12.4 Formula, Supplement, and Embedded-Image Final Review

The High-Yield General Sheet

A formula list helps only if you understand each relationship. For electricity, master Ohm's law (E = I x R) and power (P = I x E), and the series-versus-parallel rules: in series, current is the same everywhere and resistances add; in parallel, voltage is the same across branches and total resistance is less than the smallest branch. For weight and balance, anchor the chain moment = weight x arm and CG = total moment / total weight, all distances measured from the datum, and remember a negative arm sits forward of the datum. The other General must-knows live in the table below.

The Dirty Dozen is a frequent General item: lack of communication, complacency, lack of knowledge, distraction, lack of teamwork, fatigue, lack of resources, pressure, lack of assertiveness, stress, lack of awareness, and norms. NDT distinctions also recur, magnetic particle works only on ferromagnetic parts, while eddy current and dye penetrant suit non-ferrous and surface-breaking cracks, and radiographic reveals internal flaws.

The High-Yield Airframe and Powerplant Sheets

5D** (two to two-and-a-half rivet diameters from the center of the hole to the edge, never less than 2D or more than 4D), and rivet pitch of 4D to 6D center to center within a row (minimum about 3D). 5D** minimum. Hydraulic fluids are a classic trap: MIL-H-5606 is a mineral-base fluid (red), while Skydrol is a fire-resistant phosphate-ester fluid (purple), and the two are chemically incompatible and must never be mixed.

The pitot-static instruments, the altimeter, airspeed indicator, and vertical speed indicator, all run off the pitot and static pressure system.

For Powerplant, the Otto cycle drives reciprocating engines through intake, compression, power, and exhaust, with one power stroke per cylinder every two crankshaft revolutions. A gas turbine follows the constant-pressure Brayton cycle through the compressor, combustion, and turbine sections; turbofan, turbojet, turboprop, and turboshaft are its variants. The magneto is a self-contained ignition source independent of aircraft electrical power; the impulse coupling retards and intensifies the starting spark.

The propeller governor uses speeder-spring-loaded flyweights and a pilot valve to port oil and change blade angle on a constant-speed prop.

Make Formulas and Figures Explainable

Build your own review sheet during study, then practice without it. Solve a calculation, then explain why the answer makes physical or maintenance sense. Read a supplement figure, then state what a mechanic would inspect or document. This transfer matters because the DME hands you no answer options, you must explain the principle and apply it safely. Embedded images change delivery, not content, so keep studying the same systems, regulations, and calculations, and log every repeated error with its cause, not just the right answer.

The Tightest Integrative Facts to Carry In

A last-pass should drill the facts examiners reuse most. On the Powerplant side, lock the firing order concept: a typical four-cylinder horizontally opposed engine fires 1-3-2-4 and a six-cylinder Continental commonly fires 1-6-3-2-5-4, spreading power strokes evenly. Magneto timing is set so the spark occurs several degrees before top dead center; the impulse coupling delays and snaps the spark for easy starting at low rpm.

Reciprocating oil has two faces, straight mineral oil for engine break-in (it lets rings seat) and ashless-dispersant (AD) oil for normal operation (it suspends contaminants without ash deposits). A wet-sump engine stores oil in the crankcase; a dry-sump uses a separate tank with scavenge pumps.

On the turbine side, remember the energy path: the compressor raises pressure, the combustion section burns fuel at roughly constant pressure, and the turbine extracts energy to drive the compressor (and, on a turboprop or turboshaft, a propeller or rotor through a reduction gear). Igniters fire only during starting, unlike the continuous spark of a reciprocating magneto.

For the propeller, a fixed-pitch prop has one blade angle, while a constant-speed prop uses a governor: rising rpm throws the flyweights outward, repositioning a pilot valve that ports oil to change blade angle and hold the selected rpm; feathering turns the blades edge-on to stop windmilling drag on a failed engine.

Finally, fold in a few General carry-ins that examiners love: a galvanic corrosion cell needs two dissimilar metals plus an electrolyte; dye penetrant finds only surface-breaking defects; return to service after maintenance requires the correct 14 CFR 43.9 entry while an inspection uses 43.11; and the Dirty Dozen explains why fatigue, pressure, and complacency drive most maintenance errors. Quiz yourself on these out loud, the format that the DME oral will demand, so the knowledge transfers cleanly from screen to hangar.