APPENDIX IV
By Wilbur and Orville Wright
The flyer of 1903 carried a four-cylinder gasoline motor of four-inch bore and four-inch stroke. Complete with magneto, radiators, tanks, water, fuel, etc., the motor weighed a little over 200 pounds, and at 1,200 revolutions per minute developed 16 horse power for the first 15 seconds after starting. After a minute or two the power did not exceed 13 or 14 horse power. At 1,020 revolutions per minute—the speed of the motor in the flights at Kitty Hawk on the 17th of December, 1903—it developed about 12 horse power.
The flyer of 1904 was equipped with a motor similar to the first, but of 1/8-inch larger bore. This engine at 1,500 revolutions per minute developed 24 horse power for the first 15 seconds, but only 16 to 17 horse power after a few minutes run. Complete with water, fuel and other accessories, it weighed 240 pounds.
The same engine with a few modifications in the oiling device and the carburetor, was used in all the flights of 1905. A test of its power made soon after the flights of October, 1905, revealed a gain of 3 horse power over tests made just before mounting it on the flyer in 1904. This gain is attributed to the increased smoothness of the cylinders and pistons produced by wear. The small output of these engines was due to lack of experience in building gasoline motors.
During the past year further improvements have been made, and our latest engines of four-inch bore and four-inch stroke produce about 25 horse power continuously. The improvement in the reliability of the motor has been even more marked, so that now flights of long distances can be attempted without danger of failure on account of the stopping of the motor.
A comparison of the flyers of 1903, 1904 and 1905 show some interesting facts. The flyer of 1903 weighed, complete with operator, 745 pounds. Its longest flight was of 59 seconds duration, with a speed of 30 miles an hour and an expenditure of 12 horse power. The flyer of 1904 weighed about 900 pounds, including a load of 70 pounds in iron bars. A speed of more than 34 miles an hour was maintained for a distance of three miles with an expenditure of 17 horse power. The flyer of 1905 weighed, including load, 925 pounds. With an expenditure of 19 to 20 horse power it traveled over 24 miles at a speed of more than 38 miles an hour. The flights of 1904 and 1905 would have been slightly faster had they been made in a straight line, as were those of 1903.
In 1903, 62 pounds per horse power were carried at a speed of 30 miles an hour; in 1904, 53 pounds, at 34 miles an hour; and in 1905, 46 pounds at 38 miles an hour. It will be noted that the weight carried per horse power is almost exactly in inverse ratio to the speed, as theory demands—the higher the speed, the smaller the weight carried per horse power.
Since flyers can be built with approximately the same dynamic efficiency for all speeds up to 60 miles an hour, a flyer designed to carry a total weight of 745 pounds at 20 miles an hour would require only 8 horse power or two thirds of the power necessary for 30 miles an hour. At 60 miles 24 horse power would be necessary—twice that required to carry the same weight at 30 miles an hour. At 120 miles an hour 60 to 75 horse power would probably be necessary, and the weight carried per horse power would be only 10 or 12 pounds. At such high speed the resistance of the operator’s body and the engine is a formidable factor, consuming 64 times as much horse power as at 30 miles an hour. At speeds below 60 miles an hour this resistance is almost negligible.
It is evident that the limits of speed have not as yet been closely approached in the flyers already built, and that in the matter of distance, the possibilities are even more encouraging. Even in the existing state of the art it is easy to design a practical and durable flyer that will carry an operator and supplies of fuel for a flight of over 500 miles at a speed of 50 miles an hour.