Gap seals effectiveness study?

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.

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

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.

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"

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?

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.

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.

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?

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

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.