What are the Raised Dots Ahead of the Aileron?

[exchemist]

This screen shot, captured from a video, shows a row of little bumps towards the wing tip of this Embraer aircraft. Someone on another forum thinks they are some kind of navigation light, as apparently they "flash" at night.

I am sceptical. I suspect they are something to improve the airflow over the aileron, which catch the rotating beam of a beacon on the fuselage and thus appear to flash. But I'm not a pilot. Does anyone know what this wing feature is and what it does?

One for billvon, perhaps?

 

[Seattle]

Deicing? I have a pilot's license but I don't know what that is.

 

[Sarkus]

They're there to create vortices, small areas of turbulence, which helps keep the boundary layer attached to the wing at high angles of attack, and thus help prevent stalling.

The aircraft only needs them toward the end as that's where the wing will flex more, thus could otherwise start stalling before the main part of the wing would otherwise do.

It may seem counter-intuitive that you might want to deliberately create turbulence; after all, racing cars don't like following behind another as they lose performance in "dirty" (i.e. turbulent) air. They much prefer laminar flow over their aerofoils.
But ever wondered why golf balls have dimples? They create a thin turbulent boundary layer that clings to the surface of the ball, and this actually reduces the drag of the ball through the air.


Does that help?

 

[exchemist]

They're there to create vortices, small areas of turbulence, which helps keep the boundary layer attached to the wing at high angles of attack, and thus help prevent stalling.

The aircraft only needs them toward the end as that's where the wing will flex more, thus could otherwise start stalling before the main part of the wing would otherwise do.

It may seem counter-intuitive that you might want to deliberately create turbulence; after all, racing cars don't like following behind another as they lose performance in "dirty" (i.e. turbulent) air. They much prefer laminar flow over their aerofoils.
But ever wondered why golf balls have dimples? They create a thin turbulent boundary layer that clings to the surface of the ball, and this actually reduces the drag of the ball through the air.


Does that help?

That's rather what I thought. Do you know what they are called? I'd like to find a link that describes them, which I can use to settle the point. I've looked up vortex generators but those don't look like these.

 

[Sarkus]

The shape varies somewhat, but if you look at general pictures of vortex generators (and that is what they are called) on wings then they can look like the picture you posted. They may look like bumps from side-on and at a distance, but if you get up close to them you may find that they closely resemble the other images.

As for describing them, this link provides a good explanation.

As you can see, you can use them wherever the effect caused will be benefiicial. In the picture you posted it was to the end of the wing, but could be across the full length, on the tail etc.

 

[Michael 345]

They're there to create vortices, small areas of turbulence

Like the upturned tip of the wing

I can recall folding up the tips of the wings on paper aircraft I used to make around age 11 (1953)

Didn't know at the time why but the paper aircraft were more stable and traveled further with upturned wing tips

Never did see on real aircraft until much later. Wiki says Boeing put them on a 707 in 1985 but doubt that was the first time used on real aircraft

 

[geordief]

I can recall folding up the tips of the wings on paper aircraft I used to make around age 11 (1953)

Same here ,except I still make them( actually forgot how to do all the little tucks and folds the last time as my memory may be starting to deteriorate)

Those dots put me in mind of the shark skin that has apparently been incorporated into professional swimming costumes(called Speedos?) and allow the wearer to compete at a higher level of performance.

 

[Sarkus]

Like the upturned tip of the wing

I can recall folding up the tips of the wings on paper aircraft I used to make around age 11 (1953)

Didn't know at the time why but the paper aircraft were more stable and traveled further with upturned wing tips

Never did see on real aircraft until much later. Wiki says Boeing put them on a 707 in 1985 but doubt that was the first time used on real aircraft

The first idea for winglets was around 1900. Didn't really catch on as a worth-while idea until fuel prices rose in the 70s. NASA then developed them as a means of creating efficiency, as they cut down the wing-tip vortices, which create drag.

 

[DaveC426913]

Like the upturned tip of the wing

Slightly different function on the wingtip.

A lot of energy is funneled in to the vortex that's created when high pressure air spills out from under the wingtip. Winglets reduce this vortex and the energy it draws.

The design that carries this to its extreme is the circular wing which has no wingtip at all, and therefore no wingtip vortices:

 

[Sarkus]

Those dots put me in mind of the shark skin that has apparently been incorporated into professional swimming costumes(called Speedos?) and allow the wearer to compete at a higher level of performance.

That particular element of the suits that elite swimmers wear is questionable as to whether it does actually reduce drag. The shark benefits from its denticles in two main ways, or so studies have suggested: by reducing drag and by increasing thrust. But they also found that, in order to benefit, the body needs to be rather flexible... like that of a shark, for example, rather than the relatively rigid body of a human. For humans the drag-reduction and thrust improvement from the denticles is thought to be minimal, if anything at all.

However, the suits do benefit swimmers in other ways, due to other features, such as streamlining the flow of water around the body, helping keep the posture correct, and that sort of thing.

 

[Seattle]

I'm not sure what I'm looking at on that wing? To me it looks like holes in the wing and not something that would generate a vortex. Deicing systems have holes for the chemicals to drip through (as well as a rubber boot for some to inflate/deflate and knock off the ice).

I only flew Cessna 152's and 172 (so small planes). The various tips at the end of a wing are (among other reasons) for stability, self-leveling, or to create greater lift at the end to make sure that the tips stall last in order to give the ailerons control even while the wing roots are stalled. In experimental aircraft where that doesn't happen a stall can be fatal as the pilot has no control once in a stall and just flies into the ground.

The downdraft resulting from a large commercial plane is no joke. When I was on a long cross-country solo (before my final license) I had to fly down to an airport just outside Portland (from Seattle) and I was in the traffic pattern right behind a larger commercial plane.

I had no choice, that's where the tower put me. I knew about wake turbulence and was being careful but usually a small airplane wouldn't find themselves that close behind a bigger airplane on landing.

I momentarily hit the wake turbulence from that plane and it almost turned my airplane over! It's invisible so you just have to know how it works (fly above and land past where they did). It's a similar problem to potential down drafts on the lee side of a mountain.

I was going to land a helicopter on a peak in the Cascades. I had done it before several times and there was no down draft. On this particular day I was on the final approach (too close to avert) and I noticed I was descending too fast so I tried to slow things down but couldn't. Full power did nothing either.

I had time to think "is this how it's going to end?" but you have to use all of your focus to try to do something about the situation. No only did I have no control and I'm slowly getting closer and closer to the ground but I then noticed that there was no clear landing spot. The area had been logged and every space had a tree stump there.

All I could do was stay in control and ride it out and hope for the best. Luckily it was a narrow peak and I had enough altitude, even at my rate of descent, to just barely miss the peak and then it dropped off to the valley on the other side. At that point the lee side downdraft stopped and I had full control again.

Otherwise I probably wouldn't have been able to be around to bring my people skills to Sciforums.

I hope someone is able to get a more definitive explanation for the dots in that picture of a wing.

 

[DaveC426913]

I hope someone is able to get a more definitive explanation for the dots in that picture of a wing.

Sarkus' two posts cover it completely.

 

[billvon]

One for billvon, perhaps?

They are vortex generators. They generate tiny vortexes very close to the wing surfaces, thereby disrupting the laminar flow near the wing.

One of their most important functions is to make the stall break more gradual. If one wing of the aircraft stalls suddenly while the other wing is generating lift, the aircraft will roll violently towards the stalled wing. Using ailerons to try to counter this will just make it worse since ailerons increase the (effective) angle of attack of the wings when deflected downward, and thereby deepen the stall.

They also slightly reduce stall speed by ensuring laminar flow is NOT maintained. This is somewhat counterintuitive since laminar flow is a very efficient regime for an airfoil to work in. But in a laminar flow airfoil, again the stall break happens very suddenly. The turbulence created by the vortex generators ensures that any stall occurs gradually by disrupting the (primarily) laminar flow over the wing, and allows the wing to keep flying while partially stalled.

They also increase drag and reduce cruise speed at a given power setting. They are still seen as worth the tradeoff because they increase maximum takeoff weight by providing more margin against violent stalls at low airspeed, and the slowest airspeed that an airplane can get off the ground is one of the primary determinants in both runway length needed and maximum safe takeoff weight for a given runway.

 

[exchemist]

They are vortex generators. They generate tiny vortexes very close to the wing surfaces, thereby disrupting the laminar flow near the wing.

One of their most important functions is to make the stall break more gradual. If one wing of the aircraft stalls suddenly while the other wing is generating lift, the aircraft will roll violently towards the stalled wing. Using ailerons to try to counter this will just make it worse since ailerons increase the (effective) angle of attack of the wings when deflected downward, and thereby deepen the stall.

They also slightly reduce stall speed by ensuring laminar flow is NOT maintained. This is somewhat counterintuitive since laminar flow is a very efficient regime for an airfoil to work in. But in a laminar flow airfoil, again the stall break happens very suddenly. The turbulence created by the vortex generators ensures that any stall occurs gradually by disrupting the (primarily) laminar flow over the wing, and allows the wing to keep flying while partially stalled.

They also increase drag and reduce cruise speed at a given power setting. They are still seen as worth the tradeoff because they increase maximum takeoff weight by providing more margin against violent stalls at low airspeed, and the slowest airspeed that an airplane can get off the ground is one of the primary determinants in both runway length needed and maximum safe takeoff weight for a given runway.

Thanks, this is what Sarkus said too, though you have added some further detail. It looks as if this is now settled.

Good stuff.