Mylar seals for elevator

JJ Sinclair wrote:
Dave,
I recommend using mylar on all control surfaces and have added it to
the LS-3/4/6/7/8 without a problem. I sand the inside of the mylar
where the stickie will

I've always used the mylar with the adhesive already in place (I'm
curious why JJ doesn't). That's a lot easier, and one less thing to go
wrong, since you don't have to worry about contaminating the mylar
surface and getting a bad bond. I've never had the adhesive separate
from the mylar, though I've had problems with the adhesive not making a
good bond everywhere on the glider. That was due to poor preparation,
probably not enough sanding.

go with 220 and do the same to the horizontal
(just the 10mm area), then wipe both down with acetone before laying
down the stickie and mylar. Next, roll it down with considerable
pressure to insure a good bond, followed by the transition tape over
the leading edge of the mylar. Some have had mylar come loose because
they didn't do the above and or didn't remove all wax from the
affected area. Treat this with the respect it deserves, or take it to
a glider repair shop. We have had a bail-out caused by lifting mylar
on the stab.

Add "mylar and tape inspection" to your preflight: look for unbonded
spots and safety/transition tape thats brittle, peeling, or loosens
easily when you pick at it. It's easy to replace if you do it every year
or two, before it begins to deteriorate. The top side goes bad first.

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

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
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* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

I've always used the mylar with the adhesive already in place (I'm
curious why JJ doesn't)...

I've seen that stuff. Whoever puts it together doesn't sand the
underside of the mylar as JJ suggests. Your call.

Thanks, Bob K.

Eric Greenwell wrote:

I've always used the mylar with the adhesive already in place (I'm
curious why JJ doesn't).
Hi Eric,
I used some Mylar provided by the factory with adhesive already in
place on the flaps on an ASW-20 and the heat inside the trailer caused
the mylar to peal off between the mylar and the adhesive. The Mylar
was slick and had not been roughened up. This brings up another point,
recommend control locks on control surfaces while in the trailer,
especially flaps that won't otherwise stay in neutral.

I believe the main purpose of adding Mylar is to reduce drag, but if
you want added control authority, one can think about the combination
of Mylar and zig-zag. I use it on most rudders, but be careful adding
zig-zag to the elevator. I did on my LS-7 and the stall was the mose
abrupt I have ever seen..................took off the zig-zag!
Cheers,
JJ

On May 19, 6:09*am, JJ Sinclair wrote:

I believe the main purpose of adding Mylar is to reduce drag, but if
you want added control authority, one can think about the combination

I'm arguably the least experienced pilot on this thread, so I'll try
to tread respectfully - but I was under the impression that mylars are
placed over control gaps for three reasons:

1) To prevent (or at least reduce) high pressure air below the wing
from being sucked up through the control gap to the low-pressure air
on top, disturbing or separating the airflow right at the control
surface. If designed to flow properly, such airflow can be beneficial
in certain flight regimes (see "slotted flap") - but for glider
control surfaces its bad news.

2) To lessen the drag as the low-pressure air goes down the top
surface through the pressure-recovery zone and hits a big lip or gap
or sharp angle that might cause the air to separate, tumble, swirl,
etc. In other words, the mylar helps smooth the transition between
the wing and the control surface no matter what angle the control
surface is at (relative to the rest of the wing).

Take care,

--Noel

On May 19, 9:53*am, "noel.wade" wrote:

I'm arguably the least experienced pilot on this thread, so I'll try
to tread respectfully - but I was under the impression that mylars are
placed over control gaps for three reasons:

1) To prevent (or at least reduce) high pressure air below the wing
from being sucked up through the control gap to the low-pressure air
on top, disturbing or separating the airflow right at the control
surface. If designed to flow properly, such airflow can be beneficial
in certain flight regimes (see "slotted flap") - but for glider
control surfaces its bad news.

Not primarily - seals are used for that. Either tape (for top or
bottom hinged) or rolling seals (for center-hinged) control surfaces.
Mylar without seals will probably slow the crossflow, but probably not
completely stop it. My LS6 manual specifically shows how and where to
install both rolling seals and Mylar gap covers on all control
surfaces.

Mylar without the rolling seals made my LS6 sound like an RC airplane
at full throttle at about 130 knots - I figure the crossflow was
"buzzing" the mylar on the flaperons. Could turn it on or off within
a couple of knots. Made sneaky low passes a bit difficult! Quickly
fixed by properly installing seals, BTW!

2) To lessen the drag as the low-pressure air goes down the top
surface through the pressure-recovery zone and hits a big lip or gap
or sharp angle that might cause the air to separate, tumble, swirl,
etc. *In other words, the mylar helps smooth the transition between
the wing and the control surface no matter what angle the control
surface is at (relative to the rest of the wing).


What was #3? ;)


Cheers,

Kirk

It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has anyone
tried this?


"JJ Sinclair" wrote in message
...


I believe the main purpose of adding Mylar is to reduce drag, but if
you want added control authority, one can think about the combination
of Mylar and zig-zag. I use it on most rudders, but be careful adding
zig-zag to the elevator. I did on my LS-7 and the stall was the mose
abrupt I have ever seen..................took off the zig-zag!
Cheers,
JJ

On May 20, 2:25 am, "Bob Salvo" wrote:
It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has anyone
tried this?


The top side is the low pressure side Bob!

nimbusgb wrote:
On May 20, 2:25 am, "Bob Salvo" wrote:

It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has anyone
tried this?



The top side is the low pressure side Bob!

I don't think so, as the tail of just about every airplane or glider has
a download. That's how they achieve stability. So it's backward at the
tail, the top surface is indeed the high-pressure side.

On May 20, 6:39*am, Ed Winchester wrote:
nimbusgb wrote:
On May 20, 2:25 am, "Bob Salvo" wrote:

It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. *Has anyone
tried this?

The top side is the low pressure side Bob!

I don't think so, as the tail of just about every airplane or glider has
a download. *That's how they achieve stability. *So it's backward at the
tail, the top surface is indeed the high-pressure side.

Just to add to this "pressure" discussion, my elevator has a shape
similar to the trailing edge of my wing. The top-side is convex, and
the bottom-side is concave. Wouldn't that be a clue as to where the
high and low pressure areas are? I would think the convex side is the
low-pressure side, which is on top.


Dave


P.S. Any other thoughts on using mylars and safety tape on the
elevator gap?

As long as the elevators produces a force downwards, the low pressure side
is on top. This is typically the case for speeds higher than best L/D.
For speeds closer to stall speed, the elevator produces lift, and the low
pressure side is on the bottom.
For an optimum design, the elevator produces no force at all (except
drag...) at the speed of best L/D. But then, not all designs are optimum...

Bert

wrote in message
...
On May 20, 6:39 am, Ed Winchester wrote:
nimbusgb wrote:
On May 20, 2:25 am, "Bob Salvo" wrote:

It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has
anyone
tried this?

The top side is the low pressure side Bob!

I don't think so, as the tail of just about every airplane or glider has
a download. That's how they achieve stability. So it's backward at the
tail, the top surface is indeed the high-pressure side.

Just to add to this "pressure" discussion, my elevator has a shape
similar to the trailing edge of my wing. The top-side is convex, and
the bottom-side is concave. Wouldn't that be a clue as to where the
high and low pressure areas are? I would think the convex side is the
low-pressure side, which is on top.


Dave


P.S. Any other thoughts on using mylars and safety tape on the
elevator gap?