Date: Sun, 25 Feb 1996 11:02:26 -1000 From: pconnor@alkali.otago.ac.nz (Paul Connor) Message-Id: Organization: University of Otago Subject: Flexi noise OK A simple Question. When I fly my 6' flexi, I can hear it whistle through the air. What makes the noise the kite or the strings? Thanks for any thoughts on the matter Paul Connor pconnor@newton.otago.ac.nz Dunedin, New Zealand. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 25 Feb 1996 21:08:03 -1000 From: daveculp@bdt.com (Dave Culp) Message-Id: Organization: Beckemeyer Development, Oakland CA Subject: Re: Flexi noise In article , pconnor@alkali.otago.ac.nz (Paul Connor) wrote: > OK A simple Question. > > When I fly my 6' flexi, I can hear it whistle through the air. > > What makes the noise the kite or the strings? > > Thanks for any thoughts on the matter It's the flying lines, without question. I've worked for several years to minimize this, as it robs quite a lot of power, and makes these fine kites *much* less efficient. It's particularly bad on Flexifoils, as they're so fast. I've tried a couple of things: First, try smoother line (duh). Second, you might try twisted, rather than woven line, if you can find it. It's horrible for other reasons, but it has less drag--has to do with Karmen vortex shedding (You can look it up). Third, I've tried adding bits of thread along the flying line, at about 4-6" intervals. This adds drag, of course, but it attenuates the vibration in the line which couses the noise you hear, and the sum total seems less draggy (hard to test, but *I'm* convinced). Fourth, you *could* try some way of streamlining the flying lines, via adding a sheath for the line to run inside. You could profitably triple the line's diameter, if you use a good streamline shape, and still lessen total drag. This last is kind of esoteric, since the sheath must be dead light (foam?), very smooth, and you still have to have some way to wind the line back in. Anybody want to comment? -- ################################################################### Dave Culp Speedsailing | e-mail to: daveculp@bdt.com 312 Flaming Oak Drive | Pleasant Hill, CA 94596 | http://www.bdt.com:80/home/daveculp/speedsail.html #################################################################### = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 25 Feb 1996 20:44:42 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Flexi noise pconnor@alkali.otago.ac.nz (Paul Connor) writes: >When I fly my 6' flexi, I can hear it whistle through the air. >What makes the noise the kite or the strings? In life, there are always two choices. There is a good choice, which leads to peace, prosperity and happyness and there is an evil choice that leads to hatred and damnation. This is the way also with kites. You must choose your kite, your line, your wind and location. If you choose well, my son, the gods will look down on you with pleaseure and make music with your lines. If you choose ill, then they will make your kite buzz and rasp as it renders the air asunder. You have chosen wisely. Soon, you may find AoxomoxoA. I wish you well. You owe the Kite Oracle a musical chainsaw. -- 5) Take heed not of the false prophets that shall be sent amongst thy people. Frank Kenisky and Mick Parsons are known by the people but beware that others lie is wait to steal in the night the friendship and community that is rightfuly thine. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 29 Feb 1996 16:48:03 -1000 From: andreas.hardtung@recklinghausen.netsurf.de (Andreas Hardtung) Message-Id: <4h5ooq$17p@ra.ins.de> Organization: Drachenzauber Subject: Re: Flexi noise pconnor@alkali.otago.ac.nz (Paul Connor) wrote: >What makes the noise the kite or the strings? Hi, the sound comes from the line. And it gives you importand informatio: f= 1/2L * sqrt(F/(rho A)) with: f frequency, L linelenght, F force = linepull rho density of line, A Area = pi*diameter with a litle experience you can hear when your line will snap. Andreas = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Fri, 1 Mar 1996 15:47:06 -1000 From: windwiz@west.net (Dan Rubesh) Message-Id: <4h89aq$bii@acme.sb.west.net> Organization: Wind Wizard Subject: Re: Flexi noise In article <4h5ooq$17p@ra.ins.de>, Andreas Hardtung wrote: [deletia] >Hi, >the sound comes from the line. > >And it gives you importand informatio: > >f= 1/2L * sqrt(F/(rho A)) > >with: >f frequency, L linelenght, F force = linepull >rho density of line, A Area = pi*diameter ^^^^^^^^^^^^^^^^^^^^^ ??? Area (cross sectional) = pi*r^2 pi*diameter yields circumference.. Has anyone come up with tables for the rho value?? >with a litle experience you can hear when your line will >snap. > Andreas -- Dan Rubesh GO Wind Wizard windwiz@west.net FLY A P.O. Box 5747 http://www.west.net/~windwiz SPORT KITE San Buenaventura, CA 