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 At the end of the summer of 1901, the Wright brothers were frustrated by the flight tests of their 1901 glider. The aircraft was flown frequently up to 300 feet in a single glide. But the aircraft did not perform as well as the brothers had expected. The aircraft only developed 1/3 of the lift which was predicted by the lift equation using Lilienthal's data. During the fall of 1901, the brothers began to question the aerodynamic data on which they were basing their designs. So, they decided to conduct a series of wind tunnel tests to verify the results they were experiencing in flight. They would measure the aerodynamic lift and drag on small models of their wing designs using a wind tunnel in their bicycle shop at Dayton, Ohio. They built two separate balances to perform these measurements, one for lift and the other for drag. On this page we will discuss the design of the lift balance and on a separate page we will discuss the procedure the brothers used to obtain data from the balance. Because of the form of the lift equation used by the brothers, they were interested in measuring the lift generated by a model relative to the drag of a reference flat plate. On the slide we show a photo of a reconstruction of the lift balance with the parts indicated by colored leader lines. The actual balance was made from bicycle spokes and hacksaw blades and was a very delicate instrument. We are looking downstream inside the tunnel, so the wind would strike the model in the direction that you are looking. The balance is attached to the floor of the tunnel by a screw through the mounting frame (black). It could then be easily removed and replaced in the tunnel by the drag balance. On the lower cross beam (dark brown) the reference drag plates (green) are permanently attached. The cross beam is rigidly attached to short vertical axles (yellow) on each end. The vertical axles are loosely attached to arms (red) at the top and bottom so that the cross beam can move from side to side. The arms are rigidly attached to long axles (blue) that run through the mounting frame. The long axles are free to rotate in the frame as the lower cross beam moves. The arrangement of the axles and arms cause the ends of lower cross beam to move in circular arcs about the long axles with the cross beam always parallel to the bottom of the frame. At the bottom of the left long axle, a pointer is rigidly attached perpendicular to the arms. This pointer indicates the amount of rotation of the long axles on a dial at the bottom of the left axle. The upper cross beam (light brown) is also rigidly attached to short axles (yellow) which are loosely attached to the upper arms (cyan). These arms are attached to the long axle by a friction sleeve (purple). When the friction sleeve is engaged, the long axle rotates and the lower cross beam moves as the upper cross beam is moved. When the friction sleeve is dis-engaged, you can move the upper cross beam without moving the lower cross beam or long axle. The wing model is attached to the balance on the upper cross beam. The angle of attack of the model is varied between tests by pivoting the model on the bracket which attaches it to the cross beam. The brothers built models from strips of 20 guage steel (1/32 inch thick) which were cut, hammered, filed and soldered to produce various shapes. They made between one and two hundred models and made quick preliminary tests in October, 1901, to develop their test techniques and to investigate a wide range of design variables. Some of the models were used in combination to study bi- and tri-wing designs. Following the preliminary experiments, they chose about 30 of their best designs for more detailed testing. The models were numbered by the brothers and each was designed to be part of a parametric study of lift and drag by changing the value of only one design variable between models. The actual balance and models are currently kept at The Franklin Institute. You can simulate the operation of the lift balance by using our interactive tunnel simulator. Navigation.. Beginner's Guide Home Page

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