Learning to fly in the U.S. Army

by E. N. Fales

Thus were the three elements of control applied by the Wrights to their glider and the problem apparent in Lillienthal’s death was solved. The next step was to install a power plant able to maintain forward speed without resorting to coasting downhill by gravity; and therefore capable of producing a horizontal flight.

In developing a power flyer aside from the question of control the proper design was arrived at as follows:

Efficiency of Wings.—The Wrights knew from Langley and Chanute that flat wings were inefficient and useless, and curved wings essential; they did not know whether the amount of curvature mattered much. To find this out by trials in gliding would be slow and expensive. They adopted a better way—the wind-tunnel method, wherein small-scale models were tested and compared for efficiency in a blast of air. They made their wind tunnel 16 in. in diameter and created a powerful air blast through it by means of an engine-driven fan. Small models of wings were placed in the center of this confined air blast, mounted on a balance arm which projected into the tunnel from the outside. The air forces and efficiency of the models were thus measured. A large variety of shapes were tested and one was selected as best of all from the standpoint of curvature and rounded wing tips. This shape was adopted in their flyer, and though on a much larger scale fulfilled the predictions made for its efficiency in the indoor wind-tunnel experiments.

The Wright glider was, of course, a biplane model. They tested a small 6-in. model biplane and found that the two wings together were less efficient than either wing by itself. However, other considerations, such as rigidity of trussing, decided them to adopt the biplane rather than a monoplane arrangement.

Low Resistance to Forward Motion.—The Wrights used their wind tunnel also in choosing for the struts of their airplane a shape which would present least head resistance to forward motion. They found that a square strut had a resistance which could be decreased by changing the shape to resemble a fish. The resistance of the pilot himself was decreased by making him lie prone, face downward on the bottom wing.

Propeller Efficiency.—Although little data on the subject of propeller efficiency was available to the Wrights, they were able to arrive at a very creditable design wherein two propellers were used, driven from a single motor, and rotating one each side of the pilot. The mechanical difficulties which have since embarrassed the use of two propellers were less with the Wrights because they were dealing with smaller horsepowers than are in use today; they therefore were able to realize a very high propeller efficiency.

Motor.—When the Wrights were ready to apply a motor to their glider, they found it impossible to secure one light enough, and had to set about building one themselves. They adopted a four-cylinder type, water-cooled, and their aim was to save weight and complication wherever possible. Their first motor gave about 12 hp., which was raised to a higher and higher figure by subsequent improvements until it reached 20 hp. In its earliest stages it was able to give sufficient power for short horizontal flights.

Means of Starting and Landing.—One reason the Wrights could use such low horsepower was that they employed auxiliary starting apparatus to get up original speed. They knew that less horsepower was necessary to fly an airplane after it was once in the air than was necessary to get it into the air at the start, and they therefore rigged up a catapult which projected their airplane forward on a rolling carriage with great force at the start, so that all the motor had to do was to maintain the flight in air. The Wright airplane had at first no landing wheels, and was provided only with light skids on which it could make a decent landing. Present-day airplanes, of course, have wheels on which to roll both at starting and at landing and their motors are powerful enough to eliminate the necessity for a starting catapult.

(Courtesy American Technical Society and Scientific American Supplement.)