Re-curving mylar on a glider

Bob:

Are you doing the reprofiling yourself or having it done?

Ray Warshaw
1LK

Bob Fidler wrote:
After 12 years the adhesive tape used to hold the seal in place has
deteriorated to the point that your original seal installation may be
unsafe. I've seen approx. 10 years seal installations where the adhesive is
about to release the seal. A small tug on the seal itself and the seal may
slip away from the adhesive. A lost seal inflight is something we all must
avoid at all cost. Control surfaces can stop working after a total or
partial separation.

I think 7-8 years is max any seal installation should be trusted because of
the potential loss of adhesion.
Also,the seal itself has deteriated from UV ( why it has lost the heat
induced curvature) and although is safe with regard to its physical
intregrity, new ones would look a whole lot nicer and a new seal with new
adhesive, a lot safer.

I think seal installations on gliders can be potentially the weakest link in
our sport. A failed seal can kill you and we should all be aware of time
limiations.

This winter I am reprofiling my wings and quess what, my seals will be
replaced after 5 years.


bob fidler
"Eric Greenwell" wrote in message
news:JfBYg.3919$5v5.3761@trndny08...
My top surface mylar seems to have lost some of it's curvature, because it
doesn't quite touch the aileron and flaps when they are in positive
positions. Does anyone know a way to put the curve back into the mylar
without removing it? It's so well adhered and smoothly installed, I'd like
to leave it on if at all possible, but I think it may be degrading my
climb while thermalling. The mylar is almost 12 years old.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Bob Fidler wrote:
After 12 years the adhesive tape used to hold the seal in place has
deteriorated to the point that your original seal installation may be
unsafe. I've seen approx. 10 years seal installations where the adhesive is
about to release the seal. A small tug on the seal itself and the seal may
slip away from the adhesive. A lost seal inflight is something we all must
avoid at all cost. Control surfaces can stop working after a total or
partial separation.

Inspecting the seal fairing tape (leading edge of seal) before every
flight and replacing it once a year goes a long way towards keeping
seals safe. Agree though that the seal adhesive is life limited,
particularly in Arizona where it dries up.

I know of no way to restore the seal curvature but I did learn along
time ago not to tie the glider out with the elevator up as the seal
takes a set.

Andy

Bob Fidler wrote:
A lost seal inflight is something we all must
avoid at all cost. Control surfaces can stop working after a total or
partial separation.

Bob, I have heard this before, but I dont understand where the problem
would be (Other than the leading edge of the seal lifting ahead of the
control surface).Didnt most of these ships come from the factory
without seals, I know mine did.I have read stories on the Yahoo user
groups for the ASW20 about seals departing the plane inflight and other
than being a bit distresing, didnt cause any control issues.I have
flown ships with and without seals and I didnt notice any difference
..What have you encountered?

"Eric Greenwell" wrote in message
My top surface mylar seems to have lost some of it's curvature, because it
doesn't quite touch the aileron and flaps when they are in positive
positions. Does anyone know a way to put the curve back into the mylar
without removing it? It's so well adhered and smoothly installed, I'd like
to leave it on if at all possible, but I think it may be degrading my
climb while thermalling. The mylar is almost 12 years old.

Eric, I replace my seals on a much more frequent basis, I would say
that you have definetly gotten your moneys worth at 12 years.I dont
know if this is commonly accepted or not but I know of some pilots who
just wait till the seals make noise at high speeds before they replace
them.Not to worry, you can make your own seals at home in a few
evenings and they are rather inexpensive.
K Urban

About a year ago, one of my soaring buddies had a elevator seal become
separtated from the horizontal approx. 1/2 the length of the elevator behind
the safety tape. He had no idea of exactly what was his problem other than
is elevator had a small feedback of a minor flutter and it was almost
ineffective. I believe the safety tape remained intact but the major portion
of the seal behind the safety tape was raised into the slipstream. His
elevator lost the major part of its control and for a time he thought
bailing out may be an option. He did land safely but the experience was one
he would have rather avoided. I was flying that day and recall his
distressed comments while trying to deal with the issue. The point is: this
could have been avoided with understanding these seals need to be maintained
and time can deteriorate the adhesion properties of the seal.

The older the seals are, the more dangerous they become.

bob fidler
"KM" wrote in message
ps.com...

Bob Fidler wrote:
A lost seal inflight is something we all must
avoid at all cost. Control surfaces can stop working after a total or
partial separation.

Bob, I have heard this before, but I dont understand where the problem
would be (Other than the leading edge of the seal lifting ahead of the
control surface).Didnt most of these ships come from the factory
without seals, I know mine did.I have read stories on the Yahoo user
groups for the ASW20 about seals departing the plane inflight and other
than being a bit distresing, didnt cause any control issues.I have
flown ships with and without seals and I didnt notice any difference
.What have you encountered?

"Eric Greenwell" wrote in message
My top surface mylar seems to have lost some of it's curvature, because
it
doesn't quite touch the aileron and flaps when they are in positive
positions. Does anyone know a way to put the curve back into the mylar
without removing it? It's so well adhered and smoothly installed, I'd
like
to leave it on if at all possible, but I think it may be degrading my
climb while thermalling. The mylar is almost 12 years old.

Eric, I replace my seals on a much more frequent basis, I would say
that you have definetly gotten your moneys worth at 12 years.I dont
know if this is commonly accepted or not but I know of some pilots who
just wait till the seals make noise at high speeds before they replace
them.Not to worry, you can make your own seals at home in a few
evenings and they are rather inexpensive.
K Urban

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

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. ;-)

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

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"

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