Low Speed Low Power Fast Speed Higher Power
Relative Wind
Flightpath
Relative Wind
Flightpath
High Kinetic EnergyLow Kinetic Energy
Figure 6-20. Energy management: low and high kinetic energy for level flight.
Slow Flight and Stalls
As discussed in chapter 2, the maintenance of lift and control
of an aircraft in slow fl ight requires a certain minimum
airspeed and angle of attack. This critical airspeed depends
on certain factors, such as gross weight, load factors, and
density altitude. The minimum speed below which further
controlled fl ight is impossible is called the stalling speed.
An important feature of pilot training is the development
of the ability to estimate and “feel” the margin of speed
above the stalling speed. Also, the ability to determine the
characteristic responses of the aircraft at different airspeeds
is of great importance to the pilot. The student pilot,
therefore, must develop this awareness in order to safely
avoid stalls and to operate an aircraft correctly and safely
at slow airspeeds.
As discussed in chapter 2, the nose stalls while the tips keep
fl ying. Therefore, the defi nition of stall speed of the WSC
aircraft is the speed at which the nose starts stalling. The
control bar is pushed forward and buffeting is felt on the
control bar as the root reaches the critical angle of attack.
Separation of the laminar airfl ow occurs, creating turbulence
that can be felt in the control bar. There is a loss of positive
roll control as the nose buffets and lowers as it loses lift.
Slow Flight
The objective of maneuvering during slow flight is to
develop the pilot’s sense of feel and ability to use the
controls correctly and to improve profi ciency in performing
maneuvers that require slow airspeeds.
Slow fl ight is broken down into two distinct speeds:
1. V X and the short fi eld descent speed that was discussed
earlier, and,
2. Minimum controlled airspeed, the slowest airspeed at
which the aircraft is capable of maintaining controlled
fl ight without indications of a stall—usually 2 to 3
knots above stalling speed as discussed below.
The minimum controlled airspeed maneuver demonstrates
the fl ight characteristics and degree of controllability of the
aircraft at its minimum fl ying speed. By defi nition, the term
“fl ight at minimum controllable airspeed” means a speed at
which any further increase in angle of attack or load factor
causes an immediate stall. Instruction in fl ight at minimum
controllable airspeed should be introduced at reduced power
settings with the airspeed suffi ciently above the stall to
permit maneuvering, but close enough to the stall to sense the
characteristics of fl ight at very low airspeed—sloppy control,
ragged response to control inputs, diffi culty maintaining
altitude, etc. Maneuvering at minimum controllable airspeed
should be performed using both instrument indications and
outside visual reference. It is important that pilots form the
habit of frequent reference to the fl ight instruments, especially
the airspeed indicator, while fl ying at very low airspeeds.
However, the goal is to develop a “feel” for the aircraft at
very low airspeeds to avoid inadvertent stalls and to operate
the aircraft with precision.
The objective of performing the minimum controlled airspeed
is to fl y straight and level and make shallow level turns at
minimum controlled airspeed. To begin a minimum controlled
airspeed maneuver, the WSC is fl own at trim speed straight and
level to maintain a constant altitude. The nose is then raised as
the throttle is reduced to maintain a constant altitude.
As the speed decreases further, the pilot should note the
feel of the fl ight controls, pitch pressure, and diffi culty of
maintaining a straight heading with the increased side-to-side
pilot input forces required to keep the wings level. At some
point the throttle must be increased to remain level after the
WSC has slowed below it’s maximum L D speed. The pilot
should also note the sound of the airfl ow as it falls off in tone.
There is a large difference by manufacturer and model, but
the bar generally should not be touching the forward tube
at minimum controlled airspeed. For example, the control
bar would be 1 to 3 inches from the front tube at minimum
controlled airspeed. [Figure 6-21]
Control bar is moved forward,
slowing the WSC
Minimum controlled airspeed Trim flight
Power is decreased slightly
as the nose is raised to slow
to minimum controlled
airspeed
Power applied for straight-and-
level flight at minimum
controlled airspeed
Shallow turns are performed
in level flight at minimum
controlled airspeed
Normal straight-and-
level flight
Figure 6-21. Minimum controlled airspeed maneuver.
