Helicopter structure

FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
WELCOME TO CLASS
AJD 21603 ROTORCRAFT
SYSTEM, MAINTENANCE AND
ROLE EQUIPMENT
“... There are two ways to lead your life….
One is as though nothing is a miracle….
The other is as if everything is…. “

Course Outline
Assignment/Practical 50%
Quizzes/Midterm 20%
Final Examination 30%
18 weeks consisting of both lecturing and practical..
Note : Those who missed 10% of the class attendance without any
valid reason or justification will be BARRED from taking the final
examination.

Topics to be covered:
1. Helicopter Structure
2. Principles of Helicopter Maintenance
3. Routine Maintenance Activities
4. Storage Procedures
5. Basic Helicopter Ground Handling
6. Ground Handling Equipment
7. Inspection Requirement after incidents
8. Inspection Requirement after major
Inspection or component replacement.
9. Emergency and role equipment
10.Practical projects

HELICOPTER STRUCTUREHELICOPTER STRUCTURE

LESSON OBJECTIVE:
1. GAIN KNOWLEDGE ON HELICOPTER STRUCTURAL PARTS & ITS
PRINCIPLE OF CONTRUCTION, MAIN COMPONENTS MOUNTINGS
AND THE HELICOPTER LOAD PATHS
LESSON OUTCOMES:
1. DESCRIBE THE METHODS OF CONTRUCTION OF VARIOUS
HELICOPTER’S STRUCTURAL PARTS SUCH AS MAIN FUSELAGE, TAIL
BOOM, HORIZONTAL & VERTICAL STABILIZER.
2. DESCRIBE THE METHOD OF MAIN GEAR BOX, ENGINE AND
UNDERCARRIAGE MOUNTINGS.
3. DESCRIBE THE HELICOPTER LOAD PATHS

INTRODUCTION
• IN SUBJECT AIRCRAFT STRUCTURE, YOU'VE LEARNED THE VARIOUS
METHODS THAT ARE USED IN AEROPLANE CONSTRUCTION.
• YOU ALSO HAVE TOUCHED ON VARIOUS TERMINOLOGIES THAT
ARE RELATED TO AEROPLANE CONSTRUCTION.
• IN THIS SUBJECT YOU'LL LEARN SOME OF THE TERMINOLOGIES AND
METHOD OF AIRCRAFT CONSTRUCTION THAT ARE PECULIER TO
HELICOPTERS.
• THE EVOLUTION OF TECHNOLOGY AND TYPE OF MATERIALS USED
ON THE CONSTRUCTION OF HELICOPTERS HAVE CHANGED
TREMENDEOUSLY FOR THE LAST 40 YEARS.

MAJOR HELICOPTER
COMPONENTS

METHOD OF HELICOPTER CONSTRUCTION
METHODS OF HELICOPTER CONSTRUCTION CAN BE DIVIDED
INTO THREE CATEGORIES, THERE ARE:
1. TUBULAR CONSTRUCTION
2. STRESSED CONSTRUCTION
3. BONDED OR COMPOSITE CONSTRUCTION
THOUGH THE CONCEPT OF CONSTRUCTION IS VERY SIMILAR
FIXED WING AIRCRAFT, THERE ARE SOME DIFFERENCES IN TERM
OF LOAD PATHS & PARTS THAT CONSTITUTES THE STRUCTURE.

TUBULAR CONSTRUCTION
• THIS TYPE OF CONTRUCTION IS USED OF EARLY GENERATION
HELICOPTER SUCH AS BELL 47.
• TUBULAR TUBES WHICH ARE ALSO KNOWN AS TRUSSES ARE
WELDED TOGETHER TO FORM THE FUSELAGE.
• ADVANTAGES:
1. HIGH STRENGTH TO WEIGHT RATIO.
2. THE FUSELAGE CAN BE REPAIRED AT FIELD LEVEL UNLESS THERE IS
A NEED FOR A JIG FOR ALIGNMENT PROCESS.
• DISADVANTAGES:
1. HIGH COST OF MANUFACTURING.
2. DIFFICULT TO HOLD DIMENSIONS TO A CLOSE TOLERENCE.

