13.2 Takeoff and Climb Performance

ACS PA.I.F.K2 lists the factors that move the takeoff and climb numbers: atmospheric conditions, pilot technique, airplane configuration, airport environment, loading/CG, and weight. PA.IV.A–C then ask the same atmospheric and Vx/Vy knowledge for normal, soft-field, and short-field takeoffs. The knowledge test does not grade your brake-release. It does ask which way an upslope, a tailwind, or a high density altitude moves the distance, and which speed climbs you over a tree versus up to cruise altitude fastest.

PHAK: the critical takeoff is some mix of high gross weight, altitude, temperature, and unfavorable wind. Predict the distance from the AFM/POH, not from last Saturday’s roll on a cold morning.

Read a takeoff chart the way PA.I.F.K1 intends

Manufacturer pages are not standardized. Some are graphs you walk through (weight → pressure altitude/OAT → wind → surface). Some are tables with notes underneath. The notes are part of the chart. Typical trainer notes look like: decrease distances 10 percent for each 9 knots of headwind; for a tailwind up to 10 knots, increase distances 10 percent for each 2 knots; add about 15 percent ground roll on dry grass. Those percentages belong to that AFM. They are not a PHAK universal law. They show you how a real page is used.

The table below is a teaching takeoff table, invented for this lesson. It is not a real AFM/POH. Assume 2,400 lb, flaps 10°, paved level dry runway, zero wind, full power before brake release.

Worked chart example. Section 13.1’s afternoon at PA 2,000 feet / OAT 32 °C produced about 4,500 feet density altitude. Teaching table: about 1,330 feet of ground roll and 2,290 feet to clear 50 feet, climbing at roughly 505 fpm. Same airplane at sea level standard was 860 / 1,520 / 730 fpm. The “it’s a long runway” feeling from winter is not a calculation.

Apply a 9-knot headwind with a typical AFM-style “−10 percent per 9 knots” note: 1,330 × 0.90 ≈ 1,200 feet ground roll. Apply a 4-knot tailwind with a typical “+10 percent per 2 knots” note: 1,330 × 1.20 ≈ 1,600 feet. The tailwind costs you more than the equal-magnitude headwind gave back. That is the PHAK story, not a local opinion.

Weight, wind, slope, surface, technique, flaps

Weight. More weight means a higher lift-off true speed (more lift required) and more mass to accelerate. PHAK’s illustration: a 21 percent weight increase needs about a 10 percent increase in lift-off speed. Acceleration is slower and the roll is longer. Climb suffers because excess thrust and excess power both shrink.

Wind. A headwind lets you reach lift-off indicated speed at a lower groundspeed. A tailwind forces a higher groundspeed for the same indicated lift-off speed. PHAK’s comparison, which the test loves: a headwind equal to 10 percent of takeoff airspeed cuts takeoff distance about 19 percent; a tailwind equal to 10 percent of takeoff airspeed adds about 21 percent. Tailwind is not a mirrored headwind. It is worse than the headwind was good.

Slope. Gradient is height change over runway length, as a percent. A 3 percent gradient is 3 feet of height per 100 feet of length. Upslope lengthens the takeoff (you accelerate uphill) and shortens the landing. Downslope does the opposite. Chart Supplement runway footnotes are where the gradient lives.

Surface. Anything that is not hard and smooth adds rolling resistance and lengthens the takeoff. Grass, gravel, dirt, and standing water all count. Braking effectiveness on landing is a different problem (next section). For takeoff, think friction that steals acceleration.

Technique. A late rotation, an early rotation that drags the airplane in ground effect below the recommended speed, a tailwind takeoff “because the taxiway was closer,” or a failure to use the AFM flap setting are all PA.I.F.K2b items. Ground effect can trick you into lifting off slow; PHAK warns that leaving ground effect without the recommended speed, at high weight and high density altitude, can leave you unable to climb.

Flaps. Configuration is PA.I.F.K2c. The AFM, not a hangar rule, chooses takeoff flaps. First-notch flaps often buy extra CL for a soft- or short-field takeoff at the price of extra drag. Using landing flaps for takeoff, or using zero flaps when the short-field chart assumes 10°, is a different airplane than the chart.

Vx, Vy, Vg — three different jobs

Vx is maximum excess thrust. Vy is maximum excess power. They are not the same airspeed except at the absolute ceiling, where they meet and climb is zero. Until then, Vx is slower than Vy in a typical trainer. After the obstacle, accelerate to Vy. Holding Vx all the way to cruise altitude is a hotter engine and a longer clock.

Vg is not a climb speed. It is the power-off distance speed. In many trainers it sits near Vy, but you do not get to assume they are equal. Read the AFM.

Service ceiling versus absolute ceiling; gradient versus rate

Service ceiling: altitude where the airplane can still climb 100 fpm in the defined configuration (usually max continuous power, specified weight). Absolute ceiling: zero rate of climb; only one speed holds level flight. A normally aspirated trainer’s service ceiling is why a high-DA departure toward rising terrain is a go/no-go, not a personality test.

Climb rate is feet per minute — an air-mass number. Climb gradient is feet of altitude per nautical mile of ground distance — the obstacle number. Same 500 fpm into a headwind covers less ground, so the gradient steepens. Same 500 fpm with a tailwind covers more ground and the gradient flattens. Wind does not change the VSI. It changes whether you clear the trees.

Short-field and soft-field, at knowledge level

Short-field (PA.IV.C). AFM flap setting. Hold brakes, full power, check engine gauges, release. Rotate at the published short-field speed. Climb at Vx until the obstacle is cleared (or until a safe altitude if there is no obstacle), then accelerate to Vy and retract flaps on schedule. The knowledge item is the why: Vx is the angle that buys the most height in the least distance.

Soft-field (PA.IV.B). Keep rolling — do not stop and sink. Full aft elevator to unload the nosewheel. Lift off at the slowest possible speed and stay in ground effect to accelerate to the climb speed, then climb out. The knowledge item is weight transfer and ground effect, not a second published Vx.

Scenario: Alex and the uphill grass

Alex has 3,200 feet of dry grass that slopes up 2 percent toward the departure end. Density altitude is 4,500 feet, weight is near gross, and the wind is a 4-knot tailwind because the parking ramp is on that end. The teaching table’s paved, level, zero-wind 50-foot number was 2,290 feet. Grass adds roll. Upslope adds roll. Tailwind adds more than a headwind would have subtracted. Alex does not average those factors in his head and call it “about 2,500.” Alex applies the AFM notes in the order the page requires, adds a safety margin the manufacturer does not promise, and is willing to wait for a headwind or leave weight on the ramp. The chart is a prediction for a well-flown airplane. It is not a dare.