Control reversal: Difference between revisions

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{{Short description|Aeronautical phenomenon}}

'''Control reversal''' is an adverse affecteffect on the controllability of [[aircraft]]. ToThe the[[Aircraft pilotflight control system|flight controls]] reverse themselves in ita appearsway that theis controlsnot haveintuitive, reversedso themselves;pilots inmay ordernot be aware of the situation; to roll to the left, for instance, they have to push the control stick to the right, the opposite of the normal direction.

==Causes==

There are several causes for this problem:, pilot error, effects of [[high -speed flight]], incorrectly connected controls, and various [[Coupling (physics)|coupling forces]] on the aircraft.

===Equipment malfunction===

Pilot error is the most common cause of control reversal. In unusual attitudes it is not uncommon for the pilot to become disoriented and start feeding in incorrect control movements in order to regain level flight. This is particularly common when using helmet mounted display systems, which introduce graphics that remain steady in the pilot's view, notably when using a particular form of attitude display known as an ''inside-out'' display.

Equipment failure may cause flight controls to behave unexpectedly, for example the possible rudder reversal experienced on board [[United Airlines Flight 585]].<ref name="AAR01-01 Final Report">{{cite book |url=https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0101.pdf |title=Aircraft Accident Report: Uncontrolled Descent and Collision With Terrain, United Airlines Flight 585, Boeing 737-200, N999UA, 4 Miles South of Colorado Springs Municipal Airport, Colorado Springs, Colorado, March 3, 1991 |publisher=[[National Transportation Safety Board]] |id=NTSB/AAR-01/01 |date=March 27, 2001 |access-date=January 17, 2016 |archive-date=October 2, 2015 |archive-url=https://web.archive.org/web/20151002041524/http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0101.pdf }}</ref>{{rp|114}}

===Pilot error===

Incorrectly connected controls is another common cause of this problem. It is a recurring problem after maintenance on aircraft, notably homebuilt designs that are being flown for the first time after some minor work. However it is not entirely uncommon on commercial aircraft, and has been the cause of several near-accidents.

[[Pilot error]] is the most common cause of control reversal. In [[unusual attitude]]s it is not uncommon for the pilot to become [[Spatial disorientation#Senses during flight|disoriented]] and make incorrect control movements to regain level flight. This is particularly common when using [[Helmet-mounted display|helmet-mounted display systems]], which introduce graphics that remain steady in the pilot's view, notably when using a particular form of [[attitude indicator|attitude display]] known as an ''inside-out''.<ref name="jenkins-hmd">{{cite thesis |last1=Jenkins |first1=Joseph C. |title=The Effect of Configural Displays on Pilot Situation Awareness in Helmet-Mounted Displays |date=2007 |url=https://corescholar.libraries.wright.edu/cgi/viewcontent.cgi?article=1297&context=etd_all |publisher=Wright State University |bibcode=2007PhDT........44J |access-date= December 19, 2021 |format=pdf |degree=PhD |others=Jennie Gallimore (Advisor)}}</ref><ref name="aviatn-psych-outside-in">{{cite journal |last1=Previc |first1=Fred H. |last2=Ercoline |first2=William R. |title=The 'Outside-In' Attitude Display Concept Revisited |journal=The International Journal of Aviation Psychology |date=October 1999 |volume=9 |issue=4 |pages=377–401 |doi=10.1207/s15327108ijap0904_5 |url=https://www.researchgate.net/publication/232896204 |access-date=December 19, 2021}}</ref>

===Incorrectly connected controls===

Another version of the problem occurs when the amount of airflow over the [[wing]] becomes great enough that the force generated by the [[aileron]]s is enough to twist the wing itself. For instance when the aileron is deflected upwards in order to make that wing move down, the wing twists in the opposite direction. The net result is that the airflow is directed down instead of up and the wing moves upward, opposite of what was expected. This form of control reversal is often lumped in with a number of "high speed" effects as [[compressibility]].

Incorrectly connected controls are another common cause of this problem. It is a recurring problem after maintenance on aircraft, notably home built designs that are being flown for the first time after some minor work. It is not entirely uncommon on commercial aircraft, and has been the cause of several accidents including the crash of the [[Short Crusader]] before the 1927 [[Schneider Trophy]] and the 1947 death of [[Avro]] designer [[Roy Chadwick]].<ref name="avsafety-G-AGSU-crash">{{cite web |last1=Ranter |first1=Harro |title=ASN Aircraft accident Avro 689 Tudor 2 G-AGSU Woodford Airport (WFD) |url=https://aviation-safety.net/database/record.php?id=19470823-0 |website=aviation-safety.net |publisher=Aviation Safety Network |access-date=19 December 2021 |quote=''PROBABLE CAUSE: Incorrect assembly of the aileron control circuit.''}}</ref>

===Wing twist===

This problem was notorious on the [[Supermarine Spitfire]]. A series of upgrades to the wing structure helped alleviate the problem to some degree, but improvements in engine power typically offset it. This continued until a new internal design was introduced on the late-war Mark XIV version that cured it entirely.

{{main|Aeroelasticity}}

Another versionmanifestation of the problem occurs when the amount of airflow over the [[wing]] becomes so great enough that the force generated by the [[aileron]]s is enough to twist the wing itself, due to insufficient [[Torsion (mechanics)|torsional]] stiffness of the wing structure. For instance when the aileron is deflected upwards in order to make that wing move down, the wing twists in the opposite direction. The net result is that the airflow is directed down instead of up and the wing moves upward, opposite of what was expected. This form of control reversal is often lumped in with a number of "high speed" effects as [[compressibility]].

