General Principles - Climb — Page 166, Lesson 198

Let’s start with the climb phase itself. In performance terms, the climb is the stage of flight that runs from the end of the take-off phase to the beginning of the en route phase. So it’s the segment where you’ve just left the runway environment and you’re heading up toward your cruising altitude. And when we analyse the climb, we look at it in two distinct ways: the angle of climb and the rate of climb. Those are two different questions — one is about how steep the path is, the other is about how fast you gain height. We’ll deal with angle of climb first. To understand angle of climb, I want you to picture the aircraft in unaccelerated level flight first. Unaccelerated means the speed is steady — not increasing, not decreasing. In that condition, the forward acting force, Thrust, exactly balances the rearward acting force, Drag. Because those two are equal, the aircraft maintains a steady speed. So the question becomes: how much Thrust is required for unaccelerated level flight? The answer is simply the same as the aerodynamic Drag. In fact, there’s a frequently used alternative term for Drag — we call it “Thrust Required.” That name makes sense, because in level unaccelerated flight, the thrust you need is precisely the drag you’re overcoming. Now, here’s where the climb changes things. If we place the aircraft in a climb attitude, something new happens. A component of the aeroplane’s Weight acts backwards along the flight path, and that backward component is added to Drag. So now you have two rearward acting forces: the Drag itself, plus this backward component of Weight. The forward force is still Thrust. And here’s the key relationship: the larger the angle of climb, the larger that backward component of Weight becomes. Steeper climb, bigger backward pull from weight. In both the shallow and the steeper climb illustrations, the same thing is apparent — the sum of the two rearward acting forces is greater than the forward acting force. Thrust alone is no longer enough to balance everything. And if that situation were left unchanged, the aircraft would decelerate. That’s the crucial point: without some adjustment, putting the aircraft into a climb attitude with the same thrust would cause it to slow down, because the rearward forces now exceed the forward force. So the whole story of climb performance starts from this balance of forces — Thrust forward, Drag and the backward component of Weight rearward. And that backward weight component is what makes climbing fundamentally different from level flight. Let’s look at the figures to see this force balance visually.