Discussion

Air Mapping

 

(See pp. 777 and 793, July, 1927, Proceedings.)

 

Lieutenant Leonard Doughty, Jr., U. S. Navy.—A great deal of nonsense has been published recently on the subject of air mapping. The accounts of the Alaska survey in the newspapers and the Scientific American, and the present article by Lieutenant Boyden give the casual reader the impression that merely by taking a string of air pictures and pasting them together there is produced a map, “so exact as to satisfy the rigid requirements of civil engineers,” to quote Lieutenant Boyden’s article.

 

Unfortunately such is not the case. These patchwork affairs undoubtedly have their uses, and for many purposes may be adequate, even to a civil engineer. However, a degree of accuracy which might render a map suitable for planning a cow-path, for instance, might leave it practically useless for a water power project, or as an accurate survey or for directing artillery fire. In fact these mosaics cannot be called maps at all, in the engineering sense of the word.

 

In the case of hydrographic surveys, where the coast line is principally what is desired, the problem is considerably simplified, the coast line lying in a horizontal plane, and accuracy being important in only one direction, the direction of the coast line. For this problem the method described in Lieutenant Ramsey’s article is adequate. This is true, however, only because of the special nature of the case, and not, as he implies in his last paragraph, because of any lack of accuracy in “more elaborate methods.” For a land survey suitable for a civil or a military engineer more elaborate methods are indispensable.

 

A great deal of work has been done on this problem, especially in Germany. The

developments there were described by H. Luscher in Engineering (British), 123, pp. 63-65, January 21, and pp. 185-189, February 18, 1927. Notable developments have also been made by Brock and Weymouth of Philadelphia, whose process was described at length in the March, 1926, number of the Proceedings of the American Society of Civil Engineers. By this method air maps are made which are actually more accurate than the ordinary field survey. The method is extremely intricate and ingenious, and it is surprising to find it ignored in a discussion of this subject.

 

Even in constructing the ordinary mosaic map it is difficult to see how satisfactory results can be obtained without using some such process as that described in "Aerial Surveying by Rapid Methods” by Jones and Griffiths. In this method elastic bands are used to equalize the errors and distribute them evenly. Without some such method, errors are cumulative, until a point is reached where two adjacent pictures cannot be matched at all.

 

To make an accurate map the errors are eliminated as follows:

 

Errors due to lens and shutter. These are instrumental errors which can be rendered negligible by improved instruments.

 

Errors due to shrinkage and stretching of film or paper. These errors are eliminated entirely by using glass plates for both negative and positive. Their use for positives also facilitates rephotographing, illuminating, and projecting in the stereopticon.

 

Errors due to tilt. Even a small tilt, which may be ignored in a hydrographic survey, would destroy the accuracy of a land survey. The direction and amplitude of the tilt are computed by means of control points on the ground, whose position and elevation are determined by survey. The plate is then rephotographed in a frame which holds it at such an angle as to produce a rectified picture.

 

Errors due to variation in height of plane. These errors must be corrected even if small, because they affect the accuracy of subsequent steps. The variation in height is obtained by using the control points on the ground, and is corrected by re-photographing, which enlarges or diminishes the picture to the proper size.

Errors due to difference of elevation of ground. These can be corrected only by first drawing the contour lines. Even though contour lines are not required in the finished map this process must be followed to produce an accurate map. The stereoscopic sketching method described by Lieutenant Boyden produces merely an impressionistic picture, and is of course unsuitable for this purpose, however valuable it may be for other purposes. Various methods have been devised for drawing the contour lines accurately, all based on the fact that all points at the same level have the same difference in parallax in the two overlapping pictures, this parallax being measured in the direction of flight, from one of the control points. In the Brock method two overlapping plates are viewed stereoscopically, and cross hairs in the two viewing glasses appear in depth in the stereoscopic image. By moving the frame supporting the eye piece around, a point on the ground may be found at which the intersection of the cross hairs appears to lie on the surface of the ground. A series of such points are located, and joined by a pencilled line, which is an accurate contour line. Distance between plates is varied by a micrometer, an amount proportional to the difference in parallax of successive levels, and thus all the contour lines are drawn.

 

After all the contour lines are drawn, there remains the problem of eliminating the errors due to difference in level. Every point on the picture is displaced radially from the center an amount proportional to its elevation and its distance from the center. To correct this distortion, the picture is projected onto a screen of tracing paper by means of a stereopticon in such a way that the scale of the projection can be varied, the center remaining the same. The scale is adjusted to correspond to a certain level, and that particular contour line is traced on the paper, together with all adjacent topographical details, such as roads, buildings, etc. Then the scale of projection is varied to correspond to the next contour line, which is then traced, until the entire plate is covered.

