This page is a case-by-case drill for the gravity-turn pitch program from
the parent note . We take the one
master law and push it into every corner : every angle regime, the two degenerate
endpoints (γ = 9 0 ∘ straight up, γ = 0 ∘ horizontal), the sign of the
turn rate, a real launch word-problem, and an exam-style twist.
The single tool we lean on the whole way:
Intuition Read the formula like a sentence
"The nose falls over at a speed set by how sideways gravity currently is (cos γ ),
shared out over how much momentum the rocket has (v )." The minus sign says: the angle
always decreases — the rocket is always tipping toward the horizon, never back up.
Every situation this topic can throw at you falls into one of these cells. The worked examples
below are each tagged with the cell they cover.
Cell
What makes it special
Example
A. Near-vertical (γ → 9 0 ∘ )
cos γ → 0 , so γ ˙ → 0 — barely turns
Ex 1
B. Mid-turn (γ ≈ 4 5 ∘ )
cos γ large — fastest turning
Ex 2
C. Near-horizontal (γ → 0 ∘ )
cos γ → 1 , but v huge — turn slows again
Ex 3
D. Speed dependence (fix γ , vary v )
γ ˙ ∝ 1/ v — the inverse law
Ex 4
E. Degenerate: exactly vertical (γ = 9 0 ∘ )
γ ˙ = 0 — the "stuck" case, why a kick is needed
Ex 5
F. Degenerate: exactly horizontal (γ = 0 ∘ )
maximum cos γ = 1 ; check burnout instant
Ex 6
G. Real-world word problem
convert units, find turn over a time window
Ex 7
H. Exam twist: sign / integration
eliminate time, d v / d γ , over-vs-under-kick
Ex 8
The figure above plots cos γ across the whole turn. Notice the two ends (vertical and
horizontal) are where the raw turning force is smallest and largest respectively — but the
actual turn rate also divides by v , which is why the real turning bunches up early
(cell A→B) when v is still small.
Worked example Turn rate just after the kick
v = 120 m/s , γ = 8 9 ∘ , g = 9.8 m/s 2 . Find γ ˙ in both
rad/s and degrees per second.
Forecast: guess first — will the turn be a big fraction of a degree per second, or tiny?
Compute cos 8 9 ∘ . cos 8 9 ∘ = 0.017452 .
Why this step? The formula needs the sideways fraction of gravity; at 8 9 ∘ almost
all gravity pulls straight back along the path, only a sliver pulls sideways.
Plug in. γ ˙ = − 120 9.8 × 0.017452 = − 0.0014253 rad/s .
Why this step? Direct use of the one law; the minus keeps the "always tipping down" sign.
Convert to degrees. Multiply by 180/ π = 57.2958 :
− 0.0014253 × 57.2958 = − 0.0816 6 ∘ / s .
Why this step? Humans read degrees; rad/s is the natural unit of the formula.
Verify: units — [ m/s 2 ] / [ m/s ] = 1/ s , which is rad/s. ✓ And the
answer is tiny (0.08°/s), matching cell A's promise that a near-vertical rocket barely turns —
proving you must deliberately kick it.
Worked example Turn rate at
4 5 ∘
Later the rocket is at γ = 4 5 ∘ , v = 500 m/s . Find γ ˙ in °/s.
Forecast: cos 4 5 ∘ is nearly 40× bigger than cos 8 9 ∘ , but v is ~4× larger.
Net: faster or slower turn than Ex 1?
cos 4 5 ∘ = 0.707107 .
Why? At 4 5 ∘ gravity is split evenly between "slow you down" and "turn you," so the
sideways fraction is large.
Plug in. γ ˙ = − 500 9.8 × 0.707107 = − 0.013859 rad/s .
To degrees: − 0.013859 × 57.2958 = − 0.7939 8 ∘ / s .
Why? Same conversion.
Verify: compare to Ex 1: 0.79/0.082 ≈ 9.7 × faster despite the higher speed — the
big cos γ wins. This confirms cell B is where turning peaks. Units again 1/ s . ✓
Worked example Turn rate approaching orbit-like speeds
Late ascent: γ = 5 ∘ , v = 4000 m/s . Find γ ˙ in °/s.
Forecast: cos 5 ∘ ≈ 1 (maximum!) — will the turn now be the fastest of all?
cos 5 ∘ = 0.996195 .
Why? Nearly flat flight means almost all of gravity now points sideways relative to the
(near-horizontal) velocity.
Plug in. γ ˙ = − 4000 9.8 × 0.996195 = − 0.0024407 rad/s .
To degrees: − 0.0024407 × 57.2958 = − 0.1398 4 ∘ / s .
Verify: even with maximal cos γ , the huge v (4000 m/s) in the denominator crushes
the turn rate down to 0.14°/s — slower than the 4 5 ∘ case. This shows why real turning
is front-loaded : at high speed the velocity vector is too "heavy" for gravity to bend. ✓
Worked example Same angle, half the speed
At γ = 8 9 ∘ : rocket X has v = 120 m/s ; the heavier, sluggish rocket Y
has v = 60 m/s . Compare their turn rates.
Forecast: halving v — does the turn rate halve, stay same, or double?
X: from Ex 1, γ ˙ X = − 0.0014253 rad/s .
Y: γ ˙ Y = − 60 9.8 × 0.017452 = − 0.0028506 rad/s .
Why? Only v changed; the numerator is identical.
Ratio: γ ˙ Y / γ ˙ X = 2 exactly.
Why? γ ˙ ∝ 1/ v , so halving v doubles the turn.
