A brief account has already been given of the attempts made by Mr. Langley to secure a suitable gasoline engine for the large aerodrome, but the difficulties encountered in the search have not perhaps been sufficiently emphasized. At this time (1898) the automobile industry, through which has come the development of the gasoline engine, was in its infancy, and there were few builders either in the United States or Europe who were attempting anything but rough and heavy construction. Many of them were enthusiastic over the possibilities of the internal combustion engine, and were ready to talk of devising such an engine as the aerodrome would require, but few were willing to guarantee any such definite results as were demanded. However, the prospects of securing a suitable gasoline engine from a reliable builder within a reasonable time seemed so strong that it was decided early in 1898 to begin the construction of the frame on the general plan which would probably be best adapted for use with a gasoline engine, and in case it finally proved impossible to secure such an engine, to construct later a steam plant which could be adapted to this particular frame. Some tentative work on the construction of the frame was accordingly begun in the summer of 1898, some months before an engine builder was found who seemed likely to be successful in furnishing the engines. An extensive series of tests on propellers was also made at this time for the immediate purpose of determining what form and size would be best, since the dimensions of the transverse frame could not be definitely settled until it was known how large the propellers would need to be. Preliminary designs were also begun for the wings, rudders, and launching apparatus, but when the point was reached of actually making the working drawings for these, it was seen that the change in the scale of the work required many important modifications in constructional details. As the models had flown successfully only three times, and in each case under practically the same conditions, it was felt that it would be unwise to make changes in important details without first making a series of tests of the models in flight to determine the effect of such changes. It was therefore decided to completely overhaul Models Nos. 5 and 6, strengthening them in many important parts and “tuning up” their power plants, which had slightly deteriorated since they were last used in November, 1896. When the work of preparing these models for further experiments was begun it was thought that it would require at most only a few weeks, but as it progressed it was found that certain parts of the mechanical work on the engines had been so poorly executed originally that it would be necessary to practically rebuild the engines. The final result was that the power plants of both aerodromes were entirely rebuilt, and they were not ready for actual test in flight until the spring of 1899. [p132]