Flying Smart: What It Looks Like

Airplanes as we know them couldn't fly without the lift and energy (from combustion) that air makes possible. Forced air also wicks away engine and oil heat; it cools, heats, and pressurizes airplane cabins; and it powers, directly or indirectly, various flight instruments. But all that comes at a price. Speed- and energy-zapping drag is an unwelcome byproduct of lift (induced drag), and of the various pieces and parts of the airplane moving through the slipstream (parasite drag).

Wings, tails, engine nacelles, and fuselages all contribute to drag because of their form and the friction that results from air moving over their surfaces. Also, when air is "borrowed" from the slipstream for various purposes, such as engine cooling, it creates parasite drag because the airflow is impeded.

Minimizing drag while maximizing efficiency is a never-ending goal of airplane designers, and one way that goal is achieved is with the use of NACA ducts. NACA stands for National Advisory Committee for Aeronautics, which became the National Aeronautics and Space Administration in 1958. From its beginnings in 1917, NACA did groundbreaking aerodynamic research and engineering. The airfoil designs used on many general aviation aircraft today originated at NACA, as did advancements such as the type of recessed air induction inlet pictured here.

Traditional induction inlets that extend into the slipstream to "scoop" the air obviously create considerable parasite drag. NACA researchers discovered that turning the scoop inside out so that it is recessed in the engine cowl or airplane structure resulted in a much smaller loss of efficiency. There's more to it than that, of course. The shape and depth of the inlet are crucial to maximizing the intake of air while minimizing drag. The shape is formed by the divergent curved sides of the duct, and the gradually increasing depth from front to back. We can credit that graceful shape to the long-ago scientific artists at NACA.