7. For any object to fly, we have to overcome the pull of gravity on the object. We note the pull of gravity by a FORCE called WEIGHT. The weight force is always directed towards the center of the earth and will accelerate an object towards the surface of the earth according to Newton’s laws of motion. For an airplane, we overcome the weight by generating an opposing force called LIFT. This force is generated by the wings of the airplane as it moves through the air. The air resists this motion. So there is a force opposed to the motion which we call DRAG. To overcome drag, we install a propulsion system on the airplane which generates THRUST. Flying then becomes a “tug-of war” between these four forces. The motion of the airplane through the air is governed by Newton’s laws of motion with the net external force acting on the airplane determined by the relative size of the four forces.

8. The first Wright brothers correctly understood that there was a third problem that had to be solved before heavier-than-air flight was possible. The aircraft must provide some system for stability and control. Stability and control are actually opposing concepts. An aircraft can be designed to be very stable (if disturbed it will return to its original flight conditions). But a stable aircraft is hard to control. In order to maneuver the airplane, you have to overcome its stability. The designs of Lilienthal and Maxim included some aspects of stability, but the pilots could not control them during transients. The brothers decided to “make a small contribution” to the study of flight by designing an aircraft that was just marginally stable, but would rely on the skill of the pilot to control the aircraft in flight. The pilot would no longer be a passenger, but would have an active roll during flight.

9. As an object moves through the air, it is free to rotate about its center of gravity in three directions. We can draw three axes through the center of gravity to describe the motion. The ROLL axis runs from front to back. Rotation about this axis is called ROLL and it occurs when the wing tips move up and down. The PITCH axis runs through the wings and a PITCH motion occurs when the nose moves up and down. The YAW axis is perpendicular to the other two axes and points down. A YAW motion occurs when the nose moves from side to side. The brothers correctly surmised that an aircraft has to be controlled about all three axes. They decided to build moving surfaces into their aircraft to allow the pilot to change the amount of force on the surface which would create a torque about the center of gravity and rotate the aircraft.

10. This is an animated example of pitch

11. This is an animated example of roll.

12. This is an animated example of yaw.

13. This is a picture of the 1900 kite taken by Orville
This is a picture of the 1900 kite taken by Orville. It flies just fine … but there is no one on board. The brothers found that in a 20 mph wind, the kite could lift itself, but not carry a pilot. Something was wrong in their design. They measured the wind speed using an anemometer that they borrowed from Octave Chanute. The brothers also measured the forces in the control lines and the angle at which the kite flew. They flew the craft with the tail in front and the tail in back and even without the tail. They put chains on the craft to determine how much the craft could lift for a measured wind speed.

14. The brothers decided that they needed more room to work on their aircraft in 1901, so they built a hangar in which to store the aircraft. The sides of the hangar could be lifted to ease the aircraft in and out. They also dug a well out on the dunes so that they wouldn’t have to trek in water. Chanute and some of his co-workers visited the brothers as shown in the figure. Chanute is at the left on the cot and Wilbur is standing.

15. This is picture of Orville and the 1901 aircraft
This is picture of Orville and the 1901 aircraft. You can see how much thicker the wing has become. You will also notice that the brothers have not included a rudder on the aircraft. They didn’t believe that they needed one (“birds don’t use rudders”). The weight of the aircraft has grown to about 100 pounds while Orville remains at 150 pounds.

16. Here is Wilbur being launched on a glide from the side of a sand dune
Here is Wilbur being launched on a glide from the side of a sand dune. That’s Dan Tate (Tom’s Uncle) on the left and one of Chanute’s friends (Huffaker) at the right. If you look close, you can see small struts sticking up from the lower wing. The brothers used these to twist the shape of their airfoil when they determined that the wing was not generating the predicted lift. Wilbur got about 50 glides during Orville hadn’t flown yet. You’ll notice that Wilbur lies on top of the bottom wing, not hanging beneath like Lilienthal. Orville was a champion bike rider, and most people that ride bicycles very fast know that it is harder to move through the air upright than to bend over in a biker’s stance. The brothers decided to cut the drag on the aircraft by having the pilot lie flat on the wing.

17. This is a picture of the back of the tunnel
This is a picture of the back of the tunnel. It has a large opening to let the wind out. Modern engineers would call this a “free return” design. It’s not a loop like most modern tunnels. Because it is free-return, any moving things in the room outside the tunnel can effect the results inside. So the brothers had a very strict procedure for taking data. One of the brothers would run the motor, and the other brother would stand by the side of the tunnel and look in the top to observe the test and record the data.

