Accelerated and Turning Flight Stall
An accelerated stall is a stall that occurs while the aircraft is experiencing a load factor higher than 1 (1g), for example while turning or pulling up from a dive. In these conditions, the aircraft stalls at higher speeds than the normal stall speed (which always refers to straight and level flight).
Considering, for example, a banked turn, the lift required is equal to the weight of the aircraft plus extra lift to provide the centripetal force necessary to perform the turn; that is:
where:
- = lift
- = load factor (greater than 1 in a turn)
- = weight of the aircraft
To achieve the extra lift, the lift coefficient, and so the angle of attack, will have to be higher than it would be in straight and level flight at the same speed. Therefore, given that the stall always occurs at the same critical angle of attack, by increasing the load factor (e.g., by tightening the turn) such critical angle - and the stall - will be reached with the airspeed remaining well above the normal stall speed, that is:
where:
- = stall speed
- = stall speed of the aircraft in straight, level flight
- = load factor
The table that follows gives some examples of the relation between the angle of bank and the square root of the load factor. It derives from the trigonometric relation (secant) between and .
-
bank angle 30° 1.07 45° 1.19 60° 1.41
For example, in a turn with bank angle of 45°, Vst is 19% higher than Vs.
It should be noted that, according to Federal Aviation Administration (FAA) terminology, the above example illustrates a so-called turning flight stall, while the term accelerated is used to indicate an accelerated turning stall only, that is, a turning flight stall where the airspeed decreases at a given rate.
A notable example of air accident involving a low-altitude turning flight stall is the 1994 Fairchild Air Force Base B-52 crash.
Read more about this topic: Stall (flight)
Famous quotes containing the words turning, flight and/or stall:
“Like dreaming, reading performs the prodigious task of carrying us off to other worlds. But reading is not dreaming because books, unlike dreams, are subject to our will: they envelop us in alternative realities only because we give them explicit permission to do so. Books are the dreams we would most like to have, and, like dreams, they have the power to change consciousness, turning sadness to laughter and anxious introspection to the relaxed contemplation of some other time and place.”
—Victor Null, South African educator, psychologist. Lost in a Book: The Psychology of Reading for Pleasure, introduction, Yale University Press (1988)
“In all her products, Nature only develops her simplest germs. One would say that it was no great stretch of invention to create birds. The hawk which now takes his flight over the top of the wood was at first, perchance, only a leaf which fluttered in its aisles. From rustling leaves she came in the course of ages to the loftier flight and clear carol of the bird.”
—Henry David Thoreau (1817–1862)
“Old age, believe me, is a good and pleasant thing. It is true you are gently shouldered off the stage, but then you are given such a comfortable front stall as spectator.”
—Jane Harrison (1850–1928)