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Kinetic energy of Spark
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<blockquote data-quote="Blue Baron" data-source="post: 15450" data-attributes="member: 1204"><p>I've done that calculation months ago and I don't remember the details. But AFAICR I obtained an impact energy of ~50J for the Spark. I used the terminal velocity, as obtained from the body surface and mass. Terminal velocity was a bit larger than max. travel speed. That's the lower end of rubber pellets shot by the Irish police into crowds (up to 200 J, 17 deaths ...). 10 J are considered non life-threatening. 50 J still is a serious health danger.</p><p></p><p>I try to redo the calculation now:</p><p></p><p>Drag coefficient = 2 (brick)</p><p>Surface = 143 x 50 mm (assuming it doesn't fall nose first)</p><p>Weight = 300g</p><p>Air density = 1.2 kg/m^3</p><p>Terminal velocity = 18.52 m/s = 66.66 km/h = 17.5 m vacuum free fall</p><p>Energy = 51 J</p><p></p><p>The Spark core body with its rounded edges certainly has a drag coefficient closer to 1, if not smaller (i.e., better than a brick). However, with the arms and rotors extending beyond the core body, I guess this still is a reasonable assumption for the drag coefficient.</p><p></p><p>If Spark must be classified by impact energy, I would go with the "50J" figure.</p></blockquote><p></p>
[QUOTE="Blue Baron, post: 15450, member: 1204"] I've done that calculation months ago and I don't remember the details. But AFAICR I obtained an impact energy of ~50J for the Spark. I used the terminal velocity, as obtained from the body surface and mass. Terminal velocity was a bit larger than max. travel speed. That's the lower end of rubber pellets shot by the Irish police into crowds (up to 200 J, 17 deaths ...). 10 J are considered non life-threatening. 50 J still is a serious health danger. I try to redo the calculation now: Drag coefficient = 2 (brick) Surface = 143 x 50 mm (assuming it doesn't fall nose first) Weight = 300g Air density = 1.2 kg/m^3 Terminal velocity = 18.52 m/s = 66.66 km/h = 17.5 m vacuum free fall Energy = 51 J The Spark core body with its rounded edges certainly has a drag coefficient closer to 1, if not smaller (i.e., better than a brick). However, with the arms and rotors extending beyond the core body, I guess this still is a reasonable assumption for the drag coefficient. If Spark must be classified by impact energy, I would go with the "50J" figure. [/QUOTE]
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Kinetic energy of Spark