Trying to meet Langley's "desires" for less weight and more power, Balzer put together in New York the five-cylinder engine now displayed, with Manly's modifications, at Air and Space. It was originally a rotary, like his automobile engine had been: the entire engine turned around the driveshaft. But Balzer had a terrible time getting it to work properly, or to generate adequate horsepower. Manly helped him, encouraged him, nudged him and strove to get him more money. Langley shelled it out, mostly from a $50,000 grant from Congress, and fidgeted while Balzer fussed.
Time dragged on. Month after month passed. Manly's notes to Langley indicate the growing frustrations of the team. July 1899: "I am rather at a loss to explain how it is that one day Mr. Balzer thinks the present cylinders will work, and the next day he thinks that the engine will have to be rebuilt. . . ."
September 1899: "The engine for the great aerodrome is as yet unfinished, but Mr. Balzer promises to be ready with it by the 22nd of the present month. . . ."
June 1900: "The gasoline engine which was contracted for on the 12th of December, 1898, by Mr. Balzer can neither be accepted nor condemned at the present moment."
In that same letter, dated June 19, Manly agreed to "go abroad for a few weeks" with Langley to investigate alternatives. In Europe, engineers advised them against the rotary design. Lubrication, for instance, was a problem, for a rotating engine obviously throws oil away from its center. As the cylinders spin around, oil gathers at their outer ends.
Why, then, had the idea of a rotary appealed to the Langley team at all?
For one thing, its spin cooled the cylinders. Air cooling meant that the tank, pipes and pump for water cooling weren't needed--an admirable loss of weight. Also, the spin of the engine served the function of a flywheel, a feature of some early engines that helped them to run more smoothly.
But as more time passed and more problems arose with Balzer's engine, Manly decided to follow the Europeans' advice. By the fall of 1900, he had given up on the rotary concept. In September, he wrote his boss, still in Europe, that his recent effort with the aero engine had "been with the cylinders held stationary and cooled by temporary water jackets." He had turned Balzer's rotary engine into a fixed radial — and one cooled by water instead of air.
At last problems began to fade and performance improve, with an immediate leap from 6-8 hp in Balzer's rotary to 12-16 hp in Manly's radial version. More tests and improvements followed. By March 1901 the radial engine was putting out some 18 hp, but Manly foresaw the need for more. So, with funds from new grants, he replaced Balzer's heavy pistons with light ones and increased the size of the cylinders. By March 1903, the rebuilt engine was spinning the aerodrome's two propellers at the rate of 575 revolutions per minute. "The engine proper," wrote Manly, "weighs 120 lbs., and develops on test 52 brake horsepower...." In this same letter to Langley, the young assistant writes that his confidence in the engine is so complete that "I am prepared to risk myself with it in actual flight."
He didn't have long to wait. In the summer of 1903, after test flights with a quarter-scale model, Langley was ready. By September, the Great Aerodrome roosted on its catapult atop a bulky houseboat in the Potomac. Last adjustments went on as though Langley, after 17 years of working toward this climax, and now 69 years old, could hardly bring himself to reach it.