CHAPTER IX

HISTORY OF LAUNCHING APPARATUS AND FIELD-TRIALS OF AERODROMES 4, 5 AND 6

LAUNCHING APPARATUS

I have elsewhere mentioned that the difficulties of launching even a very small model aerodrome are considerable. Early experiments were tried with an apparatus something like a gigantic cross-bow, and in later years with various forms of pendulum, all of which latter brought out the inherent theoretical defect of the movement of rotation of the aerodrome, and were otherwise practically inefficient.

A device, consisting of two pendulums, one behind the other, connected by a rigid rod, from which the aerodrome could be suspended and cast off without rotation, was at one time considered, but abandoned. Experiments were also made with several forms of railroad, upon which the aerodrome was to run up to the moment of release, before the form of launching apparatus, which finally proved successful, was adopted.

All these had failed chiefly for two reasons; first, it was difficult to cause the aerodrome to be released just at the moment it attained sufficient speed to soar; second, the extensive surface presented to the wind by the wings of the aerodrome, made it necessary to provide means for holding the machine securely at several points up to the moment of release without danger of interfering in any way with the aerodrome when it was cast into the air. This proved a serious problem, which can be appreciated only by one who has seen such a machine in the open air, where its wings are subject to movement and distortion by the slightest breeze. The steps by which these difficulties were removed and the final type of launching apparatus perfected are recorded in the following pages in connection with the field-trials of the model aerodromes.

1892

As the end of the year 1892 approached and with it the completion of an aerodrome of large size which had to be started upon its flight in some way, the method and place of launching it pressed for decision. One thing at least seemed clear. In the present stage of experiment, it was desirable that the aerodrome should-—if it must fall-—fall into water where it would suffer little injury and be readily recovered, rather than anywhere on land, where it would almost certainly be badly damaged. [p093]

The shores of the Potomac on both banks were scrutinized for this purpose, from a point about two miles above Washington to below Chopawamsic Island, some thirty miles below the city. Several lofty and secluded positions were found, but in all these there was the danger that the aerodrome might be wrecked before reaching the water, or, turning in its course, fly inland; but more than this, it could be launched only on the rare occasions when the exact wind was blowing which the local conditions demanded.

Finally, the idea, which seems obvious enough when stated, presented itself of building a kind of house-boat, not to get up initial motion by the boat’s own velocity, but to furnish an elevated platform, which could be placed in the midst of a considerable expanse of water, if desired, under conditions which admitted of turning in the direction of the wind, as it need hardly be repeated that it was indispensable to the machine, as it is to the bird, to rise in the face of a wind, if there be any wind at all.

The house-boat in question was nothing more than a scow about 30 feet long by 12 feet wide, upon which a small house was erected, to be used for the occasional storing of the aerodromes. On account of the accidents which were certain to occur in the first attempts, it was fitted up with the means of making small repairs. On the roof of the house there was a platform upon which the operator stood when making a launch, and upon which were mounted the launching devices hereafter described.

This boat, shown in Plate 18, was completed in November, 1892.

1893

By the kindness of the Superintendent of the Coast Survey, the house-boat was towed in May, 1893, down to Chopawamsic Island, a small island near the western bank of the Potomac River, not far from the Quantico station of the Washington and Richmond Railroad Company. A map of the island and the adjacent land and water is shown in Plate 19.

The house-boat was at all times moored somewhere on the west side of the island, in the stretch of quiet water between that and the west shore of the river. The waters shown here are, with the exception of a narrow channel, very shallow, and, indeed, partly dry at low tide, so that there was no danger of an aerodrome being lost, unless its flight carried it a long distance away and over the land.

FIELD TRIALS[29]

Aerodrome No. 4, as shown in Plate 11, had a single midrod, a flying weight of 9 pounds,[30] and supporting surface, consisting of wings and tail, of 18 square feet. [p094] Its engines, with about 100 pounds pressure, developed an aggregate of 0.4 H. P., and lifted 50 per cent of the flying weight. The propellers were 60 cm. (2 feet) in diameter and 1-1/4 pitch ratio.

The aerodrome was intended to be launched by a contrivance called the “starter,” which was an inclined rod, hinged at the bottom, on the top of which the aerodrome was supported on a rod which was thrown down at the instant of flight, giving the aerodrome a slight forward impulse, with the expectation that it would get up sufficient initial speed to soar from the action of its propellers.

On November 18 the writer (L), with Dr. Barus (B) and the two mechanics (R and M), went to Quantico by an early train, and superintended with interested expectation the arrangements for this first trial in the open air of the mechanism which had now been over two years in preparation.

We met with an unexpected difficulty—that of launching the aerodrome at all, for though the wind was only a very gentle breeze, it was only by holding it down with the hands that it was possible to keep the aerodrome in position for the launch, during the few minutes which passed from the time it was placed upon the apparatus to the time of releasing it. Whether the launching device itself might be effective or not could not be ascertained, since it was found that nothing which could even be called an attempt to launch could be made except in an absolute calm; a condition of things very difficult for any one to understand who has not passed through the experience. The writer returned to Washington at the close of the day without having done anything, but having learned a great deal.

