Powered Parachute Flying Handbook Chapter 2 - Aerodynamics of Flight Powered Parachute Wing Pressurization and Flexibility The powered parachute has two distinctive modes: (1) inflated, it is a ram-air wing with a curved arc— a recognizable airfoil shape; and (2) deflated, it is a canopy that is either lying flat on the ground or packed into a bag. Note: Chapter 7, Takeoffs and Departure Climbs, will detail the methods of getting the uninflated canopy laying on the ground turned into a flying wing. Since the aerodynamics of the PPC do not start until the wing is completely inflated, this chapter will assume each reference to the PPC wing is to an inflated ramair wing already in the shape of an airfoil. The powered parachute ram-air wing retains its airfoil shape due to the air pressurizing the inside cells via the relative wind airflow being rammed into the front openings of the canopy—thus the term “ram-air wing.” The pressure inside the wing is much higher than the outside top and bottom because the dynamic pressure from the relative wind is converted to static pressure to pressurize the wing. The greater the speed, the greater the pressure inside the wing and the more rigid the wing. The cell openings are designed to be perpendicular to the relative wind to achieve maximum pressure from the relative wind. This static internal pressure harnessed from the relative wind is called dynamic pressure (q), and is determined by the velocity squared times the air density factor. [Figure 2-7] Note the dynamic air pressure converted to static pressure at point A is constant throughout the wing points B and C. This static pressure is always greater than the pressure outside the wing at points X and Z. Cross-port openings are placed in the ribs of each cell, connecting the adjoining cells. These cross-ports are dispersed throughout the wing (with exception to the outboard side of the end cells) to maintain positive pressure throughout. The pressure is constant inside the wing because the dynamic pressure hitting the opening is the same for each cell and the speed is the same. The cross-ports aid the complete wing in becoming pressurized during inflation and maintaining the pressure throughout the wing in turbulence. [Figure 2-8] The inflatable wing airfoil generally remains a consistent shape as designed by the manufacturer. However, pilot control of the wing to make a turn significantly changes the relative aerodynamic qualities of the PPC wing by pulling down the trailing edge similar to a flap on an airplane. [Figure 2-9] Faster speeds from smaller wings or more weight create a higher pressure in the wing resulting in higher control forces because of the higher internal pressure.