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Wonders of World Aviation

Evolutions that Increase Flying Skill and Safety

INVERTED FLYING has a technique of its own

INVERTED FLYING has a technique of its own. When the pilot has become accustomed to the upside-down position, however, he can fly in that position for long periods and can perform all the normal flying manoeuvres.

AEROBATICS are the airman’s punching bag; they make him fit to fly and they keep him fit to fly. Although aerobatics are often condemned as unnecessary and risky, they provide valuable aid in the perfection of flying , technique, and no pilot can reach the highest point of flying skill and flying safety without a full knowledge of the art.

It is difficult to say where normal flying ends and aerobatics begin, for they merge into each other. Is a vertically banked turn, for instance, an aerobatic manoeuvre? Sometimes it is, sometimes it is not. A pilot often has to make a vertically banked turn to get into an aerodrome or to avoid an obstacle when taking off from a forced landing. At such moments vertical turns become normal flying. Then there is sideslipping. A sideslip may be an aerobatic, or it may be a normal and necessary manoeuvre used when making an approach to a difficult landing area. Some manoeuvres, however, are obviously and inevitably, aerobatics, and can be considered as nothing else. The first among such manoeuvres is the loop. In aerial combat the loop has occasionally been used; but even then it is scarcely ever necessary. The loop is primarily a piece of aeronautical fooling, or practice for a pilot. Similarly the flick roll is a manoeuvre which, outside warfare, never finds an application, and which, even in warfare, is rarely used. The spin, also, is frequently used in warfare, but never in ordinary flying. In civil aviation, therefore, it is an aerobatic; but in military flying it is a normal manoeuvre.

Tmedium speed loophe loop is regarded by many pilots as the simplest aerobatic, but that view is dependent upon the degree of accuracy which is demanded. If any manoeuvre in which the machine went over on to its back and came out again the right way up were accepted as a “loop”, the pilot could almost perform it with his eyes shut. The experienced aerobatic pilot, who is also a critic of flying, knows, however, that an accurate loop is most difficult to perform, and that there are many variations of it.

In the simple, medium-speed loop the aeroplane traces what closely approximates to a circle. The procedure depends upon the type of aeroplane. With some machines a preliminary gaining of speed is essential; with others a sufficiently high speed can be acquired in level flight. When the latter type of machine is being looped, the pilot flies level and adjusts the engine throttle until the correct speed - which he has discovered by previous experience - is acquired. He then allows the nose to come up on a gentle curve. Pilots are frequently instructed to “pull the stick back” for a loop. Such a procedure, however, would never produce an accurate loop and might, with some machines, cause the aeroplane to stall when it gets on its back. The aeroplane must be coaxed up and over with the pilot maintaining proper control of it all the time. The speed falls off as the machine goes up. Thus, when the aeroplane is upside down, there is likely to be, and is in nearly all types, a tendency to turn sideways and to get off the true course. The pilot has to correct this tendency with the rudder, and he has to bring the aeroplane over on a true line so that when it comes out of the loop it goes through its own slipstream.

The action of getting up speed and then blindly pulling the stick back is not that of an expert pilot. The expert controls the machine all the way round, and at the top of the loop, when the aeroplane is inverted, it will have such a speed that the pilot will be kept on his seat by centrifugal force.

rocket loopAt no time, in a correctly performed loop, should there be any high centrifugal loading. The change of direction from level flight to an upward slant is carried out so gradually that the pilot is only slightly pressed on his seat. Similarly, when the machine is finally brought out of the loop the change of direction is gentle. In some of the other kinds of loop, such as the rocket loop, the accelerations are rather greater.

In the rocket loop the aeroplane, instead of making a perfect circle, begins by rocketing skywards in a vertical climb. A short time before it reaches the limit of this climb, and before it begins to “hang on its prop”, as the phrase goes, the pilot tips it over backwards and brings it quickly round on a small radius to complete the loop. At the beginning of the rocket climb, the acceleration must inevitably be fairly high, because the pilot is changing direction at high speed.

The difference between these two types of loop is important. In the medium-speed loop the aeroplane describes a circle; the more accurate the circle the better is the loop. The machine should complete the loop at exactly the same level as that at which it began. It would be a greater fault to lose height during such a loop than to gain it; but there should be neither gain nor loss. In the rocket loop a great deal of height should be gained. The machine should stand on its tail for an extended period; it should then tip over at the top and complete the loop in a small space so that it finishes and levels out many hundred feet higher than it began, especially if it is a high-performance machine.

the buntThere are numerous other types of loop, each of which has its special technique. The “engine-off” loop is not often seen nowadays, but it is an effective manoeuvre. To gain sufficient speed the aeroplane has to be dived for a time with the engine off. It is then taken round a rather small loop, during which, with some machines, it is possible not to lose height.

