Aviation Knowledge Levels

Knowledge Levels

• Basic knowledge for categories A, B1, and B2 is indicated by knowledge levels 1, 2, or 3.
• Category C applicants can meet either the category B1 or B2 basic knowledge levels.

Level 1 Objectives

• The applicant should be familiar with the basic elements of the subject.
• The applicant is able to give a simple description of the whole subject, using common words and examples.
• The applicant is able to use typical terms.

Level 2 Objectives

• A general knowledge of the theoretical and practical aspects of the subject is required
• Must have the ability to apply that knowledge.
• The applicant should be able to understand the theoretical fundamentals of the subject.
• The applicant should be able to give a general description of the subject using typical examples.
• The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject.
• The applicant should be able to read and understand sketches, drawings and schematics describing the subject.
• The applicant should be able to apply his knowledge in a practical manner using detailed procedures.

Level 3 Objectives

• A detailed knowledge of the theoretical and practical aspects of the subject is necessary
• Must have the capacity to combine and apply the separate elements of knowledge in a logical and comprehensive manner.
• The applicant must know the theory of the subject and interrelationships with other subjects.
• The applicant must be able to give a detailed description of the subject using theoretical fundamentals and specific examples.
• The applicant must understand and be able to use mathematical formulae related to the subject.
• The applicant should be able to read, understand and prepare sketches, simple drawings and schematics describing the subject.
• The applicant should be able to apply his knowledge in a practical manner using manufacturer's instructions.
• The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate.

Screw Principles

• A wedge is a simple machine used to apply a load.
• The distance an object raises when a wedge is driven under it is determined by the wedge's inclination.
• A steeper wedge moves an object a greater distance; a shallower wedge raises a greater weight.
• A screw is an inclined plane wrapped around a cylinder or shaft.
• The pitch (P) is the distance along the cylinder covered by one full turn of the helix.
• A shallow wedge angle produces a fine pitch thread, while a steeper angle yields a coarse pitch thread.
• When a male thread is engaged in a female thread, the entire surface area of the female "wedge" is in contact with the male.
• Greater force (F) can be exerted between the surfaces of a shallow wedge than a steeper one.
• A shallow wedge angle produces more friction and greater resistance to tightening and loosening, due to friction's dependency on the surface area.
• This is desirable in threaded fasteners, especially in smaller threads where surface area is limited.
• A coarse thread produces greater travel (P) when a thread is used to produce motion.

Screw Terminology

• Screw thread pitch is the distance in inches or millimetres from any point on a thread to the corresponding point on the next thread, measured parallel to the axis.
• The pitch of a screw is equal to one thread per square inch.
• The effective diameter, also called pitch diameter, is the diameter of an imaginary cylinder (Pitch Cylinder) that splits the fundamental triangles exactly in half.
• The minor diameter is measured between the roots of a male thread and between the crests of a female thread.
• The major diameter is the diameter measured over the crests of the thread or the roots in the female.
• The crest is the top surface joining the flanks of the thread.
• The root is the bottom of the groove joining adjacent sides or flanks of the thread in both male and female screws.
• The flank or side is the surface of the thread form connecting the crest and root.
• The thread angle is the included angle between the flanks, measured in the axial plane.
• The distance a screw thread advances axially in one complete turn is known as lead (same as pitch for a single start thread).
• The length of engagement is the axial distance two mating threads contact each other.
• The angular depth is the vertical height of the triangle formed by the intersection of extended flanks.
• The actual depth is the distance between the crest and root of the thread, measured perpendicularly to the axis.
• The fundamental triangle is formed by the intersection of extended flanks (XYZ).
• Truncation is the radial distance from the crest or root of the thread to the adjacent apex of the fundamental triangle.

Screws and Threads in Aircraft

• Aircraft hardware includes fasteners and miscellaneous small items used in aircraft manufacturing and repair.
• The correct selection and use of aircraft hardware effects the safe and efficient operation of any aircraft.
• Vibration is always present during aircraft operation.
• Aircraft maintenance must incorporate provision for safety tying or locking fasteners to prevent loosening in flight.
• Aircraft hardware is identified by the originating organization, engineering data, materials, and processes used to design and produce it.

