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center of gravity
Fuel tank
Figure 2-22. CG location with passenger shown for level flight.
Pitching Rolling Yawing
Lateral Axis Longitudinal Axis Vertical Axis
Figure 2-23. Axes of rotation.
Axes of Rotation
The three axes of rotation intersect at the CG.
[Figure 2-23]
Lateral Axis— Pitch
Motion about the lateral axis, or pitch, is controlled by AOA/
speed and the throttle. Lowering the AOA (increasing speed)
rotates the nose down while increasing the AOA (decreasing
speed) rotates the nose up.
Increasing the thrust of the propeller rotates the WSC aircraft
pitch up (nose up) to climb and pitch down (nose down) at
reduced throttle.
2-13
Weight shifted to right
Aircraft rolls to right
Creates less twist on L.H.
side with tip increased AOA
Normal lift distribution
Less lift
More lift
Creates more twist on R.H.
side with tip reduced AOA
Lift distribution with wing warped
Figure 2-24. Shifting weight to one side warps the wing by
increasing the twist on the loaded side and decreasing the twist on
the unloaded side.
Longitudinal Axis— Roll
Turning is initiated by rolling about the longitudinal axis, into
a bank similar to an airplane using aileron and rudder control.
To turn, shift the weight to the side in the direction of the turn,
increasing the weight on that side. This increases the twist on
that side while decreasing the twist on the other side, similar
to actuating the ailerons on an airplane. The increased twist
on the side with the increased weight reduces the AOA on the
tip, reducing the lift on that side and dropping the wing into a
bank. The other wing, away from which the weight has been
shifted, decreases twist. The AOA increases, increasing the
lift on that wing and thereby raising it.
Thus, shifting the weight to one side warps the wing (changes
the twist) to drop one wing and raise the other, rolling the
WSC aircraft about the longitudinal axis. [Figure 2-24] More
details on the controls that assist wing warping are covered
in chapter 3, which should be considered with use of the
controls in the takeoff, landing, and fl ight maneuvers sections
of this handbook.
Vertical Axis— Yaw
The WSC wing is designed to fl y directly into the relative
wind because it does not provide for direct control of rotation
about the vertical axis.
Stability and Moments
A body that rotates freely turns about its CG. In aerodynamic
terms for a WSC aircraft, the mathematical value of a moment
is the product of the force times the distance from the CG
(moment arm) at which the force is applied.
Typical airplane wings generally pitch nose down or roll
forward and follow the curvature of the upper airfoil camber
creating a negative pitching moment. One of the reasons
airplanes have tails is to create a downward force at the
rear of the aircraft to maintain stabilized fl ight, as explained
in greater detail in the Pilot’s Handbook of Aeronautical
Knowledge.
The WSC wing is completely different and does not need a
tail because of two specifi c design differences—a completely
different airfoil design creating a more stable airfoil and
lifting surfaces fore and aft of the CG, similar to the airplane
canard design.
WSC Unique Airfoil and Wing Design
As shown in Figure 2-2, the WSC airfoil has the high point
signifi cantly farther forward than does the typical airplane
airfoil. This makes the center of lift for the airfoil farther
forward and creates a neutral or positive pitching moment
for the airfoil. Most WSC airfoils have this unique design to
minimize negative moments or pitch down during fl ight.
Additionally, the design of the complete wing is a unique
feature that provides stability without a tail. To understand the
WSC aircraft pitch stability and moments, examine the wing
as two separate components—root chord and tip chord.
Trim—Normal Stabilized Flight
In Figure 2-25A, during normal unaccelerated fl ight at trim
speed, the lift at the root (LR) times the arm to the root (AR)
equals the lift of the tip (LT) times the arm to the tip (AT).
(LR x AR) + (LT x AT) = 0
LR + LT = Total Lift of the Wing (LW)
Adding all the lift from the wing puts the center of lift of
the wing (CLW) directly over the CG for stabilized fl ight.
[Figure 2-25A] If the pilot wishes to increase the trim speed,
the CG is moved forward. This is done by moving the hang
point forward on the wing. Similarly, to reduce the trim speed,
the hang point/CG is moved rearward on the wing.
High Angles of Attack
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Weight-Shift Control Aircraft Flying Handbook(22)
