So, I’m watching Drop Zone yesterday, Jebus help me, and there’s a scene that got me wondering about something about parachutes.
Two guys, both feet fully on the ground. One pulls the other’s ripcord, releasing his parachute. The parachute literally leaps out of the … knapsack (forgive the technical jargon), blasting a good 10 or 15 feet backwards and actually pulling the guy off his feet.
Parachutse are packed in pretty tightly and will spring out slightly when deployed. If there was sufficient wind (say, from propwash or something, not just a light breeze) it would be enough to lift a man off his feet.
There are two parachutes in the container: the main and the reserve. They are packed and deployed a little differently.
The reserve chute is designed to be deployed in an emergency. As such, it is designed to deploy very quickly. I don’t know the details of how that’s packed, but I believe there are springs involved. It will leap out of the container, but I don’t know about taking someone off their feet though, unless the deployed canopy is catching wind.
The main chute is a different story. Nothing dramatic is going to happen if it is deployed on the ground. The chute is packed into a pouch (called the d-bag) and placed inside the container. A long cord connects the pouch to a small pilot chute (about 1 foot in diameter) which is placed under the container. The main chute is deployed by yanking the pilot chute out and throwing it into the airstream, which in turn would yank the chute and the bag out of the container. If you are just standing on the ground, obviously none of that is going to happen, so you’re just going to end up with a pilot chute dangling off your ass.
The reserve pilot chute typically contains a spring about 6" in diameter and 18" long (when extended). During packing this is compressed (takes perhaps 25lbs of force) into a disk that’s about 6" x 1".
Pulling the reserve ripcord causes the pilot chute spring to expand, which causes the pilot chute to fill with air, which drags the reserve canopy out of its pack. Done on the ground - and absent some significant wind - it’s silly to think this would take you off your feet.
Waffle Decider’s description of how the main deploys is substantially correct (depending on the precise system it’s called a throw-out pilot chute or a pull-out pilot chute; when I was active the TO was much more prevalent). So is Xema’s description of the reserve.
On any modern sport skydiving system both the main and reserve canopies are folded and packed into a deployment bag, which is literally a bag, open at one end. The canopy is folded up neatly and placed in the bag and then the suspension lines are carefully S-folded up against the bag opening, with each fold of line going through a big rubber band (called a “line stow”). Each rubber band is fastened to the d-bag and it goes through a grommet on the opening flap of the bag, so the folded suspension lines hold the bag shut.
When the pilot chute hits the air (about 120mph) it acts like an anchor - pilot chute stops, skydiver keeps going at ~120mph down. As they fall, the pilot chute pulls on a long nylon web called the bridle, which extracts a tiny curved metal pin holding the main container shut. Container opens and the d-bag is pulled out. The rubber bands make sure that the suspension lines pay out nice and neatly. As the lines reach full length they pull out of the last rubber bands and the d-bag “mouth” is now open. The folded canopy is pulled out of the bag and begins to expand.
There’s also a bit of material called a slider which controls opening shock and keeps the line groups separated.
The only major difference on the reserve canopy is that rather than an external hand-deployed pilot chute it’s got a big honking spring inside the pilot chute and it’s all packed shut into the reserve container. A handle on the harness has a steel cable with a pin on the end (that assembly is the ripcord), that pin goes through a little loop of material that holds all the reserve container flaps shut against the spring-loaded pilot chute.
Pull the ripcord and the pilot chute leaps free. It’s quite powerful - I’ve deployed mine in the rigging shop when I dropped it off for a regular repack (many riggers will have you do this so you can actually feel how hard it is to pull the emergency handle and so that you’re satisfied the last guy did his job) and it shot a good ways through the air - probably 15-20 feet.
However, and this is a big however, unless there’s sufficient airflow, all that happens is the pilot chute falls on the ground, the d-bag might fall out of the harness but that’s it. The canopy is not going to deploy - it is packed to stay in the bag so that it takes a certain amount of force to come out, otherwise it’d just “explode” out in a mess when used and overly-fast openings can be dangerous.
Ah, here’s a nice set of images showing the sequence:
I have actually deployed someone’s reserve chute while they were standing on the ground (actually they were dancing, we were at a fancy dress party.) The chute popped out the back a couple of metres but had absolutely no effect on the guy (apart from pissing him off a bit.)
Sadly, some people made a lot of money from this atrocity. Businessmen are making all of the “artistic” decisions in Hollywood.
At first, it angered me; but then I became hopeful: Perhaps I too can take a dump on a roll of celluloid and make a lot of money.
However, I do not have sympathy for you. You should know what you’re getting into anytime you watch a movie featuring Gary Busey. At least Keanu Reeves was not in the movie.
C’mooooooon. Who has this in their VHS collection?
I got the big video store cardboard standup promo thingie featuring Wesley Snipes. It was proudly displayed in the livingroom until my housemates got sick of it and stuck it in my bedroom. When I moved I was going to toss it but my buddy decided that Mr. Snipes should adorn the back of his big flatbed truck, so we stapled him to the wood railing. The truck was then christened “Wesley” and provided many years of amusement until the smog laws caught up with it.
After “Drop Zone” finished filming many of the rigs used showed up at the World Freefall Convention; you could buy (and use) a piece of “film history”. I was in the plane with someone who had the fake “tandem” rig they used in some sequences (basically a standard container with some extra handles and mounting rings in place to make it look like a tandem setup).
“Drop Zone” was a little too silly from a skydiving perspective, as was “Terminal Velocity”. “Point Break” was really big in the sport though - Patrick Swayze actually did many of his own jumps, earned his license and spoke positively of the sport. The skydiving scenes were beautifully filmed with the normal errors you’d expect and that only someone into it would notice (you won’t get four minutes of freefall, you can’t have a conversation, beginners don’t hop out the door and do relative work the first time).