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First, I did a forum search on this topic and there are over 200 pages of posts.....and call me lazy but I am not going through each post.

How long does it take to hit terminal on a B.A.S.E. jump?

How long does it take to hit terminal when jumping from an airplane?

I thought of this too, but dont you hit terminal faster since you are exiting the aircraft at the same speed its flying. You not in dead air, so it would seem to me that you would take longer on a base jump to hit terminal then exiting an aircraft. And I could be wrong, just really curiouse.

Thanks in advance,

aircraft speed tends to be horizontal and is NOT a factor in standard terminal velocity (which is vertical).

would depend on the height of the cliff

surely if it was 4000 feet it would technically be faster then a 1200 foot cliff

due to the thicker air

Typically it takes about 11 seconds to go the first 1000 feet either from an object or from an airplane so in that aspect they do compare.

The difference is you have horizontal speed when exiting an aircraft so there's relative wind on which to fly.

Hope that helps

I actually didnt know that either (shocking huh). But without all the variables, what is an average time?

Lets make it easy, If I was to jump the balloon at WFFC with a base rig (sorry couln't resist) from 5000ft, how long would it take to hit terminal.

that explains it purfectly and thanks hookit. Wasnt thinking of the speed from an aircraft as horizontal, but now I got it.

thanks again.

well odds are the bas rig would be reserve free, so ya would be lighter.....

My BASE rig is around 18 pounds. My skydiving rig is about 16.

Are you basing that on experience jumping big cliffs at various altitudes?

I haven't noticed an appreciable difference from similar sized (terminal) cliffs with landing areas at sea level and 4000' above sea level.

I'm curious if your experience has been different.

Tom you know my experience.
if it was like 1 billionth of a second later it would still be a difference.

what size canopys does your skydiving rig contain?
and what is in the base rig

is the main weight diff due to canopy size or some other factor?

check his profile...

What if you were to consider the difference between summer and winter air? Based on the knowledge that hot air is less dense and more energetic and colder air is more dense and less energetic, you can hypothesize that in the winter you would have a slower, albeit minor, terminal velocity.

dude.
i have explained this before in the sliderup skydiverig helicopter question forum

1-horizontal and verticle velocity decays and increases independantly of eachother.
2-weight is NOT a factor in acceleration from gravity. it IS however a factor in actual terrminal speed. did anybody else pay attention in HS physics?
3-this question has no value other than personal curiosity, because the times it takes different eople to get to terminal has far to many variables to give the true answer. ( falling object shape/shape shifting/falling object density/ air density/humididty variables/ wind/ empty or full lungs/ etc)

but, you did specify the averager time to get to trerminal.

so....
about 8-12 seconds,

remember, skydivers LOVE to attach definates to different questions and values. because, in all reality, they like to believe that skydiving is a science and really totaly safe. BASE jumpers dont think like that. in my theory, the time to reach terminal out of an aircraft traveling at 70tas, is a lot harder to figure even a ballpark acceleration time than off a tower.

I would have thought something heavier with a smaller surface area would reach terminal slightly faster then something of the same size and lighter.

why is this not so ?

if I drop a shot-put and a tennis ball from 10ft the shot-put hits the ground first.

even if one only got in front by 1ft at the start it would still be that 1 ft a head.
or would the heavier item have a higher speed of terminal veloicity and take longer to get there as it has to go higher faster then the lighter object of eqaul mass ?

Where is yuri base when you need him.
I'm sure he will explain it and proof it with help of mathematical explanation of the phisical laws...
For myself it is not that important if it takes a second longer to reach terminal or not. When I jump I loose my feeling for time.
On a terminal jump you jump, then first it seems that you don't fall at all, then it gets faster and louder and after some time the ground gets to grow bigger very fast and then you pull. I have no idea (and I don't care) after how many seconds the stages are.

I'll take that one step further and point out that, if we were being at all pedantic about it, there's no magic time when an object "reaches" terminal velocity, but just a range of times in which most reasonable people would agree that it's "pretty much there". So the whole thing is pretty wishy-washy from the start.

There are three ways to increase terminal velocity without changing the thing that's doing the falling -- you can increase temperature, increase humidity, or increase altitude. I've attached a graph of velocity vs. time for standard conditions and a few variations ("M lower" is equivalent to increased humidity) for a jumper with a pretty normal terminal velocity.

You can draw your own conclusions. To my eye, everything but the drop from 5000 m pretty much reaches its terminal velocity in 10-12 seconds. Even the high drop seems pretty near terminal at 12-13 seconds.

i did think if it were a 2 canopy system you were jumping off them objects

18 pounds?
your sure??
I mean your arround 15 pounds right?

theoretically ... you can reach terminal more enjoyably when its 420
bueno

acceleration due to gravity is a constant, period.

in High School physics, they like the phrase "neglecting the effects of air." thus, a feather and a sandbag will fall at the same speed, in a vacuum. it explains gravity quite well and explains motion in space.

unfortunately, if the air has NO effect, there is NO aerodynamics and aircraft can't fly.

the air creates a force that fights gravity and changes acceleration patterns. roughly, much depends on the ratio of surface area to weight. compare the surface area/weight ratio of a feather to a sandbag...

people have correctly mentioned pressure, temperature, humidity, etc. as things affecting terminal velocity. I personally think the shape YOU present to the wind will can have a greater impact.

> How long does it take to hit terminal on a B.A.S.E. jump?
——————————————————————————————
Confirming everything that has been already said by the other folks, I can say the following:
You reach terminal velocity in a BASE jump exactly after the same time as in a skydive as well as in a balloon jump, which is:
1) theoritically: NEVER (you approach terminal velocity in an infinite time)
2) actually: estimating a terminal velocity of 54.402 m/s - 178.484 ft/s, you reach terminal velocity after 12" and 448 m - 1469 ft (conventionally, you CLAIM to have reached terminal velocity after a time when your actual speed is about 97÷98% of your ACTUAL terminal velocity (=determined by instruments when skydiving))
But why do you need to determine the time when you reach terminal velocity with ALL this accuracy?!?!?!?!?
After 10" you are already going down pretty fast indeed (= 51.578 m/s - 169.219 ft/s after having fallen down 343 m - 1126 ft), as well as after 8" (48.680 m/s - 159.711 ft/s and 242 m - 796 ft).

Very false. Gravity at sea level is different than gravity at the top of Mt. Everest.


Not even Witten himself would make such a bold statement and he is probably the one who at this point in time has the greatest understand of gravity.

NOBODY understands fully what gravity really is hence the total lack of its control.

We are able to "produce" all the other three forces but we have no clue, well some, how to produce gravity.


So how in the hell we sent stuff in space and men on the moon? There is a difference between external and internal aerodynamics.


Do you mean an object using air as a medium?

As a professional physicist, I can tell you that every law or theory of physics has a realm of validity. There will always be more sophisticated and more detailed ways of describing physical natural behavior. Edward Witten's work on string theory etc. is truly irrelevant here. What Hookitt says above is all that really matters in the BASE environment that a majority of us play in, so please ignore the arguing of semantics and hidden variables and irrelevant string quantum theories brought up by some. I do not have experimental data on terminal, but my soon-to-be completed device will provide data, allowing me to test it under a variety of different temperature, humidity, body positions, etc. Therefore, true variations in distances and speeds due to different conditions will soon be available for all to enjoy.

one poster tried to predict behavior based on High School physics. that frequently is Newtonian and neglects the effects of air.

when I fly or jump, I really like the effects of air. thus the H.S. physics model no longer applies.

I tried to build upon that model, to the extent required by most jumpers. (there is much I do not consult before jumping, string theory being one.)

I meant to inform at a level ALL could understand (while obviously risking offense via oversimplification). apologies if my approach annoyed.

The formula is this:

Sum of Forces = Mass * Acceleration

Now the only forces acting on the body in freefall is the friction forces from the air flying over you body. The coeeficient of friction can vary based on your clothes, the density of the air, and your body positioning. You mass is you mass and the acceleration is 9.81 meters per second squared.

All that really does is get you in the ball park.

Also realize i have only had college pyisics required for my Engineering degree. I am not a BASE jumper and I don't have any jumpsother than some AFF skydives.


The reason the shot put hits the ground first is because it has a different coeeficient of friction compared to a tennis ball.

The shot put hits the ground first because it has a higher terminal velocity. So when the tennis ball reaches its terminal velocity and stops accelerating while the shot put continues to accelerate due to its higher mass. Even if the tennis ball was polished smooth to equal the coeficient of friction of the shot put, it'd still reach terminal velocity faster, simply because its terminal velocity is much slower than the heavy shot put.

You are right it is because it has a higher mass but then that acceleration is offset by the drag forces from friction. Which goes back to your coeficient of friction. I will draw a crude free body diagram tomorrow and show the Newton equation. We had to do a bunch of crap like that in the Calculus based Physics cousrse I took. I barely got an A but I had an easier Pyhsics prior to that one which helped me out in a bunch in getting the A.

when did this become a physics forum?

8-12 seconds. the end.

Hear, hear. Bringing the finest mental masturbation to the object near you.

I wondered, too, if initial horizontal speed slows down your descent a bit. It turns out it does, but not too much.

Long story short - on a BASE jump, you reach terminal velocity about a second and a half sooner than on a jump from airplane. This is because the high initial drag on a plane jump has a vertical component which slows you down a little more.

If your terminal velocity is 120mph, you'll reach 95% of it (114mph) at 10.0s on a BASE jump and at 11.4s on a jump from airplane doing 100mph. This assumes that you maintain the same boxman body position - no lift, only drag - throughout. 11.4s is time to reach 114mph vertically; however, the total speed will reach 114mph at 10.6s (due to residual horizontal speed). So the difference is not really noticeable.

