate and lower shoe. (c) The strap pack assemblies consist of 22 laminates of inch thick stainless steel in a V-shaped configuration. The 22 laminates are retained at the outboard end by being sandwiched between a custom-machined steel bolt/nut, two titanium shoes, and a titanium spacer. (d) The strap pack assembly is attached to the lead-lag link and pitch housing at its outboard end with two aluminum bearings and a steel pin. D-7

6 (7) Pitch housings assemblies (a) The pitch housings provide the means for controlling the main rotor blade pitch angle. (b) The pitch housing is attached to the lead-lag link and strap pack assembly enabling the pitch housing to transmit cyclic and collective control inputs to the main rotor blade. (c) The pitch housing is machined from an aluminum alloy forging and provides attachment points for the feathering bearing housing and lead-lag dampers. (d) The pitch arm at the inboard end receives control inputs from a pitch change link attached to the rotating swashplate. (8) Lead-lag dampers (a) The lead-lag dampers control the lead-lag motion of the rotor blades and prevent mass imbalance (unequal blade spacing). (b) Two lead-lag dampers are attached to each pitch housing at their inboard ends and to lead-lag link at their outboard ends. (c) The lead-lag damper consists of two elastomeric laminates sandwiched between three aluminum plates. The center plate attaches to the lead-lag link through a rod end bearing and the outer two plates attach to a trunnion that is mounted on the pitch housing. (d) Shearing action of the elastomer provides the required damping. D-8

7 (9) Lead-lag links (a) The lead-lag links transmit blade lead-lag loads into the dampers, blade centrifugal force into the strap pack assembly, and control inputs from the pitch housing to the main rotor blade. (b) The machined titanium lead-lag links also provide attachment points for the leadlag dampers and the main rotor blade. (c) Self-lubricating bearing material is used to permit lead-lag motion. (d) A built-in nose-up twist orients the blade's average operational angle of attack to approximately 14 with the strap pack assembly untwisted. ( 10) Feathering bearing housing assemblies (a) The feathering bearing housing provides the pivot point for the main rotor blade flapping and feathering action and provides the mounting point for the pitch housing assembly. (b) The feathering bearing housing is located between the pitch housing assembly and hub subassembly, and is mounted on the feathering-bearing stud. (c) The feathering bearing housing is made of an aluminum alloy with a spherical elastomeric bearing mounted in the center. (d) A striker plate mounted at the lower inboard surfaces of the feathering bearing housing assembly provides the contact surface for the droop stop follower assembly s roller to ride on during startup, pitch changes, and shutdown. D-9

8 (11) Droop stop follower assemblies (a) Spring-loaded droop stop followers restricts downward blade flap excursion (one blade down, opposite blade up). They are in constant contact with the striker plates when the rotor is not producing lift. The droop stop follower assemblies also limit downward coning (all blades down simultaneously). (b) The droop stop followers are installed in the lower shoe assembly and are held in place by the droop stop ring. (c) Each follower employs a roller that bears against a striker plate mounted at the lower inboard surfaces of the feathering bearing housing assembly. (12) Droop stop ring (a) The droop stop ring restricts main rotor blade downward coning and downward blade flap excursion. It works in conjunction with the droop stop follower assembly. (b) The droop stop ring is mounted in the lower portion of the lower shoe, and is held in place on the static mast by the droop stop assembly rollers. (c) The ring has a channel cross-section into which each of four droop stop followers is positioned. (13) Ground brush assemblies (a) The ground brush assembly transfers static electricity from the main rotor hub to the static mast preventing static electricity build-up from eroding the main rotor hub tapered roller bearings. D-10

9 (b) The graphite brushes are mounted on the lower seal retainer 180 apart and are connected through bonding cables to the rotor head and blades for proper static bonding. (c) Each assembly consists of a holder, ground brush, spring, and set screws. (14) Hub retention nut (a) The hub retention nut secures the hub to the static mast. (b) The nut is threaded onto the upper portion of the static mast. Rotation is prevented by the lock ring and twelve bolts passing through the lock ring. (15) Lock ring (a) The lock ring secures the hub retention nut. (b) Four flanges on the lock ring mate with the static mast to prevent rotation of the lock ring and hub retention nut. D-11

10 (16) Main rotor drive plate (a) The main rotor drive plate transfers rotating motion from the main rotor drive shaft to drive the main rotor head assembly. (b) The drive plate is bolted on top of the main rotor hub and splined directly to the main rotor drive shaft. (c) The drive plate seal and packing retain the grease lubricant in the drive plate to lubricate the drive shaft splines. D-12

11 (17) Drive plate close out assembly (a) The drive plate close out assembly provides environmental protection when the Mast Mounted Assembly is not installed. (b) The close out assembly bolts directly to the main rotor hub and interfaces with the upper end of the non-fire Control Radar (FCR) torque tube. D-13