Another aerobatic is the inverted loop in which the machine begins and finishes in the upside-down position - a manoeuvre demanding a suitable type of aeroplane and a pilot used to inverted flying.

Many variations of the loop occur in aerobatic displays, but, as they all depend upon the introduction of other manoeuvres and the combining of these other manoeuvres with the loop they are not of great importance. A brief mention must be made, however, of the “bunt”. This is really the first part of an outside loop. The pilot pushes the nose down from level flight to the vertical and then to the inverted position.

The spin has a special importance, because it is the condition which is most frequently adopted by an aeroplane when it gets out of control. The spin has been the subject of more research work than any other manoeuvre.

In the spin the aeroplane falls in a nose-down position, twisting round at the same time in a corkscrew motion. Height is lost rapidly, and the vertical rate of descent is probably more than 65 miles an hour. The rate of rotation depends on the type of aeroplane. The pilot has little control over the rate of rotation, and almost no control over the rate of descent. He merely starts the spin and stops it again.

normal stallThe process of starting the spin is simple. The pilot stalls the machine by reducing its speed and, while so doing, he pulls the control column farther and farther back until it is as far back as it will go. When the fully stalled condition is reached - or a fraction of a second before - the pilot kicks on full rudder on the side towards which he wishes to initiate the spin. The nose of the machine then drops and, with the pilot holding the stick back and keeping the rudder full on, the spin begins.

Although the pilot has little control over the rate of spin, he can exercise some control by means of the ailerons. Some aeroplanes will spin rather more rapidly if opposite aileron is held on during the spin. Some machines, but not all, can also have their spins modified by the amount of rudder.

the spinTo extricate a machine from a spin, the pilot eases the stick forward and straightens the rudder. The easing forward of the stick alone, or the straightening of the rudder alone, will normally stop the spin. Some machines, however, require both movements before they will respond. During the spin the pilot should watch landmarks as they come round, and the extrication should be so carried out that the machine comes out facing a predetermined direction. The practice of pulling out of the spin facing any direction haphazardly is poor flying, and indicates incomplete control. Another important aerobatic is the flick roll, not often seen nowadays except with specially built aerobatic machines. The flick roll is a horizontal spin. The machine is given an impetus on a horizontal line, and the pilot then forces the controls into the spinning position, with the stick full back and the rudder full on. The aeroplane seems suddenly to break into the condition of spinning or auto-rotation, and to “flick” round quickly. The extrication is carried out as with the spin, the pilot easing the stick forward and straightening the rudder as the aeroplane comes round after completing the roll.

Slow rolls differ greatly from flick rolls, and the difference is perhaps most clearly indicated by the fact that in the flick roll the pilot does not need a strap to hold him in his seat, whereas in the slow roll he does. Naturally he will always wear a strap, but this point is made to show the difference between the rolls. In the slow roll the aeroplane is really flown round on the ailerons. There is no spinning or auto-rotation; the stick and rudder never come back and over to the spin position. The pilot tips the machine over by

moving the stick to the side, and he adjusts elevator and rudder so as to keep the machine on a straight course as it rolls over. The slow roll can be extremely slow; the flick roll, however, can never be slow, for it depends upon throwing the machine into the stalled condition and then, before the nose has had time to go down and the roll to turn into a spin, upon extricating it.

Oflick rollne other aerobatic which belongs to the spin group is the “falling leaf”. The falling leaf is really a series of incipient spins, made to right and left alternately. The machine is started to spin in one direction, checked, and then started to spin in the other direction while it loses height. All the time the nose is held up as much as possible by the rapid rudder reversals, for at the moment when the nose tends to fall the machine is on its side. The wings should tip beyond the vertical position. It is sometimes supposed that the falling leaf is a series of sideslips to right and left, but this is not so. The condition of auto-rotation is an essential ingredient of the correctly performed falling leaf.

Tslow rollhe falling leaf, like the loop, the spin and the slow roll, can be done in the inverted position. The aeroplane begins the manoeuvre upside down, the stall is done with the aeroplane on its back, and the control stick is held fully forward with full rudder while the spin is in progress. The extrication is made with the machine still upside down.

