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make coordinated turns. Designs and methods vary with
manufacturer and wing type, but all WSC wings are designed
to track directly into the relative wind.
Thrust Moments
WSC aircraft designs can have different moments caused by
thrust based on where the thrust line is compared to the CG.
This is similar to an airplane except the WSC aircraft has no
horizontal stabilizer that is affected by propeller blast.
If the propeller thrust is below the CG [Figure 2-35, top],
this creates a pitch-up moment about the CG when thrust is
applied and a resultant decrease in speed. When reducing
the throttle, it reduces this moment and a nose pitch down
results with an increase in speed.
If the propeller thrust is above the CG [Figure 2-35, bottom],
this creates a pitch-down moment about the CG when thrust
is applied and a resultant increase in speed. When reducing
the throttle, it reduces this moment and a nose pitch up results
with a decrease in speed.
With the thrust line above or below the CG producing these
minor pitch and speed changes, they are usually minor for
most popular designs. Larger thrust moments about the CG
may require pilot input to minimize the pitch and speed
effects. Most manufacturers strive to keep the thrust as close
as possible to the vertical CG while also balancing the drag of
the carriage and the wing for its speed range. This is why the
carriage must be matched to the wing so these characteristics
provide a safe and easy to fl y WSC aircraft.
Stalls: Exceeding the Critical AOA
As the AOA increases to large values on the wing chord,
the air separates starting at the back of the airfoil. As the
AOA increases, the separated air moves forward towards the
leading edge. The critical AOA is the point at which the wing
is totally stalled, producing no lift—regardless of airspeed,
fl ight attitude, or weight. [Figure 2-36]
2-19
Phase 4 Phase 3 Phase 2 Phase 1 Whip Stall
Wing comletely
stalled and very
high pitch angle
Pitch attitude for
normal dive recovery
Vertical dive
Nose rotates down
Nose is tucked under
Tumble
Figure 2-37. Whip stall to tumble phases and sequence.
Wing stalls due
to an excessive
angle of attack
Laminar airflow
Turbulence
Figure 2-36. Stall progression for an airfoil chord as the angle of
attack is increased.
Because the AOA of the WSC wing root chord/nose is so much
higher than the AOA of the tips, the nose stalls before the tips.
It is similar to stalling with the airplane canard in which the
nose stalls fi rst, the main wing (or tips for the WSC aircraft)
continues to fl y, and the nose drops due to lack of lift.
In most normal situations, the root chord/nose stalls fi rst
because it is at a much higher AOA. The tips continue to fl y,
making the WSC wing resistant to a complete wing stall. A
pilot can even bring the aircraft into a high pitch angle stall
attitude and keep the nose high. The nose stalls and rotates
down because of the loss of lift, while the tips keep fl ying
and maintain control of the aircraft.
If fl ying within the operating limitations of the aircraft and
the WSC reaches a high AOA, the nose stalls, but the tips
continue fl ying. However, it must be understood that there are
many wing designs with many types of stall characteristics
for each unique design. For example, high-performance
wings could have less twist to gain performance, which
could cause the wing to stall more abruptly than a training
wing with more twist.
Whip Stall–Tuck–Tumble
A WSC aircraft can get to a high pitch attitude by fl ying
outside the its limitations or flying in extreme/severe
turbulence. If the wing gets to such a high pitch attitude and
the AOA is high enough that the tips stall, a whip stall occurs.
[Figure 2-37]
In a WSC wing, most of the area of the wing is behind the CG
(about three-quarters). With the tips and aft part of the wing
having the greatest drag, and the weight being forward, an
immediate and strong nose-down moment is created and the
WSC nose starts to drop. Since both the relative wind and the
2-20
wing are rapidly changing direction, there is no opportunity
to reestablish laminar airfl ow across the wing.
This rotational momentum can pull the nose down into a
number of increasingly worse situations, depending on the
severity of the whip stall. Figure 2-37 shows a whip stall and
the phases that can result, depending on the severity.
Phase 1—Minor whip stall results in a nose-down pitch
attitude at which the nose is at a positive AOA and the
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Weight-Shift Control Aircraft Flying Handbook(26)
