Mylar tape wing seals - effect on wing performance

I tried asking this questionon on a different thread; it may have been too
off topic, but I didn't get much of a response:

I'm putting mylar control surface seals on the wings of a Mini Nimbus this
winter. At the moment I'm planning on fixing them to the finished wing
surface. The alternative is to rebate (recess) them into the wing. This
creates a smoother surface but costs more money and is harder to undo.

Anyone know of any research (or anecdotes) on the impact on wing performance
of leaving such seals proud of the surface? My assumption is the airflow
over the wing is pretty much turbulent at the wing/aileron join anyway, so
the impact should be minimal.

If the recommendation is to rebate, is it equally critical for the both the
upper and lower surfaces?

Simon Waddell wrote:
I tried asking this questionon on a different thread; it may have been too
off topic, but I didn't get much of a response:

I'm putting mylar control surface seals on the wings of a Mini Nimbus this
winter. At the moment I'm planning on fixing them to the finished wing
surface. The alternative is to rebate (recess) them into the wing. This
creates a smoother surface but costs more money and is harder to undo.

Anyone know of any research (or anecdotes) on the impact on wing performance
of leaving such seals proud of the surface? My assumption is the airflow
over the wing is pretty much turbulent at the wing/aileron join anyway, so
the impact should be minimal.

I think you are right. In any case, the effect of even perfectly done
fairings is small (you won't notice it, and would have great difficulty
measuring it with flight tests), especially on an older airfoil, so the
effort and cost of recessing the mylar isn't worth it. Be sure there is
an actual _seal_ (flexible tape stuck to the wing and the control
surface) installed, in addition to the mylar fairings, so air can't leak
through the gap.

--
-----
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Eric Greenwell
Washington State
USA

Simon,
Have a look at the LS 8 versions that are around (mine is a 2001
LS8-18). No mylar seals on the wings, only on the rudder and elevator
(those are not recessed). There are two internal seals on the
ailerons that keep top and bottom surfaces separated. Seems to work
well from the performance I am seeing. I would first worry about the
internal seals and then go fly a lot before spending money on Mylar!
Herb, J7

"Simon Waddell" simonFUNNYATSYMBOLleswaddells.ch wrote in message ...
I tried asking this questionon on a different thread; it may have been too
off topic, but I didn't get much of a response:

I'm putting mylar control surface seals on the wings of a Mini Nimbus this
winter. At the moment I'm planning on fixing them to the finished wing
surface. The alternative is to rebate (recess) them into the wing. This
creates a smoother surface but costs more money and is harder to undo.

Anyone know of any research (or anecdotes) on the impact on wing performance
of leaving such seals proud of the surface? My assumption is the airflow
over the wing is pretty much turbulent at the wing/aileron join anyway, so
the impact should be minimal.

If the recommendation is to rebate, is it equally critical for the both the
upper and lower surfaces?

Eric,

What you and Herbert appear to be saying is that thee mylar is only a
fairing, rather than a seal. Since the mylar is in turbulent airflow the
need for a fairing at that point seems limited. At the moment, the seal is
provided by flexible adhesive tape over the join (upper surface only).
Would I be better off (financially, yes!) to forget about mylar and stick
(not to pun) with the adhesive tape, perhaps on both upper and lower
surfaces?

Simon


"Eric Greenwell" wrote in message
...
Simon Waddell wrote:
I tried asking this questionon on a different thread; it may have been
too
off topic, but I didn't get much of a response:

I'm putting mylar control surface seals on the wings of a Mini Nimbus
this
winter. At the moment I'm planning on fixing them to the finished wing
surface. The alternative is to rebate (recess) them into the wing.
This
creates a smoother surface but costs more money and is harder to undo.

Anyone know of any research (or anecdotes) on the impact on wing
performance
of leaving such seals proud of the surface? My assumption is the
airflow
over the wing is pretty much turbulent at the wing/aileron join anyway,
so
the impact should be minimal.

I think you are right. In any case, the effect of even perfectly done
fairings is small (you won't notice it, and would have great difficulty
measuring it with flight tests), especially on an older airfoil, so the
effort and cost of recessing the mylar isn't worth it. Be sure there is
an actual _seal_ (flexible tape stuck to the wing and the control
surface) installed, in addition to the mylar fairings, so air can't leak
through the gap.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

There appears to be a misconception, that turbulent flow
requires less attention to details regarding surface discontinuity.
In fact some airfoils that maximize laminar must have a minimum
of discontinuity to prevent separation of turbulent flow.
In case of the LS 6 or 8 airfoil the turbulent flow is relative thin
as the laminar flow is not driven to the max and a relative thin
and energetic turbulent flow is maintained, hence the close tolerance of
gap and shape in the LS8 aileron transition can be done without
Mylar tape. It is always a good idea to provide an effective fairing
that assists the flow around deflect surfaces as well as pay attention
to surface details beyond laminar flow transitions.
Udo

What you and Herbert appear to be saying is that thee mylar is only a
fairing, rather than a seal. Since the mylar is in turbulent airflow the
need for a fairing at that point seems limited. At the moment, the seal
is
provided by flexible adhesive tape over the join (upper surface only).
Would I be better off (financially, yes!) to forget about mylar and stick
(not to pun) with the adhesive tape, perhaps on both upper and lower
surfaces?

Simon


"Eric Greenwell" wrote in message
...
Simon Waddell wrote:
I tried asking this questionon on a different thread; it may have been
too
off topic, but I didn't get much of a response:

I'm putting mylar control surface seals on the wings of a Mini Nimbus
this
winter. At the moment I'm planning on fixing them to the finished
wing
surface. The alternative is to rebate (recess) them into the wing.
This
creates a smoother surface but costs more money and is harder to undo.

Anyone know of any research (or anecdotes) on the impact on wing
performance
of leaving such seals proud of the surface? My assumption is the
airflow
over the wing is pretty much turbulent at the wing/aileron join
anyway,
so
the impact should be minimal.

I think you are right. In any case, the effect of even perfectly done
fairings is small (you won't notice it, and would have great difficulty
measuring it with flight tests), especially on an older airfoil, so the
effort and cost of recessing the mylar isn't worth it. Be sure there is
an actual _seal_ (flexible tape stuck to the wing and the control
surface) installed, in addition to the mylar fairings, so air can't leak
through the gap.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

"Simon Waddell" simonFUNNYATSYMBOLleswaddells.ch wrote in message ...
I tried asking this questionon on a different thread; it may have been too
off topic, but I didn't get much of a response:

I'm putting mylar control surface seals on the wings of a Mini Nimbus this
winter. At the moment I'm planning on fixing them to the finished wing
surface. The alternative is to rebate (recess) them into the wing. This
creates a smoother surface but costs more money and is harder to undo.

Anyone know of any research (or anecdotes) on the impact on wing performance
of leaving such seals proud of the surface? My assumption is the airflow
over the wing is pretty much turbulent at the wing/aileron join anyway, so
the impact should be minimal.

If the recommendation is to rebate, is it equally critical for the both the
upper and lower surfaces?

I replaced the top surface fabric tape aileron seals with mylar on my
ASW-19b. I didn't use an internal seal on the assumption that the
lower seal would stop any air migration to the top. I only had time
to do one wing before a club contest flight. I noticed a significant
roll towards the unmodified wing. The roll went away when I installed
the mylar seals on the other wing. No rebate, just faired the leading
edge of the mylar with tape.

A lot of advice has ben posted before on the perils of detatching
mylar seals. Make sure you stick them well and inspect before flight.
Also lock the control surfaces neutral when the glider is not in use.
A deflected control surface may cause the seal to take a set and may
also contribute to seal detachment.

Andy (GY)

Simon Waddell wrote:
Eric,

What you and Herbert appear to be saying is that thee mylar is only a
fairing, rather than a seal. Since the mylar is in turbulent airflow the
need for a fairing at that point seems limited. At the moment, the seal is
provided by flexible adhesive tape over the join (upper surface only).

