ESDU 09012:2009

INTRODUCTION

Parachutes are usually soft fabric devices whose shapes have
been designed to produce, upon deployment, a retarding force for
the purpose of slowing and/or stabilising a given payload during
its movement through the air. The word parachute itself
comes from the combination of the French words parare, to
protect or shield, and chute, the fall; the combination of
words in ‘parachute' actually means "fall protection". The
main design criteria are that when stowed it should have minimal
mass and occupy minimal space, and upon deployment it should
reliably open within an acceptable time frame with acceptable
transitional loads, and provide the desired rate of descent with an
acceptable level of stability.

In the development of this Item it has been borne in mind that
the end user would most likely be an aeronautical engineer or
student with little or no previous knowledge of parachute
aerodynamics or design. The aim is to provide such a reader with a
basic grounding of the aerodynamic principles of parachutes and
some familiarisation with the design solutions that have been
executed to date. The Item does not aim to be a design guide; the
design process is one which involves much multi-disciplinary
knowledge, of which aerodynamics is just one component; structural
considerations, weight, packaging, operational requirements and
cost may all have a strong, if not decisive, bearing on the final
outcome. Furthermore, it is clear that parachute systems tend to be
rather individualistic in nature and evolve largely from extensive
experimental programmes, both captive and free flight, together
with large computer models and, in some instances, CFD
simulation.

The design and development of most parachute systems is in fact
undertaken by a small number of specialist organisations and
practitioners, whose publications, both corporate and personal, are
the sources of information contained herein. The aim of this Item
is to provide a basic introduction into this highly specialised
field, with emphasis on applications relating to the airframe
industry, not only as an introductory overview but in two
particular areas that have been identified as most likely to be of
interest; the choice and sizing of aircraft braking and spin
recovery parachutes. Although far from exhaustive, these subjects
are covered in sufficient detail to offer some basic canopy size
and selection guidance.

Section 3 provides a brief historical résumé of parachute design
and usage to the present day. Section 4 outlines the main parachute
designs and provides basic aerodynamic, geometric and performance
data for each type; it also provides definitions of the main
geometric and aerodynamic parameters. Section 5 covers the effects
of the main flow and geometric parameters and Section 6 describes
the inflation process and drag area control methods, cluster
parachute systems and pilot parachutes. Section 7 provides an
introduction to stability, the added mass approximation and
trajectory analysis, and Section 8 covers the specific applications
of parachutes to vehicle braking, spin and deep stall recovery,
ordnance stabilisation, emergency escape systems, supersonic
deceleration and load extraction.