Ligne 1 : |
Ligne 1 : |
| {{ENG-CANSAT-NAV}} | | {{ENG-CANSAT-NAV}} |
| | | |
− | == Introduction ==
| + | {{COMMON-CANSAT-PARACHUTE}} |
− | 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.
| |
− | | |
− | == 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 ==
| |
− | [[Fichier:ENG-CANSAT-PARACHUTE-30.png|360px]]
| |
− | | |
− | The Flat 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].
| |
− | | |
− | == Parachute Design @ BAROM ==
| |
− | 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].
| |
− | | |
− | * [https://www.narom.no/undervisningsressurser/the-cansat-book/the-primary-mission/parachute-design/parachute-design-calculations/ Parachute Design Calculations]
| |
− | * [https://www.narom.no/undervisningsressurser/the-cansat-book/the-primary-mission/parachute-design/descent-physics/ Descent Physics]
| |
− | * [https://www.narom.no/undervisningsressurser/the-cansat-book/the-primary-mission/parachute-design/semi-spherical-parachute-design/ Semi-spherical parachute Design]
| |
− | * [https://www.narom.no/undervisningsressurser/the-cansat-book/the-primary-mission/parachute-design/cross-parachute-design/ Cross Parachute Design]
| |
− | * [https://www.narom.no/undervisningsressurser/the-cansat-book/the-primary-mission/parachute-design/flat-parachute-design/ Flat Parachute Design]
| |
− | | |
− | == 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).
| |
− | | |
| | | |
| {{ENG-CANSAT-TRAILER}} | | {{ENG-CANSAT-TRAILER}} |