What is dynamic stall?
Join Date: Jun 2006
Location: Europe
Posts: 716
Likes: 0
Received 0 Likes
on
0 Posts
A dynamic stall is a stalled condition different from a statically stalled condition, in that it is a transient, non-permanent condition, kind of hard to describe...
However, we are used to the fact that a given airfoil stalls at a given angle of attack. This (critical) angle of attack is the angle of attack that gives the highest coefficient of lift, ie, beyond this angle of attack, the CL decreases due to increased airflow separation on the upper side of the airfoil. This is measured in a static, steady-state, constant system.
However, the airflow separation on top of the wing is in reality dynamic and always changing, and during these changes you may see conditions, beyond the nominated critical angle of attack, where the airflow is less separated than in the above steady-state scenario. In practical terms, in some occasions, the stall will temporarily occur at a higher aoa than what is nominated in the paperwork. In practical use: read it, get it on the exam, forget about it.
Edit: Dynamic stall - Wikipedia, the free encyclopedia
However, we are used to the fact that a given airfoil stalls at a given angle of attack. This (critical) angle of attack is the angle of attack that gives the highest coefficient of lift, ie, beyond this angle of attack, the CL decreases due to increased airflow separation on the upper side of the airfoil. This is measured in a static, steady-state, constant system.
However, the airflow separation on top of the wing is in reality dynamic and always changing, and during these changes you may see conditions, beyond the nominated critical angle of attack, where the airflow is less separated than in the above steady-state scenario. In practical terms, in some occasions, the stall will temporarily occur at a higher aoa than what is nominated in the paperwork. In practical use: read it, get it on the exam, forget about it.
Edit: Dynamic stall - Wikipedia, the free encyclopedia
Moderator
Generally three sorts of stalls in consideration -
(a) at/near 1g stall - relevant to the AFM stall data and pilot training demonstration stalls. Generally docile characteristics for the typical civil aircraft and not the sort of stall which frightens folk when they let their guard down in routine operations.
(b) "normal" stall which can occur at various g values according to what the pilot may be doing at the time. Higher g results in higher stall speed and, due to flow unsteadiness, can result in "interesting" characteristics. Often referred to as accelerated or dynamic stall and usually the cause of (sometimes much) pilot eyebrow raising at the time. Likewise often associated with pilot technical aeronautical expressions such as "golly, gee, and gosh"
(c) stall associated with very high pitch rates (typically something in excess of 70 deg/sec or so). Due to the generation of a vortex above the wing, the pitch angle can extend well above the normal stalling angle. Generally not seen other than in very high performance aeroplanes and helicopters. There was a very illustrative RAeS paper on the subject some years ago - I have it on file somewhere but don't recall the author just now. Often referred to as a dynamic stall
(a) at/near 1g stall - relevant to the AFM stall data and pilot training demonstration stalls. Generally docile characteristics for the typical civil aircraft and not the sort of stall which frightens folk when they let their guard down in routine operations.
(b) "normal" stall which can occur at various g values according to what the pilot may be doing at the time. Higher g results in higher stall speed and, due to flow unsteadiness, can result in "interesting" characteristics. Often referred to as accelerated or dynamic stall and usually the cause of (sometimes much) pilot eyebrow raising at the time. Likewise often associated with pilot technical aeronautical expressions such as "golly, gee, and gosh"
(c) stall associated with very high pitch rates (typically something in excess of 70 deg/sec or so). Due to the generation of a vortex above the wing, the pitch angle can extend well above the normal stalling angle. Generally not seen other than in very high performance aeroplanes and helicopters. There was a very illustrative RAeS paper on the subject some years ago - I have it on file somewhere but don't recall the author just now. Often referred to as a dynamic stall
Join Date: May 2002
Location: Permanently lost
Posts: 1,785
Likes: 0
Received 0 Likes
on
0 Posts
bfisk, people should not forget about dynamic stalls. 
They can kill you very quickly. 
A late friend of mine did a beat-up of an aerodrome followed by a rapid climb and attempted roll onto his departure heading.
The C210 gave up at the attempted roll, dynamically stalled and buried itself in the ground very shortly after. 
They can kill you very quickly. A late friend of mine did a beat-up of an aerodrome followed by a rapid climb and attempted roll onto his departure heading.
The C210 gave up at the attempted roll, dynamically stalled and buried itself in the ground very shortly after.
