Stupid games and all that

Sorry about the loss...but damn

Tandem jump. "Student" and instructor strapped togethet using one extra big parachute.  Student is usually not much more than a passenger.  A drouge chute is used to keep vertical speed similar to what a regular solo jumper would fall at, around 180 mph.

Could have been a partial failure of the main chute. That might have slowed them down enough for the instructor to survive.  But what happened to the reserve (back up, secondary) parachute?

I recall an incident a few years ago where a tandem jump had a total failure.  The instructor was able to roll onto his back, saving the students life while sacrificing his own.

120 MPH I believe.

Dupe of my post above...deleted.

If at first you don't succeed..... skydiving is not for you.

So that's why they put the student on the bottom

This is serious, so I didn't laugh.

Not that you know of, anyway.

Thats probably not gonna buff out.

Wrong. Funny but wrong.

You are correct.  Brain fade on my part.

I knew an old army vet I worked with at fedex while in college that survived a parachute accident. It was one of those low altitude jumps where hundreds of guys jump out, I believe it was for some generals retirement or something. He said what saved his life was all the cypress tree branches he hit and landing in a marsh.  He showed pictures he was pretty messed up from it.

That would be a lot closer to the real speed. When tandem systems were first developed, they did not have drogue chutes and the freefall speeds were ridiculously high. The drogues slow them down to a more normal freefall speed.

Being a tandem skydiving instructor is no joke. I have *never* wanted to get that rating.

Link?

The one survival tip instructors keep to themselves. Land on the other guy.

http://longisland.news12.com/news/nyc-corrections-officer-killed-in-skydiving-accident-1.8929089?firstfree=yes

Link suggests they had a good canopy and entercountered a dust devil which collapsed their canopy or flew them into the ground.  Which would explain how one survived if it happened at a low altitude

Believe it or not, a lot of people have survived without a chute.... it wouldn't exactly be new news.

He jumped off the student right before hitting the ground

You have to get the timing just right or it doesn't work.

Alot of people don't realize that.

I saw that in a ninja turtle episode when I was a kid.  Added that trick to my moves...

There is risk in throwing one's self out of an airplane, why the big deal when someone who does willingly goes puftt?  Did he not sign 3 waivers before doing so?

Does not work at those speeds.  Partial chute deployment would be my guess.

Sorry.  I deleted that post because it was a dupe of the one above.  I corrected that.

That does seem plausible.  Otherwise a main and reserve malfunction should be very rare.

Tandem sucks if your going to jump take the accelerated freefall class and jump with your own chute.

Did it last year with my Son, a lot more than 3 waivers, seemed more like a phone book.  You can be killed, you can't sue, your family can't sue, your decendants can't sue, nobody can sue, you can die, did we tell you you can be killed??.......didn't exactly give me the warm & fuzzies but enjoyed the experience.

I hate Skydive LI. Not because of what they do. Skydiving is obviously awesome. But their post drop descent pattern is over my house and I hear it every 1/2 hour or so on the weekend when their busy. Sounds like someone's dive bombing a Jap carrier.

Sorry if I seem ignorant, but didn't Newton and Galileo show us that gravity accelerates all bodies at the same rate in the absence of any other forces acting on them?



The only other force in skydiving is air friction, which limits the velocity pretty much equally at any given altitude whether it's a solo or tandem jumper.  In fact, wouldn't a tandem jump feel more air resistance and thus fall more slowly?



I'm thinking maybe the drogue shoot was more to keep the neophyte from upsetting the orientation of the instructor's chute.



 

You ask some very good questions.

When skydiving solo or tandem, you are correct--air friction and gravity are *the* forces to consider and you are approximately right about limiting velocity equally at any given altitude if by that you mean that the air at 5,000 ft. at one location will limit velocity the same as the air at 5,000 ft. at a nearby location. Air density changes with altitude and temperature, though, so a jumper in freefall at 10,000 ft. falls a bit faster than at 3,000 ft. on the same jump. For the altitude-record setting jumps, the speed differences are quite dramatic. Not so much for the normal skydives but there is still a difference. That is not a huge factor on the typical skydive, though.

I think what you are getting at can be described like this:

Since there are two jumpers on a tandem skydive isn't there twice as much surface exposed to the relative wind, making the freefall speed of the tandem pair roughly equal to that of a solo jumper?

It would be if there were no overlap between the two jumpers' bodies, but that is not the case. In a tandem skydive, the student's torso is directly below the instructor's torso, so the student is blocking most of the relative wind that would otherwise hit the instructor. Bottom line is that there is not as much friction generated.

Looking at it from a slightly different angle, since the friction between a jumper's profile exposed to the relative wind is the dominant factor regarding freefall speed, if you were able to stack some arbitrary number of jumpers in an exact vertical column so that in effect, only the bottom jumper's profile was exposed to the wind, wouldn't their freefall speed be exactly the same as the speed of the bottom jumper if he were by himself in freefall?

