srsand1960 0 #1 January 2, 2006 If a 240 9 cell canopy has a higher aspect ratio then a 240 seven cell with the same wing load, is the rate of decent faster in a 9 cell because of the difference in performance? Does the 240 9 cell have the same span and chord as the 240 7 cell? Does a 240 9 cell canopy take longer to deploy 240 seven cell or do they deploy about the same? Is there a difference in the way you pack them? It doesn't matter how anyone else lives their life.... it matter how you live yours! Quote Share this post Link to post Share on other sites
AggieDave 6 #2 January 2, 2006 E-mail Brian Germain, you'll find him here under that name on DZ.com to PM him your question. Or you can get his e-mail from BigAir Sports' website. He's a canopy designer with many years of proven knowledge and experience under his belt that is also very easy to get ahold of to ask these types of questions to.--"When I die, may I be surrounded by scattered chrome and burning gasoline." Quote Share this post Link to post Share on other sites
FrogNog 1 #3 January 2, 2006 Aspect ratio is the ratio of the square of the span to the square of the chord. So any canopy that has a higher aspect ratio (e.g. the 9-cell in your example) will have a higher span-to-chord ratio than a canopy with a lower aspect ratio. Whether that means it has a larger span and a shorter chord depends on the size of the canopies; if the canopies are the same square footage, then the results are straightforward. The rate of descent is not dependent strictly on aspect ratio. Aspect ratio is one component that contributes to the lift-to-drag ratio of the canopy in a certain configuration (i.e. a certain angle of attack, a certain airfoil, and a certain airspeed). Rate of descent is just part of the airspeed for a canopy with a given airspeed - which in balanced flight should mean the thrust, weight, lift, and drag components are all balanced - and you have to figure out what those are based on jumper weight and the angle of attack of the canopy. Lots of interrelated stuff. Another difference between 9-cell canopies and 7-cell canopies is the thickness of the airfoil at various points. Perhaps an even larger difference (this I don't know because I have no way to know it for sure yet) is the differences in airfoils the various canopies use - I expect it varies between almost every model regardless of cell quantity. -=-=-=-=- Pull. Quote Share this post Link to post Share on other sites
skybytch 273 #4 January 2, 2006 QuoteDoes a 240 9 cell canopy take longer to deploy 240 seven cell or do they deploy about the same? That depends. Shaping will have an effect on opening speeds - an original Sabre or equivalent (ie rectangular zp nine cell) will generally open faster than a Sabre2 or equivalent (ie "tapered" or slightly elliptical zp nine cell); a Triathlon or equivalent (ie rectangular zp seven cell) will generally open faster than a Spectre or equivalent (ie "tapered" or slightly elliptical zp seven cell). The "tapered" seven and nine cells that I've jumped seem to open at about the same speed. Packing has an effect on opening speeds as well. On rectangular shaped canopies you'll likely want to roll the nose after flaking it (increases the time it takes for the nose to catch air, thus slowing the opening); on most "tapered" canopies you'll likely want to flake it then leave it hanging. Quote Share this post Link to post Share on other sites
riggerrob 643 #5 January 2, 2006 Does the 240 9 cell have the same span and chord as the 240 7 cell? >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Highly unlikely. (Unless they are obscure accuracy canopies) the number of cells usually defines the aspect ratio. Aspect ratio is the relationship (fraction) between wing span and wing chord. Span is measured from one side (end rib) of a canopy to the other (stabilizer). Some manufacturers measure span across the top skin (Para-Flite, PISA and pre-2001 Icarus) while other companies measure span across the bottom skin (i.e. Performance Designs). Chord is measured from the top leading edge - in a straight line - to the trailing edge. Most 7-cells have aspect ratios just over 2:1, while most 9-cells are in the 2.6:1 range [often shortened to "2.6"]. 7-cell: AR = 2.2 B = 109 chord = 10.45 span = 23 9-cell: AR = 2.6 B = 92.3 chord = 9.6 span = 25 This would be easier to explain with a diagram. Does that answer some of your questions about: span, chord and aspect ratio? Quote Share this post Link to post Share on other sites
riggerrob 643 #6 January 2, 2006 Deployment speed (inflation time) is determined by dozens of factors: area, suspended weight, airspeed when you toss your pilot chute, fabric type, age of fabric, size of nose openings, aspect ratio, trim, airfoil section, cross-ports, air-locks, bottom skin vents, brake line configuration, type of slider, generation?, etc. In the end, aspect ratio has only a minor affect on opening time. Quote Share this post Link to post Share on other sites
riggerrob 643 #7 January 2, 2006 Rate of descent is affected by: density altitude, wing-loading, fabric type, fabric age, line type, line trim, line age, type of pilot chute, type of slider, size of jumper, size of jump suit, etc. If your hypothetical 7-cell and 9-cell have similar fabric, etc., and the same forward speed, the 9-cell will have a slightly slower rate of descent. Quote Share this post Link to post Share on other sites
FrogNog 1 #8 January 2, 2006 QuoteChord is measured from the top leading edge - in a straight line - to the trailing edge. Actually, isn't the chord on a ram-air wing measured from where the leading edge would be if it weren't cut out to make the nose inlet, to the trailing edge (in a straight line)? (Obviously this doesn't apply to any fully-formed-nose canopies or canopies where the leading edge is not included in the inlet, but I believe both those cases together are still the minority of canopy designs.) -=-=-=-=- Pull. Quote Share this post Link to post Share on other sites
