It has been said that rudders would be little more than extraneous appendages if ailerons were designed properly. This is an obvious overstatement. Even if adverse yaw effect were eliminated, a rudder still would be required for slipping, stall/spin recovery, and countering an airplane's left-yawing tendency during climb.
But engineers have been so effective in reducing adverse yaw effect from modern airplanes that the requirement for a rudder during normal maneuvering is minimal. Pilots can roll into and out of turns with their feet flat on the floor and barely notice the consequences.
As a result, many pilots are rudder shy. This may be especially true of military pilots who learned to fly in jets and never had to cope with the idiosyncratic misbehavior of airplanes with propellers. The flight controls of jet aircraft are so exquisitely designed that rudder is seldom required in normal flight or during aerobatics. This partially explains why so many pilots tend to counter strong rolling and yawing moments during stall recovery only with aileron input, which can exacerbate loss of control.
A hefty foot — and the willingness to use it — also are needed in the event of an engine failure when one is flying conventionally configured multiengine airplanes. On June 28, 1998, however, 307 passengers and crew almost paid the ultimate price because the rudder was not used as intended.
United Airlines Flight 863, a heavily loaded Boeing 747-400, departed San Francisco International Airport's Runway 28R en route to Sydney, Australia. Shortly after liftoff and after the Boeing entered a low overcast, the number three (right inboard) engine failed. This apparently was caused by such a severe compressor stall that the resultant airframe shaking made it difficult for the pilots to read their instruments. In the meantime, San Bruno Mountain, which rises to 1,576 feet msl, loomed a few miles ahead and somewhat right of the extended runway centerline. It, too, was shrouded in fog.
Even when loaded with 200 tons of fuel, with only three operative engines the -400 has enough muscle to climb safely over the obstacle, but only when properly handled.
The mammoth jetliner yawed right in response to the engine failure; but instead of applying left rudder to counter the powerful yaw, the first officer, who was flying the airplane, incorrectly applied left aileron. Banking alone, however, was insufficient to arrest the yaw, and the Boeing jetliner entered a skidding right turn that led directly toward the mountain.
A skidding or slipping turn has a way of eroding climb performance. In addition, the deflected ailerons and raised spoilers on the left wing added substantially more drag. (Spoilers deploy automatically on the left wing when the control wheel is turned left; this kills some wing lift to help lower the wing and adds some drag to counter adverse yaw effect.)
The rest was predictable. The stick began to shake in response to a computer's sensing that the aircraft was approaching a stall. The normal response to this, of course, is to lower the nose and reduce the angle of attack. But then the ground proximity warning system began its verbal admonishment, "Terrain! Terrain! Pull up!"
In response to the urging of other pilots in the cockpit, the first officer pulled up the nose even farther and converted into altitude what little excess airspeed remained, which turned out to have been the right thing to do. The Boeing 747-400 cleared the mountain by 100 feet. It was so low that it disappeared from ATC radar, igniting controller fears that the aircraft had crashed.
This pilot might have been affected by "lazy-rudder syndrome," the reluctance to use a rudder to the extent dictated by given circumstances. Some believe that this reflects a general decline in basic stick-and-rudder skills. A commonly observed symptom of this is lowering the right wing during initial climb after takeoff to incorrectly compensate for a single-engine airplane's left-turning tendency.
At the risk of being accused of burying my head in the past, it seems that those who received their aerial baptisms in tube-and-fabric taildraggers are habitually more skillful at using their feet. Such aircraft demand an adroit and almost incessant use of rudder. Adverse yaw effect is so strong in these aircraft that one can literally turn right by moving the stick left. It was these aircraft that gave rise to the maxim that a landing is not complete and a pilot cannot relax until the machine is in the chocks and the engine is shut down.
One possible cure for lazy-rudder syndrome is to take instruction in one of these challenging aircraft. Perhaps the same could be accomplished by taking a course in aerobatics or learning to fly a glider, which has more adverse yaw effect than any other genre of fixed-wing aircraft (because the wings are so long and the ailerons are so remotely located).
Rudder usage also is misunderstood. For example, consider this definition of crabbing as published in a respected aviation dictionary: "Heading the nose of the airplane into a crosswind by use of the rudder to prevent the wind from drifting the plane off its course." Believe it or not, there are some who actually attempt to fly this way (slipping to prevent drift).
Related Articles
