What seemed like a hard opening...leg straps

[mitsuman 0]

Well over the weekend i was ale to do my level 5-8 jumps and everything went great!! except a minor injury to my back on my level 7.

First off im a student and dont know everything there is to know about skydiving.

on my level six, i noticed a had a harder pull then usual but didn't think anything of it, but on my level 7 i had a really painful hard opening. or at least what seemed to be a hard opening.

before getting on the plane i noticed that i didnt tighten my leg straps really TIGHT. in fact they were loose enough to were i had to ask my JM to check it, he said "eeh its fine", so off i went.

for my level 8, i really strapped them suckers down, because i just could not take another hit like that, and it worked. kinda disappointed in my jm for giving me the heads up when really they should have been tighter. but lesson learned!

wish i would have known this head of time! hope this helps someone new to the sport.

Hi, my names Jon, and I love to skydive.

[DougH 270]

Sorry I don't buy it.

Not having your legs straps tight enough will lead to bruises on old student gear with shot padding.

It won't lead to a hard opening that hurts your back. If you want to explain the mechanism through which lose legstraps changes the way the canopy opens (aside from opening asymetrically) I will be all ears.

Your canopy opened hard because of: how it was packed, the speed that you opened it, or just because.

"The restraining order says you're only allowed to touch me in freefall"
=P

[billvon 3,080]

>If you want to explain the mechanism through which lose legstraps changes
>the way the canopy opens (aside from opening asymetrically) I will be all
>ears.

It allows the rig/canopy system to slow down more before the person inside it sees any deceleration. This leads to a harder apparent opening.

During a hard opening, you might see 5G's momentarily as the canopy starts increasing drag to slow you down. If you are "free" within the harness, you will not decelerate as fast until you hit the limits of the legstraps. Meanwhile, the canopy/rig is slowing down at 30G's (i.e. it would be a 5G opening if your weight was included, but the same drag is going to slow down just the canopy and rig much more rapidly) - and by the time you hit the legstrap limits, there's going to be some fireworks as your body tries to re-accelerate the rig to terminal.

Since the additional play in most rigs is going to be about six inches max, and you're going to start loading the legstraps a little right away, it's usually not too bad. Take an example:

200lb jumper, 30lb rig, 200fps freefall speed
5G hard opening (i.e. 1000lbs drag during initial deployment)
6 inches play, 3 inches before anything is loaded

So you throw the PC. Parachute opens hard. Parachute applies 1000lbs to the rig. Rig starts slowing down at 30G's; you don't.

After .023 seconds the rig hits the limits of the legstraps. That rig/parachute is now going 24fps (16mph) slower than you are. You take all that load at once - on top of the 5G's that the canopy is slowing you down by.

[erdnarob 1]

Physics again sir. If your leg straps have slack in them... well expect to have a snatch force at opening which adds to the main bag snatch force and the parachute opening force.
Explanation: when you want to break a little rope attached to a parcel with your hand, you let it loose, have a swift gesture with your hand to accelerate it while holding the rope. When the rope is taut and your hand is at full speed the rope is likely to break since the force applied on a mass (the parcel) is proportional to the acceleration.
Coming back to your loose leg straps, you are going at 120 mph when you launch your pilot chute. This one almost stops as an anchor. But you keep on falling at high speed. At the line stretch you accelerate in a fraction of a second and at high speed the mass of the main bag+ the main (which is almost stopped by the pilot chute). This is the snatch force, then comes the opening force from the canopy inflation, then comes the snatch force from the slack in your leg straps since they have the tendency to stop but your body momentum when you leg straps are taut (they were loose) gives you an extra force. In this case you are adding 3 forces instead of 2. And there is no slider in the leg straps to dicrease that force!!

Learn from others mistakes, you will never live long enough to make them all.

[VTmotoMike08 0]

What are you defining as TIGHT? I have seen several students that want to cinch down the straps to almost the point of cutting off circulation (I was one). This is simply not needed. They should be firm but comfortable. It's totally OK if you can get a couple fingers under them.

Your hard opening could have been caused by loose straps, but it is much more likely that it was caused by poor packing, or the shit-happens-because-parachutes-are-unpredictable factor.