Basejumper.com - archive

Im looking for info on low jumps, direct bags in particular. Is there anyone on here who has extensive experience with them? I've seen video of them being used for the lowest BASE jumps, http://www.runtergefallen.de/videos.html like the second video on this page (59'), and heard claims of a 51' jump stood up with a direct bag but cant find the video. There doesn't seem to be too much info out there that I could find in my searches.

My questions are:

-What causes the direct bag to open that much higher than a PCA? I know that it can be held just above the jumper vs the static line where you have at least a foot or two of bridal between the PCA and where the bridal ties to the object. Looking back on old posts about this (http://www.basejumper.com/..._Direct-Bag_P1661646), there were claims of bottom skin inflation 25-35' below the exit, which seams way higher than that of a static line, so there must be something else besides those couple feet of bridal. Does it have anything to do with the fact that with the direct bag, the canopy can come out and expand immediately at line stretch unlike a static line where its still attached to the PCA until the break chord breaks therefore stripping the center cell and tensioning straight through the center of the canopy before the canopy and fall and inflate?

-With the video linked above, it appears to have 4 cells vented (although the center cell could be vented, just not visible if the vent is black) but how much would the 5th vent help? (guessing not too much although anything helps that low)

-Would you use deep or shallow brakes? I feel like deep would be better as I remember hearing it promotes slightly faster inflation and the only advantage of using shallow brakes on low stuff is if its high enough to achieve full flight, you have less of a surge and more time in full flight from shallow, but on a jump like this you wouldn't get anywhere near full flight, so PLF from deep brakes would be better than more forward speed and slower inflation from shallow.

-With and OSP 225 loaded about .65, what would the limit be in terms of how low you can go? I'm not in any sort of race to go set a new record, or do something stupid low, and obviously am going to work my way down and perform many test jumps on higher objects gathering data, but there are a few interesting objects I've been looking at, a VERY low B that would be something I would want to do once eventually if possible that I would want to know if I should just rule out immediately, a few VERY low E's and a couple power towers in some hills near me that would have some pretty cool canopy rides, and then a few other low objects that are within the static line ability range but more canopy time would be appealing and the direct bag might make it go from a semi sketchy static line to a fairly safe and easy jump.

Thanks for any input!

**Edited to add, How does a Top Skin Assist compare to a direct bag in opening height?

i am working on a reply.
Check your PM´s
Take care,
space
reply.


q1:Is there anyone on here who has extensive experience with them?

q1a:yes i am with 30 or so.


q2: What causes the direct bag to open that much higher than a PCA?

q2a: All cells in theory are loaded at the same time whereas pca starts

loading BC center cell lines.the alitude between the 2 methods are very small

on alt lost. 25 ft i would guess the differnce is.

q3: Does it have anything to do with the fact that with the direct bag, the

canopy can come out and expand immediately at line stretch unlike a static

line where its still attached to the PCA until the break chord breaks

therefore stripping the center cell and tensioning straight through the center

of the canopy before the canopy and fall and inflate?

q3a It is not center cell strip. it is outer cells slump you speak of. You

mispelled the word "Cord". I must nail you for this because sloppiness in one

part of life most likely will slop into other parts. Chord means front to back

measure of the wing.

q4:will a 5-vs-4 vented canopy help?

q4a Absolutely not in the skill range. If you cant do it without vents, maybe

you shouldnt do it at all. If 20ft makes a deadly difference maybe you
shouldnt do it at all. It takes more air to inflate a vented canopy bottomskin inflation than a nonvented.

q5:Would you use deep or shallow brakes?

q5a: You must specify the alti, the LZ etc. There is no one answer for all. be more precise.

q6:what would the limit be in terms of how low you can go (-With and OSP 225 loaded about .65)?

q6a 1 ft above the ground at zero sink rate after a perfect opening not including winds would be a safe bet. the military thougt that opening and landing should be almost simultaneous. but that is so old school (1917?).
I am not joking. a person who is shorter than the test subject can open a bit lower.
Take care, this is the best info that you will receive I think.
Space

you are welcome.
take care,
space

Would someone mind chiming in on why/how deep brakes would promote faster inflation? It seems to me that a bit more forward speed on opening would promote faster inflation. Similar to jumping in a slight headwind (object permitting) or an airplane taking off in a headwind requiring less runway. I pack deeps for anything but low stuff but if it's not necessary or even counterproductive I'm very interested.

Thanks for the info Space, and also everyone else who sent PM's. It would be awesome of some of the people who PM'd me wanted to post what they sent on here as well so in the future it will be easier for others to look up the topic instead of having to post a new thread and hope to get the same PM's.

As far as going as low as possible, it seems top skin assist will be the way to go.

Every parachute will have an optimal brake setting for opening. Deep brakes will open quicker than shallow brakes but that isn't to say that deeper brakes will open quicker than deep brakes. There's numerous things happening during opening that I couldn't post about in a concise manner so maybe a phone call to literally any canopy manufacturer would be a better option.
But one thing I can say is that it may help you to think of it not in terms of inflation but in terms of how long it takes to attain a flying/controllable parachute. The lower the critical airspeed required the sooner you will attain control. Shallow brakes equals higher airspeed which takes longer for the wing to achieve which usually results in more altitude/time consumed to attain a flying/controllable parachute (relative to each wing).

Which is why:
it makes it easier to attain its minimum airspeed. You will also notice that aircraft will usually use some degree of flaps during take off and landing for the same reason.

shallow brakes would get the canopy flying sooner as the surge would inflate the canopy IMHO. Faster inflation vs higher opening. It sounds weird but that is on your platter for sketchies from B,A,S,E,.
Take care,
space

what and how is top skin assist?
take care,
space

https://www.facebook.com/...eos/799026476779669/ is a good example. And for low jumps I use shallow brakes so the canopy is flying faster (since I'm planning on getting it into full flight) but for pushing the limits of what is possible to do, there won't be any intention of getting full flight so higher opening (deep brakes) would be better.

I understand the concept you are suggesting but I don't believe it works that way in practice as the faster flight mode requires the canopy to achieve a higher airspeed to begin flying. My personal experience is that in shallow brakes the canopy will initially surge on opening but will then fuck around as it finishes pressurizing while the deep braked opening will pressurize and fly/be controllable sooner/higher. The same can be seen when people open in deep brakes but release their brakes before full pressurization and the canopy responds poorly.

I've found that I get a longer canopy ride static lining with shallow brakes over deep brakes from a 180' A I visit semi often. But what I've found makes more of a difference is wind. 3 mph of wind makes a much bigger difference in canopy time compared to brake settings.

I am happy free falling down to 200ft and sometimes lower so most of my experience is with free fall openings.

Edit: Also when you say "longer canopy ride" do you mean Longer airtime or longer distance travelled from the object?

Regardless isn't the vented canopy going to open quicker/higher?

I would venture to say it takes longer for the vented to inflate. same amount of air to fill up more volume per meter descent.
take care,
space

You just might be wrong this time Space. Bottom skin expansion you might be able to argue (though I doubt) but not canopy inflation.