Teflon gap seal tape...

[Marc Ramsey]

I need to replace the flap/aileron gap seal tape on our LAK-17A. The
control surfaces are bottom hinged, and the gap was factory sealed on
the bottom with what is apparently ordinary polyethylene tape. The tape
cracks over the hinges, which I would have to patch periodically, plus
it shrinks over time, limiting control movement and increasing stick forces.

It seems like Teflon tape is the way to go. I poked around and found
multiple online sources of 1" x 18 yard Teflon PFTE tape with high
temperature silicone adhesive on one side, available in thicknesses from
..0035" (~$25/roll) to .0115" (~$75/roll). There are less readily
available variations with acrylic adhesive, along with "High Density"
PFTE (100% stretch instead of 300%). Does anyone have any idea what
thickness and type of tape would be best for my needs?

Thanks,
Marc

[John Ferguson]

Look for teflon tape on this page

http://www.streifly.de/Price1-00.htm

If you ask they will do you a complete kit, I'm on
my third kit and haven't been disappointed yet, third
glider in 4 years, LS7 Cirrus and Ventus cT

[[email protected]]

Not sure that tape is the way to go, Mark. I have found that properly
installed Mylas is all that is necessary. Proof--------when the seals
on my Nimbus 3 needed replacing, I eliminated the internal seals and
also got rid of that ridiculous lower mylar that went inside the gap,
never did understand the reasoning there. Replaced it with Mylar on top
and bottom, nothing else. She climbed and cruised right with another
Nimbus 3 with factory seals.
Another data point..............The ASW-20 had a terrible reputation
for dropping a wing and entering a spin, when they first came
out.................then the spin problem seemed to go away, why? Most
20's today have Mylar, top & bottom. Was the external tape triggering
separation at low speed?

Something to think about,
JJ

[Udo Rumpf]

I agree with J.J.
Make sure the edge of the tape wipes and makes contact at the bottom
of the aileron when deflected. Install samples at discrete points to find
out if you have the correct radius and position for the Mylar.
Bottom hinged flap/aileron Mylar seal require a slightly different approach
versus the top.
Regards
Udo


"Marc Ramsey" > wrote in message
m...
>I need to replace the flap/aileron gap seal tape on our LAK-17A. The
>control surfaces are bottom hinged, and the gap was factory sealed on the
>bottom with what is apparently ordinary polyethylene tape. The tape cracks
>over the hinges, which I would have to patch periodically, plus it shrinks
>over time, limiting control movement and increasing stick forces.
>
> It seems like Teflon tape is the way to go. I poked around and found
> multiple online sources of 1" x 18 yard Teflon PFTE tape with high
> temperature silicone adhesive on one side, available in thicknesses from
> .0035" (~$25/roll) to .0115" (~$75/roll). There are less readily
> available variations with acrylic adhesive, along with "High Density" PFTE
> (100% stretch instead of 300%). Does anyone have any idea what thickness
> and type of tape would be best for my needs?
>
> Thanks,
> Marc

[Marc Ramsey]

wrote:
> Not sure that tape is the way to go, Mark. I have found that properly
> installed Mylas is all that is necessary. Proof--------when the seals
> on my Nimbus 3 needed replacing, I eliminated the internal seals and
> also got rid of that ridiculous lower mylar that went inside the gap,
> never did understand the reasoning there. Replaced it with Mylar on top
> and bottom, nothing else. She climbed and cruised right with another
> Nimbus 3 with factory seals.
> Another data point..............The ASW-20 had a terrible reputation
> for dropping a wing and entering a spin, when they first came
> out.................then the spin problem seemed to go away, why? Most
> 20's today have Mylar, top & bottom. Was the external tape triggering
> separation at low speed?

When JJ and Udo agree on something it must be true 8^)

Here is what I was thinking, and I am prepared to be proven completely
wrong. First, Mylar seals (combined with anti-peel tape) appear to be
thicker than Teflon tape, so unless I'm willing to go to the trouble of
routing a groove to inset the Mylar (which I'm not), the Mylar would
seem to me to be every bit as likely to trip the airflow as the Teflon
tape. Second, the point behind external tape (or internal seals) is to
prevent airflow through the gap. Are properly fitted Mylar seals
actually going to prevent this flow? Would it make sense to use Teflon
tape to seal the gap, then put Mylar over the tape?

Thanks,
Marc

[Bob Fidler]

Mark,

We installed mylar seals on the bottom just behind the tubulator tape. We
installed the 1 1/4" wide teflon tape attaching 1/4 " to the wing just
behind the 1/2" wide adhesive for the mylar seals. The thickness of the
adhesive and the teflon is the same about .007". With the flaps pushed up to
simulate max refax ( the flap and airelon will go up farther), You can mark
the flaps and airleron only with the aircraft assemble and refaxed with full
airleron stick deflection. With the wing turned upside down and the flap and
airleron set to the previously marked position you can then apply the teflon
tape.
The teflon tape is not easy to apply and get the edge straight. I suggest
you practice on some scrap pieces before yo attempt to apply the 25' of
continuous application you will need. If someone in your club has previous
expertise you may want to ask for help.Wings and Wheels sells the tape which
is lite brown in color and costs about $50.
The last tibbit of info is that getting the teflon down flat and without
airbubbles will offer you an additional challenge. If you are an absolute
perfectionist, you may want to investigate professional installation. It
will be difficult to do without flaw.

Good Luck,
Bob Fidler
"Marc Ramsey" > wrote in message
m...
>I need to replace the flap/aileron gap seal tape on our LAK-17A. The
>control surfaces are bottom hinged, and the gap was factory sealed on the
>bottom with what is apparently ordinary polyethylene tape. The tape cracks
>over the hinges, which I would have to patch periodically, plus it shrinks
>over time, limiting control movement and increasing stick forces.
>
> It seems like Teflon tape is the way to go. I poked around and found
> multiple online sources of 1" x 18 yard Teflon PFTE tape with high
> temperature silicone adhesive on one side, available in thicknesses from
> .0035" (~$25/roll) to .0115" (~$75/roll). There are less readily
> available variations with acrylic adhesive, along with "High Density" PFTE
> (100% stretch instead of 300%). Does anyone have any idea what thickness
> and type of tape would be best for my needs?
>
> Thanks,
> Marc

[Udo Rumpf]

The hinge line can be detrimental to the relative thick boundary,
if not covered properly to guide the flow over the hinge line,
the flow could separate.( there is an exception to this if the hinge line is
used
as a transition point)

The tape you are referring to would be just a seal but would not contour
the shape.

The edge of the Mylar tape .010" plus the edge tape .002" it
should not effect turbulent flow. A gap, covered by a sealing tape could.
The Mylar seal if it wipes it will seal. If you were to have difficulties
with this
a separate seal would be the way to go, as long as it does not interfere
with The Mylar.
Sometimes if the hinge is to close to the bottom surface it would be
difficult to get a wiping action
through all the motion of the flap and aileron.
I hope I understood your question.
Udo

"Marc Ramsey" > wrote in message
om...
> wrote:
>> Not sure that tape is the way to go, Mark. I have found that properly
>> installed Mylas is all that is necessary. Proof--------when the seals
>> on my Nimbus 3 needed replacing, I eliminated the internal seals and
>> also got rid of that ridiculous lower mylar that went inside the gap,
>> never did understand the reasoning there. Replaced it with Mylar on top
>> and bottom, nothing else. She climbed and cruised right with another
>> Nimbus 3 with factory seals.
>> Another data point..............The ASW-20 had a terrible reputation
>> for dropping a wing and entering a spin, when they first came
>> out.................then the spin problem seemed to go away, why? Most
>> 20's today have Mylar, top & bottom. Was the external tape triggering
>> separation at low speed?
>
> When JJ and Udo agree on something it must be true 8^)
>
> Here is what I was thinking, and I am prepared to be proven completely
> wrong. First, Mylar seals (combined with anti-peel tape) appear to be
> thicker than Teflon tape, so unless I'm willing to go to the trouble of
> routing a groove to inset the Mylar (which I'm not), the Mylar would seem
> to me to be every bit as likely to trip the airflow as the Teflon tape.
> Second, the point behind external tape (or internal seals) is to prevent
> airflow through the gap. Are properly fitted Mylar seals actually going
> to prevent this flow? Would it make sense to use Teflon tape to seal the
> gap, then put Mylar over the tape?
>
> Thanks,
> Marc

[[email protected]]

the Mylar would
> seem to me to be every bit as likely to trip the airflow as the
Teflon
> tape. Second, the point behind external tape (or internal seals) is
to
> prevent airflow through the gap. Are properly fitted Mylar seals
> actually going to prevent this flow? Would it make sense to use
Teflon
> tape to seal the gap, then put Mylar over the tape?
>
> Thanks,
> Marc


I have seen it done this way (mylar & tape) Just have come to the
conclusion it isn't necessary. I fit foam rubber in the flap well to
seal any cross-flow at each end of flap and aileron, then the mylar
comes over this area and prevents any air from entering.

I believe the big bug-aboo with tape only is the leading edge starts to
come loose and this = some real drag on that wing.
JJ

[Marc Ramsey]

Udo Rumpf wrote:
> The edge of the Mylar tape .010" plus the edge tape .002" it
> should not effect turbulent flow. A gap, covered by a sealing tape could.
> The Mylar seal if it wipes it will seal. If you were to have
> difficulties with this
> a separate seal would be the way to go, as long as it does not interfere
> with The Mylar.
> Sometimes if the hinge is to close to the bottom surface it would be
> difficult to get a wiping action
> through all the motion of the flap and aileron.
> I hope I understood your question.

Yes, it does answer my question. I suspect the best solution is that
used by Bob Fidler on his LAK, use Teflon tape to act as both a flow
seal and a wiping surface, then put a Mylar seal over it.

Thanks to all,
Marc

[HL Falbaum]

If I recall correctly, Dick Johnson tested Sam Fly's Ventus 2 with oil flow
and found that the mylar alone did not prevent cross flow from bottom to
top. He removed the ailerons and installed S-seals and stopped the flow. As
I further vaguely recall, this did only a little for the performance! There
was considerable data scatter.

Does anyone know of any hard data that shows, one way or the other, if the
mylars are effective?

Hartley Falbaum
ASW27B "KF" USA

> wrote in message
oups.com...
>
> the Mylar would
>> seem to me to be every bit as likely to trip the airflow as the
> Teflon
>> tape. Second, the point behind external tape (or internal seals) is
> to
>> prevent airflow through the gap. Are properly fitted Mylar seals
>> actually going to prevent this flow? Would it make sense to use
> Teflon
>> tape to seal the gap, then put Mylar over the tape?
>>
>> Thanks,
>> Marc
>
>
> I have seen it done this way (mylar & tape) Just have come to the
> conclusion it isn't necessary. I fit foam rubber in the flap well to
> seal any cross-flow at each end of flap and aileron, then the mylar
> comes over this area and prevents any air from entering.
>
> I believe the big bug-aboo with tape only is the leading edge starts to
> come loose and this = some real drag on that wing.
> JJ
>

[[email protected]]

We tend to think that internal seals (and external tape) completely
eliminate any cross flow from the lower surface (hi pressure) to the
upper surface (lo pressure), but does it? Look at both ends of your
flaps or ailerons; The internal seal stops, so does the external tape.
It must or you couldn't get full down flap and full up aileron, at the
same time. The other end of these control surfaces are open also. What
does this mean? Air can, and will move laterally along the control
surface until it reaches the end and then move vertically and get to
the upper surface. We have just experienced cross flow.

The best we can do is slow it down as much as possible. I use properly
fitted mylar on both surfaces and control surface wipers (felt) at both
ends of the controls. Works for me. I also fill the flap/aileron well
at each end with foam rubber in an attempt to stop this vertical
movement of air.
JJ