18. The brothers built about a hundred different models to test their ideas in the wind tunnel. The models were made of sheet steel which was bent, cut, twisted, filed and soldered into different shapes. The brothers picked the 40 best models and did detailed, parametric studies. Between any two models, they only changed one variable, so they could determine the effect of that variable on lift and drag. At the top of the figure we see three models with the same area, but the area is distributed differently. The aspect ratio is the ratio of the span (tip to tip) to the chord (front to back). For model #1 the value is 1.0 , for #2 it is 4.0, and for #3 it is 6.0. The wing of the 1901 aircraft was like model #2. The test results showed that #3 had much better performance; higher lift, lower drag. So they would make their 1902 aircraft look like#3 instead of #2. Today you know that wings are usually long and thin, not short and fat; the brothers were the first to figure that out. The middle group of models were made to test the effects of curvature (camber) on lift and drag. The bottom set was looking at wing tip design. The brothers rather quickly determined that the whole three-dimensional shape of the wing was important for performance (not just the curvature) and that you couldn’t take data with one shaped wing and apply that data to the design of a different shape. That was what they had done with Lilienthal’s data. In fact, the brothers made a model of Lilienthal’s model and compared their results with Lilienthal’s results. Their data was nearly identical. Lilienthal’s data was correct, but the brothers and most other designers were miss-applying the results to their design. The brothers tested for about six weeks in the fall of 1901, and would base the design of their future successful aircraft on this data. They sent some of the data to Chanute, but most of the results remained with the Wrights. They alone had the most accurate aerodynamic data in the world. The models shown on his figure are the actual models used by the brothers. They are now kept at the Franklin Institute who provided these pictures.

19. The brothers built two balances to measure lift and drag
The brothers built two balances to measure lift and drag. Each model was tested on each balance. This is a picture of the lift balance. It is made of spokes and hacksaw blades. The model is mounted at the top and its lift is balanced against the drag of the four “fingers” at the bottom. The model tries to turn the long axels to the right (in this view looking downstream), while the drag plates try to twist it to the left. The two twisting forces come into “balance” at some point and the amount of twist is measured on the protractor at the bottom. With a little data reduction math, the Wrights could then calculate and tabulate the lift coefficient to be used in the lift equation for design.

20. This is a picture of the actual data and graphs used by the brothers to determine the wing design for the 1902 aircraft.

21. With the wind tunnel designed aircraft, and the new flight controls, the brothers take to the air in Both brothers fly. During the next four weeks, the brothers break all the world records for gliding; time aloft (25 sec), length of glide (650 feet), size of aircraft (30 foot wing span), weight (110 pounds of aircraft, 150 pounds of pilot), and airspeed (over 35 mph). They make over a thousand flights. At the end of the 1902 flying season, the brothers are the most experienced pilots in the world; they have learned how to fly. And they realize that all that remains for the invention of the airplane is add a motor to this glide. (Of course, they will have to make the aircraft larger to lift the motor and they will have to add propellers to generate thrust)

22. This is a picture of Wilbur maneuvering the 1902 aircraft
This is a picture of Wilbur maneuvering the 1902 aircraft. He’s in slight banked turn to the right. This is the problem that they set out to solve in The 1902 aircraft is the first machine that could be controlled in all three directions as it moved through the air. The brothers’ later patents were on the 1902 aircraft and the ability to control the machine as it moves. They didn’t actually patent the airplane of 1903.

23. Here’s a computer drawing which compares the various aircraft designed and built by the brothers. Notice how similar they are. The brothers evolved their design … they didn’t just scrap everything and start over when the early aircraft did not perform properly.

24. To move from the 1902 glider to the 1903 powered aircraft, the brothers had to add a motor. They knew the performance requirements of their motor because they knew the drag of their aircraft based on their wind tunnel results. The engine must develop 8 horse power. They estimated the weight of the engine (200 pounds) and asked several auto manufacturers if they could produce an engine to meet these specifications. No one responded. So the brothers designed and built their own engine. It is a marvel! A gasoline powered, internal combustion, 4 cylinder engine, which they designed and built in 6 weeks. They had some help from their bicycle mechanic, Charles Taylor, and had the block cast at a local foundry, but this engine was built using only the tools found in their bicycle shop. It produced 12 horsepower and weighed about 200 pounds. This is a picture of a model of the engine which was built in the 1920’s. No plans of the actual engine remain. This is a picture of the front of the engine (from the front of the airplane). The cylinders are arranged in-line and lay on their side. The timing chain is visible on the front of the engine, as are the radiator tubes connected at the top. The chains to the propellers are seen at the rear, behind the large flywheel on the back of the engine at the left. The large tube sticking out the top of the engine is the air intake.

26. This is the most famous aviation picture of all time
This is the most famous aviation picture of all time. It was taken December 17, by John Daniels of the life guard station. It shows Orville Wright on the wing of the flyer (it was his turn after losing the coin toss on the 14th) and Wilbur running alongside. In the foreground you can see the smooth sand which marks where the wing was at the time of the engine run-up. The 60 foot launch rail is seen as well as the dolly at the end of the rail below the airplane. Orville has taken off, under his own power and will land 12 seconds later at 120 feet from the end of the rail. That’s 40 yards in 12 seconds (only three times slower than a modern football player!). The flight was in a straight line and never got more than 10 feet off the ground. At the end of the flight, the plane was brought back and Wilbur took his turn, with very similar results. Orville got the next flight and staid in the air for about 250 feet. Wilbur flew the last flight of the day for 59 seconds and almost 850 feet.

27. Because they are no longer doing glider experiments, and don’t need the wind, they decide to do all their flight testing close to home. They find an available pasture at the end of the trolley line at a place called Huffman’s Prarie, just outside Dayton. They build a new hangar to house a new airplane and get ready to fly again.

28. This is a computer drawing which compares the designs of the Wright aircraft from 1903, 1904, and Notice the elevator changes on the 1905.

29. The brother write to the war department to try and obtain a contract for a “practical flying machine” but are turned down. They decide to halt flying operations until they get a contract and the patent rights. They won’t be seen in the air again until 1907 but they continue to work on increasing the power of their engines.