SansSuit 1 #1 December 9, 2013 How much does the wind direction affect the opening of a canopy? I would think that opening while facing straight into the wind would give the best (on heading) opening. How about 45 or 90 degrees off the wind line? Could that cause twists in a canopy that is susceptible to squirrelly openings?Peace, -Dawson. http://www.SansSuit.com The Society for the Advancement of Naked Skydiving Quote Share this post Link to post Share on other sites
mark 107 #2 December 9, 2013 SansSuitHow much does the wind direction affect the opening of a canopy? I would think that opening while facing straight into the wind would give the best (on heading) opening. How about 45 or 90 degrees off the wind line? Could that cause twists in a canopy that is susceptible to squirrelly openings? Almost all openings start with facing into the relative wind. Openings that start at 90 degrees to the relative wind are generally very hard and can result in injury and canopy damage. Mark Quote Share this post Link to post Share on other sites
ridebmxbikes 0 #3 December 9, 2013 I have deployed facing into the wind( headdown). Seriously, don't do it! It hurts! Quote Share this post Link to post Share on other sites
skinnay 0 #4 December 9, 2013 This also causes your lines to stretch unevenly. If you suspect you have many openings perpendicular to the wind you should return the canopy to the manufacturer for inspection. This is why I use a wrist mount compass to ensure I always open into the wind. Quote Share this post Link to post Share on other sites
angryelf 0 #5 December 9, 2013 I assume you are talking about a belly to earth deployment, with lateral winds affecting a normal parachute activation, line stretch and inflation with all other variables of opening being normal/taken into consideration/controlled/accounted for. Personally-I think it greatly affects how a canopy opens. I know for a fact low ambient winds present in the BASE environment are a HUGE factor in heading performance. How much does heading in relation to high wind affect an opening at terminal? No idea. Scientifically quantifying that variable for every canopy, orientation to wind would be tough; but I suppose doable. I think that some variables are just too much of an ass pain to dissect down to raw numbers and are part of what makes this sport fun. If you think chopping a spinning x brace that wound up for no reason is fun, that is..."Sometimes you eat the bar, and well-sometimes the bar eats you..." Quote Share this post Link to post Share on other sites
JohnSherman 1 #6 December 9, 2013 QuoteHow much does the wind direction affect the opening of a canopy? I would think that opening while facing straight into the wind would give the best (on heading) opening. How about 45 or 90 degrees off the wind line? Could that cause twists in a canopy that is susceptible to squirrelly openings? None! You are moving within an air mass which is called the wind if you are on the ground. It is only going to have an effect if you are not in the air mass and the air mass hits you. The relative wind you experience is from your movement within the air mass. Think about the boat in the water analogy Quote Share this post Link to post Share on other sites
angryelf 0 #7 December 9, 2013 Yet you can have horizontal drift in freefall?"Sometimes you eat the bar, and well-sometimes the bar eats you..." Quote Share this post Link to post Share on other sites
Trev_S 0 #8 December 9, 2013 JohnShermanQuoteHow much does the wind direction affect the opening of a canopy? I would think that opening while facing straight into the wind would give the best (on heading) opening. How about 45 or 90 degrees off the wind line? Could that cause twists in a canopy that is susceptible to squirrelly openings? None! You are moving within an air mass which is called the wind if you are on the ground. It is only going to have an effect if you are not in the air mass and the air mass hits you. The relative wind you experience is from your movement within the air mass. Think about the boat in the water analogy This is what I thought when I read it at first. However wouldn't deployment be creating such a force that it would be like sticking an oar out into the current? Quote Share this post Link to post Share on other sites
kuai43 7 #9 December 9, 2013 Trev_S***QuoteHow much does the wind direction affect the opening of a canopy? I would think that opening while facing straight into the wind would give the best (on heading) opening. How about 45 or 90 degrees off the wind line? Could that cause twists in a canopy that is susceptible to squirrelly openings? None! You are moving within an air mass which is called the wind if you are on the ground. It is only going to have an effect if you are not in the air mass and the air mass hits you. The relative wind you experience is from your movement within the air mass. Think about the boat in the water analogy This is what I thought when I read it at first. However wouldn't deployment be creating such a force that it would be like sticking an oar out into the current? I'm always amazed at some people's inability to perceive the analogy. If you stick an oar out into a current from a boat drifting in it, nothing will happen.Every fight is a food fight if you're a cannibal Goodness is something to be chosen. When a man cannot choose, he ceases to be a man. - Anthony Burgess Quote Share this post Link to post Share on other sites
