Figure 2-20. Pendulum effect is like a weight on a string,  stabilizing weight and line vertically over time. Figure 2-19. Powered parachute airfoil is locked into  position by the lines and weight of the cart. wing attachment point, the more stable the cart pitch  is from thrust moments. The higher the wing attach- ment point above the CG, the more stable the cart is  from swinging underneath and the less the cart will  pitch up when thrust is applied. Pendulum stability is the result of a number of PPC  design characteristics: there is no downward force  from a horizontal tail that must be counteracted by the  wing producing more lift; there is no weight of the tail  that must be lifted; and there is no tail to impose extra  drag on the aircraft. Gravity is the primary force that  stabilizes the aircraft using pendulum stability. A higher hang point will also better stabilize the PPC  cart in turbulence because the moment of the weight  and the larger “d” arm creates a larger stabilizing mo- ment. [Figure 2-22] The “dynamic pendulum effect” can be demonstrated  by swinging the weight around and then stopping the  swinging to notice that the weight keeps swinging  from the momentum. The swinging weight is known  as the “dynamic pendulum effect” which will be dis- cussed in detail later. For ground operations, the moment arm distance “c”  cannot be too great or the front wheel would lift off  the ground prematurely, trying to inflate the wing (see  right side of Figure 2-22). PPC designs can have different moments caused  by thrust; the propeller thrust may be above the CG (Figure 2-21 left) or go through the CG (Figure  2-21 right). Since the cart swings free in pitch, this  CG thrust moment can slightly affect the pitch of the  cart in relation to the wing.  During flight, the advantage of a high attachment  point arm “c” is less swinging around of the cart un- der the wing, and less cart “pitch up” when throttle is  applied to climb. This high attachment point creates  thrust that is now pointed slightly down to the rela- tive wind, which has two significant effects. First, it  creates a negative P-factor, counteracting increased  torque. The second effect is a disadvantage: less climb  rate or more thrust required for the same climb rate.  This is due to the increased load on the wing from the  thrust, requiring more speed and/or angle of attack to  lift the total load. [Figure 2-23] PPCs with an attachment point above the thrust line  have a pitching nose up moment as shown in Figure  2-21 (both diagrams), with a thrust line, wing attach  point, and arm “b.” There is a moment arm from the CG of the cart,  to the cart/wing attachment (see “arms” in Figure 2-22). The longer the distance from the CG to the  If flying straight and level over a perfectly flat landing  strip, then with the rear wheels 1 inch above the run- Wing Attachment to Cart Gravity Moment Thrust Line Moments 2-10