Plane & Pilot
Tuesday, July 8, 2014

What’s The Rudder’s Real Purpose?


Shedding light on the least understood and most misused control in an airplane



Proper use of the rudder on takeoff will increase climb performance.
Here's a black-and-white statement that's more fact than opinion: The rudder is easily the least understood and most misused control in an airplane. Actually, "misused" might be the wrong word. The sentence "the rudder is the control most likely not to be used when it should be," would be more descriptive.

From the very beginning, pioneer aircraft designers realized that they needed a rudder to control yaw, just like a boat. However, most thought the rudder would be the method used to turn the airplane. Again, like a boat. Turn left, left rudder, and so most designs made flat turns—no bank. Santos-Dumont, the great French designer, upon witnessing the Wrights' first demonstration flights in France, extolled the brothers' genius in using the bank to turn the airplane, thus imparting much more precise control to the craft. In so doing, however, the rudder was relegated to the role of being a trimming device rather than a primary control surface. That's when the confusion began, and it has continued to this day.

Today, far too often, when the pilot on the street is asked the purpose of the rudder, the answer will be a vaguely blank stare and fumbling words having something to do with turns. And, believe it or not, it's not unusual to run across a pilot who claims he/she was never told to use the rudder when turning (no, it really happens!).

Every pilot should be able to state in a very concise manner, in 25 words or less, the exact purpose of the rudder. It will take many more words than that, however, to enumerate the instances and the ways in which the rudder is to be used.

Simply stated, the purpose of the rudder is to control yaw. That's only nine words, so it's simpler than we thought. However, that may be an over-simplification. That definition can best be understood by studying the situations in which application of the rudder is called for and then analyzing the effect of using the rudder, as well as the effect of not using it.

Incidentally, when talking about the rudder, most folks assume the primary discussion will be centered on turns. And, yes, that's important, but that's just one of several situations where it's needed, and we'll approach those often-unexpected situations first.



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