BASE813 0 #1 November 3, 2003 I used to have an XLspreadsheet I took from the net on the drag of various PC sizes and air speeds - anyone recollect where this may have been from or does someone have a copy they could email me? michael.mchale@berkeleygroup.co.uk Thanks Michael Share this post Link to post Share on other sites
base689 0 #2 November 3, 2003 > I used to have an XLspreadsheet I took from the > net on the drag of various PC sizes and air speeds > anyone recollect where this may have been from... About the end of 2002 I gave Mick my Excel table on Freefall and P.C. drag forces for publishing on the BASE Board for anyone to see/consult it. You can find it at http://www.basejumping.net/cms/deployment.shtml: the table is under the article "Freefall + P.C. drag force" and click on the "Download/View file" button to see it. Remember to read carefully the warnings/tips in my article, and moreover, remember it is NOT the truth but just a table, that is a good representation of reality provided any factor is very close to "perfection", but when something goes wrong it is and it remains a "table"... ...when a P.C. is NOT inflated, its pulling force is 0, no matter which the airspeed is Stay safe out there Blue Skies and Soft Walls BASE #689 - base_689AT_NO_123_SPAMyahoo.com Share this post Link to post Share on other sites
BASE813 0 #3 November 3, 2003 Nice one 689! thats the one i was looking for! I lost it on upgrading my computer! - I did not realise it was you that created it!! Thanks again!! Share this post Link to post Share on other sites
becs8399 0 #4 November 6, 2003 I checked out the link for the excel spreadsheet. It's actually just what I was looking for. I put up a post on wind engineering yesterday looking for technical info about sky diving/base jumping and the effects of wind on the body. I'm having a little trouble understanding the organization of the spreadsheet, though. Is there an easier way to look at it. or is there just that much info? Becs Share this post Link to post Share on other sites
BASE813 0 #5 November 6, 2003 I found it easier and more pleasing to the eye when I deleted all the Italian (as I cant speak a work of it!!) - it unclogged it slightly. I then printed it off in sections and it was much more managable than looking at it on XL. Either that or get a fuck off 42" plasma screen to view it!! Share this post Link to post Share on other sites
base689 0 #6 November 6, 2003 > I'm having a little trouble understanding the organization of the spreadsheet, though. What do you mean? Each row contains all the parameters AT a certain delay, each column contains the information as per column heading: time, distance fallen, speed, acceleration, air pressure, drag force in N for a 48" PC, drag force in kg for a 48" PC, and so on. > Is there an easier way to look at it. or is there just that much info? I don't know about an "easier" way to look at it. Just read carefully the text above the table because there it is explained everything you need to know to read the table and to adapt the table to yourself (=to your exit weight and to your terminal velocity). Just follow the tips. Remember to change in cell C24 the "dimishing factor" from 1 to "something" else (=higher value). Leaving 1 gives you really theoretical values, just as if the PC were inifinitely rigid (=steel disk), perfect manufacture, no burble effects on the border of PC, whatever. These are issues that does NOT exist in real life. To take into account EASILY of these effects altogether, just put in C24 a value higher than 1. In MY personal table I put 1.5: it seems quite reasonable to match "reality". In fact, if you put 1.5 as "dimishing factor", after 1 s of freefall under a 48" PC the table says it pulls with 4.6 kg, that seems really reasonable. In fact, in reality, when using a 48" PC a throwing it after 1 s of freefall, it indeed opens the container and starts to extract the parachute (mine weighing about 4.2 kg): this is the reason that make me think 1.5 is quite an acceptable value. The above situation gives at 2 s a pull force of 17 kg. Really, really reasonable, provided that any force between 4.6 kg and 17 kg is capable (and responsible) to open container, to extract a 4.2 kg parachute and get it open at the 3rd s after exit. This matches perfectly with our experience. That's my justification that 1.5 as "dimishing factor" is a good and sound value. And, lastly, don't forget it is just a table: it gives you a good approximation of reality. In fact, the pulling force after 3 s of freefall of a NOT inflated PC is ZERO, not matter what the table says... Stay safe out there Blue Skies and Soft Walls BASE #689 - base_689AT_NO_123_SPAMyahoo.com Share this post Link to post Share on other sites
Faber 0 #7 November 6, 2003 i had some problems looking at it aswell,i think its about the screen settings on YOUR computer,it helped me. To use the tabel you´ll need to know how much tention your rig needs to open(ie difference in pack jobs can give different results). Nice job you did there.. keep on the hard work Stay safe Stefan Faber Share this post Link to post Share on other sites
base689 0 #8 November 6, 2003 > To use the table you´ll need to know how much tention your rig needs to open(ie difference in pack jobs can give different results). Ah ah!!!!!! You got a real point with your remark indeed!!!!!! In fact, as soon as I had my Prism in hands, sooooo many years ago, I bought in a hardware shop a spring scale (whose cost was something like 5€) with a handle and a hook, and, after having created a loop (with a knot) in my bridle, off I went measuring opening forces of my container. Without the rig donned and with the rig donned (and leg/chest straps fastened). So, yes, it is really WORTH to measure the opening forces of your containers, under various conditions (rig "alone" on the ground/rig donned and straps fastened) and under different pack jobs, so to get a good number of values. And, after that, please, TRY TO PACK ALWAYS THE SAME WAY!!!!!!!!!!!!!!!!! Stay safe out there Blue Skies and Soft Walls BASE #689 - base_689AT_NO_123_SPAMyahoo.com Share this post Link to post Share on other sites
Faber 0 #9 November 6, 2003 Quote please, TRY TO PACK ALWAYS THE SAME WAY!!!!!!!!!!!!!!!!! no alwaysthat could kill you... i even has different ways to pack for even under 400ft(ultra low).. but in big ways yes Stay safe Stefan Faber Share this post Link to post Share on other sites
base689 0 #10 November 7, 2003 > no always that could kill you... I even have different ways to pack for even under 400ft (ultra low).. but in big ways yes OK. Do not take me too literally. By "try to pack always the same way" I mean: apart from the (natural) differences due to extra low SL-extra low freefall-low-subterminal-terminal jumps, pack always the same way in the sense to put ALWAYS the same quantity of bulk of fabric in the same place within the container Does it sound better written this way?!?!?!?!? Stay safe out there Blue Skies and Soft Walls BASE #689 - base_689AT_NO_123_SPAMyahoo.com Share this post Link to post Share on other sites
Faber 0 #11 November 7, 2003 QuoteDoes it sound better written this way?!?!?!?!? it did before aswell Stay safe Stefan Faber Share this post Link to post Share on other sites
