With fairly definite plans being made for regular transoceanic air traffic, and with the far-flung net of established airways in the Americas and Europe, this appears to be an opportune time to take stock of what progress we have been able to make in air navigation. The importance of air navigation is now fully realized by the progressive airline operators, although full use of the equipment and knowledge now available has not yet been made.
The first International Congress of Transoceanic Flyers which met at Rome in May-June, 1932, emphasized the early need of a greater number of really efficient air navigators of the caliber of Admiral Coutinho of the Portuguese navy, of Del Prete, late of the Italian air force, of Harold Gatty, of Lieutenant Hegenberger, and a few others—all too few for the urgent needs of future aviation. The notable successes of the efficiently navigated aircraft contrasted with the costly failures of similar craft inefficiently navigated point a moral too obvious to be overlooked.
Since the Rome congress, General Balbo, Italian Minister of Aeronautics, has announced the projected flight of 24 seaplanes in formation from Italy to America next May via the Azores. Compare this proposed flight with the stunt flights over the Atlantic with single planes. Having mingled with the splendid officers who will lead the Italian expedition, the writer is convinced of the ability of their air navigators to conduct the formation safely on such a stupendous venture.
If in the term navigation we include blind flying, recent progress has been nothing short of revolutionary. After all, the mechanics of straight-away flying has been so standardized and simplified that the real problem of blind flying is largely that of navigating the plane in low visibility conditions. In other words, if the pilot positively knew his position, altitude, and attitude to the earth’s surface continuously, it would be scarcely more difficult to take off, fly, and land in a dense fog than in clear weather. At the same time, we get our altitude quite accurately with the altimeter, we can see at a glance what the attitude of the plane is by means of the gyro-horizon, and by the efficient use of radio and by careful dead reckoning we can, where we have the radio and other facilities, determine our position accurately in a fog. These facts, combined with the use of the rate of climb indicator, the directional gyro, and other convenient well-known panel instruments, theoretically “lick” the problem of blind flying.
For those readers who have not already learned of the momentous blind solo flights of Lieutenant Hegenberger, this knowledge will for them mark another milestone in the rapid progress of air navigation. At Wright Field in May, 1932, Lieutenant Hegenberger took off, made a short cross-country flight, and landed at the place he left without once seeing outside his plane. Not only did he accomplish a “blind solo flight,” but he did so with the standard equipment of an army plane and with the mental hazard of having to pass close to a tall chimney when coming in to land.
Hegenberger’s performance does not presage an immediate and complete solution of blind flying, yet it does point to the urgent need of the rapid extension of aids to navigation, and most important, to the urgent need for more Hegenbergers. To produce such skill requires the patient and extended training of highly intelligent air navigators.
When we pass from blind flying, the first need of the air navigator is the ability to do efficient map reading and accurate dead reckoning. The sectional air maps in process of manufacture for the Department of Commerce will improve the ability to navigate the United States by maps. For accurate dead reckoning, the first essential is the ability to steer a straight course. This is difficult to do with any but the most expensive magnetic compasses, yet a moderate-priced compass supplemented by the directional gyro makes it possible to hold the course to within one degree under ordinary conditions. Next, the biggest problem is that of determining and applying the wind drift correction. From the experience of the writer gained over several years of work, and several months concentrated tests, the Gatty ground speed and drift indicator (see Fig. 3 and p. 404) appears to be the present most practical means for measuring ground speed and drift. This device measures the ground speed without changing course, but suffers from the fact that the ground speed measured depends directly on the accuracy of the observed altitude above the ground.
For further conveniences in accomplishing dead reckoning, the air navigator has recourse to the universal plotting sheet, the aircraft plotter (Fig. 2), and the dead reckoner developed by the Hydrographic Office within the past year. Of these, perhaps the most helpful is the dead reckoner, a sheet to fit the average lap, on which are printed ground speed, wind drift tables off-course correction tables, a course converter, and the Phillips flight calculator (see page 403). The latter was adopted by the generous permission of Phillips Petroleum Corporation from the Phillips flight calculator, so popular with many aviators. This calculator is merely a circular slide rule especially designed for the convenience of the air navigator.
