Descelerator Systems Archives

If the name Theodor Knacke means nothing to you, don’t feel bad. It meant nothing to me, until last week when I learned about the man and his lifetime contributions to the field of aerodynamic decelerator systems, also known as parachutes. Many people in aviation only think about—and appreciate—the parachute if it is the only thing that will prevent a sudden stop after long fall. But just think, where would the space program be without the parachute, and the uncountable thousands whose lives have been saved by this seemingly simple device? And let’s not forget those who fling themselves from high places for fun.

When looking at the details involved, designing a decelerator system is one of aviation’s premier engineering challenges. Working with a variety of sewn together textiles an engineer must create an aerodynamic system that reliably assembles itself in midair. Sounds simple, doesn’t it? Let’s consider the parachute used in an F-18. It must fully deploy so an aviator does not come to a sudden stop after ejecting at zero speed and zero altitude. At the other end of its performance spectrum, the parachute must assemble itself in such a sequence that it does not self-destruct when it unfolds at 40,000 feet in a Mach number slipstream. And just to make it interesting, the parachute must be packed and hydraulically mashed into a solid textile brick that is wedged into the top of a seat under a canopy where the brick bakes on sunny days, freezes at altitude, is bathed it corrosive salt sea air for months and months and months.

And the engineer who wrote the book—literally—on meeting this daunting engineering challenge? Theodor Wilhelm Knacke. Don’t bother looking him up on Wikipedia. He doesn’t exist there. But he should, because among his many accomplishments is his compilation of all he’d learned about the field in Parachute Recovery Systems Design Manual. The photos on its cover depict some of the projects on which he worked. That effort began in 1930s at Flugtechnisches Institute Stuttgart (or Flight Institute of Stuttgart Technical University, FIST), which challenged him and a colleague, Georg Madelung “to develop a parachute suitable for the in-flight and landing deceleration of aircraft.” Their solution was the ribbon parachute, which led to the ring slot and ring sail parachutes that made “31 successful earth landings” of Mercury, Gemini, and Apollo spacecraft.