Re-curving mylar on a glider

[Eric Greenwell]

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

[BT]

Eric, I would think that mylar that is 12 years old would have lost its
flexibility. It gets pushed up with upward aerleron or negative flap
settings and tends to stay there or very slowly flex back down to "neutral".
So going to positve settings will be difficult.

I don't know how you could put "life" back into the old plastic, but I would
be interested to hear.

BT

"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

[bumper]

Eric,

The Mylar is originally curved by passing the strip through a set of curved,
heated rollers. Complicated enough, all by itself (g) . . . to do the chore
with the Mylars still attached to the plane is beyond my admittedly limited
experience.

bumper

"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]

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

[[email protected]]

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

[Andy[_1_]]

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

[Udo]

bumper wrote:


> The Mylar is originally curved by passing the strip through a set of curved,
> heated rollers. Complicated enough, all by itself (g) . . . to do the chore
> with the Mylars still attached to the plane is beyond my admittedly limited
> experience.

I am interested in finding out more about this roller process?
Any pictures or detailed descriptions available?
For my projects in the past, I successfully made my own curved Mylar
strips in 5ft sections

Udo

[KM]

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

[Bob Fidler]

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
>

[BB]

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?ev_id=20001207X04237&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

[Cliff Hilty]

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?ev_id=20001207X04237&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
>
>

[[email protected]]

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

[Bruce Greef]

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?ev_id=20001207X04237&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. ;-)

[[email protected]]

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"

[Ray Lovinggood]

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?ev_id=20001207X04237&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. ;-)
>

[BB]

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

[snoop]

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:

[[email protected]]

> 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"

[[email protected]]

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"

[Bubba]

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?ev_id=20001207X04237&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

[BB]

> 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
>... 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?

Guessing here: no internal seal of the aileron, or seals between
fueslage and control rods. Then, high pressure from the cockpit
ventilation escapes out the aileron hinge line. Add to this a
separation bubble forming just in front of the aileron hinge line so
the air isn't moving there anyway. If I'm right, seals and zz tape
would give a different result. But of course the mylar will be glued on
tight so we'll never know...

John Cochrane BB

[[email protected]]

A friend of mine tried to make his own curving machine, using
a length of steel pipe and a propane torch. We had great fun
watching as he burned his fingers and leaped about yelling
"Ouch ! Ouch !" and made all manner of wavy plastic, but it did
get a bit scary when he almost set his shop afire. After that he
ordered new pre-curved mylar from Germany.

See ya, Dave

PS: I'm sure Bumper could do better ! But not as entertaining.

PPS: Pipe is the wrong idea; as you pass the myler through
it heats the edges and not the area needing the curve...

PPPS: Bumper already knew that.

bumper wrote:
> The Mylar is originally curved by passing the strip through a set of curved,
> heated rollers. Complicated enough, all by itself (g) . . .

[Cliff Hilty]

I use Acetone to clean out all of the old adhesive.
It doesn't leave any residue and completely evaporates
for good clean surface. Nasty stuff though use good
rubber gloves and good ventilation. Never had any tape
come off prematurely just after the AZ sun has dried
out the adhesive.

[Cliff Hilty]

I use Acetone to clean out all of the old adhesive.
It doesn't leave any residue and completely evaporates
for good clean surface. Nasty stuff though use good
rubber gloves and good ventilation. Never had any tape
come off prematurely just after the AZ sun has dried
out the adhesive.

[Udo]

> Guessing here: no internal seal of the aileron, or seals between
> fueslage and control rods. Then, high pressure from the cockpit
> ventilation escapes out the aileron hinge line. Add to this a
> separation bubble forming just in front of the aileron hinge line so
> the air isn't moving there anyway. If I'm right, seals and zz tape
> would give a different result. But of course the mylar will be glued on
> tight so we'll never know...
>
> John Cochrane BB

If The bottom wing surface is sealed tight along the hinge line and
no high pressure is moving from the cockpit along that line
(a normal cockpit has always a slight negative pressure,
which should be controlled by the rear exhaust)
and providing the turbulent flow on top is attached at the hinge line,
the Mylar, even if only the leading edge is taped, should stay down.
If the boundary layer is thicker the Mylar may start flattering like
a
stiff flag and makes noise, but it is not lifting. Only when separated

flow exist could the Mylar stand up. With no seals on the bottom
all bets are off

On my modified HP18, in the flap region, I have a 13/4" Mylar tape
excluding the glue line, that just sits on top of the flap surface.
It does stay put and makes no noise through out the normal range,
from stall to 125kt

On an other note, the glue line should be cleaned and roughed with
# 240 grit and cleaned again. Only the best and most aggressive
3M double sided tape should be used. A 1" ball bearing with a1/4 "
wide race mounted to a handle is used to press the Mylar
down. The local area should be warmed with a hot water bottle
or similar, before pressing with a rolling motion. The point pressure
is very high and forces the glue into the smallest of surface
indentation
for that long term bound.