November 20. L, with B and M, came down again, and waited until 4.20, when, the breeze having fallen to almost a calm, the aerodrome was maintained in place on the launching apparatus with great difficulty, while it was repeatedly set on fire by the scattering liquid fuel. Finally it was let go, and fell close to the house-boat, the tail striking the edge of the platform. The immediate cause of failure was the defective launching apparatus, for the design of which the writer felt himself responsible.

November 24. L, with B, M, and R came down again to Quantico, but the very moderate wind proved completely prohibitory to any attempt at launching, and all returned again to Washington.

November 27. L, with B and M, came down to try a new launching apparatus, not different in principle from the preceding one, but of better construction. The morning was exceptionally calm, but the engines were found to be out of order, and precious time was spent in slight repairs which should have been made in the shop. At 3.30 p. m., when the engines were at last ready, the exceptional calm gave place to a very gentle and almost imperceptible breeze, [p095] which, nevertheless, again proved prohibitory to the launching, and with extreme disappointment the party returned to Washington, it being at last fully recognized that unless some ways were found of holding down all the extended supporting surfaces upon the launching piece, and at the same time of firmly clamping the body of the aerodrome until it could be dropped, as well as of releasing all this simultaneously at the critical instant, no attempt at launching was likely to succeed except in such an entire and perfect calm as rarely occurs. Independent of this launching difficulty, some way of protecting the fires from the wind had to be found, which was by no means easy, since an efficient protection meant an enclosure of them and a diminished influx of air, of which it was essential that there should be an unlimited supply.

December 1. L, with B, R, and M proceeded to Quantico. The same conditions presented themselves and the party returned, without effecting anything.

December 7. L, B, R, and M present; day overcast but perfectly calm. Taught by experience, we had everything ready, and a little after one o’clock the launch was made. The aerodrome fell directly into the boat, the rod of the starter having broken. It was little damaged, but in view of the injury and the rising wind, all other attempts were abandoned for the day.

December 11. Present, L, with B, R, and M. A new “starter” had been devised and brought down, but was not yet quite ready for use, and an attempt was made to employ the old one with the improvements suggested by experience, but, after two attempts to launch, the work was abandoned for the day, owing this time not to the launching apparatus, but to troubles in the engines and pumps, due probably to injuries received in the fall of the 7th, which were not detected until the time of the actual trial.

December 20. L, with B, M, and G, present; engine and aerodrome in order and everything apparently favorable. What seemed to be an almost entire calm came toward evening, yet once more the all but imperceptible breeze which prevailed was found to defeat all arrangements for holding the aerodrome to the launching ways before it was let go.

Trips to Quantico were also made on November 24, and December 1 and 21, of which no account is given as the very moderate wind which prevailed in each case precluded any attempt at launching the aerodrome.

It will be seen that eight trips were made to Quantico, and that, far from any flight having been made, not once even was the aerodrome launched at all. The principal cause for this lay in the unrecognized amount of difficulty introduced by the very smallest wind, irrespective of the unfitness of the launching apparatus to give the desired initial speed and direction.

In all these trials, the aerodrome rested on the launching apparatus, by which it was projected forward by means of a spring in such a way as not to interfere with the propellers. [p096]

Previous tests with the rubber-driven models had demonstrated the futility of all simple pendulum types of “cast off,” and likewise all the trials hitherto of a railroad form of launching apparatus, in which the aerodrome was mounted on a car, which had itself to get out of the way, were equally failures, so that when the device referred to above proved to be worthless, it seemed that almost every plan had been exhausted. There were, moreover, other difficulties, some of which have been indicated above, such as that of making the burners work properly in even a moderate wind during the very short time required for attaching the wings and so adjusting the aerodrome on the launching apparatus.

These difficulties, which, now that they have been overcome, seem difficulties no longer, but which then seemed insuperable, were all connected with the ever-present problem of weight. It would have been easy to make rigid sustaining surfaces which would not bend in the wind; to make fires which would not go out; and easy to overcome all the impediments which seem so trivial in description and were so formidable in practice, were it not that the mandate of absolute necessity forbade this being done by any contrivance which would add to the weight of an already phenomenally light construction. The difficulties of the flight as they were seen in the workshop were multiplied, then, beyond measure by the actual experiments in the field, and the year closed with a most discouraging outlook.

1894

The new year began without any essential improvement in the means already described, though a new launching apparatus had been devised by the writer, which was scarcely so much an apparatus for launching, in the ordinary sense of the word, as one of holding the aerodrome out over the water, and simply letting it drop from a height of about 25 feet, during which fall it was hoped (exact data being unobtainable in advance of experiment) that there would be time for the propellers to give the aerodrome the necessary soaring speed before reaching the water. This device consisted of an inverted tripod, which held the aerodrome comparatively steady by three bearing points, while a cross-bar of wood was added to prevent the wings from swaying before the launch. Previously, the supporting surfaces, wings and tail, had been put on only at the last minute. Now it became possible to keep them on in a gentle breeze for an indefinite time before launching.