Inverted flying has its special technique. When the engine is fitted to run with the machine upside down, however, inverted flying has no features which differ fundamentally from those of normal or right-way-up flying. The machine can be brought to the inverted position either by the half roll or by the half loop, and the half roll can be of the flick type or of the slow type. The pilot must be firmly strapped in with a Sutton harness or its equivalent before he can fly upside down, for if his body tends to fall away from the seat his feet will also tend to come away from the rudder bar.

AEROBATICS IN FORMATION, with streamers of coloured smoke tracing each evolution against the sky

AEROBATICS IN FORMATION, with streamers of coloured smoke tracing each evolution against the sky. For many years this was one of the most popular items of the R.A.F. Display at Hendon, Middlesex. The camera has caught the aeroplanes as they climb on the first part of a rocket loop. The leader of the formation sets the pace; the others watch him and take no notice of the ground.

When the pilot has accustomed him-self to the position, he can fly for long periods upside down. The machine can be turned and manoeuvred in the normal way, and inverted, or flat figures of eight - with the machine banked almost vertically - can be made. If, after a long period of inverted flight, the pilot dives the machine out to the normal position, he is apt to “black-out” momentarily. If he half-rolls back to the normal position this is less likely to happen. “Black-out” is the term used to describe the sensation of darkness before the eyes which has been attributed to the drawing of blood away from the head. The pilot does not lose consciousness or feel pain. All that happens is that his view is momentarily blotted out. Blacking-out can be produced by steep turns made at high speed, by pulling quickly out of a dive, or by diving from inverted to normal flight.

Fundamentally, the only remaining aerobatics are the sideslip, crazy flying and the tail slide. Tail-slides are rarely seen because they involve a certain risk the seriousness of which is not fully known at present. The tail slide can be done, however, and is occasionally seen. It is certainly a striking manoeuvre. The machine is stalled in the vertical position and held there until the speed falls off to zero. Then the machine drops back a short distance before the nose comes round with a violent jerk, so that the attitude of a vertical dive follows.

the tail slideUnless the machine is stood vertically on its tail, no tail slide will occur, but merely a stall. A steep stall, however, is a comparatively simple manoeuvre. A tail slide is difficult because the pilot has to hold the machine vertical and cling to the stick firmly, keeping it in towards him, until there occurs the drop back and the fall over to the dive attitude.

“Crazy” flying includes all kinds of sideslipping, for an essential of crazy flying is that the aeroplane is caused to move through the air at an angle to the direction in which it points. The air does not flow over the machine fore and aft, but to some extent across it. Sideslipping is the simplest instance. It is so useful that it is not generally looked upon as crazy flying, but strictly it comes under that heading.

the falling leafTo make a sideslip the pilot tips the aeroplane over on to a wing and holds it there with the rudder so that it moves sideways and forwards. There must be a certain amount of forward movement, but the amount of side movement can be adjusted by the use of the controls, and the machine can be made to drop at a small angle from the horizontal, with the wings almost vertical.

Tail wagging is another form of crazy flying, although it too has come to be regarded as a separate evolution. It is used, as is sideslipping, to reduce speed during the later stages of the landing approach. In tail wagging the pilot kicks the rudder from side to side, holding the machine more or less level in a lateral plane. A series of incipient flat turns takes place, and each one reduces the speed. In recent years the use of sideslipping and tail wagging for aiding the approach has been adversely criticized. “Rumbling” in on the engine, the machine approaching on a straight line, has become more popular.

In the early days of flying, pilots thought it essential that they should not rely upon their engines when approaching. They thought that they should so judge their approach glide that the aeroplane was in the correct position for making the landing as it passed over the boundary of the aerodrome. With the increased trustworthiness of engines and the increased use of more than one engine, the method of “rumbling” in has come to be generally accepted, and on many of the world’s leading air lines it is regularly used by the pilots. The old S bend approach, in which the machine is turned right and left as it glides in, is almost obsolete in commercial aviation. Thus the two aerobatics associated with the old form of approach - the sideslip and the tail wag - have also tended to become obsolete.

For light machines, however, both devices are useful and the sideslip, in particular, enables a landing to be made with great accuracy without engine. It is thus of value for forced-landing purposes. Crazy flying, apart from sideslipping and tail wagging, consists mainly of forcing the machine into a sideways position and holding it in that position, allowing it to be dragged along by its engine. The pilot when flying low, for instance, will turn the nose slightly up and tip the machine slightly on to one wing. With engine on, the machine can be held in this position and it can be made to skate across the aerodrome with its nose up and its wings aslant.