12 (18) Derotation unit (a) The derotation unit provides a stationary mounting point for the Mast Mounted Assembly (MMA). (b) The derotation unit bolts to the main rotor drive plate and the torque tube. (c) The derotation unit consists of an inner and outer housing separated by two roller bearings and three grease seals. D-14

13 (19) Blade attachment pin assemblies (a) The blade attachment pin assemblies attach and secure the main rotor blade to the lead-lag link of the main rotor head. (b) The pins are installed in the main rotor blade retention fitting and the lead-lag link. (c) The steel pins are an adjustable bushing type incorporating several split bushing segments, spacers, a thrust washer, an eccentric cam, and an aluminum cam. (d) Blade bonding cables are placed inside the cam handles before they are latched. D-15

14 (20) Main rotor blades (a) The main rotor blades provide the lift and directional flight capability for the helicopter. (b) The main rotor blades are attached to the main rotor head lead-lag links with two expandable bushing retention pins. The pin assembly consists of a series of split male and female conical bushings, which surround a cam activated core bolt. A nut at the lower end of the assembly retains the bushing stack and provides for adjustment of the handle closing force. (c) Each blade is 20 feet, 10 inches (250 inches) long from the centerline of the attach lugs to the tip. It transitions to a 20 aft swept tip inches from the centerline of the attaching lugs. The blades have a constant chord of 21 inches inboard of the swept tip and incorporates negative 9 of twist. D-16

15 (d) A four-cell, hybrid, stainless steel and fiberglass box beam provides the structural chord for each blade. The complete outer surface of the box beam is composed of four metallic spars fabricated from stainless steel. The four metallic spars are bonded to and completely encapsulate four preformed fiberglass spar tubes. (e) The main rotor blade root fittings are fabricated from titanium to provide the best combination of fatigue strength and fracture toughness. Five thin stainless steel doublers on both the upper and lower surface of the blade are part of the blade attaching lugs. A "U" shaped aluminum alloy root rib is installed with four bolts to provide redundant, fail-safe load paths at the root end of the blade. (f) A stainless steel, full-span (to the start of the swept tip), structural, leading edge balance weight is bonded between the metallic leading edge and the first fiberglass spar tube. Erosion protection is provided by the leading edge. (g) The aft section of the blade is composed of Nomex honeycomb core covered by inch thick aft fiberglass skins and a stainless steel trailing edge closure skin. (h) The aft portion of the trailing edge closure is the bendable trim tab used for blade tracking. (i) The blade trailing edge is scarfed off at approximately 16, inches from the centerline of the attach lugs to provide clearance for blade folding. (j) At the blade swept tip a removable tip cover allows access to the tip weights for blade balancing. Dynamic balancing is normally accomplished utilizing weights attached at the blade root. (k) A static discharge wick on the trailing edge inboard of the swept tip transition prevents the excessive buildup of static electricity. D-17

16 (21) Rotor system status display (a) Main rotor speed (N R ) is displayed as a vertical tape and a digital readout (within the tape) on the Engine (ENG) page. The N R instrument graphic is displayed in conjunction with the N P instrument of both engines. The following limits apply to the N R : 1) 110 Maximum (>110 RED) 2) Transient (YELLOW) 3) 106 High rotor warning annunciated 4) Normal Operation (GREEN) 5) 0-94 Transient (RED) (b) System related warnings are displayed on the Multipurpose Display (MPD) and Up Front Display (UFD) with associated voice warning. 1) These messages are displayed when the main rotor N R > 105%. a) UFD text - HIGH ROTOR RPM b) MPD Warning/Caution/Advisory (WCA) page - HIGH ROTOR RPM c) MPD Data Management System (DMS) page FAULTS column - None d) MPD FAULT page - MAIN ROTOR SPEED HIGH RPM 2) These messages are displayed when the main rotor N R is < 95%. a) UFD text - LOW ROTOR RPM b) MPD WCA page - LOW ROTOR RPM c) MPD DMS page FAULTS column - None d) MPD FAULT page - None 3) Voice warnings of main rotor status a) "Rotor RPM low when N R < 95%. b) "Rotor RPM high when N R > 105%. D-18

17 CHECK ON LEARNING: 1. The main rotor assembly is mounted on what component? 2. What component carries the centrifugal force load? 3. What is used to attach the main rotor blade to the lead lag link? 4. The lead lag links allow the main rotor blades to move in what direction? 5. What is the purpose of the damper assemblies? B. ENABLING LEARNING OBJECTIVE ACTION: Identify the characteristics of the tail rotor system CONDITIONS: Given a written test without the use of student notes or references STANDARDS: In accordance with TM Learning Step / Activity 1. Tail Rotor D-19

