AMT General – Quick-Review Notes

Electrical Fundamentals

• Opposition in AC circuits
  • Coil (ignoring R): inductive reactance $(X<em>L)$ • Total AC opposition: impedance $(Z)$ where $Z = \sqrt{R^2 + (X</em>L - X_C)^2}$
• Inductive reactance formula: $X_L = 2\pi f L$
• Capacitive reactance: $X_C = \frac{1}{2\pi f C}$
• Rectification element: diode
• Charge symbol: $Q$ ; unit: coulomb
• Magnetic lines pass easiest through iron
• Parallel‐circuit rules
  • Voltage equal across branches
  • Total current $I<em>T$ is sum of branch currents • Total resistance $R</em>T = \frac{1}{\sum 1/R_i}$
• Series‐circuit power: $P = VI = \frac{V^2}{R} = I^2 R$
• Voltmeter across closed switch with power on reads $0\,V$
• Example values
  • Four $6\,\Omega$ resistors, $24\,V$ source ⇒ voltage across any resistor $= 24\,V$
  • Three $6\,\Omega$ resistors, $12\,V$ source ⇒ branch current $= 2\,A$, total $= 6\,A$

Mathematics & Physics Review

• Cube: $64^3 = 262\,144$
• Binary $00001111<em>2 = 15</em>{10}$
• Gear speed ratio (driver $36$ teeth, driven $20$): $1:1.8$
• Rectangular volume: $V = lwh$ ; weight & balance moment: $M = W \times A$ ; center of gravity: $CG = \frac{\sum M}{\sum W}$
• Newton I (inertia): bodies stay at rest/motion unless acted on by external force

Weight & Balance Essentials

• Moment sign: plus / minus depends on weight location relative to datum and if being added/removed
• Helicopter weight & balance parallels airplane procedures; lateral CG critical
• “$24\%$ of MAC” expresses CG distance aft of LEMAC
• Leveling accuracy: spirit level preferred
• Scale errors: wheel chocks or set brakes give false readings
• Operating CG range found in Type Certificate Data Sheet

Fluid Lines & Fittings

• MS flareless fitting: tighten by specified turns unless torque given
• Castle nut mis-alignment within torque: back nut off to nearest hole
• Aircraft bolt torque charts assume clean, dry threads
• Overtightened flare weakens at sleeve/nut/flare
• Minimum flattening in bends: small diameter ≥ $75\%$ of original OD
• Soft Al tubing cut with hand wheel-type cutter
• Self-locking nuts allowed if bolt/nut not subject to rotation

Materials & Powerplant

• Exhaust collectors/stacks/manifolds: stainless steel
• Hung start (air starter): shut off fuel
• Start-fire: continue cranking to start & extinguish
• Nickel-cadmium vs lead-acid batteries serviced separately; dual servicing causes contamination
• NiCd liquid level drops on discharge—electrolyte absorbed into plates
• Residual fuel: known fuel remaining in tanks, lines, engine

Regulations & Documentation

• Part $65$ covers certification of airmen other than flight crewmembers
• Mechanic certificate valid until voluntarily surrendered, suspended, or revoked
• Address change: notify FAA within $30$ days
• Aircraft failing annual requires special flight permit to reposition
• Airworthiness Certificate transfers with aircraft on sale
• Installation requires documented compliance with FAA airworthiness standards
• TSO = Technical Standard Order; issued by FAA Administrator

Helicopter Fundamentals

• Raising collective increases pitch of all rotor blades → vertical lift
• Rotor system types: fully articulated, semi-rigid, rigid (flexible-beam is not standard group)

Human Factors & Safety

• Modern safety view: human error is starting point for analysis

Drafting & Blueprint Basics

• Hidden edges: medium-weight short dashes
• Center line: alternating long/short dashes
• Machine-finish symbol: finish marks
• Station numbers locate wing/stabilizer frames
• Sectional drawings: removed sections show details