EXAMPLE OF TUBULAR CONSTRUCTIONEXAMPLE OF TUBULAR CONSTRUCTION

TUBULAR CONSTRUCTION METHODTUBULAR CONSTRUCTION METHOD
1. NORMALLY 4 LONGERONS RAN THE LENGTH OF THE FUSELAGE –
THEY TOOK MOST OF THE COMPRESSIVE & TENSILE LOADS.
THEY ARE KEPT APART BY THE CROSS MEMBERS – IDEALLY
MOST OF THEM IN TENSION.
2. THE ARRANGEMENT OF THE CROSS TUBES CAN BE EITHER 'N', 'X'
OR 'W' TO COPE WITH THE SIDE WAYS LOADS FROM THE TAIL
ROTOR-FIN-TAILPLANE.
3. THE LONGERONS & CROSS TUBES FORMED THE PRIMARY
STRUCTURE.
4. THE CROSS BRACING TOOK THE INTERNAL SPACE & ARE
RELATIVELY HEAVY. STREAMLINING STRUCTURE ARE ADDED
WHICH ARE CALLED SECONDARY STRUCTURE. THEY ARE
ATTACHED TO THE PRIMARY STRUCTURE & THE WHOLE THING
IS COVERED IN FABRIC.

STRESSED SKIN CONSTRUCTIONSTRESSED SKIN CONSTRUCTION
1. USED MAINLY ALUMINIUM ALLOYS IN ITS CONTRUCTION.
2. CAN BE EITHER MONOCOQUE OR SEMI-MONOCOQUE.
ADVANTAGE:
• HIGH STRENGTH TO WEIGHT RATIO. RATIO WAS HIGHER
THAN THE TUBULAR CONSTRUCTION FOR THE SAME SIZE.
• EASY TO MANUFACTURER & FASTER.
• MORE PRECISION IN TERM OF FITTING TOLERENCE
(BECAUSE OF THE JIGS BEING USED)
• FEW REPAIR TOOLS NEEDED AT FIELD LEVEL.

STRESSED SKIN CONSTRUCTION
1. IN THE FIELD, FEW ADDITIONAL TOOLS WERE REQUIRED
FOR REPAIRS.
2. IN TERM OF FUSELAGE CHARACTERISTICS, THIS TYPE OF
STRUCTURE IS MORE DELICATE – EASILY DAMAGE.
3. FOR MAJOR REPAIRS, THE FUSELAGE WOULD REQUIRED
JIGS TO OBTAIN PROPER ALIGNMENT FOR THE VARIOUS
SECTIONS.
4. IN HISTORY, FEW HELICOPTERS WERE BUILT USING A
COMBINATION OF SHEET METAL CONSTRUCTION & THE
TUBLAR CONSTRUCTION. TUBULAR DESIGN – AREAS
WHERE HIGH STRENGTH IS NEEDED. SHEET METAL,
STRENGTH REQUIREMENTS ARE NOT CRITICAL.

SEMI MONOCOQUE

EXAMPLE OF HELICOPTER JIG – B412

SEMI MONOCOQUE CONSTRUCTION
• SEMI MONOCOQUE CONSTRUCTION CONSISTS OF A
FRAMEWORK OF VERTICAL & HORIZONTAL MEMBERS
COVERED WITH A METAL SKIN.
• VERTICAL MEMBERS CALLED BULKHEADS OR FORMERS
PROVIDE SHAPE OF THE FUSELAGE.
• THE HEAVY LONGITUDINAL MEMBERS KNOWN AS
LONGERONS, PROVIDE THE PRIMARY STRENGTH, WHILE
THE LIGHTER LONGITUDINAL MEMBERS KNOWN AS
STRINGERS GIVE A MEANS OF ATTACHING & STIFFENING
THE SKIN.

BELL 412 FUSELAGE CONSTRUCTION
CONSISTS OF 2 MAJOR COMPONENTS:
1. FUSELAGE - FUSELAGE INCLUDES THE CREW & CABIN
AREA, WINDSHIELD, WINDOWS, CREW AND
PASSENGER DOORS, PYLON & ENGINE COWLINGS AND THE
LANDING GEAR.
2. TAIL BOOM - TAIL BOOM INCLUDES THE BAGGAGE
COMPARTMENT, ELEVATOR, DRIVESHAFT & GEARBOX
COVERS, VERTICAL FIN & TAIL SKID.

