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Name: Dan
Status: student
Grade: 9-12
Location: MA
Date: December 2007

Question:
How does the shape of a parachute affect its falling speed, when all the shapes have a relatively similar surface area?



Replies:
Dan,

The basic principle of a standard parachute is drag. Drag is the amount of force required to keep an object moving through the air at a given speed, and it increases with speed. The design of a standard parachute (for someone jumping from a plane we will say) is to have enough surface area that the amount of drag equals their weight at a relatively slow and safe speed.

Now for the less than standard part. You may have seen some pictures with parachutes that were pulled into a much longer, narrower shape. This is done by restricting how far the same parachute can open. This way, the rate at which the jumper slows down is not so great right at the start of their jump. Consider that a human body can fall at around 120 MPH, and a 'safe' landing speed might be closer to 5 MPH. At 120 MPH, the force of drag on that parachute would be so great, it would likely injure the skydiver, or just break the lines it is attached with.

Now for even LESS standard parachutes. The large, square parachutes you have probably seen do not rely solely on drag to slow their user down. They are cut and trimmed so they form an airfoil as they descend. This airfoil acts like a wing, and even begins producing lift! The trade off for the reduced drop rate though is an increased forward momentum the skydiver will have to deal with once they touch down. (instead of coming straight down, they are now moving forward at the speed of a good run!) Usually, this can be turned to the skydiver's advantage though, to counter wind, or aim for a specific spot on the ground.

Ryan Belscamper


That is an excellent question, especially since the sport parachute has undergone so much development in the past 30 years that I have been jumping. Today's chutes, called wings, are just that. They are shaped so that they fly forward and develop lift just like an airplane wing. As such, they are very maneuverable and land far easier than the old round ones. They are, however, a little more likely to malfunction. If a modern chute stops moving forward with respect to the wind, it "stalls" and falls pretty much straight down rather quickly. The lift you get depends upon the surface area of the chute, its design and your weight. On the whole, they stay in the air longer than the old designs. The older chutes, called conical or spherical or just round, depended on their design to catch air to slow descent. To provide some little forward motion and control, panels of cloth were left out of the backs of the chute. Air spilled out of the gores and forced the chute forward. The mushroom shape of the canopy gave some lift, but not much. These canopies are great for going pretty much straight down and they deliver you to the ground with a pretty good thump (up to 20 mph) depending upon your weight and canopy size. Again, the rate of descent was controlled by the size of the canopy. They maneuver like a wounded elephant with a broken leg - that is rather poorly. It was impossible to "fly back up" in one of these as you can with a wing if conditions are right. Go to a local drop zone for more information. Believe me, like all folks who have hobbies, parachutists will love to talk with you and give you all sorts of ideas, prejudices and stories.

Robert Avakian


The shape of the parachute affects the parachute's drag. If the shape of the parachute is aerodynamic (spherical or tear drop shaped), the drag will be reduced, making the parachute ineffective. Scott P. Smith



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