8.A : Straight and Level Flight

To understand how to properly engage in straight and level flight it is important to first understand the primary flight controls, and the actions caused by use of these controls. The aircraft rotates around the center of gravity in three axis. These axis are pitch (around the lateral axis), roll (around the longitudinal axis), and yaw (around the vertical axis).

Pitch is controlled by the elevators. When back pressure is exerted upon the elevator control the trailing edge of the elevator is deflected up, and this decreases the camber of the elevator and creates a downward aerodynamic force. This causes the tail of the plane to move down and the nose to pitch up. This creates a pitching moment around the center of gravity (CG). The strength of this pitching moment depends upon the distance between the CG and the horizontal tail surface.

Forward pressure deflects the trailing edge of the elevator down, and this increases the camber creating more lift (i.e. less tail-down force). This causes the tail to move upward and the nose to move downward. This pitching moment also occurs around the CG.

Roll is controlled by the ailerons. When the aileron controls are deflected to the right this causes the right aileron to go up, and the left aileron to go down. This causes a decreased camber on the right wing, and decreased lift on that wing. It also causes an increased camber on the left wing, resulting in increased lift on the left wing. These changes create a combined effect that rolls the aircraft to the right. Deflecting the aileron controls to the left does has the exact opposite effect. When the aircraft rolls it pivots around the CG.

Yaw is controlled by the rudders. When the rudder is deflected into the airflow a horizontal force is exerted in the opposite direction. Pushing the left rudder pedal causes the rudder to deflect to the left, and pushing the right rudder pedal causes the rudder to deflect to the right. In each case this alters the airflow over the vertical surface causing a horizontal force that pushes the tail in the opposite direction thus yawing the aircraft around the CG.

It is easy to over-control the aircraft, and this is mitigated by maintaining a light grip on the flight controls. Try to only grip with the fingertips. This helps to exert only the control pressure needed which should be just enough to produce the desired result.

Some signs of over-controlling are jerky large movement of the flight controls, white knuckles (a death grip!), and general nervousness. If this is observed point out the situation, and demonstrate the correct light/fingertip grip as well as the pressures desired. One technique to address a consistent tendency to over-control and grip too tightly is to place a pencil on top of the middle and ring finger and under the index and pointer finger of the hand the student uses to fly. Excessive pressure will increase the force of the pencil on the fingers making it uncomfortable, and a reminder to relax. If it continues, the pencil may break providing an even more stark reminder to relax.

Each flight maneuver is first learned by reference to outside references, then by instrument references only. This integrated approach will help develop the habit of monitoring the flight and engine instrumentation.

The goal of straight and level flight training is to learn to detect small deviations from laterally level flight as soon as they occur, necessitating only small corrections.

Maintaining level flight is a matter of consciously fixing the relationship of the position of some portion of the airplane, used as a reference point, to the horizon. Over time the goal is to learn to associate the movement of the selected reference point with the forces that produce that movement. Maintaining straight and level flight in each of the three axis entails looking outside, looking inside, and making corrections.

The attention outside when maintaining pitch involves selecting a portion of the aircraft’s nose or glare shield as a reference point and keeping that point in a fixed position relative to the horizon. This will maintain a constant altitude.

The pitch attitude should be checked by periodically looking inside at the instruments. The altimeter is checked for the proper altitude itself. The attitude indicator is checked against the position of the nose relative to the horizon. The VSI will indicate any trends that may be forming. And the ASI will show a descent if the speed is getting faster, and a climb if the speed is getting slower.

If altitude is being lost or gained then the pitch attitude should be adjusted in relation to the horizon. Once done, the altimeter should be checked to determine if the desired altitude is being maintained. Elevators are the control used to adjust pitch, with forward pressure being used to decrease pitch and back pressure used to increase pitch. Note the relationship between control pressure and the aircraft’s change in attitude.

The attention outside when maintaining bank involves confirming that both wingtips are equidistant above or below the horizon. It is also beneficial to select two or more outside visual reference points directly ahead of the aircraft (i.e. roads, towns, lakes, buildings, anything) and visualize an imaginary line between them and keep the aircraft heading along that line. If the reference point moves out of alignment make the necessary corrections to realign the plane.

The bank angle should be periodically verified by checking inside at the instruments. The heading indicator should be checked to confirm that the desired heading is being maintained. The attitude indicator should be checked to confirm that the wings are level. The turn coordinator should be checked to verify that the aircraft is not turning. And the magnetic compass should be also used to verify desired heading.

If the aircraft is banking one direction or another the bank should be adjusted to return the aircraft to straight flight. This is done by exerting control pressure on the ailerons. Exert pressure on the right aileron to turn right, and the left aileron to turn left. Note the relationship between the control pressure and the aircraft’s change in attitude.

It is important to not correct headings by simply yawing the aircraft with the rudders. However, always use the rudders to maintain coordinated flight.

In straight and level flight airspeed will remain constant with a constant power setting. If power is changed this will require changes in pitch attitude to maintain altitude. When the power is changed adjust the outside reference point to properly adjust the pitch, and check instruments inside to verify changes in airspeed as well as engine RPM and/or manifold pressure.

Increased power will result in a climb if no changes are made to pitch attitude, and decreased power will result in a descent if no changes are made to pitch attitude.

The aircraft is designed so that the primary flight controls (rudder, aileron, and elevator) are streamlined with the non-movable surfaces when the airplane is cruising in straight-and-level flight at a normal weight and load condition. If the airplane is out of that balanced condition one or more of the control surfaces is going to have to be held out of its streamlined position by continuous control inputs. This can be tiring to do manually, so trim tabs are designed in to relieve the pilot of the need to hold continuous pressure. Trim the airplane by following the following procedure

Any control pressure that the pilot feels should be the result of deliberate control inputs during a planned change in airplane attitude. It should not be the result of pressure being applied by the airplane because the pilot is allowing the aircraft to assume control.