Main
fuselage
Tail
Boom

BELL FUSELAGE CONSTRUCTION FEATURES
•
AIRFRAME IS A CONVENTIONAL SEMI-MONOCOQUE STRUCTURE
OF BULKHEADS, SUPORT BEAMS, STRINGERS, AND CAST AND
MACHINED FITTINGS, WHICH ARE HELD TOGETHER BY
INTERCOSTALS AND COVERED WITH AN EXTERNAL SKIN.
1. THE PRIMARY CONSTRUCTION MATERIAL IS CORROSION
RESISTANT ALUMINIUM ALLOY.
2. OTHER MATERIALS INCLUDE TITANIUM WORKDECK AREAS,
TITANIUM FUEL CELL PANELS AND STAINLESS STEEL
FIREWALLS.
3. IT FEATURES EXTENSIVE USE OF HIGH TEMPERATURE BONDED
HONEYCOMB PANELS WITH LONG LIFE, HIGH STRENGTH &
LIGHT WEIGHT.

CONTINUE
1. NON-STRUCTURAL FIBREGLASS MOLDED PANELS ARE ALSO
USED. THESE REDUCE MAINTENANCE REQUIREMENTS &
ENHANCE THE OVERALL APPERANCE OF THE HELICOPTER BY
PRESENTING SMOOTH CONTOURS.
2. PROTECTION AGAINST CORROSIVE ELEMENTS AND
GALVANIC ACTION IS PROVIDED BY A COATING OF EPOXY
POLYAMIDE PRIMER.
3. ALL PANEL EDGES AND FIBERGLASS SURFACES ARE SEALED
AND SPOT WELDING IS NOT USED.
4. THE EXTERIOR SURFACE OF THE HELICOPTER IS FURTHER
PROTECTED BY VERY DURABLE POLYURETHANE PAINT.

MONOCOQUE CONSTRUCTION

MONOCOQUE CONSTRUCTION

THE MONOCOQUE CONSTRUCTION INVOLVES THE
CONSTRUCTION OF A METAL OR COMPOSITE MATERIAL TUBE
OR CONE WITHOUT NTERNAL STRUCTURAL MEMBERS.

IN SOME CASES IT IS NECESSARY TO HAVE FORMERS TO
MAINTAIN THE SHAPE, BUT IT IS THE STRESSED SKIN THAT
CARRIES THE PRINCIPLE STRESS IMPOSED UPON THE
STRUCTURE.

EXAMPLE OF MONOCOQUE CONSTRUCTION IN HELICOPTER IS
TAIL BOOM.

BONDED CONSTRUCTION

THE THIRD TYPE OF CONSTRUCTION INVOLVES STRUCTURE
WHOSE PARTS ARE JOINED TOGETHER BY CHEMICAL
METHODS RATHER THAN MECHANICAL.

FIBREGLASS, HONEYCOMB AND OTHER COMPOSITE
MATERIALS ARE USED IN THESE STRUCTURES BY THE USE OF
ADHESIVES, HEAT & PRESSURE.

ADVANTAGE: HIGH STRENGTH TO WEIGHT RATIOS, REDUCED
CONSTRUCTION COST BY ELIMINATING RIVETING & WELDING.

CONSTRUCTION MATERIALS OF SIKORSKY S76

STRESS AND LOADS
THE BASIC STRUCTURE OF A HELICOPTER ARE DIFFERENT
FROM THE CONVENTIONAL FIXED-WING AIRCRAFT – DUE TO
THE LOADS AND STRESSES THAT ARE PLACED ON THE
AIRFRAMES IN DIFFERENT LOCATION.
MAINTENANCE PERSONNEL MUST UNDERSTAND THIS
DIFFERENCES THROUGHLY IN ORDER TO PROPERLY INSPECT
& REPAIR THE HELICOPTER AIRFRAME