January 9. The previous day having been spent in practicing the steps preliminary to launching, so as to avoid delay in assembling and mounting the aerodrome, the writer, with Dr. Graham Bell, went to Quantico. The day was calm, and every condition seemed favorable. The aerodrome was dropped fairly, under full steam, and it fell in a nearly horizontal position, but touched the water at a distance of only 50 or 60 feet, evidently before the necessary initial speed [p097] could be impressed on it by its engines. The conclusion should have been that by this method nothing but a practically unsuitable height would suffice to start the aerodrome in a calm, though it might perhaps be done in the face of a considerable breeze.

May 25. After a considerable interval of delay, due to the river being closed by ice and other causes, Aerodrome No. 4 was again dropped from the starter under nearly the same conditions as in the trial of January 9, and with a quite similar result, the final conclusion being that this method must be abandoned. It may be added that a vertical rudder was tried on this day.

June 12. No. 4, with an improved blast, was tried at Quantico, Mr. Goode being present. The day ended in failure from another cause, the improved blast, which worked well in the shelter of the shop, but proved useless in the field, being extinguished by the feeblest wind. At this time (in June and July) I designed a horizontal railroad with launching springs and track, underneath which ran a car which held the aerodrome firmly until the moment of automatic release. This apparatus finally proved to be the successful solution of the launching problem. The description given later, with the drawing in Plate 18, shows the after-improvements, but no specific change from that in use from the first.

About this time I also arranged for certain changes in the boilers and burners, having decided that I would not go into the field without some ground for confidence not only that the aerodrome could be launched successfully, but that a steady flame could be maintained under the boilers.

October 6. No. 4, as remodelled, having a flying weight of about 14.5 pounds, a supporting surface of about 28 square feet, with a total engine power of about 0.5 H. P., and having lifted 40 per cent of its weight on the pendulum, was taken down the river for trial with the new railroad launching apparatus, and several days were spent in erecting the launching apparatus on the house-boat, and in launching “dummy” aerodromes from it for practice.

Aerodrome No. 4 then being fitted under conditions which apparently insured a good start (the center of pressure being nearly over the center of gravity, the root angle of the wing being zero, the midrod nearly horizontal, the engine working well, and with apparently ample sustaining surface) was finally successfully launched, but the hopes which were reasonably entertained proved to be unfounded. The result of this first actual trial of a “flying machine” in free air was most disconcerting, for the aerodrome, which had ‹in theory› many times the power required for horizontal flight, plunged into the water with its engines working at full speed, after a course hardly longer than that performed by the dummy. This result was at first inexplicable.

No. 4, then, did not fly at all, from some at first inscrutable cause, and it was decided to make a trial of No. 5, though it was hard to put the result of so much [p098] time, painstaking and cost to the hazard of destruction. With the experience just acquired from the trial of No. 4, the wing of No. 5 was set at an angle of about 20° with the midrod, and the tip was secured by a light cross-piece, so guyed that the wing as a whole, while set at this considerably greater angle with the rod, was stiffer than before. In addition to this, the air chamber was moved back so that the center of gravity was from 6 to 10 cm. behind the (calculated) center of pressure. These changes were made in order to insure that the front should at any rate keep up, and it did.

The aerodrome was launched successfully with the engines working under a pressure of 110 pounds of steam. The head rose continually until the mid-rod stood up at an angle of about 60°, checking all further advance. It remained in the air in a stationary position for nearly a second, and then slid ‹backward› into the water, striking on the end of the rudder and bending it. The distance flown was about 12 metres, and the time of flight 3 seconds. One of the propellers was broken short off, and the shaft was bent.

It thus became clearly evident that some cause prevented the proper balancing of the machine, which was necessary to secure even approximately the theoretically simple condition of horizontal flight. It was all-important that the angle of the front wing should be correct, but its position could not be accurately known in advance of experiment, and this experiment could only be made with the machine itself, and involved the risk of wrecking it.

These trials gave a very vivid object lesson of what had already been anticipated,[31] that the difficulties of actual flight would probably lie even more in obtaining exact balance than in the first and more obvious difficulty of obtaining the mere engine power to sustain a machine in the air. The immediate problem was to account for the totally different behavior of the two aerodromes in the two flights, under not very different conditions.

Observations of the movement of the two aerodromes through the air, as seen by the writer from the shore, seemed to show, however, that the wings did not remain in their original form, but that at the moment of launching there was a sudden flexure and distortion due to the upward pressure of the air. The time of flight was too short, and the speed too great, to be sure of just what did occur, but it seemed probable that the wings flexed under the initial pressure of the weight which came upon them at the moment of launching, and that they were in fact, while in the air, a wholly different thing from what they were an instant before, so that a very slight initial difference in the angle at which they first met the air might cause the air to strike in the one case on the top of the wings and throw the head down, and in the other case so as to throw the head up. To ascertain the extent and character of this flexure, caused, it will be observed, by [p099] the ‹weight› of the aerodrome suddenly thrown on the wings, I inverted the aerodrome and distributed a weight of dry sand equal to that of the whole machine evenly over the supporting surfaces. It was found that under the weight of the sand the extremity of the wings bent to an angle of 45° downwards (and consequently must have bent to an angle of 45° upwards in the air), a condition of affairs worse than anything that had been suspected, and seeming to demand the entire reconstruction of the wings with a strength and consequent weight for which there was no means of providing.

