NASA Logo - Web Link to

+ Text Only Site
+ Non-Flash Version
+ Contact Glenn

Computer drawing of kids page link
This page is intended for college, high school, or middle school students. For younger students, a simpler explanation of the information on this page is available on the Kid's Page.

NASA Meatball Image

Aircraft Roll Motion


Computer animation of an airliner in which the wings
 moves up and down in response to changing the aileron angle.

In flight, any aircraft will rotate about its center of gravity, a point which is the average location of the mass of the aircraft. We can define a three dimensional coordinate system through the center of gravity with each axis of this coordinate system perpendicular to the other two axes. We can then define the orientation of the aircraft by the amount of rotation of the parts of the aircraft along these principal axes. The roll axis lies along the aircraft centerline. A roll motion is an up and down movement of the wings of the aircraft as shown in the animation.

The rolling motion is being caused by the deflection of the ailerons of this aircraft. The aileron is a hinged section at the rear of each wing. The ailerons work in opposition; when the right aileron goes up, the left aileron goes down.

As described on the shape effects slide, changing the angle of deflection at the rear of an airfoil will change the amount of lift generated by the foil. With greater downward deflection, the lift will increase in the upward direction; with greater upward deflection, the lift will decrease in the upward direction. Since the ailerons work in pairs, the lift on one wing increases as the lift on the opposite wing decreases. Because the forces are not equal, there is a net twist, or torque about the center of gravity and the aircraft rotates about the roll axis. The pilot can use this ability to bank the aircraft which causes the airplane to turn.

On this page we have demonstrated an aircraft roll induced by movement of the ailerons, but there are other ways to produce a rolling motion on an aircraft. The Wright brothers used a method called wing warping. Their wings were wired together in such a way that the outer panels of each wing could be twisted relative to the inner panel. The twisting changed the local angle of attack of sections of the wing which changed the lift being generated by that section. Unequal forces on the wings caused the aircraft to roll. Many modern airliners use a spoiler to roll the aircraft. A spoiler is a plate that is raised between the leading and trailing edges of the wing. The spoiler effectively changes the shape of the airfoil, disrupts the flow over the wing, and causes a section of the wing to decrease its lift. This produces an unbalanced force with the other wing, which causes the roll. Airliners use spoilers because spoilers can react more quickly than ailerons and require less force to activate, but they always decrease the total amount of lift for the aircraft. It's an interesting trade! You can tell whether an airliner is using spoilers or ailerons by noticing where the moving part is located. At the trailing edge, it's an aileron; between the leading and trailing edges, it's a spoiler. (Now you can dazzle the person sitting next to you on the plane!)

You can view a short movie of "Orville and Wilbur Wright" explaining how wing warping was used to roll their aircraft. The movie file can be saved to your computer and viewed as a Podcast on your podcast player.

Here is a still slide of the animation:

Computer drawing of an airliner showing the motion.
 about the roll axis.

Button to Display Grade 6-8 Activity Button to Display Grade 6-8 Activity Button to Display Grade 6-8 Activity Button to Display Grade 9-12 Activity Button to Display Grade 11-12 Activity
Guided Tours
  • Button to Display Previous Page Aircraft Roll Motion: Button to Display Next Page
  • Button to Display Previous Page Control Surfaces: Button to Display Next Page
  • Button to Display Previous Page Banking Turn: Button to Display Next Page
  • Button to Display Previous Page Ailerons: Button to Display Next Page
  • Button to Display Previous Page Spoilers: Button to Display Next Page

Navigation ..

Button to Display Aerodynamics Index Button to Display Wright Brothers Index
Beginner's Guide Home Page


     First Gov Image

+ Inspector General Hotline
+ Equal Employment Opportunity Data Posted Pursuant to the No Fear Act
+ Budgets, Strategic Plans and Accountability Reports
+ Freedom of Information Act
+ The President's Management Agenda
+ NASA Privacy Statement, Disclaimer,
and Accessibility Certification


NASA Logo   
Editor: Nancy Hall
NASA Official: Nancy Hall
Last Updated: May 05 2015

+ Contact Glenn