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[blinkdude101 0]

Hello my name is Dylan and I am from Drumheller Alberta, Canada. I am doing a school project and I was hoping that someone could help me out with some information on sky diving. There are a few questions I was asked to answer and I was hoping that you could answer some of them that I could not find.
Like, How long does it take to reach terminal velocity?
How does opening the parachute affect terminal velocity?
How does the body position affect the sky divers speed?
What is the minimum height where a jumper must open their chute?
And how fast does do you fall with an open chute?
If you could answer any of these I would be very grateful.
Thank you for you time and I am looking forward to hearing from you.
Sincerely
Dylan .K.

• Quote

[michalm21 2]

first, try here

[quade 4]

Terminal Velocity is the balance between the potential energy an object (weight) and the air resistance due to drag.

Knowing this fact alone you can make a guess that questions such as, "How long does it take to reach terminal velocity?" depends entirely on how much the skydiver weighs and how much drag he is creating.

If you stick your hand out of the window of a moving car, you'll discover there is quite a bit of difference in the force created by drag just by how you hold your hand. Make a fist and that would be one value. Hold your hand horizontally so your hand cuts through the wind and that is another value. Hold your hand vertically so that it blocks the wind and that is yet another.

If you are really interested in -exact- answers, well, the questions you've posed simply do not have enough information in them. So, sorry about that.

But here's a couple of rough estimates;

An average skydiver falling belly-to-earth (imagine him simply laying down on the ground on his belly with his arms and legs out stretched) is going to fall "about" 120 mph.

A skydiver rolled up into a ball, (think a cannon ball jump into a pool) might go "about" 150 to 180 mph.

A skydiver pointed head down in a very streamlined position might go as fast as 300 mph.

Opening an old style "round" parachute simply adds drag. The bigger the parachute, the more drag.

However, most parachutes used today aren't "round" at all, they're actually flexible air-filled wings. Gliders. Depending on the circumstances, the fall rate can be reduced to zero for a short time.

quade -
The World's Most Boring Skydiver

[pilatus_p 0]

The worlds best encyclopedia

http://www.google.co.uk/search?hl=en&q=how+a+parachute+works&btnG=Google+Search&meta=

And http://hypertextbook.com/facts/JianHuang.shtml

Ross

http://www.teamtechnology.co.uk/troll.htm

[dragon2 2]

How long does it take to reach terminal velocity?

about 10 secs, presuming normal belly-to-earth body postition


How does opening the parachute affect terminal velocity?

huh? terminal velocity = freefall, opening canopy = end of freefall


How does the body position affect the sky divers speed?

a max track has a downward speed of 90 mph or so and quite a lot of forward speed
on the other hand a max headdown can reach 300 mph (downward) or so


What is the minimum height where a jumper must open their chute?

varies per country, usually 2500ft/2000ft for a regular skydive ram-air main canopy (ie, not BASE or round canopies)


And how fast does do you fall with an open chute?

anything from 0mph to freefall speeds, depending on canopy size, model, pilot weight and how it's flown

ciel bleu,
Saskia

[IanHarrop 42]

You're not far from a great dropzone.

Alberta Skydivers at Beiseker http://www.albertaskydivers.com/

Andrew Whyte runs Beiseker is a great guy and would be more than helpful with any inquires you have.

Call him to set up a time to come out to see and learn more about skydiving.

Contact information is on the website.

"Where troubles melt like lemon drops, away above the chimney tops, that's where you'll find me" Dorothy

[Andrewwhyte 1]

Hello Dylan,
My name is Andrew and I'm one of the owners just up the road at Alberta Skydivers in Beiseker. We are still open for a couple of weeks so you should try to come up either this weekend or next and have a look around. Any of the jumpers will be happy to let you buttonhole them about these topics as well as any you haven't thought of yet.

Andrew Whyte
Alberta Skydivers

[jtval 0]

[Reply]How does opening the parachute affect terminal velocity?

Huh? Terminal velocity = freefall, opening canopy = end of freefall

[jakee 1,595]

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How does opening the parachute affect terminal velocity?
This also depends on which type of aircraft you are jumping from. Here’s why.
Lots of smaller Drop zones use Cessna 182's for their jump ships. They normal let jumpers exit while flying approx 80 mph. When a skydiver exits the aircraft, they will build speed from 80 mph to 120mph (if in a RW position)
some people are bound to talk about ground speed vs. airspeed. I am leaving that out in efforts to keep this simple.

some large Drop zones use larger aircraft such as the Caravan or Cessna 208 jumpers exit this aircraft at speeds of 90-100 MPH that jumper only has to build from100mph to 120 mph.
some people are bound to talk about ground speed vs. airspeed. I am leaving that out in efforts to keep this simple.

So, again, just to generalize, From a Cessna 182 you'd have to build 40mph whereas from a Caravan (AKA Cessna 208) you only have to build 20 mph in order to hit terminal velocity. So the time it takes varies, but Dragon2 gave you a very good general answer.

Uhh, I think you've answered the wrong question there also I think you're answer is wrong.

High horizontal exit speed will not decrease the amount of time it takes to get to vertical terminal velocity.

Do you want to have an ideagasm?

[jtval 0]

Yea I did answer the wrong question. I thought I bolded the how long does it take it hit terminal velocity.



But why do you say the exi speed doesn't matter?
if you are already going 100MPH than you only have to increase approx 20 mph.

if you are exiting at 80 MPH you have to increase approx 40MPH will will take longer to reach.

I agree that if you remove all variables it would take the same amount of time every timeto reach term.

I.E.if you had zero winds, a 10,000 ft balloon, weighted that same, had the same surface area, same temperature(air density) etc.
it would take the same mount of time to reach terminal every time.

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[jakee 1,595]

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But why do you say the exi speed doesn't matter?
if you are already going 100MPH than you only have to increase approx 20 mph.

if you are exiting at 80 MPH you have to increase approx 40MPH will will take longer to reach.

Fuzzy reasoning.

In both cases you have to increase your vertical speed by 120mph. Horizontal speed doesn't come into it in that sense, although (slight tangent) I would think that a good 4-way exit actually produces a small amount of lift - which would mean higher exit speeds can take fractionally longer to reach terminal

Try searching Kallend's input on these discussions in the past, I'm sure you wouldn't want to argue against the Prof on a physics question

Do you want to have an ideagasm?

[jtval 0]

Wew're not looking for a physics degree.
I stated in my origianl post that I am GROSSLY GENERALIZING.

but during exits you don't have to increase your speeds by 120 MPH.


Admittedly some of the foward motion is lost during the transfer to downward motion but you're stating at different speeds. There is the variable I am referring to.

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[jakee 1,595]

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I stated in my origianl post that I am GROSSLY GENERALIZING.

Your generalisations are wrong.

Quote

Admittedly some of the foward motion is lost during the transfer to downward motion but you're stating at different speeds. There is the variable I am referring to.

Unless you're flying a wingsuit all of your forward motion is lost. Exit speed is irrelevant in calculating time taken to reach terminal. All it will affect is how long it takes until you're falling down the tube.

Do you want to have an ideagasm?

[pilatus_p 0]

PROF PROF PROF PROF PROF PROF!!!!!

We need kallend!!

My feeling as a complete nerd is that if you jump out dead flat, you have no downward velocity or acceleration at the instant of exit. So the instant you are out, gravity will begin to act to accelerate you downwards. Horizontal motion will have no effect on (look up vector addition in a high school textbook ) vertical acceleration or speed, but it will make your flight path parabolic in one plane of motion.

Soooo based on that, I would agree that exiting horizontally would have no effect. If you pushed DOWN or UP it might affect time to terminal FRACTIONALLY. Terminal is only the point where drag force = force due to gravity, and drag is proportional to your presented surface area and the square of your speed.

I will now go and congratulate myself for using long words in a post by having a cheese and pickle sandwich. With lard.

Ross

http://www.teamtechnology.co.uk/troll.htm

[jakee 1,595]

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I will now go and congratulate myself for using long words in a post by having a cheese and pickle sandwich. With lard.

You sick bastard! I think the argument has suffered through association with you

It is surprising how often this issue crops up though. It seems to be the 'insiders' equivalent to the non-skydiver classic of "what do you mean you fall slower than Big Dave? Everything falls at the same speed!"

Do you want to have an ideagasm?

[speedy 0]

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And how fast does do you fall with an open chute?

anything from 0mph to freefall speeds, depending on canopy size, model, pilot weight and how it's flown

Assuming it's a canopy you want to land, freefall speed is a bit over the top. Maybe the top swoopers are getting up to 85 mph vertical fall rates, but its not the norm.

Dave

Fallschirmsport Marl

[pilatus_p 0]

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the non-skydiver classic of "what do you mean you fall slower than Big Dave? Everything falls at the same speed!"

Hi Jakee

I had that convo with an actual skydiver. He maintained that everything SHOULD fall at the same speed too, though couldnt explain why they didnt. He actually got angry when I explained it and wouldnt accept that version of things. OK maybe calling him a "halfling inbred web-footed simpleton with the class and grace of an infected smallpox boil" wasnt the best way to win him round, but there was a matter of pride at stake.

Sometimes its better to keep the peace than burst someones bubble
My ex knew this principle innately and had a very special nickname for me.

All the best,

Ross "Mammothpants" L

---------------------------------------
PS Sorry for using the words "infected smallpox boil" and "burst" so close to one another.

PPS Suffered? What argument?

http://www.teamtechnology.co.uk/troll.htm

[pilatus_p 0]

Oooh ooh ooh ohh me first

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Assuming it's a canopy you want to land, freefall speed is a bit over the top. Maybe the top swoopers are getting up to 85 mph vertical fall rates, but its not the norm

http://www.skydivingmovies.com/ver2/pafiledb.php?action=file&id=1584&string=Icarus%20VX%2039

Ok he's keeping up with a wingsuit. But still very cool. The forward speed is immense!

Ross

http://www.teamtechnology.co.uk/troll.htm

[jtval 0]

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I stated in my origianl post that I am GROSSLY GENERALIZING.

Your generalisations are wrong.

[pilatus_p 0]

The question being "how long does it take to reach terminal velocity"?

Right, you asked for this one. Anyone who's scared of equations, look away NOW.

Still here? Good. You're a nerd.

EQUATIONY BIT (with the explanation - skip to discussion if this stuff bores you)
------------------------------------------------------------------

Newtons 2nd law of motion: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. If no force acts on a body, it will remain at rest or move with constant speed.

Force due to Pressure Drag = (Air Density) x (co-efficient of drag) x (area presented to wind) x ((0.5 x velocity) SQUARED)

Force due to e.g gravity = mass (your mass) x acceleration (in this case, gravity at 9.81 ms^2) or F=ma

Lets say your mass is 100kg. Apart from thr fact you need to lose weight, the force due to the acceleration of gravity on your body is

F(grav) = 100kg x 9.81 m/s^2 = 981 Newtons

We have said that terminal is when the drag force equals the down ward force, so that no net force acts on the body and hence the body travels with constant speed - TERMINAL VELOCITY

So F(drag) = 981N

In the equation above we want to know what speed will give us this value of drag. Finding a coefficient of drag for human body belly to earth, somehow, and knowing the area of the human body facing the wind:

Velocity = square root of:

Force due to drag
---------------------
(Air density) x (Area) x (Co-ef drag)

Now according to Isaac Newton (argue with him if you must)

v (final velocity) = u (starting velocity) + at (acceleration x time)

From isaacs equation then:

time = v / a


DISCUSSIONY BIT
---------------------------------------------------------------------
Now, in an ideal world, you would just find the point at which the forces balance for these equations and solve for velocity ... But this is planet earth so -

The drag increases with the square of the speed. That means, as you go gradually faster, there is a rapidly increasing force retarding your downward acceleration. So, you dont speed up quite as quickly as the simple F=ma suggests (or more accurately, a is varying all the time) - it balances itself against drag (both pressure and skin friction drag).

The upshot of all this mental masturbation, and arguably the only paragraph you were actually interested in, is that it takes roughly 12 seconds to hit terminal. I could set up a spreadsheet that would find time to terminal for different weights and surface areas of divers, but frankly I feel this post has already done more than enough to cause at least 5 backlash posts, an ass kicking from someone in the academic fraternity and a number of mildly abusive PM's. Oh and at least one person saying "yeah equations are great, by my mate bob once survived falling in a vat of molasses wearing only a kilt from 20,000 feet, so you're wrong, science boy"

Once again I have an urge for lard.

Ross

http://www.teamtechnology.co.uk/troll.htm

[AFFI 0]

Quote

The question being "how long does it take to reach terminal velocity"?

Right, you asked for this one. Anyone who's scared of equations, look away NOW.

Still here? Good. You're a nerd.

EQUATIONY BIT (with the explanation - skip to discussion if this stuff bores you)
------------------------------------------------------------------

Newtons 2nd law of motion: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. If no force acts on a body, it will remain at rest or move with constant speed.

Force due to Pressure Drag = (Air Density) x (co-efficient of drag) x (area presented to wind) x ((0.5 x velocity) SQUARED)

Force due to e.g gravity = mass (your mass) x acceleration (in this case, gravity at 9.81 ms^2) or F=ma

Lets say your mass is 100kg. Apart from thr fact you need to lose weight, the force due to the acceleration of gravity on your body is

F(grav) = 100kg x 9.81 m/s^2 = 981 Newtons

We have said that terminal is when the drag force equals the down ward force, so that no net force acts on the body and hence the body travels with constant speed - TERMINAL VELOCITY

So F(drag) = 981N

In the equation above we want to know what speed will give us this value of drag. Finding a coefficient of drag for human body belly to earth, somehow, and knowing the area of the human body facing the wind:

Velocity = square root of:

Force due to drag
---------------------
(Air density) x (Area) x (Co-ef drag)

Now according to Isaac Newton (argue with him if you must)

v (final velocity) = u (starting velocity) + at (acceleration x time)

From isaacs equation then:

time = v / a


DISCUSSIONY BIT
---------------------------------------------------------------------
Now, in an ideal world, you would just find the point at which the forces balance for these equations and solve for velocity ... But this is planet earth so -

The drag increases with the square of the speed. That means, as you go gradually faster, there is a rapidly increasing force retarding your downward acceleration. So, you dont speed up quite as quickly as the simple F=ma suggests (or more accurately, a is varying all the time) - it balances itself against drag (both pressure and skin friction drag).

The upshot of all this mental masturbation, and arguably the only paragraph you were actually interested in, is that it takes roughly 12 seconds to hit terminal. I could set up a spreadsheet that would find time to terminal for different weights and surface areas of divers, but frankly I feel this post has already done more than enough to cause at least 5 backlash posts, an ass kicking from someone in the academic fraternity and a number of mildly abusive PM's. Oh and at least one person saying "yeah equations are great, by my mate bob once survived falling in a vat of molasses wearing only a kilt from 20,000 feet, so you're wrong, science boy"

Once again I have an urge for lard.

Ross

\

WTF???

[jtval 0]

Well I think the OP would have been good with
"12 seconds for the average person to hit terminal."


but I'm glad you got that our of your system.

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[kallend 2,148]

You could just run my freefall simulation program where all the math is done, including corrections for the gradient of air density with altitude.

www.iit.edu/~kallend/skydive

By the way, just in the interests of accuracy, you reach terminal in marginally LESS time if you start with no forward speed.

Anyone want to argue?

...

The only sure way to survive a canopy collision is not to have one.

[quade 4]

Quote

Anyone want to argue?

If so, please go HERE.

quade -
The World's Most Boring Skydiver

[jtval 0]

so are you saying I was correct?


I stated the wrong reasons but the foward "push" gives you a Minute(my-noot) increase in time, right.


(probably not enough to measure with a regular stopwatch, but it still adds time.

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