FIXED – WING AIRCRAFT
FIXED-WING AIRCRAFT: 2 AREAS THAT MUST BE BUILT FOR
THE PRIMARY STRESS LOADS OF LIFT AND THRUST.
ENGINE ATTACHMENT – CARRY THE THRUST LOADS
WING ATTACHMENT – CARRY THE LIFT LOADS

HELICOPTER
HELICOPTER FUSELAGE CARRIES BOTH THE LIFT AND THRUST
FORCES AT THE SAME POINT.
THE CENTER AREA OF HELICOPTER MUST BE BUILT TO CARRY
AND PROPEL THE HELICOPTER BECAUSE THE MAIN ROTOR IS
BOTH THE WING AND PROPELLER.

LANDING
FIXED-WING AIRCRAFT MUST DEPEND ON FORWARD SPEED
FOR FLIGHT AND TO LAND SMOOTHLY, (2 DIRECTIONS) THE
HELICOPTER WILL USUALLY CARRY THE LOAD IN ONE
DIRECTION.
SOME OCCASIONS – HELICOPTER MAY CARRY BOTH LOADS –
AUTOROTATION & TAIL ROTOR LANDING FAILURE.
CONSTRUCTION PROVISION MUST INCLUDES THESE 2
ELEMENTS

VIBRATION LEVELS
HELICOPTER HAS THE HIGHEST LEVEL OF VIBRATION DUE TO
THE USE OF SO MANY ROTATING COMPONENTS.
NEW HELICOPTERS HAS LESS VIBRATION LEVEL DUE TO
INCORPORATION OF VARIOUS VIBRATION ABSORBING
METHODS – BIFILAR & NODAL BEAM.
HOWEVER THE VIBRATION STIL EXIST & TRANSFERRED
THROUGHTOUT THE AIRFRAME – EFFECT CAN WEAKEN THE
AIRCRAFT STRUCTURE.
EFFECT OF VIBRATION MUST BE CONSIDERED DURING THE
INSPECTION OF HELICOPTER AIRFRAME.

TAIL SECTION
TAIL SECTION OF HELICOPTER MUST ALSO BE CONSIDERED
DIFFERENT FROM THOSE OF THE FIXED – WING AIRCRAFT
BECAUSE OF TAIL ROTOR.
TAIL ROTOR – PROVIDES BOTH DIRECTIONAL & ANTI –
TORQUE. IN ADDITION IT ALSO PRODUCES VIBRATION.
SOME OF THESE LOADS ARE RELIEVED IN FLIGHT BY
VERTICAL FIN, THE SIDE LOAD IS STILL PRESENT ON THE TAIL
BOOM DURING ALL MODES OF FLIGHT.
HORIZONTAL STABILIZER ALSO CONTRIBUTES TOWARDS
ADD. LOAD PRESENT IN TAIL BOOM.
BECAUSE OF THIS, INSP. REQUIREMENT IS REQUIRED AT THE
TAIL BOOM JUNCTION.

CASE STUDY – AS350/355 FUSELAGE
1. USES A COMBINATION OF VARIOUS MATERIALS & IS A SEMI-
MONOCOQUE CONSTRUCTION.
2. MATERIALS USED ARE ALUMINIUM, FIBREGLASS
MATERIALS WHICH USES THE THERMOSETTING TYPE OF
RESINS.
3. STEEL IS ONLY USED WHERE IT IS ABSOLUTELY
NECESSARY.

BODY STRUCTURE
THE BODY STRUCTURE IS THE MAIN STRUCTURAL MEMBER
OF THE FUSELAGE.
IT NOT ONLY CARRIES THE LIFT & THRUST LOADS, BUT ALSO
THE LANDING LOADS.
SUPPORTS ALL OTHER MEMBERS OF THE FUSELAGE EITHER
DIRECTLY OR INDIRECTLY.
ALL THE FORCES APPLIED TO THESE MEMBERS WILL BE
TRANSMITTED TO BOX STRUCTURE.
THE TRANSMISSION ASSEMBLY, WHICH IS CONNECTED TO
THE MAIN ROTOR & ABSORBS THE COMPRESSION LOADS OF
LANDING IS ATTACHED TO THE BOTTOM OF THE BOX.
IN THE MIDDLE OF THIS STRUCTURE IS PLACED THE FULE
TANKS, WHICH IS THE MOST PROTECTED AREA OF THE
HELICOPTER.