There had been some injuries to the machines in the trials of the 5th and 6th, and these were repaired. A new float had been made for No. 4, and a new set of larger wings for No. 5. Each of these wings had a length of 76 inches and a breadth of 25 inches, making the total surface of the two 26.4 sq. ft., while that of the tail was 13.2 sq. ft., or about 40 sq. ft. in all.

October 22. When No. 5 was finally prepared for another trial, its condition was as follows:

Flying weight 22 pounds Area of supporting surfaces (wings and tail) 40 sq. ft. Sq. ft. of surface per pound of weight 1.8[32] Engine power with 115 lbs. steam pressure 1.0 H. P.[33] Power necessary to soar 0.35 H. P. Theoretical soaring speed (plane wings at 20°) 24 ft. per sec. Previous lift on pendulum 40 per cent of flying weight

October 25. The aerodromes having been taken to Quantico on October 23, and satisfactory experiments made with dummies in order to test the launching apparatus, the house-boat was carried out into midstream and moored.

Aerodrome No. 4 was launched in the face of a wind of about 1100 feet per minute. The midrod was at a very small inclination with the horizontal, about 3°. The angle (α) of the chord of the curved wing measured at the rod, where it was rigidly held, was 15°. The adjustment was such as to bring the ‹CG› immediately under the ‹CP›, without any allowance for the fact that the line of propeller thrust was below the ‹CP›.[34] The aerodrome under these conditions was launched with the head high. It made a real, though brief, flight of about 130 feet in 4-1/2 seconds, when it swung abruptly round through 90°, and, losing headway, sank continuously, finally falling backward into the water.

October 27. Aerodrome No. 4, having been repaired and guyed with wires from the wings to vertical guy-posts beneath, was launched again, but one of the [p100] guy-wires caught on the launching car, and threw the aerodrome immediately into the water with but little damage.

On the same day No. 5 was launched. The theoretical ‹CP›−‹CG› was nominally 0, but, for the reasons stated in the footnote on p. 99, was really something positive, that is to say, the ‹CP› was really somewhat in advance of the ‹CG›; inclination of midrod less than α (=20°). The aerodrome under these circumstances, while keeping its head up, at first fell rapidly, yet seemed about to rise just as it struck the water, conveying the idea that if the launching had been made with a greater initial velocity it would have risen and cleared the water. The wings visibly pocketed, however, and it was clear that some better disposition must still be made for them. The flight was 3-1/2 seconds.

No. 5 was tried again on the same day with larger wings, whose area was 40 square feet. These wings, though stiffer, pocketed a little, α=20° as before. It flew rapidly, and at first horizontally, to a distance of 100 feet or more against a five-mile breeze. It then turned abruptly round through 180°, at first falling (from loss of headway), then distinctly rising, and at the same time throwing its head up until it reached an angle of nearly 60° with the vertical, when it fell backward after a flight of between 6 and 7 seconds. The wings were evidently not yet strong enough to resist flexure.

November 21. No. 5, in nearly the same condition as before. Two extra springs had been placed on the launching car, in order to give the aerodrome a greater initial velocity than before. Everything appeared favorable, but as it left the launching track a piece flew out of the port propeller, in spite of which the aerodrome, after dropping 5 feet, rose bodily at an angle of 45° and fell backward into the water (time, 5 seconds).

Another trial was made the same day with the same aerodrome, under similar conditions, except that the angle of inclination (α) was reduced to 7°. It now, with all the other circumstances of launching like those immediately before, behaved entirely differently, plunging head downward into the water at a distance of 30 feet. Once more it was shown beyond dispute that the wings must somehow be made even stiffer.

December 8. Another trial was undertaken with No. 5, the ‹CG› being 10 cm. in front of the ‹CP› at rest. The root angle of the wings was 18°, tip angle 27°, elevation of midrod 1 in 24. The other changes made since the previous trial consisted chiefly in the increased weight due to the longer and stronger frames and shafts that were made to carry 100 cm. propellers. The flight obtained was so short that it was as unsatisfactory as before.

The aerodrome rose in the air after leaving the launching apparatus, and then slid back into the water in the plane of its own wings. On the first trial, it struck the boat, and was slightly injured; on the second, with root angle of [p101] wings 10°, tip angle 20°, the flight partook of the same character, but the machine struck the water clear of the boat.

The fact that with the ‹CG› 10 cm. in advance of the calculated ‹CP› the aerodrome steadily rose in front, seems to indicate that the rule used at that time for calculating the ‹CP› (see Chapter II) was not very accurate. This rule was based upon the assumption that the tail, having an area equal to one-third the entire sustaining surface, supported one-third the total weight (expressed by the formula ‹CP› = (2‹CP›_{wm} + ‹CP›_{tm})/3, where ‹CP›_{wm} and ‹CP›_{tm} represent respectively the ‹CP› of the wings and tail in motion), and that the ‹CP› of each surface was one-fifth its width in front of the center of figure.

