# 3 Things You Don’t Know About Aerodynamics

• The V-shaped pattern adopted by migrating birds is an energy saving manoeuvre which involves complicated aerodynamics
• Adding a simple vertical tip to a plane wing improves the aerodynamics and creates significantly more uplift
• The art of swing bowling is well documented with the position of the seam, shiny and rough sides of the cricket ball creating very different aerodynamics

If your answer to the above questions is “NO”, then consider yourself lucky. You are in for a treat today. In this article we will have a very brief introduction of aerodynamics and aerodynamic forces and then, look at frequently happening events around us. We will try to decipher how aerodynamics influence these actions which should give you an idea about how other aerodynamic events work.

Let us take a look at the basic machinery before we delve deep into the lesser known elements of aerodynamics. The fundamental forces that play a major role in every aerodynamic study are Lift and Drag. Consider an aircraft running down a runway. The IC engine will provide the thrust required to gain the momentum and gravity will exert downward force on the plane. The wings are designed to generate upward force on the plane, known as the lift force. The resistance offered by the air flowing in the opposite direction to the thrust is called the drag force. The major concern of all aerodynamics engineers is to increase lift and reduce drag. Lift can be calculated using the lift equation.

# Do you know why some planes have vertical tips at the end of the wing?

The size (length*width) of the wing is very important for aircraft designers. It represents the aircraftâ€™s capacity (cargo-weight or no. of passengers). Longer wings generate more lift, and hence, provide more weight carrying capacity. However, longer wings pose the problem of sagging and deflection (deflection is proportional to the cube of length in cantilever beams). Hence longer wings demand more reinforcing material to reduce deflection, leading to the increase in weight and fuel consumption.

In today’s world, the demand for aircraft capacity is increasing day by day, which calls for higher lift force. Due to limitations in runway and hangar sizes, engineers canâ€™t increase the length of the wing. So, what can aircraft designers do to increase lift without increasing the length of the wing?

You might be tempted to say that the solution is easy, one should increase the width of the wing. However, more width leads to more vortex generation at the tip and hence increases energy consumption. The vortex are generated due to the pressure mismatch between top and bottom of the wing and reduces the effective-length (length that helps in lift generation) of the wing. In order to increase the effective length, without increasing the actual length of the wing, vertical wing ends (called winglets) are provided to capture and reduce the vortex generation and increase lift.

# Do you know why migrating birds fly in a V-shaped pattern?

Migrating birds have to cover long distances with minimum energy consumption. In order to minimize the energy consumption in flying, they tend to align themselves in such a way that they can make the best out of the eddy currents generated by the birds ahead of them.

The leading bird generates a vortex flow of air. The upward moving air (upwash) is at an offset from the downward moving air (downwash). Therefore, the trailing birds will position themselves in the upwash region to gain lift without much effort. The upwash helps the bird in maintaining altitude just like a glider in rising air. Leading birds even change positions in a cyclic manner to avoid fatigue and spread the workload. Perhaps the best example is a flock of geese flying long distances.

# Do you know the aerodynamics behind swing bowling?

Swing bowling is a type of bowling in which a cricket ball literally changes its path in mid-air, exhibiting some fascinating aerodynamics. Every one of us has used this technique (though only cricketer Dale Steyn seems to have mastered it!). Itâ€™s time to understand the science behind it.

The cricket ball has two leather skins, sewed together by the seam. In order to generate swing, the bowler bowls in such a way that the seam is at an angle with the direction of the ballâ€™s movement. This angled seam leads to unequal pressure generation on different sides of the ball (as illustrated in the image above). The uneven seam surface generates turbulent boundary layer flow of air, whereas on the other side, the smooth surface allows laminar boundary layer flow of air (see above illustration). This pressure difference allows the ball to swing (move) in a direction perpendicular to the actualÂ  flight of the ball. Depending how the ball is held at the point of delivery it will either swing inwards or away from the batsman.