Climb Gradient
Climb angle (as a fraction) equals excess thrust divided by weight.
Formula
Variables
Example
A 2000 N thrust surplus on a 20 000 N aircraft gives a 10% climb gradient.
How it works
Climb gradient tells you how steeply an aircraft can gain altitude for a given forward force balance. It comes from resolving the aircraft’s weight into components along and perpendicular to the flight path: if thrust exceeds drag, the leftover force can support an upward component of motion, and dividing that excess thrust by weight gives the climb angle as a fraction for small-angle flight. In other words, the more thrust left over after overcoming drag, or the lighter the aircraft, the steeper the climb can be.
When to use it
Use this when estimating aircraft performance in steady climb, especially for takeoff and obstacle-clearance calculations. It is also useful in comparing climb capability at different weights, altitudes, or engine thrust settings.
Worked example, step by step
Given: Thrust, T = 48,000 N Drag, D = 36,000 N Weight, W = 240,000 N Step 1: Find excess thrust T - D = 48,000 - 36,000 = 12,000 N Step 2: Divide by weight γ = (T - D) / W = 12,000 / 240,000 = 0.05 Step 3: Convert to percent if desired 0.05 × 100 = 5% Final answer: Climb gradient = 0.05, or 5%
Common mistakes to avoid
- Using thrust alone instead of excess thrust (T - D)
- Forgetting that climb gradient is dimensionless and can be written as a fraction or percent
- Mixing up weight with mass, or using the wrong units for W
Did You Know?
Climb gradient — height gained per distance — must clear obstacles and terrain after takeoff.
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