December 12. Four days later, the tail had been moved back 21 cm., thus carrying the ‹CG› back 7 cm., but the vertical rudder (weighing 105 grammes), for which there was now no room, was taken off, which in a measure counteracted this change.

A trial was then made with the wings set at an initial angle of 8° at the root and 20° at the tip. The aerodrome was released with the engines working under a steam pressure of 90 pounds, and soared off horizontally for some distance, when suddenly it swerved to the right as though something on that side had given out, and turning quite through 180° headed toward the boat, striking the water about 76 feet away. The time of the flight was 4 seconds.

It was found upon the recovery of the machine that one of the propellers had been twisted through 90°, so that the two were no longer symmetrical. The turning may have been due to this twist or to unequal influence of the wind upon the two wings; for when I applied the sand test to the wings after returning them to Washington, it was found that they deflected so much that the grains would not lie upon them, which, to a great extent, explains the failure to secure a better flight.

Thus the end of another year had been reached, and what might be called a real flight had not yet been secured. The only progress that seemed to have been made was that the aerodromes were not quite so unmanageable and erratic in their flights as at the beginning of the year, and that it had been demonstrated, at least to the writer’s satisfaction, that the power was sufficient for the work to be done. The launching device had been so perfected that it worked satisfactorily, but the problem of balancing seemed as far from solution as before.

1895

While, for convenience in narrating the progress of the work with the aerodromes, each year has been treated as a unit, it is, of course, understood that the work itself shows no especial difference between the closing of one year and the beginning of another. Changes which had important effects were introduced [p102] at various times, but were, of course, made as they suggested themselves without any reference to time or season. But while it was customary to make, from time to time, a résumé of the progress of the work, yet at the closing of the calendar year it was the custom to make a more complete digest of just what had been accomplished during the year.

Upon thus reviewing the progress of the work during 1894, it was felt that the results which had been accomplished for such a large expenditure of time seemed small, since no real flight had been made by any of the aerodromes, and no definite assurance that a successful flight would be obtained within the immediate future seemed warranted by what had already been accomplished. But now that the principal difficulties connected with the launching apparatus had been overcome, thus permitting the aerodromes themselves to be given a fair trial, the belief was encouraged that the continuance of the actual tests of the machines, with slight changes which previous tests had shown advisable, would finally result in a successful flight.

The early weeks of 1895 were spent in a series of pendulum tests on No. 5, and in making such slight changes as these tests indicated would be advisable. As a result of small improvements introduced in the boilers, No. 5 had by the middle of March shown a repeated lift of considerably over 50 per cent, and in some tests as much as 62 per cent of its flying weight. Certain radical changes previously described in Chapter VII were also made in Aerodrome No. 4, and in the pendulum tests of it a lift of 44 per cent of its flying weight had been obtained.

Encouraged by the better results which the aerodromes had shown in the above tests, it was decided to test them again in free flight, and they were accordingly sent down to Quantico in charge of the two mechanics, R and M, Mr. Langley, accompanied by Dr. Graham Bell, whom he had invited to witness the tests, following on May 8. On the evening of May 8 No. 5 was mounted on the launching apparatus in order to drill the mechanics so that when favorable weather presented itself the aerodrome could be got ready for launching with the minimum delay.

On May 9 Mr. Langley and Dr. Bell reached the house-boat at 5 a. m., but even with the drill of the previous evening the mechanics were not able to have No. 5 ready for trial until 6.15 a. m. The principal conditions of No. 5 at this time were:

Total weight 11,200 grammes (24.6 pounds), including 800 grammes of fuel and water. Previous lift on the pendulum 54 per cent, with a steam pressure of 150 pounds. With this steam pressure the engine made about 600 R. P. M. when driving the 95 cm. propellers, which through their reduction gearing made about 500 R. P. M. [p103]

When the aerodrome was balanced for flight so as to bring the theoretical “center of pressure in motion” over the center of gravity, it was found that it was not possible to carry the center of gravity in front of this point, although it was known by experience to be necessary. Accordingly in the first trial the outer ends of the tail were pressed down by the guys so that the wind of advance tended to lift the tail and throw the head down more than if the tail had been flat. Furthermore, the float, weighing 200 grammes, instead of being placed in its normal position near the base of the bowsprit, was carried out to its extremity, this change in the position of the float alone being sufficient to carry the center of gravity forward three or four centimetres. The curved wings were set at an angle of nine degrees at the root and eleven degrees at the tip. They were well guyed, and in flight appeared to be not materially twisted or altered.

It was anticipated that the pressing down of the outer ends of the tail and the shifting of the center of gravity would cause the aerodrome to point downward in flight, and this anticipation was verified in the test. At 6.15 a. m. the aerodrome was launched at a steam pressure of 120 pounds. A perfect calm prevailed at the time and the machine started straight ahead. There was no perceptible drop at the moment it was released from the launching car, but a smooth and steady descent until it struck the water, nose down, at a point approximately 200 feet from the boat. Dr. Bell noted that the length of time the aerodrome was in the air was 2.8 seconds. One of the propellers was broken and the other one was found to have twisted its shaft one-fourth of a turn.

