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Chapters 2 and 3 of the Pilot’s Handbook of Aeronau- tical Knowledge  (FAA-H-8083-25) apply to powered parachutes and are a prerequisite to reading this book. This chapter will focus on the aerodynamic fundamen- tals unique to powered parachute (PPC) operations. 

## Aerodynamic Terms 

Airfoil is the term used for surfaces on a powered parachute that produce lift, typically the wing itself. Although many different airfoil designs exist, all air- foils produce lift in a similar manner. 

Camber  refers to the curvature of a wing when look- ing at a cross section. A wing possesses upper cam- ber  on its top surface and lower camber  on its bottom surface. Leading edge  describes the forward edge of the airfoil. The rear edge of the airfoil is called the trailing edge . The chord line  is an imaginary straight line drawn from the leading edge to the trailing edge. [Figure 2-1] 

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Relative wind  is the direction of the airflow with re - spect to the wing; it is usually parallel to and opposite the PPC flight path . Relative wind may be affected by movement of the PPC through the air, as well as by all forms of unstable, disturbed air such as wind shear, thermals, turbulence, and mountain rotors. When a PPC is flying through undisturbed air, the relative wind is parallel to and opposite the flight path. 

Angle of attack  is the angle between the relative wind and the wing chord line. [Figure 2-2] 

Longitudinal axis  is an imaginary line about which the aircraft rolls; it is also called the roll axis. The longitudinal axis is not a fixed line through the cart because the angle of incidence changes in turbulence and with loading changes. 

Angle of incidence  is the angle formed by the chord line of the wing and the longitudinal axis of the PPC cart. The cart longitudinal axis is not the same as the aerodynamic longitudinal axis defined in the previous paragraph. [Figure 2-2] Unlike an airplane, the angle of incidence can change in flight because of the flex - ible line attachment between the wing and the cart. Angle of incidence can change for different types of flight configurations and PPC designs; this is covered in detail in the “Moments” section. 

Trim angle  is the angle between the chord line of the wing and the horizontal plane when the PPC is in non- powered gliding flight. [Figure 2-3] The PPC wing is designed at a slight angle, with the chord line inclined downward to the horizontal plane to maintain the manufacturer-designed angle of attack during gliding, level and climbing flight. This “trim angle” is built into the powered parachute by the manufacturer and cannot be adjusted by the pilot moving the controls. 

Pitch angle  is the angle the PPC wing chord makes with the horizontal plane. Pitch angle is what you can see. Many pilots confuse the pitch angle, which you can easily see and feel, with the angle of attack which may not be as perceptible. [Figure 2-4] For example, the pitch angle in an engine-out glide could be minus 8 degrees, in level flight 10 degrees above the hori - zon, and in a climb it could be 28 degrees above the horizon. These are significantly different angles you easily see. Pitch angles are covered in greater detail in Chapter 6. 

Deck angle is the angle of the cart’s lower frame (from the front wheel to the rear wheels), to the land- ing surface. The deck on the lower part of the conven- tional cart frame can be used to visualize deck angle. An imaginary line between the front and back wheel axles can also be used on unconventional carts. 

