Rudder shy?

Even if adverse yaw effect were eliminated, a rudder would still be needed for slipping, stall/spin recovery, crosswind landings, and climbing.

Designers have been effective, however, in eliminating so much adverse yaw effect from modern lightplanes that the need 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 have become rudder shy. This is especially true of military pilots who learn to fly in jets and never learned to cope with the idiosyncrasies of flying airplanes with propellers attached. The flight controls of jet aircraft are so exquisitely designed that rudder is not needed during turning normal flight. This helps to explain why so many pilots tend to counter rolling and yawing moments during stall recovery using only ailerons, which can lead to loss of control.

A hefty foot and the willingness to use it are especially important when an engine fails on a conventional multiengine airplane. On June 28, 1998, however, 307 passengers and crew almost paid the ultimate price because rudder was not applied as needed.

United Airlines Flight 863, a heavily loaded Boeing 747-400, departed San Francisco’s Runway 28R for Sydney, Australia. Shortly after the Boeing lifted off and entered a low overcast, the right inboard engine failed. This was the result of such a severe compressor stall that the resultant airframe shaking made it difficult for the pilots to read their instruments. In the meantime, fog-shrouded San Bruno Mountain, which rises to 1,576 feet msl, loomed only a few miles ahead. Even when loaded with 200 tons of fuel, the 747 had enough muscle to climb over that obstacle using only three engines, but only if properly flown.

The mammoth jetliner yawed right in response to the engine failure, but instead of applying left rudder to counter that insistent yaw, the first officer, who was flying the airplane, incorrectly applied only left aileron. Banking was insufficient to arrest the yaw, and the Boeing jetliner entered a skidding right turn that led the airplane directly toward the mountain.

A skidding turn erodes climb performance. In addition, the deflected ailerons and raised spoilers on the left wing added substantial drag. (Spoilers deploy automatically on the left wing of the 747 when the control wheel is turned left; this reduces wing lift to help lower the wing and adds drag to counter adverse yaw effect.)

The rest was predictable. The control wheels began to shake in response to a computer sensing that the aircraft was approaching a stall. The proper response to this would be to lower the nose and reduce angle of attack. But then the ground-proximity warning system began its loud admonishment: “Terrain! Terrain! Pull Up!”

In response to the urging of other pilots in the cockpit, the first officer pulled up the nose to convert what little excess airspeed remained into altitude, which turned out to have been the right thing to do. The 747 barely cleared the mountain but was so low that it disappeared from ATC radar, igniting controller fears that the aircraft had crashed.

For whatever reason, this pilot was reluctant to use rudder to the extent dictated by the circumstances. Some believe that this typifies a general decline in basic stick-and-rudder skills. A commonly observed symptom of this is when a pilot lowers the right wing—instead of applying right rudder—during climb to compensate for a single-engine airplane’s left-turning tendency.

It seems that those who receive their aerial baptism in tube-and-fabric taildraggers are typically more skillful at using their feet. Such aircraft demand an almost incessant use of rudder. Adverse yaw effect is so relatively strong in these aircraft that one can almost turn right by moving the stick left.

One cure for being rudder shy is to take instruction in one of these challenging little taildraggers. Perhaps the same could be accomplished by learning to fly a glider, which has more adverse yaw effect than any other genre of fixed-wing aircraft. This is because the wings are so long, and the ailerons are so far from the fuselage centerline.

Rudder usage also can be misunderstood. Consider this definition of crabbing as published in an otherwise respected aviation dictionary: “Heading the nose of the airplane into a crosswind by use of rudder to prevent the wind from drifting the airplane off its course.” And there are some pilots who actually slip their airplanes to prevent en route drifting. I kid you not.

www.BarrySchiff.com