In case a plane stalls, what should stall first, the tip or the root of the Wing? Why?
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$\begingroup$ "should" is ambiguous as to whether it means "preferable" or "expected". $\endgroup$– AcccumulationCommented Aug 12, 2020 at 4:36
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2 Answers
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It is preferable for the wing root to stall first. If the wingtip stalls before the root, the disrupted airflow near the wingtip can reduce aileron effectiveness to such a extent that it may be impossible to control the airplane about its longitudinal axis. When an aircraft stalls at the root first, it means there’s enough airflow over the tips of your wings to prevent any rapid rolling motion during a stall, which makes the airplane more stable. It also makes your plane more resistant to entering a spin.
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$\begingroup$ If you hit stall in an aircraft then the aircraft falls out of the sky like a stone... You have to get the nose down to reestablish the airflow over the wings... $\endgroup$ Commented Aug 10, 2020 at 20:07
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3$\begingroup$ @SolarMike : Not really, not always. It still has better lift then a stone, it's just that the lift is no longer enough to maintain altitude. There are some aircraft, like the An-2, which behave like a parachute, when stalled. $\endgroup$– vszCommented Aug 11, 2020 at 5:22
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2$\begingroup$ @SolarMike : And I've been practicing stalls in a glider, and it wasn't by far as drastic. I was certainly not falling like a stone (unless I deliberately went into a spin). $\endgroup$– vszCommented Aug 11, 2020 at 9:29
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1$\begingroup$ Interesting. I think in the early marks of the Supermarine Spitfire, they purposely introduced a feature where the wing twisted slightly so that the tips stalled first. This was meant to give pilots early warning of a stall, as the tips would start vibrating as they began to stall, giving them time to recover. $\endgroup$ Commented Aug 11, 2020 at 12:57
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2$\begingroup$ @5Diraptor, with a pure elliptical wing, the entire wing stalls simultaneously. The Spitfire's wing had a slight twist that produced turbulent root stall that buffeted the airplane, giving warning that the rest of the wing was about to stall. $\endgroup$– MarkCommented Aug 11, 2020 at 20:31
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It depends on wing geometry. You need to look at the aerodynamic center of the wing, which is the center of effort for perturbation forces. The center of lift (unstalled) will usually be well forward of the aerodynamic center. As Cl increases, it is desirable to have the center of lift shift aft. This produces speed stability by lowering the nose, thus gaining speed and restoring the original Cl. This is a static stability condition - it says nothing about how the pertubation gets damped.
At local incipient stall, the local drag goes up and the local lift drops precipitously. That lost lift will have to be picked up by the rest of the wing.
In a swept back wing, if the root stalls first, the lift lost is forward of the lift that replaces it, shifting the center of lift aft.
In a swept forward wing, if the tip stalls first, the lift lost is forward of the lift that replaces it, shifting the center of lift aft.
Here's a doc on the stall characteristics of a flat swept-forward wing which naturally begins to stall at the root. - naca-tn-1797 A Study of Stall Phenomena on a 45° Sweot Forward Wing.pdf {I can spell swept, but whoever scanned and converted it couldn't ;)}