Verify: 0.0028506/0.0014253 = 2.000 . ✓ Consequence: the slow rocket Y over-turns twice
as fast, so it must be given a smaller initial kick — the design lesson of cell D.
Worked example Exactly straight up — does it ever turn?
A rocket rises perfectly vertical : γ = 9 0 ∘ exactly, any speed v . Find γ ˙ .
Forecast: with no wind, no kick, will it ever tip over on its own?
cos 9 0 ∘ = 0 .
Why? At exactly vertical, gravity points straight down the flight path — it slows the
rocket but has zero sideways component to turn it.
Plug in. γ ˙ = − v g × 0 = 0 for any v .
Why? Zero numerator kills the whole thing.
Verify: γ ˙ = 0 means the angle never changes — a perfectly vertical rocket stays
vertical forever and never reaches orbit. This is the mathematical proof that the pitch kick
is mandatory : you must manually break the γ = 9 0 ∘ symmetry. It's a true degenerate
fixed point of the equation. ✓
Worked example The burnout instant — flying flat
At the ideal burnout the rocket is horizontal: γ = 0 ∘ , v = 7800 m/s
(near orbital). Find γ ˙ and interpret.
Forecast: cos 0 ∘ = 1 is the maximum sideways gravity. Is the turn rate then large?
cos 0 ∘ = 1 (maximum possible).
Why? Flying flat, gravity is fully perpendicular to velocity — every bit of it bends the path.
Plug in. γ ˙ = − 7800 9.8 × 1 = − 0.0012564 rad/s
= − 0.07198 5 ∘ / s .
Why? The enormous v tames even maximal gravity.
Verify: despite maximum cos γ , the answer is only 0.072°/s — smaller than the
4 5 ∘ case. Interpretation: at orbital speed, this residual "gravity turn" is exactly the
curvature of the orbit itself (gravity providing centripetal turning). Units 1/ s . ✓
Worked example Angle change over a time window
Just after the kick a rocket holds roughly v ≈ 150 m/s and γ ≈ 8 5 ∘ (nearly constant) for a 10-second window. Approximately how many degrees does the
flight-path angle drop in that window? (Treat γ ˙ as constant over the short window.)
Forecast: a few tenths of a degree, a few degrees, or tens of degrees?
Instantaneous rate. cos 8 5 ∘ = 0.087156 , so
γ ˙ = − 150 9.8 × 0.087156 = − 0.0056942 rad/s .
Why? Get the per-second turn rate from the master law.
To °/s. − 0.0056942 × 57.2958 = − 0.3262 3 ∘ / s .
Why? Convert so the answer reads in degrees.
Multiply by the window. Δ γ ≈ γ ˙ × Δ t = − 0.32623 × 10 = − 3.262 3 ∘ .
Why this step? Over a short window where γ ˙ is roughly constant, angle change ≈
rate × time (a straight-line approximation of the curve).
Verify: the rocket tips from ~85° to ~81.7° in 10 s — a gentle few-degree bend, exactly the
"kick once, then coast" picture. If we'd wrongly used v = 15 m/s we'd predict a wild 32° turn,
so the units and magnitude sanity-check the result. ✓
Worked example Speed gained per degree turned (drag-free)
Using the parent note's time-eliminated form with constant thrust-to-weight n = a / g = 2 ,
drag neglected: d γ d v = − cos γ v ( n − sin γ ) . Evaluate this
slope at γ = 6 0 ∘ , v = 300 m/s , and say what its sign means.
Forecast: as the rocket turns (γ decreasing), is it speeding up or slowing down here?
Values. sin 6 0 ∘ = 0.866025 , cos 6 0 ∘ = 0.5 .
Why? The slope formula needs both, at the current angle.
Numerator. v ( n − sin γ ) = 300 ( 2 − 0.866025 ) = 300 × 1.133975 = 340.1924 .
Why? n − sin γ is thrust-along-path minus gravity-along-path; here thrust wins.
Divide by − cos γ . − 0.5 340.1924 = − 680.3849 (m/s per rad of γ ).
Why? Completes d v / d γ .
Interpret the sign. γ decreases during the turn (d γ < 0 ), and
d v / d γ < 0 , so d v = ( d v / d γ ) d γ > 0 : the rocket speeds up as it turns.
Why? Two negatives multiply to a positive Δ v .
Verify: − 680.3849 per rad = − 680.3849/57.2958 = − 11.875 m/s per degree of turn.
With thrust exceeding the gravity-along-path term (n > sin γ ), the vehicle accelerates
while bending over — physically correct for a healthy ascent. Had n < sin γ the sign would
flip and the rocket would be losing speed (an under-powered, gravity-loss-heavy climb). ✓
Recall Which cell is the "stuck" one, and why?
Cell E, γ = 9 0 ∘ exactly ::: cos 9 0 ∘ = 0 makes γ ˙ = 0 , so a perfectly vertical rocket never turns — the pitch kick must break this symmetry.
Recall Why does the fastest
turn rate NOT happen at horizontal (where cos γ is biggest)?
Because γ ˙ ∝ 1/ v ::: by the time γ is small, v is huge, and the large speed in the denominator overwhelms the maximal cos γ .
See also: Gravity turn trajectory · Angle of attack and dynamic pressure (max-Q) ·
Thrust-to-weight ratio · Gravity loss and steering loss ·
Tsiolkovsky rocket equation · Closed-loop ascent guidance (PEG / IGM) ·
Attitude control and thrust vectoring (gimbal) .