Leading Edge Slots
Slots on the leading edge of the wing.
July 1972. All 118 people on board a British Europen Airways flight from London Heathrow, died when the airliner crashed soon after take-off. An inquiry by the Air Accidents Investigation Branch said an air speed error had caused the plane to stall.
Fifty five years earlier, German World War One pilot, G.V. Lachman crashed his plane after stalling it.
A stall occurs when a wing no longer generates enough lift to keep the airplane in the air, a situation that happens when the plane is either travelling too slowly, or when the angle of its climb is too steep, or a combination of both.
Herr Lachman, recovering in hospital from his crash injuries, pondered this problem, and surmised that if a wing was made up of several smaller wings, separated by open spaces or 'slots', then air would flow through the slots and provide more lift at slower speeds.
Models he made suggested they would work, but his attempt to patent the idea was rejected.
Around the same time in England, designers at the Handley Page Aircraft Company were wrestling with the same problem. They had discovered that just before a wing stalls, airflow 'burbles', or becomes turbulent over the upper surface, increasing drag and decreasing lift.
After much experimentation, they discovered that a slot on the leading edge of the wing increased lift dramatically, in fact by an astonishing 60 percent.
In 1919, Handley Page patented the design of the leading edge slot, and it is still a common feature on light aircraft today.
Leading edge slots are generally of two types, full span and partial span.
Full span slots, as the title suggests, run the full length of a planes' wing, and are commonly found on Short Take Off and Landing aircraft (STOL), allowing slower, stall free landing speeds, and short landing runs.
Partial span slots are the norm on regular light aircraft. Due to lower drag, they allow steeper climb angles and better cruising speeds than a full span slot.
Larger aircraft have retractable 'slats'. These work in the same way as slots but are retracted at cruising speed for absolute minimum drag effect.