How important are aileron gap seals?

[soartech[_2_]]

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.

[Tony[_5_]]

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.

sealing the ailerons on my Cherokee provided a marked improvement in roll rate.

[Dave Nadler]

On Wednesday, May 22, 2013 1:20:54 PM UTC-4, 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.

Depends on the type of glider...

[[email protected]]

I have a friend who flew a DG-606 with internal gap seals. One day he went into a brutal, uncharacteristic spin that allmost 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.

[BobW]

On 5/22/2013 11:20 AM, soartech wrote:
> What is lost without them?

For the truly anal, mostly sleep! :-)
- - - - - -

> One point of glide?

It depends...!
- - - - - -

> What about sink rate?

It depends...!
- - - - - -

> Is this just for racers? My glider does not have them.
> Does anyone have any facts on this?

Facts?!? Now you've done gone and changed a relatively simple question to a
genuinely complex one!

If you're OK with conclusions drawn via observational extrapolation and the
application of "common sense" (of which the development of airplanes -
including sailplanes - has a long and rich history), gap seals are obviously
not *required* for effective aerodynamic 3-axis control.

What they *are* good for is aerodynamic efficiency and improving control
effectiveness, most commonly detectable at lower-end speeds. True for gliders
and powerplanes. This was well known in the powerplane (e.g. racing) field by
the mid 1930s.

Sealing control gaps tends to make the sealed controls act more like a part of
the larger appendage (e.g. main wing, horizontal stabilizer/elevator, vertical
stabilizer/rudder), than a separate, trailing, appendage, by reducing
(eliminating?) "cross-talk" between the higher-to-lower pressure side of the
fixed/moveable assembly. With a(n impermeable) seal in place and ignoring tip
effects, cross talk can't begin until the trailing end of the moving portion,
as opposed to beginning at the gap itself. As with everything aerodynamic,
there's books-full of complexities associated with the above claim, but the
claim is accurate.

As noted in other threads, poorly installed/worn gap seals can cause more
problems than well-installed ones fix...something to bear in mind if the
absence of gap seals on your bird bugs you. (Their absence never did on the
Schweizers I owned...come to think of it, the last glider I owned that had
[external vinyl tape] gap seals was in 1981!)

It's a safe generalization to presume - in the absence of solid information to
the contrary - that EVERYthing having to do with gliders' external surface
configurations not explicitly determined by some underlying structural
consideration, is done for (at a minimum) aerodynamic drag reduction purposes.
Gap seals (say on a tube-n-rag Schweizer) being a case in point...

Bob W.

[Eric Greenwell[_4_]]

soartech wrote, On 5/22/2013 10:20 AM:
> 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.

Are you asking about "seals" - a flexible material like tape between the
wing and control surface to prevent air from leaking between the two. It
might be external or internal.

Or, are you asking about "fairings" - generally Mylar across the top or
the bottom the wing/control surface gap to smooth the airflow across the
gap. The fairing is external only, and might also reduce the leakage
from bottom surface to top surface.

My glider came with both, but I have no idea of how much they affect the
performance. I know the top fairings can degrade the climb when they
lose their curvature after 10 years or so.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

[Peter von Tresckow]

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.

Our CFI was bitching about the lousy roll rate on the 2-33. We decided to
just put some gap tape over the aileron gap, and it actually improved the
performance markedly.

Peter

[Tony[_5_]]

On Wednesday, May 22, 2013 9:27:37 PM UTC-5, vontresc wrote:
> 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.
>
>
>
> Our CFI was bitching about the lousy roll rate on the 2-33. We decided to
>
> just put some gap tape over the aileron gap, and it actually improved the
>
> performance markedly.
>
>
>
> Peter

The 2-33 at the Wichita Gliderport has the ailerons sealed nicely and it is hands down the nicest flying 2-33 I have had the pleasure of flying.

The 'drag queens' may show the most improvement with these kind of small things because they have the most to gain!

[Evan Ludeman[_4_]]

On Wednesday, May 22, 2013 10:46:22 PM UTC-4, Tony wrote:

> The 2-33 at the Wichita Gliderport has the ailerons sealed nicely and it is hands down the nicest flying 2-33 I have had the pleasure of flying.


That may be the single most improbable English sentence ever typed :-).

T8

[Tony[_5_]]

On Thursday, May 23, 2013 11:31:14 AM UTC-5, Evan Ludeman wrote:
> On Wednesday, May 22, 2013 10:46:22 PM UTC-4, Tony wrote: > The 2-33 at the Wichita Gliderport has the ailerons sealed nicely and it is hands down the nicest flying 2-33 I have had the pleasure of flying. That may be the single most improbable English sentence ever typed :-). T8

i know its hard to believe but that 2-33 really is nice to fly. It is serial 20, very clean, well sealed, not full of dents, etc. We used to have serial 10 at our club and it was also a nice flying but less pretty glider. I've heard that at some point during the run they decreased the aileron deflection which probably had a negative impact on roll rate.

[soartech[_2_]]

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.

[Andrew[_14_]]

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.

[son_of_flubber]

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?

[[email protected]]

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

[Eric Munk]

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
>

[[email protected]]

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.