Aircraft Hardware Standards

• Various standards are used for hardware specifications in the aircraft industry.
• The most common standards include American Standards, European or French Standards and Aircraft manufacturers' Standards.
• AN standards is Airforce Navy standards.
• MS standards are Military Standards.
• NAS standards are National Aerospace Standards.
• NSA is NATO Standardisation Agency standards.
• BAC is Boeing Aircraft Corporation standards.
• FON is Fokker standards.
• AMS is Aeronautical Materials Specifications.
• Standard hardware is identified by a specification number while special fasteners must be replaced with the same part number and standard hardware.
• Difference is in the material used, the closer tolerance in its manufacture or a more critical inspection of the part.
• AN fasteners can be replaced by MS fasteners, but MS standard hardware must not be replaced by AN standard hardware.

Bolts and Screws in Aircraft

• Fastening devices for aircraft allow quick dismantling of parts requiring frequent removal and reassembly.
• Riveting or welding these parts would weaken the joint.
• Bolts and screws offer the required attachment security and rigidity.
• Bolts are used for high strength applications and screws for lower strength.
• Bolts and screws are used for fastening or holding, and each has a head on one end and a screw thread on the other.
• The threaded end of a bolt is always blunt, while that of a screw may be either blunt or pointed.
• The threaded end of a bolt has a nut secured to it.
• The threaded end of a screw may fit into a female receptacle or directly into the material being secured.
• Bolts have short thread sections and long grip lengths, while screws have longer threaded sections and potentially defined grip lengths.
• Bolt assemblies are typically tightened by turning the nut; the bolt head may or may not be designed for turning, and a screw is always tightened by turning its head.
• When replacing aircraft fasteners, a duplicate of the original fastener should always be used.

Classification of Threads

• A thread formed by one continuous groove is a single or single start thread.
• Single threads are used for adjustment and fastening, the lead (axial distance travelled by an engaged threaded part in one complete turn) is always equal to the pitch (thread distance).
• Multiple start threads consist of two or more ridges cut side by side.
• Multiple start threads increase the thread's axial travel or lead without changing the pitch and is equal to the Pitch of the thread (P) multiplied by the number of starts.

Right and Left Hand Threads

• In a right hand thread, turning the nut clockwise tightens it on a bolt.
• A left hand thread requires anti-clockwise nut turning to tighten.
• Left hand threads are used for special purposes.
• American Standard Thread is ANC, ANF, ANEF and ANP.
• The BSW, BSB, BSP British Standard Whitworth and BSPT are British Standard thread types.

American and Unified Standard Threads

• The American Standard Thread has a 60 degree angle.
• Unified Standard Threads are composed of UNC, UNF and UNEF threads.
• The British Standard Thread has a 55 degree angle.

Metric standards

• The SI Metric system is generally used in Europe.
• All metric threads have a standard thread form.

Classes of Fit

• Class 1: Loose fit
• Class 2: Free fit
• Class 3: Medium fit
• Class 4: Close fit
• Class 5: Tight fit
• Typically aircraft bolts are almost always manufactured in a Class 3 (medium) fit.
• A Class 4 fit needs a wrench to tighten, while Class 1 can be turned by hand.
• Aircraft thread of screws are generally manufactured with Class 2 fit for ease of assembly.

Measuring Thread

• A thread pitch gauge is used to identify threads on various bolts/screws
• Match a thread-pitch gauge up to the bolt to identify.
• The number indicates the number of threads per inch (TPI).

Aircraft bolts

• Typically made from hex heads with sizes ranging from AN3 (3/16 in) to AN20(2 in).
• Identified by length and diameter to make for the correct use.
• A number immediately following the prefix represents the diameter in increments of 1/16th of an Inch.
• Dash number represent the length in increments of 1/8th of an inch.

Airframe Bolts

• Made from cadmium-plated nickel steel, corrosion-resistant steel and 2024 aluminium alloy.
• Unless specified, made from cadium-plated nickel steel .
• A corrosion resistant bolt has the letter C inserted between the diameter and length designations.
• Aluminum alloy bolts are identified by "DD".
• Most aircraft bolts have markings identifying the material and/or manufacturer.
• AN standard steel bolts = raised dash or an asterisk (center of the head).
• Corrosion-resistant steel = single dash.
• AN aluminium-alloy bolts = two raised dashes.
• Letter "A" after the dash number means the bolt does not have a hole drilled through it.
• If absent, the bolt has a hole drilled.
• Suffix letter "H" indicates having a safety wire.

