Gap seals effectiveness study?

[Bret Hess]

Hi, we see lots of mylar gap seals and read lots of discussion of them. Does anyone know of an engineering study that quantifies their effect on sailplane wings or other wings? Nothing pops up quickly in Google. I'm wondering how much science there is to this practice.

I'm hoping for more than anecdotal comments. Saying that top racers all use them doesn't tell us much because so do almost everyone.

[[email protected]]

Il giorno lunedì 12 giugno 2017 07:38:22 UTC+2, Bret Hess ha scritto:
> Hi, we see lots of mylar gap seals and read lots of discussion of them. Does anyone know of an engineering study that quantifies their effect on sailplane wings or other wings? Nothing pops up quickly in Google. I'm wondering how much science there is to this practice.
>
> I'm hoping for more than anecdotal comments. Saying that top racers all use them doesn't tell us much because so do almost everyone.

To put things simple (may be too simple): think how the wing works, lower pressure on the upper surface than on the below surface, if you open a hole the air pass-by

Carlo

[Juliet11[_2_]]

On Monday, June 12, 2017 at 1:38:22 AM UTC-4, Bret Hess wrote:
> Hi, we see lots of mylar gap seals and read lots of discussion of them. Does anyone know of an engineering study that quantifies their effect on sailplane wings or other wings? Nothing pops up quickly in Google. I'm wondering how much science there is to this practice.
>
> I'm hoping for more than anecdotal comments. Saying that top racers all use them doesn't tell us much because so do almost everyone.

Look up any of Richard Johnson's flight tests before and after seals, especially the LS-4. Or any other modern sailplane. There was as much as a 5 point difference.

[Tango Whisky]

Le lundi 12 juin 2017 07:38:22 UTC+2, Bret Hess a écritÂ*:
> Hi, we see lots of mylar gap seals and read lots of discussion of them. Does anyone know of an engineering study that quantifies their effect on sailplane wings or other wings? Nothing pops up quickly in Google. I'm wondering how much science there is to this practice.
>
> I'm hoping for more than anecdotal comments. Saying that top racers all use them doesn't tell us much because so do almost everyone.

There is quite a number of gliders which require the seals in place to be airworthy.

Apart from the obvious loss of performance without seals, the air flow escaping through this area might induce flutter (which in turn will induce a loss of performance of 100%).

Bert "TW"

[[email protected]]

> Look up any of Richard Johnson's flight tests before and after seals, especially the LS-4. Or any other modern sailplane. There was as much as a 5 point difference.

Thanks. I read the two LS-4 articles, but the "after" wasn't conclusive: Different plane, different probe positions, and Dick doesn't make much of a conclusion on if the performance was better, or just measured to be better.

Is there another one where he does the same plane with the only difference the mylar seals?

[[email protected]]

>The air flow escaping through this area might induce flutter (which in turn will induce a loss of performance of 100%).
>
> Bert "TW"

Are you talking about the exterior mylar seals or the fabric "S" seals in the joint? Once the fabric seals are in place I don't think air escaping is the real issue, more of turbulence due to the dip in the sahpe, but I suppose that could aid flutter.

[Charlie M. (UH & 002 owner/pilot)]

A lot depends on the airfoil and condition of surfaces. For a 1-26 that needs paint, not much difference. On a modern airfoil with 90-95% laminar flow, it makes a bigger difference.
Most really need the internal seals, then various amounts of need for external Mylar seals.

Keep in mind, I don't think they EVER hurt performance.

[[email protected]]

If there is an effect on performance or handling, this will be different from glider to glider. It may do nothing, improve performance or even be needed to prevent flutter. There were a lot of quantitative studies done for various gliders, especially the newer ones. For which type do you need this information?

[[email protected]]

> A lot depends on the airfoil and condition of surfaces. For a 1-26 that needs paint, not much difference.

Disagree, a properly sealed 1-26 has almost 5 mph slower stall, and a crisper roll than one that is not sealed.

Kevin
92, formerly 192

[Bret Hess]

On Monday, June 12, 2017 at 11:51:11 AM UTC-6, wrote:
> >The air flow escaping through this area might induce flutter (which in turn will induce a loss of performance of 100%).
> >
> > Bert "TW"
>
> Are you talking about the exterior mylar seals or the fabric "S" seals in the joint? Once the fabric seals are in place I don't think air escaping is the real issue, more of turbulence due to the dip in the sahpe, but I suppose that could aid flutter.

I see now that some gliders don't have seals internal to the joint, and depend only on these exterior seals, so you're right about the flutter problem.

[[email protected]]

On Monday, June 12, 2017 at 3:29:43 PM UTC-6, wrote:
> If there is an effect on performance or handling, this will be different from glider to glider. It may do nothing, improve performance or even be needed to prevent flutter. There were a lot of quantitative studies done for various gliders, especially the newer ones. For which type do you need this information?

I have a PIK20E (1985 last year they were made). The manual says nothing about seals. Guys on our forum say that there is an internal fabric seal in the aileron joints. My glider has them on the wings and rudder, but not the elevator.