==Examples==

Finally the [[Wright Brothers]] suffered yet another form of control reversal, one normally referred to as [[Aileron|adverse yaw]]. In their pre-[[Wright Flier|Flier]] gliders they continued to encounter a problem where the glider would start to turn one direction, then suddenly reverse direction and spin into the ground. They eventually cured the problem by adding a moving rudder system, now found on all aircraft.

===Wright Brothers glider===

The root cause of the problem was dynamic. Warping the wing did what was expected in terms of lift, thereby rolling the plane, but also had an unexpectedly large effect on drag. The result was that the upward-moving wing was dragged backwards, yawing the glider. If this yaw was violent enough the additional speed on the lower wing as it was driven forward would make it generate more lift, and reverse the direction of the roll.

Finally theThe [[Wright Brothers]] suffered yet anothera form of control reversal, one normally referred to as [[Aileron|adverse yaw]]. In their pre-[[Wright1902 Flier|Flierglider]] gliders they continued to encounter a problem where the glider would startroll to turnin one direction, thenbut suddenlyyaw in the reverse direction, andthen spin into the ground. They eventually cured the problem by adding a movingmovable [[rudder]] system, now found on nearly all aircraft.

The root cause of the problem was dynamic. Warping the wing did what was expected in terms of lift, thereby rolling the plane, but also had an unexpectedly large effect on drag. The result was that the upward-moving wing was dragged backwards, yawing the glider. If this yaw was violent enough, the additional speed on the lower wing as it was driven forward would make it generate more lift, and reverse the direction of the roll.

''External links:''

:[http://www.cs.york.ac.uk/hise/safety-critical-archive/2001/0362.html A320 Incident]

:- incorrect maintenance led to reversal of the roll control on the pilot's controls

===Supermarine Spitfire===

[[Category:Aviation]]

Due to the high speeds at which the [[Supermarine Spitfire]] could dive, this problem of [[aileron]] reversal became apparent when it was wished to increase the lateral maneuverability (rate of roll) by increasing the aileron area. The aircraft had a wing designed originally for an aileron reversal airspeed of 580&nbsp;mph, and any attempt to increase the aileron area would have resulted in the wing twisting when the larger ailerons were applied at high speed, the aircraft then rolling in the opposite direction to that intended by the pilot. The problem of increasing the rate of roll was temporarily alleviated with the introduction of "clipped" wing tips (to reduce the aerodynamic load on the tip area, allowing larger ailerons to be used) until a new, stiffer wing could be incorporated.

This new wing was introduced in the [[Supermarine Spitfire (Griffon-powered variants)#Mk.C2.A021 .28type 356.29|Mk 21]] and had a theoretical aileron reversal speed of {{convert|825|mi/h|km/h|abbr=on}}.<ref>Jeffrey Quill OBE, AFC, FRAeS ''Spitfire - A Test Pilot's Story'' - Arrow Books 1983-89 - {{ISBN|0-09-937020-4}}

</ref>

===Boeing B-47===

The [[Boeing B-47]] was speed limited at low altitudes because the large, flexible wings would cancel out the effect of the control surfaces under some circumstances.<ref name="b-47">{{cite web |title=Boeing B-47E Stratojet USAF six-jet medium bomber |url=http://www.skytamer.com/Boeing_B-47E.html |website=www.skytamer.com |access-date=19 December 2021 |quote=''Wing "twist" limited tree-top speed to 425 knots (787 km/h) to avoid control reversal.'' |url-status=live|archive-url=https://web.archive.org/web/20101126141033/http://www.skytamer.com:80/Boeing_B-47E.html |archive-date=2010-11-26 }} {{unreliable-inline |date= December 2021}}</ref><ref name="nasa-quest-speed">{{cite book |last1=Loftin |first1=Lawrence K. Jr. |title=Quest for Performance: The Evolution of Modern Aircraft (NASA SP-468) |date=1985 |publisher=NASA |chapter=12-2: Jet Bomber and Attack Aircraft |url=https://history.nasa.gov/SP-468/ch12-2.htm |access-date=December 19, 2021 |format=On-line}} ([https://ntrs.nasa.gov/api/citations/19850023776/downloads/19850023776.pdf PDF download])</ref>

===Gossamer Condor===

Control reversal also affected the [[Gossamer Condor]], the [[Kremer prizes|Kremer Prize]]-winning human-powered airplane. When a [[wing warping]] mechanism was tried as a solution to a long-running turning problem, the effect was to turn the airplane in the opposite direction to that expected by conventional airplane knowledge. When the Condor was rigged "conventionally", the inside wing slowed down so much that it settled to the ground. By employing "backwards" wired wing-warping, the inside wingtip [[angle of attack]] was increased so that the added drag slowed that wing while the added lift allowed the airfoil to stay aloft at a slower speed. The tilted canard could then complete the turn.<ref>{{Cite web |url=http://www.humanpoweredflying.propdesigner.co.uk/html/the_gossamers.html |title=The Gossamers (Archived copy) |access-date=December 19, 2021|archive-url=https://web.archive.org/web/20150419063651/http://www.humanpoweredflying.propdesigner.co.uk/html/the_gossamers.html |archive-date=April 19, 2015 |website=www.humanpoweredflying.propdesigner.co.uk }}</ref>

==References==

{{Reflist}}

[[Category:Aviation risks]]