Difference between turbulence and imminent spin?

[MountainDude]

My understanding is that some fatal, low altitude spin accidents are caused by:
- a plane stalling and one wing dropping
- the pilot countering the wing drop with the opposite aileron input, which initiates the spin

However, a much more common reason for a wing drop is turbulence, which one corrects with the opposite aileron input.
The explanations I have seen on the web is that the pilots do not recognize their plane is stalled, so they think it's just turbulence, and yank on the opposite aileron.

My question is: is the stall horn always going to be on when the wing drops due to a stall, or are there circumstances (skid, slip...) where that is not the case?

 

[GeorgeC]

My question is: is the stall horn always going to be on...

If your plane has a working stall horn, maybe.

when the wing drops due to a stall, or are there circumstances (skid, slip...) where that is not the case?

If you stall while slipped, the wing may not drop at all.

 

[AvNavCom]

Good question and fun to think through. Here is my understanding, but I defer to any CFIs. A spin occurs when the aircraft stalls while in uncoordinated flight (usually skidding), leading to one wing being more completely stalled than the other (and thereby having asymmetric lift with the low wing being more completely stalled). This is why you need to correct with rudder rather than aileron, since the low-wing aileron is ineffective and increasing the camber of the outboard low wing via the aileron just stalls it more.

Thinking about your question (and assuming that the stall-tab/sensor is on the left wing), I suppose a very hard rightward rudder input would cause the inboard wing to lose airflow relative to the outboard wing, causing a rightward roll and nose-drop. If the aircraft speed was sufficiently close to stall already (i.e. just above the stall warning speed) and the pilot tried to correct by commanding nose-up and left-roll, the inboard (right) wing could conceivably stall before the left one does, entering the spin before the stall warning horn on the outboard wing activates.

Real-world? Probably you'd get the stall warning horn as a useless distractor right as the plane enters the spin.

 

[TCABM]

If your plane has a working stall horn, maybe.


If you stall while slipped, the wing may not drop at all.

Or in a turn.

The OPs question indicates an underlying gap in knowledge. A wing dropping in and of itself is not an indicator of a spin. Or a stall.

A spin cannot occur unless a stall has occurred. Turbulence doesn’t cause a stall, but it can result in an upset. Poor recovery from an upset could result in a stall and, if uncoordinated, develop into a spin.

 

[Rgbeard]

https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/06_afh_ch5.pdf

 

[Rgbeard]

A slipping stall is almost never an issue. The high wing in the slip drops, and almost all the time that, alone, can fix the imminent stall.

A skidding stall is a different animal.

You know the difference between a slip and a skid, right? If not, I can point you to some material.

Here's one:

Why Skids Are More Dangerous Than Slips

You may have heard that a skid during a stall is more dangerous than a slip, and it's true. But, why?

www.boldmethod.com

 

[MauleSkinner]

The OPs question indicates an underlying gap in knowledge.

Agreed…Seems to me the real question revolves around recognizing whether or not a stall has occurred. In my personal experience, turbulence-induced stalls are a very short-lived condition.

And other than doing stupid things around thunderstorms, my turbulence-induced stalls were while flying at fairly high angle of attack.

 

[Ed Haywood]

The OPs question indicates an underlying gap in knowledge.

The official motto of PoA.

 

[Ed Haywood]

My understanding is that some fatal, low altitude spin accidents are caused by:
- a plane stalling and one wing dropping
- the pilot countering the wing drop with the opposite aileron input, which initiates the spin

However, a much more common reason for a wing drop is turbulence, which one corrects with the opposite aileron input.
The explanations I have seen on the web is that the pilots do not recognize their plane is stalled, so they think it's just turbulence, and yank on the opposite aileron.

My question is: is the stall horn always going to be on when the wing drops due to a stall, or are there circumstances (skid, slip...) where that is not the case?

A spin requires yaw and roll in the same direction. So that is the primary visual cue to differentiate a spin from an uncommanded roll, in addition to the other indicators of a stall.

 

[TCABM]

I would suggest the OP examine skids. It’s not something I do much of, but I think I’ll do some the next time I go up.

I would hazard more than a few base to final stalls to spins are caused by a pilot attempting to tighten an overshoot by applying inside of the turn rudder. I expect there’s an unintentional behavior created by avoiding slow, steep turns in the pattern.

Likely root cause is failure to master basic ground reference maneuvers, specifically the rectangular pattern and turns around a point. Mastery is what the USAF used to as a “4” in the grade sheet, which is described as recognizes and prevents common errors before they occur since a skid in the base to final turn is likely to result in a low altitude stall to spin.

It would be interesting to know if there are base to final accidents in unmodified Ercoupes.

 

[Daleandee]