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What To Observe : Surface Area & Shape : Canopy Layers : Weight : String : Vents : Frame               
MOVIE 1:   40 seconds
Canopy Layers

Students frequently attempt to increase the surface area of their parachute systems in two ways -- by spreading more filters out (A) , and by stacking them up (B). Spreading out the coffee filters to make a larger, single-canopy parachute is most common. Others stack up filters vertically in a few ways.

1. One approach is to stack the coffee filters one inside another (C). Having multiple filters fitted into one another may provide the slight advantage of added stiffness to the canopy -- this would help maximize the inflated area. Students can say they want to prevent air from flowing through the paper, but this does not occur at such slow rates of descent. Real parachutes move so quickly that air passes through the material. Basically, stacking filters adds to the overall mass of the parachute system without increasing the drag. This is a lopsided trade-off, with little advantageof which to speak.

2. Another approach is to tie one filter to another with strings whose length varies according to the designer. Students may get this idea from seeing the drone parachute that helps deploy the main chute in large parachute systems. This design has problems with poor inflation because of air turbulence. The flow of air forms eddies behind the lead canopy. These eddies interfere with the flow of air into other layers, which do noit s not fill up fully with air. This partial inflation lowers the parachute's efficiency, worsens its performance, while adding more weight. Watch this page's movie to see drops of multi-tiered chutes.

3. Some multi-tiered parachute that students have been found to work quite well. Having a regular, cupped-shaped canopy, but with the weight taped to a single coffee filter oriented with its open end up (D). Essentially, the lower filter's drag lessens the overall pull of the washers on the strings and canopy. The system is stable since the parachute falls at such slow speeds that the turbulence does not disturb the inflating of the upper canopy. A real parachute that might encounter wind speeds of 6 m/sec would have a wake that would interfere with a parachute three times its width, and separated by as much distance as a few meters.


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