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 CONSTRUCTIONMETHODS OF HELICOPTER CONSTRUCTION CAN BE DIVIDED INTO THREE CATEGORIES, THERE ARE:1. TUBULAR CONSTRUCTION2. STRESSED CONSTRUCTION3. BONDED OR COMPOSITE CONSTRUCTIONTHOUGH 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 METHOD1. 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 CONSTRUCTION1. 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.


Mainfuselage

TailBoom


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.


CONTINUE1. 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 AIRCRAFTFIXED-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


HELICOPTERHELICOPTER 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.


LANDINGFIXED-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 LEVELSHELICOPTER 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 SECTIONTAIL 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 STRUCTURETHE 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 STRUCTUREATTACHED 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 PANELSTHE CABIN SECTION ATTACHES DIRECTLY TO THE FLOOR.



CABIN SECTIONMADE 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 SECTIONCONNECTS TO THE BODY SECTIONMADE 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 DEVICELOCATED 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.


Engineering

Helicopter structure