From a search of Soaring Mag, it seems external mylar curved lip seals date from about that time or later, and became popular later, and common about 10 years later. In fact in February 1986 Dick Johnson was reviewing the new Discus, and actually removed the external mylar seals because he didn't trust them. He wrote: "The ailerons are hinged near their top surfaces and they did have the normal tape seal bridging the span wise gaps between the wing and the aileron leading edges. However, a curved piece of Mylar plastic strip was attached to the wing portion by an adhesive layer at its leading edge. It curved downward in its aft direction to maintain a sliding contact with the aileron top surface. W ith the aileron in neutral the Mylar strips created a small but perhaps significant upward bulge in the critical airfoil profIle. Also, these Mylar strips cannot be observed from the cockpit in flight, and it is possible that airstream suction force over their cambered top surfaces caused the strip trailing edges to ride high and above the aileron, thereby adding drag. For the above reasons the Mylar aileron seals were removed and Ceconite polyester airseals were installed at the
wing root aileron control rod openings."

In a article a few years later about improving the 1-26, I think, Dick wrote that external mylar seals might provide a little improvement.

[Charlie M. (UH & 002 owner/pilot)]

I totally understand about sealing a 1-26, I'm co-owner of 002 and have a lot of 1-26 hours (not as many as Ron Schwartz). Wing root seals (internal and external) as well as fabric aileron/rudder/elevator seals are needed. Mylar seals make little to no difference, that was my point.

[2G]

On Sunday, June 11, 2017 at 10:38:22 PM UTC-7, Bret Hess wrote:
> Hi, we see lots of mylar gap seals and read lots of discussion of them. Does anyone know of an engineering study that quantifies their effect on sailplane wings or other wings? Nothing pops up quickly in Google. I'm wondering how much science there is to this practice.
>
> I'm hoping for more than anecdotal comments. Saying that top racers all use them doesn't tell us much because so do almost everyone.

I think the answer depends not only on the airfoil, but also on how you fly.. Sealing will help more if you spend a larger percentage of time at slow speeds where parasitic drag predominates.

Tom

[jfitch]

On Sunday, June 18, 2017 at 9:58:07 AM UTC-7, 2G wrote:
> On Sunday, June 11, 2017 at 10:38:22 PM UTC-7, Bret Hess wrote:
> > Hi, we see lots of mylar gap seals and read lots of discussion of them. Does anyone know of an engineering study that quantifies their effect on sailplane wings or other wings? Nothing pops up quickly in Google. I'm wondering how much science there is to this practice.
> >
> > I'm hoping for more than anecdotal comments. Saying that top racers all use them doesn't tell us much because so do almost everyone.
>
> I think the answer depends not only on the airfoil, but also on how you fly. Sealing will help more if you spend a larger percentage of time at slow speeds where parasitic drag predominates.
>
> Tom

Mylar seals can have two functions: one is to seal leakage, the other is to fair the airfoil contour across the gap. If you believe the marketing literature and tests, laminar flow is being achieved on these airfoils to well behind the gap, and that would not be possible without the fairing. Profile drag reduction from laminar flow is more important at high speeds where profile - and parasitic - drag predominates over induced. On some sailplanes there are rolling seals inside that seal leakage. The mylar seal is installed only for fairing.

[Roy B.]

My personal theory is that mylar seals were invented by the last guy who tried to take 20 year old white duct tape off of an open class glider wing. That's what we used to use on the underside in the old days . . .

Maybe they work. Maybe they don't. But they sure are easier to clean up.
ROY

[[email protected]]

On Sunday, June 18, 2017 at 4:24:15 PM UTC-4, Roy B. wrote:
> My personal theory is that mylar seals were invented by the last guy who tried to take 20 year old white duct tape off of an open class glider wing. That's what we used to use on the underside in the old days . . .
>
> Maybe they work. Maybe they don't. But they sure are easier to clean up.
> ROY

Doesn't sound like you have had to take 15 year old transfer tape residue off very often!
UH

[[email protected]]

I found this to be an interesting read about the design of the ASW24 sailplane. It includes an evaluation of the effectiveness of sealing the gaps and smoothing the gap with mylar seals.
http://journals.sfu.ca/ts/index.php/ts/article/view/777/735

aldo cernezzi
www.voloavela.it

[Per Carlin]

On Sunday, June 18, 2017 at 11:04:05 PM UTC+2, wrote:
> On Sunday, June 18, 2017 at 4:24:15 PM UTC-4, Roy B. wrote:
> > My personal theory is that mylar seals were invented by the last guy who tried to take 20 year old white duct tape off of an open class glider wing. That's what we used to use on the underside in the old days . . .
> >
> > Maybe they work. Maybe they don't. But they sure are easier to clean up.
> > ROY
>
> Doesn't sound like you have had to take 15 year old transfer tape residue off very often!
> UH

Not moer often than every 15 Year :)