# What's the difference between an accelerated stall and a dynamic stall?

I am a commercial pilot. I always like to understand everything in detail, so here's my question:

What's the difference between an accelerated stall and a dynamic stall? For example, in a high-speed low pass, if we yank the yoke back, which of those two stalls may occur? It seems to me that what happens'll be a little bit of both. Also, can a dynamic stall occur at less than the normal stall AoA if the pitch rate is very fast? And, last but not least, is an airplane taxiing on the ground considered stalled (the stall AoA is not reached, but the lift produced is insufficient to fly)?

• Welcome to aviation.SE! I changed your question title to make it a little more specific because we prefer to have only one question at a time (the tour may be helpful to see how the site works). For your last question about what "stalled" really means, this question might be helpful. Jun 1 '21 at 22:51
• Ok but how can the critical AoA be exceeded other than pulling Gs? To me it looks like the same thing. The only difference is that if the rate of roll is really fast we can get a brief moment of augmented lift before falling into deep stall. Jun 3 '21 at 5:33
• related: aviation.stackexchange.com/q/61750/1467, also mentioned in aviation.stackexchange.com/q/6366/1467
– Federico
Jul 2 '21 at 7:42

The two stall conditions are both under different circumstances than the low speed, static stall conditions from exceeding critical Angle of Attack (AoA), they are not one and the same however.

Dynamic stall is described in this article from the Ohia State University, in relation mainly to helicopter rotors:

Aerodynamic bodies subjected to pitching motions or oscillations exhibit a stalling behavior different from that observed when the flow over a wing at a fixed angle of attack separates.

Further reading in this article from the University of Adelaide. The stall behaviour is described as Dynamic Stall, and tied to a pitch rate of the profiles.

Accelerated stall is mainly referred to for aeroplanes subject to g-forces, such as described in this answer on this site.

So when yanking the yoke back during a high speed low pass, creating higher g-forces, Accelerated Stall seems to be the more appropriate term. The situation is of course dynamic as well...

The Ohio State article mentions dynamic stall occurring in a windmill, which is of course not an accelerated stall. So not all dynamic stalls are accelerated stalls.

Also, can a dynamic stall occur at less than the normal stall AoA if the pitch rate is very fast?

The Adelaide University article describes a pitch-up rate temporarily increasing $$C_L$$, then developing deep stall. The pictures show a leading edge vortex developing at 40° AoA (figures 3d and 3j), way higher than static stall angle. Pitch-up movement seems to delay the stall, until it occurs very dramatically without any warning.

And, last but not least, is an airplane taxiing on the ground considered stalled (the stall AoA is not reached, but the lift produced is insufficient to fly)?

No it is not considered stalled. Stall is a condition of separation of the boundary layer, which does not occur during taxiing.

• The definitions are not exclusive, so don't have to chose the more appropriate term. You simply use both if both apply. Jul 2 '21 at 5:15
• @JanHudec hence the sentence: "The situation is of course dynamic as well..." Jul 2 '21 at 5:31
• +1 for pointing out that the stall AoA in a dynamic stall is higher than in a slow, quasi-static stall. Jul 2 '21 at 11:35

There are several questions here, I will answer two of them.

A dynamic stall occurs when the wing's critical angle of attack is suddenly exceeded, as in the case of a sudden yoke pull & pitch-up.

An accelerated stall occurs when the wing loading is suddenly increased by g-forces, as in the case of adding back pressure in a steep turn.

• Your distinction between the two seems to be based on wings level vs banked, and rate of onset. Would you agree with that observation? Jun 2 '21 at 2:48
• Well, if the plane is in a coordinated turn, the wings are banked and as a result the wings are heavily loaded by the g-force that results. This seems like a chicken-and-egg situation and I do not know how to resolve it, but I'll bet peter kaempf does... -NN Jun 2 '21 at 6:23
• I'm not sure what there is to resolve, it's just a terminology question. I would actually say they are the same thing. Jun 2 '21 at 6:49
• I agree. They are both exceedances of stalling AOA induced by acceleration above 1G. Jun 2 '21 at 12:46