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

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

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. ;-)

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"

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. ;-)

wrote:

Fire away!

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

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:

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"

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"

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