Meccanica del Volo dell'Elicottero - Appunti di Matteo Cappo

Rate of climb (OEI) 12.7 m/s 2500 ft/min 12.5 m/s 2460 ft/min

General Data

Max troops seats 55 - 47 -

Crew 2 - 2 -

Powerplant rating (each) 3270 KW 4380 shp 2927 KW 3925 shp

Table 1: CH-53E Specifications faced with D-model ones.

One can notice, by reading the table, in which measure the CH-53E increased the load capa-

bility of the CH-53D. Matteo Cappo s209364 3

Technical Report: Sikorsky CH-53

CH-53E three views drawing

Figure 1: The dotted line shows the helicopter with main rotor and tail boom folded.

Matteo Cappo s209364 4

Technical Report: Sikorsky CH-53

Fuselage and cargo features

CH-53E airframe is based on D-model one, a little scaled-up and adapted for hosting the third

engine. Fuselage shape derives from S-61R Jolly Green Giant series: fuselage is watertight,

though the machine did not have a boat hull (like the S-61 Sea King), so it is not really

intended for amphibious use and only lands on water in emergencies. Lateral sealed sponsons

host fuel tanks and main landing gear and increase the floatation time and stability of the

helicopter on the water.

The primary structure is made using light alloy, steel and titanium and skin is in aluminium

with composite removable panels; cockpit section is realized in glass fibre/epoxy and an

extensive use of Kevlar to protect transmission fairing, engine cowlings and fuel tanks is

done. To conserve space on board naval vessels, the tail boom and the main rotor can be

folded using an automatic hydraulic system. The sharp break in the fuselage for the rear

ramp caused significant drag so the engineering solution to this problem was to add strakes,

known as “Elephant Ears”, to the fuselage at the ramp.

CH-53E has a flight crew of two; main cabin can accommodate up to 55 troops on folding

canvas seats along walls and in centre of cabin or 24 litters with medical attendants. There is

a passenger door on forward starboard side of main cabin and a hydraulically operated rear-

loading ramp. The internal cargo bay is about 10 m long by 2,50 m high by 2 m wide and

features a roller system for palletized cargo and tie-downs built into the floor. The CH-53E

is equipped with a single point 16330 kg (36000 lb) capacity hook or a two- points system

which are limited to a combined load of 36000 lb. The two-point system limits the swing

of the load compared to the single point system. This helicopter is capable of lifting heavy

equipment including the eight-wheeled LAV-25 Light Armored Vehicle, the M198 155 mm

Howitzer with ammunition and crew and can recover downed aircraft up to its size, which

includes all Marine Corps aircraft except for the KC-130.

Landing gear

The tricycle-type landing gear system consists of retractable dual-wheel gear assemblies and

tail skid. The main landing gear assemblies retract forward and upward into the sponsons,

each assembly has hydraulic brakes and drag strut. The nose assembly is mounted vertically

at the centerline of the helicopter, it is free to turn 360 degree about the strut and retracts

rearward and upward into the nose section of the airframe. The retractable tail skid mounted

on the underside of the tail pylon aids in the prevention of the tail rotor blades from striking

the ground when landing with nose high attitude. The tail skid is automatically retracted

when the main landing gear is retracted, or the cargo ramp is lowered and automatically

extended when the main landing gear is down and locked. The extraction and retraction of

the gears is performed by a hydraulic system: in case of hydraulics failure there is a one shot

pneumatic emergency extension system.

Matteo Cappo s209364 5

Technical Report: Sikorsky CH-53

Main Rotor

The main rotor consists of a rotor head assembly and seven rotor blades. The rotor head,

directly mounted to the output shaft of the main gearbox, is formed by the swash plate

assembly (lower non rotating part and upper rotating part) and the rotor hub. The main rotor

is an evolution of the old type rotor installed on the D-model: in fact it was a 6 bladed fully

articulated oil lubricated type. To increase lift and thrust, rotor diameter was increased from

22 to 24 m, number of blades became 7 instead of 6 and each blade had a wider chord.

In order to reduce maintenance of the main

rotor head while increasing reliability, all lu-

brication requirements were eliminated, solv-

ing also a persistent oil leakage problem. A

bearingless rotor head was introduced: a cone-

shaped spherical elastomeric bearing for pitch,

flap and lead/lag replaced hinges; the elas-

tomeric bearing is constructed of a sandwich

of rubber and metal laminates with no lubri-

cation required.

Rotor head features also seven hydraulic lag

dampers. Figure 2: D-model new bearingless rotor

Cyclic or collective pitch changes are com- head

manded to the non-rotating swash plate by a

two stage hydraulic irreversible control system; the rotating swash plate transmit the com-

mand to blade cuffs by pitch linkage. Anti-flapping restrainers and droop stops prevent

excessive flapping of the blades when the main rotor head is static or is turning at low rpm.

The anti-flapping restrainers are automatically released as rotor speed is increased to about

25 percent, while the droop stops are automatically released as main rotor speed is increased

to about 75 percent. The rotor head is primarily titanium and steel.

