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Googlemapsflow t1_itstq0e wrote

3400g is equivalent to 3400g where g is the acceleration due to gravity, g = 32.174 ft/(sec^2). 3400g's is an acceleration. By assuming the entirety of the impact is 0.0065seconds, and assuming the final velocity (V_f=0mph), we can solve the initial velocity (V_i) algebraically with the kinematic relation: at=V_i-V_f

This can be rewritten as: a*t=V_i V_i=(3400 * 32.174fpss)*0.0065s= 707.2 feet per second

there are 22fps/15mph, so

V_i = 707.2fps * 15mph / 22fps = 484.8mph

I got an impact velocity of 485mph and I'm not sure how I got it wrong.

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Googlemapsflow t1_itsv4vg wrote

I'm not wrong, it must be more to it than the basic kinematic equations cover. Even calculations using distance instead of time yield an impact speed of 390mph.

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meyerpw t1_itt449u wrote

Your assumption is that the acceleration is constant over that time.

Typically. Specifications like this would be in a half sine wave of acceleration. Although other acceleration profiles are possible

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Googlemapsflow t1_itt4wor wrote

Thanks Meyer, that makes sense. A half sine wave averages about 0.63 of peak acceleration and 485mph x 0.63 gives right at 310mph. I'm open to literature on this if you have any recommendations

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meyerpw t1_itt6bin wrote

Mll standard 810 goes into a bit of detail on shock testing,. Although it is not specific to black boxes.

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BasedOnAir t1_itzeyij wrote

You didn’t get it wrong. OP didn’t mention that the spec says it must withstand 310mph to 0mph over a distance of 18 inches. Not instant-stop over zero distance.

The wiki explains this

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Googlemapsflow t1_itznpjt wrote

to stop over a time period of 6.5msec implies that it stops over a distance. I calculated velocity over the given 1.5ft distance and it was a different impact speed. The real answer is that they reported a max velocity when speed calcs are performed assuming a half sine wave impulse. Meyer explained it to me in a different comment

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