No. 4 was ready by mid-March 1893, but Langley’s crew had difficulty throughout the summer and fall with the complicated overhead launching system. The apparatus used nine sturdy coil springs in tension, operating through two pulleys. A small launching cart, with the Aerodrome hung below, was to accelerate along the 20-foot track. At its end, an automatic release mechanism would free the model, allowing it to proceed in flight.

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Langley believed until the end of his life that less power was required to fly faster than slower. In an Aeronautical Annual article, he wrote that ‘it is necessary for an aerodrome, as it is for a soaring bird, to have a certain considerable initial velocity before it can advantageously use its own momentum for flight, and the difficulties of imparting this initial velocity…are surprisingly great.’ Believing the power requirements to be unacceptably high at lower velocities, Langley attempted to leapfrog the problem by launching at higher velocities.

Flight testing was always halted during the summer months while Langley and his family vacationed in Europe. By the middle of November 1893, however, everything looked ready for a trial. Aerodrome No. 4 was moved from the Smithsonian to the houseboat, anchored on the Potomac off tiny Chopawamsic Island.

Immediately, two problems surfaced. First, in mild breezes, the model swung wildly below the launch cart, jeopardizing a smooth run down the launch rail. Second, the burner-difficult to maintain in the best of circumstances-refused to stay lit. No attempt to launch could be made until those problems were corrected by Langley and his assistants. Over the next six weeks, nine round trips were made between the Smithsonian and the houseboat, but all efforts to make the launcher work proved fruitless.

Frustrated and desperate, in January 1894 Langley tried dropping the Aerodrome into a gentle breeze from an arm 25 feet above the water, hoping it would gain flying speed before it reached the river. Its propellers whirled at maximum rpm as No. 4 plunged straight into the frigid Potomac.

Another new Aerodrome was almost ready when Langley decided to concentrate his team’s effort on the abortive flight tests with No. 4. Throughout the winter and spring months of 1894, work proceeded to complete No. 5 and retrofit No. 4 with a bigger set of wings. No. 5 was a large machine, with a wingspan of 13 feet 8 inches, length of 13 feet 2 inches and height of 4 feet 1 inch. Weighing 30 pounds, it was fitted with a new and more powerful single-cylinder steam engine.

Trials resumed once again on October 7, 1894, after the summer layoff. The crew practiced using a new launching system. After a few throws with nonpowered ‘dummy’ Aerodromes and some minor adjustments, the launcher seemed to be working perfectly.

The rebuilt No. 4 was prepared for flight at once. Unlike previous attempts, the model launched perfectly, but then the wings twisted, plunging it into the water.

Although it was late in the day, Aerodrome No. 5 was readied for a trial. Again, the launching system worked perfectly, but as the Aerodrome left the rail, it nosed up steeply, slowed and then slid backward into the Potomac. To everyone’s surprise, Langley was ecstatic. He thought he saw signs of progress for the first time.

Over the next two months, Aerodromes No. 4 and 5 were launched numerous times. The launcher continued to work well, but the models just would not fly. By late November, the team had again retreated to the warmth of the Smithsonian’s shops, where serious static experiments were conducted to determine the strength of the wings. As Langley ordered, No. 4 and No. 5 ‘were inverted, and sand was spread uniformly over the wings until its weight represented that of the machine.’ Langley was shocked by the lack of stability and general weakness of the structure when loaded in that manner. More modifications were in order, including a new system of guy wiring for No. 5. The changes to No. 4 were so extensive that everyone felt justified in renaming it No. 6.

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