The pilot should understand that when fl ying below the
minimum drag speed (L/D MAX), the aircraft exhibits a
characteristic known as “speed instability.” If the aircraft
is disturbed by even the slightest turbulence, the airspeed
decreases. As airspeed decreases, the total drag increases
resulting in a further loss in airspeed. Unless more power is
applied and/or the nose is lowered, the speed continues to
decay to a stall. This is an extremely important factor in the
performance of slow fl ight. The pilot must understand that, at
speeds less than minimum drag speed, the airspeed is unstable
and will continue to decay if allowed to do so.
It should also be noted that the amount of power to remain
level at minimum controlled airspeed is greater than that
required at the minimum drag speed which is also the best
glide ratio speed and the best rate of climb speed.
When the attitude, airspeed, and power have been stabilized
in straight-and-level fl ight, turns should be practiced to
determine the aircraft’s controllability characteristics at
this minimum speed. During the turns, power and pitch
attitude may need to be increased to maintain the airspeed
and altitude. The objective is to acquaint the pilot with the
lack of maneuverability at minimum controlled airspeed, the
danger of incipient stalls, and the tendency of the aircraft
to stall as the bank is increased. A stall may also occur as a
result of turbulence, or abrupt or rough control movements
when fl ying at this critical airspeed.
Once fl ight at minimum controllable airspeed is set up
properly for level fl ight, a descent or climb at minimum
controllable airspeed can be established by adjusting the
power as necessary to establish the desired rate of descent
or climb.
Common errors in the performance of slow fl ight are:
• Failure to adequately clear the area.
• Inadequate forward pressure as power is reduced,
resulting in altitude loss.
• Excessive forward pressure as power is reduced,
resulting in a climb, followed by a rapid reduction in
airspeed and “mushing.”
• Inadequate compensation for unanticipated roll during
turns.
• Fixation on the airspeed indicator.
• Inadequate power management.
• Inability to adequately divide attention between
aircraft control and orientation.
Stalls
A stall occurs when the smooth airfl ow over the aircraft’s
wing root is disrupted and the lift degenerates rapidly. This
is caused when the wing root exceeds its critical angle of
attack. This can occur at any airspeed in any attitude with
any power setting.
The practice of stall recovery and the development of
awareness of stalls are of primary importance in pilot
training. The objectives in performing intentional stalls are to
familiarize the pilot with the conditions that produce stalls, to
assist in recognizing an approaching stall, and to develop the
habit of taking prompt preventive or corrective action.
Pilots must recognize the fl ight conditions that are conducive
to stalls and know how to apply the necessary corrective
action. They should learn to recognize an approaching stall
by sight, sound, and feel. The following cues may be useful
in recognizing the approaching stall:
• Positioning the control bar toward the front tube
• Detecting a stall condition by visually noting the
attitude of the aircraft for the power setting
• Hearing the wind decrease on the structure and
pilot
• Feeling the wind decrease against the pilot
• Sensing changes in direction or speed of motion,
or kinesthesia—probably the most important and
best indicator to the trained and experienced pilot.
If this sensitivity is properly developed, it warns of
a decrease in speed or the beginning of a settling or
mushing of the aircraft.
During the practice of intentional stalls, the real objective
is not to learn how to stall an aircraft, but to learn how to
recognize an approaching stall and take prompt corrective
action. Though the recovery actions must be taken in a
coordinated manner, they are broken down into the following
three actions for explanation purposes.
First, at the indication of a stall, the pitch attitude and angle
of attack must be decreased positively and immediately.
Since the basic cause of a stall is always an excessive angle
of attack, the cause must fi rst be eliminated by releasing the
control bar forward pressure that was necessary to attain that
angle of attack or by moving the control bar backwards. This
lowers the nose and returns the wing to an effective angle
of attack.
