3. Transmissions

8/12/2019 3. Transmissions

http://slidepdf.com/reader/full/3-transmissions 1/52

Rev. A Sept 18, 2007 3-4

Transmissions

Model S64F Helicopter



3-5Rev. A Sept 18, 2007

Main Gear Box



3-6Rev. A Sept 18, 2007

“F” Main Gear box

The main gearbox (M/G/B) is mounted behind the engines

and changes the angle of drive from the engine to the main

rotor head, and reduces the engine 9000 rpm.

The main gearbox contains a four-stage gear reduction

system to drive the main rotor head at a ratio of 48.609 to 1for a final main rotor speed of 185 rpm, and to drive the tail

rotor head at 850 rpm



3-7Rev. A Sept 18, 2007

“F” Main Gear Box Schematic



3-8Rev. A Sept 18, 2007

“F” Main Gear Box

A free wheeling unit at each MGB input allows for single-engine operation and auto-rotation.

The accessory section, located at the rear of the

transmission upper housing, contains mounting pads for

A/C generators, rpm sensor, APU, and hydraulic pumps. A tail take-off (T.T.O.) gear in the transmission is

coupled to the T.T.O. flange for tail rotor drive.



3-9Rev. A Sept 18, 2007

Rear Cover Accessory System

Schematic


http://slidepdf.com/reader/full/3-transmissions 7/523-10Rev. A Sept 18, 2007

Right Hand Accessory

The right hand accessory provides a location for

additional hydraulic pumps to operate: 2nd stage pump,

Hoist pump and Auxiliary pump.

The 2nd stage hydraulic pump operates the primary flight

controls.

The hoist hydraulic pump pad operates additional

equipment such as the auxiliary pump or the hoist pump.



Right Hand Accessory

Auxiliary Pump

2nd stage Pump

24132 kPa)20684 kPa)



Free Wheeling unit

The two 2nd

stage input pinion gears have a roller-ramp typeclutch which permits the freewheel units in the gearbox to

disengage the main rotor and tail rotor drive shafts when the

relative main rotor rpm exceeds relative engine rpm such as

during auto rotation, at engine shutdown, and single engine

operation



Free Wheeling Unit

Assembly

Clutch & Freewheel Housing



Accessory Section Rear cover

The main gearbox accessory

section is located on the rear of the

main gearbox.

Mounted on the rear cover are the:

1.Number 1 and number 2

electrical generators.2.The first stage hydraulic pump

3.The utility hydraulic pump

4.Oil Cooler pump

5.The tachometer Generator.6.The A.P.U. Drive gear.



Rear cover Accessory Section

(1b) No 2 generator

(1a) No.1 generator

Oil filler

(5) Tachometer (6) A.P.U. Input

Tail Take off coupling (4) Oil Cooler Pump

(3) Utility

(2) 1st stage

Oil filter



3-16Rev. A Sept 18, 2007

Rear Cover Accessory System

Schematic



3-17Rev. A Sept 18, 2007

Accessory Drive Notes

Note: Tach. Generator (5), oil cooler pump (4), and the tail

take-off coupling will not be operating during A.P.P. operations.

Note: It is important to keep this operation to a minimum to

reduce the possibility of damage or failure of freewheel rollers.



3-18Rev. A Sept 18, 2007

Tail Take Off

A tail take-off freewheel unit is incorporated in the rear coveraccessory section of the main gearbox.

When the auxiliary power plant (A.P.P.) is operating, the # 1 &

2 generators (1a & 1b), utility hydraulic pump (3), 1st stage

pump(2), and oil pump are operating; thus, providing the

aircraft with electricity, hydraulics, and the main gearbox withoil flow.

When the aircraft turbine engine(s) are operating and the

main rotor is spinning at 185 revolutions per minute (rpm), the

A.P.U. is no longer driving the accessory section. Theaccessory section is now being driven by the aircraft

engine(s) through the main gearbox.



