What is the Purpose of Spoilers on a Plane?

Aircraft · 3 min read · Sep 29, 2021
Spoilers Airplane

You have probably seen spoilers if you have flown in the window seat next to the airplane’s wing. These are devices, sometimes called control surfaces, placed on the wing’s top surface in the form of panels or plates that can pivot up and down when deployed or stowed.

Lift spoiler

The name lift spoiler comes from the main action generated by a spoiler. In general, these devices help the pilot “spoil” the lift, which means they help reduce lift from the wing. This is done at the same time the spoilers increase drag in a controlled way.

A view of spoilers of an airplane through the aircraft window.
Image Source: https://www.monolib.net/en/dictionary/spoiler/

Spoilers are used for different purposes depending on the flight stage of the airplane. For the same reason, they are divided into two categories: flight spoilers and ground spoilers.

Let’s see what the purpose of each category is.

Flight spoilers

As the name implies, these are the wing spoilers that help both airplane and glider pilots while the aircraft is in flight. But why would a pilot want to increase drag and decrease lift during a flight?

Reducing altitude

When an aircraft is trying to descend, like in the case of approaching the runway for landing, it is difficult to deal with the bit of drag produced by airliners by design. This means that they naturally increase speed in such situations, and the wings generate more lift. As a result, two things that go against the main objective: control speed and descend faster.

So, the additional drag coming from the spoiler when it is extended upward will help control the speed while performing a much steeper descent.

Control roll

When rolling or banking, ailerons are used to generate more lift on the wing opposite to the side of the roll. For example, the aileron in the left wing will be used to roll right, with the extra lift making the wing go up while the right-wing moves down.

However, generating lift with the aileron alone could be dangerous because of the extreme force involved. That amount of pressure could make the wings twist, and the aircraft could roll in the opposite direction.

To have more roll control, spoilers are used to reduce the amount of force generated by the ailerons under high-speed airflow conditions. Moreover, using spoilers when rolling makes the aircraft to stay coordinated by generating form drag on the inboard wing. This reduces the problem known as adverse yaw, a natural tendency in any aircraft that is rolling.

Flight spoilers on an aircraft wing during flight in a cloudy sky.
Image source: https://teamarcis2018.wordpress.com/category/drag/page/2/

Ground spoilers

It can be taken from the name that these are the spoilers used when the aircraft is on the ground. It is essential to highlight that flight spoilers are also used as ground spoilers most of the time. The fact is that, from all the wing spoilers, there is a section that is only used on the ground for increasing drag.

The primary purpose for increasing drag while on the ground is to improve the braking effectiveness of the wheels since that effectiveness is affected by the lift of the wings. These spoilers help reduce that lift by putting the full weight of the aircraft on the wheels.

How are ground spoilers deployed?

Usually, a pilot can be entirely focused on landing because these spoilers tend to be automatic. As soon as the airliners touch the land, they deploy ground spoilers to assist the pilot with the speed reduction until reaching taxi speed. But this is not always the case. Sometimes the pilot may be required to do it manually.

Ground spoilers or air brakes

Many times, ground spoilers are confused with air brakes or speed brakes. However, they are two different devices. Speed brakes are usually smaller and less efficient than a spoiler, so they are typically used in smaller aircraft or as a complementary device on some airliners. An example is the BAE 146.

Landing gear: How it is affected by ground spoilers

When the wheels hit down during landing, there is still some lift. Therefore, not much weight is put on the landing gear at that moment. But, as mentioned above, all the aircraft’s weight is put on the wheels when extending spoilers. This is the reason why landing gears are usually tested flight after flight in order to ensure safety.

Main landing gear of a Boeing 747-8F prototype in central view.
Image source: Olivier Cleynen

Some conclusions

It is safe to say that no modern aircraft could fly without a spoiler on its wings. The benefits provided for flight and ground control are critical.

Also, while flight idle is an option to control speed when a drop in altitude is necessary, this is not possible when flying in icing conditions. These conditions require the airplane to keep the engines generating what is known as engine bleed air to maintain the anti-icing surfaces at the right temperature.

In simple words, these and other high drag devices make the life of a pilot a lot easier.

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Jet pilot @NASA

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