Performance and Limitations

Lift, weight, thrust, drag. In steady flight, lift opposes weight and thrust opposes drag; an imbalance produces a climb, descent, or speed change.

A combination of Newton's third law — the airfoil deflects airflow downward and gets an equal, opposite upward reaction — and Bernoulli's principle, where faster airflow over the cambered upper surface lowers pressure relative to below. The pilot controls lift through angle of attack, airspeed, and (with flaps) surface area (PHAK ch 5).

Parasite (form, skin friction, interference) increases with speed; induced is a byproduct of lift and decreases with speed. They're equal at L/D-max, which is best-glide speed (PHAK ch 5).

At low airspeed (behind the power curve), more power is needed to fly slower because induced drag dominates — relevant on short final and in slow flight. In the region of normal command, more power gives more speed.

• Camber — the curvature of the wing; you change it with flaps
• Angle of incidence — the fixed wing-to-longitudinal-axis angle; can't be changed in flight
• Angle of attack — the angle between the chord line and the relative wind (PHAK ch 5)

Exceeding the critical angle of attack — which can happen at any airspeed, weight, or attitude (PHAK ch 5).

Forward CG: more stable, higher stall speed, heavier elevator forces, lower cruise speed, longer takeoff/landing, favorable stall recovery. Aft CG: less stable, lower stall speed, lighter controls, higher cruise; an excessively aft CG can make stall/spin recovery difficult or impossible (PHAK ch 5).

• Longitudinal — pitch, lateral axis, set by CG/elevator
• Lateral — roll, longitudinal axis, helped by wing dihedral
• Directional — yaw, vertical axis, from the vertical stabilizer

Each can be static (initial tendency) or dynamic (over time), and positive, neutral, or negative (PHAK ch 5).

Higher-pressure air below the wing spills around the tip to the lower-pressure air above, creating vortices — strongest when the generating aircraft is heavy, clean, and slow. Avoid by staying above and upwind of a larger aircraft's flight path and landing beyond its touchdown point.

High temperature, high altitude, high humidity, and high weight all reduce performance and increase takeoff and landing distance (PHAK ch 11).

Airspeeds: IAS → CAS (corrected for installation/position error) → TAS (corrected for altitude/temperature) → GS (corrected for wind).

Altitudes: indicated, pressure (set 29.92), density (pressure altitude corrected for nonstandard temp), true (MSL), absolute (AGL).

Pressure altitude = field elevation + (29.92 − altimeter setting) × 1,000.

Density altitude = pressure altitude + ~120 ft per °C above standard.

Air density is affected by altitude, temperature, humidity, and pressure.

• Headwind shortens the ground roll and improves climb angle
• Tailwind lengthens it
• Crosswind requires drift correction

Vx — maximum altitude gained per horizontal distance (clearing an obstacle). Vy — maximum altitude gained per unit of time (best overall climb) (AFH).

Yes — the published figure is at max gross; at lighter weight the speed is slower (the glide ratio stays about the same).

Working front to back (PHAK ch 5):

• Leading edge — meets the relative wind first
• Trailing edge — where the upper and lower airflows rejoin
• Chord line — the straight line connecting the two; the reference line for angle of attack
• Mean camber line — runs equidistant between the upper and lower surfaces; the more it bows away from the chord line, the more camber the airfoil has

The upper and lower surfaces each have their own camber, and on most wings the upper camber is greater — that asymmetry is what speeds up the airflow on top.

Load factor grows with bank. In a level turn the wing has to support the airplane's weight and generate the horizontal force that turns it, so the load factor climbs: roughly 1.15 G at 30 degrees, 1.41 G at 45, and exactly 2 G at 60. Stall speed rises with the square root of load factor, so at 60 degrees of bank the wing stalls about 41 percent faster than in level flight. That's why a steep, slow turn — especially in the pattern — is a stall setup (PHAK ch 5).

At or below Va, one full control deflection drives the wing past the critical AoA and it stalls before it can generate enough lift to exceed the +3.8 G limit — the stall acts like an aerodynamic fuse. The wing's maximum force is the same at any weight; weight only decides which happens first, the stall or the structural limit. Heavier, the wing already needs a higher AoA just to hold 1 G, so it hits the critical AoA after fewer additional Gs — the fuse blows early, and Va can be higher. Lighter, level flight takes less AoA, which leaves room to pull well past 3.8 G before the stall arrives — so Va must come down to restore the protection (PHAK ch 5).

An aggravated stall with autorotation. Both wings are stalled, but one is stalled more deeply — it makes less lift and more drag than the other, and that imbalance keeps the airplane rotating around a steep, corkscrew path. The recipe is always the same: stall plus yaw. No yaw, no spin — which is why coordination is the real spin prevention (AFH ch 5).

Skid (too much inside rudder): the low inside wing stalls first, so the airplane rolls into the turn and toward the ground — a spin entry, and at pattern altitude there's usually no room to recover.

Slip: the raised wing tends to stall first, so the roll-off is toward wings-level — still a stall, but far more forgiving.

That's why the skidding base-to-final turn is the classic killer: keep the ball centered, especially turning final.

Straight from the memory table:

Secondary controls: flaps, leading-edge devices, spoilers, and trim systems (PHAK ch 6).

The wings' shallow V shape means that in a sideslip the lower wing meets the relative wind at a higher angle of attack than the raised wing, so it produces more lift and rolls the airplane back toward level. Fuel management plays into this too: an imbalanced fuel load holds one wing low and fights the dihedral effect (PHAK ch 5).

Longitudinal (pitch): depends above all on the CG staying inside the envelope — the tail-down-force geometry only works within limits.

Directional (yaw): comes from the vertical stabilizer plus the fuselage side area behind the CG; the larger the fin and the farther aft it sits, the stronger the weathervane tendency back to coordinated flight (PHAK ch 5).

Plot total drag (power required) against airspeed and you get a U. Induced drag falls as speed builds while parasite drag rises, and where they cross — the bottom of the U — is L/D max, which is also best-glide speed. To the right, parasite drag dominates: that's the region of normal command, where more power means more speed. To the left of L/D max is the region of reversed command: induced drag dominates, so flying slower takes more power. Slow flight lives on that back side, and so does a dragged-in short final — if I get slow behind the curve and just pull, I sink harder. The fix is to lower the AoA and add power (PHAK ch 11).

Because L/D max is an angle of attack, not an airspeed. The wing's best lift-to-drag ratio always occurs at the same AoA; the airspeed just has to be whatever puts the wing at that AoA. A lighter airplane needs less lift, so it reaches that AoA at a lower speed — the glide angle and ratio stay the same, but the target number on the airspeed indicator drops (PHAK ch 11).