Parachutes

by Chris Woodford . Last updated: May 13, 2021.

Y ou’re screaming through the sky, safely tucked up in the cockpit of a jet fighter, when there’s a sudden loud bang and the engine judders to a halt. Well that’s just great, isn’t it? Here you are zooming along at maybe 2000 km/h (1200mph), several kilometers/miles above the ground and your plane has chosen this exact moment to break down! What do you do? Eject as soon as you possibly can, wait for the plane to fly clear, and then hit your parachute . With luck, you glide safely to the ground and live to fly another day. When it comes to saving lives, parachutes are among the simplest and most effective of inventions. How exactly do they work? Let’s take a closer look!

Photo: A traditional round parachute. Although military paratroopers still use them, they are now largely obsolete for recreational diving. Photo by Chris Desmond courtesy of US Navy.

Contents

  1. How does a parachute work in theory?
    • What causes air resistance?
    • Terminal velocity
    • How much does a parachute slow you down?
  2. What shape are parachutes?
  3. What are the parts of a traditional, round parachute?
  4. How does a parachute work in practice?
    • Softer landings
  5. Find out more

How does a parachute work in theory?

Photo: Square-shaped “ram-air” parachutes are much more common than round parachutes because they’re easier to steer and control. Photo by Shannon K. Cassidy courtesy of US Navy.

Throw a ball up in the air and, sooner or later, it always falls back to the ground. That’s because Earth pulls everything toward it with a force called gravity. You’ve probably learned in school that the strength of Earth’s gravity is roughly the same all over the world (it does vary a little bit, but not that much) and that if you drop a heavy stone and a light feather from the top of a skyscraper, gravity pulls them toward the ground at exactly the same rate.

If there were no air, the feather and the stone would hit the ground at the same time. In practice, the stone reaches the ground much faster, not because it weighs more but because the feather fans out and catches in the air as it falls. Air resistance (also called drag) slows it down.

Photo: Parachutes are made from strong lightweight nylon and have to be packed very carefully if they’re to open correctly when they’re deployed. Photo by Gary Ward courtesy of US Navy.

What causes air resistance?

Just because the air’s invisible, doesn’t mean it’s not there. Earth’s atmosphere is packed full of gas molecules, so if you want to move through air—by walking, in a car, in a plane, or dangling from a parachute—you have to push them out of the way. We only really notice this when we’re moving at speed.

Air resistance is a bit like the way water pushes against your body when you’re in a swimming pool—except that air is invisible! If you jump off a diving board or do a belly flop, the awkward shape of your body will create a a lot of resistance and bring you rapidly to a halt when you crash into the water. But if you make a sharp pointed shape with your arms and dive in gracefully, your body will part the water cleanly and you’ll continue to move quickly as you enter it. When you jump or belly flop, your body slows down quickly because the water can’t get out of the way fast enough. When you dive, you part the water smoothly in front of you so your body can glide through it quickly. With parachutes, it’s the slowing-down effect that we want.

If you fall from a plane without a parachute, your relatively compact body zooms through the air like a stone; open your parachute and you create more air resistance, drifting to the ground more slowly and safely—much more like a feather. Simply speaking, then, a parachute works by increasing your air resistance as you fall.

Terminal velocity

When a force pulls on something, it makes that object move more quickly, causing it to gain speed. In other words, it causes the object to accelerate. Like any other force, gravity makes falling objects accelerate—but only up to a point.

If you jump out of a plane, your body ought to speed up by 10 meters per second (32ft per second) every single second you’re falling. We call that an acceleration of 10 meters per second per second (or 10 meters per second squared, for short, and write it like this: 10m/s/s or 10m/s 2 ). If you were high enough off the ground, then after about a minute and a half (let’s say 100 seconds), you’d theoretically be falling at about 1000 meters per second (3600km/h or 2200 mph), which is about as fast as the fastest jet fighters have ever flown!

Artwork: When you reach terminal velocity, the upward force of air resistance exactly balances the downward pull of gravity and you stop accelerating.

In practice, that simply doesn’t happen. After about 12 seconds, you reach a speed where the force of air resistance (pushing you upward) increases so much that it balances the force of gravity (pulling you downward). At that point, there is no net acceleration and you keep on falling at a steady speed called your terminal velocity . Unfortunately, the terminal velocity for a falling person (with arms stretched out in the classic freefall position) is about 55 meters per second (200km/h or 125 mph), which is still plenty fast enough to kill you—especially if you’re falling from a plane!

Photo: 1) Freefall in theory: In this training exercise, the skydiver is practicing freefall by floating over a huge horizontally mounted air fan. The force of the air pushing upward is exactly equal to the diver’s weight pulling him downward so he floats in mid-air. Photo by Gary L. Johnson courtesy of US Navy.

Photo: 2) Freefall in practice: In reality, it’s not the air that moves past you—you move through the air—but the physics is still the same: once you reach terminal velocity, the force of the air on your body pushing you upward exactly equals the force of gravity pulling you down. Photo by Ashley Myers courtesy of US Navy.

How much does a parachute slow you down?

Feathers fall more slowly than stones because their terminal velocity is lower. So another way of understanding how a parachute works is to realize that it dramatically lowers your terminal velocity by increasing your air resistance as you fall. It does that by opening out behind you and creating a large surface area of material with a huge amount of drag. Parachutes are designed to reduce your terminal velocity by about 90 percent so you hit the ground at a relatively low speed of maybe 5–6 meters per second (roughly 20 km/h or 12 mph)—ideally, so you can land on your feet and walk away unharmed.

What shape are parachutes?

Photo: Paratroopers often still use round chutes because they’re an effective way to get lots of people quickly and safely to the ground in a fairly small space. This parachute drop took place in Latvia in June 2018. Photo by Gina Danals courtesy of US Navy.

Traditionally, parachutes were round (dome-shaped) and, with their dangling suspension lines, looked a bit like jellyfish as they fell. They had vent holes that allowed air to escape, which helped to prevent them from rocking about as they came down, and their lines provided very basic steering. Most modern parachutes are rectangular (a design known as ram-air ). They have a number of cells that inflate as the air “rams” into them, so they form a fairly rigid, curved airfoil wing, which is much more steerable and controllable than a dome-shaped parachute. Round chutes are still widely used by military paratroopers, because they work well for dropping lots of people together, in a fairly small area, at relatively low altitudes; paratroopers are simply trying to get to the ground quickly, not show off their skydiving technique. Recreational divers, on the other hand, consider round chutes obsolete: virtually all of them now use the ram-air design instead.

What are the parts of a traditional, round parachute?

If you’ve ever seen a parachute spread out on the ground, you’ll know it has lots of separate parts, and it can be a very tricky thing to pack back into its container so it opens correctly next time. What are all the bits and what do they do? Here are some of the more important ones, but there are quite a few more that I’ve missed out for clarity.

  1. Pilot chute: A small parachute that opens the large, main parachute.
  2. Bridle: Connects the pilot chute to the main chute.
  3. Apex or top vent: Allows a slow escape of air from the top of the main chute. This prevents air from leaking out of the sides of the canopy, which tends to rock the parachute wildly as it falls.
  4. Canopy: Main part of the parachute.
  5. Skirt: Lower part of the canopy (think of a person’s skirt hanging down).
  6. Suspension lines: Spread the weight of the parachutist evenly across the canopy.
  7. Links: Connect the suspension lines to the risers.
  8. Risers: Connect the links to the harness
  9. Control lines: I’ve drawn only one, but there can be several different ones for steering and braking.
  10. Harness and container: The harness is the part you wear (itself made of numerous components); the container looks similar to a rucksack and holds the packed-up parachute and all its bits and pieces, ready for action!

How does a parachute work in practice?

Skydivers make parachuting look easy, but it’s all a bit more tricky in practice! What you’re trying to achieve is to get a large piece of super-strong material opening out above and behind you in a perfectly uniform way when you’ve just jumped from a plane screaming along maybe ten times faster than a race car! How can you possibly pull something safely behind you under those conditions?

Parachutes are actually three chutes in one, packed into a single backpack called the container . There’s a main parachute, a reserve parachute (in case the main one fails), and a tiny little chute at the bottom of the container, called the pilot chute , that helps the main chute to open. Once you’re clear of the plane, you trigger the pilot chute (either by pulling on a ripcord or simply by throwing the pilot chute into the air). It rapidly opens up behind you, creating enough force to tug the main chute from the container. The main chute has to be carefully packed so the ropes that connect it to your harness (known as suspension lines ) open correctly and straighten out behind you. The main chute is designed to open in a delayed way so your body isn’t braked and jerked too suddenly and sharply. That’s safer and more comfortable for you and it also reduces the risk of the parachute ripping or tearing.

The force on a parachute is considerable, so it has to be made from really strong materials. Originally, parachutes were made from canvas or silk, but inexpensive, lightweight, synthetic materials such as nylon and Kevlar® (a chemical relative of nylon) are now generally used instead.

Softer landings

Parachutes were invented about a century ago, but they continue to evolve, as inventors devise ever-better ways to improve their safety and handling. Here’s a more advanced ‘chute, designed for the US Army in 2001 (and patented in 2003). It contains the same basic features as other chutes: a canopy (10, blue), a skirt underneath (12), and suspension lines (14) in four groups called risers (16), attached to a bridle (22), which supports the harness (26) and parachutist (P). But it also has two improved safety features to reduce the risk of the parachutist landing too fast and too hard. At the top, the parachute has a bridle with an extra loop of rope on either side and an electrical cutting mechanism to release it (pink, top, labeled 28). In the middle, it has what’s known as a pneumatic muscle (bright green, 24). There’s an altitude measuring device (gray, top, 34, 36, 44), which projects radar beams to the ground to measure your height and speed and figure out when the safety mechanisms need to be deployed.

How does it work? That’s shown in the artwork on the right. If the wind blows you too fast horizontally, the appropriate electrical mechanism releases one of the extra side ropes, causing the parachute to tilt to the opposite side, so reducing your speed. When you near the ground, if you’re going too fast, the pneumatic muscle shortens, pulling you much closer toward the canopy, and so reducing your speed.

What a drag!

Photo: The Space Shuttle Endeavour, coming in to land on June 19, 2002. Photo courtesy of NASA Armstrong Flight Research Center.

Using a parachute to bring a person safely to the ground from a plane is one thing. But what if you had to bring an entire plane to rest the same way? That was the challenge facing NASA every time the Space Shuttle (the reusable space plane, now-retired) came back to Earth.

During its launch phase, the Shuttle had a powerful main engine and rocket boosters to power it into space. But when it came back again, it was nothing but a glider, drifting through the air and counting on its stubby wings to carry it home.

Once it was safely back inside Earth’s atmosphere, the Shuttle hit its 4.5km (2.8mile) long landing strip at about 350km/h (220mph)—rather faster than a typical jet airplane (which lands at speeds more like 240km/h or 150mph). When the wheels were on the ground, the crew applied the brakes to bring the craft safely to a halt, but they also used a horizontal parachute called a drag chute to help. It was about 12m (40ft) across and helped to cut the Shuttle’s speed by about 75 percent before it was jettisoned.

Ever wondered what happens to your body when you skydive?

Skydiving is one of the biggest adrenaline rushes a human can experience. Free falling out of a plane 15,000ft high and quite literally dropping through the sky takes your body through one hell of a rollercoaster of emotions: Anticipation, nerves, fear, excitement, adrenaline, relief. The overwhelming mix of feelings is indescribable, but what about what’s happening on the inside?

Believe it or not, humans aren’t made to fly and the process your body goes through when skydiving is completely next level cray. Let’s start at the beginning…

Where’s the toilet at?

You’re all set in your skydiving attire, harness strapped on when suddenly… nature calls. This is your body’s way of reacting to extreme levels of anxiety which often causes you to tense your muscles, in turn putting extra pressure on your bladder, creating the need to pee. This feeling can also be caused by high levels of anxiety resulting in your brain explicitly focusing on the sensation of peeing, making it feel like you need to go more than you actually do.

Adrenaline takes over

As you make your way up the altitude levels and take in some of the most insane views you’ll ever see, your nerves switch to adrenaline. The adrenaline glands release mass amounts of cortisol (our stress hormone) into the bloodstream. This is mixed in with thyroid hormones which control our metabolism, creating maybe the highest amount of adrenaline your body will ever reach. This cultivates into a mixture of anxiety and adrenaline filled emotions as you get that one step closer to the main event.

Your heart rate goes sky high

The plane door is opened and holy f**k, shit gets REAL! All of a sudden the reality of what you’re about to do hits, the ice cold air surrounds you, you look down and see planes that look like ants and your mind goes into turmoil about how you ever thought this was a legit idea. At this point your heart rate can reach 170 bpm, nearly triple the average 60-100 beats per minute!

And then you jump

This may be one of the only times in your life when you’re completely in the moment and also completely powerless. Whether you’re screaming your head off, left speechless by the views or having a meltdown about if your parachute is going to work, one thing for sure is that you’re not thinking about anything else other than living in the present. And when you’re free fall is over and the parachute launches, there’s an overwhelming feeling of happiness, adrenaline and pure joy.

Tempted to take your body through the roller coaster of emotions? Check out our very own tandem skydive in Surfers Paradise, Australia.

How Fast Do You Fall When Skydiving?

It is very likely that your brain understands when you freefall from an airplane, you will go fast. But how fast? This is a good question as the answer involves a bit about how skydiving works. The scientific word for the maximum speed an object can achieve while falling is ‘terminal velocity’, but this speed is not the same for different objects (like people). So, how do terminal velocity, acceleration, wind speed, jump angles, and all of the other fascinating physical factors work while skydiving? Let’s have a look.

Man picking up speed after exiting the plane at Wisconsin Skydiving Center near Milwaukee

The (brief) Science of Objects in Freefall

Gravity is a constant force generated by our planet, and if our falling objects were all exactly the same size, they would indeed fall at the same speed. The overall mass of an object—how big and how heavy it is—is what causes it to speed up. At the same time, the shape of an object and how big it is causes drag as it travels through the air, thus causing it to slow down again. The combined effect of these forces is what determines the terminal velocity of an object.

The Freefall Skills of a Skydiver Can Change Terminal Velocity

It is possible for a skydiver to control their terminal velocity. While you cannot change your weight in freefall, you can change your shape and therefore how much drag you create. Managing drag allows skydivers to control their speed, meaning they can match their fall rates. Very basically, if you make yourself smaller, you go faster because of less drag. And vice versa.

In skydiving, you can also use drag to control how you move around in the sky. As you fall through the air the wind resistance amounts to a physical force that can be manipulated to move you in different directions. The best way to feel this on the ground is by sticking your hand out of a car window as the car is moving and paying attention to what happens when the air hits you at various angles. Again, very basically, if you want to go forward, you angle your body to push air away behind you.

Jumping out of a plane upside down and doing flips above the clouds at Wisconsin Skydiving Center near Milwaukee

Different Methods Of Skydiving Produce Different Speeds

The most common number associated with skydiving speed is 120mph (200kph). This is both accurate and not really very accurate. Although freefall speed is a little bit different for everybody, having a number in your brain with which to make comparisons is important and 120mph is an approximate medium speed for the belly-down orientation used for skydiving either solo or tandem (the method for a first-time skydiver).

But there are other, more advanced ways to fall through the air that involve greater speed.

Freeflying’ is when you use your body and the wind to hold your body in head-up and head-down orientations, and has a medium speed of around 160mph (+/- 260kph). ‘Tracking’ involves moving some distance across the sky in formation (or solo) and, depending on the angle, the flight can have very different vertical speeds. Most impressive of all is speed skydiving, where the goal is to point your head at the ground and go as fast as possible. The world record for speed skydiving is currently 373mph (601kph)!

Speed in Freefall is Like Nothing Else

The most important thing to understand about how fast you fall is that it feels like nothing else. There are ways to go faster than 120mph without leaving the ground, but there is no way by which to compare the sensation of the speed generated by using only your body and gravity.

Exiting the plane at 14,000ft altitude is the best bit, as you are already traveling forward at about 100mph (160kph). As you jump, your forward speed gradually turns into vertical speed over the course of the first 1,000ft (300m)—about 10 seconds into your skydive (100 feet per second!)—as you travel ‘down the hill’ in a great big graceful arc. It’s a beautiful thing.

Tandem skydiver gaining speed just after coming out of the plane at Wisconsin Skydiving Center near Milwaukee

Slowing Down With Your Parachute and Getting To Ground Safely

The duration of freefall in a skydive from 14,000ft lasts about one euphoric minute, after which (at about 4000ft) you deploy your parachute to descend the rest of the way, safely and gently touching down in the landing area a few minutes later. A parachute operates under the same forces as a human when falling (weight, drag, shape, etc.), but functions more like an airplane wing. An average parachute has a vertical descent rate of around 17mph (although much faster and sportier ones are available) with a glide ratio of 1:1. This means they fly at approximately a 45-degree angle.

Slowing down and landing with a deployed parachute at Wisconsin Skydiving Center near Milwaukee

While 120mph is thrown around a lot for marketing purposes, the true answer is much more involved in skydiving speed. This is the great thing about skydiving. It seems very simple and is in a lot of ways (go up > jump out > land) but there is so much to understand if you want to dig deeper. You can spend a whole life involved in the sport of skydiving and learn new things every day.

If you’re ready to get started on your journey, join us! Book a skydive today, contact us, or check out our first-time skydiving tips if you have any other questions!

Source https://www.explainthatstuff.com/how-parachutes-work.html

Source https://www.contiki.com/six-two/what-happens-to-your-body-when-you-skydive/

Source https://wisconsinskydivingcenter.com/blog/how-fast-do-you-fall-when-skydiving/

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