Powered Parachute Flying Handbook

Chapter 2 - Aerodynamics of Flight


A stable aircraft is one that will routinely return to its original attitude after it has been disturbed from this condition; usually this means returning to straightand- level flight after encountering turbulence that disrupts a normal flightpath. The more stable the aircraft, the easier it is to return to a straight and level position. The natural tendency of the pendulum — the PPC cart hanging under the wing — is to return to its original centered position under the wing. The pendulum design gives the PPC airborne positive dynamic stability and positive static stability for roll and pitch because the weight of the pendulum wants to return the PPC to level stabilized flight. No matter what maneuver within the POH limitations the PPC is put through (regardless of whether it is pilot induced or turbulence created), as soon as the disruptive force stops, the aircraft is designed to return to a stabilized flight condition, with virtually no pilot input. Figure 2-25 shows the movements of the PPC as it auto-corrects from a side gust of wind.

PPC Angle of Attack Characteristics

Normal Flying Conditions

For all practical purposes, the wing’s lift in a steady state normal climb is the same as it is in a steady level flight at the same airspeed. Though the flightpath has changed when the climb has been established, the angle of attack of the wing with respect to the inclined flightpath reverts to practically the same value, as does the lift. The angle of attack remains relatively constant for constant weights during stabilized flight for glide, level cruise or climb. However, wind gusts, flying in turbulence, quick uncoordinated flight (as covered later), or aerobatic maneuvers can change the PPC angle of attack. PPC limitations in the POH are specifically written to avoid any maneuver that would temporarily get the PPC into a situation of too high or too low an angle of attack. The PPC is specifically designed to fly at an angle of attack to avoid stalls (resulting from too high an angle of attack), and avoid wing collapses (resulting from too low an angle of attack). Each manufacturer specifically determines the limitations so a proper angle of attack is maintained throughout the flight operation range.

The basic design of the powered parachute is to fly at a relatively constant speed which results in a constant angle of attack. However, angle of attack can change just as with any aircraft as when a gust of wind changes the direction the air is hitting the airfoil. [Figure 2-26]

The pilot can add weight or increase loads which may also increase the angle of attack slightly.

 ŠAvStop Online Magazine                                                                                                                                                       Contact Us              Return To Books

AvStop Aviation News and Resource Online Magazine

Grab this Headline Animator