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
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
They would measure the aerodynamic lift and drag
of their wing designs using a
in their bicycle shop at Dayton, Ohio.
They built two separate balances to perform these measurements,
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
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)
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
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.
- Beginner's Guide Home Page