Aeroplane Construction and Operation

by John B. Rathbun

A very flat gliding angle is a most important feature from the standpoint of safety, as it determines the extent of the area within which a landing can be made with a dead engine. If the gliding angle is taken as 12, and the height is 2000 feet, then the radius of the circular area in which a landing is possible is 2000 × 12 = 24000 feet, and the diameter is twice this or 48,000 feet, so that we can land anywhere within a distance of over 9 miles. If the best gliding angle of the machine were only 10, this will be reduced to 2000 × 10 = 20000 feet, hence our chance of choosing a safe landing space would be cut down in proportion. The best gliding angle corresponds to a certain speed and wing angle, and must be determined by experiment, but in many machines the adjustment of the weight is such that the machine automatically picks up the best glide as soon as the motor is cut off, and needs but little correction by the elevators. Such a machine is dived slightly when the motor is cut out, and then after a few oscillations settles down and travels steadily along the proper gliding path. In trying to improve this performance, the speed indicator and incidence indicator should be carefully watched so that neither the stalling angle nor the stalling speed are approached. The best glide angle corresponds to the best flight speed and will be increased if the incidence is much below or above the incidence for the most economical flight speed.

Vertical Nose Dive. When the aeroplane is diving vertically, nose down, the center of pressure movement in some machines may oppose the elevators, thus making it difficult to straighten out into the horizontal. If pulling full back on the elevator control does not remedy matters, the control should then be quickly reversed so that there is a momentary tendency to throw the machine over on its back. This breaks up the lock, and when accomplished, the controls should be again pulled back to bring the machine into the horizontal with the elevators in the original straightening out position. The momentum swings the machine out and against the locking position, thus aiding the controls in overcoming the moment of the C. P.

Typical Gliding Angle Diagram Showing Path Inclination of Deperdussin Monoplane.

Tail Spin (Spinning Nose Dive). Spinning is due to side slipping or stalling, and sooner or later every pilot gets into this position either through accident or intention. If an accident, it may be due to the design of the aeroplane through an improper distribution of the vertical surfaces, or again it may be caused by very steep banking without an equivalent rate of turning. Incorrect manipulation of the ailerons when the machine is near stalling speed, or when gliding in a spiral of gradually decreasing radius, also causes this result. At any rate, the side slip and stall are the final cause of spin. In "Stunt flying," where a spin is desired, one of the quickest methods of getting a spin is to pull the controls all the way back and push the rudder hard over in the desired direction of spin with the motor shut off. Another way to get a spin with lots of "Pep" in it, is pull the stick clear back with the motor on, and climb until the machine is stalled, then rudder over hard with the controls still held back. The aeroplane will now fall over on its side in the direction of the rudder, and assisted by the motor which has again cut in after the peak of the climb, will give all the spin that any critic could ask for. After the stall occurs, the motor should be throttled down for it is likely to strain the plane or even break it.

There are several ways of coming out of the spin. Probably the best way, and the one that causes the least loss of altitude, is to keep the controls pulled back all the way, and rudder in the opposite direction to the spin (Motor cut out). The rudder will stop the spin, and the elevator will cause the plane to level out of the dive simultaneously, but the controls should be put into neutral as soon as leveled out or there will be another spin started in the opposite direction. A very common method used by exhibition flyers is first put the controls into neutral, and rudder opposite to the spin until it stops turning and it is then put into a nose dive. The straight nose dive can then be easily corrected by pulling back on the controls until it levels out. This latter method develops an excessive speed and requires a high altitude.

When the aeroplane is overbanked at normal speed, and the turn is not correspondingly rapid, the plane will slip down sideways into an "Inside side slip." The strong upward wind against the side of the body will turn the nose into a dive, the nose drops, and the tail will then start to swing around in a circle larger than the circle described by the nose—the dive continuing. When much below the normal flight speed, or near the stalling point, the inner ailerons are not as effective when making a sharp turn for their velocity is much reduced. When fully depressed, the inner ailerons give very little lift toward righting the machine but add to the drag and tend to spin the machine around with the inner tips acting as a center of rotation. The outer ailerons are very effective and because of the high speed of these tips, there is a strong banking tendency that eventually will result in side slip and a spin if the pilot is not experienced. Either the spin due to overbanking, or that due to low speed may be straightened out according to instructions already given.

When a turn is attempted at low speed near the ground, the student generally fails to bank up sufficiently through fear of striking the ground with the lower wing tip, and therefore gets into an outward side slip. In the frantic effort to keep the low wing up and off the ground he depresses the low aileron to the full, thus increasing the drag on the low side and starting the spin. Very much to his surprise he finds that this actually drops the low tip further instead of raising it as the outer tip is now speeding around at a tremendous clip, and the outer lift is increasing the bank against his will. Given time, and altitude, the plane will bank up until it stands on end, and in any event a bad side slip results, and the fun is on. If near the ground as assumed, either the side slip or the resulting nose dive will soon terminate matters. The moral to be derived from this experience is to keep up to speed in making a turn, to maintain a safe altitude, and in case the speed should fall off, to depress the outer aileron. The outer aileron will resist the spin if depressed, as the drag acts against the spin, and the bank thus obtained will act against the outer side slip, without destroying the velocity of the machine as a whole. In turning at stalling speed, the aileron effects are reversed, and as soon as straightened out the engine should be opened up so that the speed will be increased and the landing made as easy as possible.

If the fin and rudder surface is not sufficient for the machine, little is gained by turning the rudder to an angle greater than 15°, and in such cases it is much more effective when held parallel to the wind. If correction has been started before the spin has developed great rapidity, the rudder can first be turned to check the rotation and then turned back parallel to the wind. It is always best to shut off the engine when getting out of a tail spin, especially if the engine rotation is in the direction of the spin, since the motor torque aids the spin and acts against the controls. In case of a smash there is no danger from fire with the engine cut out.

Stunt Flying. When the student has had 20 hours or more of solo flying, and is capable of performing the ordinary maneuvers with confidence and accuracy, he is in a position to undertake stunt flying under the directions of a good instructor in a dual control machine. This tremendously increases the confidence of the student if gone about in the right way, and in his after flying experience enables him to get out of tight places that would otherwise often prove impossible. There is no doubt but what stunt flying has decreased the percentage of accidents when properly taught, and that Pegoud's original stunt of looping the loop has been one of the greatest steps in the advancements of aeronautics that we have had, if only for the fact that it taught the flyer that there was no flying attitude so bad but what there was a solution for it.