Crazy flying is made up of these three elements of sideslipping, tail wagging or flat turning, and flying on the bias. Innumerable combinations of these components are possible. The same is true of all the other manoeuvres. The highest form of aerobatics is the combination of classic manoeuvres in such a way as to form new and interesting patterns which demand a high degree of skill in their execution.

Probably the best known of the combined manoeuvres is the “spectacles”, an entertaining and difficult manoeuvre which consists of two loops following each other. Each loop forms, as it were, the frame round one spectacle lens. The manoeuvre is begun from the bridge piece between the two parts and the aeroplane is dived down and then over in an ordinary loop. Just before this loop is completed - while the machine is coming down on the far side of it and is still inverted - the pilot begins to flatten out in the inverted position.

full spectacles

He then takes the machine up and over again  in an inverted loop at the other side. This is possible only with a machine fitted with a fuel system which will feed the engine when inverted. Some of the Continental aerobatic experts do the spectacles close to the ground, so that the bottom part of each loop is only some fifty feet above the grass. There is, however, a modified form of the spectacles which can be used for machines not fitted with an inverted fuel feed system. It is known as the “semi-spectacles”.

In this evolution, the first loop is done in the ordinary way. Just before the aeroplane has completed it and is about to come down the other side, the machine is half rolled. This brings it right way up again and all that the pilot has to do is to dive down and complete a second normal loop. The half roll is done at the bridge piece between the two lenses of the imaginary spectacles.

There are various other ways of doing the spectacles; but the only orthodox way is to make one loop the right way up and the other inverted. The spectacles are not to be confused with the vertical figure of eight. In this there are again the two loops, but they are arranged as in the figure 8, above each other and not side by side.

Asemi-spectaclesgain it is possible to make a half roll at the intersection and so to make both loops in the right-way-up position. The more advanced method, however, calls for one loop in the inverted position. To join the two loops accurately together and to make the manoeuvre appear satisfactory, a good deal of practice is necessary and the pilot must exercise considerable judgment.

A series of slow rolls may be combined with a turn to form an interesting manoeuvre. The machine is taken round a wide radius turn, perhaps one of a diameter not much less than that of the aerodrome. While the aeroplane is turning it is rolled continuously in the same direction or alternately in one and then in the other direction.

To combine the turn with the series of rolls, so that there is no jerkiness and so that the manoeuvre gives the appearance of being a coherent whole, is a matter of extreme difficulty. If it is well executed this aerobatic indicates good piloting. Combinations of the half roll and the half loop are innumerable and are fairly well known. One form of turn, however, which is a relatively new manoeuvre and is effective to watch, is the aileron turn.

aileron turnIt is given this name because the machine is made to alter direction or to turn on the ailerons alone. They are used with the machine diving vertically. There is no resemblance in appearance or in control movements between the aileron turn and the spin, but in both manoeuvres the aeroplane turns about its fore-and-aft axis while diving vertically towards the ground.

In the aileron turn the machine is forced to twist about this axis by the application of ailerons as the master controls. In the spin, the elevator and the rudder are the master controls.

The combinations and changes which can be evolved from the major aerobatics are without number. The art of the aerobatic pilot is largely a matter of combining the different manoeuvres so as to make a coherent whole. He must arrange a complete programme in such a manner that each manoeuvre leads naturally to the next. There must be no long pauses while the pilot climbs steadily to regain height lost in a previous manoeuvre.

High engine power helps to reduce the time taken for gaining height. When the programme is well arranged and when the pilot has devoted adequate practice to it, however, he can maintain height during aerobatics with a medium-powered aeroplane, if it has inverted fuel feed arrangements. Many of the most famous aerobatic pilots of the present day use aeroplanes with relatively low-powered engines but with wing sections and fuel feed to suit them as well as possible for upside-down work.

The future of aerobatics is difficult to predict. It seems doubtful if any radically new manoeuvres will be invented. It is true the flat spin remains something which has happened accidentally but which is never done as an aerobatic, and cannot be done as an aerobatic in a correctly designed machine of normal type. It seems that it might become possible with future types of specially-designed aerobatic machines.


vertical figure of 8It is to the specially-designed machine that we must look for the future. The normal type, probably, has already done all that it can do, and only by the use of special machines can pilots hope to improve on the aerobatic displays of the past. The French pilot Adolphe Pegoud, before the war of 1914-18, did almost every aerobatic that is done today, including the bunt. He is remembered as the first aviator to fly upside down and as the first to loop. Both feats were performed in France during September 1913. It is in the permutations and combinations of aerobatics that many advances have been made and it is in this direction that future advances may be expected.

[From Part 3, published 22 March 1938]

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The Art of Aerobatics