Search results
Results from the WOW.Com Content Network
The drag curve or drag polar is the relationship ... of attack in a wind tunnel, ... a head wind is determined from the graph by shifting the origin to the right ...
These vary with speed, so the results are typically plotted on a 2-dimensional graph. In almost all cases the graph forms a U-shape, due to the two main components of drag. The L/D may be calculated using computational fluid dynamics or computer simulation. It is measured empirically by testing in a wind tunnel or in free flight test. [1] [2] [3]
A sample wind tunnel layout showing some typical features including a test section and control room, a machine for pumping air continuously through ducting, and a nozzle for setting the test airspeed. A wind tunnel is "an apparatus for producing a controlled stream of air for conducting aerodynamic experiments". [1]
The exact relationship is usually measured in a wind tunnel and depends on the airfoil section. The relationship for an aircraft wing depends on the planform and its aspect ratio. The graph shows that the greatest amount of lift is produced as the critical angle of attack is reached (which in early-20th century aviation was called the "burble ...
In wind tunnel tests, in which the angle of attack and airspeed remain constant, an increase in the lift coefficient ensues, [9] which accounts for the "floating" effect. Ground effect also alters thrust versus velocity, where reduced induced drag requires less thrust in order to maintain the same velocity.
The aerodynamic center of an airfoil is usually close to 25% of the chord behind the leading edge of the airfoil. When making tests on a model airfoil, such as in a wind-tunnel, if the force sensor is not aligned with the quarter-chord of the airfoil, but offset by a distance x, the pitching moment about the quarter-chord point, / is given by
The drag characteristics of a wing with infinite span can be simulated using an airfoil segment the width of a wind tunnel. [12] An increase in wingspan or a solution with a similar effect is one way to reduce induced drag. [6]: 4.10 The Wright brothers used curved trailing edges on their rectangular wings. [13]
Automotive aerodynamics is studied using both computer modelling and wind tunnel testing. For the most accurate results from a wind tunnel test, the tunnel is sometimes equipped with a rolling road. This is a movable floor for the working section, which moves at the same speed as the air flow.