BOTTOM STRUCTURE
ATTACHED TO THE BODY STRUCTURE ON THE FRONT OF THE
BOX IS THE BOTTOM STRUCTURE & CABIN FLOOR.
MADE OF 2 CANTILEVERED BEAMS EXTENDING FROM THE
BOX THAT ARE CONNECTED TO THE CROSS MEMBERS OF THE
BOX.
THE 2 BEAMS CARRY THE WEIGHT OF THE CABIN & TRANSMIT
IT TO THE BOX.
CROSS MEMBERS ARE ADDED TO THESE 2 BEAMS TO SUPPORT
THE FLOOR & THE LOWER SKIN PANELS
THE CABIN SECTION ATTACHES DIRECTLY TO THE FLOOR.

CABIN SECTION
MADE ALMOST ENTIRELY OF FROM SYNTHETIC MATERIALS
(POLYCARBONATE REINFORCED WITH GLASS FIBRE)
CONSISTS OF SUB ASSEMBLIES – CABIN ROOF, NOSE &
VERTICAL MEMBERS.
HEAT MOULDED & ASSEMBLED BY BANDING & ULTRASONIC
SPOT WELDING.
BOLTED TO THE CABIN FLOOR AND THE BODY BULKHEAD.
OTHER ITEMS – WINDOWS, WINDSHIELD & LOWER WINDOW
(ALL POLYCARBONATE)
TRANSPARENT POLYCARBONATE – SUPERIOR STRENGTH
PROPERTIES.

AS355 CABIN

REAR SECTION
CONNECTS TO THE BODY SECTION
MADE OF 3 FRAMES CONNECTED BY BEAMS TO THE BODY
SECTION.
THIS FRAME, COVERED WITH A STAINLESS STEEL FIREWALL,
ACT AS ATTAHMENT POINT FOR ENGINE.
INSIDE THIS SECTION ACTS AS A BAGGAGE AREA.
TAIL BOOM SECTION IS BOLTED TO THE REAR FRAME.

TAIL BOOM
CONVENTIONAL DESIGN – CIRCULAR FRAMES, STRINGERS &
OUTER SKIN.
STRINGERS & STIFFENERS – GIVE RIGIDITY.
ITEMS FITTED TO TAIL BOOM – TGB, TRDS, VERTICAL &
HORIZONTAL STABILIZERS.
ADDITIONAL STIFFENERS ARE ATTACED TO THE STRUCTURE.

VERTICAL & HORIZONTAL STABILIZER
LOWER VERTICAL FIN – SYMMETRICAL AIRFOIL. PROTECTED
BY TAIL ROTOR GUARD WHICH IS ATTACHED TO THE BOTTOM
OF THE FIN.
FIN IS BOLTED TO THE TAIL BOOM AT LEADING EDGE & SPAR
SECTION OF THE FIN.
TOP FIN – DISSYMMETRICAL AIRFOIL – TO OFFLOAD T/ROTOR
IN FORWARD FLIGHT. ATTACHMENT IS SIMILAR TO LOWER
FIN.
HORIZONTAL STABILIZER – DISSYMMETRICAL AIRFOIL –
PRODUCE DOWNWARD FORCE TO KEEP THE HELICOPTER
LEVEL IN FORWARD FLIGHT.
IT PASSES THROUGH THE SLOT IN THE TAIL BOOM & BOLTED
ON EACH SIDE.

ANTI-VIBRATION DEVICE
LOCATED UNDER THE PILOT’S SEAT & CREATES A NODE IN
VERTICAL VIBRATIONS IN THE CABIN SECTION OF THE
HELICOPTER.
THIS IS ACCOMPLISHED BY ADDING A STEEL BLADE WHICH
HAS A WEIGHT ATTACHED.
THIS RESONANTES WITH THE VIBRATIONS OF THE AIRFRAME.

Helicopter structure

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