At 9.45 a. m., the wings having been dried, No. 5 was again tried. The float was moved back to its normal position at the base of the bowsprit, and the guys, by which the outer ends of the tail had been depressed in the previous trial, were so adjusted that the tail was flat. The machine was, therefore, in the condition of theoretical equilibrium for rapid motion with a plane wing. All the other conditions were precisely as in the previous trial, except that the round-end 100-centimetre propellers were substituted for the 95-centimetre ones which had been broken, and a new paper-covered tail was used. The mechanic in charge was directed to let the steam reach its highest pressure consistent with a flight of one-half a minute, before launching the machine, but he seemed to have lost all sense of the length of time the fuel and water would last, as he let the engines run until almost the whole charge was exhausted before launching it. The aerodrome went off almost horizontally, then turned up into the wind and rose to an angle of about twenty degrees; then (while moving forward) slowly sank as though the engine power had given out, as in fact it doubtless had. The actual distance travelled was 123 feet and the length of time 7.2 seconds. While the exhaustion of the fuel and water prior to launching the machine had prevented what apparently would otherwise have been an [p104] exceedingly good flight, yet the fact that the aerodrome rose immediately after being launched, and continued to do so until the power gave out, was in itself very encouraging.

At 1.40 p. m. No. 5 was again ready for trial (the third one for the day), and this time Mr. Langley and Dr. Bell witnessed it from a greater distance in hopes of being able more clearly to study its behavior when actually in the air.

The previous trial having missed success through the fuel and water having been consumed before the machine was launched, special instructions were given to avoid the recurrence of this mistake. But the machine was held for probably two minutes after the burners were lighted, with very much the same result as before. The conditions of the aerodrome were the same as in the previous trial, except that the tail was a little flatter, so as to tend to make the head slightly lower in flight. It was launched at an angle of about thirty degrees with the very gentle wind that was blowing, and, apparently under the direction of the rudder, turned into the wind, the midrod rising to an angle of about twenty degrees and (as noted in Mr. Langley’s record book) “The whole machine absolutely rising during five or six seconds--a fine spectacle! Then the power visibly gave out, the propellers revolving slower. It settled forward and lost nearly all of its forward motion at the end of about seven seconds, but did not finally touch the water until ten and a quarter seconds.”

While the length of time that the aerodrome had been sustained in the air was so short that no actual flight had really been achieved, yet the results encouraged the belief that with the aerodrome more accurately balanced, it could reasonably be hoped that a somewhat longer flight would be obtained. It was, however, very evident that, although the correct balancing which would insure equilibrium for a few minutes might soon be attained, the machine, lacking a human intelligence to control it, must be provided with some mechanism which would tend to restore the equilibrium, the conditions of which must necessarily change in a machine depending on the air for its support. In order to see what could be done in this direction, it was, therefore, decided to return immediately to Washington with the machines and make some minor changes in them before attempting further flights.

By the end of May, Nos. 4 and 5 were again in readiness for a trial, and the mechanics were accordingly sent to Quantico to complete preparations for the tests. During May Mr. A. M. Herring, who had been experimenting with model machines for several years, was engaged for a few months as an assistant, and he was immediately put in charge of the field trials of Nos. 4 and 5, which were now about to be made. On June 6 Mr. Langley, accompanied by Mr. Herring, went to Quantico, and on June 7, at 5 a. m., Aerodrome No. 5 was ready for trial, but the wind was so high that nothing could be done. The wind later diminished in intensity, but the house-boat had become stuck on the beach [p105] and it was impossible to make the launching apparatus point directly into the wind, which was blowing from the rear of the boat. An attempt was made to launch the aerodrome even with the wind blowing at its rear, but it was found impossible to make the fires burn and the test was accordingly postponed. Later in the afternoon the house-boat was floated and the preparations for a test were immediately completed. At 5.42 p. m. the fires were lighted, but the burners did not work properly and the proper steam pressure could not be obtained. At 6.20 p. m. the fires were again lighted, and at 6.22 the aerodrome was launched, its midrod having an upward angle of 25 degrees, or more, with the launching track. The aerodrome moved off nearly horizontally, but seemed to be very sluggish in its movement and fell in the water about seventy feet from the boat, after having been in the air only 4.8 seconds. The damage consisted of a broken propeller and a slight strain in the main frame, the extent of which, however, was not immediately seen.

The steam pressure at the time of launching was 110 pounds, which was obviously insufficient. The aerodrome had lifted fifty per cent of its weight on the pendulum, and its sluggishness of movement seemed, therefore, unaccountable even for this pressure. It seemed probable, however, that the pressure ran down immediately after the machine was launched, on account either of the use of the light-weight burners in place of the larger and heavier ones, or of the diminution of the air pressure in the gas tank.

At 7.55 the aerodrome was again launched, and this time made a still shorter flight than before, being in the air only three seconds. A serious leak in the engine cylinder was, however, discovered just as the machine was launched, and this probably accounted for the lack of power.