The amount of movement used depends on the design of
the wing, the severity of the stall, and the proximity of the
ground. In some WSC aircraft, the bar can be left out and
as the nose stalls, the wing lowers to an angle of attack and
keeps fl ying since the tips do not stall. However, even though
WSC aircraft generally have gentle stall characteristics,
higher performance wings may not be as forgiving. Therefore
during a stall, the control bar should be moved back to reduce
the angle of attack and properly recover from the stall. The
object for all WSC aircraft is to reduce the angle of attack
but only enough to allow the wing to regain lift as quickly as
possible and obtain the appropriate airspeed for the situation
with the minimum loss in altitude.
Power application in a stall is different than an airplane. Since
power application in a WSC aircraft produces a nose-up
moment after a stall has occurred and the pitch has decreased
from the control bar movement, power should be applied.
The fl ight instructor should emphasize, however, that power
is not essential for a safe stall recovery if suffi cient altitude
is available. Reducing the angle of attack is the only way of
recovering from a stall regardless of the amount of power
used. Stall recoveries should be practiced with and without
the use of power. Usually, the greater the power applied
during the stall recovery, the less the loss of altitude.
Third, straight-and-level fl ight should be regained with
coordinated use of all controls. Practice of power-on stalls
should be avoided due to potential danger of whipstalls, tucks,
and tumbles, as detailed later in ths chapter.
Power-off (at idle) turning stalls are practiced to show
what could happen if the controls are improperly used
during a turn from the base leg to the fi nal approach. The
power-off straight-ahead stall simulates the attitude and
fl ight characteristics of a particular aircraft during the fi nal
approach and landing.
Usually, the first few practices should include only
approaches to stalls with recovery initiated as soon as the
fi rst buffeting or partial loss of control is noted. Once the
pilot becomes comfortable with this power-off procedure,
the aircraft should use some power and be slowed in such
a manner that it stalls in as near a level pitch attitude as is
possible. The student pilot must not be allowed to form the
impression that in all circumstances a high pitch attitude is
necessary to exceed the critical angle of attack, or that in all
circumstances a level or near level pitch attitude is indicative
of a low angle of attack. Recovery should be practiced fi rst
without the addition of power by merely relieving enough
control bar forward pressure that the stall is broken and the
aircraft assumes a normal glide attitude. Stall recoveries
should then be practiced with the addition of power during
the recovery to determine how effective power is in executing
a safe recovery and minimizing altitude loss.
Stall accidents usually result from an inadvertent stall at a
low altitude in which a recovery was not accomplished prior
to contact with the surface. As a preventive measure, stalls
should be practiced at a minimum altitude of 1,500 feet
AGL or that which allows recovery no lower than 1,000 feet
AGL. Recovery with a minimum loss of altitude requires a
reduction in the angle of attack (lowering the aircraft’s pitch
attitude), application of power, and termination of the descent
without accelerating to a high airspeed and unnecessary
altitude loss.
The factors that affect the stalling characteristics of the aircraft
are wing design, trim, bank, pitch attitude, coordination,
drag, and power. The pilot should learn the effect of the
stall characteristics of the aircraft being fl own. It should
be reemphasized that a stall can occur at any airspeed, in
any attitude, or at any power setting, depending on the total
number of factors affecting the particular aircraft.
Whenever practicing turning stalls, a constant pitch and
bank attitude should be maintained until the stall occurs.
In a banked stall or if the wing rolls as it stalls, side to side
Establish normal
approach
Raise nose
maintain heading
When stall occurs,
reduce angle of attack
Resume
normal flight
Increase power as
required to minimize
altitude loss
Figure 6-22. Power-off stall and recovery.
control bar movement is required to level the wings as well
as pull the bar back to reduce the angle of attack.
Power-Off Stall Manuever
The practice of power-off stalls is usually performed with
normal landing approach conditions in simulation of an
accidental stall occurring during landing approaches. Aircraft
equipped with trim should be trimmed to the approach
confi guration. Initially, airspeed in excess of the normal
approach speed should not be carried into a stall entry since
it could result in an abnormally nose-high attitude. Before
executing these practice stalls, the pilot must be sure the area
is clear of other air traffi c.
To start the power-off stall maneuver, reduce the throttle to
idle (or normal approach power). Increase airspeed to the
normal approach speed and maintain that airspeed. When the
approach attitude and airspeed have stabilized, the aircraft’s
nose should be smoothly raised to an attitude that induces a
stall. If the aircraft’s attitude is raised too slowly, the WSC
aircraft may slow only to minimum controlled airspeed and
not be able to reach an angle of attack that is high enough
to stall. The position of the control bar at which the WSC
stalls can vary greatly for different manufacturers and makes/
models. Some can stall abruptly when the control bar is inches
from the front tube.
If the aircraft’s attitude is raised too quickly, the pitch attitude
could rise above the manufacturer’s limitation. A good rule
of thumb is 3 to 4 seconds from stabilized approach speed to
pull the control bar full forward. The wings should be kept
level and a constant pitch attitude maintained until the stall
occurs. The stall is recognized by clues, such as buffeting,
increasing descent rate, and nose down pitching.
Recovering from the stall should be accomplished by
reducing the angle of attack by pulling the bar back and
accelerating only to the trim speed while simultaneously
increasing the throttle to minimize altitude loss if needed.
Once the WSC accelerated to trim speed, the control bar can
be pushed out to return back to normal trim attitude and speed.
If there is any rolling during the stall or the stall recovery
the control bar should be moved side to side to maintain a
straight heading.
It is not necessary to go into a steep dive in a WSC aircraft
to recover from a stall. This only loses more altitude than
required and should be discouraged. The nose should be
lowered as necessary to regain fl ying speed and returned to
a normal fl ight attitude as soon as possible. [Figure 6-22]
Recovery from power-off stalls should also be practiced from
shallow banked turns to simulate an inadvertent stall during
a turn from base leg to fi nal approach. During the practice of
these stalls, care should be taken that the turn continues at a
uniform rate until the complete stall occurs. When stalling in
a turn, it does not affect the recovery procedure. The angle of
attack is reduced and the wings leveled simultaneously with
power applied if needed for altitude control. In the practice of
turning stalls, no attempt should be made to stall the aircraft
on a predetermined heading. However, to simulate a turn
from base to fi nal approach, the stall normally should be
made to occur within a heading change of approximately 90°.
After the stall occurs, the recovery should be made straight
ahead with minimum loss of altitude, and accomplished in
accordance with the recovery procedure discussed earlier.
Whip Stall and Tumble Awareness
As discussed in chapter 2, the WSC aircraft does not have a
tail with a vertical stabilizer similar to an airplane, and there
is the possibility of the wing tucking and tumbling. If a WSC
tumbles, this will most likely result in a structural failure
of the WSC and serious injury or death to the pilot and/or
passenger. It is most important for the pilot to understand
tumble awareness and use all means to avoid such an
occurrence. The pilot can avoid a tuck and tumble by:
• Flying within the manufacturer’s limitations.
• Flying in conditions that are not conducive to tucks
and tumbles.
• Obtaining the proper training in pitch stability for the
WSC.
Flying within the manufacturer’s pitch and airspeed
limitations is simply adhering to the POH/AFM limitations.
Depending on the manufacturer, this could mean no full
power stalls, not exceeding pitch limits of ± 40 pitch angle,
not fl ying below the safe fl ying speed in turbulence, etc.
Manufacturer’s limitations are provided for the specifi c
aircraft to avoid tucks and tumbles.
Prefl ight preparation is the fi rst step to avoid the possibility
of a tuck/tumble to avoid fl ying in strong weather conditions.
This could be strong winds that create wind shear or strong
convective thermals that create updrafts and downdrafts. This
weather analysis is part of the prefl ight preparation weather
analysis. The second pilot decision regarding appropriate
weather while fl ying is to look at the environment during
fl ight to understand and evaluate the situation. Weather
conditions should always be evaluated as the fl ight progresses
with ADM used to determine the best outcome for the
situation. This could be turning back or landing depending
on the situation.
As a student or pilot progresses, turbulence will be
encountered. Use the procedures for fl ying straight and level
as shown in Figure 6-8. Use this exercise as a foundation for
developing pitch control awareness to keep the wing managed
with proper control bar pitch and throttle control.
For high pitch angles, the POH may have specifi c procedures
that should be followed for the particular WSC aircraft,
but the following general guidelines are provided. After
reviewing the aerodynamic aspects of the tuck/tumble in
chapter 2, refer to the following tuck/tumble awareness and
avoidance procedures.
As defi ned in the aerodynamics section, a whip stall is a high
pitch angle when the tips stall because they exceed the critical
angle of attack. This can be the result of strong turbulence
or power-on stall, pilot induced, or any combination of
these factors. A pilot must avoid all of these factors to avoid
the possibility of a whip stall resulting in a tumble, but the
following procedures are provided for tumble avoidance
in case a whip stall or a nose rotating down below the
manufacturer’s limitations is encountered.
The aircraft rotates nose down. [Figure 6-23,
Whip Stall to Phase 1] Push the control bar out to the
front tube and level wings while increasing to full power
and keeping control bar full out to reduce overpitching.
[Figure 6-23, Phase 1 to Phase 2] If rotation is so severe that
it progresses to phase 4 and the WSC aircraft is tumbling, the
ballistic parachute (if so equipped) should be deployed.
There are other weather situations in which the nose is not
at a high pitch attitude, where the back of the wing can get
pushed up and enter phase 1 without an unusually high pitch
attitude or whip stall. If pitched nose low, increase to full
power while pushing the control bar full out to reduce nose-
down pitching rotation. Generally, the control bar full out
and full throttle create a nose-up moment.
It takes extremely strong weather conditions and/or pilot
error to tuck/tumble a WSC aircraft. Experienced pilots fl y
all day in moderate turbulence, but building experience fl ying
in turbulence should be approached slowly and cautiously to
determine the pilot and aircraft capabilities and limitations.
A Scenario
The following is one example of a scenario that could lead to
a tuck/tumble. It is based on a viable training program in one
location but lack of experience in another location.
A student obtains his or her pilot’s license with the minimum
number of hours for the pilot certifi cate. The new pilot trained,
soloed, and obtained his or her license only in conditions near
the ocean where there was typically an inverted midday sea
breeze with little to no convective turbulence (thermals). This
developed confi dence for fl ying in winds up to 15 knots but
no experience was gained in thermals. In fact, the pilot was
not aware that strong thermals could be hazardous.
Now, with a new license, the pilot visits his parents in the
middle of the high desert of Colorado. Unfamiliar with
the local conditions, the new pilot gets a weather report
of winds to 15 knots, something the pilot has experienced
before. By the time the pilot arrives at the airport, discusses
the situation with the airport offi cials, and sets up the WSC
aircraft, it is 2:00 in the afternoon. The wind is generally calm
but increasing to 15 knots occasionally. There are towering
Phase 1 Whip StallPhase 2Phase 3Phase 4
Wing completely
stalled and very
high pitch angle
Any nose down
rotation—pilot pushes
control bar full
forward and applies
full throttle
Vertical dive—
pilot continues
to hold control
bar full forward
and full throttle
ose rotates dow
Nose is tucked under—
pilot continues to hold
control bar full forward
and full throttle
Tumble—with complete
loss of control of aircraft, it
will most likely have
structural failure.
Use ballistic parachute
system (if so equipped).
Figure 6-23. Whip stall/tuck/tumble sequence.
cumulus clouds in the sky surrounding the current airport
similar to clouds that the pilot had seen far inland from where
he or she took instruction and soloed.
The pilot takes off in relatively calm winds, but it is unusually
bumpy air. Without any experience in the high desert or with
thermal conditions, the pilot has misjudged the conditions and
is fl ying in strong thermal convection. The new pilot climbs
out trying to get above the turbulence, which usually works
near the beach because of the mechanical turbulence near the
ground. However, the turbulence increases.
