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Aircraft Controls

Guiding Question

How does an airplane fly?

Objectives

Describe the laws of Newtonian motion.
Apply the principles of Newtonian motion to flight.
Introduce the terminology of flight.
Exhibit the use of an airplane's air surface controls with a model airplane.
Experiment with air surface controls using paper gliders.

Concepts

Thrust. Results from the expansion of air after it was compressed along its path through a jet engine, or thrust results from the acceleration of air over the propeller of propeller powered aircraft.
Drag. Frictional resistance caused by the air as it travels along the surface of the airplane.
Gravity. The attraction between any two bodies, such as an airplane and the earth.
Lift. Is the upward force resulting from air flow across the airplane's wings. Lift results from the pressure difference between the top surface and bottom surface of the wing.
Bernoulli's Principle. The faster air travels over an object, the less pressure there is on that object.

Principles

Trajectory. the direction an object is traveling.
Speed. the average rate an object travels along its path, or how fast an object travels between two points along its trajectory.
Velocity. the speed and direction that an object travels at any particular moment.
Force. a property related to the mass and acceleration of a body or object.
Mass. a unit of measure that describes the amount of material an object has independent of the effect of gravity.
Distance. the total length an object travels when moving between two points of location.
Displacement. is the most direct measure of length an object travels when moving between two points of locations independent of the object's path.
Acceleration. the rate at which an object changes its rate of travel per unit length at any particular moment during its trajectory.
Pressure. Force acting per unit area (P=F/A)
Air Pressure. Force of air dependent upon its mass acting per unit area
Friction.
Yaw. The pivoting movement of the aircraft around its vertical, Z axis caused by use of the rudders.
Pitch. The motion of the airplane around its lateral, Y Axis caused by use of the elevators.
Roll. The motion of the airplane resulting in movement around its longitudinal, X axis caused by use of the ailerons.

Materials

Paper
Pencil

Room Preparation

Explain lesson and hand out lesson pages to students.

Safety Preparations

None

Procedures and Activities

Every day, aircraft fly through the skies from one point to another. For takeoff, landing, and the entire time in between, the pilots must adjust the controls to ensure that the aircraft remains on the correct flight path. Sometimes the airplane is maneuvered in a smooth fashion (when there are passengers on board) and sometimes the aircraft is maneuvered very abruptly (during an air show).

Any time the airplane's flight path is changed, it is because the pilot (or autopilot) is moving the control stick. The control stick is connected to different parts of the airplane. These parts of the airplane are called control surfaces and are labeled in the diagram below.

Today we are going to build our own aircraft and flight test it to see how to control its direction of flight.

Each control surface has a specific function in controlling the direction of flight of the airplane. Each of their functions is listed below:

Elevators. These are usually located in the back of the airplane and are used to make the airplane climb or descend. The pilot controls them by pushing or pulling on the control stick. The name we give to the motion they control is pitch.
Ailerons. These are usually located on the wings and are used to make the airplane tilt. The pilot controls them by moving the control stick left or right. The ailerons are connected so that when one goes up the other goes down. The name we give to the motion they control is roll.
Rudders. Like the elevator, these are usually located in the back of the airplane, but their function is very different. In fact, their function is similar to that of the ailerons because they help the airplane turn. The pilot controls the rudders with foot pedals which are appropriately called rudder pedals. The pilot steps on the left pedal to move the rudder to the left (left rudder) or on the right pedal for right rudder. The name we give to the motion they control is yaw.

The elevators, ailerons, and rudders are the three basic controls on an aircraft, and they control the three types of motion described above, pitch, roll, and yaw. To make our description of the airplane's motion a little more scientific and mathematical, we are going to introduce the axes of the airplane.

The three axes of the aircraft are labeled X, Y, and Z. Each axis also has a name - longitudinal (X), lateral (Y), or vertical (Z). To understand what each of these axes means, let's first examine the longitudinal axis. Imagine a pole running through the airplane along the X-axis line. Now, ignore everything else except the X-axis and let the airplane roll around the X-axis.

The figure below shows what happens. The right wing went down and the left wing went up, causing the plane to roll right. The motion around the longitudinal axis is called roll motion, and remember that in order to roll right, the right aileron points UP, and the left aileron points DOWN. Likewise, the motion around the vertical axis is described as yaw and the motion around the lateral axis is described as pitch.

Remember that when the rudder points to the RIGHT, the plane yaws right, and when the elevators are UP, the plane pitches up.

Additional Comments

The controls you were introduced to here are the basic controls of a conventional style airplane. In recent aircraft some of these controls have been combined (ailerons and elevators) or left out. Many of these airplanes have what is called fly-by-wire control systems where a computer is connected to the pilot's stick and the computer operates the controls to make the airplane do what the pilot wants. Some new airplanes are so unstable that a human pilot would not be able to fly them if there was no computer in the control system. These are usually used in the military, NOT for carrying passengers, so don't worry! Of course, these airplanes still can't fly without the human pilot either, so keep test flying your model for practice until you can fly the real thing. The best way to understand these motions is to study them with your own airplane by doing your own flight testing.

Flight Test Experiments

After constructing your own glider try the following experiments:

Try to make your airplane roll to the right by adjusting the ailerons. Remember that when the right aileron goes up the left one goes down and vice versa. Record your observations below: Aircraft Rolls Right if the Right aileron is deflected _____ and the Left aileron is deflected ______. Aircraft Rolls Left if the Right aileron is deflected _____ and the Left aileron is _________.
Make the airplane climb steeply. Beware that when the airplane's pitch is too great, the wing stalls and the airplane falls. Airplane Climbs when the ____________ is deflected ____________. Airplane Descends when the __________ is deflected ____________.
Try to control the yaw motion of the airplane. Airplane yaws to the right if ______ is deflected to ________. Airplane yaws to the left if _______ is deflected to ________.
As an experienced test pilot, would you say that an airplane can control the yaw motion without affecting the roll or pitch?
Can you easily control the pitch of the airplane without affecting the roll or yaw of your airplane?
What happens if the lift is greater than the weight (gravity force)? What happens if the thrust is greater than the drag?

Evaluation

Summarize the experiment and discuss the students' results.

During class discussion, note if students understand the concepts of gravity, lift, thrust, and drag and ensure they know the effect of each of the control surfaces (elevators, rudder, ailerons).

Distinguish the effect of flaps and ailerons. These structures are both components of the wing and may easily be confused or misinterpreted by the students.

Ask the students what control surfaces they would use to cause each of the following motions: pitch, yaw, roll.

Discuss possible extensions; e.g. relate the lift of an airplane to the effect of buoyancy while you swim.

Link to Careers

Identify careers that may be associated with the lesson.

Aerospace Engineer
Mechanical Engineer
Airline Pilot
Military Pilot
Astronaut
Auto Industry
Aerodynamicist