Clevis Bolts - AN21 to AN36

• Clevis bolts (AN21 to AN36 standards) are loaded in SHEAR only.
• Domed head (typically slotted/recessed to accept a screwdriver (to use if needed)
• Unique feature: Short portion of the shank is threaded (has a long grip length) increasing its shear strength

Nuts

• MUST have locking devices to prevent the nut from falling off
• Self locking type (Locks onto a bolt on its own vs non-self locking type)

Self-locking Nuts

• Prevents loosening
• 2 common types: fiber/nylon type and all-metal
• To install, screw until the chamfer is able to protrude through the insert.
• At least ONE thread needs to protrude past the nut
  • If more than 3, replace the bolt or use a washer
• The dash number will specify both diameter and the number of threads

Low Temp Self locking Nuts

• Nylon wont work if temperature exceeds 120 degrees C.
• AN365 = Held by a nylon insert above the screw threads/
• AN364 = Thin but made for shear loads and not tension. Made for clevis bolts without drilled shanks.

Wing Nuts

• Needed when parts are removed frequently without needing tools.
• Made from metal or brass.
• Sizes fit number 6 machine screws up to .

Aircraft Cable

• The equipment, testing and manufacture of aircraft, all control cables meet CASA's CAO 180
• Typically made from carbon or stainless steel.
• Stainless are better in the long term due to lower corrosion.

Types of Aircraft Cable

• Nonflexible 1x7 or 1x19 - Stranded once (Nonflexible)
• Flexible - Standed 7 times (Fair)
• Extra Flexible 7 - 19 - Standed 7 then standed again 19 times (Common Type).
• Cables are pre-formed

Proof Loading Steel Cable

• Run for the required amount of time after terminals are installed.
• Usually around 60 percent of yield force

Tools used to control cables

• Pulleys that align changes in direction
• Fairleads to protect against frame

Bowden and Teleflex Control cable

• Outer and control cables used for control
• Teleflex are more for pushing and pulling.

Cable Drums

• Almost always for trim tab systems
• The wheel turns, and thus actuate the line

Cable Terminators

• A special crimp tool (Nicopress) use copper rings to create the bond and termination

Swaged Terminators

• The sleeve is swaged to the cable by approved process

Important Notes

• After swaging sleeve, must be certain to use the before and after gauge to confirm

Shackle Pin

• Fork and Joints that Shear

Throttles

• It is important to have a very precise pressure/force on the flight controls

Bearings

• It's important to have no movement and good stability

Bearing installation

• Bearings need good contact/alignment to prevent damage
• Retention methods used depend on load

Bearing and Housings

• Retaining Rings and staking are 2 different methods to use.
• If a high strength location is needed for an area you can do staking
• A staking tool can deform bearing material too.

Staking

• Airframe and control bearings may be retained by interference but maybe not with vibration and axial loads.
• A staking methods may be used

Swaging

• A rolling tool is used to roll metal around after the BEARING outer race.

Gears and Transmissions

• Gears are used with bearings/shafts to transmits power and increase rotational speed.
• A gear is a toothed wheel transmitting motion from one shaft to another.

Classification

• Spur (straight teeth, noisy.)
• Wheel (big gear) and Pinion (smaller) which help rotate.
• All other is called: helical or worm gears and beveled

Reduction Gear Assembly.

• Classified by the number of steps.
• Can reduce speed but increase torque

Idler Gears:

• Intermidiate gear
• To make output rotate in same direction.
• The presence is still effective

Gears

• Gear Ration = Teeth Driven / Drive to increase the torque ratio. A low gear helps in take off.

Gears in Helicopters

• Spur and then spur helical tooth/groove.

Epicycle Gearing

• Also for Helicopters (Can do high reduction)
• Made of: inner sun gear, a planetary and gear ring.

Differental Gearing

• Similar setup to bevels.

Plain Bearings

• Sliding between the surface and radial loads being piston based
• The "Journal Load" is a pison engine and is at right angles
• Grooves that help distrubite the lubricant are grooved.
• Shell" bearing is common. (Ex. big or crankshaft).

Belleville Washer

• Small stack and can make smaller deflections

Thrust Ratings

• Roller bearing and taper roller load ratings can vary.

Thrust bearing

• Used in end of engine shafts and used to distribute loads
• Always have some diamternal clearece.

Diametrical Clearence

• With in the clearecen, a film remains moving. designed to reduce and also to support and provide heat expansion with the fitting.
• Grouped by tolerance

Aircraft Cables

• 6.10 Series used for aircraft controls/pulleys/bowden/stiff system and is located all over the plane.
• These are done using digital or flexible control.

Springs are

• Elastic and be pressed/twisted with a force.
• Typically use steel and some other metals.
• Used to store energy.
• Motive of power with items /light suspensions with shock absorbency.

Springs are

• Usually from metal.
• Special steel/chromuim and moly. There are flat springs for high loads.

Torsion

• Shaft/section to restore energy and has specific character

Key/Cotter Pins

• Are used to create joints with loads and is held/safe wired.