parachute(20pts)

Will a parachute with a hole on top land in a shorter time than other parachuhte?And what are the difference between them?

Please answer in English and do mot copy from yahoo knowledge.

1 個解答

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  • 1 十年前
    最愛解答

    A1:

    Parachutes are generally used to slow the descent of a person or object to Earth or another celestial body within an atmosphere. Drogue parachutes are also sometimes used to aid horizontal deceleration of a vehicle (an airplane or space shuttle after touchdown, or a drag racer). In this case, the lower speed of the descending object (i.e. skydiver) prevents him from injuring himself due to shock when reaching the ground.

    A2:

    Design

    General

    A parachute is made from thin, lightweight fabric, support tapes and suspension lines. The lines are usually gathered through cloth loops or metal connector links at the ends of several strong straps called risers. The risers in turn are attached to the harness containing the load.

    Deployment systems

    Freefall deployed parachutes are pulled out of their containers by a smaller parachute called a pilot chute.

    A way of deploying a parachute directly after leaving the aircraft is the static line. One end of the static line is attached to the airplane, and the other to the deployment system of the parachute container.

    Types of parachutes

    1. Round parachutes

    An American paratrooper using an MC1-1C series 'round' parachute

    Round parachutes, which are pure drag devices (i.e., they provide no lift like the ram-air types), are used in military, emergency and cargo applications. These have large dome-shaped canopies made from a single layer of cloth. Some skydivers call them "jellyfish 'chutes" because they look like dome-shaped jellyfish. Rounds are rarely used by skydivers these days. The first round parachutes were simple, flat circulars, but suffered from instability, so most modern round parachutes are some sort of concial (i.e Strong 26 foot diameter Mid-Lite found in pilot emergency parachutes) or parabolic (picture a flat circular canopy with an extended skirt) US Army T-10 static-line.

    Some round parachutes are steerable, but not to the extent of the ram-air parachutes. An example of a steerable round is provided in the picture of the paratrooper's canopy; it is not ripped or torn but has a "T-U cut". This kind of cut allows air to escape from the back of the canopy, providing the parachute with limited forward speed. This gives the jumpers the ability to steer the parachute and to face into the wind to slow down the horizontal speed for the landing.

    2. Annular & pull down apex parachutes

    A variation on the round parachute is the pull down apex parachute - invented by a Frenchman named LeMoigne - often referred to as a Para-Commander-type canopy, named after the first model of the type. It is a round parachute, but with suspension lines to the canopy apex that applies load there and pulls the apex closer to the load distorting the round shape into a somewhat flattened or lenticular shape. At first glance, para-sailing canopies resemble Para-Commanders, but have fewer vents. Para-sailing canopies are normally towed aloft behind cars or boats.

    Often these designs have the fabric removed from the apex to open a hole through which air can exit, giving the canopy an annular geometry. They also have decreased horizontal drag due to their flatter shape, and when combined with rear-facing vents, can have considerable forward speed around 10 mph (15 km/h). Para-Commanders usually have large stabilizers hanging down the sides.

    A 'square' ram-air parachute

    參考資料:

    The discussion on designs of parachutes is well over 8,000 words which is available at http://en.wikipedia.org/wiki/Parachute

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