Section 2: Loading and Performance — Four Forces, Load Factor, and Where the CG Belongs

Roll, pitch, yaw - identical vocabulary for fixed-wing and rotorcraft. Fixed wing: ailerons at the wingtips move opposite to roll; the elevator pitches; the rudder yaws. On the quad transmitter the same words map to sticks: right stick left/right IS aileron/roll, right stick forward/back IS elevator/pitch, left stick left/right IS rudder/yaw, left stick up/down is throttle. He's blunt about why this matters: 'there will be questions on the test almost 100% guaranteed about airplanes.'

Lift, weight, thrust, drag - on a quad, the motors play the wing's role. Lift acts at the center of pressure (CP, also called center of lift); in straight-and-level flight lift equals weight, and the imbalance either way is a climb or descent. The two mechanisms: Newton's third law (a tilted surface deflects air down, the reaction pushes up) and Bernoulli (air over the longer top path speeds up, pressure drops, and 'high pressure moves toward low pressure' - up through the wing).

Angle of attack is the angle between the RELATIVE WIND and the CHORD LINE (leading edge to trailing edge) - and lift rises with both airspeed and AoA: 'the faster we go, the more lift we create.' One orientation rule worth engraving: 'lift is always going to be perpendicular to the relative wind' - which is exactly why banking converts some of it into turning force.

PARASITE drag rises with airspeed and has three faces: form drag (shape), interference drag (junction turbulence - his mnemonic 'one plus one equals three': a wing joined to a fuselage drags more than both measured separately), and skin friction (rivets, chipped paint, bug splatter). INDUCED drag is lift's tax: it exists only while lift is being made, grows with angle of attack, and - the counterintuitive half - DECREASES as airspeed increases.

A stall happens when the wing exceeds its CRITICAL ANGLE OF ATTACK and airflow separates from the upper surface, collapsing lift. Low airspeed is the usual road there, but 'a wing can stall at any airspeed' - a fast, steep dive with an abrupt pull-up does it too. Fixed-wing recovery: lower the nose, reduce AoA below critical. Quadcopters essentially cannot stall - the motors make the lift and keep spinning at any attitude.

The exam's favorite subtlety: the critical angle itself 'remains the same regardless of gross weight' - weight and CG change the SPEED at which you reach that angle, never the angle.

Load factor is the G-load the structure feels - the 'resultant load' - and it climbs with bank angle: 60° = 2G (a 10 lb aircraft momentarily weighs 20 lbs to itself), 80° ≈ 5.7G, 85° ≈ 11.5G. The FAA's own sample figure: a 30° bank = 1.154. Because stall speed rises with the square root of load factor, a 45° bank adds 20% to stall speed (20 mph becomes 24).

His worked disaster: stall speed 15 mph, cruising at 20 - a five-mph cushion. Roll into a 60° bank and load factor 2 pushes stall speed to ~25 mph, five mph ABOVE current airspeed. The aircraft stalls mid-turn with no warning change in speed. He ties it to real fatal accidents in manned aviation: slow, low, steep turn to final.

STATIC stability is the INITIAL tendency after a disturbance: positive (noses back toward equilibrium - the cup rocking upright), neutral (continues without worsening - the cup rolling on its side), negative (diverges - the cup going over). DYNAMIC stability is what happens over TIME given positive static stability: positive dynamic damps the oscillation out; neutral dynamic oscillates forever at constant amplitude; negative dynamic makes each swing bigger.

Vocabulary first: CG is where weight acts and the craft balances; CP is where lift acts (nearby but distinct); ARM is the distance from CG to an applied force; MOMENT is arm x force. On a fixed wing, lift ahead at the CP makes a nose-down moment; the tail pushes DOWN to counter it. Move the CG AFT and the arm shrinks: less tail-down force needed, so better cruise, more range, shorter takeoff - paid for with less stability, easier over-control, and a lower stall speed. Move it FORWARD and everything mirrors: slower, less range, longer takeoff, but more stable and easier stall recovery.

The limits are the ENVELOPE, and beyond them is not degraded performance but uncontrollability: too far forward and the nose never lifts; too far aft and it stalls the moment it's airborne. Quad translation: CG centered among the four motors - offset loading overworks and overheats the heavy side's motors and tips the aircraft on takeoff. Two accident receipts: an unsecured 360 camera shifting mid-flight downed a DJI Matrice; a failed cargo strap shifted a C-130's CG aft with fatal results.

Altitude thins the air, so each prop rotation grips less of it - less lift, mushy controls. Heat and humidity both thin it further; a hot humid summer afternoon is the worst combination. Cold has a different failure mode: it saves the air density but drains BATTERY performance. Weight compounds everything - a heavier craft needs more speed or more AoA, both of which add drag, stretching takeoff and landing distances and flattening climb. Pre-flight environmental checks close the chapter: level launch surface, wind (fixed-wing launches INTO it for free relative wind), and obstacle clearance with margin.