The aerodynamics of a turn: How an airplane turns

I take your point, but the power aspect seems like it’s clearly because lift is reduced when you can’t the wings and you need to be increase power if you want to avoid losing altitude.

It could be an oversight because the intended audience is pilots. I think the answer might be that nose up increases the chance of a stall, so more power is added to increase airspeed and therefore lift. I'm not a pilot though, I found this article when trying to understand how simply tilting the wings causes a turn.

> lede asks "why you need to add back pressure and power" and then only explains back pressure

It's a good question. From 5-22 of the FAA's Pilot's Handbook of Aeronautical Knowledge:

"An aircraft is not steered like a boat or an automobile. In order for an aircraft to turn, it must be banked. If it is not banked, there is no force available to cause it to deviate from a straight flight path. Conversely, when an aircraft is banked, it turns provided it is not slipping to the inside of the turn. Good directional control is based on the fact that the aircraft attempts to turn whenever it is banked. Pilots should keep this fact in mind when attempting to hold the aircraft in straight-and-level flight.

Merely banking the aircraft into a turn produces no change in the total amount of lift developed. Since the lift during the bank is divided into vertical and horizontal components, the amount of lift opposing gravity and supporting the aircraft’s weight is reduced. Consequently, the aircraft loses altitude unless additional lift is created. This is done by increasing the AOA until the vertical component of lift is again equal to the weight. Since the vertical component of lift decreases as the bank angle increases, the AOA must be progressively increased to produce sufficient vertical lift to support the aircraft’s weight. An important fact for pilots to remember when making constant altitude turns is that the vertical component of lift must be equal to the weight to maintain altitude.

At a given airspeed, the rate at which an aircraft turns depends upon the magnitude of the horizontal component of lift. It is found that the horizontal component of lift is proportional to the angle of bank—that is, it increases or decreases respectively as the angle of bank increases or decreases. As the angle of bank is increased, the horizontal component of lift increases, thereby increasing the rate of turn (ROT). Consequently, at any given airspeed, the ROT can be controlled by adjusting the angle of bank.

To provide a vertical component of lift sufficient to hold altitude in a level turn, an increase in the AOA is required. Since the drag of the airfoil is directly proportional to its AOA, induced drag increases as the lift is increased. This, in turn, causes a loss of airspeed in proportion to the angle of bank. A small angle of bank results in a small reduction in airspeed while a large angle of bank results in a large reduction in airspeed. Additional thrust (power) must be applied to prevent a reduction in airspeed in level turns. The required amount of additional thrust is proportional to the angle of bank."

The article just omitted the last paragraph.

(You may notice the outside/downward aileron causing the bank by increasing lift also increasing drag, thereby causing the plane to yaw outward [2].)

[1] https://www.faa.gov/sites/faa.gov/files/07_phak_ch5_0.pdf Page 5-22

[2] https://en.wikipedia.org/wiki/Adverse_yaw

You don’t always have to add power, only if you don’t want to slow down during the turn, or if you don’t want to change your vertical speed. All other things being equal, making a turn will create additional induced drag, which will either change your rate of acceleration (slowing down, or reducing your forward acceleration if you were accelerating) or the change in drag will cause you to change your vertical speed, trading potential energy for forward impulse. If you want to maintain speed and your rate of climb or decent (including neither climbing nor descending) you will have to add power.