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What To Observe : Surface Area & Shape : Canopy Layers : Weight : String : Vents : Frame               
MOVIE 1:   6 minutes 30 seconds
 

Vents

Vent openings can be located at the top or apex of a cup-shaped canopy, or near the canopy's skirt or perimeter. They can help in meeting two design criteria: stable flight and a full inflation of the canopy. Since most parachutes tend to oscillate, having a method for lessening or dampening that behavior is important. Vents work by allowing a portion of column of air that a parachutes displace to pass through the canopy, which reduces swinging.

But are there tradeoffs associated with this benefit? Many student designers focus on the positive effects of a change in a design, while neglecting to consider drawbacks. Most students would predict that vents holes reduce drag by reducing the surface area of the chute. Actual tests show that for vent holes up to 15% of the area of the chute, there is no reduction on the overall drag force for a chute using vents compared to one without. Thus, you get the benefits of greater stability, but not the drawbacks of loss of drag force, when you use vents up to 25% of the total canopy area.

You might want to review the movie to hear again about how air flows through vents to give the benefits of more stable flight without loss of total drag force.

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