Definition
The set of aerodynamic and mechanical forces — lift, weight, thrust, and drag — acting on an aircraft as it transitions from level flight into a climb and during steady-state climb. When climb is initiated, the wing's angle of attack momentarily increases to produce excess lift, but once a steady climb is established, lift is again roughly equal to weight. The defining feature of a steady climb is that thrust must exceed drag by an amount sufficient to support a component of the aircraft's weight that now acts rearward along the flightpath. Rate of climb therefore depends on excess thrust (or excess power) available beyond what is needed to maintain level flight at that airspeed.
Plain English
When an aircraft climbs, the same four forces are at work as in level flight, but they balance differently. Climbing is not done by lift pulling the airplane up — it is done by the engine producing more thrust than is needed to overcome drag. That extra thrust is what carries the aircraft uphill. In a steady climb, lift and weight are still about equal; it is the surplus thrust that buys the altitude.
Context Anchor
Seen when studying climb performance, pitch-and-power control, and why an airplane climbs more slowly when it is heavy, hot, or high.
Derivation
Force comes from the Latin word fortis, meaning strong. In aviation, a force is a push or pull on the airplane. That helps here because a climb is explained by looking at which pushes and pulls are acting on the airplane and in what direction.
Why Pilots Care
Correct understanding prevents over- or under-powering the climb, maintains airspeed margins, and explains why climb rate decreases with altitude or weight.
Analogy
It is like riding a bicycle uphill. You are not only pushing through air; you are also working against gravity pulling you back down the hill.
Grounding Statement
Picture the airplane flying up a sloped path: some of its weight pulls straight down, and part of that pull acts backward along the slope.
Intuition Check
Common wrong assumption: in a climb, lift must be greater than weight. Better idea: in a steady climb, extra thrust—not extra lift—is what overcomes the backward pull caused by weight along the climb path.
Example Sentence 1
On a hot day at a high-elevation airport, the engine produces less power, so the forces in climbs leave little excess thrust and the rate of climb suffers.
Example Sentence 2
Because lift only has to oppose the perpendicular part of weight, the airplane can climb at a lower angle of attack than many pilots expect.