Skipping the lengthy derivations, for BASE jump the speed V follows this differential equation:

dV/dt = g*(1 - (V/Vt)^2)

where t is time, g = 9.8m/s^2 = 32ft/s^2 is acceleration of gravity, Vt = 120mph is terminal velocity. This equation can be solved analytically:

V = Vt*(e^(2*g*t/Vt) - 1)/(e^(2*g*t/Vt) + 1)

where e = 2.718281828459045...

(BTW, this formula can be used to derive freefall chart with a step less than 1s. Johhny? )

For an airplane jump, we have two equations for horizontal Vx and vertical Vy components of speed:

dVx/dt = - g*(V/Vt)^2*Vx/V
dVy/dt = g*(1 - (V/Vt)^2*Vy/V)

which can be solved numerically using finite differences, see the attached spreadsheet.

The only useful result of this masturbation is that if you want the softest opening possible on a hop-n-pop, wait 2 seconds before pitching (see how the green line, the total speed, makes a minimum of 85mph at 2s). This is based on 100mph jumprun (Twin Otter). For King Air, wait more. For Cessna, wait less.

Yuri

see, now that was actually some useful information, because it relates to people!

when was the last time anybody saw a tennis ball and a shotput huckin' a 2-way?

I predict that video will be posted in reply to this question.

true

to expand on what you wrote:
Mass * A(gravity) - aerodynamic forces = Mass * A(total)

understanding A(total) depends on how someone calculates the aerodynamic forces... it is not simple.

Yuri might be right, I do not know his starting assumptions.

overall, incorrect.

granted, friction plays a significant role in boundary layer conditions.

but shape typically impacts the resulting forces much more. that is why Cessnas use tapered fairings. they are much more costly to manufacture than a simple piece of tubing. but it makes a huge difference.

remember, the coefficient of friciton would be the same for a painted tube or a painted fairing. but the fairing has more surface area. defining forces only on friction would mean the faired strut would generate MORE drag than a simple tube.

as the fairing is for more costly to manufacture, and would represent greater drag, why do it?

the answer is the profile drag on the fairing is far less than that of a tube. shape matters.

edited to add
to clarify, the discussion above meant to explain why Cessna streamlined the wing support strut. it also explains why manufacturer moved away from wire cross-bracing. (just in case I mislead with my choice of terms.)

Correct. ma = mg - Drag. At terminal velocity (a = 0), Drag(Vt) = mg. Since the drag is proportional to the square of speed, at speed V drag will be Drag(V) = Drag(Vt)*(V/Vt)^2 = mg*(V/Vt)^2. So,

ma = mg - mg*(V/Vt)^2

a = dV/dt = g*(1 - (V/Vt)^2)

QED

This is a precise equation and it only assumes that you maintain the same boxman body position. The exponential solution above is a precise solution of this equation and can be used to generate precise freefall chart with arbitrary timestep and duration (the spreadsheet contains the freefall chart with 0.1s step to 20s).

For a jump with non-zero initial speed, there are two equations for the components of speed. They are derived similarly.

it looks like you created ratios of Bernoulli's dynamic pressure...
[sarcasm]
what about changes in density as you descend? what about compressibility effects?
[/sarcasm]

it's a nice little derivation to show the relationship between acceleration and velocity. did you do something as simple to come up with the speed calculations?

Acceleration is the derivative of speed: a = dV/dt. This gives us the differential equation for speed:

dV/dt = g*(1 - (V/Vt)^2)

Integrating

dV/(1 - (V/Vt)^2) = g*dt

gives us inverse hyperbolic tangent on the left side and g*t on the right:

Vt*arctanh(V/Vt) = g*t

or

(1/2)*ln((1 + V/Vt)/(1 - V/Vt)) = g*t/Vt

and finally

V(t) = Vt*(e^(2*g*t/Vt) - 1)/(e^(2*g*t/Vt) + 1)

Fun, heh?

All based upon the very simple hypothesis that drag is proportional to the square of the velocity and the coefficient of drag is invariant. Given the simple assumptions, yes, the solution is a closed analytic form. The end result in reality though is still 9 to 12 seconds depending on humidity, temperature, jumpsuit, jumper, and aerials. The numbers by Yuri_Base seem reasonable but I would question having any digits beyond the decimal point. Too much splittin' hairs and an unrealistic level of accuracy given the nature of the experimental system. I say let's just make a jump instead!

bms..you drop the 420 bomb alot on the internet, but when you were at my house, you wouldnt go near the real deal w/ a ten foot pole...

im a fake

ain't that what Yuri just said?

his variables include time and terminal velocity.
so all that stuff about shape, friction, humidity, etc. get incorporated into the terminal velocity.

guess we need someone all instrumented up to figure out that number. GO FOR IT!