Level flight, climb, descent and glide

Use path components, not a memorised picture

A constant-speed climb and a pull-up can have different lift requirements at the same pitch attitude.

Steady path balance

With thrust aligned to a straight steady path, L = W cos γ and T − D = W sin γ. Positive excess thrust supports a climb; a descent can be maintained with thrust below drag.

The rate of climb is V sin γ, using TAS in consistent units. For small γ, gradient ≈ (T − D)/W and rate ≈ excess power/W. Air gradient and ground gradient differ when wind changes ground speed.

Separate transient and steady effects

Pulling up curves the path and needs additional normal acceleration. The resulting lift can exceed weight even before a steady climb is established. That transient extra lift also raises induced drag.

A climb at constant indicated speed is not automatically a constant-TAS climb. As density changes, the exact energy balance can include a kinetic-energy term.

Air gradient and ground gradient are different

An aeroplane climbing at TAS 100 m/s with vertical speed 5 m/s has an air climb gradient approximately 5%. If a uniform 20 m/s headwind reduces horizontal ground speed from about 100 to about 80 m/s, the ground gradient is approximately 5/80 = 6.25%. The engine did not produce more excess power; the aircraft covers less horizontal ground during the same height gain.

With a 20 m/s tailwind, the approximate ground gradient becomes 5/120 = 4.17%. Obstacle geometry is ground referenced, so the distinction matters even though the same air-relative climb can be maintained. Exact calculations should use the appropriate horizontal speed and angle rather than the small-angle approximation when necessary.

Use the steady-path equations to calculate the air-relative condition first. Then add the specified wind vector to obtain ground progress. The glide laboratory holds still air deliberately; it cannot silently answer an obstacle-clearance question with wind. The aircraft’s approved performance and operational procedures remain necessary for the actual departure assessment.

Weight supplies the power in a glide

Without useful thrust, gravitational potential energy pays for drag and any speed change.

Glide angle and L/D

In a steady power-off glide, D = W sin|γ| and L = W cosγ. Thus tan|γ| = D/L. Best still-air glide angle occurs at maximum L/D for the relevant configuration.

For an unchanged polar, greater weight requires a higher speed at the same optimum CL. The ideal still-air glide angle remains the same, while the rate of descent is greater.

Wind changes ground reach

A headwind reduces ground distance per unit height lost at a fixed air-relative condition. Tailwind increases it. Selecting speed for maximum ground range in wind is a separate optimisation from best still-air L/D.

The laboratory illustrates a straight steady glide in still air. Real range must include turns, configuration, terrain, propeller/engine state and the approved speed guidance.

Invert the glide-ratio requirement

A possible landing area lies 10 km horizontally away with 800 m of available height above its plane. The ideal still-air L/D required is 10,000/800 = 12.5. If the aircraft’s relevant supplied polar permits only L/D = 12, the ideal straight glide reaches 9.6 km, before allowing for turns, margins, wind or configuration changes.

A still-air L/D of 15 gives 12 km of geometric reach in the same simplified comparison. It does not automatically make the site operationally attainable: a turn costs height, terrain may intervene and an engine or propeller state can change drag. Headwind also reduces ground reach for a fixed air-relative glide condition.

Use the laboratory to solve for the L/D needed at the stated height, rather than treating the plotted path as an aircraft flight forecast. Raise height while holding L/D and speed fixed, then vary speed at a fixed ratio. Explain why range changes with height while the descent rate changes with speed in this intentionally isolated model.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.