Air Tactics And Aircraft Design

Refinement in design of aircraft has reached a point where the possibilities of important improvements are diminishing. Retracted landing gears, internally braced structures, and careful streamlining have developed a very clean general form. In the last year, developments in the cowling and cooling of aircraft engines have greatly reduced the drag of the power plant. There are still opportunities for aerodynamic improvements, but the designer will find his greatest opportunity in the field of design for tactical application.

Recent years have produced a profound change in tactical and strategic conceptions for aircraft. There has come an appreciation of the fact that enemy aircraft are not the primary objectives. The primary objectives are on the surface. The real measure of aircraft’s effectiveness lies, then, in its striking power against surface objectives. Modern design recognizes this and tends toward increased bomb loads and gun power.

To the layman, warfare involves opposing battle lines at grips with each other, and the outcome, to the lay mind, is the result of the defeat of one by the other. Carrying this thought to the extreme, one might imagine the issues of a war being determined by a fight between the heavyweight champions of the countries concerned. The military man knows that the real objective is to destroy the will to fight of the nation as a whole. This may come about as the result of the defeat of one of the armies, but since forces are usually fairly well-matched, the final result more often comes as a result of siege or blockade. In other words, the will to fight of the populace is usually destroyed by indirect means. It is right here that the capacity of aircraft may produce a profound change in the strategic conceptions. For one thing, aircraft are able to operate in three dimensions. They have enormous velocities, and are able to employ speed and deception to such a degree that there is no real opposition. This means that in the war of the future, aircraft will strike directly at industrial and military centers behind the lines. The possibilities of effective defense are so remote, while those of strong offense are so great, that modern aircraft design is leaning almost entirely toward the development of offensive power.

Parenthetically, it is interesting to speculate upon the influence of the foregoing facts upon a nation’s willingness to go to war. Realization on the part of the people of a nation of the fact that they will be the targets of the enemy’s attack may possibly prove a profound deterrent. It seems likely that peoples will only expose themselves to these hazards under real stress.

To the military man, it may be interesting to study the influence of these strategic and tactical conceptions on modern aircraft design. Any study of this subject involves some knowledge of the controlling characteristics of aircraft. These are, of course, well known to many, but are not so clear to others. At the risk of repetition, we will review them briefly here.

We may roughly divide their characteristics into two categories: (1) performance, and (2) striking power. The performance characteristics of primary interest are speed, climb, endurance, maneuverability, and stalling speed. Superior speed is important, since it gives the pilot ability to initiate or break off an action. Since the altitude advantage is one of the outstanding tactical advantages in individual combat, its importance is well known. In an attack, the altitude advantage may enable the attackers to attain their objective unmolested. Maneuverability is of obvious importance in combat. Landing speed is a factor whose value is well known in aeronautics, but not so well appreciated by the layman.

The excellence of aerodynamic design may be measured by “speed range,” that is, the spread between the low speed and the top speed of aircraft. The low speed of the airplane is a function, among other things, of the wing loading, that is, the ratio of the gross weight of the airplane to the wing area. This is measured in pounds per square foot. For a given speed range, the top speed will naturally be fixed by the low speed. There is, therefore, great pressure to increase the top speed at the expense of the low speed. This is accomplished by reducing the total wing area, and thus the drag of the airplane. Manifestly, there are limits to this procedure which must be considered.

The minimum speed of an airplane strongly influences its landing and takeoff characteristics. On the smooth, prepared fields, high minimum speeds are possible. On rough fields, rough water, or on the decks of aircraft carriers, lower minimum speeds must prevail. In time of war, most aircraft will be operating from poor landing and take-off areas. It is of importance, then, that in peace time we do not lose sight of the war-time operating conditions, since aircraft suitable for peace time might be useless in time of war.

In the last year, two important developments have strongly affected the performance of aircraft. The introduction of flaps on wings has materially reduced the landing speed for a given normal wing loading. The introduction of controllable angle propellers has improved the take-off characteristics by about one-third. A controllable angle propeller performs a function similar to that of a gear shift in an automobile. Both of these developments have influenced speed by raising the practical minimum speeds for prepared landing fields.

Referring now to the striking capacity of aircraft, we find two weapons, the machine gun and the bomb. Machine guns are of the fixed type, firing forward, and of the flexible, or free, type covering other angles. The airplane must be maneuvered to bring the fixed gun into use. Maneuvering the airplane disturbs the employment of the free gun. Bombs may be dropped from high altitudes in approximately horizontal flight, or from a low altitude from the end of a high speed dive. The number and arrangement of weapons depend upon the type of aircraft in which they are to be employed.

We are interested in four basic types of military airplane: (1) pursuit; (2) observation; (3) attack; (4) bombardment. Each of these airplanes can be used in a limited way on the missions of the others, but we will want to look into their primary purposes.

The pursuit planes of the World War were originally single-seaters equipped with a fixed gun firing forward, usually through the propeller. Performance was a fundamental requirement, since their primary objective was enemy aircraft. While on the tactical offensive against enemy aircraft, they were on the strategic defensive, and we may generally classify pursuit airplanes having gun power and limited bomb carrying capacity as defensive aircraft- Pursuit airplanes can carry a limited number of bombs without impairing their efficiency as pursuit aircraft. This weight of bombs is so limited that a pure pursuit type cannot take the offensive against major surface objectives. It can be used in an attack on minor objectives and against personnel where both guns and bombs are , used. However, a single-seater carrying a heavy bomb load can be used effectively under certain conditions.

This type is effective where no important enemy opposition is to be expected, or where superior speed and ceiling enable it to avoid enemy pursuit. It loses some of its effectiveness, however, when intercepted by enemy pursuit. If attacked, the single-seater bomber, having no rear gun protection, must maneuver to defend itself. In doing so, it is diverted from its surface objective quite as well as if it had been shot down. Since the bomb load has affected the performance of the single-seater as a pursuit airplane, it will engage under a handicap even after it has dropped its bomb. The employment of this type of airplane has involved a lot of discussion. The proponents of the type point out that the chances of its being intercepted and engaged are remote, and the type will have sufficient performance superiority to let it bring home its striking power. Opponents consider it a single-seater pursuit whose primary functions have been impaired by the addition of a bomb load. There is, of course, plenty of room for argument here, and plenty has been indulged in. These factors have caused a division of the single- seater pursuit into two classes, the so- called “jockey” type, of maximum performance, carrying guns only, and the light bomber type, with impaired performance, carrying guns and heavy bombs.

One answer to the criticism of the single- seater bomber is to make it a two-seater with an additional free gun for protection. Aircraft of this type will be employed in formation against surface objectives, and, cruising in company, will use their free guns for mutual support. In general, the margin of performance between the single- seater dive bomber and the two-seater dive bomber is small. There is a certain amount of opinion, therefore, to the effect that all dive bombers of heavy loads should be two-seaters. Another way of expressing this is that any heavy bomb is entitled to a free gun and gunner to protect it. A single-seater pursuit attacking a formation of two-seaters will meet with strenuous resistance, and the two-seaters can be expected to go through to their objective with reasonable success.

Clearly, our two-seater bomber can be employed on observation missions. With a radio set and extra fuel substituted for the heavy bomb load, it becomes an excellent scout. This results in the two-seater scout bomber coming into general use today. In fact, it can be said without fear of contradiction that a two-seater scout which cannot also employ a heavy bomb is obsolete.

Toward the end of the World War, when aircraft were being used on other than combat missions, it was found that the rear gun of a two-seater greatly increased its defensive effectiveness against single-seaters. This brought forth the idea of the two-seater pursuit. The margin of performance between contemporary single- seaters and two-seaters has never been very high. There are those who claim that the margin is not of sufficient importance to warrant the retention of the single-seater. They point out that the superior gun power of the two-seater more than outweighs the advantages of the performance of the single-seaters. Proponents of the single-seater point out that the fixed guns of the two-seater are useless in individual combat unless the airplane is maneuvered. When this happens, the usefulness of the free gun is greatly impaired, so that it, with its passenger, become only dead weight. Single-seaters vs. two-seater pursuits have furnished many wardroom arguments and will probably continue to furnish them.

It is possible to build a two-seater scout bomber whose performance as a two- seater fighter will not be materially impaired. By incorporating the extra weight and drag incident to the bomb or extra fuel load in detachable equipment, the airplane can be changed into a very effective two-seater pursuit with a lighter fuel load and its normal guns and ammunition. In other words, one airplane can perform these three functions quite well.

Here, again, there is plenty of room for argument. There are those who insist that any attempt to perform multiple functions with one airplane will impair the performance of any one function as a primary function. Proponents will point out that no country can afford to own aircraft capable of performing special functions only. The cost would be prohibitive and the tactical employment of these types extremely complicated. They are willing to sacrifice some performance for tactical flexibility and economy. There is much to be said in favor of considering the two-seater as a fighter-scout-bomber type.

This type merges naturally into the attack type designed primarily for action against surface objectives on land. Contemporary attack airplanes are two-seaters having the maximum number of machine guns forward, for use against troops, and carrying the maximum number of small bombs for the same purpose. They differ from the dive bombing type in that the large bomb is not now considered important.

By bombardment we usually mean the horizontal bomber. Performance is important so far as it aids in mobility and defense against enemy pursuit. Ceiling is important as protection against anti-aircraft gunfire. In their present form, these ships are multi-place, designed to carry the maximum bomb load and the maximum fuel load, with a machine gun protection which will insure adequate defense against enemy attack. Flexible guns are mounted in wind-proof turrets designed to cover all angles of approach. From this point of view, multiple engine installation is most important. In some designs, multi-power plants are dictated by the size of the airplane and the limitations of the engines, but in others they are deliberately installed to permit covering all angles adequately, and particularly to give forward protection without maneuvering. The seagoing counterpart of the landplane bombardment is classified under the heading of “Patrol.” This name is a carry-over from the war when the aircraft were used primarily in patrolling against submarines. As time progresses and a better appreciation is had of the importance of a striking force, Navy patrol plane design is being more strongly influenced by armament.

The increased importance of this factor has served to focus attention on the importance of the potentialities of patrol in controlling sea lanes. Aircraft of this type, of sufficient size to be habitable and largely self-sustaining, can be used effectively over wide areas. The factor of size is now being recognized as one of major importance. Until recently, it was more or less generally accepted that beyond a certain limited gross weight of the order of 40,000 pounds, the useful load would decrease with size. Recent Clipper ships have disproved this theory. The advent of the controllable angle propeller, combined with improvement in power plants, and in aerodynamic design through the introduction of flaps, has revolutionized design ideas. It is now quite clear that the useful load increases rapidly with increase in gross weight. This means, commercially, that larger airplanes become economically' self- sustaining. In the military field, it means that much longer ranges, with much greater bomb loads, will soon be available. This opens up a completely new conception. If it is true that design of small aircraft is rapidly becoming static, it is equally true that design in the larger sizes is in a state of flux.

In Europe, particular attention is being paid to development of the attack and bombardment types. Recent months have seen the development of multi-engined aircraft of enormous gun power and heavy bomb load. These are primarily designed for attack deep into enemy territory upon industrial and military centers. Advocates of the type claim that it has such capacity as to enable it to control an enemy territory without actually occupying it.

From the carrier point of view, the maintenance of a minimum number of types is of paramount importance. Tactical situations are ever changing. It is difficult enough to assign the proper numbers of each different type to each carrier to meet the estimated situations. It is even more difficult to dispose the different types on the carriers as to have them ready at the proper time. It appears, then, that the development of a two-seater, fighter- scout-bomber type is of paramount importance, and the ultimate objective may well be the concentration of this type alone upon carriers. This will involve the sacrifice of some performance characteristics, but the tendency seems to be in this direction because of the advantages of flexibility and economy when the primary mission of offensive against surface craft is given full consideration. This meaning is further fortified by the fact that the chances of interception by enemy pursuit of superior performance are remote.

In the foregoing study, we have considered only the elements of an interesting problem. It is manifest that there are innumerable details of design of great interest. They involve the power output and dependability of the engines, the distribution of the useful load between fuel and armament, the distribution of the armament and other equipment for maximum effectiveness, and many other features of design. The investment in a single experimental aircraft is small compared to the investment in a single surface vessel. This permits a very active experimental development with keen competition. As a result, changes and improvements come rapidly.

As time goes on, the chances of striking technical improvement in smaller airplanes diminish. Strategic and tactical conceptions are in process of change. As we have seen, these greatly influence the elements of aircraft design. We may therefore look for rapid design changes in the future. The greatest opportunities lie in the field of large aircraft.