Control reversal: Difference between revisions

Revision as of 11:53, 4 April 2008

Revision as of 07:10, 16 May 2008

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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.{{Fact|date=February 2007}}

Due to the unusually high speeds that the [[Supermarine Spitfire]] could be dived at, this problem of aileron reversal became apparent when it was wished to increase the lateral manouverabiltymanouverability (rate of roll) by increasing the aileron area. The aircraft had a wing designed originally for an aileron reversal airspeed of 580 [[Miles per hour|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_variants_part_two#Mk.C2.A021_.28type_356.29|Mark XXI]] and had a theoretical aileron reversal speed of {{convert|825|mi/h|km/h|abbr=on}}.

Finally the [[Wright Brothers]] suffered yet another form of control reversal, one normally referred to as [[adverse yaw]]. In their [[1902 glider]] they continued to encounter a problem where the glider would roll in one direction but yaw in the reverse direction, then spin into the ground. They eventually cured the problem by adding a movable [[rudder]] system, now found on all aircraft.

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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 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.

This issue also affected the [[Gossamer Condor]], the [[Kremer_prizesKremer 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.{{Fact|date=February 2007}}

==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

'''References:'''