Not only had the tests which have just been described indicated that there was a lack of power during flight, although previous pendulum tests had repeatedly shown lifts greater than fifty per cent, but, furthermore, the wings themselves, while appearing perfectly capable of supporting the aerodrome when viewed with the machine stationary, were seen to flex to such an extent in flight that it seemed probable that much of the power was consumed in merely overcoming the head resistance of a large portion of the wings which had lost all lifting effect.

During the fall and winter, as recorded in Chapters VII and VIII, Aerodrome “New No. 4,” which had been reconstructed during the summer, and which upon test was found radically weak, was almost entirely rebuilt and afterwards known as No. 6. Important changes were also made in No. 5, which greatly increased its strength and power. The improvements, however, which contributed more than anything else to the marked success achieved in the next trial of the aerodromes, were those which had to do with the nature and disposition of the sustaining surfaces and the means for securing equilibrium. [p106]

It will be recalled that in the more recent trials the apparent causes of failure had been the inability to provide sufficiently rigid wings, the great difficulty of properly adjusting the relative positions of the centers of pressure and gravity, and the lack of any means of regaining equilibrium when the balance of the aerodrome had in any way been disturbed. In the fall of 1895, accordingly, it was finally decided to employ a second pair of wings equal in size to the first or leading pair. This not only added greatly to the stability of the aerodrome, but also made it possible, without any alteration in the plan of the frame, to bring the center of pressure into the proper position relative to the center of gravity. In addition the plan of constructing the wings was modified by the introduction of a second main rib, which, placed at approximately the center of pressure of the wings, made them much stiffer, both against bending and torsion. The two pairs of wings now became the sole means of support, and the tail which had hitherto been made to bear part of the weight of the aerodrome, as well as assist in preserving the longitudinal equilibrium, was now intended to perform only the latter function. It was placed in the rear of the wings and was combined with the vertical rudder. Further, in adjusting it on the aerodrome, it was set at a small negative angle and given a certain degree of elasticity, as described above. This device proved to be a most efficient means of maintaining and restoring the equilibrium, when it was disturbed, and its value was apparent in all future tests of the models.

1896

The important changes in the steam-driven models which had been begun in the previous fall, and which in the case of No. 4 had been so extensive as to convert it into a new aerodrome, No. 6, were continued during the early spring, and it was not until the last of April that the models Nos. 5 and 6 were ready for actual test in free flight.

The condition of No. 5, which made the first successful flight, is given in the data sheet for May 6, 1896, and its general form at this time may be seen in the photograph of May 11, Plate 27A. Although the changes described above, as well as the modifications in the boilers and burners of both aerodromes had undoubtedly effected a great improvement in every detail of the machines, the disappointments experienced in the preceding years prevented any great feeling of confidence that the trials which were now to be made would be entirely successful. On May 4, however, the two mechanics, Mr. Reed and Mr. Maltby, were sent down to Quantico with Aerodromes Nos. 5 and 6, and Mr. Langley, accompanied by Dr. Graham Bell, who had been invited to witness the tests, followed on the afternoon of the 5th. On May 6 the wind was so very high all the morning that a test was found impracticable. During the forenoon, however, the wind gradually died down, and by 1 p. m. was blowing from six to ten miles an hour [p107] from the northeast. At 1.10 p. m. Aerodrome No. 6 was launched, but the guy-wire uniting the wings having apparently caught on one of the fixed wooden strips which held the wings down, the left wing was broken before the aerodrome was really launched, and the result was that the machine slowly settled down in the water by the boat, breaking the propellers and slightly injuring the Pénaud tail.

After removing No. 6 from the water, No. 5 was placed on the launching car and immediately prepared for a test. At 3.05 p. m. it was launched at a steam pressure of 150 pounds and started directly ahead into the gentle breeze which was then blowing. The height of the launching track above the water was about twenty feet. Immediately after leaving the launching track, the aerodrome slowly descended three or four feet, but immediately began to rise, its midrod pointing upward at an increasing angle until it made about ten degrees with the horizon and then remained remarkably constant at this angle through the flight. Shortly after leaving the launching track the aerodrome began to circle to the right and moved around with great steadiness, traversing a spiral path, as shown in the diagram (Plate 19). From an inspection of the diagram it will be noticed that the aerodrome made two complete turns and started on the third one. During the first two turns the machine was constantly and steadily ascending, and at the end of the second turn it had reached a height variously estimated by the different observers at from 70 to 100 feet. When at this height, and after the lapse of one minute and twenty seconds, the propellers were seen to be moving perceptibly slower and the machine began to descend slowly, at the same time moving forward and changing the angle of inclination of the midrod until the bow pointed slightly downward. It finally touched the water to the south of the house-boat at the position shown, the time the machine was in the air having been one minute and thirty seconds from the moment of launching. The distance actually traversed, as estimated by plotting its curved path on the coast-survey chart and then measuring this path, was approximately 3300 feet, which is the mean of three independent estimates. This estimate of the distance was checked by noting the number of revolutions of the propellers as recorded by the revolution counter, which was set in motion at the moment the machine was launched. On the assumption that the slip of the propellers was not greater than fifty per cent, the 1166 revolutions as shown by the counter would indicate a distance travelled of 2430 feet. As it was felt very certain that the slip of the propellers could not have amounted to as much as fifty per cent, it seemed a conservative estimate to place the length of flight at 3000 feet, which would mean a rate of travel of between 20 and 25 miles an hour. The circular path traversed by the aerodrome was accounted for by the fact that the guy-wires on one of the wings had not been tightened up properly, thus causing a difference in the lifting effect of the two sides. [p108]

The aerodrome was immediately recovered from the water and preparations made for a second test, the machine being launched again at 5.10 p. m. at a steam pressure of 160 pounds. The conditions were the same as at the first trial, except that the wind had changed from north to south and was perhaps of less velocity than before. The path traversed by the aerodrome in this second trial was almost a duplicate of the previous one, except that on account of the change in the direction of the wind the machine was launched in the opposite direction. In tightening up the guy-wires, which had not been properly adjusted in the previous test, they were probably tightened somewhat too much, since in this second test the aerodrome circled towards the left, whereas in the first flight it had circled towards the right. The aerodrome made three complete turns, rising to a height of approximately sixty feet with its midrod inclined to the horizon at a slightly greater angle than before. The propellers again ceased turning while the machine was high in the air and it glided forward and downward and finally settled on the water after having been in the air one minute and thirty-one seconds. The distance travelled was estimated as before, by plotting the path on the coast-survey chart, and was found to be 2300 feet.

During these flights several photographs were secured of the machine while it was actually in the air, some of the pictures being taken by Dr. Bell and others by Mr. F. E. Fowle. The clearest of these are shown in Plates 20, 21, and 22.

Just what these flights meant to Mr. Langley can be readily understood. They meant success! For the first time in the history of the world a device produced by man had actually flown through the air, and had preserved its equilibrium without the aid of a guiding human intelligence. Not only had this device flown, but it had been given a second trial and had again flown and had demonstrated that the result obtained in the first test was no mere accident.

Shortly after returning to Washington, Mr. Langley left for Europe, but before doing so he gave instructions to the workmen to remedy the small weaknesses and defects which had been found in Aerodrome No. 6, and to have both aerodromes ready for trial before his return in the fall.

After returning in the fall, Mr. Langley again had Aerodromes Nos. 5 and 6 taken down to Quantico for trial, and this time had as his invited guest Mr. Frank G. Carpenter. On November 27 a test was made of Aerodrome No. 6, the general disposition of which at this time may be learned from the description in Chapter X, and the photographs in Plates 29A, 29B. The model was launched at 4.25 p. m. with a steam pressure of 125 pounds. The aerodrome went nearly horizontally against the wind, and descended into the water in six and a quarter seconds at a distance of perhaps 100 yards. After the machine had been recovered from the water, it was found that a pin had broken in the synchronizing rod which connects the two propeller shafts together, and that the counter, which showed 495 revolutions of the propellers, had been caused to register [p109] inaccurately on this account. The balancing of Aerodrome No. 6 had been made the same as that of No. 5, but in No. 6 the line of thrust was twelve centimetres higher, and this fact, which had not been taken into account in determining the proper balancing for No. 6, seemed to be sufficient cause for the aerodrome coming down into the water so soon after being launched. Darkness had descended before the aerodrome could be recovered and prepared for a second trial. On the next day, November 28, a high wind prevailed in the morning, but in the afternoon it became comparatively calm, and No. 6 was launched at 4.20 p. m. under the same conditions as on the preceding day, except that the float, which weighed 275 grammes, was moved back from the bowsprit eighty centimetres in order to make the machine lighter in front. The aerodrome was launched at a steam pressure of not much over 100 pounds, the air draft for the burners being temporarily bad. The midrod made an angle of approximately three degrees with the horizontal. On account of a slight rain, which had occurred just before the machine was launched, the wings were wet and the weight of the entire aerodrome was doubtless as much as twelve kilos. Immediately on being launched the aerodrome started directly ahead in a gentle south wind, moving horizontally and slowly turning to the right and appearing to approach dangerously near to some thick woods on the west shore. However, it fortunately continued turning until it pointed directly up the beach with the wind in the rear. It then moved more rapidly forward, dipped and rose but once, and this very slightly, and continued its remarkable horizontal flight, varying not more than two yards out of a horizontal course, and this only for a moment, until it finally descended into the bay at a point nearly in a line between the house-boat and the railroad station at Quantico. Upon being recovered, it was found to be absolutely uninjured, and another flight would have been made with it immediately but darkness had descended. The time of flight, as determined independently by two stop-watches, was one minute and forty-five seconds. The number of revolutions of the propellers was 2801, or at the rate of 1600 R. P. M., which, with an allowance of fifty per cent slip, should have carried the aerodrome a distance of 4600 feet in one and three-quarter minutes. While the distance from the house-boat in a straight line to the point at which the aerodrome descended was only about 1600 feet, yet it was estimated by those present that this straight-line distance was certainly not greater than one-third the total length of the path traversed, which would mean a distance of something like 4800 feet. The length of the course, as plotted on the coast-survey map and afterwards measured, was 4200 feet, and it, therefore, seemed safe to say that the total distance travelled was about three-quarters of a mile, and the speed was, therefore, about thirty miles an hour.

[p110]