The tracing thus produced is an accurate engineering survey, and any number of adjacent ones may be united to cover any area. Inasmuch as such improved methods, which are more rapid, economical and accurate than ordinary surveying, are in existence, it is hard to see why they are not more widely adopted.

 

Flight Training of Student Naval Aviators

(See page 764, July, 1927, Proceedings.)

 

Lieutenant Commander Harold E. Snow, U. S. Navy.—My views in the following discussion are based largely on my observations as a student at Pensacola from August, 1926, to December, 1926, and my Flight Record Book shows but twelve hours, thirty-five minutes solo in N9’s. Incidentally I was most fortunate in having as my instructor—Lieutenant Studley.

 

Since, "a little learning is a dangerous thing,” I will confine my remarks to the earlier stages of primary training in sea planes.

 

The article under discussion covers the established procedure and routine training at Pensacola completely. Lieutenant Stud- ley, whose student days were long ago, does not give much space to the reactions on the part of the student during his first two or three weeks at the air station, which have an important bearing, psychologically, on his early flights. At least, this is the student’s viewpoint of the early stages of flight training. From the moment that an officer arrives in Pensacola, he finds himself in a strange environment. He experiences new joys, disappointments, thrills, all in his day’s work. The uncertainties and hazards of the game produce in him a feeling of tenseness and exhilaration. His relative values rapidly change, and he has a new outlook on life. A "war-time psychology” as distinguished from a “peace-time psychology” is in the air at Pensacola. This nervous excitement felt by the student of little or no previous flying experience normally grows less as time goes on. He is afflicted at first with air-shyness, a perfectly natural state of affairs. A real taste for flying has to be cultivated, notwithstanding much that has been said to the contrary by air enthusiasts. If a student feels perfectly natural in his first tail-spin, there is probably something wrong with him.

I have dwelt on the initial impressions of Pensacola and the flying game because I consider them of some importance. The fact that all this newness has to be assimilated, leads up to the question as to whether two hours of familiarization hops given a novice, place him on a par with another student who has had twenty to thirty hours in the air previous to his arrival in Pensacola.

 

Lieutenant Studley states that an officer with no flying experience has no appreciable disadvantage. Nevertheless, the enlisted men detailed from the air squadrons, that take the aviation pilot course, average a high percentage of successful graduates; and older officers are now given preliminary training at Hampton Roads, or elsewhere, before ordering them to Pensacola, as are Naval Academy graduates beginning with the class of 1926.

 

It seems to me that the “feel of the air” is not a heaven-sent gift to the majority of students, but is something that must be developed. The man of some air experience has a head start in learning to fly.

 

Before I departed for Pensacola, one of the pioneers in aviation gave me advice to the effect that if lie were in my status, lie would go to a Curtis Flying School, learn how to fly, keep it dark, and then go to Pensacola. So there is a difference of opinion as to methods of preparation for Pensacola.

 

Undoubtedly some fliers are born and not made, as are some sailormen. But we have many distinguished naval officers who had no heritage of the sea; and, as aviation is in its veriest infancy, there must be many aviators who never dreamed that their careers would be in the air. They went into aviation for a dozen different reasons, without any call of the blood; and today, after the necessary preliminary training, augmented by many flight hours, are doing splendid work as aviators. This condition is still more in evidence in the older officers performing duties in connection with aviation, who had many years at sea before turning their thoughts to flying.

 

A story that can be vouched for is told relative to the training of pilots during the war. In a certain class of students at Cape May, New Jersey, every candidate for flying honors completed the course and qualified as an aviator—with but a single exception. The particular man that did not pass was looked upon as a “freak.” Surely all of these men were not born fliers.

 

Under present day methods, it appears as though some promising talent is lost through intensive weeding-out early in the course. Even a born flier may be stunted in his youth if he has a bad fifteen minutes when his ten hour check for solo is given.

I wish to offer a suggestion or two relative to the ten-hour check for solo. From a student’s point of view it appears practicable, and in a larger sense, it is more in accordance with “Courts and Boards” procedure as conducted elsewhere in the service, than is the present system.

 

To begin with, a student, after finishing ten hours dual instruction, should be checked by two officers, irrespective of his rating by his own instructor, or of his rating by his first check instructor. Upon the completion of his first check hop, the check instructor should leave the plane agreeably—if noncommittally—without further word to the student. The practice of giving the student a lecture or “friendly talk” at this time serves no useful purpose in nine cases out of ten. The student’s mind is not in a receptive condition, a lengthy talk produces a mental blur on the part of the student, and very likely, if the student’s faults were “skids on the right turns” and "slips on left turns,” he would quote his instructor the reverse a few minutes later. The check instructor, following the hop, should assign marks to the student, in taxiing, take-offs, turns, spirals, landings, etc., but he should drop this card in a box: “a secret ballot.”

 

Twenty minutes later, the student should be taken on his second check hop, and the second check flight instructor, in complete and voluntary ignorance of what has gone before, should likewise make a secret ballot. The vote of the student’s inspector, and of each check instructor should be given equal weight, and the votes should be gone over by the senior officer attached to the Flight School. One vote “to retain” should be sufficient for the student to continue the course. It is believed that this scheme would tend to do away with a very real evil. There exists in the student’s mind the feeling that failure on a first check always spells defeat.

 

Under the present system an instructor will not tell his own student if he has recommended him for “drop.” It is acknowledged to be bad for the morale of the student. But a failure on a first check hop is most emphatically known to a student by a “thumbs down’’ given him by a check instructor. Immediately there is a tremendously bad effect on the morale of the student—a big handicap under which he starts his second check flight.

 

Again, under the present system, consider how a second check flight instructor possibly feels about a student’s ability after a first recommendation to “drop.” Being human, it is easier to agree with the first instructor, especially when a subsequent crack up by the student might in some mysterious way be laid at the door of No. 2 check, should he pass the student.

 

Instruction in flying cannot be absolutely standardized, and after a student has once soloed, further formal checks such as the above seem unnecessary.

There are other qualifications besides inherent flying ability that determine whether a candidate will pass successfully through Pensacola.

 

One day in the classroom at the ground school, there was a general discussion as to why so many students were failing to qualify. There were many reasons advanced and the discussion provided much entertainment. At last, the instructor asked a student how much he (the student) believed personality to be a factor in going successfully through the course. The student answered that he believed “it should have nothing to do with it.” The instructor, in turn replied, “It has everything to do with it."

 

With that in mind, it might be well to mention that flight instructors should be chosen for their ability as instructors, their broader view of aviation and its needs, and their personality. They leave an indelible impression on the student whether he is dropped or retained. Some flight instructors have no place in the scheme of things at Pensacola, cither by ability or choice. If personality makes one fly, there are many instructing, that should be wearing their wings on a much higher plane than an earthly one. Others may be “hardboiled,” but are eminently fair, and are highly respected. If the best interests of aviation are to be served, all should be handpicked.

 

There are several features of the course that were discussed by students, that I will merely mention in passing.

 

1. Bias the psychiatric test as now conducted in additional to the physical examination, any great value? It is all mysterious to the person being examined and what it accomplishes is by no means clear.

 

2. Has the practice of “thumbs up” and “thumbs down” a real place in the course? Does not the scoreboard savor a little of hostility between instructor and student?

 

3. The minds of some instructors seem to be overburdened with “percentages.” To make this clear, I will state that before I took my first hop, I was told by “higher authority,” how many spins, how many crack ups, how many serious accidents, and how many graduates there would be in the class. It would be refreshing if all parties would try the experiment of forgetting about percentages.

 

4. At the risk of dwelling too much on “check hops” I am going to make a comparison between two check instructors “A” and “B.” I go up with “A,” and from start to finish it is clear what he demands of me. I concentrate on flying and pass the check. At a later check I draw “B.” From the time the plane takes off until the final taxi to the beach, there is a lack of harmony— two minds are trying to operate the plane, and flying suffers. I may feel that I flew fairly well—I find out that I didn’t do what was expected of me. Students and instructors sometimes fail to speak the same language. Is the student always at fault.

 

5. “Manner in emergencies”—if not up to the standard, will immediately disqualify a student irrespective of brilliant airwork. This is as it should be. But nearly all emergencies may be simulated. Why not drill and drill upon this phase of flying until it becomes instinctive? Go over the same emergencies enough times to impress vividly on the student’s mind what to do. It takes a year or two to train an officer of the deck to stand a good watch and be ready for emergencies; and “manner in emergencies” may become second nature if plenty of emergencies are given.

 

6. It is agreed that one of the most vital needs of the service is more aviators. Certain high standards have to be met at Pensacola to turn out the finished product.

Nevertheless, if the attitude toward the newcomer were, “You are welcome, and you are not going to get the boot. You are here now—we’ve got you, and we are going to teach you how to fly if it is humanly possible”—if that were the attitude, maybe it would be a step in the right direction.