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Hey guys,

I have a math/physic project and I was wondering exactly what equations you should use while basejumping. I am actually going to start skydiving school in march and for a the project I want to do it on something I'm looking forward to do. So far all I've found is Pythagorean Theorem and how to calculate the amount of time in the air, but in a vacuum. I'm not quite sure if there's a equation you need in order to put in effects of wind variations and such. Does anyone know any equations that could help me??

Thanks for the help and take it easy guys,
Bobby aka: JTwo.

P.S. Thanks for allowing me to join the boards.

BASE JUMPING = STUPIDITY

This is the only equation in base that I am aware of and think about before I jump. "This is the stupidest thing I have ever done, but I like it!"

Lock the thread. That is the best response ever.

Dave, what about the time you hooked up with the two guys at the same time while you were on spring break at Cabo and knowing one had chlamydia?

 
OK, I'll bite.

Drag=.5Dencity*velocity^2*Cd*S
Look up dynamic pressure

Cd, coefecent of drag, is the tough part. But I'll tell you how to cheat. Termanal velocity is 176ft/sec at sea leval. For the most part Cd and S stays the same, body position and weight(cube square law) affect it but if you stayin the same position you can treat those as a constant and use that one point to find a working number to use at other speeds and dencities(elevations). As to dencity(roe) look up standard atmospheric model. Basicaly it's a model of the pressure and dencity of the atmasphere based on assumptions about how the temp changes with altitude. It's good enough for goverment work.

Now if I've suficantly confused you, here's your home work.

Problem 1
Create a freefall chart Starting from exit from an airplane at 13,000 ft. Post graphs to this thread of altitude and speed vs time.

Problem 2
Create the same graphs for exit from a 2,000 ft antena.

Problem 3
Create a graph showing the forwards throw, the path followed by a jumper, exiting from an air craft flying at 13,000 ft assume the airplane is flying at 120 mph(176 ft/sec). Hint: Treat X and Y independently assume y'=0 and x'=176 at exit.

Problem 4
Add wind to the graph in problem 3. Assume 50 ft/sec at 13,000 ft assume that the jumper goes through a shear layer at 8000 ft where the wind drops to 15 ft/sec, it's a head wind to the aircraft. Assume he will open his canopy at 3000 ft, assume x' now equals wind speed and y' now equals 18 ft/sec. Hints: remember wind affects the aircraft speed above the ground and that the drag in x is based on the jumpers speed relative to the wind.

Bonus

Useing the same wind as Problem 4. One jumper leaves the airplane at time 0. He is a free flyer, his termanal velocity is 250 ft/sec at sea level. he opens at 3,500 ft. A second jumper, a belly flyer with a termanal velocity of 176 ft/sec, leaves the plane 5 sec later he opens at 2,500 ft. Plot both of there paths on the same graph.


Yes, I know I'm a mean bastard.

Lee

Wingsuit Equations will solve all your problems, and then some.

http://www.basejumper.com/cgi-bin/forum/gforum.cgi?post=2911175

Can be used for no-lift freefall as well (e.g. to calculate freefall chart, etc.)

A+ on your exam and better sex life guaranteed!

Yuri

as Lee implied, there really is no way to predict the effects of the air without making a ton of assumptions.

Cd will change with AoA and body position.
AoA will vary.
good luck calculating the air density... (it varies with humidity with no way to calculate it simply.)
on short jumps, how high do you elevate on exit?
updrafts?
downdrafts?

sure, assumptions and simplifications can be made. but you failed to point out how you plan on using the numbers. thus, what kind of margin of error can you tolerate?

for example, what is pi?
3?
3.14?
3.14159265?

you might as well ask a baseball pitcher for the equations they use to throw a baseball...

order of operations is important on this one, as it is a central theme and unified theory equation for our sport:

[{(Jumper who knows it all) + mad skillz)*wingsuit}+easy exitpoint access]= new fatality list entry

 
There's nothing wrong with assumptions as long as you understand them. Rocket science is one of the most screwed up branches of engennearing. We don't normaly like to admit this but none of our equasions work. Almost with out exception there is a fudge factor in it. Some constant used to tweek it to make it match the experamental data. and even then it's only good over a certin domain.

The atmospher is a good example. the standard atmospheric model is an excelent mathmatical model which basically means that it has nothing to do with reallity. But surpriseingly it's good enough to work with. and with a simple correction for pressure and temp, Density Altitude, basically your just shifting the graph it works quite well. Ever been on an airliner? Fudge factors, experamental data, and assumptions. That's how the world really works and that's how things really fly. Sorry but that's the bruttal truth. Que the geek. Some one will now step in raveing about all the new advances in computer modeling. Let me say that these are all good tools but that they run on just as many assumptions as the old school shit I've been describing. The real danger is that you don't always get to peek in side the black box to see what's really happening. With out full understanding it can be hard to predict where the models will break down and it's hard to tell when they will start to lie to you. And don't ever think that a computer wont lie to you.

I smell a high school student here. Let's keep on a level that he can follow and turn into his teacher.

Lee

HAHA yeah I'm a senior in highschool and we have to do a project on something we enjoy. I do cliff jumping, but BASE has more physics to it then cliff jumping. Thanks for all the equations, and I'm excited to see the dumbfounded expression on my teachers face with the one.

Thanks for all the help so far and as confusing as it is, it's really interesting.

Bobby aka: Jtwo

CHLAMYDIA IS TREATABLE! GET OFF ME!!!

Sub-terminal fluid flow cannot be mathematically modeled, it is too chaotic. Folks with awesome pack jobs and good exits into no wind conditions who get 180s cannot grok this.

if you wish to mess with your teacher, try this one...

tell him/her that it is impossible to go faster than the speed of sound.

the speed of sound is actually how fast molecules run into each other. look at it like the ability of the molecules to a) know something is coming and b) to get out of the way. neither can happen if an object is going faster than the speed of sound. thus the air molecules must just stack up like a wall in front of the object.



basically, that is all true. as the molecules pile up, they create the famous shockwave. the shock wave heats up the air. this raises the speed of sound (as it is dependent on temperature). the heat and pressure of the shockwave can even change the air chemistry. all of the above permits the air to accelerate and pass around the object.

supersonic compared to the air ahead of the shockwave.
subsonic in the air behind the shockwave.

want to calculate that?


(personally, I'd rather jump.)

very good comparison.

I know a guy that did his theasus on exactly that.

Lee

I've read some bullshit over the years on this forum but i have to say that this is probably the most accurate, sensible and best advice that anyone has ever posted!
You should make up some t-shirts with that quote on- i'd buy one (in jade of course.)
Dantheman.

I've said how stupid BASE jumping is many times, but I'm starting to think that it only feels like the most stupid/dangerous thing I've done.

Just to name a few things I've done that were prob more stupid and or dangerous but didn't feel half as dangerous or stupid at the time:

-Getting a masters degree to teach middle school students.
-Driving an F-450 with a 40-50 foot trailer for over 16 hours several times, struggling to stay awake, with only a 15 min crash coarse on how to drive a trailer.
-Drinking twentysomeodd beers at the DZ one night.