# Presentation: 239032

## Slide 1

## Slide 2

**Notes:**
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.

## Slide 3

**Notes:**
Before the Wrights, people believed that there were two big problems to be overcome before heavier-than-air flight was possible. The first was the aerodynamics of the airframe. It had to be shaped just right to produce high lift and low drag. It had to be light (because you had to lift it) yet be very strong so that it was safe to operate. The other problem involved the propulsion system. The motor had to be light weight, yet develop sufficient power to move the airplane through the air. And the motor had to be coupled to some kind of propeller which would convert the output of the motor (shaft rotation) into thrust. So the propeller had to be very efficient and have little performance loss.
Around the world, there were two “schools” of scientists and engineers who were trying to solve these problems. Lilienthal (Germany), Percy (England), and Chanute and Herring (United States) were attacking the aerodynamics problems by building and flying small hang gliders between 1890 and 1900. Ader (France), Maxim (England), and Langley (United States) were attacking the propulsion problems.

##                         Hiram  Maxim -  1894

-                         Hiram  Maxim -  1894
- 6000 pound aircraft ,  2  steam engines,  18 foot  props

**Notes:**
A good example of the propulsion school of thought is the work of Hiram Maxim. In 1894, he built a large, steam-powered flying machine. The plane weighed 6000 pounds, had a wing span of more than 120 feet, was powered by two steam engines pushing two 18 foot propellers, and carried a crew of four. This plane actually got a few inches off the ground in a test flight in 1894 ... but it was hit by a gust of wind and fell over. Maxim had no control system on his aircraft.

##                 Otto  Lilienthal

-                 Otto  Lilienthal
- Years  of  Glider  Experiments

-    Killed  in  glider  accident
-                     1897

**Notes:**
This is the best example of the aerodynamics school of thought. Here are two pictures of Otto Lilienthal flying. Lilienthal was a German engineer who was studying the flight of birds. He created a large swing-arm device on which he would mount models and measure the lift and drag of the models. He published these results and the Wrights obtained copies of them from the Smithsonian in 1900. Lilienthal used the information to build a variety of “hang gliders”. He constructed the large hill shown in the picture and would jump from the top of the hill and glide to the bottom. His aircraft were rigid and he would hang below the wing and attempt to balance the craft by swinging his body from side to side. He performed these flights for 5 years between 1892 and 1897, accumulating nearly 5 hours of flight time. Unfortunately, in 1897, he was killed during a flight when a gust of wind pushed him into a stall. He fell in from 40 feet above the ground. The Wrights read about his death and correctly understood that Lilienthal could not provide enough control to his aircraft by simply shifting his weight. Something else was needed.

## Slide 6

**Notes:**
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.

## Slide 7

**Notes:**
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.

## Slide 8

**Notes:**
This is an animated example of pitch

## Slide 9

**Notes:**
This is an animated example of roll.

## Slide 10

**Notes:**
This is an animated example of yaw.

## 1899

**Notes:**
In 1899, the brothers began their investigations. They knew they needed to allow the surfaces of their aircraft to move, but did not know how to do it without large, heavy, mechanical devices. While talking to a customer in the bike shop, Wilbur was absent-mindedly twisting a long thin box that normally contained an inner-tube. He noticed that deflecting the corners of the box provided a higher angle on one end and a lower angle on the other. This was exactly the shape change that he was considering for his aircraft. So he talked to his brother and they decided to build a kite to test out the concept.

## Slide 12

**Notes:**
These are drawings from the Wrights which detail the design of a kite, built in 1899, to test their ideas for “wing warping”. Wing warping was their terminology for twisting the wing tips to produce roll on the aircraft. The kite was a about 5 feet from tip to tip and was rigged such that pulling on the 4 control lines would twist the wing tips. Wilbur test flew the kite and discovered that he could maneuver it at will. He even chased youngsters that came to watch him fly. Wing warping worked on a small scale, but would it work on a larger, man-rated machine?

## Slide 13

**Notes:**
This is a computer drawing of the first man-rated aircraft to be built by the brothers. Their idea was to build a craft that was large enough to lift a single pilot and the weight of the craft. Since the pilot would be in control of the craft, piloting experience was very important. Lilienthal, in 5 years, had accumulated 5 hours of flight time; not enough in the opinion of the brothers. They wanted to get 5 hours of flight time in a day! To do this, they would fly their aircraft as a kite. Two lines connected to the wing tips would hold the craft stable over the ground. The pilot could then train for hours to perfect his skills. They wrote the weather service to find the highest sustained winds in the country. The answer was the outer banks of North Carolina. So they decided to test at Kitty Hawk.

