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How Dihedral Keeps Your Wings Level

RobBixbyPhotography

Dihedral helps you keep your wings level, but how exactly does it happen? It may not be what you think. Let's take a look.

What Is Dihedral?

First off, what the heck is dihedral? Dihedral is the upward angle of an aircraft's wings. Check out the picture of the Boeing 777 below:

Jonathan Palombo Photography

See how the wings angle upward? That dihedral makes the 777 more laterally stable, or in other words, more stable when it rolls left or right. And it's not just large jets that have dihedral like this. It's found on almost every aircraft out there.

A Lack Of Stability

So why do aircraft need dihedral in the first place? If your aircraft didn't have it, you'd spend a lot of time keeping your wings level. Here's why:

When you bank an airplane, the lift vector tilts with it. And when that happens, your airplane starts slipping in the same direction, in this case, to the right.

The problem is, if you have a completely straight winged aircraft, there's no force that will bring the airplane back to wings-level flight without you intervening. While that may be good for an aerobatic aircraft or fighter jet, it's not a very desirable characteristic for general aviation aircraft or airliners.

How Dihedral Fixes The Problem

When you add dihedral, you add lateral stability when your aircraft rolls left or right. Here's how it works: let's say you're flying along and a wind gust hits your plane, rolling it to the right. When your wings have dihedral, two things happen:

1) First, your airplane starts slipping to the right, which means the relative wind is no longer approaching directly head-on to the aircraft, and instead is approaching slightly from the right. This means that there is a component of the relative wind that is acting inboard against the right wing.

2) Second, because the relative wind has the inboard component, and because the wings are tilted up slightly, a portion of the the relative wind strikes the underside of the low wing, pushing it back up toward wings level. What's really happening here is the low wing is flying at a higher AOA, and producing more lift.

The more dihedral an aircraft has, the more pronounced the effect becomes. But for most aircraft, they only have a few degrees of dihedral, which is just enough to keep the wings level during small disturbances, like turbulence, or bumping the flight controls in the cockpit.

Dihedral Comes At A Cost

Dihedral isn't always good, and like almost every design factor, it comes with a cost. In this case, there are two costs: increased drag, and decreased roll rate.

Wings with dihedral don't produce lift vertically. Instead, there's a vertical component, and a horizontal component. So when you're flying straight and level, your lift is not 100% vertical.

And, the same dihedral effect that keeps your wings level in turbulence, works against you when you try to roll right or left. When you put an aircraft into a bank, the dihedral effect constantly tries to return your wings to level. With enough dihedral, your roll rate is dramatically decreased.

Putting It All Together

Dihedral is the upward angle of an aircraft's wings, which increases lateral stability in a bank by causing the lower wing to fly at a higher angle of attack than the higher wing. What it really means is that you can fly more hands off, even in turbulence. And a more hands off, stable airplane, is good for almost anybody, especially when you're trying to manage multiple things in the cockpit.

Colin Cutler

Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at colin@boldmethod.com.

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