Abstract
Parachute Systems (PS) can be readily used by small Unmanned Aircraft Systems (UAS) for risk mitigation and aircraft recovery. To date there has been limited research into the fundamental dynamics of parachutes at low Reynolds numbers,with existing studies focusing on larger parachutes. An understanding of the dynamics is needed to establish sound guidelines for parachute design and for their use during UAS operations. Existing design guidelines are reviewed and the key parachute design parameters are identifi ed. The validity of the existing guidelines applied to lower Reynolds number parachutes is explored through a series of wind-tunnel tests. It was found that existing design guidelines underpredict the key parameters of inflation time and peak forces for parachute deployments at typical UAS operating speeds. The ramifi cations on the design and operation of small UAS are discussed.
Highlights
For Unmanned Aircraft Systems (UAS), the primary safety related hazards are: 1) a collision between an Unmanned Aircraft (UA) and other airspace users; and 2) the controlled or uncontrolled impact of the UA with terrain or objects on the terrain (Clothier et al 2015)
This paper explores the validity of existing parachute guidelines, and in particular those described in Knacke (1992), for small UA
The objective was to explore the validity of generally accepted design guidelines through a comparison with experimental results obtained from wind-tunnel testing
Summary
For UAS, the primary safety related hazards are: 1) a collision between an Unmanned Aircraft (UA) and other airspace users; and 2) the controlled or uncontrolled impact of the UA with terrain or objects on the terrain (e.g., people or structures) (Clothier et al 2015). As discussed in Clothier et al (2015), parachute systems are one of a number of devices and procedures that can be employed by UAS operators to reduce the risk to people overflown, and secondarily, to the UA and its payload. Small commercial UAS currently exhibit a high unreliability due, in part, to the use of commercial off-the-shelf components, the limited redundancy in flight critical systems, and the uncontrollability of the UA given a failure. A principle resource is Knacke’s Parachute recovery systems design manual (Knacke 1992). The design guidelines established in Knacke’s design manual, hereafter referred to as Knacke’s guidelines, are derived from experimental testing of large parachutes at Reynolds numbers (Re) on the order of 107. The vast majority of small UA (e.g., of maximum takeoff mass less than two kg) currently operate at much lower Re (in the order of 105) and at altitudes below 400 ft above ground level (this operational height limit is due to regulatory constraints as opposed to the operational capability of the UA)
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