93005 (805) 659-5769 (voice & fax) T.B.N.K. Member: AKA & KTA = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Fri, 1 Mar 1996 12:55:51 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Flexi noise andreas.hardtung@recklinghausen.netsurf.de writes: >the sound comes from the line. > >And it gives you importand informatio: > >f= 1/2L * sqrt(F/(rho A)) > >with: >f frequency, L linelenght, F force = linepull >rho density of line, A Area = pi*diameter I love it when people give such *good* answers. Independant of windspeed eh? Does this mean that the vibrations will be symetrical, even in a bowed line (which is bowed asymetrically due to different apparent windspeeds) How best do we damp such oscillations? We can add any amount of drag to any part of the line for damping. How do we work out the minimum amount of drag required to "adequately" damp the line? How do we work out where to place the damping? This isn't idle curiosity... Andrew -- NO CARRIER = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 4 Mar 1996 15:48:10 -1000 From: andreas.hardtung@recklinghausen.netsurf.de (Andreas Hardtung) Message-Id: <4hg6pr$ep1@ra.ins.de> Organization: Drachenzauber Subject: Re: Flexi noise andrew@tug.com (Andrew Beattie) wrote: >andreas.hardtung@recklinghausen.netsurf.de writes: >>the sound comes from the line. >> >>And it gives you importand informatio: >> >>f= 1/2L * sqrt(F/(rho A)) >> >>with: >>f frequency, L linelenght, F force = linepull >>rho density of line, A Area = pi*diameter >I love it when people give such *good* answers. >Independant of windspeed eh? Does this mean that the vibrations will be >symetrical, even in a bowed line (which is bowed asymetrically due to >different apparent windspeeds) Oh no. Not independent of the windspeed. Pull is dependend on windspeed. And pull is nearly constant on the line (not direction but the amount). Only lineweight decreases pull >From kite to ancor - and thats not mutch difference when the line is whisteling. >How best do we damp such oscillations? We can add any amount of drag >to any part of the line for damping. How do we work out the minimum >amount of drag required to "adequately" damp the line? How do we >work out where to place the damping? Hmm. You want to reduce drag - so for me adding drag sounds paradox. Adding a (or more) weight(s) could be the way to go. A weight in the midle of the line could split the line in 2 sctions. That would mean that L is now linelength/2 and f is doubled. Chances are good to reduce amplitude - and drag. >This isn't idle curiosity... But i never tryed it Andreas = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 4 Mar 1996 15:48:09 -1000 From: andreas.hardtung@recklinghausen.netsurf.de (Andreas Hardtung) Message-Id: <4hg6pp$ep1@ra.ins.de> Organization: Drachenzauber Subject: Re: Flexi noise windwiz@west.net (Dan Rubesh) wrote: >In article <4h5ooq$17p@ra.ins.de>, >Andreas Hardtung wrote: >>rho density of line, A Area = pi*diameter > ^^^^^^^^^^^^^^^^^^^^^ ??? >Area (cross sectional) = pi*r^2 >pi*diameter yields circumference.. Uhh, sorry you are right. >Has anyone come up with tables for the rho value?? No, i have not. But rho in g/cm^2 for the usual materials is about 1. spectra about 0.9 polyester about 1.0 - 1.2 kevlar a litle more. Andreas = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 5 Mar 1996 21:32:01 -1000 From: daveculp@bdt.com (Dave Culp) Message-Id: Organization: Beckemeyer Development, Oakland CA Subject: Re: Flexi noise > >How best do we damp such oscillations? We can add any amount of drag > >to any part of the line for damping. How do we work out the minimum > >amount of drag required to "adequately" damp the line? How do we > >work out where to place the damping? > > Hmm. You want to reduce drag - so for me adding drag sounds > paradox. Adding a (or more) weight(s) could be the way to > go. > > A weight in the midle of the line could split the line in 2 > sctions. That would mean that L is now linelength/2 and f is > doubled. Chances are good to reduce amplitude - and drag. > > >This isn't idle curiosity... > > But i never tryed it Andreas, etcetera, *Please* expand on this. My news server has messed up, and I just got this thread today. I've spent *hours* (days, months) on this issue, and am becomming desperate for answers. The issue relates to increasing L/D in kitesailing systems. This will significantly increase boatspeed, buggyspeed, and efficiency when sailing to windward; a critical course. Rather than adding weights, I've been working with adding bits of string, thread, mylar, etc., at intervals along the line. My intent is to damp the ossicillations, shortening your L value. I've tried intervals as short as 1" (*lots* of bits of thread!) Of course, there's a trade-off, adding friction drag to reduce vibration drag. Can