10 | MAGAZINE 02

T

he stall is a situation that no pilot

wants to go through. he classic

deinition of stall refers to a de-

tachment of the air low from the

airfoil, making the lit to be lost.

his may occur in aircrats and in helicopters

as well. his situation happens when it is sur-

passed the critical limit of the angle of attack

of the wing or the main rotor blades.

Stall may also occur inside the turbines,

when the same phenomenon of air detach-

ment takes place, but from the compres-

sor vanes caused by turbine overspeed or

some compressor anomaly, such as wear or

breakage. However, there are some varia-

tions that should be remembered here.

hey are essential to prevent entering into

the situation, or if it does happen, to get out

from it.

VARIATIONS

Being within the aircrat center of gravity

(CG) is one of the stall recovery condi-

tions. If the CG is too far to the tail, when

surpassing the envelope limit, the pilot

may have diiculties in driving the nose

forward in order to have enough forces

generated with the elevator tabs to com-

pensate excess weight. Without being able

to reduce the angle of attack, the aircrat

will continue stalled until impact on the

ground.

Stall speed is not a ixed value for all

situations, but the angle of attack at which

an aircrat will stall will be the same ir-

respective of speed, weight, load factor or

density altitude. Each aircrat has its criti-

cal angle of attack, which varies between

16 and 20 degrees.

It shall also be remembered that there

are three conditions for entering into

stall: Power-of, power-on and in acceler-

ated lights (such as in very steep turns, in

which the load factor increases with incli-

nation, thus increasing the aircrat weight

and the need of lit).

In helicopters, stall occurs when too

much angle of attack is demanded from

the blades at hovering or with extremely

low speed, with low air density, high alti-

tudes and high temperatures. he engine

is not able to ensure constant RPM of the

main rotor because of the great drag gen-

erated due to the steep angle of the blades,

making it to be reduced until it does not

longer produce lit.

A simple way to prevent this emergen-

cy situation is to be within the limits set

forth by the manufacturer regarding the

aircrat performance and within the limits

of weight and balance.

Remember that when we are talking

about stall, we have to think far beyond

the takeof, climbing and inal approach

speed of aircrats, or the maximum power

of helicopters. We have also to think about

continuing observing the limits of each

piece of equipment, in each condition that

we are lying.

AERO ANSWERS

HOW DO I PREVENT

THE STALL?

What leads to this dangerous situation and

what has to be done to prevent it