What’s the reason for keeping a hole in the center of a parachute?

What could happen if there was no hole in the center of parachute to let some of the air escape? Up to the beginning of the Second World War the paratroopers used parachutes without holes and consequently faced two serious risks.

1. When the folded parachute opened up it stopped the free fall with a sudden jerk. This jerk was severe enough to wrench muscles and joints of the bones very painfully. A hole in parachute allowing the air to escape opened it gradually applying gradual brake on the free fall but this aspect had not been taken into consideration in those early days.

2. Another risk encountered by the paratroopers was uncontrollable pendulum like swinging movement of the descending parachute. Increasing pressure of air filled up in the dome-shaped parachute raised one side in a swinging motion to let the air escape. Then followed a movement in which opposite side swung upward as air pressure increased in that part. These swings continued uncontrollably till the time of dropping on the ground. If the paratrooper happened to be at the end of a swing at the time of impact on the ground his slanted body would fall helplessly sideways rather than making a controlled landing with both the feet on the ground followed up with a roll over. A sideways fall would be painful and might even fracture the hip bone. Such accidents tool place from time to time in those days.

Today’s parachute is extremely safe because of ventilator like hole in the center. This hole allows air to escape so the parachute does not swing the paratrooper like a pendulum. Further, the folded parachute opens without jolting him.

Additional reading:
Parachute (Wikipedia)

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