1894
The aerodrome, No. 4, which has just been described, had not been put to the test of an actual flight, for reasons connected with the difficulties of launching, which are more fully described elsewhere; but, when the completed machine was more fully studied in connection with the unfavorable conditions which it was seen would be imposed on it in trials in the open air, many possibilities for improvement presented themselves. It was seen, for instance, that a better design might be made, in which the engines, boiler and aeolipile might be placed so that the center of gravity of each would lie in the same vertical plane as the central line of the aerodrome. In order to do this the construction of a single midrod, which was the distinguishing feature of Old No. 4, had to be essentially departed from, the midrod of this new one, No. 5, being opened out into two rods, so to speak, which were bent out so that the open space between them furnished a sufficiently large hull space to hold the entire power generating apparatus. In arranging the machinery within this hull, it was provided that, as the water and fuel were expended, the center of gravity of the aerodrome would shift little, and, if at all, backward relatively to the center of pressure.
Instead of the two small engines, which it will be remembered were mounted on the cross-frame in No. 4, a single engine with a larger cylinder, having a diameter of 3.3 cm. (1.3 in.) and a stroke of 7 cm. (2.76 in.), capable of developing about 1 H. P. was used. This engine was mounted within the hull near the forward end and drove the propellers by suitable gearing. [p065]
In addition to these radical changes many important improvements were made in the different parts. Internal compartments were built in the separator, so that even if the water was displaced by the pitching of the aerodrome, it could still perform its functions properly. The pump was provided with a ratchet, so that it could be worked by hand after the burners were lighted, and before enough steam had been raised to enable the engine to run it. An active circulation was thus maintained in the coils of the boiler as soon as the burner was lighted and before the engine was started, which prevented the tubing from being burnt out, as had frequently happened previously. The wing construction was also improved and many other changes were introduced, which will be treated separately.
In the meantime, No. 4, which had been damaged in the attempted launching in November, 1893, was strengthened and prepared for another trial which took place in January, 1894.
By the end of the first week in February, the engine of No. 5 was ready for trial, and with a boiler pressure of about 80 pounds per square inch, apparently developed 0.56 H. P. on the Prony brake, when making 800 revolutions per minute. To accomplish this called for such good distribution of steam in the cylinder, that it is doubtful if the power could be exceeded at that speed and pressure.
It was, however, apparent that it was desirable to have a boiler capable of supplying steam for at least one horse-power, and that in order to do this, there must be an improvement in the aeolipiles. The problem consisted in arranging to evaporate more than 500 cu. cm., and in fact as nearly as possible 1000 cu. cm. (61 cu. in.) of water per minute, and, since from 200 to 300 cu. cm. per minute had already been evaporated, this was not regarded as impossible of accomplishment. The theoretical advantages of gasoline had for a long time been recognized, as well as the very practical advantage possessed by it of keeping lighted in a breeze, and several attempts had been made during the latter part of the previous year to construct a suitable burner for use with it. These had not been very successful; but in view of the increasing demand for a flame of greater efficiency than that of the alcohol aeolipiles, it was decided to resume the experiments with it.
Accordingly, a gasoline evaporator was tried, consisting in the first experiment of a gasoline tank with nine flues, through which steam was passed. A flow of steam gave a rapid evaporation of gasoline when the pressure did not exceed 5 pounds. The chief difficulty with the burner employed was that the supply of gasoline gas would rise and fall as the steam rose and fell, conditions just the opposite of what was really desired. On the other hand, it was thought that this gasoline tank would form a real condenser for the steam, so that a [p066] portion of the exhaust steam would be condensed and be available for use in the boiler again. The gasoline vapor had many advantages over the alcohol; but it was at first possible to evaporate only 120 cu. cm. of gasoline in a minute.
In the experiments that were made at this time (March 9) with gasoline, the main object in view was to obtain a smooth blue flame at 10 pounds pressure. There had been failures to accomplish this, owing to the high boiling point of the liquid, and while the work was in progress it was still evident that the problem of the boiler and the flame which was to heat it had not been solved. A Prony brake test gave, at 130 pounds pressure, 1.1 H. P. with about 1000 revolutions of the propellers; but this was with steam supplied from the boiler of the stationary shop engine.
On April 1, 1894, the following record was made of the condition of Aerodrome No. 5: