THE ZOOM MANEUVER
Flight
Below the 1-G Stall Speed
The Zoom Maneuver is an
altitude-gaining maneuver where the nose of the aircraft is pitched
excessively nose-high and then gently unloaded
to a light positive G. The attitude of the
aircraft is allowed to decrease so as to pass through level flight
well below the 1-G stall speed while the pilot keeps the wing below
the critical angle attack and, therefore, in the normal flight
operating envelope.
This exercise is presented in the first flight of the
Upset Recovery Training and
Emergency Maneuver Training courses and is
typically the trainee's first exposure to aerodynamic concepts and
flight regimes not experienced in conventional flight
training.
Referring to the V-G Diagram
below, we see a distinct boundary shown as a curved white line
between the Stall Region (light blue) and the Normal Flight Region
(dark blue). The shape of this boundary is a function of the design
of the wing and defined by the critical angle of
attack for a given wing configuration (ie. flap
setting, for example). When the critical angle
of attack is exceed, the aircraft is in the
Stall Region. As the vast majority of pilots
spend their entire aviation career living along
the 1-G line on the V-G diagram, the Zoom
Maneuver is a great tool to demonstrate the
normal flight envelope below the 1-G stall
speed. On this V-G Diagram, we can see the 1-G
stall speed for this wing configuration is approximately 63 kts.
Exploration of the stall
above the 1-G stall speed falls under the category of Accelerated
Stalls and is covered later in the APS program.
Although there is a specified
1-G stall speed for every aircraft (~ 58 knots in the Extra 300/L), it
is possible for an aircraft to fly below the 1-G stall speed without
stalling. This is a characteristic of all aircraft. Stall speed is a
function of angle of attack and an aircraft can stall at any speed
if critical angle of attack is exceeded. Stall recovery involves
reducing the angle of attack. If we carry this to a logical
conclusion, we should be able to fly below the 1G stall speed
without stalling if we are commanding less than 1-G. This is an
important concept to understand for stall and unusual attitude
recoveries because unloading the aircraft does several things for
us: (1) Gets us further away from the critical angle of attack and
therefore further from a stall; (2) Makes the ailerons (or spoilers)
more effective for roll control due to reduced angle of attack and
induced drag; (3) Helps maintain energy in terms of airspeed due to
reduced induced drag resulting in more
controllability; etc....
It is important for the
client to recognize the aircraft needs to
maintain a slight positive G-loading during unloaded recovery
maneuvers (at no time is negative or zero
G-loading an targeted flight condition) to ensure the engine is not starved of fuel and/or oil.
Other tremendously important benefits of being
unloaded to a light positive g-loading,
especially in any overbanked or nose-high
recoveries, is discussed in more detail in later
exercises. More information on the V-G Diagram
and how the techniques developed in the zoom
maneuver are related to effective upset recovery
can be found at:
click here.
Let's watch a demonstration of The Zoom Maneuver
in the
Extra 300L ... please note that this
maneuver should not be attempted without the guidance of an
experienced instructor and the use of a suitable
aircraft.
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