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The Aerodynamics Of A Turn

Erik Brouwer

Have you ever wondered why you need to add back pressure and power when you start a turn? Learning how to turn an airplane is one of the first things you'll do during flight training, but many pilots don't know the aerodynamic backstory that makes turning so interesting. Here's what you need to know:

The Forces In A Turn

All forces can be divided into vertical and horizontal components. In straight-and-level, non-turning flight, all of your lift is acting vertically, and no lift is acting horizontally. But as you bank your airplane and begin a turn, a component of lift produced by the wing acts horizontally, which is why your airplane turns.

Why Do You Need To Add Back Pressure To Maintain Altitude?

If you roll into a turn using only ailerons, your vertical lift decreases and your horizontal lift increases. The airplane tends to descend during aileron-only turns.

To keep your vertical lift the same (so you don't descend), you need to increase total lift by increasing your angle of attack (AOA). So how do you do that? Simple: you apply back pressure on your elevator. As you apply back pressure, you're actually raising the nose and getting a higher angle of attack during a turn.

You're "loading the wing" as you increase back pressure to compensate for reduced vertical lift. There is a downside to increased loading though: your stall speed increases. As you increase your wing's angle-of-attack with back pressure, you start approaching your airplane's critical angle-of-attack and risk entering an accelerated stall. This is exactly why you were taught that your stall speed increases during a steep turn, for instance.

And it's not just level turns that increase your wing's angle-of-attack. In a descending base-to-final turn, you have a reasonable amount of back pressure to control your descent rate. Between your high AOA and low speed, it's a recipe for a stall-spin accident.

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Putting It All Together

In simple terms, your aircraft turns by redirecting the lift created by your wings. And to maintain altitude in a turn, you need to create more total lift, so that your vertical component of lift opposes your aircraft's weight. Easy enough, right?

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and commercial pilot for Mokulele Airlines. He holds multi-engine and instrument ratings, and is an aviation student at the University of North Dakota. He's the author of the articles, quizzes and lists you love to read every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures at http://www.swaynemartin.com.

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