This is sufficient to stop the airflow through the gap. Many gliders use
a single internal tape that works with a "rolling" motion. I believe
this seal is more important than the mylar fairings (I think "fairing"
is a better description, since the real sealing is done by the internal
tape, though the mylar would provide some sealing if there was no
internal tape). I don't know if this internal seal can be done on the
Mini Nimbus. The external seal you describe sounds like it would
interfere with the proper fitting of mylar fairings.

Any of the seals - tape or mylar - must be properly fitted to avoid
control problems. Even the simple external tape can cause problems if it
comes loose on the front edge, or shrinks enough to prevent full control
deflection. The mylar has caused more problems than the simple tape,
however.

Would I be better off (financially, yes!) to forget about mylar and stick
(not to pun) with the adhesive tape, perhaps on both upper and lower
surfaces?

Probably! There is no need for tape on both sides, as it's job is to
stop the airflow between the wing and control surface. Without clear
evidence of value for the Mini Nimbus, like well done flight tests, I'd
avoid the effort, expense, and potential safety risk of the mylar.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Direct question to the group.

My Nimbus 2C has Mylar on both the upper and lower aileron gaps plus an
internal seal. The lower gap Mylar "fairing" is in only fair condition.
Should I just remove it?

Bill Daniels


"Eric Greenwell" wrote in message
...
Simon Waddell wrote:
Eric,

What you and Herbert appear to be saying is that thee mylar is only a
fairing, rather than a seal. Since the mylar is in turbulent airflow
the
need for a fairing at that point seems limited. At the moment, the seal
is
provided by flexible adhesive tape over the join (upper surface only).

This is sufficient to stop the airflow through the gap. Many gliders use
a single internal tape that works with a "rolling" motion. I believe
this seal is more important than the mylar fairings (I think "fairing"
is a better description, since the real sealing is done by the internal
tape, though the mylar would provide some sealing if there was no
internal tape). I don't know if this internal seal can be done on the
Mini Nimbus. The external seal you describe sounds like it would
interfere with the proper fitting of mylar fairings.

Any of the seals - tape or mylar - must be properly fitted to avoid
control problems. Even the simple external tape can cause problems if it
comes loose on the front edge, or shrinks enough to prevent full control
deflection. The mylar has caused more problems than the simple tape,
however.

Would I be better off (financially, yes!) to forget about mylar and
stick
(not to pun) with the adhesive tape, perhaps on both upper and lower
surfaces?

Probably! There is no need for tape on both sides, as it's job is to
stop the airflow between the wing and control surface. Without clear
evidence of value for the Mini Nimbus, like well done flight tests, I'd
avoid the effort, expense, and potential safety risk of the mylar.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

"Bill Daniels" wrote:

Direct question to the group.

My Nimbus 2C has Mylar on both the upper and lower aileron gaps plus an
internal seal. The lower gap Mylar "fairing" is in only fair condition.
Should I just remove it?

An airfoil expert of greatest fame once told me that the smoothness of
the underside of the wing is most important for achieving minimum
drag. More so than upper surface...
Thus I would assume a Mylar fairing, if correctly installed, is most
significant on the lower surface: you should replace it with a new one
if it's not perfectly attached or shaped.
Whether a Mylar fairing is truly beneficial to a Wortmann airfoil I
don't know, but I guess the aerodinamic noise of an aircraft could be
a good indicator of low drag; if your friend will report of a lower
noise level during high speed finishes, I think you may be pretty sure
drag has been reduced. (?)

My limited experience relates only to normal adhesive tape used to
seal the gap on the lower surface of my former DG400. When, in very
hot wather, the tape on the left wing started to slide backward (from
the tape's leading edge towards the aileron) creating a vertical bump
(about 3 to 5 mm high), the glider was more and more steering to the
right. Anxiety about landing grew as I needed 2 hands on the stick to
just keep the glider straight and level.
It all finished before landing (good!) as the tape eventually fell
off.
The effect on the behaviour of the glider was opposite to what I would
have expected (should have been: bump=drag=left wing down and back...)
Maybe it has had something to do with the principle of "Guerney
flaps"?

Aldo Cernezzi