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Ligne 1 : − == Introduction ==+ − The CanSat use a parachute to slow it down when getting back to the earth. Otherwise the CanSat would crash! − − The parachute is also used to maintain the CanSat in the proper position to properly orientate the antenna! This is essential to receive telemetry data. − − The [https://www.narom.no NAROM site in Norway] did publish "The CanSat Book" containing lot of useful information. − − The most interesting parts concerns [https://www.narom.no/undervisningsressurser/the-cansat-book/the-primary-mission/parachute-design/ the Parachute Design]. − − == Parachute opening & tenseness == − The process of parachute opening and air flow capturing is a violent process. The tenseness on the fabric, wire, hook may be really impressive at the opening. − − So you need to select strong fibres and realise strong assemblies. The ideal materials are those used for human parachute (Nylon Cord, [https://en.wikipedia.org/wiki/Ripstop Ripstop Nylon]). − − == Fundamentals parameters == − The followings parameters are primary values to use when designing the CanSat's parachute. − − * '''Mass''' : between 300gr and 350gr. − * '''Velocity''' : between 8 m/s and 11 m/s (about 29 Km/H and 40 Km/H). − * '''Drag Coefficient''' : the [https://en.wikipedia.org/wiki/Drag_coefficient drag coefficient] depends on the parachute shape and the fluid used (''Air'' in this case). − − === Drag Coefficient === − * Semi Spherical Parachute : 1.5 (narom), 0.77 (in the table below) − * Cross Shape Parachute : 0.8 − * Flat, Hexagone Parachute : 0.8 − − [[Fichier:ENG-CANSAT-PARACHUTE-20.png]]<small><br />Source: [https://www.launchwithus.org/lwu-blog/2016/02/17/parachute-size-estimator-for-high-altitude-balloons Parachute Size Estimator]</small> − − === Estimate the Drag Coefficient === − You can make a drop test from a given height of your CanSat with the parachute. − − When terminal velocity is known (measured), you can deduce the ''Drag Coefficient'' from the estimated velocity in free chute (if the CanSat were not equipped with a parachute). − − == Flat Circular Parachute == − The parachutes are extremely common in the hobby rocketry fields. Thanks to their simple design, they are cheap and easy to manufacture. They also offers reliable parachute. − − The trade-off is the Draft Coefficient (Cd) which is not as high for a given cloth diameter. It is hard to go wrong with a flat circular (or flat hexagonal) parachute. − − The typical drag coefficients range goes from 0.75 to 0.80. − − You may also find some informations about flat parachute on this [https://www.narom.no/undervisningsressurser/the-cansat-book/the-primary-mission/parachute-design/flat-parachute-design/ NAROM page]. − − == Resources == − * [http://www.nakka-rocketry.net/paracon.html Parachute Design and Construction] by Richard Nakka − * [https://gallery.mailchimp.com/c4ab65df2b61279e33d7ee72b/files/HAB_Parachute_Size_Estimator_v1.0.xlsx Parachute Size Estimator tool] using imperial unit system ([https://www.launchwithus.org/lwu-blog/2016/02/17/parachute-size-estimator-for-high-altitude-balloons Launchwithus.org])<br />See [https://www.launchwithus.org/lwu-blog/2016/02/17/parachute-size-estimator-for-high-altitude-balloons this article which explains how to use it]. − * [http//www.sunward1.com/imagespara/The%20Mathematics%20of%20Parachutes%28Rev2%29.pdf The Mathematics of Parachute] (pdf). −
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