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Trailing edge flutter


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#1 bake

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Posted 06 September 2009 - 05:12 PM

My SLE has a flutter that starts at the shallowest portion of the V (closest to the leading edge) in the trailing edge at speed, from there the faster I fly it the more the flutter moves down the panel to the bottom of the V. This only happens on the left wing.

So far I have tried tightening up the bungees but the flutter persists, next may be to run a small line in the trailing edge to try and stop it (this used to work on hang gliders) Perhaps this is from being my first Rev and hitting the ground too many times stretching the sail?

How do you judge proper tension on the bungees? I see them as the only way to tune the sail?

Edited by bake, 06 September 2009 - 05:13 PM.

What could possibly go wrong?

#2 kitecowboy

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Posted 06 September 2009 - 05:20 PM

My SLE has a flutter that starts at the shallowest portion of the V (closest to the leading edge) in the trailing edge at speed, from there the faster I fly it the more the flutter moves down the panel to the bottom of the V. This only happens on the left wing.

So far I have tried tightening up the bungees but the flutter persists, next may be to run a small line in the trailing edge to try and stop it (this used to work on hang gliders) Perhaps this is from being my first Rev and hitting the ground too many times stretching the sail?

How do you judge proper tension on the bungees? I see them as the only way to tune the sail?


well I'm not sure but the tension problem may be in your bottom lines. if you dont keep them tight while moving forward the sail flutters (this is JBs favorite sound, I learned) try keeping tension on them and if you lose your forward drive you can adjust that with letting out top lines at handles.

if this is all wrong the corrections will soon follow. ;)
Cowboy, rocks in your pockets couldn't hurt.

#3 Kitelife

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Posted 06 September 2009 - 05:32 PM

Ya, based on the description, I'd say you need a bit more brake (longer top or shorter bottom lines).

Flutter when you go "all out" forward is normal, but it shouldn't happen during general controlled flight.

John Barresi

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#4 bake

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Posted 06 September 2009 - 06:32 PM

Ya, based on the description, I'd say you need a bit more brake (longer top or shorter bottom lines).

Flutter when you go "all out" forward is normal, but it shouldn't happen during general controlled flight.


Just the one side fluttering is what has me puzzled..... adding a little brake will be easy enough to try, I just assumed you could let those lines go slack in flight like my traction kites. So if my lines are all equal how much should I shorten the rear lines by to start?

Sure wish I could fly with some experienced Rev guys.

Edited by bake, 06 September 2009 - 06:33 PM.

What could possibly go wrong?

#5 Kitelife

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Posted 06 September 2009 - 06:47 PM

The bottom lines should *not* be slack, no hardly... The Rev flies best with tension on all four lines, favoring the lines for whichever way you want to fly.

Think of it in terms of cupping the sail, not sheeting it. ;)

Folks generally use an extension to lengthen their top lines by anywhere from 4"-9".

As for the one wing only issue, try a bit more brake overall, make sure your lines are even length, and let us know what it does then?

John Barresi

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#6 Watty

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Posted 06 September 2009 - 08:14 PM

Just the one side fluttering is what has me puzzled..... adding a little brake will be easy enough to try, I just assumed you could let those lines go slack in flight like my traction kites. So if my lines are all equal how much should I shorten the rear lines by to start?

Sure wish I could fly with some experienced Rev guys.



Bare in mind, that by shortening the bottom lines, we do not mean cutting them. Simply add pigtails to your handles (a length of line with a series of knots on it for adjustment) and pull the bottom lines in a couple of knots, or let the top ones out a couple of knots. I just want to make sure you don't go butchering a perfectly good line set because of a misunderstanding.

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#7 big bri

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Posted 06 September 2009 - 10:53 PM

Hands moved up or down the Handles can do the flutter thing[usually to high on handles].Try flying and move your hands to extremes and see if it stops or gets worse.That should then tell ya what break to add or take away when adding the Pig Tails[Leaders].

Great point Watty.We explained[Badly] shortening lines once to someone and he did just chop them shorter.Our fault for a bad explination,but ther was also what we call,The Paul Factor,going on.

BRIAN...

#8 bake

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Posted 07 September 2009 - 07:27 PM

Great point Watty.


ditto, possibly I wouldn't have done the obvious
What could possibly go wrong?

#9 JeffD

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Posted 08 September 2009 - 04:40 AM

It seemed counter-intuitive but I followed the advice on keeping strong break even in the lowest winds and..............it worked!

The verticle dive check for flutter, add break to loose it, really illustrated the break idea for me. Over a bit of time I've been increasing and its helped increase control.

It also increases feedback from the kite and that is always good.

#10 Havin'aBlast!

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Posted 23 March 2012 - 11:55 AM

Was looking around before I started a new thread, and I know that re-starting an old thread isn't always the best thing to do but my thoughts seemed to fit quite well, here.

I have a Blast - a little abused as it was my first Rev and I went through four center leading edge spars quite early on. I have no doubt that the sail is not as it was when new.

Since starting to fly again, I've noticed the Blast is really noisy - a bit farty, if you like. This evening I was flying on a hill in really light winds and the flutter from the trailing edge was very noticeable and came on with pretty much any forward movement. I could see it loose from the ground.

I am pretty confident that it's not line setup that's causing it - I've got a pretty good feel for how it flies and have been adjusting my grip and line lengths to a point where it feels right, I (and it) will only fly (powered, rather than floating) with appropriate tension on all four strings. With the Blast, it feels quite hard to get it wrong, if you know what I mean.

Here's what's on my mind that I'd like to run past folk here:
  • leading edge bungee tension - fairly high
  • vertical bottom bungees tension - fairly high
  • trailing edge - flappy
On the Blast, are there bungee tensions on certain spars that affect the trailing edge? For example, I don't know, loosing the inner verticals and keeping the outers tight?

If not, can you reinforce or pleat a trailing edge to take up the slack in the fabric, assuming that my power lust has stretched it? I'm not going to get a new sail for it if I can tune/adjust the frame/bungees and/or make minor modifications to the sail.

Very interested to hear anyone's comments, or to flag up topics/posts already on here that I may have missed.

Regards,
Matt.

[Edit - posted too soon :blushing: - the following thread (Making less noise) actually already contains more appropriate discussion - recutting sail, leech lines and catenary - nevertheless, any comments on the aforementioned topics or any fresh advice?]




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