you think of a way to quantify this? Any seat-of-the-pants guesses? Suggestions? -- ################################################################### Dave Culp Speedsailing | e-mail to: daveculp@bdt.com 312 Flaming Oak Drive | Pleasant Hill, CA 94596 | http://www.bdt.com:80/home/daveculp/speedsail.html #################################################################### = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 6 Mar 1996 18:52:15 -1000 From: daveculp@bdt.com (Dave Culp) Message-Id: Organization: Beckemeyer Development, Oakland CA Subject: Re: Flexi noise >Hi, >the sound comes from the line. > >And it gives you importand informatio: > >f= 1/2L * sqrt(F/(rho A)) > >with: >f frequency, L linelenght, F force = linepull >rho density of line, A Area = pi*diameter ^^^^^^^^^^^^^^^^^^^^^ ??? Area (cross sectional) = pi*r^2 A couple of questions: 1) Will this formula truly hold for kitelines, whose length/diameter ratios are extremely large, or was it formulated for shorter (relatively) structures? I'm wondering if the effective length is something shorter than the entire line length. I'd suspect that the line oscillates about several (many?) nodes along the line's length. 2) Does this take into account the *roughness* of the flying line? I know steel is relatively very smooth, and that the Spectra line I fly is much rougher than the Spectra line Andrew flys. Surely this has some effect? 3) How can we determine the actual drag caused by the kitelines? (and, of course it's corrallary, how can we minimize this?) Richard Synergy's excellent web site on high altitude kiting alludes to a formula for line drag for steel line, but I can't find the actual formula, nor do I know how to modify it for woven Spectra lines. Thanks! -- ################################################################### Dave Culp Speedsailing | e-mail to: daveculp@bdt.com 312 Flaming Oak Drive | Pleasant Hill, CA 94596 | http://www.bdt.com:80/home/daveculp/speedsail.html #################################################################### = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 7 Mar 1996 15:40:59 -1000 From: andreas.hardtung@recklinghausen.netsurf.de (Andreas Hardtung) Message-Id: <4ho3h6$428@ra.ins.de> Organization: Drachenzauber Subject: Re: Flexi noise Hello Dave, missed your articel in news but got it by mail: (rho * A) is the same as weight/lenght - so you can put your line on a balance and devide by the length to get the correct value and avoid my messed up formular for A. (pi*r^2 or pi*d^2/4 is correct) > A couple of questions: > > 1) Will this formula truly hold for kitelines, whose length/diameter > ratios are extremely large, or was it formulated for shorter (relatively) > structures? I'm wondering if the effective length is something shorter > than the entire line length. I'd suspect that the line oscillates about > several (many?) nodes along the line's length. The formular should be universal. I KNOW it is correct for guitars and other instruments. Yes, it's very possible that ther are more than one nods. Let's calculate: a very normal single liner. These are conditions i know i can hear the line. 0.5/100(m)*sqrt(500(Newton)/(1(g/cm^3)*pi*0.0005(m)^2)=F(Hz) 0.005(1/m)*sqrt(500(kg*m/s^2)/(0.001(kg)/(0.000001(m^3)*3.14*0..00000025(m^2))) 0.005(1/m)*sqrt(500*0.000001(kg*m*m^3)/(0.001*3.14*0.00000025(kg*m^2*s^2))) 0.005(1/m)*sqrt(0.0005(kg*m^4)/(7.85e-10(kg*m^2*s^2))) 0.005(1/m)*sqrt(636942.6752(m^2/s^2)) 0.005*789.09(1/s) 3.99 Hz :-( Bad. 4Hz is mutch to low to hear it. There must be more nods! > 2) Does this take into account the *roughness* of the flying line? I know > steel is relatively very smooth, and that the Spectra line I fly is much > rougher than the Spectra line Andrew flys. Surely this has some effect? I GUESS there is a effect. Not in frequency but in amplitude. > 3) How can we determine the actual drag caused by the kitelines? (and, of > course it's corrallary, how can we minimize this?) Richard Synergy's > excellent web site on high altitude kiting alludes to a formula for line > drag for steel line, but I can't find the actual formula, nor do I know > how to modify it for woven Spectra lines. Yes, i saw the site and could not find the formular too. I guess he wants to sell his book. (It's rare in germany :-( ) (By the way - i would not set to mutch hope in his formular - look at his assumptions) Some time ago i tried to calculate drag of kitelines (singel liners) and wrote a litle program. But sound was not included. If i can find and translate it, i will post a litle summary here. Line-diameter and -surface are the parameters i dealed with. Noting unexpected at all. > Thanks! Please excuse my english. Andreas --- May the wind be with you --- ---Mvge der Wind mit Dir sein--- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =