lesson 4 - three-axis control
Connection to the Wrights:The Wrights were first to develop a fully controllable airplane; they understood that flying machines needed to have three-axis control in order for flight to be safe.
To control the pitch of their first glider, they used an elevator mounted in the front of their glider (the Wrights called it their "front rudder"). To control roll and to turn, they developed "wing-warping." To control yaw, they perfected the rudder.
Objective:To determine how the Wright brothers controlled their canard glider in three dimensions. To determine why rudders are necessary in preventing adverse yaw.
Description:In this activity, students construct inexpensive canard gliders out of straws, manila file folders, paper clips and tape. Students learn how to control their gliders by warping the wings and by adjusting the rudder and forward elevator. These simple experiments demonstrate control of roll, pitch and yaw.
Materials and tools:
Background information concerning control:
Pitch is the motion of the airplane as its nose points up or down. Today, movable control surfaces called "elevators" are used to control the up and down motion of the airplane along its lateral axis.
The elevator on the Wrights' glider was in the front, what Wilbur called a "happy accident of design." In later years, Orville noted, "we retained the elevator in the front for many years because it absolutely prevented a nose dive such as that in which Lilienthal and many others since have met their deaths." Today this arrangement with a small wing ahead of a large wing is known as a "canard" configuration, the French word for duck, perhaps because of the similarity to the flying profile of the bird. Around 1910, the elevator and rudder were located together at the tail, because engines needed to be located at the front of the airplane.
Roll is the tilting motion of the airplane when one wing rises or falls in relation to the other. Wing warping was the method used by the Wrights to control roll: to raise the right wing, cables twisted the leading edge of the right wing upward, increasing the angle of attack of the wing and the amount of lift. As a result, the right wing rises. Meanwhile, the left wing drops because cables simultaneously decrease the angle of attack and lift on the left side.
Today, movable control surfaces called "ailerons" control roll. There are two ailerons responsible for banking the airplane, one mounted in the trailing edge of each wingtip. When an aircraft banks to the left, the left aileron deflects upward, and the right aileron deflects downward. The force of air on the defected control surfaces causes the left wing to drop and the right wing to rise, producing greater lift on the right wing. The lower, right aileron results in a greater angle of attack, which results in greater lift. The lift is less on the left wing, and thus, the left wing drops. The airplane banks to the left.
Yaw is the twisting motion as the nose turns left or right. Rudders control yaw.
Although airplanes turn due to the action of ailerons, rudders are necessary to guarantee that the airplane turns more efficiently.
The Wrights discovered a disturbing phenomenon when they were trying to turn their 1901 glider. When attempting to make a turn to the left, the leading edge of the right wing was warped up to increase angle of attack and lift. The leading edge of the left wing was warped down. As expected, the glider's right wing raised and the glider began to bank to the left. However, instead of turning to the left, the glider pivoted about the higher tip of the right wing and turned to the right! This truly dismayed the brothers. Today, this phenomenon is known as "adverse yaw." After much thought and testing, a movable rudder was added to the glider to prevent the phenomenon.
Adverse yaw may occur when the leading edge of one wing is warped upward, thus increasing the angle of attack, lift and drag. Essentially, the increased drag on this wing slows it down. Meanwhile, the other wing has relatively little drag and quickly pivots around the tip of the slow wing. The addition of a movable rudder prevents adverse yaw from occurring.
How to make a Wright (Canard) Soda Straw Glider
This image illustrates the relatively safe parachute-style response following a stall of the canard configuration used by the Wright brothers. The violent spin and nosedive typical of a rear-tailed configuration upon stalling is depicted at the right.
Working with canard glider
Just for fun:
Extension - Building a modern straw glider