Aerodynamic detail? Structural?

[Dirty Rotten Flieger]

Anybody know what the tiny "wing fence like" thing that runs along in front of the aileron is. Not the actual wing fence but the little bracket thing behind it running 90 degrees adjacent. 

 

I've been looking at this thing for years and wondering why they put it there. 

 

 

 

Edited May 18, 2024 by Dirty Rotten Flieger

[Ala13_ManOWar]

Haven't the faintest, never noticed. Probably some aerodynamic stuff. Maybe a fence for the aileron hinge right behind? at high speeds sometimes it's a problem when airflow comes in between control surfaces. But no idea.

 

Hope some fellow member knows about it. Intriguing.

[Dirty Rotten Flieger]

here is another view of it.  I used to wonder if it was some kind of vortex generator. It must be there for a reason.  Maybe it's just a stop for doing maintenance. If you disconnect the actuator and lift the aileron it will rest against the little bracket at 95 degree or so. 

 

 

 

Edited May 20, 2024 by Dirty Rotten Flieger

[zerO_crash]

As you know, at higher mach-speeds, the MiG-21Bis (as well as any of the heavier modifications retaining the larger spine) had a issue with directional stability. That's to say, the aircraft introduced adverse yaw characteristics. There are many ways to solve such a deficiency, one being spoilers. At the same time, you don't want to have a speed brake (spoiler) constantly introduce drag. The idea, was then to have a solution where the collective total, would retain the planes original directional stability properties.

 

One of the additions, was the SAU (AFCS - AP) - specifically the "Stability" mode. All pilots flying the later MiG-21 iterations, chief amongst "Bis", considered it a standard to fly with the "Stability" engaged. The other addition, were these spoilers, which due to their size, barely affected the aircraft subsonic. However in supersonic, where the airflow is greater, they did their job of counteracting some of the unwanted yaw instability. 
 

If you look up ealier MiG-21s, going back to the former layout (among them, spine size), you'll notice that these spoilers are not there. That's because the earlier variants didn't have as much problem with directional stability.
 

For one, consider the bigger air-intake on the later versions (Tumansky R-25-300). At supersonic speed, the spike would have to move the shockwave further away from the centerline, resulting in the airstream hitting a smaller part of the vertical stabilizer. That, along with more weight around the centre (spine), is what ultimately caused the later MiG-21s to need the aerodynamic modifications. (There are more, less obvious, changes as well).

Edited May 20, 2024 by zerO_crash

[Ala13_ManOWar]

Wow, great post mate, coupled with a great explanation. Thanks mate!!

[zerO_crash]

My pleasure!

[Dirty Rotten Flieger]

Thank you Zero_ crash,

I've been looking at that little spoiler for ten years and your explanation is very much appreciated. 

I love this little jet and looking forward to gunning down some F4 Phantoms 

Edited May 22, 2024 by Dirty Rotten Flieger

[zerO_crash]

Glad to hear that, and my pleasure!

 

If you are deep into MiG-21, I suggest watching these interviews. It adds meat around the bone, to say the least. Fantastic material, you'll enjoy them both: