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By Rick M
#79013
I just noticed on DbyD's latest video that he has some trailing edge flutter between the last two ribs. You can just make it out during each of his highest speed runs in the video.

The only video I've taken of myself flying revealed the same thing on my Sport 2. Whenever my airspeed got into the low 40's I could see the flutter. It was only in the one spot (between the last two ribs). I only saw it on one wing in my glider because that's the way the camera was pointing. I don't know if the other wing has the problem.

I was talking to my instructor today when I remembered this and mentioned it to him. He said it needs to be fixed ASAP. Flutter = Bad.

Dave - we need to chat with Rob about this. Mark (my instructor) mentioned tightening the battens a little to see what effect it has. He said one thing NOT to do is touch the thread running through the trailing edge of the sail.

Has anyone already solved this issue?
User avatar
By dievhart
#79023
Rick,
My lightspeed 4 (2001) is doing the same thing at the same place.....
I've noticed it is when the VG is on and the sprogs are a bit lower....
But there is just so much slack that it flutters:cuss: I see it get tighter with the VG off (sprogs tips go up and take out the extra bit that flaps)....
Just a few weeks back I was watching it close while flying fast at the Fort in my CG harness...so I set it up in the yard to take a closer look...see...
I know the preditor (and others) put an extra batten in there, but it seems there must be an adjustment somewhere to fix this???
Any other Lightspeed (NOT "S"), Sport 2 pilots have this issue...
Diev
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User avatar
By relate2
#79025
The only way I have seen trailing edge flutter taken out is with some of the tandems that fly at Stanwell, they insert a plastic tie in the eyelets where the baton bungee goes at the spot where the sail flutters and pinch the sail half and inch or so.

I once spoke to Steve Moyes about sail flutter and he said tightening up the batons using just the bungees doesn't do much to take out the flutter. You need to pinch the sail or even take it back to the factory and get them to pinch the sail and sew it in place.

I guess if you have a wing that did not have the eyelets to pinch you would have to have the sail sewn to take out the slack.
User avatar
By CHassan
#79034
AP gave me some advise that, to me was, counter intuitive until I thought about it. Loosen your tip wands. If you can adjust the tip do that, or take a little off the end. This makes the wand "stiffer", and causes the tip to pull more lateral on the trailing edge.
This was soon backed up by Steve P of WW telling me the same.

This will require me to cut my wands as I'm not seeing any other way to adjust them shorter, so i've not actually gotten around to do that yet.
User avatar
By Nibs
#79038
I have the same issue on my U2.... but only with the VG on. The more VG, the worse it is.

I called WW about this a while back and they sent me this:

============================================================

There are several factors that can cause flutter in the trailing edge at the tips.



1) A combination of loose leading edge sail tension (the tension on the sail anchor strap that attaches near the end of the rear leading edge) and overly tight tension carried by the tip wand will slacken the trailing edge, because the excess tension along the leading edge applied to the tip wand causes it to bend inwards and thus reduces the spanwise tension the wand puts on the sail. This can result from the sail anchor webbing strap stretching over time, from the adjustment on this strap having been loosened (on those gliders where the strap is adjustable), or from the wand adjustment being too tight. If the glider has an adjustable sail anchor strap, the strap should be tightened until, with the glider fully set up, the sail mount webbing is snug at VG loose and progressively tighter at higher VG settings. If the glider has a fixed length sail anchor, this adjustment can be obtained by shortening the length of the tip wand as necessary.



2) Tip battens adjusted too loose - if the four shortest battens at the tip are not tight enough there will be insufficient tension along the trailing edge. The shortest batten has a string on it and the next three have adjustable lever tips. With the glider completely set up, tighten the first three lever rib adjusters. Usually 3 to 5 turns (counter clockwise) on the shortest, 2 to 4 turns on the second shortest, and 1 to 3 turns on the third shortest will do the trick. On the shortest batten, adjust the string to where it requires a quite firm pull to install the second loop of string onto the batten tip.



