460 0 #1 October 20, 2004 I read in Scientific American a few months ago about the effect of bumps on the leading edge of wings. It turns out that whales have evolved fins this way to reduce drag, increase lift, and dramatically increase the performance envelope available with a wing section. A bumpy leading edge can create rotating vortices that cause unusual effects that can be exploited. This concept has created a furor in the aerodynamics community. I believe this should be a long term research item for canopy design; it may or may not be feasible on a parachute but it is nevertheless interesting to contemplate. Quoting some of the results: The sleek flipper performance was similar to a typical airplane wing. But the tubercle flipper exhibited nearly 8 percent better lift properties, and withstood stall at a 40 percent steeper wind angle. The team was particularly surprised to discover that the flipper with tubercles produced as much as 32 percent lower drag than the sleek flipper. http://www.ascribe.org/cgi-bin/spew4th.pl?ascribeid=20040511.071106&time=07%2026%20PDT&year=2004&public=1Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174 Share this post Link to post Share on other sites
peterk 0 #2 October 20, 2004 I think this is an interesting concept. Golf balls have dimples to encourage air to not separate as it curves around. However, I don't think it would help to dimple a wing such as a canopy... There are several other ways to encourage flowing air to follow the curvature of the wing, and postpone airflow separation (stalling)- vortice generators, laminar flow, etc... Most of my limited experience is outside of the ~15mph airspeed, non-rigid nature, and shape of BASE canopies... I was also thinking that small pieces of yarn taped to the inside, top, and bottom of canopies can easily demonstrate airflow patterns, especially near stall, and can be videotaped with the small bullet cam setups. Thin camera wires and big balls could rollover from a legal bridge, in daylight, and get some potentially valuable research video data... I wonder what would be the best way, or if it would be advantageous, to disrupt the smooth airflow surrounding and within a canopy. I also think some kind of cross braces could smooth the marshmallow factor inherent to 7-cells, where the lift vectors of a cell would be used primarily upwards, instead of the wasteful arch that we see with bulbous 7-cell BASE canopies... I don't know, anyone stay at a Holiday Inn Express recently?--------------- Peter BASE - The Ultimate Victimless Crime Share this post Link to post Share on other sites
TomAiello 26 #3 October 21, 2004 Perhaps not the canopy, but what about the leading edge of a wingsuit?-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Share this post Link to post Share on other sites
Erroll 80 #4 October 21, 2004 QuoteI was also thinking that small pieces of yarn taped to the inside, top, and bottom of canopies can easily demonstrate airflow patterns.....? This thread may be of some interest. Share this post Link to post Share on other sites
460 0 #5 October 21, 2004 The bumps are at the leading edge of the fin, not on the top or bottom skin of the canopy. They are not like tachengerts, etc., to create turbulent flow. Whales have evolved a semi-regular series of bumps on the front of their fin wing. The front is where most of the drag originates and can the most crucial part of the wing design. Rotating vortices are setup on the leading edge of the whale wing in the vicinity of the bumps.Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174 Share this post Link to post Share on other sites
nicknitro71 0 #6 October 21, 2004 I've read the article when it came out. Intersting findings. To summirise the results below 8.5 deg (alpha) the lift curve of the smooth vs. scalloped edge is statistically unchanged. However at higher angles the lift produced by the scalloped wing is much higher. From 10.3They later mentioned that this type of leading edge is comparable to vortex generators on aircraft wings. As for canopies if you look at the leading edge you see that is more scalloped than smooth due to the how the cells are sewn. As for WS I think the front deflectors like those found on the S3 come pretty close to this princliple.Memento Audere Semper 903 Share this post Link to post Share on other sites
base311 0 #7 October 21, 2004 I suppose this is the same article?? http://www.sciencenews.org/articles/20040904/bob9.asp I guess I have to wonder if it will make a difference that water is an incompressible fluid and air is a compressible fluid. Either way, many things aero and hydrodynamic have been copied from water-going creatures... There's an always been an interesting debate over whether to wax or not to wax a competition sailboat hull. Perhaps the same forces are at work here. http://www.thebeachcats.com/OnTheWire/www.catsail.com/archives/v3-i2/feature4.htm Anyway, parachutes operate in an aerodynamic realm that is hard to quantify... same for sails, kites and any low-speed, deformable wing. Interesting stuff. Gardner Share this post Link to post Share on other sites