## 1900

**Notes:**
The brothers had an idea, but no working knowledge of aerodynamics. So Wilbur wrote to the Smithsonian and asked for information. The Smithsonian, in 1900, was a research agency and had its own team headed by Samuel P. Langley which was building powered models. In 1897, Langley had built a steam powered aircraft with a 5 foot wing span which flew for over 3000 feet. The Smithsonian sent Wilbur four pamphlets, one by Langley, one by Lilienthal, one from a French writer, and one from Octave Chanute, who had a group of “hang gliders” flying near Chicago. The pamphlets contained the best aerodynamic data and theory of the day. Based on the data, the brothers began to size and design their aircraft. Also, at this time, Wilbur began to write to Octave Chanute. They corresponded nearly every week for the next ten years. Copies of these letters form an important historical record of the invention of the airplane.

## Slide 15

**Notes:**
This is an important slide which shows the lift equation as understood by scientists in 1900. It was known that the aerodynamic lift and drag of an object depends on the square of the velocity of the air passing the object and linearly on the surface area of the object. They knew that there was a dependence on the local atmospheric pressure and they characterized this by a pressure factor “k” called the Smeaton coefficient after the man who first determined its value. The Smeaton coefficient was the drag on a one square foot flat plate moving at one mile an hour with the flat side into the wind. It was a reference value that they thought would be easy to measure. All other aerodynamic measurements would be made relative to this reference. Smeaton had measured the value to be .005 pounds, although other researches obtained values that varied by more than 100 % (.002). The engineers knew that lift also depended on the shape and inclination of the object to its motion and they characterized this value by a lift coefficient “cl”. The brothers used tables of lift coefficients that were generated by Lilienthal in the design of their aircraft. They used this equation to tell them how big to make their wings. They estimated the weight of aircraft (50) plus pilot (150) to be 200 pounds; that’s “L”. They were going to fly at about 20 mph, k was .005, and cl was about .5. So they would use two wings; each wing being 5 feet by 20 feet.

## Slide 16

**Notes:**
In the fall of 1900, they arrived at Kitty Hawk and camped out on the sand dunes. Here’s a picture taken by Orville of Wilbur doing the dishes. The two long poles on the side of the tent were the spars of the wings of the kite. In the rest of this presentation we shall show a lot of photographs taken (mostly) by Orville Wright. The brothers were some of the first inventors to use photography to document their experiments.

## Slide 17

**Notes:**
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.

## Slide 18

**Notes:**
This is Tom Tate, the son of the local postman who would hang the camp of the Wright brothers. He was also the first pilot of their aircraft. They allowed him to sit on the wing and be “kited”, although the craft never got more than a few feet above the ground. On the last day of their stay at Kitty Hawk, the winds were high (30 mph) and Wilbur flew the craft on 12 flights as a glider. He was launched from the edge of a sand dune and glided to the bottom (about 300 feet). He tested out the roll control of the aircraft, which worked as planned.

## 1901

- Flying

**Notes:**
The brothers returned to Dayton and analyzed the data that they had recorded in 1900. Something was wrong in their design, but they decided to press ahead. For 1901, they would design a larger wing, since lift depends on the area. With a rectangular wing, there were two ways to increase area; increase the span (tip to tip), or increase the chord (front to back). They decided to increase chord. Wilbur reported his results to Chanute and invited him to visit them at Kitty Hawk that summer.

## Slide 20

**Notes:**
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.

## Slide 21

**Notes:**
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.

## Slide 22

**Notes:**
Here is the 1901 aircraft being flown as a kite. Wind is from the left; the brothers put their tail in the front of the aircraft. Notice the high inclination (angle of attack) of the aircraft. This indicates that the wing isn’t very efficient and has to be inclined at a large angle to generate enough lift to pick up the weight. Also note that, though it is July and the temperature and humidity are near 100, the brothers wear suits, ties, and hats while doing their experiments. As in 1900, the brothers measure everything that they can when they fly the 1901. But there are indications that the aircraft doesn’t perform very well. They estimate that it is only generating 1/3 of the lift predicted by their design.

## Slide 23

**Notes:**
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 1901 .. 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.

## Slide 24

**Notes:**
Here’s Wilbur on a glide. He was able to use the moving elevator for pitch control and warped the wing tips for roll control. He normally flew close to a hill so that he could accurately determine the angle at which he was flying. It was easy to measure the angle of the hill, but hard to determine the angle in flight. So he flew parallel to the hill side. Sometimes when he tried to bank and turn, the aircraft spun out of control in yaw. They called it “well digging”  because one wing tip would become nearly motionless while the aircraft spun about that tip in a flat fashion.

## Slide 25

**Notes:**
By flying parallel to the side of the hill, and measuring the angle of the hill, the brothers could use the math shown on this slide to determine the ratio of lift to drag. They could also predict what that number “should” be from Lilienthal’s data. Those two numbers didn’t agree. So the brothers began to doubt the accuracy of Liliienthal’s data. 

## 1901

- Testing

**Notes:**
When they returned from Kitty Hawk to Dayton, they were very discouraged. It appeared that, after two years work, they were going nowhere. It looked like the best data in the world was full of errors. They were encountering unexpected problems, like the “well digging”.  And they only had a few successful flights under their belts, not the hours that they thought were necessary to become good pilots. They were ready to give up. But Chanute asked them to come to Chicago and speak before the Western Society of Engineers about their ideas and flight experiments. Wilbur reluctantly agreed and they started to analyze their data from 1901.

## Slide 27

**Notes:**
The brothers used their flight data and the equations for lift and drag to determine a more correct value of the Smeaton coefficient. They found the value to be .0033, while most other researchers were using .005 as measured by Smeaton. The difference would explain some of the problems that they were seeing in the lift. They had used .005 in the design and if the real value was .0033, they would make their wings too small to lift the design weight. As it turns out, the brothers were very accurate in their new value for the coefficient. Modern measurements, using sophisticated instruments and computers, have determined that the actual value is .00327.

## Slide 28

**Notes:**
Wlibur was going to Chicago and was going to report that he thought there were errors in the Smeaton coefficient and maybe in Lilienthal’s data as well. To check their results, they decided to do a model experiment. They mounted a wheel on a bicycle as shown in the figure. On the wheel they mounted two models; a flat plate and an airfoil. When they would ride the bicycle, the wheel would turn until the forces on the airfoil and the flat plate were balanced. They could measure the angle that the wheel turned. They could also predict what that angle should be by using math and the data from Lilienthal. If the prediction did not match the results from the experiment, there must be something wrong in the data. And that’s exactly what happened.

## Slide 29

**Notes:**
The bicycle experiment produced some useful results, but they really couldn’t control the conditions of the experiment. The wind could blow from the side, the model would bounce up and down, and it was hard to ride, steer, and take data all at the same time. So while Wilbur was in Chicago, Orville built a crude wind tunnel to test their models in a more controlled environment. The Engineers in Chicago were amazed at how much work the brothers had accomplished and encouraged Wilbur to keep at it. When he got back to Dayton and saw Orville’s tunnel, they decided to build a bigger, better wind tunnel and take their own data. This is a picture of a model of that tunnel. In this front view, you can see the fan which pushed air through the tunnel. This was actually a bad design. Modern tunnels pull air through the tunnel, not push, because there is an unsteady wake that comes off the blades of the fan. The wake goes through the test section where the model sits and causes things to be very unsteady and hard to measure. The brothers built an egg-crate device just downstream of the fan to solve this problem. The fan was connected to an engine used in their bicycle shop to power their tools. The tunnel is about six foot long and a foot and a half square in the test section. The test section is at the open window at the top of the tunnel.

## Slide 30

**Notes:**
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.

## Slide 31

**Notes:**
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.

## Slide 32

**Notes:**
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.

## Slide 33

**Notes:**
This is the drag balance, which is similar to the lift balance. The forces on the model twists the mounting axels until the forces are balanced. The amount of twist is measured as an angle. Then math is used to turn the angle into a drag coefficient which is used in the design equations.

## Slide 34

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

## 1902

**Notes:**
The brothers designed and built a new aircraft for 1902 based on their wind tunnel tests. They headed back to Kitty Hawk for the third time in the fall of 1902.

## Slide 36

**Notes:**
Here is the 1902 aircraft being flown as a kite. Comparing with the kite picture of the 1901, we see that this is a very efficient design. The kite flies nearly overhead. You will also notice that the brothers have added a rudder at the right. They hoped that this would solve the “well digging” problem encountered the previous year. But it initially caused even more problems. At first, the brothers used a fixed tail. But when the plane started to yaw, it would become even more unstable and snapped around back to front. Orville figured out that the tail should be movable, like the elevator. Wilbur decided to tie the controls to the wing warping controls. 

