May 18, 2005, 4:08 AM
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Balloon altitude
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Hi I've been offered a balloon jump of agl between 3000ft and 5000ft.
I was a little concerned about exiting at the lower end as getting out at 3000ft is my normal pull altitude! Is this normal, to people just hop and pop?
No it isn't. 3000' is adequate but not plenty. A hop and pop from a balloon has quite different dynamics than a hop and pop from a plane due to the absense of any initial airspeed. For someone with 101 jumps, accustomed to deploying at 3,000ft, I'd not recommend 3,000 ft for a first balloon exit.
i've done balloon jumps from as little as 4k all the way up to 7k.. 3000 is certainly 'do able' even with a skydiving rig (paying attention to your packing will make it less scary) but i wouldnt recommend it as a first balloon jump..
the first 1000 feet will take alot longer than your used to, and the 'ground rush' will be much more intense than your used to as well... at 100 jumps that might be a bit overwhelming.. but ymmv
if its a range of 3000-5000, see if you can get out last as you will gain 'extra' altitude that way
I will be doing my first baloon jump in august. My instructor advised me not to get out under 4000 ft, even though I have hop and poped a few times from 2500 ft from a cesna
I have not done mine, but I`ve got some info. I think 3000feet won`t be the biggest problem. Picking the right landing area could be. I was told that I have to pick my landing area by myself from midair. So prepare for landing off and without the help of any (artificial) wind indication.
I might be wrong here but I beleive the first 1000 feet is the first 1000 feet regardless of what you're jumping out of. The time to cover the first grand doesn't change because you're jumping an Otter or any other moving aircraft. Anybody know the physics?
If you ever do that with a modern skydiving rig and a normally sized PC, be prepared to tow it for a while. It will definitely add to the rush. Enjoy the suspense as your wait for the airspeed to build enough to pull your main pin. Then, feel the rush as the D-bag lazily leaves your back, and teeters in the air while your tight, skydiving line stows slowly pop loose. Betcha get aline twist or two to add to the fun, as well. Remember, a good stable exit will be helpful.
No. You risk gear damage or a malfunction when you PCA someone at subterminal speeds unless your gear is designed for it _and_ the person assisting knows exactly what they are doing. It's useful for low BASE exits (I've done it a few times) but not a good idea for your first balloon jump with skydiving gear.
Which, in my opinion, is the biggest safety concern with low altitude balloon exits. Someone without BASE jumping experience may attempt to exit the same as they would an airplane, and will be on their back about 3 seconds after exiting. One should assume an unstable exit on their first balloon jump, so altitude should be included to allow for that. If they are stable, then so much the better!
As for time for the first 1000', the world is not ideal, but the time to fall 1000' will be the same, for all intents and purposes, with a balloon and aircraft. The fact that some people use their forward speed to produce lift on exit, i.e. a head high exit, does implies there will be slight differences, but basically physics says that the first vertical 1000' will take a fix amount of time no matter the horizontal velocity
I wouldn't worry about the spotting part, you're going to be going real slow, and directly downwind, so it's a lot less challenging than spotting from a plane. Take some binoculars with you for spotting and leave them in the balloon, everything is going to be going real slow until you jump, so just be sure you haven't overlooked any power lines, fences, swamps, etc. and have an alternate if possible. Good luck, that sounds like a lot of fun.
I might be wrong here but I beleive the first 1000 feet is the first 1000 feet regardless of what you're jumping out of. The time to cover the first grand doesn't change because you're jumping an Otter or any other moving aircraft. Anybody know the physics?
The vertical component of velocity is almost zero whether jumping from an aircraft or a balloon (assuming the vehicle's not ascending or descending). With an aircraft you have an initial forward velocity, you take that momentum out the door with you. So while you're on the "hill" you still have airflow and a degree of control, if you arch you'll tend to fall stable, and every skydiver should know that you initially stabilize oriented in the direction of the flying aircraft until your vertical velocity builds.
Due to the initial airspeed, resistance & aerodynamics I'd expect an aircraft jump actually gives you slightly more fall time in the first few hundred feet if you fly on the hill, but the difference is probably negligable. The real issue is the initial air flow on the hill that gives you the control to fall stable.
Exiting an aircraft you usually don't have an appreciation of your angular momentum on exit, your body position and the forces of air usually dominate anything you do. If you jump from a stable platform at zero air speed your initial orientation and angular momentum are a significant factor. If you exit a baloon on your side or with a slight tumble you will stay on your side or keep tumbling unless you know how to counter that acrobatically. You may not know how to correct for it until you've been falling for several seconds and can start to use the airflow to fly your body.
(This post was edited by dorbie on May 18, 2005, 11:50 AM)
As for time for the first 1000', the world is not ideal, but the time to fall 1000' will be the same, for all intents and purposes, with a balloon and aircraft. The fact that some people use their forward speed to produce lift on exit, i.e. a head high exit, does implies there will be slight differences, but basically physics says that the first vertical 1000' will take a fix amount of time no matter the horizontal velocity
Actually physics doesn't say that at all. Since drag goes as v^2 at these Reynolds numbers, there's a non linearity that results in the horizontal component of velocity having an effect on the vertical component of drag, and vice versa.
the first 1000 feet will take alot longer than your used to
The force of gravity is the same at 3000 ft from a balloon or a plane. It will take the same amount of time to reduce your altitude by 1000ft, assuming equivalent non tracking body positions. The forward inertia does not affect the force of gravity.
Since drag goes as v^2 at these Reynolds numbers, there's a non linearity that results in the horizontal component of velocity having an effect on the vertical component of drag, and vice versa. ...
This sounds very interesting, but I'm guessing there is more to it than can be covered in a single sentence. Do you have a link, perhaps?
the first 1000 feet will take alot longer than your used to
The force of gravity is the same at 3000 ft from a balloon or a plane. It will take the same amount of time to reduce your altitude by 1000ft, assuming equivalent non tracking body positions. The forward inertia does not affect the force of gravity.
There are two major forces acting on a falling body, the force of gravity and the force of air resistance.
There is a difference between the force of air resistance acting on a body falling from a balloon and the vertical component of air resistance acting on a body falling from a plane on the "hill", it depends a lot on what the body is doing too IMHO but speaking in idealized terms you fall slightly longer from an aircraft.
No it isn't. 3000' is adequate but not plenty. A hop and pop from a balloon has quite different dynamics than a hop and pop from a plane due to the absense of any initial airspeed. For someone with 101 jumps, accustomed to deploying at 3,000ft, I'd not recommend 3,000 ft for a first balloon exit.
Within 5 seconds from exit the jumper will be doing 85 mph, which is about the same airspeed as an Otter exit, and with a loss of altitude of only 370 feet. So they'll be at 2,630 feet AGL with plenty of airspeed to get stable for deployment. Since minimum opening altitude is 2,000', this should be sufficient for most jumpers.
For this particular person with 100 jumps and used to opening at 3,000', it's a personal judgement call.
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