mark 107 #9 January 2, 2006 QuoteActually, isn't the chord on a ram-air wing measured from where the leading edge would be if it weren't cut out to make the nose inlet, to the trailing edge (in a straight line)? (Obviously this doesn't apply to any fully-formed-nose canopies or canopies where the leading edge is not included in the inlet, but I believe both those cases together are still the minority of canopy designs.) We're only talking about 1 or 2 significant digits for the aspect ratio, so I don't think it matters. Would be nice to know, though, if only for knowing. Mark Quote Share this post Link to post Share on other sites
JohnMitchell 16 #10 January 2, 2006 Quote Actually, isn't the chord on a ram-air wing measured from where the leading edge would be if it weren't cut out to make the nose inlet, to the trailing edge So wingspan times chord would not equal square feet for a canopy? Or maybe the stated size of a canopy includes the phantom nose! Makes me laugh to think I could be "paying for" part of the airfoil that's not really there. Quote Share this post Link to post Share on other sites
riggerrob 643 #11 January 2, 2006 Actually, isn't the chord on a ram-air wing measured from where the leading edge would be if it weren't cut out to make the nose inlet, to the trailing edge (in a straight line)? >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Hee! Hee! That all depends upon which manufacturer you quote. Different manufacturers use different methods for measuring chord. At least they agree on starting at the trailing edge, then some of them measure unsewn top skin fabric, some measure top skin fabric after it has been sewn, some measure in a straight line to the top leading edge reinforcing tape, some measure to an imaginary "stagnation point" and I suppose a few even measure chord along the bottom skin. Hah! Hah! Are we driving you crazy yet? The PIA standard measures chord from the trailing edges - in a straight line - to the top leading edge. Quote Share this post Link to post Share on other sites
FrogNog 1 #12 January 2, 2006 I realized right after I posted my question that I was refering to an (as in, "one single kind of") aerodynamic measurement that need have nothing to do with the numbers manufacturers report. And I have to admit that describing the chord of a wing with part of it missing has to be a little difficult. Does one describe the aerodynamic effective wing, or the actual sewn wing? Now, here's an interesting question: when a canopy does that "breathing" thing in turbulence, how much are the chord, span, and max chord thickness changing? -=-=-=-=- Pull. Quote Share this post Link to post Share on other sites
tso-d_chris 0 #13 January 2, 2006 QuoteIf a 240 9 cell canopy has a higher aspect ratio then a 240 seven cell with the same wing load, is the rate of decent faster in a 9 cell because of the difference in performance? Does the 240 9 cell have the same span and chord as the 240 7 cell? Does a 240 9 cell canopy take longer to deploy 240 seven cell or do they deploy about the same? Is there a difference in the way you pack them? PIA defines aspect ratio:QuoteAspect Ratio: Standard definition; Span2/area; which for a rectangular planform reduces to span/chord. On a rectangular canopy with no taper, this works out to span / chord. If a nine cell canopy has a higher aspect ratio than a seven cell canopy of the same size, it will have a different span and/or chord. All else being equal (usually not realistic), a higher aspect canopy will have a lower rate of descent than a lower aspect ratio canopy. Essentially, there is no difference in packing a nine cell canopy and a seven cell canopy, except that there is extra fabric and lines on a nine cell. For Great Deals on Gear Quote Share this post Link to post Share on other sites
srsand1960 0 #14 January 2, 2006 So, there will be different results in the formula depending on what the manufacturing company is and where they measure the Span? It doesn't matter how anyone else lives their life.... it matter how you live yours! Quote Share this post Link to post Share on other sites
srsand1960 0 #15 January 2, 2006 If so many factors are involved with canopy openings then how does one determine what kind of configuration is the best? It doesn't matter how anyone else lives their life.... it matter how you live yours! Quote Share this post Link to post Share on other sites
srsand1960 0 #16 January 2, 2006 That answers this question to where I understand it rob. If they are the same, just more cells, the rate of decent is a little slower on the higher cell. Therefore I am also concluding from this that I will be able to obtain a little more lift on the landing. What about the number of cross ports? Do they help lift by allowing equal air distribution? It doesn't matter how anyone else lives their life.... it matter how you live yours! Quote Share this post Link to post Share on other sites
srsand1960 0 #17 January 2, 2006 Well, Rob there is some of this that is going over my head. However, I will find out what the definitions are on the words that I'm not familiar are then hopefully the parts of the puzzle will solidify in my cranium It doesn't matter how anyone else lives their life.... it matter how you live yours! Quote Share this post Link to post Share on other sites
srsand1960 0 #18 January 2, 2006 This answers my question about the packing. I work with TSO/ISPF... I take it that tso-d is your session and that you are familiar with MVS It doesn't matter how anyone else lives their life.... it matter how you live yours! Quote Share this post Link to post Share on other sites
tso-d_chris 0 #19 January 2, 2006 QuoteThis answers my question about the packing. I work with TSO/ISPF... I take it that tso-d is your session and that you are familiar with MVS Actually, TSO-D refers to The Skydiving Outlet - Deland. I sell gear. For Great Deals on Gear Quote Share this post Link to post Share on other sites
srsand1960 0 #20 January 2, 2006 OH In my business it stands for Time Share Option for a Multiple Virtual Storage Interactive System Productivity Facility. Sorry... It doesn't matter how anyone else lives their life.... it matter how you live yours! Quote Share this post Link to post Share on other sites