18 a. Tail rotor assembly (1) The tail rotor assembly provides anti-torque and directional flight heading capability for the helicopter through the pilot and CPG foot pedals. (2) The tail rotor assembly is installed on the tail rotor gearbox output shaft. (3) The tail rotor assembly is a four-blade, semi-rigid, teetering, single head design. It is 9.2 feet in diameter and turns in a clockwise direction. The assembly uses a one-piece steel non-rotating swashplate. The blades have a narrow angle spread of 55. (4) Tail rotor assembly major components (a) Tail rotor head assembly (b) Tail rotor blade assembly D-20

19 b. Tail rotor head assembly (1) The tail rotor head assembly provides attaching points for the tail rotor blades and the means to drive the blades. (2) The tail rotor head assembly weighs 39.1 pounds and is mounted to the curvic coupling using three stud and nut combinations. (3) Tail rotor head assembly major components. (a) Fork assembly (b) Elastomeric bearings (4) (c) Tail rotor hubs (2) (d) Strap assemblies (2) D-21

20 (4) Fork assembly (a) The fork assembly is mounted to the output shaft of the tail rotor gearbox and provides mounting points for the two tail rotor hubs. (b) The fork assembly is made of titanium and consist of a short and long fork set 55 apart. (c) The inboard section of the assembly consists of two integral clevises 180 apart that provide attachment for the drive links. A curvic coupling provides positive interface with the tail rotor gearbox output shaft. (d) The fork assembly consists of one long and one short fork. 1) Secured to the sides of the long fork is an aluminum plate clamp which provides a mean for securing the deice harness. 2) The fork assembly drives the rotating swashplate via the drive links. (e) The fork assembly contains two teetering stops. The teetering stops are integral with the forks and restrict the teetering action of the hubs. 1) The outboard stop is integral with the fork and has a polyurethane bumper bonded to each end of the stop. 2) The inboard stop assembly is bonded to the fork and contains polyurethane bumpers bonded to each end of the titanium stop. (5) Elastomeric bearings (a) The elastomeric bearings are bonded to the outboard end of the forks and allow the hubs to teeter on the forks. (b) The bearings are constructed of a series of thin metal conical shaped sleeves separated by rubber. D-22

21 c. Tail rotor hub (1) The tail rotor hub is installed on the fork assembly and provides the mounting point for the tail rotor blades. (2) The hub is made of titanium and has a delta hinge attachment. (3) Threaded stainless steel bushings provide mounting security. Shims are installed between the bushing and folk assembly to properly center the hub. (4) Four bearing journals (two each side) mate with the pitch change bearings in the root end of the tail rotor blades. (5) A rubber dust shield is mounted at the hub base. d. Strap assemblies (1) The strap assemblies provide for attachment of the tail rotor blades to the hubs and transmit centrifugal loads from the blades to the head assembly. The straps provide feathering motion of the blades by twist, which allows the blades to change pitch angle. (2) The strap assemblies pass through the hub and are mounted at the center with threaded bushings. (3) Each stainless steel laminate strap set consists of 21 or 22 laminates approximately 24.8inches in length and inch thick. D-23

22 e. Tail rotor blade assemblies (1) The tail rotor blade assemblies provide thrust to maintain the desired heading during hovering flight and aircraft trim during forward flight. (2) The tail rotor blade assemblies are mounted over the hub and secured to the strap assembly by a Preload Indicating (PLI) washer, bolt and nut combination. (3) Each blade is inches long and has a cord of 10 inches. Spanwise balance weights are located beneath the tip caps. (4) Tail rotor blade assembly components (a) Pitch horn The pitch horn is riveted to the root fitting and provides attachment for the pitch change links, the deice blanket electrical receptacle, and the static bonding cable. The pitch horn contains a steel bushing to attach the pitch change link. (b) Root fittings The root fittings are made of aluminum forgings, with four, aluminum doublers. The root fitting and doublers are joined to the spars by adhesive bonding and metal fasteners. The inboard section of the root fitting provides the blade attachment points. D-24

23 (c) Self-lubricating Teflon R bearings Two self-lubricating Teflon R bearings are bonded to the inside diameter of the root fitting. The bearings allow blade rotational movement around the hub. (d) Deice receptacle A deice receptacle is attached to the outboard end of the root fitting. An aluminum alloy conduit extends from the receptacle along side the root fitting into the blade. A strap attached to the inboard end of the root fitting provides a means of securing the conduit. (5) Tail rotor blade construction (a) The number 1 spar makes up the leading edge; it is made of stainless steel. A deice heater blanket is bonded to the spar. (b) The number 2 spar is constructed of aluminum alloy and the inside portion contains unidirectional fiberglass. (c) The number 3 spar makes up the trailing edge and is constructed of aluminum alloy. Eleven aluminum honeycomb stiffeners are bonded into the spar to add strength to the blade. They are spaced equally spanwise at 3.25-inch intervals. (d) Each spar is lined with unidirectional bonded fiberglass to retard crack propagation. D-25

24 CHECK ON LEARNING: 1. What type of tail rotor system is installed on the AH-64D? 2. What component carries the centrifugal force load? D-26