mjosparky 4 #10 December 9, 2013 angryelf Yet you can have horizontal drift in freefall? John, do you want to explain it to him. SparkyMy idea of a fair fight is clubbing baby seals Quote Share this post Link to post Share on other sites
angryelf 0 #11 December 9, 2013 If you have multiple currents (relative wind of 112 kts and, say a horizontal breeze of 40 kts) and you "stick a paddle in it"-it has to affect you to some degree. For the boat analogy I offer this: a boat in a consistent current will move with that current-I agree. But, float that same boat in a big river going 6 kts downstream/midstream and let it roll past a small tributary pumping out a 1/4 of the main river's volume at 3 kts and I guarantee it will affect the boat in the main current! Where it hits the boat, mass of the boat, amount of water the boat is drawing, how much initial and secondary stability the boat has, whether the boat is sideways (broached) in the current, etc will add to the variables. Sticking a paddle into the 3 kt side current adds an infinite new layer of variables... What if you have wind velocities varying in the 200-800 vertical feet it takes your canopy to open, while you decelerate? Hypothetically, lets say at pitch we have 20kts from 270, but as the canopy's outer cells are inflating winds are 10 kts at 250. This will have to impact the opening to a small degree! "wind" is 3 dimensional in skydiving. It has to have some (minor, yes) impact on the whole deployment sequence. It affects how planes and canopies fly, it affects us in freefall, why would it suddenly stop affecting us because we dumped a PC? I'm not a scientist, and without investing a fortune in doing hundreds of jumps, charting heading, freefall delays, exact weather readings, perfectly consistent deployment altitudes/barometric pressures/etc and then plugging it all into a computer to get some abstract numbers that really won't affect my openings (skydiving, that is) a great deal-I don't have a way to "prove" the above "hypothesis". At the end of the day-I'm making it up as I go and maybe I'm dead wrong... I learned why bigger Sabre 1's had secondary brake lines a few years ago by stubbornly hammering at what I thought was the right answer-so maybe this will be another one of those learning experiences. Or maybe it will be another fun internet discussion that gets people thinking.-Harry "Sometimes you eat the bar, and well-sometimes the bar eats you..." Quote Share this post Link to post Share on other sites
shropshire 0 #12 December 9, 2013 angryelfYet you can have horizontal drift in freefall? Relative to what? .. What are you measuring against? (hint please don't say the ground !!) (.)Y(.) Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome Quote Share this post Link to post Share on other sites
flyhi 24 #13 December 9, 2013 QuoteThis is why I use a wrist mount compass to ensure I always open into the wind. Since they refused my request for a sarcasm font, I really can't tell. Are you serious?Shit happens. And it usually happens because of physics. Quote Share this post Link to post Share on other sites
flyhi 24 #14 December 9, 2013 QuoteAlmost all openings start with facing into the relative wind. Openings that start at 90 degrees to the relative wind are generally very hard and can result in injury and canopy damage. The wind at altitude is 060 at 15 kts. The wind at 3000 ft is 080 at 10 kts. Jump run was 060. You tracked off at 330. What do you do at pull time wrt the relative wind?Shit happens. And it usually happens because of physics. Quote Share this post Link to post Share on other sites
mark 107 #15 December 9, 2013 flyhiQuoteAlmost all openings start with facing into the relative wind. Openings that start at 90 degrees to the relative wind are generally very hard and can result in injury and canopy damage. The wind at altitude is 060 at 15 kts. The wind at 3000 ft is 080 at 10 kts. Jump run was 060. You tracked off at 330. What do you do at pull time wrt the relative wind? Here's how to calculate what to do for your example: 060 x 15 = 900 080 x 10 = 800 060 x 330 = 19800 Total: 900 + 800 +19800 = 21500 According to Theodore Knocke (see pages 340-341), the optimum drag coefficient is at 21500 is: pi / (1.16 ^ 2) = 2.3335 21500 / 2.3335 = 9213.6276 7986.4968 / 090 = 102.3736 kts = 117.7297 mph. So your best bet is to face 90 degrees to the wind at about 120 mph. At our drop zone, we used to have a placard by the door to help folks with this, but what we found was that on break-off everybody would track the same direction for optimal openings. Now only one jumper gets the optimal openings and the others are all basically screwed. Mark Quote Share this post Link to post Share on other sites
skydiverek 63 #16 December 9, 2013 Physics professor and skydiver with thousands of jumps, John Kallend, wrote here on DZ.com that you will "become one with the (horizontal) wind" only after 8 seconds in freefall. So, if the horizontal wind is 40 mph, then you will be moving 40 mph (in freefall) against the ground, only after 8 seconds. Quote Share this post Link to post Share on other sites
angryelf 0 #17 December 9, 2013 quote: What are you measuring against (don't say the ground)? For the purpose of this discussion: The space between two points. Point A: The point at which the skydiver (who is perfectly neutral on his/her belly) throws the PC into the relative wind. Point B: When the canopy is inflated. I'm saying that wind lateral to the "column of air the jumper is moving in" will play a part in heading performance between the two points. I agree that the jumper is a column of air. I just think the column is a twisting/bent/dynamic column that is at an angle from the ground to the plane (reference points of import if we look at the whole jump). Where I'm disagreeing is that this column of air is like a really long toilet paper tube. -Harry"Sometimes you eat the bar, and well-sometimes the bar eats you..." Quote Share this post Link to post Share on other sites
mark 107 #18 December 9, 2013 angryelfquote: What are you measuring against (don't say the ground)? For the purpose of this discussion: The space between two points. Point A: The point at which the skydiver (who is perfectly neutral on his/her belly) throws the PC into the relative wind. Point B: When the canopy is inflated. I'm saying that wind lateral to the "column of air the jumper is moving in" will play a part in heading performance between the two points. I agree that the jumper is a column of air. I just think the column is a twisting/bent/dynamic column that is at an angle from the ground to the plane (reference points of import if we look at the whole jump). Where I'm disagreeing is that this column of air is like a really long toilet paper tube. -Harry Is the spinning worse in higher winds? And are you equally likely to spin clockwise as counter-clockwise? Considering Coriolis effect, does it work the same in the southern hemisphere? Mark Quote Share this post Link to post Share on other sites
JohnSherman 1 #19 December 9, 2013 QuoteAccording to Theodore Knocke (see pages 340-341), the optimum drag coefficient is at 21500 is: pi / (1.16 ^ 2) = 2.3335 Clairification please: Parachute Recovery Systems Design Guide by Theo Kanacke is not numbered by page number just chapter number and chapter page. There is no page 340-341. I assume I have the wrong book. What is the title of the one to which you refer. Quote Share this post Link to post Share on other sites
Divalent 137 #20 December 9, 2013 JohnShermanQuoteAccording to Theodore Knocke (see pages 340-341), the optimum drag coefficient is at 21500 is: pi / (1.16 ^ 2) = 2.3335 Clairification please: Parachute Recovery Systems Design Guide by Theo Kanacke is not numbered by page number just chapter number and chapter page. There is no page 340-341. I assume I have the wrong book. What is the title of the one to which you refer. He was quite obviously trolling (as are a few others). For all practical purposes, if you are stable belly flying, there will be no relative wind other than the vertical one hitting you in the belly from below. You can create a significant horizontal relative wind by going into a tracking position, but that's about it. I doubt anyone could delibarately create a horizontal relative wind of any significance by side sliding or back sliding in an otherwise controlled manner. So pretty much the relative wind at deployment in free fall from an otherwise stable position will be mostly from the direction of the ground, plus any "in-your-face" horizontal component that the jumper might have created by tracking prior to pulling. The only possible exception I can think of is if there is a zone where the winds aloft change significantly in their direction near where the jumper is deploying. Quote Share this post Link to post Share on other sites
CSpenceFLY 1 #21 December 9, 2013 After reading through this thread I understand why people have such a problem with the airplane on the treadmill problem. Quote Share this post Link to post Share on other sites
wolfriverjoe 1,523 #22 December 9, 2013 CSpenceFLY After reading through this thread I understand why people have such a problem with the airplane on the treadmill problem. Yeah... Seriously, unless there is a very strong wind shear, right at or before opening (8 sec ~ 1500ft) there will be zero horizontal component to the relative wind (unless induced by the jumper through tracking or similar)."There are NO situations which do not call for a French Maid outfit." Lucky McSwervy "~ya don't GET old by being weak & stupid!" - Airtwardo Quote Share this post Link to post Share on other sites
Ron 10 #23 December 9, 2013 QuoteYet you can have horizontal drift in freefall? Thats WHY you have drift in freefall."No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334 Quote Share this post Link to post Share on other sites
Divalent 137 #24 December 9, 2013 RonQuoteYet you can have horizontal drift in freefall? Thats WHY you have drift in freefall. Well, I think you can have a formation sliding directionally in their column of air (for example, if the formation is tilted because all the heavies are on one side of a ring and all the floaters opposite). That is sometimes refered to as "drift", and potentially can be cause for two consecutively exiting groups to get closer to each other, but it's not relevant to the question posed by the OP. That sort of movement would all end when they break off and track for separation. Quote Share this post Link to post Share on other sites
angryelf 0 #25 December 9, 2013 This thread has been fun, thanks!"Sometimes you eat the bar, and well-sometimes the bar eats you..." Quote Share this post Link to post Share on other sites
