A/c stalls whenever stalling angle of attack is reached boundary layer separates from surface of the wing lift decreases and a/c stalls.
Stalling angle is always fixed for a particular a/c but stalling speed varies under different conditions.
A/c can stall at any air speed and at any attitude. It need not be in a nose high attitude for stalling to occur.
At any altitude the Indicated stalling speed remains the same, but with increase or decrease in the altitude the True Air Stalling Speed changes, due to TAS changing with different altitudes.
In a turn the load factor increases, and the lift requirement to support the weight of the a/c increases as bank angle increases, the angle of attack is increased to produce more lift and to maintain a/c flying level, else it will start descending.
With increase in Load Factor stalling angle is reached at a high airspeed or we can say that in a maneuver, stalling speed increases.
Factor affecting stalling speed-
(i) Weight – Weight increases, stalling speed increases 10% increase in weight requires stalling speed to be increased by 5% e.g. If a/c Wt is 10,000 lbs stalling speed is 100kts. If weight increases to 11,000 lbs new stalling speed will be 105 kts.
(ii) Power – With power a/c stalls at a lower air speed and without power at a higher air speed. Power on stalling speed is less than Power Off stalling speed. Because the thrust is divided into two components,
(a) one acting in the direction of thrust and other in direction of the Lift.
(b) Slipstream from propeller stream lines the boundary layer (only in propeller driven Tractor type a/c)
(iii) Load factor– Ratio between the total air load imposed on the wing to the weight of a/c.
Load factor increases in a maneuver.
In a level flight load factor= 1
In a climb or descent Load factor is less than one.
In any maneuver load factor is more than one.
Turn is a simple maneuver in which load factor is more than one.
(a) Lift supports the weight of the a/c and if it is less than weight a/c will sink- stick is pulled back to compensate loss in the Lift.
(b) Provides the centripetal force for turning.
In a turn flying at the same IAS, the drag is more than in a straight and level flight. Therefore to compensate, the power is increased (because air speed is decreasing.)
If power is not increased air speed will decrease.
In a turn the Lift requirement is more than weight.
Therefore load factor is more than one.
In a turn load factor depends only on angle of bank and not on air speed.
| Angle of Bank | Load Factor | Increase in stalling Speed |
| 15° | 1.04 | 1.02 % |
| 30° | 1.15 | 1.07 % |
| 45° | 1.41 | 1.18 % |
| 60° | 2.0 | 1.41 % |
| 75° | 3.86 | 1.97 % |
The increase in Stalling speed can be calculated by using the Under root of the Load factor to get the new stalling speed at different angles of bank.
Load factor increases stalling speed increases.
(iv) Lift augmenting Device – Devices which increase Lift. They decrease stalling speed, they also change the stalling angle. Stalling speed is affected by: –
(a) Weight
(b) Power
(c) Load factor
(d) A/c Configuration.
Stalling Angle is not affected by:-
(a) Weight
(b) Power
(c) Load factor.
(v) Wind/velocity has no effect on stalling speed stalling speed up wind and down wind remains the some.
(vi) Height – Stalling speed (indicated stalling speed) will not change with increasing in ht.
Although as altitude increases True Air Speed increases therefore True Air stalling speed also increase but we don’t calculate True Air speed for stalling speed calculations in flight, because we have IAS in A/c cockpit.
With increase in weight stalling angle is reached at a higher air speed.
With increase in load factor stalling angle is reached at a higher air speed. We can say in a maneuver Stalling speed increases.
Lift Augmenting Devices- Increases Lift, or increases CL therefore CL maximum increases and stalling speed decreases.
Altitude- Indicated stalling speed remains same at all altitudes.
Air Density changes in air density will not affect stalling speed.
Wind velocity- Upwind or downwind the stalling speed remains the same, but we Take off into the wind because ground speed decreases and Take off run also decreases.
Position of Centre of Gravity affects Stalling speed-
Forward C.G – Increases stalling speed.
Rearward C.G – Decreasing stalling speed.
Stalling angle is changed only by lift augmenting devices it will not be affected by Weight, Power, Load factor, Position of C.G etc.
Stalling angle- all Trailing edge flaps decreases stalling angle.
All Leading edge lift devices, Kruegger flaps, Slats etc. increases Stalling angle.
Slats and Slots increase Stalling Angle.