[Eric Greenwell]

snoop wrote:
> 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

Been there, done that, didn't work out so well. I had to replace the
mylar on the outer half of the ailerons when the winglets were
retrofitted to my glider. It took several attempts to get them to stay
on properly longer than a month or two at a time. Money isn't the issue
- it's safety and convenience. The factory mylar shows no signs of
losing it's adhesion: I can tug on it, I can see through the mylar to
the carbon fiber it's glued to, and the glued area is uniform, clear,
and black.

When I was having this problem, I talked to Martin Heide (the ASH 26 E
designer), and he said "I have that problem on my glider, too! I must go
down to the factory floor and find out what they are doing". Sadly, he
didn't get back to me, and in the meantime, I got the aileron pieces to
adhere adequately. Looking at the glue through mylar, the joint does not
look as uniform as the original factory portion.

And you will be interested to know the wing mylar never had safety tape
on it, but the elevator and rudder mylar did. Without the safety tape,
it's easy to inspect the glued area. I do replace the safety tape on the
top of the elevator every 2-3 years, but the tape on the bottom of the
elevator and on the rudder lasts much longer. I don't remember needing
to replace it.

--
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

[Ray Lovinggood]

John,

You are correct: No seals at the butt rib for the
control rods (one of the things I've been meaning to
do. For the past ten years...)

No internal seals at the ailerons.

This old bird does have zz tape on the wing, but not
as the 'safety tape' for the mylar. That would be,
of course, way too far back for this fat old airfoil.
The zz tape was on it when I bought it.

Ray

At 22:06 16 October 2006, Bb wrote:
>> 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
>>... 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?
>
>Guessing here: no internal seal of the aileron, or
>seals between
>fueslage and control rods. Then, high pressure from
>the cockpit
>ventilation escapes out the aileron hinge line. Add
>to this a
>separation bubble forming just in front of the aileron
>hinge line so
>the air isn't moving there anyway. If I'm right, seals
>and zz tape
>would give a different result. But of course the mylar
>will be glued on
>tight so we'll never know...
>
>John Cochrane BB
>
>

[bumper]

Follow the acetone with denatured alcohol as a final cleaner. McMaster-Carr
does sell an acrylic adhesive "primer". I tested some, though not a very
good test, and could not discern any improvement over tape adhesion without
the primer. In both cases the tape stuck well.

I is important to apply the tape when it is warm or use a heat gun to
pre-heat the surfaces. As others have mentioned, sand all surfaces to be
bonded, including that portion of the Mylar. I use a 1/2" wide bearing
mounted in a wood handle to apply pressure to the mylar/tape bond.

The Mylar curing machine was one that Larry Mansberger had. I think he said
that Rick Wright either built it or helped. No pictures, but it looked a bit
like an old film projector, though the Mylar had a more direct path. Mylar
passed over a heating element and then through a curved roller, probably
aluminum, to impart the set and remove the heat.

all the best,

--
bumper ZZ (reverse all after @)>
"Dare to be different . . . circle in sink."
Quiet Vent kit and MKII yaw string

"Cliff Hilty" > wrote in message
...
>I use Acetone to clean out all of the old adhesive.
> It doesn't leave any residue and completely evaporates
> for good clean surface. Nasty stuff though use good
> rubber gloves and good ventilation. Never had any tape
> come off prematurely just after the AZ sun has dried
> out the adhesive.
>
>
>

[Papa3]

bumper wrote:
> Follow the acetone with denatured alcohol as a final cleaner. McMaster-Carr
> does sell an acrylic adhesive "primer". I tested some, though not a very
> good test, and could not discern any improvement over tape adhesion without
> the primer. In both cases the tape stuck well.
>
> I is important to apply the tape when it is warm or use a heat gun to
> pre-heat the surfaces. As others have mentioned, sand all surfaces to be
> bonded, including that portion of the Mylar. I use a 1/2" wide bearing
> mounted in a wood handle to apply pressure to the mylar/tape bond.
> >
> all the best,
>
> --
> bumper ZZ (reverse all after @)>
> "Dare to be different . . . circle in sink."
> Quiet Vent kit and MKII yaw string

Agree with all of Bumper's notes above. When I re-did the mylar on my
LS4 wings after doing some gelcoat work, I followed all of the above
procedures. Since the adhesive we are using is a pressure sensitive
adhesive (PSA), it's important to make sure that you apply a uniform
and comprehensive pressure on the joint. I wasn't smart enough to use
a roller, but I found that a plastic putty spreader worked pretty well.
I did notice a distinct improvement in performance when both the
wing and the tape were pre-warmed to about 70-75F.

P3

[KM]

wrote:
> A friend of mine tried to make his own curving machine, using
> a length of steel pipe and a propane torch. We had great fun
> watching as he burned his fingers and leaped about yelling
> "Ouch ! Ouch !" and made all manner of wavy plastic, but it did
> get a bit scary when he almost set his shop afire. >
> See ya, Dave

Dave,
Here is what I do.I buy the 7 mil sheets (I figure it provides less
friction than the 10 mil) and roll it up inside of a peice of carpet
roll tube.Then I bake it at about 160 in the oven for 30 minutes.Then
cut it into strips and use scotch 665 double sided tape to adhear it to
the wings and 3M 850 mylar tape for the safety strip.I can do top and
bottom of my flaps ailerons and tail a couple times over for about 50
bucks.I replace it every 3 to 5 years and I have never had a
problem.This does seem a little less entertaning than your buddys
method, but it works fine.
K Urban

[[email protected]]

Unless you've ot a *really* long oven, that leaves you with
a lot of small pieces, no ? Its a lot nicer (and easier to apply
with proper technique) to have longer strips, no ?
Best Regards, Dave

KM wrote:
> Dave,
> Here is what I do.I buy the 7 mil sheets (I figure it provides less
> friction than the 10 mil) and roll it up inside of a peice of carpet
> roll tube.Then I bake it at about 160 in the oven for 30 minutes.Then
> cut it into strips and use scotch 665 double sided tape to adhear it to
> the wings and 3M 850 mylar tape for the safety strip.I can do top and
> bottom of my flaps ailerons and tail a couple times over for about 50
> bucks.I replace it every 3 to 5 years and I have never had a
> problem.This does seem a little less entertaning than your buddys
> method, but it works fine.
> K Urban

[KM]

wrote:
> Unless you've ot a *really* long oven, that leaves you with
> a lot of small pieces, no ?

Dave, you are correct, the pieces are just over two feet long.I use a
peice of the 850 mylar tape at every joint.The main motivation for
doing this is to get a thinner seal.I use 7 mil sheets (I have heard
some guys go a little thinner), and all of the commecial seals that I
have found are 10 mil or bigger.I bought my ship from a guy who was
good freinds with Wil Shumman (SP?), and this is where the idea
originated.Wil Shumman did alot of work on airflow and wing profiles
and such, and he felt thinner would be better.Now I am not an
aerodymamical engineer, so maybe I am just perpetuating folklore, but
these seals work pretty good for me and they seem to provide a little
less control friction.

> Its a lot nicer (and easier to apply
> with proper technique) to have longer strips, no ?

No argument on the easier part ;). Actually, I use a homeade jig to cut
the strips (Then carefully shave the edges smooth) and a template to
install each strip and it comes out looking pretty clean.Usually guys
have to look very close to see that there are a bunch of peices of
mylar, and not one continual strip.A little practice doesnt hurt.I fly
an ASW20 in some pretty good desert conditions, so I am at high speeds
quite often, and I have never had a problem.

> Best Regards, Dave

Best Regards, K Urban

[Udo]

wrote:
> Unless you've ot a *really* long oven, that leaves you with
> a lot of small pieces, no ? Its a lot nicer (and easier to apply
> with proper technique) to have longer strips, no ?
> Best Regards, Dave

Hi Dave,
In fact it is much easier to apply shorter pieces.
Do you mean that proper technique can not be used, when applying
shorter pieces?
I am able to make six foot long pieces. (I do not use an oven)
I find five feet optimum for me as there would be one break in the
aileron section.
and two in the flap area. I use a .002" self adhesive clear Mylar tape
over the break.
The reason for covering the tight butting joint is, when wiping the
wing for cleaning,
the rag does not catch the corners.
There's is an advantage to making custom seals, one can get a curve and
thickness
for the Mylar that is right for your ship. This may not apply for most
modern gliders
as the factory installs them and it can provide after market seals.
There are many older
gliders were some after market seal may not be ideal.
Udo