Part 3

As a result of these experiments, all carefully carried out and minutely recorded, they obtained a body of data on air pressures and on the aerodynamic properties of wings, control surfaces, and structural parts. The extent and reliability of the information from these tests far exceeded anything that had ever been available to other experimenters or was to be available for at least another decade. Their friend and correspondent, Octave Chanute, marveled at the speed and accuracy with which this laboratory research was carried out. The Wrights themselves soon came to realize that these scientific experiments, on which they had embarked with considerable reluctance, were in fact the most valuable part of all their work in that they gave them accounts and detailed knowledge on which to base the design of flying machines.

The wind-tunnel experiments concluded in December 1901 made it possible for the Wrights to abandon the trial-and-error method of construction that had gone into their 1900 and 1901 gliders and to solve the basic problem of the correct design for lifting wings. Now they were able to devote their time to the two other major problems that had to be solved before human flight could be accomplished: a system for obtaining full control in the air, and the addition of an engine and propellers to the aircraft.

_Glider Experiments, 1902_

The Wrights had faith in the tables of air pressure compiled from their wind-tunnel experiments. Their new knowledge was incorporated into a larger glider which they built based on the aerodynamic data they had gained. Now they wanted to verify those findings by actual gliding experiments. At the end of August 1902, they were back in camp at Kill Devil Hills for the third season of experiments. Battered by winter gales, their camp needed repairing. They decided to build a 15-foot addition to the combined workshop and glider-storage shed to use as a kitchen and living quarters. Their new living quarters were "royal luxuries" when compared with the tent facilities of previous camps.

The new glider had a wingspan of 32 feet, 1 inch; a considerable increase over the wingspan of 22 feet for the 1901 glider. Its lifting area, 305 square feet, was not much greater than the glider of the previous year. Their wind-tunnel experiments having demonstrated the importance of aspect ratio, the brothers made the wingspan about six times the chord or fore-and-aft measurement instead of three. Weighing 112 pounds, the glider was 16 feet, 1 inch long. In the 1900 and 1901 gliders, the wing-warping mechanism had been worked by movement of the operator's feet. In the 1902 glider this mechanism operated by sidewise movement of the operator's hips resting in a cradle on the lower wing. Wilbur wrote his father from camp, "Our new machine is a very great improvement over anything we had built before and over anything any one has built."

This was the first Wright glider to have a tail, consisting of fixed twin vertical vanes, as well as a front rudder. The tail's purpose was to overcome the turning difficulties encountered in some of the flights with the 1901 glider by maintaining equal speeds at the two wingtips when the wings were warped. The tail was expected to counterbalance the difference in resistance of the two wingtips. If the wing on one side tended to swerve forward, then the Wrights thought the tail, being more exposed to the wind on the same side, should stop the glider from turning farther.

The tail on this glider, however, caused a new problem that had not occurred in their previous gliders. At times, when struck by a side gust of wind, the glider turned up sidewise and came sliding laterally to the ground in spite of the effort and skill of the operator in using the warping mechanism to control it. The brothers were experiencing tailspins, though that term did not come into use until several years later. When tailspins occurred, the glider would sometimes slide so fast that the movement caused the tail's fixed vertical vanes to aggravate the turning movement instead of counteracting it by maintaining an equal speed at the opposite wingtips. The result was worse than if there were no fixed vertical tail.

While lying awake one night, Orville thought of converting their vertical tail from two fixed vanes to a single movable rudder. When making a turn or recovering lateral balance, this rudder could be moved toward the low wing to compensate for the increased drag imparted to the high wing by its greater angle of attack. Wilbur listened attentively when Orville told him about the idea the next morning. Then, without hesitation, Wilbur not only agreed to the change but immediately proposed the further important modification of interconnecting the rudder control wires with those of the wing-warping. Thus by a single movement the operator could affect both controls. Through the brilliant interplay of two inventive minds, all the essentials of the Wright control system were completed within a few hours.

The combination of warp and rudder control became the key to successful control of their powered machine and to the control of all aircraft since. (Modern airplanes--and indeed Wright planes after the middle of their 1905 experimental season--do not have the aileron and rudder controls permanently interconnected, but these controls can be and are operated in combination when necessary.) Together with the use of the forward elevator, it allowed the Wrights to perform all the basic aerial maneuvers that were necessary for controlled flight. The essential problem of how to control a flying machine about all three axes was now solved.

