
Dutch roll is an
aircraft
An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...
motion consisting of an out-of-
phase combination of "tail-wagging" (yaw) and rocking from side to side (roll). This
yaw-roll coupling is one of the basic
flight dynamic modes (others include
phugoid,
short period, and
spiral divergence). This mode resembles the motion of a skier who is simultaneously yawing and rolling from side to side. This motion is normally well damped in most light aircraft, though some aircraft with well-damped Dutch roll modes can experience a degradation in
damping as
airspeed
In aviation, airspeed is the speed of an aircraft relative to the air it is flying through (which itself is usually moving relative to the ground due to wind). In contrast, the ground speed is the speed of an aircraft with respect to the sur ...
decreases and
altitude
Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometr ...
increases. Dutch roll stability can be artificially increased by the installation of a
yaw damper. Wings placed well above the center of gravity,
swept wings, and
dihedral wings tend to increase the roll restoring force, and therefore increase the Dutch roll tendencies; this is why high-winged aircraft often are slightly
anhedral, and transport-category swept-wing aircraft are equipped with yaw dampers. A similar phenomenon can happen in a trailer pulled by a car.
Stability
In aircraft design, Dutch roll results from relatively weaker positive
directional stability as opposed to positive
lateral stability. When an aircraft rolls around the longitudinal axis, a
sideslip is introduced into the
relative wind
In aeronautics, the relative wind is the direction of movement of the atmosphere relative to an aircraft or an airfoil. It is opposite to the direction of movement of the aircraft or airfoil relative to the atmosphere. Close to any point on the su ...
in the direction of the rolling motion (due to the lateral component of lift when the wings are not level). Strong lateral stability (due to the more-direct airflow past the down wing, which has been pivoted forward by the slip) begins to restore the aircraft to level flight. At the same time, somewhat weaker directional stability (due both to greater drag from the wing which is now generating greater lift, and by aerodynamic force on the vertical fin due to the yaw) attempts to correct the sideslip by aligning the aircraft with the perceived relative wind. Since directional stability is weaker than lateral stability for the particular aircraft, the restoring yaw motion lags significantly behind the restoring roll motion. The aircraft passes through level flight as the yawing motion is continuing in the direction of the original roll. At that point, the sideslip is introduced in the opposite direction and the process is reversed.
There is a trade-off between directional and lateral stability. Greater lateral stability leads to greater spiral stability and lower oscillatory stability. Greater directional stability leads to spiral instability but greater oscillatory stability.
Mechanism
The most common mechanism of Dutch roll occurrence is a yawing motion which can be caused by a number of factors. As a swept-wing aircraft yaws (to the right, for instance), the left wing becomes less-swept than the right wing in reference to the relative wind. Because of this, the left wing develops more lift than the right wing causing the aircraft to roll to the right. This motion continues until the yaw angle of the aircraft reaches the point where the vertical stabilizer effectively becomes a wind vane and reverses the yawing motion. As the aircraft yaws back to the left, the right wing then becomes less swept than the left resulting in the right wing developing more lift than the left. The aircraft then rolls to the left as the yaw angle again reaches the point where the aircraft wind-vanes back the other direction and the whole process repeats itself. The average duration of a Dutch roll half-cycle is 2 to 3 seconds.
The Dutch roll mode can be excited by any use of
aileron
An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement aroun ...
or
rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, airship, or other vehicle that moves through a fluid medium (usually air or water). On an airplane, the rudder is used primarily to counter adverse yaw ...
, but for flight test purposes it is usually excited with a rudder singlet (a short sharp motion of the rudder to a specified angle, and then back to the centered position) or doublet (a pair of such motions in opposite directions). Some larger aircraft are better excited with aileron inputs. Periods can range from a few seconds for
light aircraft
A light aircraft is an aircraft that has a Maximum Takeoff Weight, maximum gross takeoff weight of or less.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 308. Aviation Supplies & Academics, 1997.
Light aircraft are use ...
to a minute or more for
airliners.
Tex Johnston describes the Dutch roll as "...an inherent characteristic of swept-wing aircraft. It starts with a yaw. In a 35-degree swept-wing airplane, a yaw is accompanied by a simultaneous roll in the direction of yaw. The roll is caused by changing lift factors as the airflow path over the wing changes. For example, in a left yaw the left wing slews toward the rear so that airflow is displaced spanwise from its normal front-to-rear path over the airfoil section. That reduces lift. Simultaneously, the advancing right wing gets more chordwise flow, and so its lift is increased. In combination the two conditions create a left roll. Similarly, a yaw to the right results in a roll to the right. An oscillation is set up."
Rolling on a heading
Dutch roll is also the name (considered by professionals to be a misnomer) given to a coordination
maneuver generally taught to student
pilots to improve their "stick-and-rudder" technique. The aircraft is alternately rolled as much as 60 degrees left and right while
rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, airship, or other vehicle that moves through a fluid medium (usually air or water). On an airplane, the rudder is used primarily to counter adverse yaw ...
is applied to keep the nose of the aircraft pointed at a fixed point. More correctly, this is a rudder coordination practice exercise, to teach a student pilot how to correct for the effect known as
adverse aileron yaw during roll inputs.
This coordination technique is better referred to as "rolling on a heading", wherein the aircraft is rolled in such a way as to maintain an accurate heading without the nose moving from side-to-side (or yawing). The yaw motion is induced through the use of ailerons alone due to aileron drag, wherein the lifting wing (aileron down) is doing more work than the descending wing (aileron up) and therefore creates more drag, forcing the lifting wing back, yawing the aircraft toward it. This yawing effect produced by rolling motion is known as adverse yaw. This has to be countered precisely by application of rudder ''in the same direction'' as the aileron control (left stick, left rudder – right stick, right rudder). This is known as synchronised controls when done properly, and is difficult to learn and apply well. The correct amount of rudder to apply with aileron is different for each aircraft.
Name
The origin of the name Dutch roll is uncertain. However, it is likely that this term, describing a lateral asymmetric motion of an airplane, was borrowed from a reference to similar-appearing motion in
ice skating. In 1916, aeronautical engineer
Jerome C. Hunsaker published: "Dutch roll – the third element in the
ateralmotion
f an airplaneis a yawing to the right and left, combined with rolling. The motion is oscillatory of period for 7 to 12 seconds, which may or may not be damped. The analogy to 'Dutch Roll' or 'Outer Edge' in ice skating is obvious."
In 1916, Dutch Roll was the term used for skating repetitively to right and left (by analogy to the motion described for the aircraft) on the outer edge of one's skates. By 1916, the term had been imported from skating to aeronautical engineering, perhaps by Hunsaker himself. 1916 was only five years after G. H. Bryan did the first mathematical analysis of lateral motion of aircraft in 1911.
Notable incidents
* On October 19, 1959, on a
Boeing 707
The Boeing 707 is an early American long-range Narrow-body aircraft, narrow-body airliner, the first jetliner developed and produced by Boeing Commercial Airplanes.
Developed from the Boeing 367-80 prototype, the initial first flew on Decembe ...
on customer-acceptance flight, the yaw damper was turned off to familiarize the new pilots with flying techniques. A trainee pilot's actions violently exacerbated the Dutch roll motion and caused three of the aircraft's four engines to be torn from its wings. The plane, a brand new 707-227, ''N7071'', destined for
Braniff
Braniff Airways, Inc., operated as Braniff International Airways from 1948 until 1965, and then Braniff International from 1965 until the cessation of air operations, was an American airline that operated from 1928 until 1982 and continues to ...
,
crash-landed on a river bed north of Seattle at
Arlington, Washington, killing four of the eight occupants.
* On August 12, 1985,
Japan Air Lines Flight 123, a
Boeing 747SR, exhibited a Dutch roll in combination with
phugoid cycles after losing all hydraulics following the loss of its vertical stabiliser due to an improperly-repaired rear pressure bulkhead rupturing from
metal fatigue
In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striation (fatigue), striati ...
. It would ultimately crash in the deadliest single-aircraft accident in history.
* On March 6, 2005,
Air Transat Flight 961, an
Airbus A310
The Airbus A310 is a wide-body aircraft, Aircraft design process, designed and manufactured by Airbus Industrie GIE, then a consortium of European aerospace manufacturers.
Airbus had identified a demand for an aircraft smaller than the Airbus ...
, was involved in a Dutch roll incident following structural failure of the rudder at cruising altitude after departure from
Juan Gualberto Gomez Airport,
Varadero,
Cuba
Cuba, officially the Republic of Cuba, is an island country, comprising the island of Cuba (largest island), Isla de la Juventud, and List of islands of Cuba, 4,195 islands, islets and cays surrounding the main island. It is located where the ...
. The aircraft returned to the airport with serious structural damage and one flight attendant slightly injured.
* On May 3, 2013, a
McConnell AFB, KS (USAF)
KC-135R, ''63-8877'', flown by a
Fairchild AFB, Washington aircrew, broke up in flight about eleven minutes after taking off from
Manas Air base in
Kyrgyzstan
Kyrgyzstan, officially the Kyrgyz Republic, is a landlocked country in Central Asia lying in the Tian Shan and Pamir Mountains, Pamir mountain ranges. Bishkek is the Capital city, capital and List of cities in Kyrgyzstan, largest city. Kyrgyz ...
, killing all three crew members. It was determined that a rudder power control unit malfunction led to a Dutch roll oscillatory instability. Not recognizing the Dutch roll, the crew used the rudder to stay on course, which exacerbated the instability, leading to an unrecoverable flight condition. The over-stressed tail section detached and the rest of the aircraft broke apart soon after. The aircraft was at cruise altitude about 200 km west of
Bishkek before it crashed in a mountainous area near the village of Chorgolu, close to the border between Kyrgyzstan and
Kazakhstan
Kazakhstan, officially the Republic of Kazakhstan, is a landlocked country primarily in Central Asia, with a European Kazakhstan, small portion in Eastern Europe. It borders Russia to the Kazakhstan–Russia border, north and west, China to th ...
.
* On October 30, 2015 a
Leonardo-Finmeccanica-Helicopters Division (formerly
AgustaWestland)
AW609 prototype crashed in Italy killing its two pilots. The Italian
ANSV established that Dutch roll during a high-speed test was the probable cause.
* On May 25, 2024,
Southwest
The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A '' compass rose'' is primarily composed of four cardinal directions—north, east, south, and west— ...
Flight 746, a
Boeing 737 MAX 8, registration N8825Q, experienced a Dutch roll during a flight from
Phoenix Sky Harbor International Airport to
Oakland International Airport. Post-flight inspection revealed damage to the standby power control unit (PCU). There were no injuries among the 175 passengers and six crew members.
See also
*
*
*
Dutch angle, a camera technique that places things in frame at an angle
References
External links
Articles
*
What Is Dutch Roll, And How Do You Prevent It?h2>
Videos
* A Dutch roll during a test flight of a
Tupolev
Tupolev ( rus, Туполев, , ˈtupəlʲɪf), officially United Aircraft Company Tupolev - Public Joint Stock Company, is a Russian aerospace and Arms industry, defence company headquartered in Basmanny District, Moscow.
UAC Tupolev is succes ...
airliner. Anecdotal information points to yaw damper malfunction as the cause. Aircraft landed safely.
Dutch Roll animationAutoflight #12 Yaw Damper
{{DEFAULTSORT:Dutch Roll
Aircraft aerodynamics