Main rotor blades The rotor blades are attached to extenders, which connected to titanium

cuffs receive pitch command from linkage. Rotor blades have a Nomex honeycomb internal

construction bonded to a cold formed 10 m tubular titanium spar; the assembly is wrapped in

composite glass fibre and epoxy skin. Moreover abrasion strips bonded to the leading edge

prevent damage from dust and adverse weather conditions. The airfoil used is SC1095 and

◦

has a 16 twist. Each main rotor blade is fitted with the “In-Flight Blade Inspection System”

(IBIS): spar is pressurized with nitrogen (10 psi) and incorporates a spar pressure indicator

to detect eventual cracks. Crack detection is performed using radioactive Strontium 90: if

pressure in the blade decreases the pressure indicator on the root of the blade exposes a small

radiation source; a radiation detector located aft of the main rotor pylon area send a warning

signal to helicopter monitoring system that alerts the crew.

Matteo Cappo s209364 6

Technical Report: Sikorsky CH-53

Tail rotor

The tail rotor is a four bladed one and provides lift as well as anti-torque functions. Respect

◦

to CH-53D, tail rotor was increased to 6,1 m diameter and canted 20 to the left: the added

third engine moved helicopter centre of gravity backward, unbalancing the machine during

hovering. So a canted rotor that provide lift towards ground (so pitch up moment) has been

◦

installed. Furthermore E-model has a larger 18 left canted vertical stabilizer and a larger

inverted-gull asymmetric tailplane on tail rotor pylon right side. The tail rotor pitch change

is accomplished by a 2 stage hydraulic servo.

(a) Tail rotor view. (b) Canted tail rotor pylon.

Figure 3: CH-53E Tail rotor assembly views.

Figure 4: CH-53E performing air-to-air refuelling.

Matteo Cappo s209364 7

Technical Report: Sikorsky CH-53

Transmission system

The transmission system consists of two nose gearboxes, a main gearbox, an accessory gear-

box, an intermediate gearbox, and a tail rotor gearbox. The freewheeling units can disengage

the engines during autorotation, or one or two engine for single or dual engine operation, or

any time engine rpm decreases below rotor rpm.

Figure 5: CH-53E Transmission system.

Main Gearbox The maximum rated 9798 kW (13140 hp, take-off) main gearbox features

bevel gears and a two stage planetary and couples the three engine inputs providing output

power for the main rotor, tail rotor, and accessory gearbox when it is not being driven by

◦

the Auxiliary Power Plant (APP). The main rotor shaft is tilted 5 forward to provide a level

fuselage at cruise speeds.

Nose Gearbox The nose gearboxes forward of the No. 1 and No. 3 engines contain high

speed bevel gears and connect engines output shaft with the main gearbox changing the drive

angle. The No. 2 engine input is directly into the main gearbox accessory section.

Accessory Gearbox The accessory gearbox drives main helicopter utilities. It is driven by

the main gearbox when engines are in function and by the APP before engines start-up. APP

is connected to the accessory gearbox through a shaft and a clutch, which is disconnected as

soon as the main gearbox rpm exceeds APP rpm.

Matteo Cappo s209364 8

Technical Report: Sikorsky CH-53

Intermediate and Tail Rotor Gearbox To power the tail rotor, the main gearbox supplies

torque to the tail drive shaft, which is segmented by a series of elastomeric couplings. In

order to allow the folding of the tail boom, the tail drive shaft can be split thanks to a discon-

nect coupling. The intermediate gearbox changes the angle of drive and provides a reduction

in angular speed before the tail gearbox. Finally the tail gearbox, a right angle drive gearbox,

provides the last reduction and powers the tail rotor.

Gearbox angular speeds [rpm]

Gearbox From To IN OUT

Nose GB Engine Main GB 14280 6323

Nose GB Accessory GB 6144

Main GB Engine No.2 Main rotor 6323 179*

Intermediate GB 4271

Interm. GB Main GB Tail GB 4271 2628

Tail GB Interm. GB Tail rotor 2628 699

Table 2: Gearboxes angular speeds. *: 100% N

r

Each of the six gearboxes has an individual oil lubrication system and drives its proper

pumps; because of the importance of lubrication, the main gearbox has a primary and an

auxiliary system. Oil pressure and temperature data can be monitored on the instrument

panel in the cockpit. The gearboxes have chip detectors that will cause chip detector lights

to go on when chips in the systems are detected.

Engines

In order to increase load capabilities of the D-model the main adopted improvement was the

installation of a third engine. Three General Electric T-64-GE-416 free turbine turboshaft

engines supplies power to the transmission system. The third engine is nested on the back of

the machine behind the rotor shaft, the engine intake sits to the left of the rotor shaft.

Each engine has a maximum rating of 3270 kW (4380

shp) for 10 minutes, intermediate rating of 3091 kW

(4145 shp) for 30 minutes and maximum continuous

power rating of 2756 kW (3695 shp).

To extend engine life in hostile environments (based

on experience in Vietnam), an Engine Air Particle

Separators (EAPS) was installed upstream of the en-

gine air intake. EAPS removes visible moisture, sand,

dust, etc. from the engine inlet air by using an elec-

tric powered cyclonic motion: foreign particles mi- Figure 6: Mounted EAPS.

grate towards the walls of the tube and are exhausted

overboard while clean air continues into the engine.

Matteo Cappo s209364 9

Technical Report: Sikorsky CH-53

Each engine has an independent oil syste