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Photo of the Wright 1901 wind tunnel drag balance.

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 drag balance and on a separate page we will discuss the procedure the brothers used to obtain data from the balance. On the drag balance, they measured the ratio of the drag of the model to the lift of the model. Then, knowing the lift from the lift balance, they could determine the drag of model.

On the slide we show a photo of a reconstruction of the drag 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 at the side of the balance and the wind would move from the right to the left across the model. The balance is attached to the floor of the tunnel by a screw through the mounting frame (green). It could then be easily removed and replaced in the tunnel by the lift balance. The balance consists of two cross-beams (brown) which are rigidly attached to short vertical axles (yellow). The vertical axles are loosely attached to arms at the top (red) and bottom (cyan). 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 cross beams moves. The arrangement of the axles and arms cause the ends of 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 right 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 right axle.

The model is rigidly attached to the balance on the cross beam. To change the angle of attack of the model, the whole frame is rotated about the mounting screw. The brothers built models of their wing designs using materials available in their bike shop. Strips of 20 guage steel (1/32 inch thick) 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. 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 models are currently kept at The Franklin Institute.

You can simulate the operation of the drag balance by using our interactive tunnel simulator.


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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Jun 12 2014

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