At first glance, you would think so, but that's not how it works. The reason becomes clear when you look at the forces involved. The force generated by air friction at terminal velocity (acceleration = 0) has to equal the weight of the jumper(s). In the case of the arbitrary number of jumpers stacked vertically in freefall, the weight is a lot higher than the weight of a solo jumper. Since the profile exposed to the wind is the same as the solo jumper, though, and the force generated by air friction increases with speed, to reach an equilibrium state of terminal velocity (acceleration = 0) then the speed *must* be increased to balance out the extra weight.

Back to your question. There *is* more surface area exposed to the airflow with a tandem pair but that difference does not come anywhere close to balancing out the increased weight.

I think where it gets confusing thinking about it is the emphasis they put in physics courses regarding two falling bodies in a vacuum. In a vacuum, a feather will fall alongside a bowling ball because there is no air friction. What they don't emphasize so much is the fact that the two bodies are constantly *accelerating*. Skydivers in freefall, if they maintain the same body position throughout the freefall, stop accelerating after about 10 - 12 seconds, and that is where it is pretty easy to see (when you look at the forces that must be balanced) that the freefall speed of a tandem pair without a drogue is a lot faster than that of a solo jumper.

Regarding the drogue contributing to stability, yes it does do that in freefall and that's a good thing, but that is not it's primary purpose. It's primary purpose is to slow the freefall so that there is less wear and tear on the equipment and the jumpers bodies when the parachute is deployed. After the parachute is deployed, the drogue is collapsed to reduce drag that would slow the forward speed of the parachute.

Make sense?

You are supposed to post "double tap".

Crazy.

The title states that the parachute did not open when that is not known to be true.  Some statements contradict it.

Everything but that phrase makes sense.  I'm unclear how adding weight (as opposed to altering frontal area) affects terminal velocity at any given atmospheric density.  After all, g=9.8m/s²



I know that in a powered aircraft/rocket/etc. thrust is used to overcome drag.  But in a skydiver scenario, be it solo, tandem, or 'stacked,' the only force acting against vertical drag is gravity.  And the acceleration known as 'gravity' is the same, regardless of the mass (or weight) of the falling body.



Is it possible that stacking two bodies on top of each other in a tandem configuration actually lowers drag by some aerodynamic principle related to their shape as a tandem?  (Add aerodynamics to my list of 'not-a-clues'...



 

g=9.8m/s is the max caused by gravity, a feather does not accelerate at that rate due to air resistance, just as a skydiver reaches terminal velocity when their weight is equal to the force of the air against them. The tandem jumper has double the mass, thus double the weight.

Kharn

Posted Via AR15.Com Mobile

It's known that the parachute did deploy. A dust devil, or other air disturbance caused the malfunction, near the ground. Just like with everything else the media reports on, they get most of the details wrong.

 

Once again, bring physics into GD and the derp comes out.

Blue Skies

I can think of lots of safer things to do in my spare time.

My one and only time skydiving (tandem with instructor) was with my buddy and his dad.

Me and my buddy landed first and watched his dad come in behind us.  His instructors chute got tangled and failed to fully open so they ended up pulling the reserve and came in rather hot.  The instructor was white as a ghost and my buddy's dad was all smiles because he had no fucking clue what had just happened.  

They had some chump on hand packing the chutes and he screwed that one up somehow.  

Fun sport, but if shit goes south, you'll have a good 60 seconds to contemplate your life.

Media reporting Skydiving accidents is alot like them reporting firearm crimes.  Every gun crime reported by Media is an AK47 assault rifle, and every skydiving accident is because "the parachute didn't deploy".  They are both right about the same amount of time. (Almost never)


Onyx

I would think they would fall faster for the same reason that you use less fuel when following behind a semi on the freeway.

http://www.youtube.com/watch?v=laXQv7zvbp4

This happened very local to me. As I understand it the parachute opened and everything was going fine until they hit some sort of wind current (called a dust devil) that collapsed the parachute. They were too low to deploy a reserve shoot. The wind current is invisible so there was no way to avoid it and once it happened they were too close to the ground to do anything.

I heard that the instructor is not expected to live.

I have been thinking about trying skydiving this summer and this is the facility I would have done it at. Oddly enough this doesn't dissuade me, if anything it makes me more interested since you know there is some legitimate danger.

I think where you are getting off track is that intuitively, most people look at freefall as being a condition of weightlessness and it *is* in the sense that if you were to somehow step on a scale while in freefall (with the scale being in freefall with you) it would indicate that your weight is zero. That is because of the lack of a fixed reference. Since the jumper is in a condition of weightlessness, it would seem to make sense that weight is an irrelevant factor.

Look at it this way. At terminal velocity, the jumper's freefall speed is roughly constant if the jumper maintains the same body position. Since speed/velocity is constant, acceleration is zero and (since F=MA), there *must* be a net zero force.

That requires the force created by drag to be directly offset by some other force. The other force is the weight of the jumper(s).

Another way of looking at it is to consider that the forces in freefall are very similar to the forces experienced by a jumper under a round parachute. The heavier the load is under a round parachute, the faster its descent rate will be. I'm sure many ARFCOM members can verify that.

Jumping out of a perfectly good airplane and all, so yeah...


TC

Dust devils are extremely dangerous to skydivers.

9.8m/s/s is the ACCELERATION due to gravity. It's independent of terminal velocity.