Faber 0 #51 April 23, 2007 Quotethe burble comes into effect. it has to. the thing is that you place your pc outside the burble as you exit in a way that it already is inflated as you start faling away,then it only need to build up the force that you have adjusted your pins to pop at.. I do agree that used in a wrong way its bad juju Stay safe Stefan Faber Share this post Link to post Share on other sites
tfelber 0 #52 April 23, 2007 I have a hard time with discussion of a burble in zero to low airpeed conditions. The burble created, if any, in these low jumps is so close to the jumpers back that a PC released at arm stretch would have a very hard time getting "caught". I think what is often referred to as burble effect is more times than not an actual bridle/pin/velcro hang up. This clears as the airspeed increases and looks like a PC caught in the burble of a terminal freefall. Share this post Link to post Share on other sites
wwarped 0 #53 April 23, 2007 Quotei still think that 4' bridals are a bad idea. the burble comes into effect. it has to. now if you got over your aversion to s/l... exit an antenna s/l. wind at your back. you can see the tied off pilot chute inflated already. now have a tail wind exiting from the ironwork of a bridge, holding a shortened bridle with a pre-inflated pc. where is the burble? in front of you! it is a tailwind! if you customize your gear to have very light closing forces, you will likely drop away from the pc and NOT tow it very far. by the time you build up enough speed to have a significant burble above you, the pc is long gone. o.k. it is just more theory. (but I trust greeny's experience...) DON'T PANIC The lies in learning how to throw yourself at the ground and miss. sloppy habits -> sloppy jumps -> injury or worse Share this post Link to post Share on other sites
greeny 0 #54 April 25, 2007 Bridle Length for Low free fall: If I am taking any sort of delay I keep the full 9ft of bridle so my PC is clear of the burble. Most of my low freefalls so far I have kept my full 9ft bridle. As I exit I throw my PC underarm ‘UP’ to bridle extension. The Idea is to get the PC above me at bridle extension just as I start to drop. This causes the tension to comes on the fully extended bridle and inflate / keep the PC inflated. I have seen the pitch done ‘overarm’ like throwing a basketball, but underarm works better for me. As I said the idea is to get the PC 9ft above my head so as I put tension on the bridle (by starting to fall) the PC just rolls over and inflates. I have 25 Freefalls from 173ft, 3 from 160ft & 1 from 190ft all using the above technique. The biggest inconsistency I have noticed is getting the PC inflated first time, every time. When my throw up technique works right my pins are being pulled as the PC comes back past head height on the exit ledge. When the PC does not reach bridle extension at the time the tension comes on the bridle it can drop me anything up to 20ft lower. This is the time it has taken for my PC to inflate and lift. Problems can come from: PC not thrown hard enough, it never reaches 9ft PC reaches bridle extension too early and starts to descend again Anything that causes slack in the bridle will mean that slack has to be taken up before the PC inflates and grips the air. I believe there is almost no burble due to V-low airspeed and head high body position. My main reason for trying shorter bridles on low freefall is to find a way to get the PC inflation more consistent. I have got 5 or 6 jumps on is an ‘Arms Length Bridle’ This bridle was cut so when my right arm is at full extension I have 2inchs of slack from my pins to my PC attachment point. So far for my low ‘short bridle jumps’ I have laid the PC on the top of my hand and just left it in the air on exit. I have video of this working perfectly (5.9sec canopy ride from 173ft) but I have also had it drop me low. I think the hesitation in this case was because the PC center line as not extended and there for the PC took time to inflate. A way I now prefer but have not jumped bellow 200ft yet is to stand on the exit and holding my PC by the attachment point I wave it in the air to inflate it. I do this inflation wave up and down. I exit as I get it to the top thereby having a fully inflated PC as I leave the exit point. The reason for the short bridle is to put tension on the PC and keep it inflated as soon as you exit. If you use 9ft bridle and exit with a PC preinfated the tension is not there until you have fallen to bridle extension, thereby giving a chance for the PC to close up again and hesitate before re opening. I need to play with this more but think it will work well. My thinking is that if I can get my PC inflated perfectly every time it will remove one of the major variables from my low freefall. On my PC Throw up jumps this variable has been about 20 – 30ft Exiting from 160ft I have a margin of error that can cover this, but as I try to come lower this will no longer be acceptable I know 143ft has been freefalled and believe 120ft is repeatable if we can get it consistent. The 120ft estimate is based on my current opening altitudes / canopy times off 170ft & 160ft freefalls. As Tom said: “Predictability ought to be the main goal of an ultra low freefall system”. Greeny My set up: Rig 1) FOX 265, ZP Top skin, Multi, 5th Line with ‘Normal’ V-Tec vents, in a Vertex 2 Rig 2) FOX 243, ZP Top skin, Multi, 5th line with enlarged V-Tec and short lines, in a DP (By enlarged V-Tec I mean I had my V-Tec doubled in size on all cells (except the end cells) including the center cell. My lines we also shortened by 10% to cup the canopy more there by keeping more of the air trapped under the bottom skin and driving it through the vents. The 5th line also helps with this by pulling more of the tail of the canopy down. This canopy pressurizes fast. Share this post Link to post Share on other sites
TVPB 0 #55 April 25, 2007 Quote more consistent. QuoteMy thinking is that if I can get my PC inflated perfectly every time it will remove one of the major variables from my low freefall. The above are keys to doing lower margin of error activities more safely! Consistency, and minimal variability. Now imagine this conversation regarding a 100ft freefall?????? p.s. regarding the technique of pre-inflating by waving the p/c around: be very wary and careful of bridle / pilot chute / hand entanglement. It does happen. Especially when the conditions are a little windy as this will add a third dimension of possible error inducement. R.e the underarm throw, be very wary of bridle routing. I am sure you are considering these anyway. Regarding object turbulence, it starts as soon as a mass starts moving through the air. By definition, when the mass moves through the air, it displaces air particles and they have to go somewhere and do something. At lower air speeds little swirling eddies begin to be created because the particles are pushed rapidly to the side of the mass. They then want to fill the void (vacuum) that is created behind the mass as it moves through the air. This is the reason why p/c get stuck behind people's backs. At lower airspeed the strength of these air movements is less than at higher air speeds and they cover less area (i.e. the body induced burble increases its volume as the mass increases its descent rate). But the affect is still there. Watch a p/c as in inflates using the techniques you are discussing. There are two main reasons why it does not anchor better/quicker/more symmetrically than it does: one is the lack of initial tension and pressurisation, and the other is localised turbulence induced by air movements around BOTH the exiting body (which are caused by the body moving through the air) and the object (which are caused by air moving around the object). The first reason can be caused by technique issues (unsymmetrical throw, offset throws, improper location and placement of bridle and p/c materials during the throw, etc), and equipment issues (manufacturing quality, wear and tear of gear, etc). If you consider EVERY single variable and take the right corrective action, your ability to safely perform low freefalls increases. Thanks for posting the info and your experimentation. Stay Safe - Have Fun - Good Luck The above could be crap, thought provoking, useful, or . . But not personal. You decide. Share this post Link to post Share on other sites
Ten48 0 #56 April 26, 2007 Quote Rig 2) FOX 243, ZP Top skin, Multi, 5th line with enlarged V-Tec and short lines, in a DP (By enlarged V-Tec I mean I had my V-Tec doubled in size on all cells (except the end cells) including the center cell. My lines we also shortened by 10% to cup the canopy more there by keeping more of the air trapped under the bottom skin and driving it through the vents. The 5th line also helps with this by pulling more of the tail of the canopy down. This canopy pressurizes fast. I think I remember watching that canopy surging backward on opening when you were jumping during the "Yuri Incident." Did you ever sort that issue out? It's time now! My time now! Give me mine. Give me my wings! - MJK Share this post Link to post Share on other sites
greeny 0 #57 April 26, 2007 My canopy was built as a specialist low freefall canopy; it was never intended to go past 1 sec delays. When you saw it being jumped there it was also set in excessively deep brakes, which have since been adjusted. Vents on most canopies have been sized to give you a balance between pressurisation on all delays and not driving backwards excessively on any. Mine was designed around a 0-1sec delay only. Before Todd built the canopy for me he told me if I took it past a 1 sec delay it would back up on opening. This backing up is caused because so much air enters the canopy through the enlarged vents that once the canopy is full pressurised the extra air still coming in has no where to go but out of the nose. This air rushing out of the nose is what drives the canopy backwards. Sub 200ft freefall (instant delay) & Static line the canopy is working great, it is both pressurising and transitioning from open to flying very fast. Greeny Share this post Link to post Share on other sites
Calvin19 0 #58 April 29, 2007 LOOK WHAT YOU GUYS DID TO A SUPER LOW JUMP NEWBIE/MORON!!!!! email to me- Quoteoh i've decided from reading on dz.com i'm not going to use a PC anymore. when i'm ready to pull on freefalls i'll flail and hit the packjob. it'll work.. right? the risk of having my PC catch on something just isn't worth it.. so it's off now. i set him straight, i told him that you have be at least at 600' for this to be a good idea, and heading performance is nil. so he will be ok. Share this post Link to post Share on other sites