Aircraft stall speed is not fixed. Learn how weight, bank angle, flaps, altitude, icing, power and centre of gravity change it.
Aircraft stall speed is the speed at which a particular aircraft reaches its critical angle of attack under a defined weight, load factor, configuration and power condition. It is not one permanent number: extra weight, manoeuvring load, wing contamination and configuration changes can move the indicated speed at which the stall occurs.
In our Aviation & Real-World Flying coverage, we treat published stall speed as a reference tied to stated conditions, not as a universal aerodynamic boundary. An aircraft can stall at almost any airspeed or attitude if the wing exceeds its critical angle of attack. Our explanation of critical angle of attack, altitude loss and stall recovery covers the underlying mechanism.
Is aircraft stall speed a fixed number?
No. The critical angle of attack is broadly repeatable for a given wing configuration, but the speed required to reach it changes with the lift the wing must produce.
A published figure therefore applies only to specified conditions: aircraft weight, flap and gear position, power setting, centre of gravity and load factor. The aeroplane may reach its critical angle at a much higher speed during a steep turn or abrupt pull-up than during an unaccelerated, wings-level deceleration.
What factors raise or lower stall speed?
Weight and load factor produce the most predictable changes, while configuration, contamination, power and centre of gravity introduce aircraft-specific effects.
| Factor | Usual effect | Key qualification |
|---|---|---|
| Higher weight | Raises stall speed | The wing must generate more lift at the same load factor. |
| Higher load factor | Raises stall speed | Occurs in level turns, pull-ups and turbulence; bank angle alone is not the direct cause. |
| Flaps or leading-edge devices | Usually lower stall speed | The amount depends on the selected setting and aircraft design. |
| Ice, frost or other contamination | Raises stall speed and weakens warning cues | Even small contamination can alter the wing shape and make the break less predictable. |
| Power or thrust | Aircraft-specific | Propeller slipstream, thrust direction and pitch effects can change both speed and stall behaviour. |
| Forward centre of gravity | Usually raises stall speed slightly | A conventional tail normally needs more downward force, increasing the lift demanded from the wing. |
| Aft centre of gravity | May lower the measured speed slightly | It also reduces stability and can make recovery considerably harder. |
| Turbulence | Reduces the usable margin | A gust can add load factor or angle of attack faster than the pilot or autopilot can respond. |
Gear extension mainly adds drag, although it can also alter airflow and pitching moment. Use the aircraft manual rather than assuming the gear will change stall speed by a standard amount.
How do weight and bank angle change stall speed?
At an unchanged configuration and load factor, stall speed varies approximately with the square root of aircraft weight:
new stall speed = old stall speed × √(new weight ÷ old weight)
A 20% weight increase therefore raises stall speed by about 9.5%, not 20%. This relationship is useful for understanding the trend, but operating speeds must still come from the approved aircraft data.
Load factor follows a similar square-root relationship:
accelerated stall speed = 1g stall speed × √(load factor)
A coordinated 60-degree banked level turn produces about 2g, so the stall speed is roughly 1.41 times the wings-level value. If the pilot allows the aircraft to descend and unloads the wing, the same bank angle need not produce that increase. The distinction between bank and load factor is shown clearly in our guide to reading the load-factor and stall boundary chart.
Does altitude affect stall speed?
At the same weight, configuration and load factor, calibrated stall speed remains broadly similar with altitude during ordinary subsonic flight, but true airspeed at the stall increases as air density falls.
The indicated figure is also broadly similar, subject to instrument and position error. This means the aircraft covers more distance through the air during the same manoeuvre at altitude. Ground speed may be higher or lower again depending on wind.
At very high altitude, the simple rule becomes inadequate. Mach effects, reduced thrust, slower acceleration and narrowing separation between low-speed and high-speed buffet leave less room for correction; our coverage of high-altitude stall margins and avoidance explains that case separately.
Which published stall-speed number should I use?
Use the figure from the aircraft flight manual or pilot's operating handbook that matches the actual weight and configuration.
VS0normally refers to the stalling speed or minimum steady speed in the landing configuration.VS1refers to the stalling speed or minimum steady speed in a stated configuration.- KIAS and KCAS are not interchangeable. Position and instrument error can be significant near the stall, so check which unit the table uses.
- Power condition matters. Do not apply a power-off stall figure to a power-on manoeuvre without aircraft-specific data.
- Stall warning speed is not stall speed. The horn, light, stick shaker or buffet should occur before the aerodynamic stall.
These definitions and their relationship to operating speeds are covered in our guide to VS, VS0, VS1 and other aviation V-speeds. Approach speed is not simply the point at which the aircraft stalls; it includes a prescribed margin and may require adjustments for wind, failures or other conditions.
How can I check stall speed in a flight simulator?
A meaningful simulator check requires the same conditions as the published test; most apparent discrepancies come from comparing different weights, configurations or speed units.
- Match the aircraft state. Set the published weight, centre of gravity, flap position, landing gear and power condition.
- Remove outside disturbances. Use calm air with icing disabled unless those effects are the subject of the test.
- Decelerate steadily. Maintain coordinated flight and avoid abrupt pitch inputs that create an accelerated stall.
- Record separate events. Note the first warning, buffet, loss of control effectiveness and actual aerodynamic break rather than calling all of them the stall.
- Check the units. Confirm whether the reference is KIAS or KCAS and whether the simulator display includes instrument error.
A mistake we see constantly is testing with full fuel, passengers or payload and comparing the result with a minimum-weight handbook figure. Controller calibration, turbulence and an add-on's flight-model limitations can also affect the result, but those should be investigated only after the test conditions match.