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Technically what differences are there between a take off and a stall?

From what I understand, when stalling the aircraft will lose lift when a certain angle is met. On a takeoff the aircraft will pitch the nose up but the effects are different.

What affects this? Is it the effect of the relative airflow or something else?

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    $\begingroup$ Stall is explained here and takeoff here. $\endgroup$ – fooot Apr 25 '15 at 17:55
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    $\begingroup$ Specifically, stall is the point at which raising the angle of attack any further creates less lift. Rotation during a take-off run will use angles of attack lower than that (or else their flight will be very short.) $\endgroup$ – reirab Apr 25 '15 at 21:37
  • $\begingroup$ Also, stall's occur when the turbulent flow of air causes disruptions in the lift being generated. $\endgroup$ – Zizouz212 Apr 25 '15 at 21:41
  • $\begingroup$ Also see Is there always a stall if you exceed a certain angle of attack? $\endgroup$ – Qantas 94 Heavy Apr 25 '15 at 23:18
  • $\begingroup$ @reirab That should be the answer +1 $\endgroup$ – Rhino Driver Apr 27 '15 at 19:24
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On take-off the pitch is increased to increase lift, but only to a point well before stall occurs. An aircraft's minimum speed is defined by the maximum lift it can create before the flow over the wings stalls, and the high-pitch attitude is only attained when the aircraft flies faster than that. As soon as lift is sufficient for lift-off, further pitch increases are increasing the flight path angle. If the aircraft keeps accelerating during the initial climb, stalling is impossible.

Technically, both are very different. Their only commonality is that they involve high angles of attack.

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A stall, technically, is a departure of turbulent airflow over the top of the wing due to an extreme angle of attack. When this happens the wing no longer generates lift as designed. In most "everyday" aircraft scenarios the most common reason for a stall is a combination of insufficient speed and too high a nose pitch. Aerobatic aircraft including fighter jets can encounter stall scenarios in other ways, including intentionally (several maneuvers involve intentional stalls; the 3-D equivalent of intentionally entering a skid in a car).

When taking off, an aircraft typically does not exceed the maximum angle of attack for its current speed; if it did, the aircraft would stall and likely crash. The aircraft instead accelerates to a speed in excess of the forward stall speed of the aircraft, and then gently pitches upward to gain altitude. To the average passenger, especially a first-timer, it may not look or feel "gentle" to have the aircraft pitch 15-20 degrees up in the air, but during that maneuver the AOA remains very shallow.

To assist heavier aircraft (or those designed for faster cruise speeds) in getting off the ground quickly and/or at a lower speed, the flaps can be positioned in a moderate setting, often specifically designated as a "take-off" setting, to increase the lift the wing generates at lower speeds. This happens through a combination of increasing the effective upper surface of the wing, and also directing the airflow leaving the wing downwards. In a "clean" configuration (the most aerodynamic setup for cruising, which includes no flaps), the minimum speed at which the wing can still generate lift will be higher.

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  • $\begingroup$ Stall is usually the departure of turbulent airflow. When pressure gradients are steep, laminar flow is hard to maintain. The skid analogy is apt. $\endgroup$ – Peter Kämpf Apr 27 '15 at 18:49

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