As the pilot is climbing to a pattern altitude of 1,000 feet
AGL at full throttle, the aircraft is pitched nose up while the
pilot lets the force of the updraft raise the nose. Never has
the pilot felt the nose rise with this type of force before. The
pilot is shocked and disoriented at this high pitch attitude,
but eventually lets up on the throttle. But now at an unusually
high pitch angle, the WSC nose fl ies into the downdraft of
the thermal. At the same time, the updraft is still pushing up
on the tips of the wing while the downdraft is pushing down
on the nose creating a forward rotation with a weightless
sensation. Before the pilot knows it, the wing is rotating
pitch down for a vertical dive. [Phase 1 in Figure 6-23] The
student remembers from training that “in a nose down rotation
into a steep dive the control bar is pushed full forward and
full throttle applied” and initiates this corrective action. The
pilot reaches the vertical dive, but because of the corrective
action the WSC aircraft recovers from the dive and proceeds
back to land safely.
What went wrong? What were the errors? How could this
near catastrophe have been avoided?
• In a new area and unfamiliar with the conditions, the
new pilot should have asked the local instructor or
other pilots about the conditions for the day. Local
WSC pilots are a great resource for fl ying the local
conditions, but pilots of any category aircraft are
knowledgeable of the conditions and could have
provided advice for the new pilot. This might have
prevented the new pilot from attempting this fl ight.
• Flying in a new environment and not understanding
the power of midday thermals in the high desert should
have forced the new pilot to scrap this midday fl ight.
The pilot should have started fl ying in the morning
when there is little thermal convection and gained
experience and understanding about the weather in
this new area.
• Better preflight planning should have been
accomplished, especially in a new location. The pilot
should have known to obtain convective information
and realize it was going to be too bumpy for his or
her limited experience. The pilot was accustomed
to seeing towering cumulus clouds where he or she
trained, but they were way inland and not in the normal
fl ying area. Here clouds were observed all around.
• Site observations indicated strong thermal activity.
Observation of winds picking up to 15 knots and then
becoming calm normally indicates thermal activity.
The pilot was familiar with steady 15 knot winds,
but did not understand that calm wind increasing
cyclically to 15 knots indicates thermal activity.
• The pilot did not initially react to the updraft and
resultant high pitch angle properly because pitch
management habits had not been developed. The pilot
hit the updraft and allowed the force of the updraft
to move the control bar forward, increasing the pitch
angle while not letting up on the throttle immediately.
Both the control bar forward and full throttle forced
the nose too high, creating the high pitch angle and
whip stall condition. At the same time, the WSC
aircraft fl ew into the downdraft, starting the nose-
down rotation.
• If the pilot had reacted quickly, pulled in the bar while
letting up on the throttle and immediately going into
the strong thermal, the high pitch angle would not have
been achieved and the strong forward rotation would
not have happened so abruptly.
After the series of errors occurred, the pilot fi nally performed
the preventive action to avoid a tumble—from the basic
training of “If the WSC is at a high pitch angle and the
nose starts to rotate down to a low pitch angle, increase to
full power while pushing the control bar full out to avoid a
tumble.”
Chapter Summary
Knowledge of the effects and use of the controls is basic to
develop a “feel” of the aircraft and become accustomed to
“attitude” fl ying. This is the basis for all fl ight maneuvers. The
four basic WSC fl ight maneuvers requiring pilot profi ciency
are:
• Straight-and-level fl ight.
• Level turns.
• Climbs and climbing turns.
• Descents and descending turns.
Once the basic maneuvers are mastered, the steep turn allows
the pilot to achieve maximum performance from the aircraft.
Energy management techniques provide the basis for fl ying in
different atmospheric conditions and introduce the student to
precise pitch and power control. Slow fl ight and stall provide
the pilot an awareness of the ability of the WSC to fl y at the
lower end of the WSC performance.
Whip stalls and tumbles are unique to WSC fl ight, and pilot
awareness and avoidance is an important concept for WSC
pilots to understand.