3-19Rev. A Sept 18, 2007

Tail Take-off

Assembly (T.T.O)

Free

Wheel

Gear



3-20Rev. A Sept 18, 2007

APU Drive

Clutch

Drive Shaft



3-21Rev. A Sept 18, 2007

Auxiliary Power Unit

The Auxiliary Power Unit (A.P.U.) provides temporary powerfor the aircraft.

The A.P.U. drives the centrifugal type clutch assembly

mounted on the lower aft section of the rear cover.

The clutch couples the A.P.U. to the main gearbox by

engaging when the A.P.U. is operating at approximately 75%

and disengaging when the M/G/B speed (rpm) becomes

faster than that of the A.P.U.

The A.P.U. drives the accessory gear box at 8,000 rpm

The tail take off is driven at 8,025 rpm by the MGB.



3-22Rev. A Sept 18, 2007

Spline Warning

The Spline adapters help eliminate gear spline wearand thus increase gear life.

Spline adapters are inserted into many of the

accessory drive gears.

All hydraulic pumps that do not use spline adaptersneed to be removed from the main gearbox to grease

the internal drive splines every Phase 4 (150 hrs.).

Warning: Only use special tools to insert and remove

adapters



3-23Rev. A Sept 18, 2007

Spline adapter pictures

The spline adapters

(vespals) are made from

phenolic plastic.



3-24Rev. A Sept 18, 2007

Thomas Coupling

The Thomas couplings are mounted between the enginedrive shafts and input flanges of the main gearbox input

housings.

The Thomas couplings absorb engine torque and engine

to gearbox vibrations.

The Thomas couplings are dynamically balanced and

must be replaced as an assembly.

The outer three washers can be replaced if damaged or

lost. All replacement washers must be the exact same

weight.



3-25Rev. A Sept 18, 2007

Thomas Coupling Heavy Mark

Heavy Mark



3-26Rev. A Sept 18, 2007

Thomas Coupling notes

Any damage to the disks or other components of thecoupling may cause excessive vibration and the coupling

must be replaced.

When replacing Thomas Coupling input flange use anti-

seize on splines

Thomas couplings and engine high-speed shafts will be

identified with a residual heavy mark.

It is important to remember to off set these marks 180

degrees (Or as close to 180º as possible.)



3-27Rev. A Sept 18, 2007

MGB Lubrication Description

Lubrication is accomplished by a self-priming wet sump

system.

The oil pump, attached to the main gearbox sump,

circulates oil for main gearbox lubrication and cooling.



3-28Rev. A Sept 18, 2007

F-Gear Box Lubrication Schematic





3-30Rev. A Sept 18, 2007

Oil Filter

The oil filter consists of a cover, bowl, bypass valve, andcartridge with filter elements. Filter elements can be

bronze mesh or Monel mesh. Both are 40 micron nominal.

It is mounted on the lower right side of the main gearbox

accessory cover, and it filters all main gearbox oil betweenthe oil pump and oil cooler.



3-31Rev. A Sept 18, 2007

Oil Filter

Installation



3-32Rev. A Sept 18, 2007

Oil Filter Bypass

If the filter becomes clogged, a bypass valve opens,allowing the oil to bypass the filter.

The oil cartridge should be removed, and the filter elements

should be cleaned and inspected every 150 hrs.



3-33Rev. A Sept 18, 2007

Oil strainer Description

A strainer in the lower part of the main gearbox consists of asleeve, retainer, and screen.

A chip detector is mounted inside the strainer. The strainer

prevents large particles from entering the pump and causing

damage.

The strainer may be removed and inspected without draining

the main gearbox by turning the outer sleeve 90º

Note: The Strainer should be removed, inspected, and

cleaned every 150 Hrs. with the oil filter.





3-35Rev. A Sept 18, 2007

Oil Pump



3-36Rev. A Sept 18, 2007

Oil Pressure

Main Gear Box Oil is Mobil 626. The main gearbox oil pressure normal operating range is 50-

65 psi (345-448 kPa). The oil pressure is adjusted at the oil

pump which is located on the sump.

A pressure transmitter located on the aircraft transmissiondeck sends an electrical signal to the Pressure Indicator

located in the cockpit.



3-37Rev. A Sept 18, 2007

MGB Pressure Transmitter

Pressure

Transmitter



3-38Rev. A Sept 18, 2007

Oil Pressure Warning

When oil pressure at the furthest point from the pump dropsbelow 13-17 psi (90-117 kPa). the low oil warning switch on

the main gearbox actuates, causing the caution “trans oil

press” light to illuminate.

The switch is located on the lower front right side at the lowerMGB support.



3-39Rev. A Sept 18, 2007

Oil Temperature

The main gearbox temperature indicating system consistsof an indicator, a resistance bulb located on the main

gearbox sump, just after the oil screen, and circuit

breakers.

The temperature resistance bulb converts the temperature

of the oil system to an electrical signal supplied to the

“trans oil temp” indicator at the center of the instrument

panel.



3-40Rev. A Sept 18, 2007

Hot Oil Warning

The main gearbox hot oil warning system consists of a

caution panel capsule, (Trans Oil Hot ), temperature Plug Stat

Switch, signal adapter unit, and a circuit breaker.

The temperature Plug Stat Switch is located in the secondary

manifold above the right hand input.

The Temperature Plug Stat Switch actuates when oiltemperature is over 121 ºC illuminating the caution-advisory

panel “Trans Oil Hot” light.

When the oil temperature drops below 121ºC the light will go

off.





3-42Rev. A Sept 18, 2007

Chip Detectors

The electrical chip detectors provide an indication of metalaccumulation in the main gearbox.

The chip detectors are located on the bottom of the oil sump

and in the strainer assembly.

The two chip detectors are wired together in parallel.



3-43Rev. A Sept 18, 2007

Chip Detector Diagram

MGB Sump

Chip Detector

MGB Screen

Chip Detector

Caution Panel

Press to Test

On Left Main

Gear Leg

il S Chi D



3-44Rev. A Sept 18, 2007

Oil Screen Chip Detector

When enough

conductive material

bridges the contacts

of the magnetic

detector, a ground is

provided, allowingcurrent to actuate a

relay that illuminates

the “Chip Main

Trans” light capsule

on the caution- advisory panel.



l C l



3-46Rev. A Sept 18, 2007

Oil Cooler

Oil C l



3-47Rev. A Sept 18, 2007

Oil Cooler The oil cooler has a thermostatic bypass valve, which will

cause the oil to flow into the radiator core when the oil

temperature exceeds 70C.

Also, oil will bypass the core if pressure exceeds 50 psi

(345 kPa) differential. Note: Oil cooler assembly must be removed with the main

gearbox if the M/G/B is removed for making metal.

MGB I



3-48Rev. A Sept 18, 2007

MGB Input

I S l R l



3-49Rev. A Sept 18, 2007

Input Seal Replacement

R B k



3-50Rev. A Sept 18, 2007

Rotor Brake



R B k



3-52Rev. A Sept 18, 2007

Rotor Brake

Rotor Brake Assemble

Rotor Brake Disc

R B k



3-53Rev. A Sept 18, 2007

Rotor Brake

Shaft Seal

A face-type (carbon)

seal is used the rotor brake

shaft.

The carbon seal consists of

two matched components:the seal assembly and the

seal mating ring.

The mating surfaces of the

carbon element and thering are lapped to

extremely close fit,

providing the sealing

action.

MGB O ti l Ch k



3-54Rev. A Sept 18, 2007

MGB Operational Check

New, overhauled or repaired main gearboxes receive a fullload run-in at the factory and require no further break-in run.

However, an operational check is required in addition to the

pilot pre-flight check to ensure proper installation and that

the lubrication system is working properly.



Documents

3. Transmissions