The trials of the 1902 glider were successful beyond expectation. Nearly 1,000 glider flights were made by the Wrights from Kill Devil, West, and Little Hills. A number of their glides were of more than 600 feet, and a few of them were against a 36-mile-an-hour wind. Flying in winds so strong required great skill on the part of the operator. No previous experimenter had ever dared to try gliding in so stiff a wind. Orville wrote his sister, "We now hold all the records! The largest machine we handled in any kind [of weather, made the longest dis]tance glide (American), the longest time in the air, the smallest angle of descent, and the highest wind!!!" Their record glide for distance was 622½ feet in 26 seconds. Their record glide for angle was an angle of 5° for a glide of 156 feet. The 1902 glider had about twice the dynamic efficiency of any other glider ever built up to that time anywhere in the world.

By the end of the 1902 season of experiments, the Wrights had solved two of the major problems: how properly to design wings and control surfaces and how to control a flying machine about its three axes. Most of the battle was now won. There remained only the major problem of adding the engine and propellers. Before leaving camp, the brothers began designing a new and still larger machine to be powered with a motor.

It was the 1902 glider that the Wrights pictured and described in the drawings and specifications of their patent, which they applied for in March of the following year. Their patent was established, through the action of the courts in the United States and abroad, as the basic or pioneer airplane patent.

_The Motor and the Propellers_

Home again in Dayton, the Wrights were ready to carry out plans begun in camp at Kill Devil Hills for a powered machine. They invited bids for a gasoline engine which would develop 8 to 9 horsepower, weigh no more than 180 pounds or an average of 20 pounds per horsepower, and be free of vibrations. None of the manufacturers to whom they wrote was able to supply them with a motor light enough to meet these specifications. The Wrights therefore designed and built their own motor, with their mechanic, Charles E. Taylor, giving them enthusiastic help in the construction.

The engine body and frame of the first "little gas motor" which they began building in December 1902 broke while being tested. Rebuilding the light-weight motor, they shop-tested it in May 1903. In its final form the motor used in the first powered flights had 4 horizontal cylinders of 4-inch bore and 4-inch stroke, with an aluminum-alloy crankcase and water jacket. The fuel tank had a capacity of four-tenths of a gallon of gasoline. The entire power plant including the engine, magneto, radiator, tank, water, fuel, tubing, and accessories weighed a little more than 200 pounds.

Owing to certain peculiarities of design, after several minutes' run the engine speed dropped to less than 75 percent of what it was on cranking the motor. The highest engine speed measured developed 15.76 horsepower at 1,200 revolutions per minute in the first 15 seconds after starting the cold motor. After several minutes' run the number of revolutions dropped rapidly to 1,090 per minute, developing 11.81 brake horsepower. Even so, the Wrights were pleasantly surprised since they had not counted on more than 8 horsepower capable of driving a machine weighing only about 625 pounds. Having a motor with a power output of about 12 horsepower instead of 8, the Wrights could build the machine to have a larger total weight than 625 pounds.

The motor was started with the aid of a dry-battery coil box. After starting, ignition was provided by a low-tension magneto, friction-driven by the flywheel. No pump was used in the cooling system. The vertical sheet-steel radiator was attached to the central forward upright of the machine.

When the brothers began to consider designing propellers, they unhappily discovered that the forces in action on aerial propellers had never been correctly resolved or defined. Since they did not have sufficient time or funds to develop an efficient propeller by the more costly trial-and-error means, it was necessary for them to study the screw propeller from a theoretical standpoint. By studying the problem, they hoped to develop a theory from which to design the propellers for the powered machine. The problem was not easy, as the Wrights wrote:

What at first seemed a simple problem became more complex the longer we studied it. With the machine moving forward, the air flying backward, the propellers turning sidewise, and nothing standing still, it seemed impossible to find a starting point from which to trace the various simultaneous reactions. Contemplation of it was confusing. After long arguments we often found ourselves in the ludicrous position of each having been converted to the other's side, with no more agreement than when the discussion began.

