Watch the video above to get an idea about the relationship between pitch and power, and also under what parameters the airplane flies at most efficiently.
Of course, big powerful airplanes are cool, but in reality, most of the training aircraft we fly have relatively little power with max horsepower ratings somewhere between 100-180hp. Since this isn’t enough power to make the airplane climb vertically like a fighter jet, we need to think about how best to manage the available power we have at any given time.
Think about the power curve this way:
If you have 100hp engine, and cruising along at full throttle you are going 100mph, then you have no available power left over because it is taking ALL of your power just to go 100mph in level flight. Now if it only takes 80% throttle (or power setting) to go 80mph in level flight, you still have 20% power leftover that you could get out of the engine by pushing the throttle forward more. This extra 20% could then be used to either go faster or if you maintain the same airspeed, it will make you climb.
This basic relationship is why you will always hear your CFI say; power controls altitude, pitch controls airspeed. Meaning, adding or reducing power affects your rate of climb or descent, while pitching the nose up or down (pulling the yoke back or pushing it forward) will control the airspeed. You cannot simply “pull back” or “pull up” and make the airplane go up, without sacrificing airspeed. To compensate for the loss of airspeed, more power is needed.
Remember: every airplane has a certain speed, which is most efficient to keep it flying. Any faster than that specific speed will take more power, and any slower than that speed will also take more power to maintain level flight.