Aerodynamics / Flight Controls

More than likely, your airplane uses Mechanical Flight Controls.  These are basic connections of rods, cables, and pulleys that are connected to the control stick or yoke.

More complex aircraft may require a hydro-mechanical / hydraulically actuated controls.  Modern airliners and military aircraft use computer-assisted fly-by-wire designs.

At its simplest, an aircraft has ailerons for roll, elevators for pitch, and rudder for yaw.  By altering the angle at which these control surfaces hits the air, you are changing the airflow.  This causes the resulting change in rotation about the axis.

Ailerons control roll about the longitudinal axis.  Ailerons oppose each other.  For example, if you turn to the right, the right aileron rises above the wing and the left aileron dips below the wing.  The downward aileron increases camber of the wing and thus increases lift - raising the left wing above the right wing and causing the plane to roll right.

Keep in mind that turning the controls to the right is not all that is required to turn right.  Back pressure on the elevators is needed to aid in lift and carry the airplane about the turn (horizontal component of lift)




Adverse Yaw results when the raised wing is creating higher drag than the lowered wing.  Thus, while the plane is rolling right, the nose is yawing left.

It is more pronounced at low speeds.  Rudder may be used to combat adverse yaw by use of coordination.

Differential Ailerons - combat adverse yaw by having one aileron raised a greater distance than the lowered aileron.  Thus there is greater drag on the descending wing combating the tendency to yaw in the opposite direction.

Frise-Type ailerons - pivot on an offset hinge.  Thus, when the aileron moves up, it also has a portion that is below the wing creating drag.  This helps equalize the drag on the aileron on the opposite wing that is deflected down.  This design also has a slot which allows airflow to accelerate and maintain positive control at high angles of attack.

Some aircraft have an interconnected Aileron & Rudder system.  When a turn is initiated, the rudder also deflects to coordinate the turn and avoid adverse yaw.  The system may be overridden if a slip is desired.

Flaperons are a combination of ailerons and flaps.  These are also often separated slightly from the wing to allow improved control at high angles of attack.

Elevator controls pitch about the lateral axis.  Remember that the horizontal stabilizer is in essence an upside-down wing, so up elevator results in a tail down force, which pushes the nose up.

A T-Tail configuration is used on some aircraft and have pros and cons.  Because the elevators are out of the slipstream, flight is smoother and with less vibrations.  For the same reason, elevator effectiveness is not as strong at low speeds due to the reduced airflow from the engines over the elevators.  It also reduces warning buffets leading up to a stall.

CG plays a major role in this as well.  Aft CGs make it difficult to get the nose down in all tail configurations.  A forward CG makes it difficult to flare properly during landing.

Stabilators combing the horizontal stabilizer with an elevator.  The leading edge moves when control inputs are altered.

An Antiservo Tab is attached to the trailing edge of the stabilator to decrease sensitivity.  They deflect in the same direction as the stabilator thereby increasing the force required to move it.  It may also have a balance weight

Canards are essentially horizontal stabilizers located in front of the main wings.  Rather than force the tail down to cause a pitch up like an elevator, canards also generate lift.  In theory, this is more efficient because it is creating less drag.  However it can also create more turbulence over the main wings, which would result in greater induced drag.

The Rudder controls movement about the vertical axis.  In a sense, the rudder generates sideways lift.  In propeller aircraft, slipstream increases effectiveness of the rudder.

V-Tail design uses two slanted tail surfaces to function as elevator and rudder.   The control surfaces on these, called ruddervators.  They are linked so that the control wheel moves both surfaces.  Rudder pedals may also be used for directional control.  Dutch Roll tendency is increased with this design.

Trim Controls are designed to alleviate pressure on the controls - making the pilots job easier.

Trim Tabs are the most common and involve a tab attached to the trailing edge of the elevator.  When nose up trim is set with the trim wheel, the trim tab deflects down - forcing up elevator and subsequently a lowering of the tail (ie raising of nose).

Balance Tabs are similar to trim tabs.  The main difference is that the trim tabs are linked to the main control surface rod.  If a deflection is initiated by the main control surface, the tab automatically moves in the opposite direction.

Antiservo Tabs move in the same direction as the trailing edge of the stabilator.  Remember that not only are they used to decrease sensitivity, they can be adjusted to trim the aircraft.

Adjustable Stabilizer designs are found on larger aircraft and pivot about its rear spar by using a trim cable or trim motor.


Flaps are often defined as high-lift devices (and subsequently high drag).  They are used to conduct steeper approaches without increasing airspeed.  There are 4 main types:  Plain, Split, Slotted, and Fowler.

Plain flaps are the simplest.  It simply adjusts camber of the wing.

Split flaps deflect from the lower surface, but drag is created as well because turbulent air is produced behind the airfoil.

Slotted Flaps have a greater coefficient of lift because there is a duct that enables airflow through the slot to the upper surface.  This delays airflow separation - producing lots of lift with less drag

Fowler Flaps are a variation on the slotted flap.  It changes wing camber and wing surface area.  It slides backward on tracks.

Slots are found on the leading edge.

Fixed Slots direct airflow to the upper wing surface and delay airflow separation to higher AOA.  Wing camber unchanged.

Movable slats contain segments that move on tracks.  At low AOA, these are held flush by pressure against the leading edge.  As AOA increases, high pressure area moves aft allowing slot to move forward.

Leading edge Flaps increase lift and camber.

Leading edge Cuffs are fixed aerodynamic devices.  This allows airflow to attach to the upper surface of the wing easier - decreasing stall speed and enabling higher AOA.

Spoilers are high drag devices, or in a sense speed brakes.  On gliders they can be used to roll.  The possibility of adverse yaw is reduced because the spoiler decreases lift and increases drag ensuring that the plane rolls and yaws in the direction of the intended turn.