## Slide 37

**Notes:**
With the wind tunnel designed aircraft, and the new flight controls, the brothers take to the air in 1902. 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)

## Slide 38

**Notes:**
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 1899. 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.

## 1903

**Notes:**
The brothers returned to Dayton and immediately began work on the powered aircraft.

## Slide 40

**Notes:**
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.

## Slide 41

**Notes:**
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.

## Slide 42

**Notes:**
This is a view of the engine and the “cockpit” from the rear. The hip cradle is the U – shaped object at the left, the motor is on the right. The four cans are the combustion chambers. Exhaust gas exited the motor at the bottom ... right next to the pilot. The motor had no muffler or exhaust pipe. The flywheel is visible at the right with the chains connected to the propellers. The object on this side of the flywheel is the magneto which produced the combustion spark in the combustion chambers. You can also see the “instrument panel” to the right of the hip cradle. There is Chanute’s anemometer at the top to measure airspeed and a stop watch at the bottom.

## Slide 43

**Notes:**
Here’s another view of the engine ... tipped on its side so we can see underneath. The combustion chambers are now at the top, the flywheel to the right. The shafts located near the combustion chambers hold the cams which push the followers which open the exhaust valves in the proper order.

## Slide 44

**Notes:**
The brothers decided to use two propellers on their aircraft in order to move a lot of air to produce thrust. They wanted the propellers to rotate in opposite directions to cancel out the gyroscopic moment. The propellers were connected to the motor by chains. So the brothers put a half twist in the chain to the left propeller to produce counter-rotating props.

## Slide 45

**Notes:**
All of the parts of the 1903 aircraft were built in Dayton and shipped to Kitty Hawk. The brothers arrived in Kitty Hawk for the fourth straight year in late September of 1903. They had left the 1902 glider behind at the end of the previous year, so they started 1903 by constructing a hangar to house the new 1903 aircraft. Then they set to work assembling the 1903. They kept up their piloting skills by flying the 1902 during this time as well. This is picture of Wilbur working on the 1903.

## Slide 46

**Notes:**
When they had finally assembled the 1903, they rolled it out of its hangar and took some pictures. The shed on the right is the hangar built in 1901. The brothers slept in the rafters of this hangar behind the window over the door. The hangar for the 1903 is at the left with the aircraft on its launch rail. The completed aircraft with its motor weighed about 550 pounds ... too much for two guys to lift and it had no wheels. So the brothers made a rail from 4 sections of 15 foot 2x4’s and would push the airplane along the rail on a dolly with a bicycle hub for a wheel. They would pick up a section of the rail after the plane passed and moved that section to the front and in this way could move the airplane to the launch site. This was the first time that the entire airplane had been assembled; it was too big to assemble and test in Dayton. The propellers rotated on shafts which were connected to the motor by a series of sprockets and “bicycle” chains. When the motor was first started, a propeller shaft broke because of the vibrations. They had to send back to Dayton for some new, stronger shafts. When they arrived and were tested, they also cracked. The brothers had tried to save weight by using tubular shafts and the shafts weren’t strong enough. So Orville went back to Dayton to oversee the production of solid shafts and returned with them. With the solid shafts, they had problems keeping the propellers attached to the shafts. This was solved with some contact cement used to hold bicycle tubes onto rims in those days. The brothers had only calculated the thrust which should be generated by the propellers. To check their calculations, the rigged a series of pulleys to the aircraft and connected the end of the ropes to some weighed bags of sand. They then fired up the engine and measured how much sand was necessary to just keep the plane from moving. This was a direct measurement of the thrust and very similar to a modern engine test stand. With the thrust determined, they knew that they would be able to get off the ground.

## Slide 47

**Notes:**
This is a rear view of the assembled 1903 airplane. Kill Devil Hill, the sight of the glider experiments, is in the background. The dolly on which the plane rests is seen at the bottom of the landing skids. The thin propellers are clearly seen in this view. The brothers spent almost two months developing the theory, building the propellers, and testing them in their shop in Dayton. It is one of their major accomplishments. Propeller design, at the time, was based on marine (nautical) propellers and everyone else (Maxim, Langley, etc.) had designs which were very flat, large at the tip, and only about 25% efficient. 75% of the power of the engine was not being converted into thrust. The brothers looked at the propeller differently; they saw it as a rotating wing. So the principles discovered for wing design was applied to their propellers. In addition, they used their wind tunnel data to pick the proper cross-sectional shape. They twisted the propeller from hub to tip because the tip moves at a different lateral speed than the hub. The result was a propeller design that was 66% efficient ... almost what we see today. The brothers not only invented the airplane control system, they invented the modern propeller. On this photo you will also notice the wing droop from center to tip. This is called a cathedral (the opposite of dihedral) design and made the plane very responsive to roll inputs.

## Slide 48

**Notes:**
On December 14, 1903 the brothers took the plane out for its first flight. They flipped a coin to pick the first pilot, with the agreement that they would alternate flights. Wilbur won the toss and climbed on board. The motor was started  and brought up to speed and the plane moved down the launch rail. Wilbur pulled the nose up and stalled the plane a few feet off the ground. The plane landed hard and broke the front elevator as shown above. The brothers decided that this really didn’t constitute a successful flight, since Wilbur wasn’t in complete control. They would repair the elevator and try again.

## Slide 49

**Notes:**
This is the most famous aviation picture of all time. It was taken December 17, 1903  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.

## Slide 50

**Notes:**
All four flights of 1903 are characterized by a bucking movement of the aircraft. All flights were in a straight line and the pilot had to really battle the plane for control. Something was wrong. On the last flight, Wilbur landed hard and broke the front elevator. They think that they can fix it, but the plane was caught by gust of wind and tumbled across the sand, breaking the engine off its posts. John Daniels tried to secure the plane but was caught up in the wreckage and received some bruises and scratches. Flying was over for 1903. The brothers cabled their father in Dayton that they would be home for Christmas and had been successful on four flights. But the brothers knew that there was still a lot of work to be done ... all the problems had not been solved.

## 1904

**Notes:**
The brothers recognized that they had a pitch problem. The 1903 aircraft was unstable in pitch. They didn’t know the cause (which is the short distance between the front elevator and the aircraft center of gravity). They knew it was related to the center of gravity (cg) of the aircraft and they decided to design a new airplane for 1904 which would have a different center of gravity than the 1903. They decided to move the cg aft. They move the radiator to the rear, the engine slightly back, and re-design the rudder to be slightly larger and more aft.

## Slide 52

**Notes:**
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.

## Slide 53

**Notes:**
Here’s a picture of a launch at Huffman’s Prarie. It turns out that they really did need the high winds of Kitty Hawk, even with a powered plane, because it shortens the take-off roll. They have trouble getting airborne in early 1904. They have built a slightly larger engine and have some problems with it. To compensate for the low winds, they build a catapult launcher (just like modern aircraft carriers). A large weight is pulled to the top a tower shown at the right. When the weight falls it pulls a line which is attached to the front of the airplane and pulls it along the ground. This solves the wind problem, but they quickly discover that they have moved the cg in the wrong direction. The 1904 aircraft is more unstable than the 1903. So they lash 70 pound of iron bars under the nose to improve the handling of the 1904. Now it flies, but not very well because it is carrying extra weight.

## Slide 54

**Notes:**
On September 20, 1904 an important milestone is achieved. The airplane takes off, executes a turn near the end of the field, flies to the other end of the field and executes another turn, returning to the take-off spot. Wilbur completes the first circuit of the airfield. The ability to maneuver an airplane was their original goal in 1899. They complete nearly 100 flights during the flying season of 1904. The longest is about five minutes with four circuits of the field.

## 1905

**Notes:**
In 1905, they design and build another new aircraft. This is the 6th aircraft which they have built since 1900. The 1905 is built to correct the instabilities which were first seen in 1903. The radiator and other equipment is moved back to the front of the aircraft. The elevator is increased in size and moved an additional 10 feet forward. Flying continues at Huffman field.

## Slide 56

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

## Slide 57

**Notes:**
With the 1905 aircraft, the invention of the airplane is completed. The brothers can stay aloft until the plane runs out of fuel (35 minutes). They execute figure eights (flat, not vertical since they still don’t seat belts) and they begin to fly higher, over the trees. They have submitted the patent forms on their 1902 aircraft, but the patent has not yet been granted. People traveling on the trolley line can see them flying and the brothers begin to worry that someone may steal their ideas.

## Slide 58

**Notes:**
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.