He soon became convinced that the mathematical formulas given in the books concerning the increase of power with increase of velocity were all wrong. “At that rate, a swallow would have to have the strength of a man!” he exclaimed. He devised a sort of whirling table with surfaces like wings to test with exactness just how much horse-power was required to hold up a surface of a certain weight while moving rapidly through the air, and by this means discovered and demonstrated the fundamental law of flight, known as Langley’s Law, which tells us that the faster a body travels through the air the less is the energy required to keep it afloat.
After proving that birds are held up like kites by pressure of the air against the under surface of their wings, he made experiments to show that their soaring flight is aided by “the internal work of the wind,” that is, by shifts in the currents of air, particularly by rising trends, which the winged creatures utilize by instinct. Watch a hawk as it circles through the air, dipping its wings now at this angle, now at that, and you will realize that the wind is his true and tried ally. He trusts himself to the sweep and swirl of the air, just as a swimmer relies on the buoyancy of the water.
Having demonstrated so much through experiments with his whirling table, Dr. Langley determined to construct a real flying-machine, with wide-spreading planes to sustain it in the air while it was driven along by a steam-engine which furnished power to the propellers. This machine, which he called an “aërodrome” (air run), was put to the test on the sixth of May, 1896. Dr. Alexander Graham Bell, who was present at the trial and who took pictures of the machine in mid-air, declared, “No one who witnessed the extraordinary spectacle of a steam-engine flying with wings in the air, like a great soaring bird, could doubt for one moment the practicability of mechanical flight.”
Now that he had succeeded in solving the problem from the scientific standpoint, Professor Langley wished to leave the task of developing the idea in a practical, commercial way to others. There was, however, a popular demand for him to carry on his experiments with a model large enough to carry a man, and $50,000 was appropriated for the purpose by the Government on the recommendation of President McKinley and the Board of Ordnance and Fortification of the War Department.