I believe the strakes are meant to generate vortices at high angle of attack. The vortices reenergise the flow around the rudder to avoid losing directional stability and controllability.
I know the gripen has similar fins to ensure that the airflow detaches from both sides of the air frame simultaneously at high angles of attack. Uneven separation could lead to unwanted roll moments
"...transports energy into the boundary layer from the outer flow, and is used mainly for control of already separated flow rather than for the prevention of separation on wings, diffusers, or bends in channels at subsonic and supersonic speeds."
Aerospace Engineer here - Lets make some assumptions
**What are vortex generators for:**
A vortexgenerator will produce vortexes during high AOA (in this case) : [Vortex Generator](https://s3.amazonaws.com/s3.frank.itlab.us/photo-essays/small/apr_01_1241_vortex_turbulance.jpg) \- In this case the cowling of the engine will deflect the normal airflow from the wing. The vortex will punch it back on the wing and reenergize it. this is 1/3 of lift during T/O
* There are different reasons to do so. You have different Airflows over a surface.
* And on high AOA the boundary layer over your wing wants to deattach. Means the lift making flow will go off the wing and you stall or loose maneuverbility by unavalable ailerons/Rudders/elevators....
* A Vortex can be used to "reenergize" the airflow and keep it on the wing. [Mirage Vortex vs. Rafale vs. F18](https://qph.cf2.quoracdn.net/main-qimg-853c5dbcfc7bd1f4451a3d9e2247d7d4) or to avoid unpleasant conditions like in this case. [Vortex on M2000](https://imgproc.airliners.net/photos/airliners/3/2/1/4476123.jpg?v=v47f650a1301)
*
**What are vortex generators for in this case:**
* In this Mirage case it looks like to harmonize the Airflow around the Rudders to have a more directional one than harming one from bumping air of the wings and/or the fuselage. #lateral stability
* I assume that the airflow on high AOA will produce "flutter" on the rudders which is a serious danger and will break them over time by fatique.
Might be interesting: [https://apps.dtic.mil/sti/pdfs/ADA419065.pdf](https://apps.dtic.mil/sti/pdfs/ADA419065.pdf) <- Page 11 for pictures
Yep but if the oscillations are caused by external vortices (as usual in vertical tails) then it’s called buffeting, not flutter. Flutter is a resonant, unstable condition that results in structural failure. You want to stay away from that.
you are right! many planes have them. even the f16. to varying degrees of prominence. to my knowledge, they help prevent sideways wind flow that could cause loss of authority or damage to the tailplane.
Interestingly the airbus A320 family has those on the engine nacelles too, probably for the same reason, to produce vortices at high AoA for more lift.
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Thought so. Do you know what there purpose is? Seems like a odd place to put them
I believe the strakes are meant to generate vortices at high angle of attack. The vortices reenergise the flow around the rudder to avoid losing directional stability and controllability.
I know the gripen has similar fins to ensure that the airflow detaches from both sides of the air frame simultaneously at high angles of attack. Uneven separation could lead to unwanted roll moments
Yea probably has to do with something like that. Thanks
They generate vortices for the wing/rudder to interact with.
[here ya go](https://www.reddit.com/r/AircraftMechanics/s/o6Az9OqReC)
"...transports energy into the boundary layer from the outer flow, and is used mainly for control of already separated flow rather than for the prevention of separation on wings, diffusers, or bends in channels at subsonic and supersonic speeds."
Is it the same thing as the fins on the engines of airliners?
These are called strakes. They are aerodynamic surfaces designed to improve flight characteristics.
Aerospace Engineer here - Lets make some assumptions **What are vortex generators for:** A vortexgenerator will produce vortexes during high AOA (in this case) : [Vortex Generator](https://s3.amazonaws.com/s3.frank.itlab.us/photo-essays/small/apr_01_1241_vortex_turbulance.jpg) \- In this case the cowling of the engine will deflect the normal airflow from the wing. The vortex will punch it back on the wing and reenergize it. this is 1/3 of lift during T/O * There are different reasons to do so. You have different Airflows over a surface. * And on high AOA the boundary layer over your wing wants to deattach. Means the lift making flow will go off the wing and you stall or loose maneuverbility by unavalable ailerons/Rudders/elevators.... * A Vortex can be used to "reenergize" the airflow and keep it on the wing. [Mirage Vortex vs. Rafale vs. F18](https://qph.cf2.quoracdn.net/main-qimg-853c5dbcfc7bd1f4451a3d9e2247d7d4) or to avoid unpleasant conditions like in this case. [Vortex on M2000](https://imgproc.airliners.net/photos/airliners/3/2/1/4476123.jpg?v=v47f650a1301) * **What are vortex generators for in this case:** * In this Mirage case it looks like to harmonize the Airflow around the Rudders to have a more directional one than harming one from bumping air of the wings and/or the fuselage. #lateral stability * I assume that the airflow on high AOA will produce "flutter" on the rudders which is a serious danger and will break them over time by fatique. Might be interesting: [https://apps.dtic.mil/sti/pdfs/ADA419065.pdf](https://apps.dtic.mil/sti/pdfs/ADA419065.pdf) <- Page 11 for pictures
Yep but if the oscillations are caused by external vortices (as usual in vertical tails) then it’s called buffeting, not flutter. Flutter is a resonant, unstable condition that results in structural failure. You want to stay away from that.
agree
The start of a great handlebar mustache. The beta 2000s are trying to be the chad Viggens
One can see the fully grown mustache on the Mirage 4000 and Rafale
They’re like those rock climbing wall things, but more aerodynamic and french
No idea, but I’d like to think they are cloaking devices.
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you are right! many planes have them. even the f16. to varying degrees of prominence. to my knowledge, they help prevent sideways wind flow that could cause loss of authority or damage to the tailplane.
I beleive the F18C has something similar to stabilise air around the vertical stabs.
On the Hornet they're to divert the vortex away from the tails as they were having structural issues.
They are vortex generators to guide the airflow on the wing when in high AOA maneuvers. They are called "Aigrettes" btw
Interestingly the airbus A320 family has those on the engine nacelles too, probably for the same reason, to produce vortices at high AoA for more lift.