3) Trailing edge string adjusted too loose or stretched (if the glider is so equipped – late model Sport 2’s, U2’s and T2’s no longer have the trailing edge string). To adjust this string, first de-tension all of the battens. Un-do the knot where the trailing edge string exits the jam cleat near the wing tip. After unwinding the string from the cleat, take a pen and mark where the string exits the cleat. With a pair of needle nose pliers, wind the string around the pliers several turns. (This is so you don't strip the coating off the string) Pull the string 7/8 inch and then re-cleat it. Re-wind the string around the cleat several turns as it was before and tie a new knot.



4) In severe cases, where the sail has been fluttering for some time, and the trailing edge hem has stretched or the sail resin has partially broken down, you may need to effect a takeup along the trailing edge hem itself. There are a few easy ways to do this without requiring that the sail be removed from the airframe for sail work.

a) You can put a twist in the first loop of the string on the shortest batten before engaging it on the batten tip, and then adjust the second loop to a very firm tension. This changes the angle with which the string pulls on the trailing edge in such a way as to apply more direct tension along the hem.

b) You can install a small zip tie through the two grommets to which this string attaches, and pull the grommets together, which will apply further tension directly on the trailing edge hem.





We have successfully removed some severe flutter (even at trim speed) from a number of Sports, U2s and T2s with these methods. The trick is catch the flutter early, because if you allow it to continue for a long time, the resin in the sail breaks down and the sail will require work to solve the problem. If none of the above adjustments are sufficient to remove the flutter, then the final fix is to have the trailing edge of the sail re-scalloped to correct the balance of tension between the sail body and trailing edge hem. This requires that the sail be removed from the airframe, and sent to us.
User avatar
By red
#79042
I do not have this problem, or a Sport 2, but I would not want to try a zip tie to "fix" this problem, as a first move. I *can* see using a small bungee cord in place of the zip tie, though, running between the sail grommets. The bungee should have enough tension to pull out the slack that allows the flutter, but then stretch enough to allow using the VG, without the VG stretching the sail even more than it is. One such bungee, on each side of the panel that flutters, might do the trick. A zip tie would not have any "give" to it, and using full VG might stretch the sail even more, then. If the bungees did NOT help, *then* I might want to try stronger methods.
relate2 wrote:The only way I have seen trailing edge flutter taken out is with some of the tandems that fly at Stanwell, they insert a plastic tie in the eyelets where the baton bungee goes at the spot where the sail flutters and pinch the sail half and inch or so.
I once spoke to Steve Moyes about sail flutter and he said tightening up the batons using just the bungees doesn't do much to take out the flutter. You need to pinch the sail or even take it back to the factory and get them to pinch the sail and sew it in place.
I guess if you have a wing that did not have the eyelets to pinch you would have to have the sail sewn to take out the slack.
User avatar
By Skyhighwoman
#79063
My Litesport Moyes is fluttering badly.

I think we are now discovering the downfall of the curve tip.
:cuss: :cuss: :cuss:
User avatar
By sg
#79089
Discovering? Ive been telling people curved tips suck for years :lol:

Ive NEVER had an issue with sag/flutter, turns, broken wands, and warped wands. Doesnt do anything for performance, just "looks sexy". :lol:

I love the super easy to pop in / pop out collapse-able tip rib on my stealth :mosh:

The real advantage to curved tips, is the shorter pack up length of the glider. Now THAT I really like. Lower tip inertia too, assuming you can really tell the difference.
User avatar
By AIRTHUG
#79097
I'm with SG... curved tips are like an ANTI-VG. Pull the VG to make the sail tighter so you can go faster and farther. Now we have tip wands that flex when you go faster and make the sail looser? WTF

I don't even like how they look, but maybe that's just me...

I learned to do wingovers on an Ultra-Sport, and it never flapped... now I have a U2 and when I really ball up and dive it flaps...

I will say I flew a T2C a couple weeks ago, and it wouldn't flap no matter how fast I went... but I don't have $8,000 for a new glider, and I don't do competitions, so I probably don't need all that performance anyways...
User avatar
By sg
#79110
A brand new T2C probably wont flap, but give it a few hours :wink:
My Stealth is 8+ years old, and wont flap in a ball up dive
User avatar
By Jason
#79117
mine don't flap, my glider was made in 1997, never had a problem with flutter and i don't fly slow
User avatar
By danG
#79143
My low-hour horizon flaps (less so with newer, probably stiffer, tip wands replaced under warrantee).
Grrr...

My many hundreds of hours Formula is smoothy-smooth!
User avatar
By saltoricco
#79146
Jason wrote:mine don't flap, my glider was made in 1997, never had a problem with flutter and i don't fly slow
That's because you're flying a Sensor. :P Bob says it is very possible to build round wing tip gliders with trailing edges that don't flutter. His Sensors have a 1/16" Dacron string that runs through the entire trailing edge, plus a sewn in Kevlar band. Course there is more to a straight trailing edge, like the amount of tension of the tip wand. Trailing edges don't have to flutter.

Holger
User avatar
By dievhart
#79216
One can see in my second photo with the VG off the sail goes up in the back (dive recovery system) then in the third photo with the VG full on the sail drops down and we get the flutter from that extra sail.....
My Lightspeed has always done it at high speeds, so I don't thinks it's a sail streching issue. Well actually maybe it is....
If we don't fly our gliders around with lots of VG on most of the time that sail is always being pushed up by our sprogs, well over hours and hours of flying like this = flutter when we actually put on lots of VG........:surrender:
Folks, I think I just found our issue...we don't fly around with enough VG on
(and who would on a brand new glider?) but it seems like this is whats going on.....
I checked for the adjustable sail tensioner on mt LS4 but mine is not adjustable so I'll be taping the tip of my wands and taking a hacksaw to it .125 at a time....
I'll have to take more pics when I'm done.
User avatar
By CHassan
#79218
dievhart wrote:..
If we don't fly our gliders around with lots of VG on most of the time that sail is always being pushed up by our sprogs, well over hours and hours of flying like this = flutter when we actually put on lots of VG........:surrender:
Folks, I think I just found our issue...we don't fly around with enough VG on
Not true. When in flight with little to no VG, your sail is farther from being held up by the sprog. Less tension = more billow = TE flying higher.
It is when you pull VG and the wing flattens out that the sail may be resting on the sprog. (With the Sport 2 I think this is the case, thus pitch pressure is maintained. Where a higher performance wing gets noticeably easier to pitch, the Sport 2 really doesn't lose much pitch pressure. My Opinion)

I don't remember if it was AP or Vrezh, I think one of them posted a video from the keel looking out over the trailing edge, you can see the effect the VG has on the sail!
User avatar
By dievhart
#79225
Ah yes, I remember AP's video of the twist/washout that was just from flying around.....
It still seems this would be fixed by keeping our VG on most of the time from when we get the gliders.....the built-in washout / twist in our wing (that the VG removes) is what causes the flutter....
If thats the case though how does the straight tips deal with this? Is it that our tip wands flex that much when we use the VG.....and stiffer (newer) wands is the answer...
I do need a backup pair so I could get some new (fiber or carbon?) and use my current ones as the backup pair....
I'm going to have to point a camera out there and play around too...
Diev
User avatar
By Windlord
#79227
Curved tips? Hmmmm! :crazy:
IMO, I prefer the ol' tried n' true design. :thumbsup:
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User avatar
By DBrose
#79229
I used zip ties around the battens in the gromet holes and it worked for my Eagle164 as mentioned ealier. I was also gunna say use a bunch of hair spray if that don't work. But my Fusion has a flutter....after I washed it, seemed to have gotten worse, my dirty glider didn't flutter...arg!
DB
User avatar
By Jason
#79230
so much for curved tops :ahh:
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