However, in a few months the brothers untangled the conflicting factors and calculations. After studying the problem, they felt sure of their ability to design propellers of exactly the right diameter, pitch, and area for their need. Estimates derived from their formulas led to their propellers operating at a higher rate of efficiency (66 percent) than any others of that day. The tremendous expenditure of power that characterized experiments of other aeronautical investigators up to that time were due to inefficient propellers as well as inefficient lifting surfaces.

The Wright propellers, designed according to their own calculations, were the first propellers ever built by anyone for which the performance could be predicted. After tests, their propellers produced not quite 1 percent less thrust than they had calculated. In useful work they gave about two thirds of the power expended--a third more than had been achieved by such men as Sir Hiram Maxim and Dr. Langley.

The brothers decided to use two propellers on their powered machine for two reasons. First, by using two propellers they could secure a reaction against a greater quantity of air and use a larger pitch angle than was possible with one propeller; and second, having the two propellers run in opposite directions, the gyroscopic action of one would neutralize that of the other. The two pusher-type propellers on the 1903 powered machine were mounted on tubular shafts about 10 feet apart, both driven by chains running over sprockets. By crossing one of the chains in a figure eight, the propellers were run in opposite directions to counteract torque. The propellers were made of three laminations of spruce, each 1-1/8 inches thick. The wood was glued together and shaped with a hatchet and drawshave.

_The Powered Machine, 1903_

The 1903 machine had a wingspan of 40 feet, 4 inches, a camber of 1 in 20; a wing area of 510 square feet; and a length of 21 feet, 1 inch. It weighed 605 pounds without a pilot. The machine was not symmetrical from side to side; the engine was placed on the lower wing to the right of center to reduce the danger of its falling on the pilot. The pilot would ride lying prone as on the gliders but to the left of center to balance the weight. The right wing was approximately 4 inches longer than the left to provide additional lift to compensate for the engine which weighed 34 pounds more than the pilot.

Fore-and-aft control was by means of the elevator in front, operated by hand lever. The tail of the machine had twin movable rudders instead of a single movable rudder developed in the 1902 glider. These rudders were linked by wires to the wing-warping system. Their coordinated control mechanism was worked by wires attached to a cradle on the lower wing, in which the pilot lay prone. To turn the machine to the left, the pilot moved his body, and with it the cradle, a few inches to the left. This caused the rear right wingtips to be pulled down or warped (thus giving more lift and raising them) and the rear left wingtips to move upward, and at the same time the coordinating mechanism introduced enough left rudder to compensate for yaw. The rudder counteracted the added resistance of the wing with the greater angle and the resulting tendency of the machine to swing in the opposite direction to the desired left turn, as well as aiding the turn on its own account.

On September 25, 1903, the Wrights arrived once more at their Kill Devil Hills camp. They repaired and again used the living quarters which they had added to the storage building in 1902, called their "summer house." Their 1902 glider, which they had left stored in this building after that season of experiments, was again housed with them in the building. They erected a new building to house the powered machine alongside the glider-storage and living-quarters building and commenced the chore of assembling the powered machine in its new hangar. Occasionally they took the 1902 glider out for practice. After a few trials each brother was able to make a new world's record by gliding for more than a minute.

The first weeks in camp were a time of vicissitudes for the Wrights. Assembling the machine and installing the engine and propellers proved an arduous task. When tested, the motor missed so often that the vibrations twisted one of the propeller shafts and jerked the assembly apart. Both shafts had to be sent back to their Dayton bicycle shop to be made stronger. After they had been returned, one broke again, and Orville had to carry the shafts back to Dayton to make new ones of more durable material. The magneto failed to produce a strong enough spark. A stubborn problem was fastening the sprockets to the propeller shafts; the sprockets and the nuts loosened within a few seconds even when they were tightened with a 6-foot lever.

It was then that the weather acted as if it were threatening the brothers not to venture into a new element. A gale swept over their camp with winds up to 75 miles an hour. As their living quarters rocked with the wind, and rainwater flowed over part of the floor, the Wrights expected to hear the new hangar building next door, which housed the powered machine, crash over completely. "The wind and rain continued through the night," related Wilbur to his sister, "but we took the advice of the Oberlin coach, 'Cheer up, boys, there is no hope/' We went to bed, and both slept soundly."

It became so cold that the brothers had to make a heater from a drum used to hold carbide. Wilbur assured his father:

However we are entirely comfortable, and have no trouble keeping warm at nights. In addition to the classifications of last year, to wit, 1, 2, 3, and 4 blanket nights, we now have 5 blanket nights, & 5 blankets & 2 quilts. Next come 5 blankets, 2 quilts & fire; then 5, 2, fire, & hot-water jug. This as far as we have got so far.

At last the weather cleared, the engine began to purr, their hand-made heater functioned better after improvements, and, with the help of a tire cement they had used in their bicycle shop, they "stuck those sprockets so tight I doubt whether they will ever come loose again." Chanute visited their camp for a few days and wrote November 23, "I believe the new machine of the Wrights to be the most promising attempt at flight that has yet been made." Both brothers sensed that the goal was in sight.

The powered machine's undercarriage (landing gear) consisted of two runners, or sledlike skids, instead of wheels. These were extended farther out in front of the wings than were the landing skids on the gliders to guard against the machine rolling over in landing. Four feet, eight inches apart, the two runners were ideal for landing as skids on the soft beach sands. But for take-offs, it was necessary to build a single-rail starting track 60 feet long on which ran a small truck which held the machine about 8 inches off the ground. The easily movable starting rail was constructed of four 15-foot 2 x 4's set on edge, with the upper surface topped by a thin strip of metal.

The truck which supported the skids of the plane during the takeoff consisted of two parts: a crossbeam plank about 6 feet long laid across a smaller piece of wood forming the truck's undercarriage which moved along the track on two rollers made from modified bicycle hubs. For take-offs, the machine was lifted onto the truck with the plane's undercarriage skids resting on the two opposite ends of the crossbeam. A modified bicycle hub was attached to the forward crosspiece of the plane between its skids to prevent the machine from nosing over on the launching track. A wire from the truck attached to the end of the starting track held the plane back while the engine was warmed up. Then the restraining wire was released by the pilot. The airplane, riding on the truck, started forward along the rail. If all went well, the machine was airborne and hence lifted off the truck before reaching the end of the starting track; while the truck, remaining on the track, continued on and ran off the rail.

With the new propeller shafts installed, the powered machine was ready for its first testing on December 12. However, the wind was too light for the machine to take-off from the level ground near their camp with a run of only 60 feet permitted by the starting track. Nor did they have enough time before dark to take the machine to one of the nearby Kill Devil Hills, where, by placing the track on a steeply inclined slope, enough speed could be promptly attained for starting in calm air. The following day was Sunday, which the brothers spent resting and reading, hoping for suitable weather for flying the next day so that they could be home by Christmas.

On December 14 it was again too calm to permit a start from level ground near the camp. The Wrights, therefore, decided to take the machine to the north side of Kill Devil Hill about a quarter of a mile away to make their first attempt to fly in a power-driven machine. They had arranged to signal nearby life-savers to inform them when the first trial was ready to start. A signal was placed on one of the camp buildings that could be seen by personnel on duty about a mile away at the Kill Devil Hills Life Saving Station.

The Wrights were soon joined by five lifesavers who helped to transport the machine from camp to Kill Devil Hill. Setting the 605-pound machine on the truck atop the starting track, they ran the truck to the end of the track and added the rear section of the track to the front end. By relaying sections of the track, the machine rode on the truck to the site chosen for the test, 150 feet up the side of the hill.

The truck, with the machine thereon, facing downhill, was fastened with a wire to the end of the starting track, so that it could not start until released by the pilot. The engine was started to make sure it was in proper condition. Two small boys, with a dog, who had come with the lifesavers, "made a hurried departure over the hill for home on hearing the engine start." Each brother was eager for the chance to make the first trial, so a coin was tossed to determine which of them it should be; Wilbur won.

Wilbur took his place as pilot while Orville held a wing to steady the machine during the run on the track. The restraining wire was released, the machine started forward quickly on the rail, leaving Orville behind. After a run of 35 or 40 feet, the airplane took off. Wilbur turned the machine up too suddenly after leaving the track, before it had gained enough speed. It climbed a few feet, stalled, and settled to the ground at the foot of the hill after being in the air just 3½ seconds. This trial was considered unsuccessful because the machine landed at a point at the base of the hill many feet lower than that from which it had started on the side of the hill. Wilbur wrote of his trial: