How important are aileron gap seals?

Thanks for all the good info, especially the narratives of actual
experience. I was thinking of gap "fairings" as opposed to internal
gap seals
mostly because I suspect internal seals are very difficult to install.
External gap "covering" seems more easily done.
It is interesting to know that this affects roll rate as well as glide
performance.

I imagine external seals are much more critical/effective on high-performance gliders where transition to turbulent flow occurs aft of the aileron and flap hinge lines. Otherwise a nice gap could certainly cause earlier transition.

Typically, on older gliders where transition occurs ahead of the hinge line the manufacturer recommends Tesa tape on the bottom hinge only. Having a smooth/flush seal isn't so critical anymore since the flow is already turbulent. However, it's still effective because it's a pressure barrier and prevents flow through the control gap.

On Wednesday, May 22, 2013 3:49:32 PM UTC-4, wrote:
I have a friend who flew a DG-606 with internal gap seals. One day he went into a brutal, uncharacteristic spin that almost killed him. He got out of the spin at very low level. The glider was thoroughly checked to try to understand why it had reacted that way. It appeared that the internal aileron gap seals had failed. After replacement, the glider went back to its usual benign flight characteristics...

Now, everything will depend on the type of glider and the type of ailerons. Some older gliders had ailerons with a gap, by design.

Why would failure of a gap seal cause a spin?

On Wednesday, May 22, 2013 12:20:54 PM UTC-5, soartech wrote:
What is lost without them? One point of glide? What about sink rate?

Is this just for racers? My glider does not have them.

Does anyone have any facts on this?

Thanks.

When I got my LS8-18 off the boat in 2001 it did not have any mylar external seals on the top or bottom of the ailerons. It did come with two internal roll-seals on each side that seem to work very well. I'm still flying that way and have no indications that my glider's performance is lacking - quite the opposite. Aileron forces are delightfully low, no friction, no break-out forces. The gap itself is in the turbulent part of the wing and additional sealing would hardly make a difference. This would be different on a -27 or -29 where the bottom flow is laminar into the aileron/flap area and Schleicher is using seals consequently.
I like the simplicity of my set-up.
Herb

RTFM.

There's many gliders out there that according to the maintenance manual
have to have certain types of sealing for (mostly) ailerons and elevator.
This is for a reason (as the guy with the DG600 pointed out, and I can also
claim a close call in an LS4 where I lost control at high speed due to a
mylar sealing peeling away partially, cost me 2000 feet to get it back,
nearly bailed out).

As an inspector I find that seals are probably the single most neglected
bit of glider maintenance. There's actually a couple of countries in EUrope
specifically warning about the possible aerodynamic consequences of
sealings missing or (worse) partially coming off. Older (wooden) gliders
tend to be less critical than newer (glassfibre) ones.

- Check you manufacturer's recommendations. They usually know what they
are doing, and some manuals are very thorough.
- Check your gap seals' condition regularly.

At 13:52 24 May 2013, wrote:
On Wednesday, May 22, 2013 12:20:54 PM UTC-5, soartech wrote:
What is lost without them? One point of glide? What about sink rate?
=20
Is this just for racers? My glider does not have them.
=20
Does anyone have any facts on this?
=20
Thanks.

When I got my LS8-18 off the boat in 2001 it did not have any mylar
externa=
l seals on the top or bottom of the ailerons. It did come with two
interna=
l roll-seals on each side that seem to work very well. I'm still flying
th=
at way and have no indications that my glider's performance is lacking -
qu=
ite the opposite. Aileron forces are delightfully low, no friction, no
bre=
ak-out forces. The gap itself is in the turbulent part of the wing and
add=
itional sealing would hardly make a difference. This would be different
on=
a -27 or -29 where the bottom flow is laminar into the aileron/flap area
a=
nd Schleicher is using seals consequently.
I like the simplicity of my set-up.
Herb

Le vendredi 24 mai 2013 02:00:05 UTC+2, son_of_flubber a écrit*:

Why would failure of a gap seal cause a spin?

It probably didn't really cause the spin on the DG-606, but the spin happened in a situation (speed, inclination, etc.) where it normally shouldn't have happened, and it probably hampered recovery. Airflow over the ailerons would be severely affected.