Friday, October 9, 2015

The Slot Design Tactic to Defend Stall

In 1930s, Lockheed Electra was one successful aircraft. It was twin-engine propeller aircraft that pushed the boundaries of air travelling. Airlines that had this aircraft were able to break new industry horizons with comfort and speed.

When they were modified with more powerful engines, at higher angle of attack - the wing tips enter stall leading the aircraft to enter spin and eventually crash. 

Lockheed had to come up with a solution to defend the stall. 

Stall can only be defended by airflow. So what they need was extra airflow to create lift and delay boundary layer separation. 

The solution was elegant implementation of a natural phenomena called Coanda effect.

The Coanda effect is the tendency of a fluid jet to be attracted to a nearby surface. The principle was named after Romanian aerodynamics pioneer Henri Coanda who was the first to recognize the practical application of the phenomenon in aircraft development. (Ref: Wikipedia)

Here is a video for better understanding of Coanda effect:

Now how can we implement this in aircraft? Of course, fixing a rotating fan on a wing is ridiculous. 

They came with solution called slot. 

Slots are basically holes in the wings. These holes are shaped like that of a letter box. 

The rightly placed holes in the wings cause the high pressure air from below to flow above. This give extra air flow which in turn defend stall. 

Leading-edge slats are quite commonly used in many slow speed aircraft. It was first implemented by a company called Handley Page which patented these designs. 

Even though it gave extra air flow in high angle of attacks; it caused way lot of drag in higher speeds. This was solved by retractable slots called slats. 

All modern aircraft use slats to defend stall at low speeds to make it safe to fly.

When you fly next time, notice the leading edge slats. Hopefully you realize the impact it has on the aircraft and you, the passenger flying in it. 

Thank You guys for reading.

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