Learning to fly in the U.S. Army

by E. N. Fales

3. The Fuselage May Have Become Warped Upward or Downward.—This would give the tail plane or horizontal stabilizer an incorrect angle of incidence. If it has too much angle, it will lift too much, and the airplane will be “nose-heavy.” If it has too little angle, it will not lift enough and the airplane will be “tail-heavy.”

4. The Tail Plane May Be Mounted upon the Fuselage at a Wrong Angle of Incidence.—If this condition exists, it must be corrected by making a change at the fittings. If nose-heavy, the tail plane should be given a smaller angle of incidence. If tail-heavy, it should be given a greater angle of incidence; but care should be taken not to give it too great an angle, because the longitudinal stability entirely depends upon the tail plane being set at a smaller angle of incidence than is the main surface, and if that difference is decreased too much, the airplane will become uncontrollable longitudinally. Sometimes the tail plane is mounted on the airplane at the same angle as the main surface, but it actually engages the air at a lesser angle, owing to the air being deflected downward by the main surfaces.

Alignment Errors, Lateral.—The machine manifests a tendency to fly one wing down. The reason for such a condition is a difference in the lifts of the right and left wings, assuming the motor torque is already taken care of by washout. That may be caused as follows:

1. The Angle of Incidence of One Wing May Be Wrong.—If it is too great, it will produce more lift than on the other side of the airplane; and if too small, it will produce less lift than on the other side—with the result, in either case, the airplane will try to fly one wing down.

2. Distorted Surfaces.—If some part of the surface is distorted, the lift will not be the same on both sides of the airplane, which, of course, will again cause it to fly one wing down.

3. The Ailerons May Be Set Slightly Wrong.—This may be due to one control cable being longer than the other, or one of the aileron horns being bent or twisted. This condition can easily be detected by setting the aileron control—in neutral and checking up the position of the ailerons.

Alignment Errors, Directional.—If there is more resistance on one side of the airplane than on the other the airplane will, of course, tend to turn to the side having the most resistance. This may be caused by the following conditions:

1. The Angle of Incidence of the Right and Left Surfaces May Be Unequal.—The greater the angle of incidence, the greater the resistance. The less the angle, the less the resistance.

2. If the Alignment of the Fuselage, Vertical Stabilizer, the Struts or Stream-line Wires Is Not Absolutely Correct.—That is to say, if they are turned a little to the right or left instead of being in line with the direction of flight—then they will act as a rudder and cause the airplane to turn off its course.

3. If Any Part of the Surface Is Disturbed It Will Cause the Airplane to Turn off Its Course.—If, owing to the leading edge, spars, or trailing edge becoming bent, curvature is spoiled, that will result in changing the amount of resistance on one side of the airplane, which will then develop a tendency to turn off its course.