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Note the component of weight acting along the flight
path. This component of weight is called thrust by
some but is more accurately the weight component
providing the forward force.
Figure 2-15. Typical forces in gliding flight, with no engine
thrust.
Weight
Weight is a measure of the force of gravity acting upon
the mass of the PPC. It is the force that opposes lift,
and acts vertically downward through the aircraft’s
center of gravity. Weight consists of everything directly
associated with the powered parachute in flight:
the combined load of the total PPC (wing, risers, engine,
cart, fuel, oil, etc.), people (clothing, helmets,
etc.), and baggage (charts, books, checklists, pencils,
handheld GPS, spare clothes, suitcase, etc.). In stabilized
level flight, when the vertical component of lift
is equal to the weight force, the PPC is in a state of
equilibrium and neither gains nor loses altitude.
Because the trim angle is set at the factory, the PPC
airspeed is predetermined, before takeoff, by the
weight of the aircraft and the wing design. The more
weight, the more forward airspeed is generated.
Therefore, gravity is the primary force for creating
forward speed — pulling the wing through the relative
wind while airborne. The forces in gliding flight
Thrust
Compared to an airplane, as discussed in Chapter 3
of the Pilot’s Handbook of Aeronautical Knowledge,
thrust serves different purposes in the PPC: (1) it is
used to accelerate the PPC to flying speed while inflating
the wing (2) it is used to climb when at high
thrust, cruise level at medium thrust, and descend at
lower thrust. Variations in thrust have negligible effect
2-8
on PPC airspeed which remains relatively constant
whether climbing, descending, or in level flight.
When enough thrust is added to produce level flight,
the relative wind stream becomes horizontal with
the earth; the angle of attack and speed remain about
the same. Just as described in the Pilot’s Handbook
of Aeronautical Knowledge for the airplane, thrust
equals total drag for level flight. [Figure 2-16]
When in straight-and-level unaccelerated flight:
LIFT (L) = WEIGHT (W)
and
THRUST = TOTAL DRAG (DT)
Figure 2-17. Powered parachute in climbing flight.
Figure 2-16. Powered parachute in level flight.
Center of Gravity
The center of gravity (CG) is the theoretical point
of concentrated weight of the aircraft. It is the point
within the PPC about which all the moments trying to
rotate it are balanced. The most obvious difference in
the center of gravity for a PPC is the vertical position
compared to an airplane, as it is much lower than the
wing. The Pilot’s Handbook of Aeronautical Knowledge
accurately states the center of gravity is generally
in the vertical center of the fuselage. The same
is true for the PPC. However, the PPC wing is high
above the fuselage (cart) creating the unique pendulum
effect flying characteristics of the PPC (which
will be covered in detail later).
In a two-seat PPC, the second seat is typically behind
the pilot’s seat, and the center of gravity is usually
located directly over the rear passenger seat. Therefore,
the center of gravity location does not change
significantly with or without a passenger. Fuel tanks
are typically located near the center of gravity so
any differences in fuel quantity will not significantly
change the center of gravity fore and aft with different
fuel quantities.
When excess thrust is added to produce climbing
flight, the relative air stream becomes an inclined
plane leading upward, while angle of attack and speed
remain about the same. Just as described in the Pilot’s
Handbook of Aeronautical Knowledge for the airplane,
the excess thrust determines the climb rate and
climb angle of the flight path. [Figure 2-17]
2-9
Axes of Rotation
Motion about the lateral axis or pitch is primarily
controlled by the thrust of the propeller moving the
PPC pitch up (nose up) to climb and pitch down (nose
down) at reduced throttle.
Turning happens about the longitudinal axis and is the
result of the rolling motion similar to an airplane with
aileron and rudder control. To turn, pull down the wing
trailing edge on the side you want to turn to with the
steering controls. This creates drag on the corresponding
trailing edge of the wing, thus dropping the inside
wing, and rolling the PPC into a banked turn. [Figure
2-18]
There is not significant turning about the vertical axis
because the PPC wing is designed to fly directly into
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Powered Parachute Flying Handbook动力伞飞行手册(16)
