If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
Re-curving mylar on a glider
Same thing happened to a Ventus B a while back on the
elevator. Since I fly a Ventus B and I fly it in AZ I have decided not to use external seals on the elevator at all. It is internally sealed. My wings and rudder are internally sealed and both sides of the rudder have mylar however only the bottom of my wings, flaps and ailerons, are externally sealed. I have found that I do not have to replace the bottom seals very often +5 years, but the tops I would have to do every year in the AZ sun and that is flying every weekend form March through Oct Friday thru Sunday putting it away for the weekdays At 14:54 16 October 2006, Bb wrote: IThere have been several accidents resulting from seals coming loose, and causing a 'spoiler' effect on the control surface. One is here http://www.ntsb.gov/ntsb/brief.asp?e...07X04237&key=1 I think there was at least one Grob crash in Germany. Some manuals specifically state there has to be tape on the elevator. So, yes, this is a serious issue. Since hearing of the first crash, 'check condition of mylar and hold-down tape' has been part of my critical assembly check. John Cochrane BB |
#12
|
|||
|
|||
Re-curving mylar on a glider
Control surface seal security is very much overlooked both by pilots and A&Ps doing daily and annual inspections. Safety tape, is the tape along the leading edge of the mylar, is generally good for 2-4 years, depending on the climate and storage of the glider. The tape may look good, i.e. no part of it is lifting off the surface, but when you start to remove it you see that the adhesive has lost its gripping power, and the tape pulls off quite easily, and is brittle. If any section of the safety tape has started to lift off it is time to replace all the safety tapes. Use the stuff sold by our glider supply dealers, it is well proven and has a better than average gripping power. Anything to do with control surfaces is not the place to cut corners on materials. Don't buy your safety tape at Harbour Freight!! Mylars last a bit longer but their life depends on storage conditions also. They can get very brittle, and over time the adhesive looses its holding power. If you replace the safety tape on a regular basis this presents an opportunity to carefully inspect the mylars. An old, brittle mylar will likely break if you try to re-curve it. This stuff is not cheap to replace, but neither is repairing your glider because of an accident due to loss of control surface effectiveness. Most A&P do not understand the critical nature of control surface seals, especially if they do not look at a lot of gliders. Power planes do not use this technology and so when they see these seals they just avoid them for fear of getting into something they know nothing about. Robert Mudd A&P/ I.A. Moriarty, New Mexico |
#13
|
|||
|
|||
Re-curving mylar on a glider
BB wrote:
IThere have been several accidents resulting from seals coming loose, and causing a "spoiler" effect on the control surface. One is here http://www.ntsb.gov/ntsb/brief.asp?e...07X04237&key=1 I think there was at least one Grob crash in Germany. Some manuals specifically state there has to be tape on the elevator. So, yes, this is a serious issue. Since hearing of the first crash, "check condition of mylar and hold-down tape" has been part of my critical assembly check. John Cochrane BB Finally - one undisputable advantage of the all flying tail on my Cirrus. ;-) |
#14
|
|||
|
|||
Re-curving mylar on a glider
Eric is getting soundly hammered for trying to extend the life of his
mylar seals, so I'll add some fuel to the fire. My ASW 24 mylar seals will be 15 years old in a few months. Yeah, they don't quite touch the aileron control surfaces when they're in full positive deflection, but otherwise they look fine (wings and tail). And there's an internal seal underneath so I'm not worried about leakage. I did replace the safety tape this year and that was overdue. I had noticed a few edges lifting up last year (it's on my checklist, too, see below) but simply taped them down until I could replace it. The adhesive on the safety tape was, indeed, powdery--at least on the upper surfaces, but when I tugged on the mylar, it seemed fine. Perhaps because the mylar is thicker (less UV transmitted) and is itself under a layer of safety tape? The adhesive under the safety tape on the underside of the wing was more difficult to remove than the upper-surface stuff. I'm very safety conscious. And I have direct experience with seals lifting up: my old LS-3 began pitching down suddenly one year at the U.S. nationals when carrying water ballast because a few inches of the cloth sealing tape on the elevator upper surface was lifting up about 1/2 cm in the airflow. It was difficult to find at first because it looked fine on the ground. That said, the downside of replacing mylar seems to be that, for some reason, you'll never get it stuck as well as the factories do it. Or so I hear from some of the experts. There have been numerous threads on this subject on RAS in the past and I'm not surprised that owners have to replace their seals every few years once they've ripped the original ones off. I've also heard some horror stories of guys who replaced the mylar at some expense and trouble and then had it lift off within a year. I'm careful with mine: the ship is never tied out and it lives in the trailer with control locks that keep the surfaces in the neutral position. And so far it still looks good, just like Eric's. So I'll probably watch it and replace only when it's given me a reason to. Fire away! Chip Bearden ASW 24 "JB" |
#15
|
|||
|
|||
Re-curving mylar on a glider
Bruce,
Ditto on my LS1-d. However, this summer I did have the mylar on the lower surface of one wing give some problem. The 'safety' tape kept the mylar from leaving the ship, but the mylar somehow broke away from the double-sided tape and it rotated 90 degrees, more or less and was perpendicular to the wing. Of course, this happened in flight. So, I was flying around with a 30 mm high spoiler in front of the aileron. The length of the 'spoiler' must have been five feet (1.5 meters). This started on the first leg of a 300 km FAI triangle. Since the airplane flew fine, except for some 'into the draggy wing' stick I had to hold during the flight, everything went fine. So, how did the mylar rotate 'up' and create the spoiler, even though the leading edge of the mylar was taped to wing? Why didn't the airflow keep the mylar pushed down against the wing? If you know, please tell me! I guess some airfoils are more susceptible to problems with mylar than others. Ray Lovinggood Carrboro, North Carolina, USA LS1-d At 16:12 16 October 2006, Bruce Greef wrote: BB wrote: IThere have been several accidents resulting from seals coming loose, and causing a 'spoiler' effect on the control surface. One is here http://www.ntsb.gov/ntsb/brief.asp?e...07X04237&key=1 I think there was at least one Grob crash in Germany. Some manuals specifically state there has to be tape on the elevator. So, yes, this is a serious issue. Since hearing of the first crash, 'check condition of mylar and hold-down tape' has been part of my critical assembly check. John Cochrane BB Finally - one undisputable advantage of the all flying tail on my Cirrus. ;-) |
#16
|
|||
|
|||
Re-curving mylar on a glider
|
#17
|
|||
|
|||
Re-curving mylar on a glider
C'mon guys, break loose with the $120 and go buy some new mylar, pink
tape, and safety tape. Why hang your neck out for tape? Clean out all that dust and crud while you have the old tape off. You'll feel better every time you fly. It's cheap insurance! Snoop wrote: |
#18
|
|||
|
|||
Re-curving mylar on a glider
No fire, a cheer. You've pointed up an important issue. Many of us have
seen replacement seals come off in a few months, even when done professionally by reputable shops. So, we keep the factory seals on as long as possible, and sometimes just a bit longer. Really, life would be so much better if we could trust that replacement mylar would stick. What are the factories doing the first time around that we aren't doing for replacements? Is it just a better job of sanding/cleaining the surfaces? John Cochrane BB I wish I knew, John. One reputable repair shop with excellent relationships with German manufacturers expressed amazement and, to be fair, initial concern that my seals were so old. But when I described my situation, he said, well, if they're still attached well, replace the safety tape and just keep an eye on them because you'll never get new seals to adhere as well as the factory does. He said the performance of the Mylar itself (i.e., curvature or tension) wasn't really a question; the issue was the adhesive. I've seen several postings that describe sanding/cleaning the surface of both the wing and the Mylar as well as how to apply the adhesive and the seals, the proper temperature and pressure to use, etc. But when more than one expert says the factory stuff is much better, I, too, have to ask what it is that they are doing different. What's the secret formula??? In the meantime, I acknowledge some risk in leaving the old seals in place. But I find it difficult to prove (as opposed to intuitively "knowing") that replacing the seals makes it any less likely that I will have a failure. Chip Bearden ASW 24 "JB" |
#19
|
|||
|
|||
Re-curving mylar on a glider
Does anyone have any actual knowledge (as opposed to conjecture) of
whether the incidents involving Mylar seal failures have occurred for factory vs. replacement seals? I'm genuinely eager to do the right thing. But having been warned by some experts that the factory seals adhere much better, I'm reluctant to trade one unknown for another. Any real data out there? Chip Bearden ASW 24 "JB" |
#20
|
|||
|
|||
Re-curving mylar on a glider
Ray Lovinggood wrote:
Bruce, Ditto on my LS1-d. However, this summer I did have the mylar on the lower surface of one wing give some problem. The 'safety' tape kept the mylar from leaving the ship, but the mylar somehow broke away from the double-sided tape and it rotated 90 degrees, more or less and was perpendicular to the wing. Of course, this happened in flight. So, I was flying around with a 30 mm high spoiler in front of the aileron. The length of the 'spoiler' must have been five feet (1.5 meters). This started on the first leg of a 300 km FAI triangle. Since the airplane flew fine, except for some 'into the draggy wing' stick I had to hold during the flight, everything went fine. So, how did the mylar rotate 'up' and create the spoiler, even though the leading edge of the mylar was taped to wing? Why didn't the airflow keep the mylar pushed down against the wing? If you know, please tell me! I guess some airfoils are more susceptible to problems with mylar than others. Ray Lovinggood Carrboro, North Carolina, USA LS1-d At 16:12 16 October 2006, Bruce Greef wrote: BB wrote: IThere have been several accidents resulting from seals coming loose, and causing a 'spoiler' effect on the control surface. One is here http://www.ntsb.gov/ntsb/brief.asp?e...07X04237&key=1 I think there was at least one Grob crash in Germany. Some manuals specifically state there has to be tape on the elevator. So, yes, this is a serious issue. Since hearing of the first crash, 'check condition of mylar and hold-down tape' has been part of my critical assembly check. John Cochrane BB Finally - one undisputable advantage of the all flying tail on my Cirrus. ;-) A lot of us use 3M adhesive remover to get the sticky up after removing the mylar and transfer tape. Don't apply new transfer tape until you clean the 3M adhesive remover off or the new tape will come loose in a short time. I like to clean up with Acyli-Clean from Dupont on the surface prior to putting the transfer tape down. Available at auto paint stores. A friend bailed out of his Ventus A some years back because the mylar came loose in front of the elevator. Don't cut corners here. WM |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Glider transponder on? | Sam Spade | Instrument Flight Rules | 5 | September 15th 06 05:45 AM |
Aerodynamics of carrying water | Gene Whitt | Soaring | 54 | October 19th 05 07:24 PM |
Bad publicity | David Starer | Soaring | 18 | March 8th 04 03:57 PM |
"I Want To FLY!"-(Youth) My store to raise funds for flying lessons | Curtl33 | General Aviation | 7 | January 9th 04 11:35 PM |
I wish I'd never got into this... | Kevin Neave | Soaring | 32 | September 19th 03 12:18 PM |