When we move from dead reckoning to radio as applied to navigation, we find a subject requiring considerable training and study to master, but which thereafter the comparative notice can use to advantage in many ways. Radio phone not only gives weather conditions and other information of vital importance, but also directional beams to hold a plane on it course, to establish its position, and for landing blind.
There is a natural tendency, perhaps partly due to mental laziness, to pin complete faith to any method which once proves of practical value. Some will say, “dead reckoning is all I need.” Another will say “radio will replace other methods of navigation.” I have heard successful navigators knock radio and say “celestial navigation and dead reckoning will do the trick.”
The truth is that we need all means at our disposal for the safe navigation of aircraft. In fact, everything we have in stock at present is scarcely enough to bring a plane through under all conditions. At present in the United States the available information and equipment are far ahead of the accomplishments of the average air navigator. The reason is that our air navigators as a rule lack the necessary training. This lack of training is the more noticeable when we compare the methods in vogue in Germany, for instance, with the amount of training required in this country. In Germany a four-year course including sea training is required of transport air navigators. No such requirements are made in the United States.
It can be said, however, that more and more encouragement is being offered to efficient air navigators in this country, and that the Department of Commerce gives a special license to those who are especially qualified. Furthermore, it is readily seen that there is not enough competition in the practical navigator class due to the lack of sufficiently skilled men in this science.
The writer has spent many months studying celestial air navigation and for that reason might see more advantages in it than are warranted. Making reasonable allowances for this natural predilection, it is clear that more strides are being made in this branch than any except perhaps radio, and that in its use it is taking on more of a practical nature, and less of theory. For example, methods are already available in the star altitude curves and in the precomputed altitude method whereby the determination of position resolves itself almost entirely to the observation of the altitude and time. The one remaining weak link in celestial navigation is the lack of an entirely suitable sextant (see Fig. 1). In the writer’s opinion, the best available type is the Bureau of Standards’ aircraft sextant. It appears to have the greatest number of advantages and fewest disadvantages.
An important contribution by the Navy Department is being made in the preparation of the Air Almanac for 1933. This publication will replace the Nautical Almanac for the airman’s use because it is especially designed for the convenience of the practical air navigator. It is further predicated that it will be preferred by most marine navigators over the present Nautical Almanac.
An interesting method for determining position by celestial navigation is now in vogue in France. I refer to special maps by Louis Kahn of Paris on which distances may be measured fairly accurately by means of a series of scales, and on which the declinations of heavenly bodies are recorded. The basic principle of celestial navigation is that the observer’s position is on a circle with the center at the subsolar or substellar point of the observed body and with a radius equal to the zenith distance. To say this another way, a line from heavenly body to the center of the earth determines the “geographical position” or substellar position of the body: the altitude subtracted from 90 is the distance of the observer from this substellar position. The substellar position is readily determined on the earth by substituting latitude for the declination and longitude for the body’s hour angle, and an arc struck on the chart with this position as the center and with a radius equal to the zenith distance gives at once, and directly on the map, the required circle of position.
The French claim sufficient accuracy, and if this is borne out, the method will undoubtedly prove popular. Harold Gatty is convinced that it is entirely practical in use. It is interesting to note that this general idea was used on the NC-4 flight in 1919. The necessary chart was designed by Dr. G. W. Littlehales, of the U.S. Hydrographic Office, and the method described in the Naval Institute Proceedings for March, 1918. On seeing the idea taken up again someone remarked, “there is nothing new under the sun.”
To sum up, the need for deter methods and equipment for air navigation is already urgent; new and efficient equipment and methods (except an entirely suitable sextant) together with adequate information are already available; while the weak link remains the lack of skilled air navigators in sufficient numbers.