How Can a Plane Stall With Its Engine Running?
Airflow below and beyond the critical angle of attack. FAA, Airplane Flying Handbook, Figure 4-2. Public-domain U.S. government illustration. Source and rights.
When a car stalls, its engine stops. So hearing that an airplane has stalled can conjure the wrong picture: a silent engine and a suddenly helpless machine.
But an airplane’s wing can stall while its engine is still running. The important failure is in the airflow around the wing.
What has the wing done to lose so much of its lifting ability?
The crucial angle
A wing meets air at an angle called its angle of attack. This is measured against the oncoming airflow, not against the horizon. The distinction matters because an airplane’s direction of travel and the direction its nose points are not always the same.
As that angle increases, a wing can produce more lift up to a point. Beyond its critical angle, flow separation becomes extensive and its lifting performance deteriorates. That aerodynamic condition is the stall.
Example SM701 airfoil lift curve based on XFOIL calculations—not a universal stall speed or a flight measurement. Botag; vector version by Mysid. Released into the public domain. Source and rights.
Why “too slow” is only part of the story
Slowing down is one common route toward a stall. To maintain lift at lower speed, an airplane may need a higher angle of attack. Eventually it can reach the critical angle.
But there is no single speed below which every airplane stalls and above which a stall is impossible. Weight, configuration, and loading affect the speed associated with the condition. An airplane can reach a critical angle at a higher speed during a demanding maneuver.
The FAA emphasizes that exceeding the critical angle is the defining issue. The airspeed number alone does not explain the wing’s state.
Smoke and yarn tufts reveal airflow at a 42-degree angle of attack on NASA’s specially modified F-18 High Alpha Research Vehicle. A research aircraft with special controls, not a normal-aircraft stall limit. NASA photograph, public domain. Source and rights.
The engine and the wing have different jobs
The engine supplies propulsion. The wing develops aerodynamic forces from the airflow around it. Those functions interact, but a running engine cannot guarantee that the wing remains below its critical angle.
That is why “the engine was still running” does not rule out an aerodynamic stall. Likewise, an engine failure does not automatically mean the wings have stalled; an airplane can glide with suitable airflow and attitude.
This follows our earlier story about pressure and lift. The wing does not simply need air nearby. It needs an effective flow pattern around it.
The word sounds like an engine problem. In this case, it describes the wing.
Sources and image credits
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